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solid fiberglass transom

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goatman1

Contributing Member
why doesnt anybody just replace the rotted plywood transom by just layering on the fiberglass to a desired thickness???
 
up here in Canada our dollar sucks
4"x8"x1.5" coosa board is $650 usd plus shipping
$1000 cad plus shipping plus id still need to epoxy it and clamp it, let it cure for 24??? hrs and glass it in and then gelcoat
thats alot of work and alot of money

i can glass it in for $600 cad and its alot less work
all i need is fiberglass matt, polyester resin, hardener and gelcoat plus it can be done in 1 day

thank you for the reply, i didnt know if doing it was a no no for some reason.

1-sheet of 5/8-marine grade plywood is $200 cad and id need 2 sheets plus the same installation/time costs of the coosa
which would put me at $600 cad
 
Plywood flexes. Anything that you replace transom wood with needs to have similar characteristics to the plywood that was removed. I assume you are trying to figure out a way to never replace the transom wood again?

Here's my two cents:

The engineers spent a lot of time figuring out what makes sense in terms of availability price & weight then tested it. Change materials and you are now on your own. You can do your own calculations on payload and flex then run sea trials. Honestly that just sounds like swimming upstream to me.

Consider the skyscrapers. There is a reason they aren't just built of solid concrete, it would snap in half in an earthquake. They are built of a number of different materials, some soft some hard which in combination provide enough flexibility to withstand the forces of nature and enough rigidity to stand up to the forces of gravity. I know your boat is not a skyscraper, but it just illustrates the importance of the engineering that goes into these things.
 
goatman1 said:
I really don't think transoms are engineered that deeply tbh. I've seen people using foam lol
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I think that depends on the boat goatman. A johnboat has been relatively unchanged for a long time, but check out some of the new stuff coming out now. Just one example below. Do you think some engineering went into that boat? My guess is yes. Granted that in a previous era a lot of ship and boat design came from models and trial & error but in the modern era there can be a lot of engineering involved (depending on the vessel of course). As much as a skyscraper? probably not, that was just intended to underscore the idea that someone spent some time thinking about this somewhere along the line. They figured out something safe, functional and economical.


If you have a good idea what you want to do and you are confident in a new approach then go for it dude! But in that case I have no idea what you are doing on a forum asking others for an opinion, lol! I'm not trying to discourage you from trying something new. Just giving you my two cents. I have burned trying to re-invent the wheel before.

Can you get away with foam in a transom? I'm sure that some boats in some conditions would work but there is no way that works for every boat. For instance a small John boat on a beaver pond with an electric trolling motor might get away with it, but would you install a foam transom on a 4,000 LB boat, running over 200 Horsepower 30 miles from shore in the Pacific ocean? I personally would not but if it's your boat it's your choice haha!

For fun, what kind of boat? What kind of horsepower?
 
racerone said:
I use hollow composite hockey sticks to replace plywood transom plywood.
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Also, what type/ size of boat? Any idea of the weight? What engine/ how much thrust are you putting on that? How often and hard are you using that? Has it lasted for more than 10 years with heavy usage regularly hitting WOT? If you are telling me hockey sticks work, we want to see the receipts.
 
racerone said:
I use hollow composite hockey sticks to replace plywood transom plywood.
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Also, I am really curious how you came up with the idea of hockey sticks! What even made you think of that? Is it the durability?
Maybe I need to switch to hockey sticks, are they expensive? Clearly I don't hockey.

Makes me wonder if you are Canadian! Haha!
 
Ok, I'm just jabbing on this now to make a point.

This is completely sarcastic, hopefully it gets a laugh. Hopefully it illustrates my point without ticking anyone off. What I wrote below is purely for a laugh gents. Please do not take this too seriously. My questions about the hockey sticks are not though. That is seriously interesting to me. I do want to know more about that.

So I just realized. I have this older kayak that is somewhat rare in that it has a transom at the back. this transom is a plastic shell, without anything inside of it. So based on the fact that this kayak exists, and that it has an empty transom with nothing but air inside we now have proof that little to no design goes into transoms and that you really don't need any backing at all! anything from a kayak to a 4,000 Lb. deep sea rig! All you need is air inside your transom!!! You cannot underthink a transom. It is not a vital part of the boat that keeps water out and handles all of the thrust and steering needs of the boat. They never leak, and a motor has never ripped a transom of a boat before.

Picture of the kayak that proves this concept!!
kayak 2.jpg



Ok, now joking set aside. You could have a foam filled transom, you could have an air filled transom, you could have a transom with a vanilla creme center like an oreo. I have no idea what you are working on, I have no idea what that specific boat needs, I have no idea where you are using it and what body of water you are going to be in if something happens to fail. Until we have that info, there is no way you can get solid specific advice on what you need inside. All of that set aside I think the advice that you can't go wrong by coming close to matching what was there is still pretty solid advice. I didn't say you have to use plywood. What i wrote was "needs to have similar characteristics to the plywood that was removed". So if you pull out some plywood and want to use carbon fiber sheets for instance, my advice means that I would be looking to see that it is the correct thickness (so that the motor has enough to bolt onto) enough rigidity (to handle the payload), and enough flex (to handle the rigors of your environment). For me, I really have to worry about this. I am slamming into ocean swells at 28 knotts. I need the flex, I need the payload and if I have a problem I am deep off the coast and I am going to be treading water for a while waiting for help. I don't have a choice but to consider these factors. Furthermore my transom is buried. Requires removal of aluminum sheets, transom shield, engine, outdrive, batteries, plumbing, hydraulic reservoir, blower, bait tanks, deck and more. For me if I gamble on something like this and it doesn't work out I am re-doing many many hours of work. I just assumed you also wouldn't want to gamble with doing a bunch of work twice either; thusly my advice that you can't go wrong if you think about coming close to hitting the same specs for the replacement. But then again, maybe your transom wood is much easier to get to than mine. I just cant gamble on mine. Your situation may be different.
 
