Here are Norm Cross' thoughts on Constant Camber which might help people evaluate what they are promoting. From Dec 14, 1982 Norm's comments are in parentheses, I put in a few using brackets.
Subject: Constant Camber cold molding construction.
This is in reply to the number of inquiries I have had wanting to know why I do not use this method of construction.
I will try to explain my reasons.
When I designed my first round bottom double-diagonal plywood hull
in 1966 I wanted to design a hull that would be simple to plank. The radiused section seemed ideal. I designed a variable radiused hull having a very large radius at the bow section. From the bow aft the radiuses became progressively smaller so that the smallest section was at the transom.
This early design was a better shape than the present constant camber section. It had a lot more room because of the more ideal radius midship.
This was a nice hull shape but it was not a round bottom hull shape below the waterline, it was only a radiused version of the early AYRS/Piver 90 degree bottom hull ( but did not have the reserve buoyancy aft at the transom that I now felt was required).
I then modified the hull shape from the midsection to the transom to provide more reserve buoyancy aft.
This was a improvement over the variable radiused hull but still not the ideal hull shape.
I finally decided that the ideal hull shape should be close to an elliptical section with a veed shape at the keel
I have used this hull shape, with slight modifications for the last 10 - 12 years. It is a good compromise; good hull shape, good accommodation and still easy to plank. Hundreds of my trimarans have been built using this hull design.
My personal feeling is that if I used the constant camber hull design I would be going backward over 16 years in hull design. It is just too big a compromise I would have to make.
My main objections to the constant camber design are:
1) Limited accommodation, narrow width of the main hull. You have to build a longer boat to get the same accommodations as you would in a more ideal designed hull. a bigger boat means more cost for berthing and haul outs.
2) More wetted surface as it is a radiused version of the 90 degree hull. [hurts light air performance- Cav]
3) Too much rocker on the keel
profile. [Hurts top speed performance -Cav]
4) Low buoyancy aft ( you could almost all it a double ender) will have a tendency to hobby horse if weight is not kept midship. [ Hurts all performance.]
5) Deeper main hull draft
6) Center of buoyancy is very close to 50% of wateriline length, placement of weight is very critical.
7) Lower carrying capacity for a given length.
This is too much of a compromise when you consider that building the hulls mount to about 20% of the total construction time.
If you desire to build a trimaran
with no wing deck
accommodation (which incidentally could be a wet boat) I feel that it would be better to spend the small amount of extra time it takes to build the ideal hulls (modified ellipse) and end up with a better boat.
For an easier and less expensive way to build I suggest sheet plywood
. I'm in the process of designing several sheet plywood, open wingdeck designs with hull shapes similar to my Cross 10,5 trimaran
. [Cross 12M-Cav]
The reasons for using sheet plywood are:
1) It is an easy and fast material to work with.
2) It does not require a great deal of fairing or finishing.
3) Cost of marine
plywood per sq. ft. is much less than 3-4 layers of veneer plus glue and fastenings.
4) No molds to make.
Compare the accommodations and hull design of the different designs and decide if you want to make that compromise.
Norm sent this out with his plans portfolio and it is as valid today as it was 30 years ago. CC boats require an organized team to make the panels
and must have the bulkheads shaped to the skin meaning no patterns. They aren't that much different in the water than those old Pivers. The Searunner has sections that allow it to approach the ideal hull shape and being sheet plywood construction has the advantages posted above. We have noticed that Searunners tend to perform better than CC boats out in the real world as does our Nicol. Being able to precut all those parts
make for a faster overall build. ike a cylinder mold
boat once the CC skin is completed things start slowing down fast- Check out the unfinished boats that have been appearing on the market. Those Cross, Searunners, Horstmans etc... got old because their builders finished and went sailing. I do think many of the CC boats are atractive and wouldn't reject a good one but I would certainly build something else if starting fresh.