71 22-2 Flatback Re-build Watch and Comment Please

[Marcel4t]

Okay cool.  I just looked up the meaning and origin of Tumble home, it's that inwards curve on top part of hull.  Old ships used to put a lot of it on their boats to make it really hard for enemies to board their boat, as the curve would be greased up and they would tumble (fall) home into the sea. 

[RickK]

I never totally got the bow out of my transom, even with fairing.  Not a big deal, but it is not flat across the width.
Here are a couple examples of transom rebuilds to give you some ideas
http://classicaquasport.com/smf/index.php?topic=9991.0

https://forums.bateau2.com/viewtopic.php?f=10&t=11294

[Marcel4t]

Okay, so tell me if this looks okay. 
I took a sheet melamine and screwed a straight 2 x 4 to the back to keep it stiff.
I tried screwing the skin to the melamine from the back, but the glass would just break.  So I screwed from the inside, first counter sinking a hole in the inside skin, drilling a very small hole out the back of the melamine (so I knew where the screws are later) and then screwed the skin onto the melamine from the inside with stainless steel screws.  I waxed the melamine several times. 
My plan is to take a small hole saw and drill out around the screws from the outside and take the melamine off (since the screws will be glassed over on the inside).  Then I can cut the screws down, grind them below the surface, and the heads will stay in there.  Hope this makes sense.Thoughts on leaving the screw heads in their?

[theFunsmith]

I think that will get you flat, but I wouldn't leave screw heads in place. I would grind them out and fill after the transom is rebuilt. Even more so if they aren't stainless. moisture finds its way into places you wouldn't think it can. Rusting metal swelling inside your glass isn't optimal. An ounce of prevention.

[mshugg]

Why not bolt through your melamine, skin and through your core.  You can use squares of polyethylene and backing pads on the inside of your skin.  Kind of like this:



The bolts just tap out.  Then you have 3/8” holes to fill.  Otherwise, the screws will be at the center of your pilot for your hole saw, not a recipe for success.

[Marcel4t]

Humm...I thought of that too...I was wondering how I could lay up the first layers of glass straight before putting in the core.  Do you think I could lay up 3 layers of glass, with the transom skin all wavy, then put core in and clamp it, and it should straighten everything out? 

[Marcel4t]

I think that will get you flat, but I wouldn't leave screw heads in place. I would grind them out and fill after the transom is rebuilt. Even more so if they aren't stainless. moisture finds its way into places you wouldn't think it can. Rusting metal swelling inside your glass isn't optimal. An ounce of prevention.

I was thinking of that also as a possibility, id have to get through 3 layers of glass to get to screw heads, but shouldn't be that hard to do? 

[mshugg]

Humm...I thought of that too...I was wondering how I could lay up the first layers of glass straight before putting in the core.  Do you think I could lay up 3 layers of glass, with the transom skin all wavy, then put core in and clamp it, and it should straighten everything out?

With epoxy, yes.  Put the hardner in the refrigerator, have your glass cut to size, and be prepared to work quickly.  I wouldn’t attempt it with poly or vinylester.

[dirtwheelsfl]

You should be able to put 3 layers in and let cure, then come back and sand a bit before gluing in the core. I wouldnt try to do it wet on wet,, too much going on. Those 3 layers wont lock the shape in. Once the core is glued in then your pretty much stuck with the shape/fairness...

[RickK]

Marcel4t, are you able to see the pictures in the links I posted above? If not, google "Photobucket patch" and install for the browser you're using.

[Marcel4t]

You should be able to put 3 layers in and let cure, then come back and sand a bit before gluing in the core. I wouldnt try to do it wet on wet,, too much going on. Those 3 layers wont lock the shape in. Once the core is glued in then your pretty much stuck with the shape/fairness...

The thing is that without screwing the skin down, its pulled away from the melamine around 1" in some places.  Its strange that it's warping in so much like it is.

Marcel4t, are you able to see the pictures in the links I posted above? If not, google "Photobucket patch" and install for the browser you're using.

Rick, yes I am able to see those pics, thank you for the links, I think Im just having a different issue than some people in that my outer skin is so warped but I'm trying to save it.   

I slept on it and woke up deciding to cut away some of the skin, maybe leave a 4-5" lip.  It's loaded with holes anyways.

[mshugg]

Dirt’s advise is good.  He’s done a lot of kick a** rebuilds.  Even with three additional layers, your outer skin will remain quite flexible.  Think fishing rod.  They are fiberglass and flex a lot.  After your three layers, just use a knotched trowel to apply your bonding mix (cabosi/resin).  You could also include a layer of CSM here if you want.  Then, when you clamp and bolt your core to your melamine mold, it will pull things flat.

Even though your outer skin has holes, it will make it far easier to keep your boat’s shape.

[RickK]

If you are going to cut most of the transom out (which might be the best way), remember to secure a piece of wood across the beam of the hull (especially at the rear) in a few places to secure her shape.
Don't forget that you'll need to lay in resin fillets all around the inside of the transom, to round out the corners so the 1708 can traverse the corner (that stuff doesn't bend real easy) and remember that PVC pipe thing I linked to - now is the time to lay that in.


PS: look through the rebuilds done by Dirt and see what tips you can pic up. The boy's good. 

[Marcel4t]

Yea, so I tend to over think things sometimes.  I went back and screwed from the outside, while the screws were still on inside holding the skin flat.  I then removed the inside screws and cut off the ends of the screws sticking out.  Skins is flat.
The first screws I used were fine thread which I don't think held as strong as course thread. 
Thanks for all the input.  You'll see I do this sometimes were I geek out over small things.
Now onto laying fillets, 3 layers of glass, then Coosa. Im excited!

[FL.flatback]

Looking good so far. Getting the transom in is a big step. Keep the pics coming 👍