transom plywood problem

[saxis]

I found the plywood in my '68 14' Fleetform's transom rotten. This boat has a "dovetail" stern, where the plywood stretches across the entire stern, leaving open pockets in the corners, and is glassed to the floor and on each side, and of course to the 1/4" of glass that is the actual transom between the two "dovetails". I cut around the inside of the transom to free the plywood from the sides and floor and chiseled it away from the 1/4" glass transom. I cut a new transom from 3/4" plywood, but the plywood is painted, front and back. I noticed the resin did not stick to this paint very well, so I sanded and scored with tiny holes as much as I could so the resin can soak into the wood. If I do this all around the plywood and sand/rough the paint really good will it hold up? I'm mounting an Evinrude Lark VII 40hp to this boat.<br /><br />Thanks

 

[lark2004]

Re: transom plywood problem

It should be ok if you can remove all the paint, clean the dust off with a clean damp rag, absolutly no solvents or chemicals! one more trick is put the timber out in the sun and let it warm up, then bring it inside and coat it with resin as it cools down. This will cause the fibre of the timber to draw the resin into it.<br />I would also consider making the transom out of two pieces of 3/4 ply, laminated together.

 

[prockvoan]

Re: transom plywood problem

A transmon is 2" thick,2 sheets of plywood is a must!Why not just spring for a new sheet of 3/4" treated plywood,cost around $30 or less.<br />Cut it out to size,(2 peices)glass(resin) inbetween,clamp them together using screws and clamps.After its set,then install it in the boat,glassing it to the transom,using screws and clamps.Just drill thru the outside of the transom for the screws,remove them after the glass resin sets,then fill the holes with resin then top it off with a little gelcoat putty.

 

[saxis]

Re: transom plywood problem

Thanks for the replies. The original transom had 3/4" plywood running the length of the stern, glassed around the edges and to the transom. The part of the transom that actually holds the motor is only about 20"wide x16" tall, due to the dovetail stern. The stern of this boat is pretty narrow, so the plywood is only glassed to about 20"x16" of the transom, and it had 8 bolts holding the plywood to this part also. On the outside of the transom was another piece of plywood about 18"x12" that wasn't glassed, but was sealed with what looks like silicone caulking around the edges, and the bolts came through this plywood aslo, giving it the 2" thickness. I'd imagine the plywood on the outside kept the glass from being damaged by the motor mounts.<br /><br />Here is a picture of what my boat is...<br /> http://www.boatsunited.com/Boats_for_Sale/view.php?ad=000067 <br /><br />If you look close, you can see how the motor mounts between the dovetails. <br /><br />Also from my post "1968 Fleetform" in Boat Topics and Questions, I got a reply that these boast have problems the the transom cracking, and I'm assuming they crack at the corners of the dovetails. It looks somewhat weak there. My plan is to take out the painted plywood, clean up the transomcorners, add a layer of glass that wraps around these corners, glass in a new 3/4" plywood and bolt it on also, glass the plywood over and overlap the edges to glass to the sides like it was originally, and install the 3/4" plywood plate on the outside. The glass will also wrap around the top of the transom over the 2 pieces of plywood. This is how the transom was done originally, but I am adding a little to the strength of those corners. It rotted from wear on the top of the transom (motor mounts rubbing) and water was allowed to seep between the plywood and transom. <br /><br />Sorry for making this so complicated. I've heard this is an odd design (but looks awesome!), and seems harder to work with than a straight stern. <br /><br />Does it sound like this will hold up well enough?

 

[prockvoan]

Re: transom plywood problem

Why not just do the same as the old transom,but install the piece that was on the out side,add it to the inside.

 

[jimmythekid]

Re: transom plywood problem

i would thicken it up for sure, sounds like that piece thats was on the outside caulked in was added on later at some point, maybe not tho.put it all on the inside and laminate together, and glass all in completely. plywood is cheap, i would start with fresh wood without paint. The resin has to be able to soak into the wood to be effective.<br /><br />cool looking boat, with a color matching engine awsome!!!

 

[Yacht Dr.]

Re: transom plywood problem

Its hard to tell from the picture<br /><br />NO PAINT on glass areas ( where your gonna tab in your transom must not have any paint what-so-ever !! ) treat them as described below.<br /><br />All plywood that you use in transoms must be resin treated to allow the glass-plywood bond.<br />Use a 50/50 resin to acetone mix and treat plywood bond areas..either tabing or full plywood trasom replacement.( might absorb 3 coats or so )<br /><br />After scuffing use a 25%-75% acetone/resin mix treating the wood again.<br /><br />Scuff again..use full resin coating again..scuffing all resin bond areas again for glass tabbing or bonding.<br /><br />Clean with Acetone between scuffing and coatings<br /><br />make sure your tabing to the transom/hull joint is clean and done correctly.. all it takes is for one bond to break then you will see your 40 everrude slingshotting over your head in some high water.

 

[saxis]

Re: transom plywood problem

Thanks for the replies!<br /><br />

Originally posted by jimmythekid:<br />cool looking boat, with a color matching engine awsome!!!

Thanks, but this is not my boat. Mine looks a "little" rougher around the edges, and is red/white with blue strip, and same colored Lark 7 on back... I hope it looks nearly that good when I'm done... <br /><br />Yacht Dr. - Thanks for detailed instructions on this! Just want to clarify a few things... I use acetone to thin the resin and paint it on BEFORE I glass the plywood in? And what is the proper way to tab in a transom?? I do have some experience glassing Cedar-strip canoes, but that is about the extent of it. Thanks again!

