Mainsail Flotation

Moderator: GreenLake

Postby jdoorly » Sun Dec 12, 2010 1:24 am

Well, so far I've done 5 design revisions, made prototype 1, made more revisions, and I'm currently building prototype 2. As the mast flotation takes shape I uncover problems and get new ideas, but there's still some things I can't know until I test it in the Spring, like what is the minimum amount of flotation necessary vs. how much windage can I live with?

The current design is simple and modifiable: Just a tube of white ripstop nylon that I can stuff various amounts of styrofoam boards into. It will stay attached to the sail because the tube, which folds around the bolt rope and around both sides of the sail and is fastened to itself at the leach, has a hole on the boltrope/fold that captures the top sail slug. The tube can expand and contract to hold more or less layers of styrofoam. Prototype 2 has a max of 6 layers of 0.69" thick boards (4.1") or 19 lbs of flotation. I expect to taper the leach side and end up with 15 lbs. However, there is some possibility that the thickness of the flotation will provide a 'plate affect' reducing the induced drag and increasing the aerodynamic efficiency of the sail area below it, instead of just providing the expected inefficient windage. I'll stick some yarns 'round about it and see...

Below this 'upper' flotation is 2.5 inches of just mainsail followed by an optional flotation to be deployed when I feel like it. The 'just mainsail' is to allow the mainsail to flake properly. The optional flotation works the same as the upper, but it is more aerodynamic in that is is 1 layer thick (0.69") on each side but is about 15" in height giving it about 17.5 lbs bouyancy. The styrofoam should have cuts in it from top to bottom every inch or so to make the board more flexible. That's a cut (3/32 +/- 1/32) every 2 inches on one side then on the other side offset 1 inch and cut every 2" so it bends equally both ways.

I found some even cheaper styrofoam at Home Depot and it's in a much more manageable size: Cellofoam Poly Panel EPS Insulation and a $7.25 package is 6 pcs 3/4" (actually 0.69") x 14.5" x 48" which is 1.7 cu ft! And it's white! (It is not however, flame retardant, which seems strange a building material having less flame retardant in it than humans.) I tested it and it's 60 lbs of flotation per cu ft. I also tested seam glue which holds ripstop moderately well in sheer, and double sided tapes; some are ferocious and some act like 'sticky notes' on ripstop material.
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Postby GreenLake » Sun Dec 12, 2010 9:08 pm

Foam.

I would think if you were to be able to get flat sheets of the kind of foam that's used in pool noodles, that would be the best.

That foam is stiff enough, but remains more flexible than a batten and would influence your sail shape less, in my view. I would expect it would stand up to abuse better, because it can't break.

I've had a sheet of this stuff that had been used as packing material, and I've been using it for years in the bottom of my boat to do things like rest the motor on. It doesn't like point loads, which will lead to permanent dents, but in a pocket like yours it would probably be fine.

Interesting consideration with the "end-plate" effect.

I chuckled over your aside about the flame retardants. You're supposed to encase this stuff in wall-board. I don't think nylon pouches are up to code. :roll:
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Postby jdoorly » Mon Dec 13, 2010 12:32 am

Hi GreenLake, no doubt there are better and more expensive choices for foam. I particularly like minicel foam ($40/cuft) and have used it extensively on my kayaks. But in the development phase, where there is so much waste, I like cheap! I've only got 1 board left of the package of 6 I bought! The pfd flotation I bought has funky shapes and needs to be 'puzzled' together somehow, the styrofoam make the most sense for me now.

I've heard a lot about swim noodles on this site, but I'm not familiar with them myself. What kind of foam are they?
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Postby GreenLake » Mon Dec 13, 2010 1:58 am

Per Wikipedia they are made from polyethylene foam.

The foam sheet I mentioned, I got for free, from packaging :) , but I admit, I haven't found another sheet like that. If you purchase, polyethylene are offered on the net for $30/cu ft (but as 1" sheets).

A pool noodle will set you back $2.00 (or less). They have several pounds of flotation (see the other thread where this was discussed). That price seems about 1/2 of what the sheets are sold for on a per volume comparison.

The water absorption is not 0, but they are rated between .02 and .06 pounds / sq ft. For an above the waterline application like your masthead flotation that would be fine.
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Postby Alan » Mon Dec 13, 2010 12:28 pm

Backpackers' foam pads (plain Ensolite foam, not the more expensive air-filled kinds like Thermarest) might work. The foam is similar to pool noodles and it's about 1/2 inch thick.
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Postby jdoorly » Mon Dec 13, 2010 3:10 pm

Baysailer, I keep hoping for flotation benchmarks and data in the replies and nearly missed your valuable contribution! Since the upper stays are well below the masthead we can deduce that flotation attached to the head of the mainsail should still work well with 1 or 2 reefs in the mainsail. Thanks for experimenting!
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Postby ctenidae » Mon Dec 13, 2010 5:14 pm

Alan wrote:Backpackers' foam pads (plain Ensolite foam, not the more expensive air-filled kinds like Thermarest) might work. The foam is similar to pool noodles and it's about 1/2 inch thick.


A bit denser than noodles though, I think. Might not get the same floatation per cf, but is probably more flexible.
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Postby GreenLake » Mon Dec 13, 2010 7:19 pm

Polyethylene foam is commonly sold from 1.7lbs to 6lbs. While that's over a factor 3 in weight, the ratio of buoyancy is only 54/58.3 which is so close to a factor 1 as to be negligible for flotation that's less than a cu ft in volume.

It would matter if you tried to achieve neutral buoyancy - as the kids who wanted to float their underwater robot (link in the other thread). But for John's application, both types of foam would float just as well, and you'd be hard press to observe a difference.

