Stability, propulsion system and rudder evaluation of a riverine support vessel to optimize its...

Stability, propulsion system and rudder evaluation of a riverine support vessel to optimize its operational performance

Javier Serrano Tamayo, Naval Mechanical Engineer Naval Academy “Almirante Padilla” Colombian Navy, Office of Education

Tel: (57) (1) 2742410 [email protected]

Abstract—The present article summarizes the study of the stability and the hull integration with the propulsion system of a riverine support vessel, in order to optimize the efficiency of the propulsion plant and improve its maneuverability in its operations area. The relevance of this study originated from the fact that the vessel originally was a Tug Boat converted into a mother vessel to transport troops. Other vessels of the same type were used in operations to control public order, due to the lack of methodology in the conversion process the end results is not optimal.

To initiate the work, it was necessary to forego a Field review that permitted to measure the vessel in 3D; modeling and executing the estimation of weight and components of the vessel using SWBS (Vessel Work Breakdown Structure), as well as determining the location of its center of gravity (CG), work performed using GHS software (General Hydrostatics) and Rhinoceros.

An important evaluation for the criteria of stability was

applied using standards such as DDS-079 USN and 046CFR170 USCG. Once a study was undergone, the resistance was predicted using systematic series with the NAVCAD software, as well as the optimal propeller selection and evaluation in terms of fuel consumption and operating autonomy. In regards to the controllability system, a study was performed utilizing the current rudder in which recommendations were formulated in achievement of the appropriate one, better located and which absorbed the propeller turbulence, as well as state of the art recommendations to improve maneuverability.

The results turned to a stable vessel and the

improvement in the propulsion system efficiency, which showed an increased in speed, cavitations reduction and longer range. The applied rudder remarkably improved maneuverability as well as coursekeeping. Keywords—Fairing, weight estimation, loading

conditions, stability criteria, squat effect, propeller efficiency, rudder selection, Schilling rudder.

I. INTRODUCTION

he consolidation of the Democratic Security Policy in Colombia requires the highest possible performance of naval vessels, for which the Navy exercises sovereignty

over the navigable rivers of the motherland. Within the organization, the Riverine Brigade has twelve riverine tugs built in the 80’s to serve as a tugboat and cattle transport vessel , work done until at the end of 90’s when they were stranded and converted in riverine supported vessels. But here was the extent of repairs, without considering that the change in mission required a different conception of the other components of the vessel, particularly the integration of the hull with the propulsion system.

The increase of weights, was construed by the shielding made out of steel plates and sand interspersed, suggests that there have been significant variations in displacement and in the vertical position of the CG, so it was necessary to study the loading conditions and to evaluate its transverse stability with acceptable criteria for such boats, like DDS 079-1 NAVSEA, U.S. Navy for intact stability. The main engine, designed to develop an average of Rated Power 180 BHP @ 1800 RPM did not exceed 1500 RPM in its best case, indicating it was overloaded or the propeller was not properly projected. In the same term, it was a desire to overcome the presented cavitations. Regarding the rudder, manoeuvrability was being affected by a tactical diameter that could be reduced.

The purpose of this document is to summarize the

studies undergone to evaluate the stability as well as to show the procedures to obtain an optimal and commercial propeller, and calculation to design a rudder that significantly improved manoeuvrability. This study solved a problem of poor performance of a vessel in the river due to a partial adaptation of a towing vessel as a personnel carrier with capacity of a mother vessel. This pattern of study could also be replicated in the same type of vessels presenting similar problems.

T

II. 3D MODELLING OF THE VESSEL

For the hull measurement was created a table of offsets, which were drawn stations from conspicuous points it contains, which are referenced to an initial usually corresponds to one of the ends of the hull.effect it was taken as a reference point (0,0,0) point of intersection of the imaginary tip of the bow with the line to the height of the baseline. Most of the specially the parallel section, keeps a depth of 1.2 m has a sharp rise at the bow and slight one at

Once the measurements were obtained

information of the hull shape collected, the offsets was developed in order to organize information and to take the first record of the shape lines of the s

Table I. Table of offsets format for one s The information collected and entered in the

table offset format, necessarily had to be supplemented and verified with different available information of the

The first introduction of data was attained with

satisfactory results in semi-tunnels shapestern section and parallel. In the bow the results were less favourable given the muddy terrain, which led to a long process for shape lines refinement, known as fairing

Fig. 1. Reference point for the table of imperfections details at the bow

The fairing of a hull is intended to avoid discontinuities,

voids or tipping points that result in concentrating sgreater resistance and lack of aestheticsshipbuilding, is of great importance, since after the

3D MODELLING OF THE VESSEL

was created a table of offsets, from conspicuous points it

contains, which are referenced to an initial origin point that usually corresponds to one of the ends of the hull. To that

reference point (0,0,0) point of bow with the center Most of the vessel,

section, keeps a depth of 1.2 m and has a sharp rise at the bow and slight one at stern.

Once the measurements were obtained and the , the first table of

in order to organize information and take the first record of the shape lines of the stations.

ffsets format for one station

The information collected and entered in the produced format, necessarily had to be supplemented and

verified with different available information of the vessel.

as attained with highly tunnels shape, definition of the

stern section and parallel. In the bow the results were less hich led to a long

known as fairing.

erence point for the table of offsets and

at the bow

is intended to avoid discontinuities, voids or tipping points that result in concentrating stress,

aesthetics in design. In pbuilding, is of great importance, since after the faired

shape is passed to the program to define the optimize the material, since the steels have a high cost in the construction process. To change the lines and applied fairing using Rhinoceros software, which worked the vessel's hull as a series of surfaces. First from checkpoints were "pulling" those imperfectthe hydrodynamic shape of the hull.

Fig. 2. Checkpoints used to the bow fairing

After long hours of iterpoint by point, was reached amodel in 3D.

