Wave Piercing Bows

For submerged bodies, far enough below the surface so that wave making isn't significant, shape of the forebody doesn't significantly affect drag as long as flow over the forebody is attached.

 

We should definitely look to nature for inspiration and hints in design, but
the ultimate task is to improve on nature, IMO.

 

With such intelligent, philosophical posts, I'm a little embarrassed that I'm just looking at various bows as a fashion accessory.

 

But we don't have the same materials, fabrication methods and control systems available for use as nature. So sometimes we might be able to improve but other times we struggle to come close to matching nature.

Of course it's a different situation if you take one particular function or attribute by itself, but then you are dealing with different "SORs".

 

Me too sorta. :]

 

Yes, but we are far superior in many ways too .
We could go on at great length about this, so let's not

 

I don't think this is a correct analysis, but maybe would happen if the reverse bow was an add-on and not formed by the hull profile. A reverse bow should be the result of more buoyancy at the waterline - as this is pushed down it has a greater and greater reaction force pushing the bow back up. If the hulls are narrow at the waterline and flared, then the reserve of buoyancy does not even act until it is pushed down. Probably a bigger factor for pitchpoling is the effect of the wide flat deck of a conventional hull acting as a brake when submerged and tripping the hull.

I see the difference between the profile of my F16 and tornado hulls, the reverse bowed F16 hulls almost resemble the tornado hulls upsidedown. The F16 can be pushed far harder downwind, even to the point of submerging the hull because the buoyancy is always in effect and not in reserve and because the very fine deck profile doesn't trip the boat.

 

After the bows are fuliy submerged the lever arm is shortened the deeper they go. The lessened tripping tendency do to the deck shape is the safety valve. A cruising boat should spend some time considering the ease of working on the decks and bows though. That is where you wind up setting headsails and leading lines to bows for chutes, docking etc....Having a safer working platform for cruising is worth throttling down a bit earlier.

 

Pointers? Strapless? Logs On?

 

Just to point out my particular situation, the boat is controlled from the forward cockpit, making those factors a lot less relevant. On the inner forestay is a self tacking blade. On the outer forestay is a screecher. I may get a kite too, but it is not used so often. The boat will spend nearly 100% of time at anchor and I always use a bridle setup. In short, going forward is done at the boat's overall centerline.

This would be a change in the shape of the foam piece added on to the bow, not a change in the length of the deck.

 

I humbly disagree with this analysis. The horizontal lever arm might be smaller, but the vertical one increases when one bow becomes submerged and the other hull starts to rise. That, plus the fact that both the hull drag and the sail forces increase considerably (and hence the tripping moment of the forces) when tripping action has started, means that the mechanism of pitch-poling is self-fueled and nearly irreversible in absence of quick reaction by the crew. A more buoyant (not wave-piercing) bow acts in the initial phases of the capsize, by making it more difficult for the bow to go all the way below the water surface. It is all well explained in the links Ad Hoc has posted in his last reply.

Here is a nice AC Cup video coverage form Naples, for everyone to enjoy some wavepiercing action (and also a nice show of a pitch-poling dynamics, at 1:10) : http://www.youtube.com/watch?v=nHyTJ2FIllg
Also to be noted - how strongly the sail drive force pushes the bow down, due to lack of buoyancy in the bow sections (at 1:47, for example).

I fully agree with this consideration, as already stated in one of previous posts.

Cheers

 

The bouyancy from the normally submerged portion of the hull does not increase as it's pushed further underwater.

The increase in buoyancy from submerging a portion of the hull will be equal to its volume multiplied by the density of water multiplied by the gravitational constant. The rate of increase in buoyancy will be proportional to the waterplane area.

As a reverse bow with tumblehome is submerged below its waterplane area will decrease and the rate of the increase in buoyancy will decrease. For a flared bow the waterplane area will increase as it is submerged and thus the rate of increase in buoyancy will increase.

 

I understand what your saying here but if the bow of the boat with the reverse bow is carried forward from position of the standard plumb bow how is there less volume? Surely what you have is more volume and an extension of the waterline? I can see the point if the waterline length was shortened by cutting back the existing plumb bow and would agree there is less buoyancy than an equivalent plumb bow for the same waterline length.

 

If the the bow of the boat with the reverse bow is carried forward from position of the standard plumb bow then yes, there will be additional voume forward - the added volume of the add-on reverse bow. But an add-on flared bow would also increase the volume, and if submerged due to pitching would have increased buoyance faster than an add-on reverse bow with the same static waterline. The reverse bow shape doesn't have any advantatge over a plumb or flared bow with regards to added buoyancy.

 

I assume that's nearly 100% of time when not underway at anchor rather than tied to a dock etc, not that it will spend nearly 100% of total time at anchor.