A Seil in California

[John hartmann]

Re: A Seil in California

Just another thought to stir the pot a bit, would be an unboomed but fully battened standing lug, without the sprit boom. If the bottom batten is stiff enough, it would prevent the sail from developing deep draft when sailing down wind. Ben Fuller has such a set up on his Antonio Dias designed Harrier, Ran Tan, and it works well. I had Ran Tan in mind when I asked my sail maker (Stuart Hopkins, of Dabbler) to make Waxwing’s sails, and he suggested I experiment with the sprit boom, which I also find works well and is easy to live with. With or without the sprit boom, sheeting angles are important for best function, just as Tom said.

[pez_leon]

Re: A Seil in California

What a great discussion. Thanks Tom, John, and calsign222 for your thoughts on rigs. I'm convinced that the right rig boils down to the personality of the sailor. Maybe we need some kind of a personality test, something in the style of Cosmopolitan magazine. What's the right rig for a "Samantha"?
I'm leaning toward the unbattened boomless lug because I tend toward Tom's benignly apathetic style of sail trimming. What's more, the boomless rig is already drawn, and of the many options I think it'd be the simplest for me to sew from a sailrite kit.

James

[pez_leon]

Re: A Seil in California

I wonder if anyone might weigh in before I send a question off to the designer. I had an idea rattling around that I'd shape the foils in this boat to NACA profiles. (I've done it before for a rudder on a larger boat and enjoyed the process). Having read a bit more (including Alex Zimmerman's excellent article in this month's Small Boats Monthly) I realize that the factor limiting my ability to shape a hydrodynamic centerboard will be the board's width. The plans call for a board with a chord length around 35 cm. To make a NACA 0012 profile, I'd need a thickness of 12% or around 4.2 cm. That's about twice the specified board thickness.
I'm a neophyte and don't want to haul off and make major changes to a great design. Maybe a more traditional hull shape like this doesn't benefit from a hydrodynamic foil? If I did make the board twice as wide, I'd also need a wider CB case, a wider CB slot in the sole, and perhaps other changes. I'm sure each of these might have their costs, but if they're small enough they might be worth paying for increased efficiency. I don't plan to enter any races in this boat but I do enjoy making progress to windward in what at least feels like an efficient craft. If you have any thoughts I'd enjoy hearing them. Would you bug a designer about this idea, or would you just make the board as planned?

James

[John hartmann]

Re: A Seil in California

I would make it as planned. A “thin foil” with rounded edge and a taper over the trailing 1/3rd will be fine, and so will your windward performance.

[pez_leon]

Re: A Seil in California

Thanks John, that's reassuring. If it's good enough for waxwing, it's good enough for me.
My question is more academic than practical and I'm sure reflects my ignorance. It seems that "thin" (<1", or approximately 6% of cord width) centerboards are common in designs by Vivier, Oughtred, Lilistone, and plenty of other designers who are vastly more knowledgeable than I'll ever be. On the other hand, everything I find written specifically about foils suggests that a profile twice as thick or more would be beneficial. These designers obviously know what they're about, so what's the advantage of the "thin" board? If anyone wanted to opine I'd be curious to hear it.

[Slacko]

Re: A Seil in California

If you make it to NACA006 it will be 1/2 as thick and fit the centrecase.

[WI-Tom]

Re: A Seil in California

I would make it as planned. A “thin foil” with rounded edge and a taper over the trailing 1/3rd will be fine, and so will your windward performance.

That's my conclusion as well. Of course, being a non-"type A" sailor who has never sailed with a fat NACA foil, you'd be wise to take my comments with a pillar of salt.

But it's easy to round off the leading edge and taper the back of a thin foil as John says, which will provide far superior performance compared to a flat board.

Tom

[cracked lid]

Re: A Seil in California

The advice I have seen and followed regarding NACA profiles on thin boards is to use the profile for a thicker foil in order to leave enough material to preserve the board's strength, and just leave it flat where it is thinner than the NACA profile. Flat sided boards with leading and trailing edges shaped to NACA profiles are evidently pretty close in performance to boards with the full profile they are based on.

Because of the flat sides they are pretty easy to make using templates and sanding jigs as shown here: https://www.storerboatplans.com/foil...ormance-by-10/

[callsign222]

Re: A Seil in California

The advice I have seen and followed regarding NACA profiles on thin boards is to use the profile for a thicker foil in order to leave enough material to preserve the board's strength, and just leave it flat where it is thinner than the NACA profile. Flat sided boards with leading and trailing edges shaped to NACA profiles are evidently pretty close in performance to boards with the full profile they are based on.

Because of the flat sides they are pretty easy to make using templates and sanding jigs as shown here: https://www.storerboatplans.com/foil...ormance-by-10/

This +1
basically keep the board as drawn and tart it up a bit with some nice shapes

The best thing about spending a bit of time on this is that the not only does the boat handle a bit better and maybe it's a bit faster, but the slow speed maneuvering characteristics are significantly improved. Everyone shapes for speed, but I see the most benefit at slower speeds in tight places. This is nice for docking, ghosting creeks, and other such things.

