Hey guys, I'm fairly new to boat building (though not to composite design/construction, sailing, windsurfing, etc.)

I've been looking at various small boat designs, in particular those for light racing cats (F16 looks like a very interesting class), and wondering about the mast designs which are most common...and why.

The Olympic class planing bathtub pictured in my avatar has a traditional non-rotating tracked mast into which a sail is hoisted with a halyard. No news there. My windsurfing gear uses a simple round tube of a mast onto which the sail's luff sleeve slides like a sock. No news either. And I'm reading that newer high performance cats use rotating elliptical tracked masts -- sharp low drag leading edge, tricky to use, and they probably stall more frequently than traditional blunt masts.

A hypothesis: The windsurfer style mast/sail with a sock (OK, luff sleeve) would seem to offer almost as low a drag profile as the more fancy and expensive rotating masts, at lower cost and weight. For small racing dinghies and cats, the difficulty of rigging and hoisting a sail should be fairly minor if one uses a universal joint at the mast base to permit rigging in the horizontal position and uphauling the sail after that. (How about a water start?) Boom, spreader(s), shrouds, and jib/spi halyards can be attached at cutouts in the luff sleeve, after downhauling, as is a windsurfer's double boom.

I'm guessing that there are boats with the windsurfer-style sail design around somewhere, and I just haven't found information about them yet. Does anyone in this group know about such vessels? Has any of you guys tried one? Is there some technical reason this just won't work, or a vast international conspiracy suppressing luff sleeves? Inquiring minds are looking for a #$!*ing clue...

Have you seen the Moth?
http://www.bladerider.com.au/news/2007_april.html

Darryn

Hmm, I'd seen videos of moths, but nothing which clearly showed the rigging. That seems like exactly what I was thinking about...scaling it from about 8 square meters to about 15 would just be a matter of engineering, and figuring out procedures to handle a larger sail (I was surprised to see the standard Moth sail is just 8.0 m^2, as that would be a pretty ordinary size for racing windsurfers...I'm not much of a racer, but I've sailed 9.0).

Interesting that camber inducers are common on Moth sails...it seems that on the windsurfing side, cams go in and out of style as hemlines on dresses go up and down.

Following your lead, I did stumble onto
http://www.moth.asn.au/pocket_luff.html
and related sites; the linked site has a nice opinion piece about "pocket luff" sails (a more dignified name than "sails with socks" I suppose).

Perhaps a good followup question would be, what's the largest pocket-luff sail out there? Windsurfers usually go up to about 12.5 m^2, seldom much more.

Thanks for the tip!

Largest pocket luff sail? I think Wharram use those on some of his smaller designs in the 20-28 foot range?



<img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" /> I think you will find that there is more to it than "just" engineering <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" /> <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" /> Probably going to take a while, some elbow grease and a serious amount of banging your head in the proverbial concrete wall. <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

Hey, I said scaling, not building. <img src="http://www.catsailor.com/forums/images/graemlins/tongue.gif" alt="" />

But your point about how much fuss is involved in going from the idea to a functioning product is well taken. Sorry for sounding as if I were trivializing the tribulations.

Did not mean to kill your enthusiasm! Go on with the thinking and have fun with it. That is how progress is made and I would hate to know I might have killed off some constructive work.

No worries about damaging enthusiasm. It's better to be realistic at every stage; and for a noob, tips about what's easy and what's hard and what things have been done successfully in the past are worth their weight in carbon.