Glass or Kevlar over xps for transom?

brsoo

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Jul 23, 2015
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Has anyone on here tried making another way to build a small outboard transom out of something other than glass over wood?

My main concern is wieght savings for old lighter aluminum boats....

aluminum? Cracks or too heavy?

Xps foam with fiberglass? Cut a X into it and glass that also?

Xps foam with Kevlar?

Are these methods too much money to where carbon core or coosa are just as pricey?

My personal outboard is ~100lbs
 

brsoo

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Jul 23, 2015
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My idea is to cut transom shape from 2" xps foam. Then cut a X through it. Cutting into 4 pieces. then fiberglass the 4 pieces together. After that encapsulate the whole transom in glass. This would create a x of glass right where the motor mounts on... Maybe add a aluminum plate over that?

I'm guessing $50 materials? Weighing around 10-15lbs
Vs wood at 25-40lbs?

Is this a bad idea?
 

zool

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Seems like a lot of fuss to save a few lbs..since its an aluminum boat, no need to glass anything, just take a few layers of exterior plywood, coat it with epoxy, and paint it...you'll save the weight of the glass and it will last a long time. JMO
 

brsoo

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Yeah. I made one of plywood. I just can't believe the weight. It seems like overkill for a 100lb motor!
does anyone know of a cost effective synthetic board or foam?

Pictures of my overkill...
 

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zool

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Its not just the weight of the motor u need to be concerned about, but the torque under load, or twisting force...I like to error on the side of overkill.
 

Woodonglass

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I agree, The weight of the motor is the least of your concern. If you ever hit a submerged log you want the transom to be strong. Use the wood!!!:nod:
 

brsoo

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Soo I wanted to answer my own question with a deeper explanation to hopefully help anyone with the same concerns.

Pour in and coosa board transoms end up weighing more or close to the same as wood. Your paying for rot preventative

XPS foam with fiberglass might work for a while with a small sub 60lbs? I wouldn't try it tho.

Aluminum is not great for structural purposes in my opinion. It would likely still be heavy with the amount of materials.

So wood really is the best thing for the job.

Or posibly XPS and carbon fiber. But id rather spend $50 then $100+
 

Scott Danforth

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my perspective as we use stainless, carbon and aluminum on a daily basis at work

a proper aluminum structure would weigh less, however be about 5x the cost of simple wood (at volume) with some paint to cover it. for a single transom, assume 10x to account for scrap and incidentals

carbon fiber covered foam would not handle the squishing of the clamps. a properly engineered carbon layup would cost you 8x the cost of simple wood (at volume) with some paint to cover it. for a single transom build, with scrap, etc, expect to pay about 15-20x. plus you have to do the FEA on the carbon

kind of hard to justify spending more than $50 on a sheet of plywood, some tite-bond III and a quart of rustoleum

you can re-do a tinny transom in an afternoon and be catching fish by evening and have it last decades
 

brsoo

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I now understand why its that simple. Btw I weighed mine again its just under 18lbs. Really not terrible..

I am however curious how you guys use aluminum? Do you have any examples or pictures of the work?
 

GA_Boater

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I now understand why its that simple. Btw I weighed mine again its just under 18lbs. Really not terrible..

I am however curious how you guys use aluminum? Do you have any examples or pictures of the work?

Have you priced a hunk of aluminum the same size as the transom you already made and show in post #4?

Have you priced fabrication cost for an aluminum structure to replace the transom you already made and show in post #4?

Why haven't you slipped the transom in and gone boating after you have a transom you already made and show in post #4?

Why am I :confused: about all the talk to save a few pounds against 18 pounds for the transom you already made and show in post #4?

I can't remember any fabricated aluminum transom project in the forum that ever made it off the drawing board.
 

Ned L

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Hmmm,..... ......... what you show in post #4 ideally has the grain running in the wrong direction. You really want the majority of the grain running port-starboard.
Shouldn’t be any problem for a smaller outboard.
 

JASinIL2006

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A 5-ply sheet will have 3 plies running one direction and two plies running at 90 degrees. The sheet will be stonger in the direction in which the greater number of plies are oriented. Is it enough of a difference to worry about wnen part of a layup of thickened resin and fiberglass? I don’t know, but I guess it wouldn’t really matter.
 

Scott Danforth

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I now understand why its that simple. Btw I weighed mine again its just under 18lbs. Really not terrible..

I am however curious how you guys use aluminum? Do you have any examples or pictures of the work?

only a very few people have done an aluminum fabrication using plate, tube, and sheet. of the 3 that I have actually seen photos, only one was laid out properly.

you dont want to do a solid sheet of aluminum. currently a sheet of 5083 aluminum thick enough for a transom would cost you about $4k with current pricing. the 6000 series would be greatly less expensive, however a thick plate of aluminum as a transom would weigh 3 times that of plywood.
 

dingbat

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A 5-ply sheet will have 3 plies running one direction and two plies running at 90 degrees. The sheet will be stonger in the direction in which the greater number of plies are oriented. Is it enough of a difference to worry about wnen part of a layup of thickened resin and fiberglass? I don’t know, but I guess it wouldn’t really matter.
Agree... but ran across this researching the issue

http://www.woodnewsonline.com/DTEW/1306jun/downtoearthwoodworker4.html
 

Ned L

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I suppose some plywoods may be equally stiff in both directions, but I have never seen one that is stiffer across the face grain.
 

Woodonglass

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Not All Plywood is the same!! The quality and # of plies used will ultimately determine its overall strength. With 3/4 " plywood with at least 7 plys, it's NOT a critical issue on which direction the Face Grain runs. As stated in your article the inner plies can significantly affect how the sheet "Deflects" Since a transom is installed vertically AND it's two layers thick with the addition of Resin and Glass. The debate on "Which Direction is best" is really a moot point. Just Know that it will be completely Structurally sound and will last as long as the boat, IF it's properly installed, Maintained and Cared for!!!
 
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