Fig. 3. Final 3D m

III. FORM COEFFICIENTS AND HYDROSTATIC CURVES

Form coefficients are used to show the shape of the hull and provide an estimation of powerfeatures of the studied vessel reflected in its main coefficients

28.715.31

2.126 3

⋅=

mm

mCB

28.7

976.4

⋅=

mCM

⋅⋅

∇=

⋅

∇=

M

PBLAL

C

Once the coefficients

curves were calculated which affected the vessel’s stability at

2 shape is passed to the program to define the cut-off to optimize the material, since the steels have a high cost in

To change the lines and view the hinoceros software, which worked

's hull as a series of surfaces. First from checkpoints were "pulling" those imperfections until giving

shape of the hull.

Checkpoints used to the bow fairing

After long hours of iterations station by station and

point by point, was reached an acceptable and reliable

Final 3D model

III. FORM COEFFICIENTS AND HYDROSTATIC CURVES

Form coefficients are used to show the shape of the hull on of power. According to the basic vessel is a full forms vessel, as

reflected in its main coefficients.

)1(8.07963.07.0

3

≈=⋅ mm

)2(9765.07.0

976 2

=⋅ m

m

)3(8168.0==⋅

∇

M

B

M C

C

CT

Once the coefficients were obtained, the hydrostatic which indicated different values that

stability at variable water lines. It is

3 customary to calculate the curves with the vessel at flat keel (no trim), which is often shown in auxiliary curves. The drafts range is shown from the minimum possible, when the vessel fully shedding (light weight) to the highest possible, with the boat fully loaded.

Nowadays, these calculations are made by stability

software, in general the important factor is to select the most appropriate software and enter the information carefully and make sure that the program delivers useful results, as well as user friendly and consistent with the particular form to be integrated. In this case was used GHS (General Hydrostatics), but before obtaining the corresponding values the tanks of the vessel must be edited into the model for make the calculations properly.

Fig. 4. Model including the different tanks.

Once this was done, a program was developed to obtain

the coefficients of form and hydrostatic curves as shown.

Fig. 5. Curves of form, trim cero, heel cero.

Fig. 6. Hydrostatic curves, trim cero, heel cero.

IV. WEIGHT ESTIMATING

To study the loading conditions were necessary to know the weight of the vessel and all its components, as well as the bending moment respect a reference point. Three conditions were considered for study: lightship, minimum operation condition and full load. But, when the project began, before using SWBS, some methods for structure weight calculation were studied satisfactory results were not achieved.

Studied method Results

Benford method Little displacement Danckwardt method Little L/D ratio Lamb method Little length Mandel method Ilogical value Gilfillan method Just for bulk carriers Murray method Ilogical value Osorio method Could be use as a reference J.L. García G. method Very little value Table II. Weight estimating methods for main features1

Considering that no method satisfied the accuracy

required to determine the weight of the vessel, proceeded to weigh it according to each one of its components. Detailed procedure for weighting and CG estimation is determined in SWBS (Vessel Work Breakdown Structure) which is a detailed summation of weights designed by the U.S. Navy, which considered the vessel as a set of elements condensed in seven structural groups, detailing all the components of light ship and dead weight.

Group Concept

100 Hull structure 200 Propulsion plant 300 Electric plant 400 Command and Surveillance 500 Auxiliary Systems 600 Outfit and Furnishings 700 Armament M Margins F Loads

Table III. SWBS structural groups

There are basically three types of weight according to our knowledge of them. The first is that which we know its CG with certainty, and their properties. The second is a type of weight in which the weight and centre of gravity are likely known. The majority of the vessels weight is collected. While there is some information available, the weight or CG is not defined, which could cause variations of displacement of the CG and more time and delay in detailed design. The third are margins, which are integral part of weight estimating and are expected to reflect the weight of the vessel or KG at the time of delivery.

1 Taken from MIEZOSO Manuel, “Ecuación del desplazamiento, Peso en Rosca y Peso Muerto”, ETSIN, UPM, Madrid, 1990.

The CG location of a combined loaded svessel may be regarded, can be calculated multiplying the weight of each component by the distance from the reference point (0,0,0), to find moments in the three coordinates, which makes a final sum and are divided over the total weight. The CG location is determined when the distance from each of the three planes has been established. The importance of its determination is that it exerts a bending moment on the axes x, y, z that affects the trim, heel, and KG height of the vessel. Once weighing the vessel’s components finished the loading conditions.

V. LOADING CONDITIONS

Chapter 096 of the Naval Ships’ Technical Manual (NSTM) which deals with weight and stability define the loading conditions for surface vessels. For thweight conditions were selected: Light Operating Condition and Full load.

A. Light Ship.

Combine elements of the vessel from the group 100 to 700, ready for service in every aspect. While excluding the dead weight must take into account some weights as: fixed ballast (if applicable), basic spare parts, machinery for fluids in minimum levels of operation.

B. Minimum Operating Condition.

The vessel has the least possible stability characteristics to survive in normal operation. The liquid cargo is included in such a manner that seeks to keep a good trim, but otherwise the components of the dead weight depend on both the type of vessel and its service.percentages for the components of deadwein the next table, which is presented below. operation condition, because many tanks most often high weights remain constant. Crew Same as full loadAmmunition 1/3 of full loadProvisions and stores 1/3 of full loadLubricants 1/3 of full loadFood and drinking water 2/3 of full loadFuel 1/3 of full loadLoad 1/3 of full loadBallast tanks Empty Passengers Same as full loadTable IV. Percentage of variable loading for minimum

operating condition3

Note: The above table related only values according to the characteristics of the load of the vessel

2 NAVAL SEA SYSTEMS COMMAND, Naval Ships’ Technical Manual.Chapter 096, pg. 96-4. 1996. 3 NAVAL SEA SYSTEMS COMMAND, Design Data Sheet 079, Stability for surface ships of US Navy, pg II-11.