 

[Yacht Dr.]

Re: transom plywood problem

Yes..thin down the resin on the wood multiple times as described in my post..that way the resin is actually imbedded in the wood ( not just the first layer of wood that some would resin coat (( only makes one layer of the ply good for your bonding.. soak it in ! ))<br /><br />once you have your wood "conditioned" you lamitate that into your transom ( or conditioned for your second layer of plywood) <br /><br />your proper way of laminating your trasom is as follows...<br /><br />1. grind all tab points ( 12 inches on your hull and transom )<br />2. use first only fiberglass "mat" (I use 2 layers of mat- 1 1/2 ounce mat to start with..then woven glass..then mat,wovin,mat,wovin..rince and repeat till build up is good. )<br /><br />I dont want to sound redundant..lemme explain..<br /><br />Mat is your bonding glass..wovin is your structural...you MUST use mat between your structural and or primary glass they will not bond..use them in conjunction.

 

[saxis]

Re: transom plywood problem

Gotcha, thanks! Just 1 more question... Do I use strips of glass to lay in the corners where the plywood joins the hull, or do I cut the pieces large enough to cover the entire transom and overlap these corners? Seems it would be pretty tricky to get one piece to form around the corners.<br /><br />Thanks again!

 

[Yacht Dr.]

Re: transom plywood problem

Just tab your transom in with strips at first.<br /><br />personally..id go 2 mats..woven..mat..woven..mat..woven<br /><br />if you want to cover the whole transom with glass..thats good..and not really that hard..<br /><br />use plastic tightly to get your template..then cut your glass about 1" larger then that plastic template..use one layer of "mat" along the inside of your hull..then one layer (finish) with one layer of woven roving. then gel coat over it tinting to approxamate color looking professonal. this serves as two fold..structural..and cosmetic..<br /><br />your tabbing of glass is the most important..if you tab correctly..there is nothing that will tear it apart unless you try to go land boating hehe.. <br /><br />YD

 

[BillP]

Re: transom plywood problem

For best results use styrene instead of acetone to thin poly resin and for cleaning surfaces to be glassed. Acetone works but doesn't give the chemical bonding link of styrene. Styrene is made for mfg and thinning poly and superior to acetone in these applications.<br /><br />Not mentioned yet is to use "laminating" resin. It stays tacky for days to weeks and requires NO sanding between coats if still tacky. Liquid wax (aka "Modifier C") can be added to the final coat if you don't want it tacky immediately after kicking. Normal procedure is to do a final "fill" coat with mod c added to give a tack free finished surface.<br /><br />"Finishing" resin alreay has the wax and drys tack free everytime. Sanding is required between coats if they are done at different times.

 

[Yacht Dr.]

Re: transom plywood problem

Hate to say this..but I disagree with you..Acetone is more volitile..means it evaporates much quicker..cleans better..<br /><br />you wont get a "chemical" bond unless you laminate between windows <br /><br />if you laminate any kind of resin within a day id say you wont get a structural bond ( there are some..but more expensive then your normal resins (( Im not talking to the average boatshop here )) Im not gonna get too tech on these peeps doing it themselves<br /><br />Most resins your gonna buy isnt gonna be addative

 

[saxis]

Re: transom plywood problem

Thanks guys. This sounds way better than what I had originally planned to do!

 

[BillP]

Re: transom plywood problem

Originally posted by Yacht Dr.:<br /> Hate to say this..but I disagree with you..Acetone is more volitile..means it evaporates much quicker..cleans better..<br /><br /><br />you wont get a "chemical" bond unless you laminate between windows <br /><br />if you laminate any kind of resin within a day id say you wont get a structural bond ( there are some..but more expensive then your normal resins (( Im not talking to the average boatshop here )) Im not gonna get too tech on these peeps doing it themselves<br /><br />Most resins your gonna buy isnt gonna be addative

YD,<br />Disagreement is ok with me but...I don't understand what you are talking about with "windows" or "most resins your gonna buy isnt gonna be addative."<br /><br />You're right to an extent, acetone cuts some chemicals that styrene doesn't. Use it first if you don't sand the surface properly. Use acetone as a prewash if you want but the last wipedown should be with styrene. It gives a chemically linked bond superior to using acetone. It isn't my opinion, its frp industry standard backed by 50+ yrs of continued use. <br /><br />Doubting Toms should do the following test...Take four pieces of cured poly. Glue two piece together with plain poly resin as the glue and prep them with acetone as the "cleaner". Glue the other pair with resin but use styrene as the "cleaner". Let cure overnight and try to pry them apart. The set wiped with acetone will pop loose from each other easily. The styrene parts will be 10x more difficult to pry loose...if you get them loose. <br /><br />Thinning with acetone...The short of it is a young gelcoat that shows porous swirls is the sign of acetone as the thinner. SeaRay found this out in the mid 1970s when their head lamination guy substituted acetone to save costs. The porous swirls quit happening when they started using the correct thinner. <br /><br />Laminating resin revisited...Glassing later without sanding is the whole reason for its use. That's why 99.99% of all poly production boats are built with it. They build the hull, let it sit a few days to cure and then glass in the stringers, transom, etc without sanding. You can't sand laminating resin anytime soon anyway because it clogs up the paper. All laminating resins are like that, cheap or expensive.<br /><br />bp