Need help on Fiberglassing Procedures

[85Sunbird]

I'm in the process of replacing the transom in my 85 17' Sunbird outboard. I've got the motor off and all the rotten wood out and the inner skind cut out. (I was unable to save that). My question is, if I go back with a wood transom how many layers or resin and mat should I use to glass the new wood back in? I'm planning on gluing the two peices of plywood together with resin. Once I get the new wood in place then glass over it to make the new inner skin. What type resin and size mats do you guys recomend using for this? I was going to go the seacast route but it was going to cost about $500 in just that so the budget wouldn't allow. <br /><br />Thanks,<br />Jason

 

[BrettNC]

Re: Need help on Fiberglassing Procedures

Use alternating layers of cloth and mat to achieve at least the thickness of the original fiberglass lay-up.

 

[85Sunbird]

Re: Need help on Fiberglassing Procedures

Thanks Brett,<br />What thickness cloth and mat should I use? Also I have heard of people coating the plywood with Resin and letting it cure before they start any glassing. Is this true? If so, how ling do you let it cure?<br /><br />Thanks,<br />Jason

 

[fishingdan]

Re: Need help on Fiberglassing Procedures

Always pre-coat plywood with epoxy before laminating glass to it. It is not necessary to let it cure. Apply unthickened epoxy to the plywood, let it sit for 10 minutes or so and then move forward with the glass. <br /><br />If possible, apply all of the layers of glass in one session. Squeeze out any excess epoxy.

 

[Chinewalker]

Re: Need help on Fiberglassing Procedures

Hi Sunbird,<br /> You can take a look at my Starcraft project where I am doing exactly as you're planning. I am using West System epoxy, which I would recommend anywhere you're using glass-to-wood bonding. Polyester resin is fine for glass-to-glass, but for glass-to-wood, go with the epoxy.<br /><br />- Scott<br /> http://www.pfs-ware.com/smith

 

[85Sunbird]

Re: Need help on Fiberglassing Procedures

Thanks Scott,<br />One question for you. I noticed on one of your pics that you had small peices of scrap plywood fastened to the transom board. What were you doing with those? Were they screwed to the transom to help lock in place while it sets up?<br /><br />Also......the way my boat is and because I haven't removed the top, I'm not able to put the transom back all in one peice. I have to peice it back in there in 2 peices. Will I get just as strong of a bond if I epoxy them in as I would if I used one single peice?<br /><br />Thanks again,<br />Jason

 

[Chinewalker]

Re: Need help on Fiberglassing Procedures

Hi Jason,<br /> Yes, those blocks of wood are acting as clamps to hold the outer layer to the inner two layers. I'm doing each layer one at a time, allowing each to fully cure before adding the next one. The first layer I screwed to the outer skin from the outside, while the next few layers were able to be screwed to that first layer. It has worked quite well so far as you can see the added layer being pulled up snug to the established layers as the screws tighten. I used the wood blocks to help distribute the force of the screws across a broader area so I didn't get a golf-ball look to the plywood, or something akin to adding buttons to upholstery where it pulls the middle in but not the area around it.<br /> If you are able to overlap the layers of your transom wood so that all of the seams don't fall in the same place, you should be alright. I would imagine that if you could affix a layer of glass cloth over the entirety of each layer you'd be even better off. The transoms in all three of my Starcrafts weren't covered with any sort of sealant, although they may have been treated with something when made 30 years ago - it's not there anymore. I'm no expert myself, but the method I'm using is kind of an amalgamation of successful methods I've seen outlined here, which results in a better lasting and overall stronger transom than they ever were when new. They were mass produced and cheaply at that....<br /><br />- Scott

 

[gspig]

Re: Need help on Fiberglassing Procedures

I'll add what I just finished. I have a transom that I had to replace with partial sections. The deck and hull on my boat don't separate and the rear gunwhale is deep. I replaced the transom with 2 layers of 3/4 exterior plywood, I didn't use the pressure treated because of varying opinions of resin adhesion. The first layer was cut into 2 pieces horizontally, the cut line was above my I/O cutout. I glued this layer to the outer skin with West System Epoxy and used silica filler. The second layer of ply was cut into 3 sections vertically. Main concern with this cut was to make sure the section with the I/O cutout was braced behind the hull stringers. I glued this layer with epoxy and silica filler. I also used SS screws for clamping and securing the plys together. I then used polyester resin and layed a sheet of fiberglass cloth over the inside of the new transom. I cut out the I/O hole and drilled the mounting bolt holes and coated the exposed wood with poly resin.

 

[85Sunbird]

Re: Need help on Fiberglassing Procedures

Thanks guys fir all the help. That clears up alot. I had originally thought for glueing the two peices of plywood together and then glueing them to the transom hull. So basically you guys are saying it would be better to glue in one oaice at the time till you have the desired thickness.....right?<br /><br />Thanks again,<br />Jason

 

[Chinewalker]

Re: Need help on Fiberglassing Procedures

Hi Jason,<br /> I did it that way because I wanted each layer to be attached to both the hull and the previous layer. I know people who have gone the all one piece route with good results, too. It's also easier to work with individual layers, as all four together would be quite heavy and harder on blades and sanders to shape. <br /> Also, my transom had buckled quite badly due to the rotted plywood and weight of the Chrysler 85. Each sheet of plywood I had had a bit of a curve to it and I was afraid that if I laminated them seperately, it may not have taken a true flat plane, which might lead to further troubles when I tried attaching it to a less than perfect transom surface. <br /> I guess the bottom line is that as long as you're working with good materials and take the time to keep things trued up and clamped tight as you go, there isn't really a wrong way to go about it. Epoxy is great stuff and very forgiving if things get a little sloppy.<br /><br />- Scott

 

[jheron]

Re: Need help on Fiberglassing Procedures

If you don't want to loose any strength you need to make a scarf joint Do a google search for Scarf joints in plywood and you will understand <br />regards Jon

 

[85Sunbird]

Re: Need help on Fiberglassing Procedures

Chinewalker,<br />Let me ask you this. I know epoxy is better than Poly Resin but will Poly resin do just as good of a job in bonding all this together using mat? I'll have a fortune in epoxy if I have to go that route. Just curious thats all. Also....is it required that I use Roven on the transom instead of fiberglass mat?<br /><br />Jheron,<br />Thanks for the link......that makes alot of since to me now.<br /><br />Thanks again guys,<br />Jason

 

[Chinewalker]

Re: Need help on Fiberglassing Procedures

Hi Jason,<br /> All told, I have used about one gallon of epoxy in my transom, totalling about $70 (epoxy and hardener). If you're using 3/4" ply, then you shouldn't even need that much, as you'll have two fewer layers than what I'm using. I think my transom may be a bit smaller than yours, too.<br /> Also, Poly has a very sketchy history in regards to bonding to wood. From what I've read here, it's fine for bonding glass to glass, but it doesn't bond well to wood or epoxy (unless it's been prepped). <br /> I had some fairly fine weave fiberglass cloth onhand, so that's what I'm using between my layers of plywood. I think it would be referred to as woven roven. <br /><br />- Scott (Learning as I go...)

 

[BillP]

Re: Need help on Fiberglassing Procedures

Look back at the last 50 yrs of transoms that worked flawlessly if rot didn't set in. Small boats were 2 layers of 3/4" exterior ply set in the back of the hull after it was glassed. The plys weren't glued or screwed together...just set against the hull. The whole area was glassed over and doubled/trippled up around the edges. The ply was contained all around with glass. There are no problems doing it that way today with polyester resin.