In the interests of balance for anyone (like me) who comes on this discussion too late to participate, I'd like to put another point of dissenting view to the OP's central assertion.
My objection is very broadly similar to one raised in post 38, although he's making a somewhat different point to mine (but valid too, it seems to me)
The OP talks of decoupling the vessel from the energy of the waves, which is an admirable aim, but then commits a logical non sequitur by talking as though this can best be achieved by reducing the speed of the vessel through the water
This makes sense to me in the situation where the waves are not breaking forwards, so I have no trouble with it in that circumstance.
And I freely admit that even in storms, this covers the situation almost all of the time - very few of us will ever see more than a handful, at most, of deep ocean waves breaking entirely down their front face, as opposed to spilling some or all of the crest down the back, which is what 99% or more of so called "breaking" waves are really doing when you pay close attention.
[Of course there is an exception for waves which hit something, such as your boat. Then the crests routinely detach and travel forwards.]
I say this because it's well known that there is no mass transfer horizontally in an ordinary wave train. The particles of water
, viewed side on, orbit back to their starting point each wave, unless there's an underlying current
This all changes when the wave front becomes so steep that the crest can 'exit the system' and fall under the influence of gravity down the fast-moving face of the wave. At this point there can be collossal horizontal mass translation, and sitting there stationary is not an optimum way of 'decoupling the energy of the storm from your yacht'. In fact, it's almost the opposite. The only way you could do worse would be to motor
rapidly towards it (and even this might be better, if you made it over the top before it broke!)
Certainly it is better to be anchored to the body of water by the bow (or even the stern) than to be anchored side on, or in almost all cases than to be drifting side on, as you can well imagine with the thought experiment
in a surf break. But such anchoring
will take massively strong gear
if the wave is very large, with a significant crest.
If the aim is to avoid coupling to the kinetic energy of the avalanche of water coming down the flank towards the yacht, it is (at least in theory) necessary to travel in the same direction at the same speed as the avalanche.
This is not literally practicable because the speed is unrealistically high. The ramp
down which the avalanche is travelling is itself moving at maybe 40 knots, and the water tumbling down it is effectively in freefall.
However if the vessel is designed to be able to skid off at considerable speed down the face of such waves without tripping over its own appendages or bow (and ideally in such a way that, if caught beam on, it will tend to bear away so as to run away end-on) then we are a lot closer to the ideal the OP sets up, of NOT coupling to the kinetic energy.
Imagine a surfboard plonked in mid ocean in such conditions. Even one not strong enough to survive your weight in the middle with both ends on blocks, will survive the worst a breaking wave can do, and it may even stay sunny side up.
Adding a ballasted keel
would NOT improve its chances, in fact, I would venture, quite the opposite. I can't say for sure that internal ballast would not be an improvement, however.
I'm straying from the topic, which is that it's the speed Delta
, or difference
, between the mass translation of the wave and that of the vessel, which causes energy coupling (which is a Bad Thing, when there's lots of energy on tap).
I guess this points inexorably towards some sort of skimming dish, with appendages retractable except at the stern, buoyant, high lift
in the forebody, low freeboard, and (when keel
is retracted) with the centre of mass at about mid height relative to the side profile (not
the underwater profile)
There needs to be some way of ensuring this vessel can reright if the attempt to decouple is - or more accurately: the attempt to AVOID tripping, is unsuccessful, but the mast
is not likely to survive if it inverts in such circumstances. *
For a small deep sea vessel, this implies to me the whole design of the vessel would have to prioritise the hypothetical encounter with this (very unlikely) circumstance: either a (very strongly built) catamaran
- but I don't know pretend to know much about this option ... or a strong but relatively light monohull
, with a lifting ballast keel independent from deep appendages aft. (The latter acting like the fletches of an arrow)
Ideally the ballast keel would be hydraulically operable, using an accumulator. This would enable the ballast keel to be immediately deployed if the vessel should invert. Would probably have to be a swing rather than a dagger so the center of mass did not rise too high, because a skimming dish needs a minimal draft
in the canoe body.
This all hardly seems worth doing, except in the specific case of sailing in the few parts
of the world where such waves are --let's say, while still infrequent, not unheard of.
*Possibly for a small vessel, say 10 to 11m, with a short rig, given that we can now look, via satellite
, at wave heights in developing systems which have not reached us, it might be feasible to engineer
a rig which could preemptively be dropped and secured at sea. You'd only do this if a sufficiently ugly system was in the offing - but you'd have to made a decision early, when the motion of the boat was still moderate, and this seems unlikely in practice.