The CG location of a combined loaded system, as a may be regarded, can be calculated multiplying the

weight of each component by the distance from the CG to a reference point (0,0,0), to find moments in the three coordinates, which makes a final sum and are divided over

location is determined when the distance from each of the three planes has been established.

determination is that it exerts a bending moment on the axes x, y, z that affects the trim,

. Once the process of finished came to define

CONDITIONS2

Naval Ships’ Technical Manual which deals with weight and stability define the

For this case three conditions were selected: Light Ship, Minimum

ombine elements of the vessel from the group 100 to 700, ready for service in every aspect. While excluding the

eight must take into account some weights as: fixed ballast (if applicable), basic spare parts, machinery for

the least possible stability characteristics rmal operation. The liquid cargo is included

a good stability and , but otherwise the components of the dead weight

and its service. Accurate for the components of deadweight are defined

table, which is presented below. This is a critical many tanks are empty and

Same as full load full load full load full load full load full load full load

Same as full load ge of variable loading for minimum

Note: The above table related only values according to vessel case.

Naval Ships’ Technical Manual.

NAVAL SEA SYSTEMS COMMAND, Design Data Sheet 079,

C. Full Load.

The vessel is fully loaded, plus the light vessel in accordance with theof its design.

Once the weights, CG’sthe three axes were completely defined, and set the loading conditions to study. Theunderstand the behaviour weight distribution. For this were developed.

Fig. 7. Loading curves for min

VI. STABILITY CRITERIA

The addition of weights due to the "shield" installed, consisting of three steel plates of ¼the middle of them throughout the superstructure of the vessel which added a total weight of 17 tons, initial stability criteria for surface shipsDDS-079 of the USN and 46CFR Part 170 USCG.

Standard DDS-079 begins by estafor spacing between transverse bulkheads and the collision bulkhead. To be considered effective, the main transverse bulkheads must be spaced a minimum distance of 10 feet + 0.03 LBP (length between perpendiculars) separated. The measure for the vessel Since 10 ft = 3,048 m and 3,048 m + 0,03 (31,15 m) = 3,98 m

Moreover, one of the transverse bulkheads can as collision bulkhead in order to limit the flooding of the compartment closest to the bow, must be located approximately 5% to stern, measured from the perpendicular (FP).

The measure for the vessel casetotal length is (0,05 x 31,5 m = 1,575 m) m behind 00 station, then, be compared with the 2D tanks distribution

4

is fully loaded, i.e., the total dead weight in accordance with the characteristics

CG’s and their bending moments for the three axes were completely defined, and set the loading

. The information was organized to of the vessel according to their

or this purpose the loading curves

Loading curves for min. operating condition

STABILITY CRITERIA

The addition of weights due to the "shield" installed, ting of three steel plates of ¼" with 2 cm of sand in

hem throughout the superstructure of the which added a total weight of 17 tons, required of a stability criteria for surface ships using the standard

he USN and 46CFR Part 170 of used by the

079 begins by establishing a requirement for spacing between transverse bulkheads and the bow collision bulkhead. To be considered effective, the main transverse bulkheads must be spaced a minimum distance of 10 feet + 0.03 LBP (length between perpendiculars)

vessel case would be: LBP = 31,15 m,

3,048 m + 0,03 (31,15 m) = 3,98 m ≈ 4 m

Moreover, one of the transverse bulkheads can be used collision bulkhead in order to limit the flooding of the

to the bow, must be located approximately 5% to stern, measured from the forward

vessel case would be 5% of the (0,05 x 31,5 m = 1,575 m) and the FP is 0,35 station, then, 1,575 + 0,35 = 1,925 m. This can

be compared with the 2D tanks distribution.

5

Fig. 8. 2D Tank distribution and bulkhead spacing

As it can be seen; a less spacing of bow and stern peaks,

as recommended by the standard, also the location of the machinery room affects the spacing of the cellar and the water tank aft. On the other hand, the forward collision bulkhead is 2.1 meters from the station 00, which is a somewhat higher than the minimum requirement as set by the standard technique.

Furthermore, the standard states warships have to bear threats and external influences, which can affect stability. The main threats are:

1. Beam wind combined with rolling. 2. Haevy lifting over one side. 3. Towing forces. 4. People crowding over one side. 5. High speed turning. 6. Top icing.

The first and the last two pose no threat to the vessel

considering its characteristics and surroundings. The other three could represent a risk regarding the safety of the unit, which is an appropriate stability measure attained by comparing the curves of upright arm with the curves of threats of heel. Factors to be considered are the static angle of heel with its associated arm upright as well as the dynamic stability reserve.

To edit these threats sums were made from the three arms of heeling simultaneously, which are described by mathematical formulation to obtain a most critical arm, that the multiplied by the displacement for each load condition; calculate the most critical moments that were imposed on the GHS program to check the set criteria. • Heavy lifting over one side

∆××= θcosaWHA (4)

• Towing forces

( ) ( )∆×××××××= 38cos2 32

θhSDSHPNHA (5) • People crowding over one side

θcos)/( ∆×= aWHA (6)

On the other hand, standard 46CFR provides a criterion about minimum permissible metacentric height, which is important for stability analysis which must be equal to or greater than the following for each load condition:

The value of factor P for service in shallow waters4,

defined according the standard as those that have no special risk, such as most rivers, harbours, lakes, etc.., is defined by the following equation:

The value A is the lateral section of the projected vessel above the water line and the value H to the height from the center of area A through the center of the submerged area or about the midpoint of draft.

The value of W corresponds to the displacement for each load condition and the value of T at the lower angle between 14˚ or half of the freeboard.

Finally, the program was edited and were obtained satisfactory results in terms of stability, which were predictable, considering its high B/T ratio = 6, even in the minimum operating condition.

Table V. GHS run to check stability criteria

In order to not move the centres of gravity of each tank

caused by the free surface effect, the software calculates a total value of heeling moment to artificially alter the position of CG.

