BoatBanter.com - Can a 45' sailboat survive a 50' wave ?

Following is from www.seriesdrogue.com
and I scoff and mock all you scared weard little guys,like Jax, who
will no doubt cry foul, because someone with a commercial interest in
this subject dares make a post.

Worst Case Breaking Wave Strike
I have chosen the case of the Winston Churchill in the 1998 Sydney
Hobart race as an example of a worst case breaking wave. The Churchill
was a classic wooden sloop of 25 tons displacement and 55 ft. LOA. Of
the experienced crew of 9, two perished in the accident.

From "Fatal Storm' by Mundle. "A sea came out of nowhere", said
Stanley, " I could feel it from where I was in the aft coach house. It
picked the boat up and rolled it down its face - 25 tons of boat- into
the trough at a 45 degree angle. It was like hitting a brick wall when
we hit the bottom". A crewman below reports that a sudden motion of
the ship picked him up and threw him 7 ft. He observed that 8 ft of
the heavy timber bulwark and planking had been torn off near the
leeward shrouds, and the ribs were exposed. . The boat filled rapidly
and sank in a matter of minutes.

This is an unusual type of accident. Although there are records of
many storm casualties, I am aware of no documented instance of a well
found yacht of the size and reputation of the Churchill and crewed by
an ample group of expert sailors, suffering such catastrophic
structural damage that it sank in a matter of minutes. How could this
possibly happen? The severity or the storm was extreme but by no means
unprecedented. There are numerous reports of large sailing yachts
surviving hurricanes of the same general magnitude. Although yachts
have been lost in such storms I have been able to find no record of
comparable structural damage.

History shows that the probability of a yacht being capsized and
damaged by a large breaking wave is strongly influenced by the
displacement of the vessel. Yachts under 35 ft. have a poor history
while yachts over 50 ft are rarely capsized and damaged.

The nature and extent of the damage incurred by the Churchill is also
most unusual. The vessel was designed by Sparkman and Stevens and was
maintained to the highest standard. Yet the heavy timber bulwark was
shattered, the planking gone and the ribs exposed.

There is no question of the fact that the leeward bow of the boat was
driven into solid green water at an extremely high velocity, far
higher than would be expected in a simple contact with a breaking
wave. We now have a technical understanding of how such a destructive
force can be generated. Observations from many experienced sailors on
a number of the SH yachts provide data which permit a sound
engineering analysis of the performance of the waves and the boats in
the race.

Water forces are applied to the hull of a yacht by two means, buoyancy
forces and dynamic forces. Buoyancy forces are the familiar pressure
forces which keep the boat afloat. They never reach sufficient
magnitude to damage a well found yacht.

Dynamic forces result from the motion of the boat relative to the
water, either as a result of the boat velocity or the water velocity
due to wave motion. A speeding power boat can be destroyed by striking
solid water. Similarly, a sailing yacht can be destroyed if it is
accelerated up to a high speed by a breaking wave strike and then
impacts solid green water in the preceding trough. This is the fate
that befell the Churchill.

To understand this phenomenon we must consider the concept of energy.
A moving car or boat has energy. This form of energy is called kinetic
energy. Kinetic energy is measured in foot-pounds. Kinetic energy can
be calculated by the formula KE=1/2 (w/g) times (v squared). Where w
is the weight of the car or boat, g is the acceleration of gravity
(32.2 ft/sec) and v is the velocity in ft./sec.

Thus a 3,000 lb. weight traveling at 30 mph (44 ft./sec.) would have a
kinetic energy of 90,000 foot pounds. Now...and this is very important
to our understanding of the Churchill disaster...if the moving vehicle
strikes an object, the kinetic energy determines the severity of the
collision and the extent of the damage.

In addition to energy due to motion, a vehicle can possess energy due
to height. This type of energy, also measured in foot pounds, is
calculated simply as the height times the weight. A 3000 lb car
hoisted to a height of 50 ft. would have 150,000 foot pounds of
energy. If dropped from 50 ft to a solid surface, the car would
dissipate this energy in damage. If the car was compressed by 2 ft.
the average force during the impact would be 75,000 pounds. If it
landed on its top and compressed four feet (because it was softer) the
average force would be 37,500 lbs. .These numbers (compression and
force) are not precise but the product must be the same to satisfy the
energy balance.
more of the same at my site
regards
Bryan

Rich Hampel wrote in message ...
What will happen to a 45ft. boat being hit by a 50 ft. wave ...... Not
much if the wave isnt steep as the boat will simply lift over the wave.
The *steepness* of the wave is important; and, It all depends o n the
posiition of the boat vs. the oncoming wave, with being broadside to
the wave and steepness of the wave (and whether its breaking or not.)
that is thw worst case. Breaking waves (the tops of the waves sliding
down the front of the wave in a big 'show' of air filled foam are the
'nasties' that break boats. If the boat is moving, the expertise of the
helmsman (able to dodge breaking waves by steering around them, etc. is
vitally important as is the 'stability' or sea-worthniness of the boat.
A 50 foot wave is no big deal if it isnt a 'steep wave'. An
approximate 25-30 ft. wave if steep enough can easily roll a 45ft boat
- depends on if its broadside, etc.

The inbuilt stabilty is the factor of how a boat survives adverse
waves; a lightweight broad beam boat will tend to be vastly more
unstable than a heavy, deep, narrow boat ... the lightweight boat
having sometimes the advantage of being able to sail away from bad
weather faster than a heavy boat.

When the sea state is dangerous there are techniques that can be used
to survive --- such as using a parachute anchor and holding the bow
about 45 degrees to the oncoming waves. The boat will 'slip' slightly
backwards and the turbulance of the slip on the surface will cause the
waves to 'break' before they hit the boat, etc.

Its not the height of the waves but the steepness of the waves and
especially if the wave is so steep that the top of wave is 'breaking'
that is so dangerous.

hope this helps.

. net,
wrote:

I saw the news earlier this week about the 591' ship
Explorer with 681 college students on board getting
hit by a 50' wave.

What will happen if a 45' sailboat gets hit by the
same wave ?

Does it make a difference which way the boat is facing
when it gets hit by a wave this big ? If it does then
which way is the best way ?

I was told that a good boat can correct itself even if
a big wave turns it upside down. So can you just strap
yourself to your bed and go to sleep ?

Are the windows likely to break and let the water in
so that the boat can sink after getting hit many times ?

What else do you think can happen ?

Thanks for your help.