Composites transoms, why not 100% fiberglass?

DeepBlue2010

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We been debating the subject of wood cores on this forum for very long time. We also discussed the Seacast route and I believe we all agree that Seacast would have been our first choice if it wasn’t so expensive and requires a dam to be fabricated sometimes.

Recently, I have been thinking about all fiberglass transoms. With the new fabrics on the market now such as biaxial and tri-axial, can we put together a 100% fiberglass transom that has the same strength as plywood for the thickness?

And if so, can someone think of any good reason why this will not work? Cost is one I am aware of. Also the process of laminating that much thickness is exothermic and must be scheduled to avoid generating much heat to avoid “cooking” the laminate. Any other thoughts?
 
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JASinIL2006

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I think the cost would be a big part of it. You would need a lot of cloth and a decent amount of resin to lay up a 2" thick transom. I bet it would be plenty strong, though.
 

Woodonglass

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It's been discussed several times. I'll see if I can find the Old Threads. Here's what I'd recommend. Dig up some scraps and make a sample, say 12" x 12" x 1 1/2" thick and see how long it takes and how much it weighs. Then multiply that by the average transom size. and the time and effort it takes + the Costs. Report back and let us know if you think it would be worth all of it.:D;)
 
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Scott Danforth

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it would be stronger than wood, and about 5x the cost of a wood core.
 

zool

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I guess it all comes down to why bother...we know production mfg's wont spend the time/money to make a product that will long outlast their warrantees or even their solvencies and expect to compete.

And for us rebuilders.....our new ply transoms will far outlast our interest in most boat models, if built right.....

Most rot starts at fastener holes or thru bolts....so those areas can easily be over-drilled and filled with resin....
 

DeepBlue2010

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Thanks for all the thoughts guys. I just want to make it clear that I wasn?t promoting the idea, I also did not do any significant research on it before I posted. I was only offering it for debate to get a quick feedback based on knowledge and experience if it is doable/practical or not.

Since I posted, I performed a back of the napkin calculations.. The results render this idea non practical at all
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The weight of a 1 foot square of 1708 (2 inch thick) all things included (fabric and resin) = 22.1792 Ib
The weight if 1 foot square of marine ply (2 inch thick) all things included (2 layers of 1708 with resin) = 6.29646 Ib

That is 3.522488 order of magnitude increase in weight. Not good
 
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gm280

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There are lots of other materials that could offer superb strength and being less weight as well. But COST precludes most of those issues. They do make a honeycomb aluminum material that if covered with polyester or epoxy would be very solid and light weight too. But try buying such materials and you would think you are buying an entire new boat. They also make honeycomb synthetic materials that way as well. So there are materials that could be used if you had the money. If you ever seen those materials used on aircraft, it would amaze you at the light weight and supper strength.

And then you can get into exotic materials as well. Titanium honeycomb is even lighter and stronger as well. But forget trying to buy those materials. But one thing you have to remember, if you can get better materials with stronger strength, then it doesn't have to be as thick to support the engine either. So an interesting topic. JMHO!
 

DeepBlue2010

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Yes, this last point about thickness is what I was thinking about.I calculated weight for 2 inch thickness while I am sure I don't need that much for the strength. I only did that for the required clearance to install the outdrive. BTW, Coosa is a really good core as well next to what you mentioned above
 

Ned L

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All good points. I think there may be another reason why a wood core just 'works' really well for transoms. Traditionally, outboards (and most small ones still today) rely on the typical two 'screw clamps' to keep it on the back of the boat. The wood core still provides a certain amount of 'squish' for the clamps to squeeze into and get a better grip on.
As an example, if you take a "C" clamp and clamp it to a piece of wood it takes very little clamping force to prevent you from being able to slide it around. Now take that same "C" clamp and clamp it to a piece of smooth steel and I think you will find that you must tighten it quite a bit more to stop it from being able to be slid around or moved on the steel. -- The same principle applies to transoms.
 

DeepBlue2010

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But with outboards you are not directly clamping on the wood core but on the fiberglass inner and outer skin if it is fiberglass hull or on the aluminum if it is a tiner
 

Ned L

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But with outboards you are not directly clamping on the wood core but on the fiberglass inner and outer skin if it is fiberglass hull or on the aluminum if it is a tiner

I understand and agree. However, I still think you would be surprised how still that little bit of give in the core might make a differance.

........or not.
 
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DeepBlue2010

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One thing I know for sure is that I wish the choices were just simpler :D One day, maybe
 
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hadaveha

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I have allways wonders about fiberglass skins, if you have a rotten donor glass boat, cut it up the sides, tops, any other areas where u could cut some basic sheets of fiber glass, and cut them all to shap glass the together, I got the idea from a fellow that built dog houses out of boat skins
 

jbcurt00

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Not a lot of transom sized pieces of FLAT fiberglass skins on a boat, besides the transom, at 3/16in per, thats what, 8 boats you need transoms out of? After getting the rotten wood off? I guess it'd only be 4 if you salvaged the inner and outer skins.......

Yeah, no thanks....
 

zool

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I understand and agree. However, I still think you would be surprised how still that little bit of give in the core might make a differance.

........or not.

Yup, and....

If the layup schedule was epoxy and a heavy cloth, you would get enough elasticity/flex to achieve similar imprint hold........as opposed to a brittle poly layup....but it sure would cost more.....again, hard to beat an encapsulated ply schedule..to go boating for 20+ yeas on the cheap...
 

Woodonglass

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Well...Maybe this guy REALLY has it all figured out. Simple, nearly UNSINKABLE, prolly will NEVER ROT(if you used PVC Planks for the deck), inexpensive to operate. Hmmm,,, I Wonder???
images
 
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gm280

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Well...Maybe this guy REALLY has it all figured out. Simple, nearly UNSINKABLE, prolly will NEVER ROT(if you used PVC Planks for the deck), inexpensive to operate. Hmmm,,, I Wonder???
images

That would certainly work...UNTIL another boat comes by and flips it all over... :facepalm:

And I really don't think that would be a good idea in the ocean either. :eek:
 

Woodonglass

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Darn, I just KNEW this would get somebody ALL RILED UP and start a good ole' ruckus!!!!! Guess I'll have to think of something else!!!:heh:
 
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