bonding transom

i have finally got the transom ready to glue to the original structure of my boat. do i use resin for glue to original structure or do i use pl its a fiberglass/gel coat structure.also should i lay a bead of pl at the bottom of the transom. boat is a 84 malibu with a 5.0 omc. thanks

Re: bonding transom

I'm doing same thing today. I'm bedding mt transom in thick pl and using pl to adhere to hull.I will use screws thru transom to pull wood tight and then marine tek holes when remove screws. It may not be best but from my mock ups with pl it will outlast my use of this boat.

Re: bonding transom

does the pl on the transom need to be lay'd in beads, kinda like a race track, or does it have to put on then spread like carpet glue so the whole surface is covered? thanks

Re: bonding transom

I recommend using a notched trowel to spread the glue over both surfaces. Just like you do when gluing carpet. It worked great when I glued the two sheets of ply that made my transom.
I did however use resin and conventional methods to bond the transom to the inside skin. I was worried about the PL leaving voids or not curing completely down in the middle of transom. I will be using PL to bond/ bed my stringers when the time comes.
The main reason I went with resin to bond the transom wood in is that it is a proven method used for years, using PL is new. I also tried gluing fiberglass with PL as a Test. I used dirty pieces so consider that, but the PL came apart pretty easy. Try your own test on some clean pieces and let us know. I think PL is great for bedding because it builds up thick and remains flexible. But I am still a bit skeptical when it comes to bonding fiberglass.

Re: bonding transom

I wouldn't recommend using PL to stick the wood to the transom. Use a layer of CSM (chopped strand mat) and resin. You want that entire piece of wood, with no air gaps, bonded to the transom skin and strengthened with the CSM.

Re: bonding transom

so should i make the resin to bond the transom to the original structure like jelly so it will hold and not run, if so what can i use to make the resin jelly like. im using poly resin. thanks

Re: bonding transom

I'm not sure I follow. Coat the transom board with resin, lay CSM down on top of that, wet out the CSM, get rid of air bubbles, then put the transom into the boat and clamp it.

There's no need to thicken it. The CSM will hold it in place well enough. Some might dribble out, but that's no big deal.

Re: bonding transom

ok i get it now. when i cut the wood out my template was not 100% perfect and i have gaps between the bottom of the transom and the hull, can i use pl to fill the gaps or should i use resin and if i have to use resin is there a special way to mix it so it wont ooze out of the gap? thanks for the help danond

Re: bonding transom

U need cabosil ( also called aerosil or fumed silica) available where resin is sold. You also need chopped fiber and possibly another thickener like talc (talcum powder) or micro balloons.
Cabosil is a thickener known for making a smooth texture that is easily spread. It is also light weight if that is a concern. Cabosil is basically exploded glass that will not absorb water.
The chopped fiber (1/2" or less) is just that, chopped up fibers of fiberglass. It is used to add strength to the mix. If no fiber is used the resin alone can fracture making it weak.
Talc is just a basic inexpensive thickener. I mix cabosil and talc to save cost. Talc is cheap but heavy.
Micro Balloons is a filler/thickener that makes the finished surface easier to sand. The tiny microsphears are normally used as a finishing filler when added to resin. (recommended only with finishing resin, not laminating resin) Micro balloons can also be used as a thickener for filling, filleting and fairing resin that needs to be sanded smooth.

The basic idea is this. You need to make sure that the surfaces you wish to bond are clean, fair and well mated. Mated- meaning they match up well and will lay flat, one to the other. You need to use Chopped strand mat to promote adhesion of both surfaces. The mat will help to flatten each mated surface and give plenty of surface area. Poly resin is a poor glue, the CSM will give a smoother, more regular surface and will add strength to the bond. The filler is used to add mush factor and proper bedding.
Wet each surface to be bonded with catalyzed resin and cover them with saturated CSM. Then coat each surface with thickened resin. Clamp them together with enough force to cause a little bit of thickened resin to mush out all the way around the perimeter of the glued parts. Do not clamp too tightly, just enough to cause a little mush to ooze out. This insures that you are pressing enough to get good contact throughout the whole piece. Let it cure and remove the clamps. WALLA! bonded.
Epoxy resin is a different animal. Epoxy has much greater adhesion properties. It is often not necessary to use CSM to bond two parts with epoxy resin. You still need to watch for mush factor however. When using epoxy it is still very important to insure that you are using thickened resin to bond irregular parts. Normally thickened epoxy is all that is needed to get a good bond. Remember to watch for the mush!
Hope this clarifies things a bit. Drew

Re: bonding transom

Sorry for the newb question here. What does "PL" stand for?