But, there's another consideration and that is weight aloft. For masthead flotation, weight aloft definitely counts. So in that case, he would be best off getting the 1.7lbs type.

I'm thinking it might be possible to sew polyethylene foam directly to the sail w/o using an enclosing tube. Or, instead of a tube, with a single layer of spinnaker cloth as a cover. The stuff's pretty tough, but high winds may be a match for it, so some cover may be needed to keep the threads from pulling out.
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Postby seandwyer » Tue Dec 14, 2010 11:58 am

Hey Guys,

Isn't that stuff they sell at Home Depot called sill seal (or whatever proprietary name they give it) the same material? It's the stuff they lay on top of a concrete foundation wall before putting down the boards that are bolted to the sill. It's spongy and looks and feels like the same sort of foam. They sell it in big rolls and I think there may be more than one width and thickness. I bet you could get some of that, cut a section and roll it up like a ho-ho - or to Greenlakes suggestion, sew two layers into the sail on both sides.

Anyway - I think it is the same kind of closed cell foam as the noodles are made of.
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Postby Peterw11 » Tue Dec 14, 2010 8:45 pm

The rubbery, closed cell, material is indeed polyethylene foam (I worked in the packaging business in a previous life and we used to manufacture the stuff).

It is the same material used in sill seal, and also used in high end electronic packaging (our main customer base, back when computers were still built in this country).

Check out packaging material vendors, and foam converters, in your local area. They use tons of the stuff and usually have a lot of offcut waste that they'll probably let you have for nothing.

IIRC, you want 1 or 2 lb foam. That's the lighter and more flexible stuff.
They make it in densities up to 9 or 10 lbs. which is too heavy and stiff for your application.
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Postby jdoorly » Fri Dec 17, 2010 10:57 pm

I apparently neglected to search the web for "mainsail flotation" previously, and I apologize for this oversight. There is quite a bit of info resulting from that search phrase, here's some...

There's more on the Flying Scot mainsail flotation, which is a 'sock' design of 30 Lbs bouyancy, including one or more failure reports due to flotation getting old, soggy, and/or disintegrating. However, it is all very anecdotal and without data. But I will take it and the discussions here as a design constraint to make my final prototype out of high quality durable closed cell foam (not styrofoam or other questionables). Also one experimenter on the FS forum tested the bouyancy of his manufacturer's flotation and found it to be 46 Lbs of bouyancy, not 30!
http://www.fssa.com/fsforum2/topic.asp?TOPIC_ID=752

There's an interesting discussion on capsize recovery below, the gist of which is 'the hardest part of recovery is getting back in the boat', apparently us old farts have some difficulty performing accrobatics and feats of balance...
http://www.fssa.com/fsforum2/topic.asp?TOPIC_ID=960

Hobie Cat has an optional masthead flotation some people call the ' Hobie football'. It looks like a blimp, is attached to the mast, is aerodynamic, and spins around into the wind like a telltail. Couldn't find a bouyancy for it, but I think capsized catamarans, being wider and with a pontoon way up in the air probably have potentially more wind and wave forces pushing them from capsize to turtle position, and thereby will need more bouyancy than a monohull. But then again, nothing I see in this entire search result sets any standard or benchmark for 'safety' or guarantee of performance (especially Laser).
http://www.hobiecat.com/sailboats/wave/photos/

Wayfarer, if my chinese is up to snuff this is a sock with 35 Lbs bouyancy, which, even by scandineuvion standards is overkill unless your in 6 footers with a gail blowing up your bustle. The color choice is may be limited to blonde.
http://www.wayfarer.dk/index.php?option ... &Itemid=33

There's a relavent flotation patent with a twist, the 'standard' sock design with multiple verticle seams which make pockets that rectangles of flotation fit into allowing the flotation to conform to the curve of the sail, among the many claims.
http://www.patentstorm.us/patents/56010 ... ption.html

Capri 14 sock (18.6 Lbs bouyancy) very pretty $230.
http://www.catalinadirect.com/index.cfm ... entCat=275

Xenon dinghy (14.7') masthead flotation pack (3.7 Lbs bouyancy each optional panel)
http://www.thexenon.org/node/12

Laser Aid to flotation, makes me laugh, then cry.
http://lasersailing.ch/newpage/E-Teilze ... ctions.pdf

So, what's it all mean? What should we do with this avalanch of webwisdom? I dunno.
Last edited by jdoorly on Fri Dec 17, 2010 11:19 pm, edited 1 time in total.
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Postby GreenLake » Sat Dec 18, 2010 1:58 am

Thanks, John, that was thorough. 8)

All that's left is to build a few test patches and collect data! 8)
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Postby jdoorly » Sat Dec 18, 2010 6:21 pm

I just found more info on the Hobie float: There are 2 sizes, the bigger one is 59 Lbs of bouyancy, the smaller is 32 Lbs. Wow that's the biggest one yet! A full cubic foot squished into a bulbous foil. What an eyesore. They should paint it in sky camo! I bet the masthead doesn't even get wet! But, this is the one to have in rough conditions. See page 19 of this pdf...
http://static.hobiecat.com/digital_asse ... atalog.pdf
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Postby GreenLake » Sun Dec 19, 2010 4:42 am

The don't look "traditional" but I've seen them on the fleets of youth sailing programs and you can get used to the looks. They probably didn't have the "mama bob".
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Postby bdpvt » Sun Dec 19, 2010 12:26 pm

Check out the Mastfloat Buoyancy Bag from APS. Nicely made with 8 litres of bouyancy for $60. Luckily I have never "tested" how well it works, but I feel better having it up there when the wind is blowing hard.
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