Safety at Sea Seminar Seaworthiness and Safety Yacht Design 102 Paul H. Miller Dept of Naval...
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Transcript of Safety at Sea Seminar Seaworthiness and Safety Yacht Design 102 Paul H. Miller Dept of Naval...
Safety at Sea Seminar
Seaworthiness and SafetySeaworthiness and SafetyYacht Design 102Yacht Design 102
Paul H. MillerPaul H. MillerDept of Naval Architecture, Ocean and Dept of Naval Architecture, Ocean and
Marine EngineeringMarine Engineering
US Naval AcademyUS Naval Academy
Safety at Sea Seminar
Seaworthiness: A Definition“To be
seaworthy, a vessel must be able to defend itself against the perils of the sea…”
A classic example of a “seaworthy design.”
Safety at Sea Seminar
The Big Picture: “Design” in Context
1993 Marine Board Casualty
(of vessels) Study
12% Design and Construction Issues
88% Owner and Operator Issues!
Safety at Sea Seminar
Owner and Operator Issues
• Training• Practice!• Education:Safety at Sea Seminars!
• Maintenance (Inspect, Maintain, Repair)
• Crew Fatigue• Motion? (Bigger is better)• Work load? (Smaller is better!)
Safety at Sea Seminar
Owner and Operator Issues Example:1998 Singlehanded Farallones Race
32 Miles Out into the Pacific and Back
Fifteen (exciting) Minutes after 79 Boats Started
Safety at Sea Seminar
• 1 Hour Later
• 25-35 knot winds
• 12-20 foot waves
• 1/3 Dropped Out
• 1 Vessel Required USCG Support
• Swan 47!
• Flooded
• Hatches Improperly Secured!
Safety at Sea Seminar
• First to Finish
• F/27 Trimaran
• Ave Speed 9.8 knots
• First On Handicap
• 28’ Herreshoff Rozinante Ketch
• Ave Speed 7.2 knots
The Moral of the StoryBoth boats were easy to sail, reef, and steer!
Safety at Sea Seminar
Design and Construction:Three Basic Rules
(Sail or Power)
1. Keep Water Out of the Vessel!
2. Be Able to Direct the Vessel’s Course!
3. Keep the Vessel Upright!
These requirements often conflict with other goals, such as speed or “roominess”!
Safety at Sea Seminar
1. Keeping the Water Out
• Structure• Wood, Fiberglass, Carbon, Metal, (even
Ferro-Cement!) are all acceptable, if sufficient Factors of Safety and quality ($?) construction are used
• Reputation of Designer and Builder are a clue, “standards” are another
• Thoroughly Survey for Current Condition Prior to Each Passage (“PreFloat”)
Safety at Sea Seminar
1. Keeping the Water Out (2)
• Structural “Negative Indicators”• Leaks around through-hulls, hull-deck joint,
keel bolts• Noticeable flexing of hull panels that cause
joinerwork or furniture to move, doors jammed
• Broken joints (tabbing)• Stress cracks
Safety at Sea Seminar
1. Keeping the Water Out (3)
• Watertight Integrity• Hatches sufficiently strong, bedded and
lockable (from inside and out)• Hatchboards sufficiently strong and
securable (ditto)• Redundant bailing capacity
Safety at Sea Seminar
American Bureau of Shipping Guide for Offshore Racing Yachts
The Elements of Boat Strength by Dave Gerr
Structures References
Safety at Sea Seminar
2. Directing the Vessel’s Course (2)
• Rudder and Keel• Sufficient area• Keep attached!
• Weak links• Shaft to tiller/quadrant• Shaft to blade• Cable, sheaves (Think
Simple! Tiller?)
Safety at Sea Seminar
Suggested Equipment References
US SAILING:Safety Recommendations for Offshore Sailing
or
Safety Recommendations for Cruising Sailboats
Safety at Sea Seminar
3. Keep the Vessel Upright - Stability
• Wind and waves are trying to tip the boat over
• Ballast, hull shape and crew weight are trying to keep it uprightDon’t rely on crew weight!
Safety at Sea Seminar
3. Static Stability
• Buoyancy Force acts upward through the center of submerged volume
• Weight Force acts downward through the Center of Gravity
B
W
Sum of the Forces equals Zero!
Safety at Sea Seminar
3. Static Stability When Heeled
B
W
Horizontal distance between Center of Gravity and Buoyancy is Righting Arm (RA)
Righting Moment= Righting Arm x Boat Weight= “Stability”W
“Give me a lever and I will move the earth!”
Safety at Sea Seminar
3. Static Stability When Really Heeled!
B
WW
Moral: A Low Center of Gravity is Nice!
Safety at Sea Seminar
3. Static Stability - Beam Effects
B B
WW
Righting Arms!
W
“Form Stability”“Ballast Stability”
Safety at Sea Seminar
3. Static Stability Lessons• Beam Provides Stability at Small Angles (<40)
• A Low Center of Gravity Always Provides Stability
• For the Same Initial Stability a Narrow Boats Needs a Lower CG (More Keel Ballast-More Weight?)
RM
Heel Angle0 90 180135
Positive Righting Moment - Boat Will Return Upright
Negative RMBoat Will CapsizeLimit of Positive Stability
Safety at Sea Seminar
3. Static Stability Curves
RM
Heel Angle0 90 180135
Narrow Boat - Ballast Stability
Beamy Boat - Form Stability
With Water Sloshing Inside!
Safety at Sea Seminar
3. Dynamic Stability• A Vessel’s Response
to Gusts and Breakers is a function of:• Static Stability (RA x
Boat Weight)• Roll Mass Moment of
Inertia• Surface Area• Roll Damping• Luck!
Uh Oh!
Safety at Sea Seminar
3. Dynamic Stability• Roll Mass Moment of Inertia
• = Sum of (weights x “distances from CG”2)!• Separate weights vertically (preferably lower
so as to get more RM!)
• Surface Area• Reduce Contact Area - dodgers, sails, etc.
• Roll Damping• Keel Area Down Low (Bulbs?)
Safety at Sea Seminar
3. Dynamic Stability
“Ballast Stability” vessels tend to follow gravity!
“Form Stability vessels tend to follow the water surface!”
Safety at Sea Seminar
3. Stability Suggestions
• Capsize Screening Formula (a rough guide)
2
64)( 3
1
lbsBoatWeight
Beam
• LPS >130 for cruisers (may be available from US Sailing for a sistership, or ask a yacht designer)
Safety at Sea Seminar
3. Effect of Size• The Static Stability
Curve, Damping and Mass Moment of Inertia terms do not have “length” factors.
• Displacement, draft, submerged area, beam, and center of gravity are more important!
Size is relative!
Safety at Sea Seminar
“Desirable and Undesirable
Characteristics of Offshore Yachts”
by the Technical Committee of the Cruising Club of
America
ComprehensiveReferences