displacement hulls and concave decks

I’m looking to experiment with displacement hulls and concave decks. I’ve been trying to think of how to shape them into the blank, wondering if anybody has advice? Tom? It would almost seem that your rail banding the bottom? What about scooping out the deck after the bottom’s been glassed? Thanks- cheg

I’m looking to experiment with displacement hulls and concave decks. I’ve > been trying to think of how to shape them into the blank, wondering if > anybody has advice? Tom? It would almost seem that your rail banding the > bottom? What about scooping out the deck after the bottom’s been glassed? > Thanks- cheg What are hulls?

As far as displacement hulls, it’s a fairly complicated bottom design and the waves need to be lined up with some power. Basically a displacement hull is a bottom with varying degrees of convex curve that allows the board to roll onto the rail easily from a more forward position on the board. This is combined with a deep, high aspect single fin placed up pretty far up on the board. The roll in the bottom toward the nose causes drag which in turn pulls the board up into the pocket. The reverse V bottom which we are currently riding in powerful waves is the modern interpretation of the displacement hull. The dislacement hull lends itself to a forward riding position, so a lot of old school single fin guys enjoy riding them. As far as concave decks go, you shape them just like you do a bottom concave. Shape the deck FLAT and turn your rails leaving them pretty beefy due to the fact that you’ll be removing some of the deck. If you don’t leave the rails full enough and put too much concave in the deck, the board won’t paddle or plane very well. Carry the concave all the way out to the top of the rail line.These boards were popular with a lot of the underground guys in 1971-72 and were REALLY fast! It could be fun to bring them back with a modern drive train! When you talk about glassing the bottom then scooping out the deck, that’s pretty much a kneeboard thing. Between the weight of all the glass and no flotation it’s not advisable. I made a ton of spoons in the late 1960’s but never a stand up board with this construction. I was in Hobie’s factory about 1970 and they were actually doing a board with the spoon construction; I believe it was Corky Carroll who actually rode it and I’m not sure of the outcome. Since we never saw it again, either it didn’t work or it ripped and Hobie didn’t want to put the energy into it($). I would imagine the prior is probably correct. aloha

As far as displacement hulls, it’s a fairly complicated bottom design and > the waves need to be lined up with some power. Basically a displacement > hull is a bottom with varying degrees of convex curve that allows the > board to roll onto the rail easily from a more forward position on the > board. This is combined with a deep, high aspect single fin placed up > pretty far up on the board. The roll in the bottom toward the nose causes > drag which in turn pulls the board up into the pocket. The reverse V > bottom which we are currently riding in powerful waves is the modern > interpretation of the displacement hull. The dislacement hull lends itself > to a forward riding position, so a lot of old school single fin guys enjoy > riding them. Displacement hulls sound like something that would work well for outside backyards or a similar wave? You mention varying degrees of convex curve. Is it correct that it flattens towards the nose and tail keeping it stronger under your stance? I have a 9’4" Bushman that he used a lot of “rolling V” works great, is “rolling V” the same sort of concept as a displacemnt hull? Aloha

i’m more old school vee tail, flat middle for planning and take or leave the nose concave.i want to replace the vee with a single concave with the thinking of giving the board some squirt.this combining with a smaller 1+2 or thruster fin set up to replace my “big” single fin mind set.so far it seems like these fin combinations slow my board down.too many times i pull out the side bytes and the disliked board comes alive.any thoughts before i pull the trigger or once old school always old school. thanks