Light floats

I really like this idea !

Opinions please.

 

The neat thing about glass on the inside is it lets you use less resin by not filling the weave. The cloth is thoroughly wetted but the extra coats for the smooth surface you need outside are eliminated giving a higher glass to resin ratio. For the same weight you could use thicker cloth.

It doesn't however protect the wood from damage though it can help prevent penetration. I'd consider light glass on the outside for the minor abrasions and finishing/refinishing base and the above mentioned glass technique used inside.

Kevlar on the inside is very much better than glass for puncture resistance so if that is the objective it should be considered. Unlike glass though it only has strength in tension. Carbon is another fiber to be considered.

For racing it is worth looking into.

 

Cav,
I agree, a very lightweight cloth under the waterline as a base for anti foul would help in future refinishing work. i.e.. prevent scraping/sanding into the wood.

 

It's a real bugger to glass the inside --with all the frames and stringers. Lots of opportunity for slopping in extra unwanted weight.
I think it is quite unnecessary. If you hit a rock it's going to punch through anyway.

 

OS7,
I would glass as soon as panels are scarfed together, before installing the stringers, then just proceed as per.
1.75oz Kevlar would be perfect !

 

That is the way to do it alright. If you've never worked with kevlar practice on a test piece first. It tends to float in the resin and fuzz around the edges. A grinder is better than a sander for knocking off rough edges. Stay with it until the resin gets tacky to make sure it is own. A squeegee is better here than a brush. I've heard it can absorb water through those edges so make sure they are well sealed. It is why I think it is better inside a boat so don't let those amas sit full of rain water.

 

I assume you would glass the inner face of the ply before fitting it on the boat

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Options

I haven't had time to make any test panels, but from past projects, I am leaning towards mostly 4mm ply with carbon backing in the high load areas on the inside only- applied before the stringers go in. Carbon's low-stretch properties complement wood better than anything else, and on the inside, doesn't add very much weight. I only glass tape the keel on the outside of the floats, as they are not in the water very much at rest. (One is always clear, and the other is only immersed about 3". I only bottom paint about the bottom 5" of the floats.)
I have priced out the options, and ply/carbon/glass/epoxy is about 60% the cost of foam/glass/epoxy, and the ply seems more "dock proof". I will have to deal with the moisture/ventilation issue. Another savings, for me, is avoiding constructing a 24' layout table for foam/glass, a substantial cost and labor expense.
I "think" I can keep the total 23' ply float weight below 150 lbs, including a-board trunks, and if so, save over 100 lbs total weight from my current 21' floats. I would like that B

 

The Bucc sides are pre built with the stringers then folded into place, so the innerglass/other fabric would be done before the stringers and fitting. The bucc method would work on many of your boats too.

 

Sorry Guys, but I will stick to my guns that all is needed is two coats of epoxy on the inside and three on the outside.
The sheets of ply can be pre coated on the inside before cutting and butting the panels, When the stringers and gunnels are epoxied in place the inner faces of those longerons are automatically sealed for ever.
The three remaining faces of the longerons can be quickly roller and brush coated with epoxy before the ply panels are wrapped around the frames.
It's important that the outside of the panels are not given their three coats of epoxy until the hull is completely panelled, so that the panels are not too stiff to wrap properly. Glass tape/Epoxy is all that is required on the finished seams. Overall glassing, inside or out is entirely unnecessary.
Bruces tri is a living example of that.

I note that mention on the thread to foam/glass construction is done with Glass/Epoxy. Foam glass construction is best done with Glass/Polyester or Vinylester. Lighter, cheaper and quicker than Epoxy and just as durable,---but not Glass/ Polyester on Plywood.

 

Yes, OS

I agree, I don't need much glass on the outside, just enough tape to cover the staples/nail heads on the keel as I tend to sand thru to them. My float bottoms, with just epoxy, are still fair after 40 years, no need to "improve" them. The only rot in my float bottom skins came from voids in the fir ply, a problem I don't expect to repeat.
Since I plan on using 4mm ply, I do think I need the carbon inner layer in the high load areas- fore and aft of the forward beam bulkheads, and around the chain plate attachment. Not a lot of total area, but the carbon adds important stiffness and strength without much weight.
I haven't used poly resin in twenty years, so I am out of practice. Another reason to KISS and build with what I am used to. I would be a lot more interested if I could find a reasonable source for small quantities of building foam. B

 

Define 'reasonable'
Small quantities √
Reasonable ?
http://search.defender.com/?expression=foam core

 

Foam price

Yes, I think $6-$8 a square foot for foam is unreasonable From some friends in the industry, the cost to manufacture 3/8" foam is under 75 cents a square foot- the mark-up is too much. One of my floats would use over 160 sq ft, at those prices, about $1000 a float, plus glass inside and out-and still needing more glass or carbon in some places. 4mm ply runs about $1.50 a foot and doesn't have to be glassed, so under $350 total for ply, the rest of the wood needed, and some glass tape. The required carbon and either poly or epoxy are going to be about the same for either type of construction. B

 

Bruce I am appalled at the price of foam you mention.
At the time we were building foam/glass hulls good quality foam was as cheap as chips

 

Why the cost of foam?

OS, that price was off the "Defender" website. Definitely not the best price around, but they are about the same as other small lot suppliers here. I think "good" foam can be had at around $3 a foot, but that is still expensive, and you have to buy at least a case at a time. At this time, at least in the USA, the various "brands" of core are each single source/distributor/importer, and they are taking advantage of their monopoly with their prices. I won't accuse them of price fixing, but $20-$30 a pound for a foam product is excessive Go figure. If the prices go up much more, we will be back to hollowing out logs for our floats-where we started to begin with. B