Fleece/cotton fiberglass boat

I worked for Television as a set maker for 6 years !! we made any thing and everything you can think of and most was done in glass to be light weight and robust !!
I also worked in industrial fibreglass a while as well again we made anything and everything thrown out way . Nothing was impossible !! aluminium wire frames were used for outside work as it doesn't corrode and lasts for long time .
I been making boats for the last 30 years 150 foot long down to models 600mm long sail yachts and race boats power boats and F1&F3 Tunnel boats ,off shore and circuit races . even dabbled into Carbon fibre helicopter panes and small aircraft parts along with micro lite and hover craft !!
What do you think ??

 

A saturated skin as the OP suggests isn't comparable to a SOF build, even if it does have an internal structure, which frankly isn't needed.

There's really only two approaches for something like this - thin skin with frame or thicker skin without a frame. Both have been done, though again the skin needs to be load bearing if it's rigid. SOF skins aren't load bearing, they just keep your socks dry.

 

if thicker skin... why remove frame work?

 

No longitudinal stringers Spencer, other than the mid and two sides ?

 

I would have quite a bit more structural support I was simply trying to provide a quick example

 

The same reason strip planked, glued lapstrake and solid skin 'glass boats don't have them. Generally, you want to keep things light, so you engineer the structures for the loads you need to tolerate and if you can clean up the inside, with a sans frame method, all the better.

This doesn't mean you should design for no frame, but as an option it's usually preferred, for several reasons.

 

Tunnels said: 'you can also use aluminium wire to make your frame and use a hot glue gun to hold it together and then pull a fine glass cloth over the frame and resin that'

Hell, as kids we used this technique to make toys and stuff. We used fine chicken netting. Our resin was flour and water, our fabric newspaper.

I intend to use the same technique on a custom roadster car body one day. One can play with the wire mesh to get desired shape, then build up fairness with layers of something that will sand. This becomes the mould.

Full scale clay models are still used in new car designs. Ya cant beat eyeballing !

M

 

First off, SOF using Nylon needs to be pulled tight when being stitched up. More normally non-calendered Dacron is used, which heat shrinks by around 10 to 20% in both directions. See this thread: http://www.boatdesign.net/forums/boat-design/beautiful-skeleton-37456.html where there are several examples, including my own SOF rowing boat, Aero.

Aircraft covering used to be un-shrunk linen, or cotton, that was sewn in place then either water shrunk, or more commonly dope shrunk, to get it tight. Nowadays fabric covered aircraft almost all use Dacron, as it's far easier to use, much stronger, a fair bit lighter and tends to last a lot longer (and, as it happens, I had a hand in designing an aircraft that used Dacron skins, and have covered a fair few over the years).

Nylon is sort of OK for a small kayak, but tends to expand when it gets warm (so the skin goes a bit floppy) and Nylon also absorbs water, gaining weight and causing the fibres to swell slightly. Having said that, I know that some SOF kayak builders do use ballistic Nylon, despite the extra work involved in getting it tight.

The major downside with conventional SOF isn't strength or impact resistance, it's the poor abrasion resistance that painted fabrics tend to have. One way around this is to use an abrasion resistant skin, like a neoprene covered Nylon (as used in the old Klepper canoes), but this is heavy and doesn't shrink, so the frame has to be made to expand to keep the skin tight.

My intention is to rip the heavyweight Dacron skin off Aero:



and replace it with Ultralight Dacron (from Polyfiber). I'll then coat this with epoxy and lay up a Kevlar/glass/epoxy outer skin, rather like covering a ply hull. The weight will go up slightly, but it should give me a pretty tough hull that will withstand being dragged up a beach, for example.

 

The fabric would need to be tightly woven to stop the resin running straight through it, wouldn't it ? I am starting to warm to this idea !

 

The aircraft Dacron (brand names Polyfiber/Ceconite) is very tightly woven. Even very thin paint doesn't really flow through it. Resin lays on it pretty well, the only downside being that the cloth itself doesn't bond well to resin. Not an issue really, as the mechanical bond from the resin that flows into the fabric will be plenty good enough to stop the GRP skin coming adrift. This photo gives an idea of how the fabric looks on the frame before being painted:




The frame does need to be pretty stiff, though, as the shrinkage force when ironing the fabric to get it tight is considerable. The longitudinal stringers need to be fairly stiff and well supported by frames to prevent the fabric bending them in when it shrinks. Some, maybe all, of the frames could be temporary, though, as once the GRP skin has been laid up the hull shape will be established and the tension effectively removed.

If the temporary frames are removed, then the hull will almost certainly require some form of stiffening internally. However, it may be that a couple of permanent ply frames could be used together with a bunch of temporary stiff cardboard ones. The result would probably be at least as stiff as a conventional stitch and glue type hull.

 

That is surely a better choice (dacron) that the tee-shirt cotton fabric mentioned by the OP.

 

Yes, I think it is. It's not that expensive (http://www.aircraft-spruce.com/catalog/cspages/polyfiberuncertified.php) at around $9 US/ yard for 2 yard wide lightweight cloth. I used the heaviest duty Ceconite when covering Aero and even that was only around $17 US/yard.

For use under a GRP skin then the lightest fabric would be fine, as even that gets drum skin tight when ironed.

 

"Ironed" as in ironing a shirt ? Does that shrink it ?

 

Yes, exactly like that. It's pretty temperature sensitive when being ironed, so the iron needs to be set to pretty much the right temperature first, but it really is dead easy to do. There is a guide here: http://www.ceconite.com/articleshrinking.htm that pretty much tells you all you need to know about it.

 

Thanks for your helpful information Jeremy.