Controlling Shrinkage

[drewpster]

I have to replace the transom on my tri-hull. I plan to remove the cap and possibly the inner skin of the transom to access to old core. I plan to replace the old wood with new marine ply and replace the inner skin. I may either totally reglass the inner skin or glass the old skin back in depending on how much damage I do removing the old core. I am not a big fan of the chainsaw technique due to bonding issues.
I have two concerns. One; I plan to do the work with the hull on the trailer. The trailer supports the boat via two bunks that run along the bottom of the boat and extend past the transom about 6 inches. Should I add support to the hull sides or anywhere else to prevent warping?
Two; It is likely that I will have to build the new transom out of two pieces of 3/4 ply to make the proper thickness. (cut from a template then bonded together) When I glue the two pieces how can I better insure that the new wood will not warp due to resin shrinkage? I was planning to bond the two pieces with mat and poly. Should I consider epoxy? All the rest of the work will be done with poly because I am as broke as my boats.

 

[erikgreen]

Re: Controlling Shrinkage

To control shrinkage, I suggest wearing a well insulated swimsuit, perhaps with some padding


On topic, however... I'd suggest epoxy if at all possible. It glues stronger than poly, it won't shrink (neither should poly) and it smells better. More importantly it forgives many construction mistakes.

You should be ok with a bunk trailer, those support the hull pretty well. If you're still in doubt, do a search on this board for "hull stabilization" or "hull support".

Your transom won't warp if you glue it correctly. I'd suggest cutting peices of the core to size, laminating them under pressure on a flat surface, then puttying them in place with "peanut butter" which is resin plus fillers.

Erik

 

[tashasdaddy]

Re: Controlling Shrinkage

as you should know i've been laminateing transom for some years using PL premium. also using it the glue the wood to the existing outer skin. i use sheetrock screw to hold the 2 layer together, the take them out and fill the holes.

http://www.stickwithpl.com/Products.aspx?ID=fef65cc9-47bf-4802-aaa9-a343f2ef9458

 

[Mark42]

Re: Controlling Shrinkage

Before you remove the cap, take careful measurements across the hull (width) at a few places as high as you can under the gunnels. Mark the hull where you measured with a permanent marker and number or letter the locations, record the measurements on paper accordingly. Then after removing the cap, the boat can be re-measured to see if there was any bowing or deflecting. If there is, straps or rope can be looped around the hull and tightened until the measurments are correct.

It will just take a few minutes to take and record the measurements. Better safe than sorry.

 

[ondarvr]

Re: Controlling Shrinkage

Like Erik said, plus stay out of cold water.


You mentioned the transom, but not the rest of the wood, like floor and stringers, if the transoms bad the rest can't be far behind.

If all you do is the transom (removing the inside skin) then there shouldn't be a problem with the hull distorting on the trailer.

When you glue the sheets of plywood together, brace it with metal or wood until it cures. You can also glue them together in place on the transom, this way it will form a little better to the shape of the transom. You can clamp it, or through bolt it to hold it in place and to pull everything together.

There a bunch of pics on bonding and clamping the plywood, some use glue instead of either type of resin. Do a search.

 

[ondarvr]

Re: Controlling Shrinkage

I need to type faster, two more responses before I hit submit. TD must be just adding to his post count.