Nick

Re: bonding transom

One more question for tonight. I just ordered (today) some 1708 biaxial fabric that I plan to use for bonding the transom boards to the boat and between each layer of wood. Should I use CSM instead? I thought the 1708 would work well, but can use it for something else if it really wont work for bonding the transom.

Here is the 1708 that I'm talking about:
http://www.uscomposites.com/specialty.html

Thanks,

Nick

Re: bonding transom

NickAndJena said:

Sorry for the newb question here. What does "PL" stand for?

Nick

Click to expand...

PL is a polyurethane that comes in a tube like caulk or maybe in bulk as well. It's waterproof and a good bonding agent, but I too would not use it on a transom. Transom clamps are also good.

Re: bonding transom

Very new to this web site and am looking for some direction. I have a 1989 Baha Cruiser with twin 302 fords. Next spring we are required by our insurance co. to get a survey. While getting things ready for this year I noticed that the bottom of my transom in rotted. Do I have to replace my complete transom board or just the rotted area?

Re: bonding transom

cdkakes - start a new thread by hitting the "new thread" button at the top of the Boat Restoration and Building forum page.

Re: bonding transom

Thanks, sorry for the inconvenience.

Re: bonding transom

NickAndJena said:

One more question for tonight. I just ordered (today) some 1708 biaxial fabric that I plan to use for bonding the transom boards to the boat and between each layer of wood. Should I use CSM instead? I thought the 1708 would work well, but can use it for something else if it really wont work for bonding the transom.

Click to expand...

I think 1708 already has CSM stitched to the back of it. If I am right than you do not need to buy separate CSM to do the job, it is already attached to the back of the fabric.

A basic fiberglass layup goes like this,
(2) layers of CSM (1) layer of roving (1) layer of CSM to hide the stitched welt in the finished surface.

A layer of csm should always go between layers of stitched cloth, like biaxial.

If memory serves 1708 is made with a CSM layer on the back of the fabric. When you lay it make sure the 1708 goes CSM side down. You may need some extra CSM to cover the welt of the fabric if you are working up to a smooth finished surface.

example= Wood-CSM-CSM-fabric-CSM-CSM-finished surface.

I generally omit using stitched fabrics for bonding. The added fabric will add allot of bulk and thickness that it not needed. In turn it is a good idea to use fabric if strength/ thickness is needed in what you are laying up.

It is not a good idea to lay stitched cloth against stitched cloth. It will not bond well using poly resin. The heavier the cloth the worse the problem gets.

Re: bonding transom

thanks again for all the help. last transom question i hope, the boat is a malibu 84 ski boat with a omc v/8 I/O. the engine is mounted to the stringers and the drive is bolted to the engine i still dont understand why the transom needs to be more than 2 inches thick? all that was bolted to the transom was the swim steps, speedo pickup, and the big rubber boot. when i removed the transom in chunks it was only 1/2 inch ply, ive installed 3/4 ply trying to make it better/stronger. should i double up on the 3/4 ply or just leave it alone, if i double up on the ply i can have to start the template above the plug kinda, since there is no room down there, it will look like a smaller triangle in the larger triangle. any suggestions, thanks again for the help

Re: bonding transom

66mstgfsbk said:

thanks again for all the help. last transom question i hope, the boat is a malibu 84 ski boat with a omc v/8 I/O. the engine is mounted to the stringers and the drive is bolted to the engine i still dont understand why the transom needs to be more than 2 inches thick?

Click to expand...

it doesnt..........

the reason that the transom is 2 inches thick.....is because that is the tollreance that is needed between the transom outter and inner plate....(im not framillar with omc's but i think the actual thickeness is about 1 3/4...!

if your transom is thicker than that you will have to grind away some if it. (around the t plate)



as far as the bonding between the transom and existing glass.
forget 1708...!.......wrong fabric for the job!
go hull....csm..(1.5 oz)..csm....wood.. csm wood then you can use your 1708 to back stop the whole sha bang.....but 1708 is not a particually good bonding material.

cheers
oops

Re: bonding transom

thanks again for all the help

Re: bonding transom

OMC Cobra transom thickness is the same as Mercruiser. Between 2" and 2&1/8".