transom core alternatives

hey all you pro brainiac type folks. i was just browsing my newly acquired jamestown catalog and i came across for the first time the fabled composite transom material. does anyone here have personal experience with AIREX PXc board? or Corecell? or Divinycell H80? im always looking for some way to get the wood out of transoms when i replace them but so far i havent found anything cost effective and durable enough. ive seen some foam transoms compress and ive heard that some composite core materials can get soft when the boat is in the sun too long even. any real world experience with this stuff is greatly appreciated. thanks guys.

 

"so far i havent found anything cost effective and durable enough"....can only agree.

 

If you like to replace wood, you need some heavier foam. Wood is at 500 kg/m3 upwards (30 lb/ft3).

So please do not expect a 80 kg/m3 (5 lb/ft3) to do the job.

This effectively disqualifies the PVC foams, but the heaviest types.

Try your luck with these foams:

PVC 200 or 250 kg/m3 (Airex C70, Dininycell H200)
Core-Cell A1200, or S1200 or S1800
Coosafoam or Airex PXc

 

I've had the same trouble, looking to replace wooden elements, but when you count all the physical attributes AND the price point, it's extremely difficult to compete with wood.

 

Yes, wood is hard to beat in terms of structural value and price. My guess is that, if installed correctly, wood should be able to last.

We all know that when encapsulated correctly, in epoxy, all drill holes well protected, it should last forever. But no idiot-with-a-drill should ever come near the transom.

My only concern would be the constant "wicking" due to the dynamic loading.

 

I've now been around long enough to have seen my own work from 30 years ago and it looks great, in many case not much different then it did when I original did it.

As always this assumes a reasonable level of care and maintenance is continued through it's life.

 

All core needed to be treated correctly. It does not like to be compressed and water is its greatest enemy.

Heat is also a factor. On a hot day, under the sun, the deck reaches temperature of 200 degrees. Enough to reach the tg of most resins. The transom is the least of your worries.

I have always used marine plywood for transoms with outboard because it is simple. Whether it is foam, end grain balsa, or ply, you must always seal the hole with resin. As an extra precaution, use silicon rubber sealant on the bolt and always use Fender washers to spread the load. You know those oversized washers with relatively small holes. These are for light loads. If you need to support heavier load, local reinforcing is required. First, a heavier density core is inserted in the bolt area, then extra reinforcement is added to the skin (inner and outer).

You might think it is an overkill but anti-compression bushings are used to prevent overtightening the bolts. These are sleeves that go over the bolt whose length is slightly less than the thickness of the laminate.

Even single skin laminate is not immune from these compression. Laminate do not like to be compressed and the first one to crack is the resin, heat wil reduce the strength of the laminate, creep (laminate relaxation) will set in the laminate under prolonged load. It is not unusual for bolted hull to deck joint to have some loose bolt once in a while due to heat and creep.

 

Coulda, wooda, shoulda lasted that encapsulated wood, but commonly used resins aren't waterproof so no surprises dry rot develops ! As for the cost, if you are competing with others who are less scrupulous about the long term durability you may have to think about it, but if doing the job for yourself, it is a no-brainer, no bloody wood !

 

You could completely build a new transom with very little core and just enough plywood where the motor gets mounted only !!
Have on a few occasions done rebuilds but used solid glass and given it shape to get strength and lightness !!!A flat panel will bend and twist but a panel that had curves wont twist and wont bend !! I will leave you with that thought for the moment . :?::idea:
Last transom had a old 75 omc motor and after the rebuild had a extra long Yamaha 115 v4 and built in set back of 450 mm that gives more room in the cockpit and made the power trim much more responsive and a better performing boat all round .

 

Coosa bluewater 26 should be fine for a transom.

 

Coosa bluewater 26, now there's an idea, great stuff. A 1.5" panel that's as big as a sheet of plywood is only $550 bucks, so this should be the first choice . . .

 

Well, that is a bargain, in boating terms...

 

Use Marine plywood then a couple 3/4" sheets would under $150.00

 

Yes, Steve and the whole point, to my first post on this thread.

 

thanks a lot for your input guys, youve certainly given me some things to look at and think about. it seems that if i do my job right i shouldnt have to worry too much. but then again a fool and his drill will soon find its way through the hull of a boat. im sure im not the only one whos seen a boat mounted to the trailer via the seat mounting screws. so it seems that the real issue is cost, and i should do some research and maybe shell out a bit of up front expense to work with some of this stuff and then present it to the customer as an option.
now im sure most of you will suggest using epoxy in the layup and bonding on this stuff, do you know if poly will even stick to it? i suppose i would work it pretty much just like wood when i lay it up? how hard is this stuff to cut and drill compared to wood? again i cant say how much i appreciate the information and above all first hand experience you all toss my way.