Fig. 9. Stability curve for min. operating condition

VII. BEAM VESSEL ANALYSIS

GHS also gives structural information provident of the vessel by a percentage comparison of the maximum stress that the vessel will entail riding a trochoidal wave against its tensile strength, as well as providing information for shearing and bending moments of the beam vessel. Determining the design section modulus, Z, which must find continuous material in the middle section, an acceptable bending stress σad must be introduced into the

4 United States Coast Guard. 46CFR. Subdivision & Stability. Part 170. Subpart E – Weather Criteria, pg. 85

)7()tan(TW

PAHGM ≥

)8()1309(028.0 2LP +=

6 equation. Vessels below 61m in length the strength requirements are based in locally induced stresses than in longitudinal bending ones.

For practical purposes was created a spreadsheet of the Moment of Inertia and Section Modulus (SM), adding the structural components that go along at least 40% of the beam vessel, which are related to the master frame, obtaining a value of 206251.36 cm3, equivalent to 2062.51 cm2-m SM of the studied vessel . Once the modulus section and the values of the wave applied were calculated, this data and the values of modulus of elasticity and tensile strength of vessel material were introduced to the program.

Finally, the program receives information from a beam vessel with some evenly distributed weights and other locals, which is subject to hogging and sagging, and is compared in terms of percentage with the characteristics of the material of construction of the vessel indicating if it will be able to navigate properly in terms of structural resistance.

According the results obtained can be concluded that meets the structural requirements satisfactorily, comparing percentage of maximum stress suffered by the vessel with the material is no more than 3%.

Fig. 10. Beam vessel longitudinal resistance

VIII. RESISTANCE

For this case, the resistance curve was made using systematic series of the software NAVCAD. It has series of models ran in certificated towing tanks. The engineer ability is not just to match the series consistent with the vessel, but read and obtain useful information of the results presented.

The most appropriate series is selected according form curves, main ratios and Froude number. To make the best selection were studied the displacement hulls similar with characteristics of ARC Sejerí.

Method studied Result Basic formula Very wide range Holtrop method Low BWL/T (2.1-4.0) Oortmerssen method Low BWL/T (1.9-3.4) U. Denmark method Low LWL/BWL(5-8), 4.4 USNA YPseries method Characteristics match Series 60 Round bilge Series U. Brit. Columbia Unevenly shapes Series Nordstrom y YP 81 High death sliver Series 64, SSPA, y Dutch Planing hulls

Table VI. Systematic series analysis

The series chose was the U.S. Naval Academy. After that was necessary to complete information for using NAVCAD in three datasheets: Environment, Hull and Appendices. All data were taken for the full load condition in which resistance is greater. Some values were required to calculate independently, but many of them are calculated by the software.

Fig. 11. Hull Data in NAVCAD

The wetted surface required a special report on GHS for

its importance in the frictional resistance:

)9(

21 2SV

RC FF

ρ=

With regard to the environment in shallow waters such some sectors of Caquetá River, the most significant effect on resistance is squat effect. First of all, there is a significant variation in the water flow around the hull as the water passing under and going sideways faster than in open waters with a reduction in pressure and a sinking of the bow or the stern (squat), as well as an increase in trim and therefore the resistance, determining the maximum allowable velocity without bottoming.5 Taylor and Tuck define squat as the change of draft and trim of a vessel that is the result of variations in hydrodynamic pressure on the hull, in its movement at any water depth.6

5 LEWIS Edward, “Principles of Naval Architecture”, The Society of Naval Architects and Marine Engineers, 2nd Revision, Vol. II, Ch. V, Section 5, Pg. 42, 1988. 6 HERREROS Miguel, ZAMORA Ricardo y PÉREZ Luis, “El fenómeno squat en áreas de profundidad variable y limitada”. XXXVI Sesiones

Section Modulus = 2062.51 cm2 - m

(1) Weight, 1 = 0.1 T.M./m

(2) Point weight, 1 = 0.7 T.M

(3) Buoyancy, 1 = 0.02 T.M./m

(4) Shear, 1 = 0.04 T.M.

(5) Stress, 1 = 0.0001 T.M./cm2

After entering the characteristics of the hull of the

vessel that provide resistance in NAVCAD and studied how they affect the speed of the vessel, resulting in resistance curve presented below.

Fig. 12. Vessel case resistance curve

This graph shows the increase of resistance the speed. The vessel will respond readily to without significant opposition, but from 14 mrises sharply and the vessel will require a much larger machine or an optimal propulsion system that allows maximizing the actual configuration.

IX. SQUAT EFFECT INFLUENCE

The vessel must be designed for the subcases where there is displacement of supercritical region in the case of planning hulls.

Fig. 13. Design regions

técnicas de Ingeniería Naval. ETSIN Universidad Polítécnica de Madrid, Pág. 2, 2000. 7 HOFMAN M. and KOZARSKI V. Shallow Water Resistance Charts For Preliminary Vessel Design. International Shipbuilding Progress. 47, Number 449. Pg. 63. 2000.

Resistance Curve

0

3.6

7.2

10.8

0

3.6

7.2

10.8

0

3000

6000

9000

12000

15000

18000

21000

24000

0 2 4 6 8 10 12

Speed (kph)

Resis

tan

ce (

New

ton

s)

After entering the characteristics of the hull of the that provide resistance in NAVCAD and studied

t the speed of the vessel, resulting in

case resistance curve

This graph shows the increase of resistance as well as will respond readily to low speeds

ion, but from 14 mph the slope will require a much larger

propulsion system that allows

SQUAT EFFECT INFLUENCE

be designed for the subcritical region in of ships and the

planning hulls. 7.

técnicas de Ingeniería Naval. ETSIN Universidad Polítécnica de Madrid,

KOZARSKI V. Shallow Water Resistance Charts For International Shipbuilding Progress. Volume

The previous graph shows clearly the peak of the

critical region.

To understand better how affects the squat effect predictionwas used to compare squat effect increasing speed step by step, allowable depth to be able to navigate the subcritical region. On the other hand drastic increase in the total resistance when the depth decreases to critical levels.

