Dorpie? Shory? Shanoe? ... Dorpedo?

Mulling over design for a ~30' proa vaka, to be built of ply/glass, mostly stitchnglue-ish. Vertical bows, but as much floatation at the ends as possible.
Some rocker. Narrow flat sole, say 30" midships, tapering to 2"at bows. What is an optimum easy-build hull shape for a non-heeling hull? I've been looking at sharpie and dory shapes. I'm trying to get much lateral resistance without excessive wetted surface. I can't see any argument against moderate flare midships - 15-30 deg.

Rocker in the order of 1/2"- 3/4" per foot would give me ~8-9" at bows. This would give me room for a long shallow keelson/skeg/cutwater at bows to add rudder support and lateral resistance without sacrificing shallow draft. (ie the 'keel' line bow to bow would be close to straight, a relatively solid scarfed (laminated?) beam, say 2x8"). It strikes me that while long foils are more efficient, contra monohulls, there is no need to get the weight extremely low (ie bulb keel).

Grateful for any (knowledgeable) opinions, thx

 

I think you need to read, read, read, Rob Denney at Harrypro uses little if any rocker as the hulls don't tack.

 

with respect sir, I have been reading reading reading, and thinking, thinking, thinking and designing, designing designing. What would you have me read?

I am well aware of the harry designs, and how particular they are. Very interesting boats, great designer. In some quarters they are not regarded as proas.

 

With respect it might help if you told us wether it is Atlantic or pacific, I'm going to assume you are in the quarter that thinks Harry's are not proas, otherwise there would have been no need to mention it.
Richard Woods has written a great article on hull shapes here.
http://sailingcatamarans.com/hullshapes.htm

 

Also, have a look at the Buccaneer 24 build method, would work for a proa just nice.

 

Did you get a look at Derek Kelsalls build techniques.
http://www.kelsall.com/UniqueKSS/WhatIsKSS.pdf

I reckon it would produce great Proa Hulls, with minimum work.

His earlier technique with plywood has been praised highly for speed and effectiveness.

FWIW - I consider Harryproa concept ( actually first proposed in "21st Century Multihulls by Joe Norwood" to be the ultimate in Proa concepts.

 

Hello Rwatson and Redreuben

> FWIW - I consider Harryproa concept ( actually first proposed in "21st Century Multihulls by Joe Norwood" to be the ultimate in Proa concepts.

very hard to find book . But he has a paper on his Falcon proa in http://www.ayrs.org/Catalyst_N03_Jan_2001.pdf In which he says it steers with the fwd rudder ! if I read correctly (!)

FWIW I did not speak against Harryproas, I think they are excellent and fascinating.

redreuben - "I'm going to assume you are in the quarter that thinks Harry's are not proas, otherwise there would have been no need to mention it."

see above. With respect, you mentioned it, I was responding (with an aside).

IMHO When one embraces the shunting asymmetrical format, there are many ways to slice the cake. I'm interested in the design space. Denney has pursued one radical approach. Brown et al, another, perhaps more 'conventional'. I'm taking a long look at the Atlantic, knowing well its fall from favor and the yawing problem. Nor do I I presume I can better the work of Newick at al ...

redreuben - "With respect it might help if you told us wether it is Atlantic or pacific, "

As far as I can see, for a conventional atlantic or pacific, the (underwater) hull shape must be similar, even if one is talking asymetrical hull shapes. (Not talking leepods etc) so for brevity I left it out. Why do you think it matters?

rwatson - "Did you get a look at Derek Kelsalls build techniques".

yes, I'd seen these pages previously. thankyou. As I said I'm interested in ply/glass build. Not resin infused foam, for which I have neither space nor experience.

"Richard Woods has written a great article on hull shapes here. "

- you are right, very nice, very useful, thankyou!

He offers support to my inclination to build sharpie-like flat bottom, but narrow to prevent slamming. "I haven't designed any deep V boats for a long time because of the pitching and light wind speed problems. I have found the flat bottomed or single chine hulls are as simple to build and are more efficient hull shapes." He also warns of low Cp, which I am very conscious of. Getting bouyancy fwd while maintaining a fine entry is one of those impossible boat design compromises.

redreuben - Couldn't find much details of the Bucaneer hull/build (from the pic, deep V ?), but this was useful -
http://smalltridesign.com/Trimaran-Articles/Trimaran-Hull-Performance.html
thanks!

 

Fair enough. Dont forget my other comment though "His earlier technique with plywood has been praised highly for speed and effectiveness."

The way he put his plywood hulls together was terrific. You might be able to find an old build blog, or some cheap plans from earlier designs.

I have found him to be quite approachable, so direct contact might yield some info.


May I also add, for a proa, or any multihull for that matter, V shaped hulls will always be more effective, both for leeway control and 'wave slicing'

For my money, V hulls dont amount to much extra work. Perhaps if you used the Wharram technique, and left room for some flat bottom on the centre 1/3rd of the hull ?

 

The Buccaneer 24 build instructions are here;
https://messingaboutinboats.wordpress.com/tag/buccaneer-24/
The floats are single chine, the main hull double chine, simple, clever assembly method.
More info and discussion here;

http://www.boatdesign.net/forums/multihulls/buccaneer-24-trimaran-25159.html

http://www.boatdesign.net/forums/multihulls/buccaneer-24-builders-forum-28496.html

 

ok, thanks, Ill pursue it.

I would have thought the deep V was the simplest hull to build. The main drawback being high wetted area. And of course the Cp demon. The Wharram technique is pretty much exactly what I've been pursuing - though of my own origination. But to ward of theCp demon, I carry the flat, very narrow to both bows. 30" wide midships, tapering to 2-3" at the (vertical) bows.

I've toyed with flaring the gunwales out all the way to the bows, again to maximise reserve bouyancy as far fwd as possible, while still presenting a fine entry in flat water. So each bow would be a half cone vertically, tapering from a 6-8" semicircle on deck down to 2-3" at the 'keel' where it meets the sole.

 

thankyou! sorry for delay