Double layer bottoms

[Jim Dodd]

Just received an email from a first time cedar strip canoe builder, not from this site !

That after just a couple of times in the water. He noticed a crack in the glass, running paralel to his strips in between the keel and the bilge, of his canoe.

He confessed to over sanding the 1/4" strips.

I guess what I'm trying to do is convince people of the benefit of double layering the bottom of their strip built canoes.

Jim

 

[BWCA66]

I guess what I'm trying to do is convince people of the benefit of double layering the bottom of their strip built canoes.

Jim

I,m assuming you are talking about the "football"? Inside or outside?

 

[Peach Canoe]

How much does the extra outside layer weigh?

My Caribou S solo canoe is 15' 3" by 31.5" max width. If I use the DWL (4" WL) as the footprint of the football, it's about 2.9 square yards. Using 6 oz E or S-glass, that's 17.4 oz of cloth, plus another 17.4 oz for resin = 34.8 oz. or 2.175 LBS. That will encapsulate the fibres, but you may wish to use more resin to fill the weave, and then sand it flat without removing much cloth.

The extra cloth and resin covering the football and out to bottom of the stems, adds about 2 LBS to a boat this size. I cover from the keel up to the 4" WL end-to-end.

 

[MacCamper]

So now you have me nervous!!!

 

[Peach Canoe]

I have to qualify my earlier note on the weight of the extra layer. I cover the entire 4" waterline, stem to stem.

 

[Jim Dodd]

I,m assuming you are talking about the "football"? Inside or outside?

Yes, this would be in the football area.
I have always doubled the outside, and it's been fine. This also provides added abrasion resistance.
Some will advocate adding the extra layer to the inside. This would strengthen the hull, but not help in the abrasion dept.

Peach, that's about what I figured also, for extra weight.

Jack. It will depend on how aggressive you sanded your hull. Keep an eye out for it. Really it's an easy fix, to sand the interior, around the crack, and add resin and cloth, feather the edges of the patch, and varnish.
Sorry, I didn't mean to scare you, just keep an eye out.

Jim

 

[Mihun09]

On the first stripper we built we only used one layer of 6 oz and used the boat for 4 years without the cracking you indicated Jim. We did add the second layer on the football this Spring, but only due to the compression break and our abundance of hidden granite up this way. I wouldn't think cracking would happen on every boat just because one person encountered it.

 

[Jim Dodd]

I wouldn't think cracking would happen on every boat just because one person encountered it.

I agree ! But I've been encountering this especially in the first time builders, quite a lot.
It's disheartening to spend the amount of hours it takes to produce a strip built canoe and have this happen.
Again this seems most prevalent when the football area is over sanded.

Jim

 

[MacCamper]

Looking at the inside of my canoe last night got me thinking about this issue. Perhaps fortunately for me, there is an overabundance of resin inside upon my football due to my spreading challenges during construction. On one hand it bothers me that it is relatively thick, on the other there is added integrity, I think. Thus, no worries here. Also, the additional protection layers added to the stem sections on the outside of the canoe extend back roughly one third in each direction.

Time will tell...of course I be packing some gorilla tape just in case.

Mac

 

[memaquay]

In the 20 plus strippers I have built, cracking only happened once. This was not due to oversanding, but the nature of the cedar. I was using red cedar from old telephone poles. It was extremely dry. I applied the resin and fill coats on the outside. When I flipped it over, it sat for a week or two before I could get to it. Variable humidity must have caused the cedar to swell and retract....there were a few long cracks, all along the turn of the bilge area. Perhaps if I had sanded and glassed it within a day of turning it over, it might have been OK. One of my students built a solo using the same wood (I had a ton of it), and the exact same thing happened. I have never had this happen with white cedar or white pine. I never felt good about that canoe, although I did manage to salvage it. I gave it away as a decoration to one of my friends who liked to have pretty things in her barn.

 

[Iskweo]

Like Karin said, my boat is 4 years old and we only now added another layer due to torpedo damage. I am hard on boats and while the xtra layer is a good idea we never did have cracking. We also had issues with super dry cedar this year and it sure is a pain to work with. We do most of our builds in the winter when the garage is dry dry dry from the heater so humidity is never an issue.