Fig. 14. Squat vs. Spe

The previous graph shows the squat effect variation increasing the speed of the

The curve corresponding to

three critical regions and a that added to the full load bottoming, being impossible conditions.

The problem of the squat effect and difference in the curves for one and three meters, raising the need to know the minimum depth to avoid this undesirable peak navigation, for which somecurves between 1 and 3 m

The first iteration resulted in the critical region even show up to 2.5 m deep, but the vessel will bottom with only values less than 1.7 m, nearly load vessel, 0.87 m, which shows the true importance of the squat phenomenon.

12.6

14.414.76

15.1215.48

15.84

16.2

12.6

14.414.76

15.1215.48

15.84

16.2

14 16 18

7

graph shows clearly the peak of the

o understand better how the change in the river deep the squat effect prediction, the software NAVCAD

to compare squat effect at various depths, and increasing speed step by step, determine the minimum llowable depth to be able to navigate the subcritical region. On the other hand will be seen, graphically, the drastic increase in the total resistance when the depth decreases to critical levels.

Speed curve at four depths

shows the squat effect variation as

speed of the vessel for different river depths.

The curve corresponding to one meter deep, has the a 0.32 m peak in the critical area

full load draft, 0.87 m, causes the vessel impossible the navigation is in such

The problem of the squat effect and difference in the curves for one and three meters, raising the need to know the minimum depth to avoid this undesirable peak for safe

some iterations were made with 3 m deep.

The first iteration resulted in the critical region even show up to 2.5 m deep, but the vessel will bottom with only values less than 1.7 m, nearly the double the draft for full

which shows the true importance of the

Fig. 15. First iteration between 1.5

The second iteration also presented in all curves the peak values, in other words, up to 2.9 m deep will be a spontaneous effect of trim, affecting safe navigation of the unit. For that reason only for depths equal to or greater than 3.0 m, the vessel will sail in a subcritical zone.

Moreover, the following graphics shows the importance on resistance of the vessel. In the firstcurve of 1 m deep shows an important differefollowing three, with two meters apart, while it is observed a minimum difference of total resistance from 3 of difference.

Fig. 16. Resistance curves for 1 – 9 meters deep

Second graph is a zoom of the first, rejecting the meter deep curve in order to see the difference in when the vessel is in the subcritical region.

. First iteration between 1.5 – 3 m

The second iteration also presented in all curves the up to 2.9 m deep will be a

spontaneous effect of trim, affecting safe navigation of the only for depths equal to or greater than

subcritical zone.

shows the squat effect . In the first one, the difference with the

following three, with two meters apart, while it is observed from 3 to 9 m, six

9 meters deep

econd graph is a zoom of the first, rejecting the one the difference in resistance

in the subcritical region.

The curves have similar characteristics, three to six meters deep curves which affect the performance speinstalled power.

Fig. 17. Resistance curves for

X. SELECTION OF OPTIMAL PROPELLER One of the initial important requirementsbut not changing the current configuration motor or gearbox due to budget problems. On the other hand the pronouncedcurve from 14 kph away, discard the changing idea solution is to work out with reference to the existing diesel engine and gearbox in order to determine thappropriate propeller with the help of Propulsion system technical • 01 main diesel engine DD • 01 gearbox Twin Disc DD

2.45:1. • 01 three blades fix pitch propeller,

36”diameter, 32”pitch. With the engine performance curve available to work with NAVCAD, we can combine it curve and compare the speed of the machine with the power supplied to the axis and the maximum speed to achieve by the vessel in its current statethe next graph.

0 1 2 3 40

10000

20000

30000

40000

Rto

tal N

PREDICCIÓN MANACACÍAS-3m.nc4




RT

at

SEJERÍ SQUAT PREDICTION 3.0 m. nc4




0 1 2 3 40

10000

20000

30000

40000

Rto

tal N





RT

at





8 The curves have similar characteristics, but between

deep curves is a difference of 4000N, which affect the performance speed of the vessel with the

Resistance curves for 3 – 12 meters deep

X. SELECTION OF OPTIMAL PROPELLER

important requirements was more speed, the current configuration by a larger

due to budget problems.

pronounced slope of the resistance discard the changing idea and the

with reference to the existing diesel in order to determine the most

appropriate propeller with the help of NAVCAD.

Propulsion system technical data of ARC Sejerí:

main diesel engine DD671L, 180 BHP@1800 RPM

Twin Disc DD-5091V, reduction ratio:

three blades fix pitch propeller, B Series,

With the engine performance curve available to work with combine it with the vessel resistance

and compare the speed of the machine with the power supplied to the axis and the maximum speed to

in its current state, as can be seen in

4 5 6 7 8 9 10

Vel kts





T difference of 4000N at max. speed: 8.4 kts

SQUAT PREDICTION 3.0 m. nc4




4 5 6 7 8 9 10

Vel kts





T difference of 4000N at max. speed: 8.4 kts





Fig. 18. Resistance and engine curves comparison

This curve shows an abnormal performance of the engine, which is working below the nominal speed, reaching only up to 1500 rpm, as was evident in the records of the engine. These low revolutions affect the engine's performance promoting carbon in combustion chambers.

In addition, the propeller expanded area was obtained involving it in a paper drawing to AutoCAD for the necessary calculation.

Among other parameters to select is the application of a cavitation criterion for which was determined to choose the Keller equation.8

( )( )

3.03.12

kDpp

TZ

A

A

vOO

E +−

+=

This criterion may be implemented by the software and

gives an indication to establish if EAR allows an pressure differential. However, the equation leaves aside variables that affect cavitation such as the influence of the wake and blade geometry.

These variables are absorbed by the software that

involves these factors and calculates an overall percentage of cavitation in the current propeller as well asproposals.

To study the laws that govern the propeller behavior is tested with no hull in front which is known as "open water".

