Reducing weight of a Strip built hull

[Jim Dodd]

So lately, I finished up another Composite canoe. Where I use a stripper as a Male mold.
After I varnished the inside. It Dawned on me.
Why did I use Fill coats, two of them, to fill the weave of the fiberglass cloth ?

If I would have used a Saran Wrap type plastic, over the Wet out coat ? I wouldn't have needed the two fill coats, that I usually do.

I'm going to play with this on my next build.

I tried Peel Ply with no success, years ago. First it doesn't conform well to the shape of a hull. Second it still needed another fill coat to finish.

I use Window Heat shrink film, as a release, on my Male mold, and the Composite copy..
The finish on the inside of my composite, is smooth.
Now I need to wrap the outside of my composite, or stripper, after the wet out coat, and call it done!

Saving two fill coats would have a major weight saving effect !

What do you think ?

Have we been ignoring this weight saving Idea too long ?

Jim

 

[Gamma1214]

I'm not sure where you're saving the weight Jim. Is it on the inside of the stripper? I only use a wet-out coat (no fill coats) on the inside because I like the texture & extra grip.

On the exterior, I'd think you'd want to bury the weave. I've only had one scratch get into the weave so far but I'd be afraid every scratch would get deep into it with just a wet-out on the exterior.

 

[dutchlennart]

It could be , weight savings are looking after all things. From the bolds you use to put the seat in , the species of the wood , the cloth of teh glass or...

in the end working on your body to keep strenght up and weight down. Is to me more important before i hit 70. Then get the weight down from 20 tp 18 or something similar.

 

[Jim Dodd]

I'm not sure where you're saving the weight Jim. Is it on the inside of the stripper? I only use a wet-out coat (no fill coats) on the inside because I like the texture & extra grip.

On the exterior, I'd think you'd want to bury the weave. I've only had one scratch get into the weave so far but I'd be afraid every scratch would get deep into it with just a wet-out on the exterior.

The weight savings is from glassing, the outside of the canoe.
The weave is buried. so no fill coats required.
The weight savings is from not needing extra epoxy, to fill the weave..

So I need to be more clear.

Here is a simple test. Take a piece of cloth, lay it on some plastic, or wood if you'd like. Doesn't matter if it is S-glass, or E-glass.
Wet it out with mixed resin. Lay a piece of plastic, plastic drop cloth, on top.
Let cure, pull the plastic . You will see the weave of the cloth is filled, and perfectly smooth..
No need for fill coats.

The real test is to get a film of plastic, over the hull, while the epoxy, in the wet out coat, is still wet.

This would be easy if you were adding an extra layer of cloth, over just the Football.

Still working on it !

Jim

 

[Jim Dodd]

It could be , weight savings are looking after all things. From the bolds you use to put the seat in , the species of the wood , the cloth of teh glass or...

in the end working on your body to keep strenght up and weight down. Is to me more important before i hit 70. Then get the weight down from 20 tp 18 or something similar.

Picking up a 50# canoe and portaging it, is harder than doing the same with a 30# canoe.
It doesn't matter how much you weigh, or how in shape you are.

Problem, is reducing the weight of a canoe. Reducing the amount of resin needed to build a hull, by say 30% , without sacrificing the strength of the canoe ? Is a big thing !

This is all food for thought. My next canoe ! Right ?


Jim

 

[Gamma1214]

I'll certainly have to try that on some test panels before my next build. I'm not sure I understand the mechanics of it, though... How would the glass be completely buried? Does it float away from the hull during the wet-out? I mean, I suppose it would but I never would have thought it was enough to completely bury the weave if it were compressed with plastic.

You're exactly right; the only reason that I use fill coats is to bury the weave so, if it can be done during wet-out, that would be far better IMO.

I'll have to grab the roll of Saran Wrap & give it a try (but not til Fall... I'm way behind schedule already)

 

[Cruiser]

Hi Jim,
If you use .4 - .5 oz per foot per fill coat, you will be pretty close to the real answer as long as you don't apply heavy. The fill coats on my new canoe weighed in at 7.4 oz over 17 feet .... quick and dirty 7.4/17 times your boat will give you a number in the right ball park for what you could expect.
It is actually what I am planning for the thwarts, which are somewhat more easily shrink wrapped than a whole boat.

Brian

 

[Jim Dodd]

I'm surprised I hadn't thought of this before.
Getting a plastic layer, on the tumblehomed area of the wetted hull? Might be a real challenge !
Much easier over just the football.

As far as actual resin savings ? I was just throwing out a guess.

So what triggered this thread ? When I pulled my Composite hull, off the heat shrunk plastic, on the Male stripper hull.
I noticed how smooth it was, and the weave was completely filled.
Had I plastic wrapped the outside of the composite ? It too would have been smooth, with the weave buried.

I've been going over ways, to get the plastic on the wetted surface of the hull, without wrinkles.
Small areas, like the bias strips on the stems, is easy, with tape.

Now for the hull.

Jim

 

[zekabl]

Clear poly sheeting? https://www.uline.com/BL_4001/Clear-Poly-Sheeting. Quite spendy for the heavy gauge stuff.

 

[Cruiser]

Whatever plastic you pick, needs to be able to handle the epoxy, what about that shrink wrap they use for boat storage?

 

[Jim Dodd]

I've used drop cloth plastic, Visqueen, and window heat shrink plastic, all with good release.

