Alternative materials for transoms

I'm trying to find alternatives to wood in transom materials. I know plywood reigns supreme, but I'm looking for viable alternatives. The application is for outboards from 90-200 hp. If anyone has alternatives to plywood that you've used successfully, please let me know.

Also, if anyone has experience using PXc 385 I'd be interested in hearing how that worked.

Thanks very much!

 

Just a thought, are you opposed to plywood cos it gets rotten....if so that is because the transom mounts drilled thru it have not been prepared corrrectly, a well made plywood transom, glassed in will NOT go rotten UNLESS there are holes drilled thru it and not correctly finished. The holes need to be filled solid with glass and then drilled out undersize to the fillings, so that there is resin still sealing the wood, not simply drilled thru and bogged with goop in the lost hope that it will remain waterproof.

 

You can use the high density foams. Divinycell 250kg/m3 or similar from other brands.

I used coosaboard bluewater 20 in my transoms, the density is around 300kg/m3 IIRC...

Either way, synthetic options are much more expensive than plywood, but no rot, ever...

 

Landlubber: From what I've read (don't you love things that start like that)... wood needs a certain percentage moisture to rot and just the smallest amount of air. When the wood goes into the transom it already contains some of the moisture needed to rot, but not enough. If you layer it in fiberglass, you're not really doing anything because fiberglass without gel coat (from what I've read) allows moisture to pass through. According to a post on this forum it allows over 10% more moisture through so in the end a wood transom has 17-20% moisture which is enough to rot over a period of time even if it's entirely glassed in. Of course you could gel-coat inside and out too and that will help but here's the trick; throw in a crack or two or some new holes from a repower 5-10 years down the road and you're on the road to a rotting transom at some point. Maybe it's 50 years from now, but it's still going to happen.

With all that said, I'm looking for alternatives because I know that wood rots and the best way to deal with it even once the boat is out of my control and some ham-fisted marine mechanic starts drilling holes, is to make sure there isn't any wood in the first place. Just my .02 cents.

 

Plywood correctly coated with epoxy will last well. Millions of boats nowadays depend on epoxy to seal a core of wood. Not just the transom. There are threads here about exactly what you are doing. Any NA would recommend epoxy/plywood for your repair.

 

Sucking in transom packers is a better way !not perfect but better!!

During the process of making a transom packer normally its fabricated from layers of ply wood glued together ! then clamped and even screwed But I never see that ooze of excess glue around all edges!!, its just slap , spread and squeeze and hope for the best !! Im personally in favour of fitting transoms onto very resin wet glass layer and vacuuming them in place so the excess resin finds its way into a high percentage of the glue air pockets within the plywood its self specially round the edges where there's end grain and just painting on coats of resin is only allowing soakage to penetrate . where as Vacuum is forcing the resin much further that relying on soak and hope !! I'm Also in favour of drilling lots a smallish bleed holes all the way through the packer to help and promote even better and more resin penetration .
I am a stickler when I walk round the workshop for picking up off cuts and hole cut-outs for stern drives etc. and looking really closely at how good the construction and glue spread has taken place during its assembly and its fitting into the boat !!
Some I have seen over the years are really scary and when held up to the light its possible to see through from one side to the other !! not stuck at all !! gaps between the transom and the glass 1 or 2 mm wide in places !! it possible to push a thin knife blade full length into the groove and not find the bottom !!! so what sort of a chance is it that water wont find its way into there ??

 

Sure use epoxy, no question that it is far better than polyester, but the process is what matters most.......

 

Not to hijack my own thread but....

Thanks for the info so far. I'm aware that I can use plywood and seal it and wrap it in a bunch of "stuff" to help prevent rot. In fact there's a patented chemical treatment used by a window company that actually prevents rot at a molecular level. For a nominal fee I could dip wood in that and call it a day.

BUT my question wasn't how to prevent rot in wood so I'm just trying to get the thread back on track. My question was about alternatives to wood in a transom. What works well, what have people used, etc. Do some work better when glassed in than others? Why did someone choose product A over product B? You get the idea. I have no experience with them and I'm looking to learn from the experiences of others.

 

If you want light weight and the cost is not the driving consideration, a honeycomb would be my choice.

 

DOSENT mater what resin you use if the workmanship is poor and not up to scratch then its a waste of time and materials !

 

"DOSENT mater what resin you use if the workmanship is poor and not up to scratch then its a waste of time and materials !"

....yep, applies to synthetic materials, wood, ply or anything else....ta.

 

Well, resin systems do matter, considerably, if you compare the highs and lows, but workmanship and attention to detail also are as important as Tunnels mentions.

There are several core materials that can be used for a transom, but you have to make a list of what you want, generate a budget of what you can tolerate and what you absolutely need. Plywood rules, simply because pound for pound it's cost effective, easy to work, accepts goo and fasteners well and is stiff and strong for it's weight/stiffness/strength/price point.

Matching these qualities is tough. You can easily find materials that are lighter, stiffer and ultimately stronger, but cost several times as much, with more difficult "details" to address with less than skilled labor. This is the butt kicker in these comparisons. Price and ease or working are the usual issues.

So, look around, there's lots of options, but when you compare all the things you need to consider for a core, plywood will be near the top as usual.