8 LEWIS Edward, “Principles of Naval Architecture”, The Society of Naval Architects and Marine Engineers, 2nd Revision, Vol. II, Ch. VI, Section 7, Pg. 183, 1988.

Resistance and engine curves comparison

performance of the main which is working below the nominal speed,

evident in the records These low revolutions affect the engine's

carbon in combustion chambers.

In addition, the propeller expanded area ratio (EAR) a paper and passing the

for the necessary calculation.

Among other parameters to select is the application of a which was determined to choose the

)10(

may be implemented by the software and allows an acceptable

he equation leaves aside affect cavitation such as the influence of the

absorbed by the software that an overall percentage as well as the other

To study the laws that govern the propeller behavior it is tested with no hull in front which is known as "open

LEWIS Edward, “Principles of Naval Architecture”, The Society of Naval Architects and Marine Engineers, 2nd Revision, Vol. II, Ch. VI,

The results show an excess increases, obtaining a value of 11.2%, above the 5% acceptable, according to the criterion applied.

According the report problems: First, the engine is maximum output is less than 150 HP to 180 HP available arevolutions from 1200 to 1500 average rpm, which causes carbon in combustion chambers of enginescurrent propeller has a cavitation problem the blades and reducing maximum speed of the vessel is 8.4 kts, which is likely to increase with an optimal propeller.

NAVCAD on the menu of comparison up to three different propellers andselection for optimize the p

The diameter is optimal restrictions in geometry. The first iteration was done for and 4 blades propellers.

Fig. 19. Optimum pitch selection for 3 and 4 blade

propellers with the same diameter

The next graph has a gripitch and therefore the value of the P/D, the speed curve can be moved to the apex of the curve of the engine performance.

The current propeller is 32"a P/D of 0.889. If this value P/D, keeping the same diameter, the software recommends a new pitch of 0.5545 m and consequently

In reporting results also identified a reduction of cavitation due to pitch change meeting the criteria set, but kept the value of the differential pressure between the two sides of the blade, which is within acceptable values.

9 results show an excess of cavitation as the speed

increases, obtaining a value of 11.2%, above the 5% acceptable, according to the criterion applied.

the current propeller has three irst, the engine is underutilized; its current

maximum output is less than 150 HP to 180 HP available at revolutions from 1200 to 1500 average rpm, which causes carbon in combustion chambers of engines. Second, the

cavitation problem that is wearing their thrust. Third, the current

maximum speed of the vessel is 8.4 kts, which is likely to propeller.

on the menu of propeller data allows a three different propellers and have a

e pitch.

he diameter is optimal due to the semi-tunnel The first iteration was done for 3

Optimum pitch selection for 3 and 4 blade with the same diameter

grid that shows that lowering the and therefore the value of the P/D, the speed curve

to the apex of the curve of the engine

he current propeller is 32" pitch and 36" diameter, for this value is decreased to obtain an ideal

P/D, keeping the same diameter, the software recommends and consequently a P/D of 0.607.

In reporting results also identified a reduction of change from 8.4% to 3.6%, thus

teria set, but kept the value of the differential pressure between the two sides of the blade, which is

10

Fig. 20. Optimum and current P/D comparison showing the

performance area at max engine RPM

From the reports, analysis concluded that the optimum propeller is one of three blades with optimum pitch, as can be seen in the graph below:

Fig. 21. Comparative curve of propellers efficiency at open

water

An additional consideration is geometry comparison between a GAWN and B-Series propeller. Normally, these applications use a propeller with a larger EAR, and GAWN used to be bigger, slower and may become more efficient. However, the results of the run widely favored B-Series. The reason is that this optimization is just of the propeller, the motor and the gear box remained the same.

Figura 22. Comparative curve between B-Series and

GAWN geometry propellers

Finally, the designed propeller was consistent to a commercial one, Aquapoise 45 of Teignbridge Propellers Ltd., found to be a better fit, which presented the highest efficiency and acceptable parameters of cavitation according the criterion established.

Once selected the optimum propeller, a comparison against the previous showed a moderate increase in speed but a significant reduction of cavitation.

Moreover, although in the current configuration the engine is only reaching a maximum of 1500 RPM, is consuming more fuel than if it develops its maximum speed. The results of the runs show a difference of nearly half a gallon per hour for the maximum speed of 15 kph, finally running over several days are three days of operation, which is a significant additional cost, avoided by installing an appropriate propeller.

XI. RUDDER SELECTION

Optimizing the rudder includes three basic aspects: governability, which is the ability to maintain the desired course; maneuverability, defined as the controlled change in the direction of movement; and change of speed, which is the controlled change of speed variation including stopping and reversing9.

Two criteria were used to meet the rudder area requirement. The first, Lamb & Cook, establishes a general rule of 2% of the area product of the length at water line by the average draft, and to this type of vessels particularizes by 2.5%. The second is a general formula of Det Norske Veritas, that criterion is based on the following formula:

9 LEWIS Edward, “Principles of Naval Architecture”, The Society of Naval Architects and Marine Engineers, 2nd Revision, Vol. III, Ch. IX, Section 1, Pg. 191, 1988.

2 3 4 5 6 7 8 9 100.44

0.46

0.48

0.50

Vel kts

Pro

pEff

BS-3: 0.914x0.813x0.450

BS-3: 0.914x0.555x0.450

BS-4: 0.914x0.530x0.610

1 2 3 4 5 6 7 8 90.40

0.42

0.44

0.46

0.48

0.50

Vel kts

Pro

pEff

BS-3: 0.914x0.555x0.450

BS-3: 0.914x0.546x0.800

GA-3: 0.914x0.503x0.800

+

×=

2

251100 LBP

BLBPTAR

Replacing with known data of ARC

barge that pushes in certain operations:

26

5.5251

100

)2626(75.0 mmAR

++

+×=

Therefore, 0.5 m2 is the minimum required rudder area

However is required a little increasing for direction (concept of governability), particularly for small vessels, so the minimum required rudder area of the is 0.6 m2.