This guy used foam but the glass is what gives strength and the foam keeps the boat light. Maybe its the Thermalite stuff people are using
Its not that I think i know better than you or others, I just don't agree that engineers were calling for plywood

 
PS when you said foam I was thinking Styrofoam. I thought you were making an argument for Styrofoam.

It made me think of this guy.
foamy.jpg
 
Can we agree that no one should put Styrofoam in a transom? Unless maybe its a kayak? haha.

I don't think I know better either. I don't want to think that I am better than anyone else on here. If we see things differently then we might have an opportunity to learn something from each other. Clearly we both mis-understood each other at different points in the conversation.
 
im leaning more toward the thickness of the transom would be the engineered part with a list of acceptable materials to get to that thickness, then it would turn into an industry standard. weve had plywood, foam and balsa cores.
now we have coosa and thermolite stringers and transoms
these composites are not cheap and are a finished manufactured product
fiberglass is a composite material also but we can get it as a raw material
thermolite is a vinyl composite and a 1/2" panel can be used as flooring on 1 foot centers or 300mm centers if it gets glassed into place
5/8 plywood can go 16 inch center
i guess i need to find out how thick fiberglass needs to be, to be used as flooring on 1 foot centers
heres a chart for fiberglass floor panels
www.brown-campbell.com

Load Information - Floor Panels - Specialty Products - Fiberglass | Brown-Campbell

Brown-Campbell fiberglass floor panels load information.
www.brown-campbell.com www.brown-campbell.com
 
Goatman, You probably aren't wrong. It sounds like the fiberglass is giving you a lot of strength on your vessel. So it could be that you really just need the appropriate thickness.

The link says the information was moved.

Are you still trying to decide on material? I hope its going well!
 
im just waiting to get on a lift to do a 280 to 270 leg swap, if i have to swap out shields ill do the transom in glass between the stringers
 
theydrewa31 said:
Lets see some pictures of that.
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I’ve seen the build, but don’t have pictures. Carbon fibre hockey sticks, tucked in tight together, & secured with laminated matting/resin… It’s bombproof, wAayyyy stronger than the original build.
Let’s be honest, the builders used plywood, ( and sometimes poor layups) because it was cheap, & a high school kid shown how to use a chopper gun could do it.
 
Where can I get some hockey sticks in bulk! That honestly sounds really cool. I imagine that took a good deal of time! I wonder if it takes a lot of resin?

Edchris177 said:
Let’s be honest, the builders used plywood, ( and sometimes poor layups) because it was cheap, & a high school kid shown how to use a chopper gun could do it.
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I 100% agree. They were in the business of making money right? It's not always about the materials, sometimes the labor can significantly increase the cost of production. Who knows how they decided the material. No doubt there are better or cheaper options, especially for us guys who are going to do it ourselves and save on the labor! Not to mention that depending on how old the boat is there could be new materials available. I wasn't trying to make an argument for plywood; I was trying to say that you can't go wrong if you at least match the strength of what was removed. Honestly I'll concede the point that there may not have been a lot of engineering or design involved, especially if it is an older vessel.

Believe it or not I am actually eyeballs deep in a transom repair myself. Grappling with the same set of questions in a slightly different set of circumstances. Availability and cost are pretty much making the decision for me. I have not been able to find marine ply in my area. I am not in a "hockey" playing area of the world, so sadly I feel like that might not be an option for me. In my case it is an aluminum vessel, and the transom is simply a sheet of 5052 aluminum on the outside with 2" of plywood on the inside. With the transom wood removed the aluminum sheet moves like you wouldn't believe. I feel like there is a solid 1.5" of deflection without the wood in there. In my case that wood (or whatever backing material I decide on) is providing a majority of the strength, and the aluminum is providing a semi-flexible layer of skin. To Goatman's point I think there are other vessels that are getting some of the strength from elsewhere, and the material properties may not be as important for the filler.
 
Newer boats are getting strength from curves in the hull.----Think like nature , and egg has a very strong shell simply because of the shape.
 
goatman1 said:
why doesnt anybody just replace the rotted plywood transom by just layering on the fiberglass to a desired thickness???
Click to expand...
Back to the original post, I have rebuilt a transom using Seacast Pourable Transom Material and it worked fantastic. I'm not sure how much it costs these days, but if I were to rebuild another transom I would use this material again. Pour it once and never worry about transom rot again.

On my 1997 Ranger the entire transom and stringer system is solid resin-fiberglass from the factory.
 
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