Has anyone done any tank testing on bow shape. Without access to a tank my guess is that the slab slightly negative angled bow ( wave piercer ) as is now becoming the norm is actually more about ease of getting out of the moulds than true shape. I have heard that a slight bulb on the very bottom is the best. Any views

The negative bow angle is a direct result of the fact that the deck is narrower then the hulls or keel line. That is all that is to it.

Some builders make up all kinds of fancy stories, but only the direct result of redistributing the volume in the vertical sense. It will take more effort to get a straight bow line with these kinds of hulls, and most likely without any benefit, so why do it ?

Wouter

Appreciate that the deck is now smaller than the below water line shape will give a negative rake on the bow. No my question is that I have read somewhere that the critical bow to keel line should be a rounded bulb rather than a blunt line. Some of the olympic skulling boats are going this way along with quite a few aircraft to minimise drag at the critical points, any views as I suspect quite alot of drag is created at this point.

The prime motivation for raking the bow in reverse is to use less material (smaller surface area for same overall waterline length as well as the obvious result of carrying the bow bouancy lower, therefore less weight (no matter how little the difference it all counts especially in the “ends” of a hull). The effects of an aft raked bow over a vertical one is of an unmeasurable performance difference (if there is any difference at all) To have a "bulb" entry at the bottom of the bow on a cat is very debatable. The bulb effect is of value primarily only if it is maintained continually beneath the water surface level, if it breaks the surface it generates much more drag than a fine entry.

I think Darryl is rigth overhere. The bulb needs to be underwater constantly. The rake in the hull shape is just a nice looking aspect and weight/volume reduction. On the flyer A-cat there is also the same shape and we found out that the shape of the nose feels like a brake when the nose goes to deep in the water.

Thanks,

Klokkie
A-cat Ned-7 / Blade F16 distributor