However, the reality of ARC Sejerí was differentrudder had a total area of 0.68 m2, and with the two rudders configuration a total of 1.36 m2, too much area without benefit for the vessel, so the vessel can operate with just one rudder without affecting the area requirement

Fig. 23. Comparison of one of the two old rudders against the installed

Because of a single rudder could be placed a

tunnel middle, behind the propeller, the concept of the highest possible rudder improved its aspect rathe greater lift to increase the rudder angle involved. The next graph shows the evolution curves of the depending on the angle involved with rudders for different aspect ratios, allowing understandingimportance.

(11)

ARC Sejerí plus the

2

2

5.026

5m=

minimum required rudder area. However is required a little increasing for stability in

), particularly for small , so the minimum required rudder area of the vessel

was different. Each and with the two rudders too much area without a

can operate with just requirement.

. Comparison of one of the two old rudders against

could be placed at the semi-middle, behind the propeller, the concept of the

aspect ratio, the higher to increase the rudder angle involved. The

shows the evolution curves of the lift coefficient depending on the angle involved with rudders for different

understanding the concept

Fig. 24. Increasing of liftratios at different rudder angles

The rudder of ARC Sejerí

chord of 138 cm for an aspect ratio of 0.49, curves of the previous graphof a defective rudder.

Adjusting the height of the rudder to the diameter of the

propeller in order to absorb all its turbulent flow, it was determined a height of 88 cmrudder area had been determined deduced to 68 cm, to a final aspect ratio of 1.3, increased significantly the lift force.

The position of the rudder was another critical aspect, since there was much separation between the rudder and propeller.

Instead of one-design considerations of rudder is its ease of fabrication, installation, i.e., rudders were hung from the transom, the distance between the start of the rudder,propeller core was 92 cm. Tpropeller radius, in this case, no more than 44 cm, so that the rudder blade can absorb

Moreover, the trim towards the bow small portion of the upper ruddervibration, erosion and wear, direction due to external interference. Twas installing the rudder stock, supported by three bushings and nut up at the top to easily absorb the is completely protected and water covered.

11

lift coefficient for different aspect

ratios at different rudder angles. Source: PNA, Vol III.

Sejerí had a height of 65 cm over a of 138 cm for an aspect ratio of 0.49, i.e., outside of

revious graph, which gave a clear indication

of the rudder to the diameter of the propeller in order to absorb all its turbulent flow, it was

88 cm. On the other hand, as the had been determined at 0.6 m2, the chord was 68 cm, to a final aspect ratio of 1.3, increased

The position of the rudder was another critical aspect, since there was much separation between the rudder and

considerations of rudder is its ease fabrication, installation, i.e., rudders were hung from the

transom, the distance between the start of the rudder, and . This distance must not exceed a

in this case, no more than 44 cm, so that the rudder blade can absorb as water flow as possible.

towards the bow allowed to show a small portion of the upper rudder above waterline, causing

erosion and wear, and undermines the stability of direction due to external interference. The practical solution

installing the rudder stock, supported by three bushings and nut up at the top to easily absorb the propeller flow and is completely protected and water covered.

Fig. 25. Previous position of two rudders

position of one rudder layout

Furthermore, a system of two rudders propeller must be avoided10, unless the requirements of minimum rudder area require it. This layout effects of interference between the rudders whenturning, especially with compensate ruddersway, the propeller flow is lost amid the rudders, which does not take advantage of the turbulent flow from it.

Another design factor to consider is the degree of compensation11, which is given in terms of the coefficient block, equivalent to 0.8 for ARC load condition, so its range of balance rbetween 0.265 to 0.27012. This concept refers to the rbetween the blade area ahead of the rudderstocktotal blade rudder area, to facilitate turning of the vessel (concept of maneuverability).

Once defined the dimensions of the rudder, the most appropriate profile must be selected. In thejungle, the available technology just allowed plate rudders, but in meeting and training team, this process improved significantly with the introduction of a recent technology rudder buildingSchilling rudder.

Just try to explain the features of thdeserve another paper, but let us summarize the most important advantages. The rudder major innovation istall angle is bigger than 35°, as is used in others, 70° without loss of water flow, due to itthe form of “fish-fin”. The manufacture, like the NACAin one piece, so do not require additional maintenance. It has great stability in direction, which consumption. The lift coefficient is also high when the vessel going astern (concept of speed changing

The following graphs show the significant difference in the tactical diameter as well as the higher lift coefficient a vessel using Schilling rudder, comparing conventional NACA and a movable flap rudder.

10 LEWIS Edward, “Principles of Naval Architecture”, The Society of Naval Architects and Marine Engineers, 2nd Revision, Vol. Section 17, Pg. 365, 1988. 11 PEREIRA Heber, “Teoría del Buque”, Timones: Teoría y sus efectos evolutivos sobre el buque. Pg. 261, 1984. 12 Ibid 9.

layout vs. current layout

Furthermore, a system of two rudders behind one , unless the requirements of

it. This layout generates of interference between the rudders when the ship is

rudders. The same is lost amid the rudders, which does

not take advantage of the turbulent flow from it.

the balance ratio or , which is given in terms of the

ARC Sejerí at full range of balance ratio should be . This concept refers to the ratio

rudderstock over the area, to facilitate turning of the vessel

the dimensions of the rudder, the most . In the Colombian

the available technology just allowed building flat and training with the welding

improved significantly with the rudder building, the

the features of this rudder, would summarize the most

important advantages. The rudder major innovation is the , as is used in others, rising to

70° without loss of water flow, due to its cross section in . The manufacture, like the NACA, is

additional maintenance. It has great stability in direction, which benefits fuel

coefficient is also high when the concept of speed changing).

the significant difference in as well as the higher lift coefficient of

, comparing with a rudder.