The Boat shrink wrap might be ideal !
Especially if you form it to the hull, prior to laying it over the wetted cloth.
Eliminating wrinkles.
Great idea Cruiser !

Jim

 

[Jim Dodd]

Clear poly sheeting? https://www.uline.com/BL_4001/Clear-Poly-Sheeting. Quite spendy for the heavy gauge stuff.

That is some great variety, at reasonable cost.
Thanks Brian!

Jim

 

[gumpus]

I had a carbon/kevlar Bell Yellowstone with resin/gelcoat so thin that the fabric printed through on the bottom. If I ran over a thin stick it sounded like running your fingernail over a window screen. It did not seem to affect the boat's performance or strength in any way.

 

[alsg]

That's how I do patch/repairs: lay a piece of smooth plastic over the west out fiberglass and get a smooth result with minimal sanding. I think this could work but the hard part will be getting plastic to closely follow the shape of the outside of the hull. Maybe a vacuum bag would help?

 

[ThatPaddlingGuy]

So lately, I finished up another Composite canoe. Where I use a stripper as a Male mold.
After I varnished the inside. It Dawned on me.
Why did I use Fill coats, two of them, to fill the weave of the fiberglass cloth ?

If I would have used a Saran Wrap type plastic, over the Wet out coat ? I wouldn't have needed the two fill coats, that I usually do.

I'm going to play with this on my next build.

I tried Peel Ply with no success, years ago. First it doesn't conform well to the shape of a hull. Second it still needed another fill coat to finish.

I use Window Heat shrink film, as a release, on my Male mold, and the Composite copy..
The finish on the inside of my composite, is smooth.
Now I need to wrap the outside of my composite, or stripper, after the wet out coat, and call it done!

Saving two fill coats would have a major weight saving effect !

What do you think ?

Have we been ignoring this weight saving Idea too long ?

Jim

I have no experience (yet - lurking around here soaking up information like a sponge!) with building strippers but I have shaped and glassed a fair number of surfboards, as well as some other oddball fiberglass projects/boat repairs etc, so I am pretty confident in my glassing abilities when I am able to afford the materials and the time, and clean up my shop. That said, my concern would be this: I would be worried that while the finish comes out clean and smooth (no fill coat required), it may also be quite hard to make sure you have a really tight laminate with no extra resin in the glass. In my experience resin loves to sit under the glass and sort of 'float' the glass up off the surface/core. the trick would be getting the minimal amount of resin required to both laminate and fill coat the glass in one go, without any extra reservoirs floated around on the hull. That's where vacuum bagging comes in, in my experience... I would be worried that you could end up with a heavier hull in the end.

That said you may well be fully considering that and have a better way of applying it than I am imagining! Everything is worth trying once!

And also, Jim, thank you personally for all the great threads and insights of yours that I have dug through elsewhere on this forum. I appreciate all the daydreaming and planning it has given me! Can't wait to build my own one day.

Cheers!

 

[Boatman53]

I have a problem, yesterday a friend from another forum (Old Woodworking Machines) stopped by the house and offered me a whole roll of 5’ wide Kevlar and Carbon Fiber, one each. The immediate problem is he lives in California and that’s where the rolls are. He is willing to drive them here next year when he comes back to visit his daughter. I certainly don’t need that much of either fabric. Should I take him up on the offer? At this time I don’t know the weights of or types of weaves and won’t till he gets back home next month or so. If it comes together I’ll be offering it up here for the cost of shipping and a donation to some charity.
I’ll keep you posted.
Jim

 

[memaquay]

For me, the biggest weight suck is the trim. Gunwales, thwarts, seats can often account for 1/3 of the weight if one is not careful.

 

[Gamma1214]

...Should I take him up on the offer?...

Absolutely. Sounds like you've got a great plan for dispersal of any excess.

For me, the biggest weight suck is the trim. Gunwales, thwarts, seats can often account for 1/3 of the weight if one is not careful.

Agreed. Not to stray from Jim's search for opinions on fill coats but I've often wondered about people's trim preferences... I think Canoecraft recommends inner & outer gunwales at 3/4 inch each for a total of 1 1/2 inches. Right or wrong, I've been using 1/2 of that (3/8 inch each) and the boats seem plenty strong enough.

Of course, I've yet to hang a seat from the gunwales but, when I do, I'm not planning on using a 3/4 inch gunwale from stem to stern.

How light has anyone else gone on some of this stuff?

 

[Jim Dodd]

I have a problem, yesterday a friend from another forum (Old Woodworking Machines) stopped by the house and offered me a whole roll of 5’ wide Kevlar and Carbon Fiber, one each. The immediate problem is he lives in California and that’s where the rolls are. He is willing to drive them here next year when he comes back to visit his daughter. I certainly don’t need that much of either fabric. Should I take him up on the offer? At this time I don’t know the weights of or types of weaves and won’t till he gets back home next month or so. If it comes together I’ll be offering it up here for the cost of shipping and a donation to some charity.
I’ll keep you posted.
Jim

That is an Awesome deal !

 

[Jim Dodd]

So I have a new idea .
You have all seen large motor boats shrink wrapped, with a blue plastic.

I'm going to check into getting my 38 Spl, without outwhales.
Shrink wrapped.
I could then easily pull a Kevlar copy from it !

My recent, Kevlar 38 Spl., at 16'3" with a 2.5# seat, came in at 37#

Jim