Late-night inspirations

Sometimes it's fun to get a bit carried away with design work. Even if it does cut into sleep a bit.

Yesterday was that kind of day. "Katy's busy", I thought around dinnertime, "I can probably spend a few minutes on some sketches for the big cat".

By now, I should know better. There's no such thing as "a few minutes" on that project. By eight o'clock, a new hull form concept was staring back at me from the upper monitor. By nine, rig parameters and approximate performance envelopes to go with it. Ten PM, and the relationships between the hulls, rig and foils were more or less sketched out. The next time I checked the clock- well into the general arrangement and main structural members in the Rhino3D model- it was half past midnight.

I kind of like it when that happens. If I'm so wrapped up in it that I get carried away, it's a sign that the design is on a good track.

This particular project- an 8 to 10 tonne ocean catamaran for long-term family cruising- is in no particular rush to hit the water. It's a concept boat. It's about trying out new ideas, evaluating unusual configurations and layouts, stripping out complex and expensive design features to see what happens without them. Each iteration gets only a few hours- a dozen hours, tops- just to see what would happen. Can we take a Wharram-like attitude in favour of minimalist simplicity, but with modern hull and rig forms efficient enough to sail at or near wind speed? What if we ditch the usual enclosed bridgedeck cabin in favour of extra length and extra living space in the hulls- how much build time do we save, and how will the crew handle it? How would a short-handed crew manage a pair of stayed rotating masts- or perhaps a pair of unstayed wing masts, or crab claw sails hanging from A-frames? Is there a simpler way to build cross-deck structure, one that doesn't involve a huge investment in tooling and labour?

Frankly, this stuff is fun. It's engineering at its most enjoyable- building up a design, then stripping it down to its essential core to figure out what really works and what doesn't. Almost any problem can be solved by throwing enough cash, enough time and enough staff at it; the mark of a good engineer is a solution that, through elegance and ingenuity, solves the same problem faster and with fewer resources.

Maybe this kind of exercise is a waste of time. These aren't billable hours, after all- while fleshing out concepts is a critical early stage of the custom design process, few clients are interested in paying for dozens of half-finished concept drawings that will never be used.

It's my time, though, and I'd much rather waste it on interesting yacht concepts than on Survivor 47: Detroit (or whatever else happens to be on channel three-oh-something at midnight on a Tuesday). Who knows- maybe, after enough different takes on this boat, one might jump fully formed from the monitor and scream "build me!"


I ought to mention that the apparent speed of the design process varies drastically at different points along the way. Getting a clear statement of requirements, arguably the most critical step, sometimes takes ten minutes and sometimes takes months. An initial concept iteration, like I described above, can take rough form in a few hours- but will take at least a week of solid work, beyond what I described above, to clean up, discuss and tweak to the point where it can be thoroughly assessed. Then it has to simmer in the client's mind for a while before going ahead with simulations, model tests, detailed calculations and all the other work that's necessary to get it to the point where we can definitively say "here is the design". And then comes the tedious bit- drawing and specifying every bit of the design in a way that ensures it'll be built as intended.




Wharram Tiki 38 w/ unstayed biplane crab claw sails

I noticed a biplane junk rigged Tiki 46 by a gentleman named Bertrand and thought this is really cool. I am currently starting a build on a 38 but have time to contemplate ideas to free up all that deck space the same way but thought... "Ok an unstayed biplane... then considered , why not use the crab claw on this idea.instead of the junk" The polynesian canoes gained huge lift as the air came across the bows, so using this idea... maybe just maybe this would be worth considering... no models as of yet but what thoughts do you have in these regards from an engineering stand point?

Crab claws

Matthew's picture

I do like the crab claw rig. And I'm not the only one - Marchaj's famous experiments on sail efficiency showed it to be a remarkably powerful sail for its size and weight.
The big downside of a crab claw rig, as I see it, is that no-one has yet devised a reliable and convenient way to reef them. Structurally and aerodynamically, a biplane crab claw could have a lot going for it, but if you have to completely furl the sails when a different rig would be able to keep going on the first or second reef point, average speed is likely to suffer.

Well, there are those who are

Well, there are those who are using this rig ( crab claw) with great efficiency and love their simplicity. Reefing? No... as I was told, one must forget about the western mind set in these regards. The sail is tilted to various angles in various wind conditions. People like the world famous Hans Klaar and lets not forget about the guy now going on over a decade sailing a Wharram Tama Moana design in the South Pacific. (Forgot his name) Anyways, Beat Rettenmund sailed a few years as well in his Tiki 38 Schooner rigged Crab claws and simply dropped the larger main and used the smaller in various wind conditions, which he stated was not really difficult, but Beat didnt use the tilting method as Klaar.
CC masts are much much shorter than regular masts and the bury would be a much larger % than typical unstayed masts. So I would think increasing strength considerably. Just an idea. Simple inexpensive unstayed with high bury%.

Add new comment