LEWIS Edward, “Principles of Naval Architecture”, The Society of Revision, Vol. III, Ch. IX,

PEREIRA Heber, “Teoría del Buque”, Timones: Teoría y sus efectos

Fig. 26. Tactical diameter rudder. Source: Japan Hamworthy & Co.

Fig. 27. Lift coefficient comparison in turns going ahead and astern. Source: Japan Hamworthy & Co.

Considering the advantages of the Schilling rudder anin order to make a significant innovation in maneuverability, the rudder profile. In the tests, the tactical four to just two lengths, as well as an excellent steering, maintaining a steady headi

12

actical diameter improving using the Schilling

. Source: Japan Hamworthy & Co.

Lift coefficient comparison in turns going ahead

Source: Japan Hamworthy & Co.

the advantages of the Schilling rudder and a significant innovation in vessel

maneuverability, the rudder was built according to this the tactical diameter decreased from

, as well as an excellent steering, maintaining a steady heading.

13

Fig. 28. 3D view of Schilling rudder and the built one for ARC Sejerí, according corresponding model.

XII. IDENTIFICATION OF NON-STANDARD

PRACTICES

Current shielding is made of a combination of three ¼” naval steel plates with two layers of sand of 2 cm thickness between the plates, with a composed specific weight of 222 Kg/m2.

Comparing this shielding with the ballistic steel used for the construction of riverine support vessels build by Cotecmar is nearly six times less than the weight of the current assembly. This certificated steel is just one 3/16” ballistic steel plate with 50 Rockwell C hardness and a specific weight of 37.5 Kg/m2. This means that if the calculated weight for shielding, as detailed in SWBS was almost 18 tons, with the application of ballistic steel would be only 3 tons.

Moreover, the combination of three steel plates in addition to two sand layers estimates that it could give better protection than ballistic steel. However, Cotecmar test is made by firing a rifle AK-47, 7.62 calibers at a distance of 15 meters, with satisfactory results, while Riverine Brigade tests, with the same rifle and distance, the bullet never reached the third plate, but did damage even in the second one. This would weaken the structure and allowing for the passage of moisture into the arena, gaining more weight, and thus less stability.

Today, the procedure have been improved using

injected polyurethane instead of sand which has allowed better results in the ballistic tests, as well as weight reduction.

The difference that can have some benefit of this non-standardized procedure is the installation costs. One square meter of certificated steel installed in a riverine support vessel built by Cotecmar requires 37.5 kg of steel at a cost of $ 40.000 pesos kilogram installed, for a total of $ 1'500.000 pesos per square meter. On the other hand, the square meter, with the replacement of sand by injected polyurethane, worth $ 700.000 pesos.

However, this difference, slightly more than double, offset certified security costs and the remarkable difference benefit the stability of the vessel.

On the other hand, the steel with the sand assembly have additional costs associated with lower load capacity and increased fuel consumption which affects directly the operating costs, thus offsetting the installation costs.

XIII. CONCLUSIONS

The vessel keeps a good initial stability instead of the

almost 18 tons added by the superstructure shielding, revealed in the stability evaluation, according criteria applied to the calculations, as was expected, considering is high B/T ratio of 6.

The engine installed is operating below its rated speed, that cause carbonization of the combustion chambers, speed lost and higher maintenance costs.

The propeller installed aboard exhibits relatively good performance characteristics, however the optimal recommended will reduce cavitation, improve efficiency, and such, will reduce fuel consumption, extending the vessel range.

The reduction of cavitation at an optimal level will prevent blade erosion, loss of thrust and generation of noise and vibration in the hull.

The rudders of the vessel were inefficient due to its low aspect ratio (0.43) and a low balance ratio (0.12), as well as its wide distance from the propeller (1.5 times propeller diameter), which leads to design a rudder more efficient and better placed to improve the maneuverability and general performance of the vessel .

The type of shielding installed does not affected the

initial stability seriously, but has done some damage associated with an uncertified armor, less stability, less cargo capacity and higher fuel consumption.

The lack of an appropriate methodology and an investigative process in the project of vessel conversion lead to a non optimal result, thus economic damage in operating costs, instead of at the beginning there is an apparent saving in repairing costs.

14 REFERENCES

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Service on Rivers and Intracoastal Waterways”. 2003. [2] ASTM. A 131/A 131M – 04. Standard Specification

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[4] CHRISTOPOULOS, R & LATORRE, R., “River

Towboat Hull and Propulsion”. SNAME. Great Lakes and Great Rivers Section, January 1982.

[5] FAIRES, Virgil M. “Diseño de Elementos de

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[8] HERREROS Miguel y SOUTO Antonio, “La

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[9] HOFMAN Milan y KOZARSKI Vladan.

“SHALLOW WATER RESISTANCE CHARTS FOR PRELIMINARY VESSEL DESIGN”. International Shipbuilding Progress. Volume 47, Number 449, 2000.

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Enrique. El timón Schilling, mejora relevante en la maniobrabilidad de un buque. Escuela Técnica Superior de Náutica y Máquinas de Coruña. Revista Marina Civil.

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[16] MARTIN DOMINGUEZ Ricardo, “Cálculo de

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[17] Massachusetts Institute of Technology. “Lectures of

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[19] MIEZOSO FERNÁNDEZ Manuel, “Ecuación del

desplazamiento, Peso en Rosca y Peso Muerto”, Escuela Técnica Superior de Ingenieros Navales, 1990.

[20] NAVAL SEA SYSTEMS COMMAND. “Naval Ships’

Technical Manual. Chapter 096, Weights And Stability”, August 1996.

[21] PEREIRA Heber, “Teoría del Buque”, Timones: Teoría y sus efectos evolutivos sobre el buque, 1984.

[22] SAUNDERS Harold E., ”Hydrodynamics in ship

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[23] STRAUBINGER. Erwin; CURRAN, William;

FIGHERA, Vincent. Fundamentals of Naval Surface Ship Weight Estimating. En: Naval Engineers Journal. Mayo 1983.

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