Transom fabrication using Kay-Cel - are seams ok?

[jrs151]

Attempting to minimize product waste - (cough cough ... pain threshold on the wallet).

Going to rebuild the transom on my 18ft Holiday using 25lbs Kay-Cel (aka Coosa-like board). My transom is 1.5" thick, measures 74" x 27" roughly. Here's the dilemma ... my local supplier sells only whole sheets ( 96" x 48" ) of the stuff. The 1.5" sheet runs about $655 ( ouch! ) and little less half would be completely wasted. The 3/4" sheet runs $355, BUT I couldn't get two whole pieces cut out of one sheet, thus two sheets would put me at $710 ( sting ! ), and agian, tons of waste.
So while gazing at my current transom I noted "it" is not one contiguous piece either! Looks to be two 3/4" marine ply glued ( resin ) together and sectioned around the splashwell area. So my question is ... could I apply the same fabrication standards to Kay-Cel ?? I figure staggering any seams (as not in the same spot as the other layer) and a good clamping resin-in, it should be fine right? Should I tab-in the seams as extra measure, and/or would glassing-in 3/4 oz on both sides be good enough??

Here's my old ply transom:



Here's a mock-out fabrication plan and estimate cut pattern from a 4' x 8' stock 3/4" Kay-Cel ( scaled to size ) :




^^
||

Oh ! And yes ... the splash well is going bye-bye ? will be repowering to an "offshore" bracket. Bringing the transom full accross should alone add more stiffness. Plus the bracket will come with inside braces too for added stiffness.

Whadayathink ??

 

[crkranz]

Re: Transom fabrication using Kay-Cel - are seams ok?

I wouldn't do it that way. Here is how I would do it, much stonger....

 

[jrs151]

Re: Transom fabrication using Kay-Cel - are seams ok?

Pure awesome !
Your design offers at least one contiguous layer while minimizing total seam-age and away from high stress areas - aka engine/bracket mount.
Thanks !

How about any glassing?? Any I add to the inside sandwich or outer skins will push me over the 1.5 max thickness ??

 

[64osby]

Re: Transom fabrication using Kay-Cel - are seams ok?

Budget moans - Begs the question - Why Kay Cel? A transom of outdoor ply or Marine ply epoxied would cost about 1/3 of what your proposing and would provide all the strength needed. It would also free up $$$ for the OB bracket and other equipment for the boat.

crk - nice layout option.

 

[jbcurt00]

Re: Transom fabrication using Kay-Cel - are seams ok?

Budget moans - Begs the question - Why Kay Cel? A transom of outdoor ply or Marine ply epoxied would cost about 1/3 of what your proposing and would provide all the strength needed.

^^^ yep

Agreed, nice re-work on the layout CR

 

[jrs151]

Re: Transom fabrication using Kay-Cel - are seams ok?

Budget moans - Begs the question - Why Kay Cel?
....

weight

My budget concerns have already been taken into account regarding ply & composite decision, thus taking into account all pros/cons and my person preferences. My bad for not more accurately qualifying my budget lead-in remark as it was more directed to total composite cost, NOT the overall transom repair cost. Hence going composite - I'm not trying to overly pay for too much of it if I don't need too. Would you blame me?
Like anything else in life - it's not a foreign concept to concede to higher costs if it reasonably means less long-term future moisture penetration worries (less future sealing, 5200 on screws, hoping I did a good enough initial job on resin sealing, etc...)
I simply like the worry-free, install it and forget it, predictable product expectations of going composite.


CR, I think I'll settle on this slight tweak from your layout to facilitate easier cuts, and to offset any center seams :

 

[crkranz]

Re: Transom fabrication using Kay-Cel - are seams ok?

Not that it is a big deal either way, the reason I put the seam in the middle of my layout is that on my transom there is a brace right at the middle, so the seam of the two little pieces would be supported. Not sure where the transom braces are on your boat, but might be something to consider.

 

[jrs151]

Re: Transom fabrication using Kay-Cel - are seams ok?

Got it !
Thanks again for the tip

 

[barbosam]

Re: Transom fabrication using Kay-Cel - are seams ok?

kay-cell as in the polystyrene floor insulation? Maybe I'm thinking of the wrong product. You said its similar to coosa which makes me think glass reinforced urethane foam somewhere around 24lb density. I have always used airex pxc also known as extreme 2000 or penske board.

Anyway short answer is I would suggest glassing both sides. I don't care what they claim in their advertisements none of these foams are a direct replacement for wood with out being sandwhiched between glass.

I don't want to lecture, I don't know how much homework you've done or what experience you have with it. If you want more info I can go into more detail. Just let me know.

 

[jrs151]

Re: Transom fabrication using Kay-Cel - are seams ok?

Not at all barbosam, I appreciate your advice on glassing as I was kinda leaning towards it too.
My only concern is inadvertently increasing total thickness past the 1.5”. Thus some strategies might entail using a low oz mat & careful resin quantities. Another idea, being that the transom is mostly “open” on in the inboard side, is to NOT glass all the way out to the side edges and the bottom where the 1.5” thickness is really going to be a concern due to the aluminum supports that secure the transom in-place.

As far as Kay-Cel, their polystyrene flooring - no. Their Polyurethane reinforced panel - yes. Different product. It is equivalent in construction as Coosa, Airex, & Penske board. So add yet another brand-name to your suite of known high density glass reinforced urethane foam panels.

 

[barbosam]

Re: Transom fabrication using Kay-Cel - are seams ok?

ya I'm going to have to find out more about Kay-cell, I never heard of that brand, especially if they are cheaper.

The main downside to these polyurethane foam materials is their lack of compressive strength. For example when you try to tighten the four bolts to mount and outboard the bolt heads and washers will sink into the material and you will never reach the required torque as the bolt continues to sink in. this is where the glass helps. it disperses the load and helps but does not completely eliminate the problem unless it is very thick. You will still need to use very large oversized backing plates on all fasteners.

The material is really a core material and not so much a plywood replacement. Its high density, and more importantly thickness, contribute to the stiffness of a fiberglass sandwich panel but the strength is in the glass. the chopped glass strands in the foam do more for screw retention than anything else. There are some varieties of foam that use continuous strands of woven glass that can help add some strength by dispersiing loads but do little for improving compressive strength and won't do much at all if you piece it together.

speaking of piecing it together, if you do the glass sandwhich panel method you can install the foam in as many pieces as you wish, the foams main purpose is to add thickness to the panel and there by increasing its stiffness. I doesn't matter if the foam is one piece or 50, its going to create the same thickness panel.

also in regards to your concerns of fitting the new transom in the aluminum channel, you can always route out or otherwise remove some of the thickness of the foam at the bottom before glassing to reduce the overall thickness in the last couple inches. just be sure to make a 30 to 45 degree transition when stepping down to the thinner area, this will make laying the glass infinitely easier than trying to lay it over two 90 degree corners to step down the thickness.

 

[jrs151]

Re: Transom fabrication using Kay-Cel - are seams ok?

Great information ! Nice tip on pre-routing / bevel. I agree on you compression concerns and will take that into account.

FYI

This write-up references all types of high-density composites, including Kay-Cel towards the bottom: Structural polyurethanes: Bearing bigger loads : CompositesWorld

This supplier is local for me, but also has an online store : Panel, Fiberglass Reinforced Polyurethane, 25 lb Density, 3/4" thick x 48" x 96", Kay-Cel RB25TD