Lcb / Lcf

[SuperPiper]

Of course it's possible to get the transom out of the water, if the bow is pitched down low enough. The stern wave gets magically quiet when the 1st mate sits with her legs through the bow pulpit (and the cockpit gets quiet too, teeheeehee). I've not yet confirmed whether this produces a speed increase.

Sailors talk about "climbing the hill" when the boat is at/near hull speed. That may be because the sketches of a boat in that situation usually shows it with the bow UP while climbing the bow wave. The advantage of a small boat is that it can be kept level by simply shifting some weight. Instead of CLIMBING the hill, my little boat can attempt to PLOW through it. Is there an advantage in that?

My little boat does not have a wave-piercing bow.

Bonus points if you can make reference to LCB and LCF.

[Eric Sponberg]

There is no advantage in plowing through a bow wave if it causes your speed to decrease. Pull the mate back and give her a kiss, and you'll likely get more speed and mileage than you thought possible.

Most design analysis regarding LCB and LCF happens in still water--the boat is not moving--hence the general term for these things and others regarding the submerged volume, Hydrostatics = still water. Your scenario of the boat climbing the bow wave is a dynamic situation in which changes in LCB and LCF are momentary, and we are not too concerned with them, really. We may find them instrumental in analyzing pitching, yawing, and rolling motions--hull rotational dynamics--but necessarily speed.

Eric

[SuperPiper]

I read 'em all. Some really good stuff in that thread.

But I think that the 1 post that meant the most to me was by MikeJohns at Post #266. He explained the dynamics of the centre of buoyancy and the centre of gravity with respect to the centre of flotation. I had to read it more than once to comprehend all that he was describing.

Thanks Mike.

[SuperPiper]

In post #242 of the Sponberg thread, Eric discusses the Bruce Number. It is used to describe the sail power for multihulls:

" . . . a Bruce Number greater than 1.0 meant that the boat speed could exceed the true wind speed on some points of sail in some conditions."


So, why can't monohulls make use of Bruce Number? It would be handy if the minimum 1.0 BN could be used to match sail area to displacement.

What a great series! The thread is pumped full of good info.