Loadings affecting on boats and small craftMarkku Hentinen 2016

Local loads

• Hydrostatic pressure• Hydrodynamic pressure

– Slamming-loads– Local loads due to pressure distribution on planing hulls

• Rudder loads• Keel loads• Propeller bearing support forces• Loadings due to engine/tanks/other heavy installations

and equipment• Loadings due to deck equipment (strong points for

attachments, winches, cranes)• Ice loads

Slamming-pressures on fast planing craft

• Pressure is proportional to the square of the relativevelocity between wave and hull bottom multiplied byconstant k.

• k-value is dependent on the bottom shape; the anglebetween water and hull surfaces.

• At small angles of incidence (< 3 ) the air trapped underhull makes determination of k-value difficult.

• Peaks of slamming-pressures are transient and verylocal.

• Equation used in NBS-rule:

Slamming-pressures on fast planing craft

• Equation in ISO-standards:• where ncg is dynamic loading factor coming from

accelerations at the Lcg:

• Based on methods by Fridsma&Savitsky

nk L

Bv B

B

kkv

cgwl

c

c

x

L

ar

0 07810

0 084 5012 2

, ( . )( ) g

missä = trimmikulma ( 4 )uppouma(ton)

L vesiviivapituuspalleleveys

= pohjanousu ( 30 )= iskun pitkittäisjakauman kerroin= pinta - alreduktio

= nopeus

WL

Trim angleDisplacementLength of waterlineChine breadthDeadriseLongitudinal distribution factorArea reduction factorSpeed

DESIGN PRESSURES FOR FAST PLANING BOATSMarkku Hentinen, MScTech, Gunnar Holm, MScTechVTT Manufacturing Technology, EspooWhy very high pressures can occur?• Frequent slamming "normal"• High vertical accelerations can be allowed by the crew

Measurements of bottom pressures, strains and vertical acceleration were carried out for NV 96

Calculation methods for slammingloads

The problem is connected to the reliableprediction of:• the relative speed between the water

and the hull surfaces• the coefficient k´s value as a function of

steepness of the bottom• acceleration values for the landing

phase of the boat - it is to be noted thatdue to the light displacement and highspeed the motions are highly non-linear.

min:s01:36,000 01:36,050 01:36,100

Luotsi11

Paneeli1 Paneeli2 Paneeli3 leikkaus1 leikkaus2

pystykiiht.

kPa

125

100

75

50

25

0

-25

-50

g

25,0

22,5

20,0

17,5

15,0

12,5

10,0

7,5

5,0

2,5

0,0

-2,5

Slamming pressure during a typical slamming situation calculated from bending stressesof the panel, shear stresses of the stiffeners. Vertical acceleration near the panel is also shown.

Vertical acceleration at CG

0

20

40

60

80

100

120

140

160

30 35 40

V [kn]

a [m/s ]

DnV HSLC,DSPL=4090 kgLloyd´s SSC,DSPL=4090 kgMeas. (NV96),DSPL=4090 kgDnV HSLC,DSPL=4455 kgLloyd´s SSC,DSPL=4455 kgMeas. (NV96),DSPL=4455 kgDnV HSLC,DSPL=4725 kgLloyd´s SSC,DSPL=4725 kgMeas. (NV96),DSPL=4725 kg

Comparison of the calculated and the measured acceleration values.

Global loads

Rigging loads on a 40’ sailing boat

Rudder loads in a 40’ sailing boat

Scantlings of keelfloors and bolts ina 40´ sailing boat

Additionally.grounding loads,see ISO 12215-9