[nrs5000]

Re: A Seil in California

I think I remember reading somewhere on the forum that there are low hanging gains to be made just from shaping the leading edge to a parabolic rather than round shape, and tapering the trailing edge.

[pez_leon]

Re: A Seil in California

I've been intensely busy with everything except the boat. On the few days I've had a chance to get out to the shop, air quality has been so bad that I've hesitated to linger outside (or in my open air workspace). Some days this can all add up to a lot of pent-up pressure and a real desire for manual, tactile work. Thankfully there's parts of this project that can be done in the house.
My sail kit from Sailrite showed up last Friday.




I spent a couple of very happy hours this weekend working on patch assemblies. At first I made the mistake of trying to work while my kids were awake. If you add in the cats this made for a crew of five rascals and scallywags, all of whom had different approaches to, and opinions on, the project. Is the thread for eating, or for tying gordian knots? Should we crush tomatoes into the dacron, or just grapes, and wouldn't this be a great place to cough up a hairball? No one could agree on what to do next. I'd like to report that the ragtag bunch of misfits finally pulled together to win the championship and finish the sail. I cannot. The best solution has been to save the project for nights after kid bedtime
I'm very pleased with the kit from sailrite. Everything they shipped looks top notch, and it really is hard to mess up the overall assembly. I'm less pleased with my stitching. I'm assured that from any distance it looks just fine; personally I can't help but notice all the errors. But I'm not too bent out of shape. In a couple years I'll look at the wild zags and drunken, unfair lines of thread and remember happy nights stuck inside with sleeping kids and wretchedly unhelpful cats.

James

[Bruce Bateau]

Re: A Seil in California

James-

I really enjoy and empathize with your posts. Up here in Oregon we had about two weeks of off the charts hazardous air. Add cats and small children into the mix and yes, that is sure to be slow down to work. I learned to sew sails about eight years ago when a friend and former pro sailmaker helped me out. Once a week we'd transform my living room into a sail loft. Out went the rug, chairs, and couch. I stopped him from putting tacks into my fir floor to hold materials in place. Instead, my kids (who were in late elementary school) were conscripted to help, but were kept away from The Beast. That being a commercial size sewing machine that I was warned would comfortably sew through sail cloth, plywood, and fingers.

Sewing was one of my favorite parts.

And no fingers or children were physically harmed in the process.

Good luck.

-Bruce

[nrs5000]

Re: A Seil in California

Boy can I relate! I have been working on my mast which is too big to do anywhere but outside, and the bad smoke days were just lost as far as getting anything done -- not to mention the toll on keeping the kids cooped up inside.

[seasnail]

Re: A Seil in California

Hi James,

I believe you can make NACA 00XX foils in any thickness you want. The 0012 and 0009 foils are just pre-calculated thicknesses. I'm not an expert by any means, that's just the conclusion I came to after a bit of reading.

Use this calculator with camber set to 0%

http://airfoiltools.com/airfoil/naca4digit

If you're worried about strength you can make the boards out of laminated solid wood instead of plywood. You can also cut a groove on either side of the board and lay in unidirectional carbon fiber strands, see this article for more: https://www.epoxyworks.com/index.php...-centerboards/

Richard Woods has a reputation for designing fast boats and he specifies 5% thick daggerboards on his strider catamaran, so there are high performance boats with thin foils. See here for a strider going fast: https://www.youtube.com/watch?v=KNyyHo-O-xs

This looks like a great project and I'm looking forward to seeing your progress!

Nick

Edit: When you calculate the foil make it longer than the finished board so the trailing edge is 2-3mm thick and squared off, not razor sharp and fragile.

[pez_leon]

Re: A Seil in California

I believe you can make NACA 00XX foils in any thickness you want... If you're worried about strength you can make the boards out of laminated solid wood instead of plywood. You can also cut a groove on either side of the board and lay in unidirectional carbon fiber strands, see this article for more: https://www.epoxyworks.com/index.php...-centerboards/

The advice I have seen and followed regarding NACA profiles on thin boards is to use the profile for a thicker foil in order to leave enough material to preserve the board's strength, and just leave it flat where it is thinner than the NACA profile.

basically keep the board as drawn and tart it up a bit with some nice shapes

Thanks for all this advice on the boards. I've got the blanks just about complete (laminated solid ash) and will probably use the NACA 0012 profile with flats, as described by cracked lid. I have been planning to lay paracord into a groove around the permiter of the board to strengthen the leading and trailing edges. I think it'll be sufficient for my needs, but then again, there's something satisfying about even just saying "unidirectional carbon fiber".
I really appreciate all your advice.