JEM Watercraft

As my brother always tells me, "There's no such thing as a stupid question, only stupid people who ask them"
In that vain, here goes another.
I've noticed alot of builders fiberglassing the inside of their boats as completely as the outside.
Is there a reason for this? I'm sure it adds strength, but could a person get by with glassing the outside completely, and just taping the seams on the inside??Or is there some "dire" consequence if only one side has complete coverage, while the other side doesn't??
Please throw me a bone here guys!!

Lee

It can be done.

Glassing the entire inside help give the hull better stiffness. It also sheaths the wood to prevent any checking (small surface cracks that can develop in less quality ply).

Much depends on the design. If you have a multi panel, by the time you taped just the seams, you could have covered everything in glass and saved yourself the trouble of having to feather the edges of the tape.

Finally, depending on design, the ply may required the extra stiffness complete coverage provides.

Yep, All that Matt said and more.

Here is why I choose to completely cover the inside of my hulls in cloth.

Cloth only on the outside of your boat provides some strength and scratch and impact resistance.

Cloth on the inside as well, provides disproportionatly greater impact and structural strenghth. In the event of a hard impact on a rock or similar, an unglassed inside boat will be more likely to have the ply fracture because the stresses are in tension and all that is holding the ply on the inside of your boat together is the woodgrain and the little resin that has penetrated it. Add to that wetted out fibre-glass cloth and that impact or tension strength is multiplied many times. Well worth the extra effort and expense.

I am soon to start a build on a 16.5" Sasquatch that Robin and I hope to use to run the Mary River here in Queensland when it flows.
Mainly a gentle and slow flowing river but with genuine but short, class 3 rapids in places.

There will be hard impacts on this boat and plenty of them and I am confident that my beliefs and the way in which I make this magnificent canoe will be sufficient for the job. I wouldn't even think of attempting it in a boat that was not completely sheathed.

Lee, the answer to your question is two words: hull integrity. If you don't do it, it may not mean much for weeks, months, years. Until one day, you hear CRACK-K-K-K!

Again, the answer is two words: "OH $H!T"

Ok! y'all have convinced me. Glass the inside it is.
Now, should I do that before the shear is installed or after??

Lee

Which model are you building? The instructions should give details regarding the best time to do this.

Matt,
After all the nice "tings" I've said and "thot" 'boutcha! I was really wondering if anyone had DEVIATED from the written instructions and glassed BEFORE the shear so they didn't have the addition of that inside corner to deal with while glassing the inside.
There I've done it!! I've questioned the designer!! Forgive me!

Besides, it's better to ask forgiveness than permission, right??
Like my brother said. "No stupid questions... just stupid people that ask them!!"

Lee

The instructions should mention a couple different ways to do it. But I can't be sure until I know which model you have.

Easy way it to apply clear packaging tape to the area where you plan on installing the gunwales. Glass the interior and right over the tape. When it all cures, sand near the edge of the clear tape and the glass will come off in a clean line.

After all the nice "tings" I've said and "thot" 'boutcha! I was really wondering if anyone had DEVIATED from the written instructions

G'day Lee,

I have done it this way but that was only because I was too lazy to follow the build instructions.

Seemed to work OK but the oldest of my Jem boats is not yet two years old. so I don't think I should recommend it.

What I do now is glass the entire inside of the boat and just as the resin goes touch dry, but well before it cures, I scrape the cloth Where the shear clamps are to go off with a carbide scraper.

I then completely fill the cloth with further coats of wesin - wet on wet. That is, I apply a layer of resin, wait till it is touch dry - usually 2 or 3 hours here, scrape off the lumps and bumps and then apply another coat and so on.

In between coats, I prepare my shear clamps so that they are ready to install and with the last coat, I paint the wood flour/resin glue onto the shear clamps and clamp them in place BEFORE the last coat of resin goes hard. This is truly wet on wet but seems to work very well.

Sounds like what I'd had in the back of my mind when I was thinking about the process. thanks Mick