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Opinion on transom core thickness. 1.50" or 2.25”?

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Opinion on transom core thickness. 1.50" or 2.25”?

Old 02-10-2019, 10:24 AM
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Originally Posted by kln View Post
I would look at the overall panel span to determine thickness. Just shooting from the hip and it being a catamaran with a comparatively small transom area two layers would probably be sufficient with proper lamination.

Stupidity is relative. There is a difference between stiffness and "strength" (as you call it) introducing shape Into a panel doesn't make it any stronger. But it will make it more stiff.

Maybe (rigid strength) is stiffness?
Aren't you the big proponent for flexible is better???

I am no fan of coosa myself. And I wouldn't see any reason to advocate laminate between the layers but, Transom core is a funny thing. Plywood will rot if its compromised, but a high percentage of the overall strength is supported by the core itself. couple that with its compression strength its hard to beat for the cost.

Composite panels don't rot. But they really don't perform as well in compression. You increase the laminate but many times the force of just tightening engine fasteners can compress the core. The result of this is the laminate skin's that you are relying on for strength become compromised.

As for a solid glass transom. I dont see a problem. But to argue that a solid glass laminate will out perform a properly executed sandwich panel..and be lighter?

Well....that's questionable
Well there you go trying to install some logic to counter the BS that comes from the far East
I've done a couple solid fiberglass transoms and several more with a minimum amount of core, I've posted this one previously and tunnles gave it an approving nod, keep the unsupported square to a minimum with tall hull stringers and the engine mounting bolts gaining a purchase in the stringer tabbing...
Contrary to what tunnles is constantly suggesting, good design is not necessarily intuitive or simple... Otherwise there wouldn't be so much poor design out there.
Old 02-10-2019, 08:46 PM
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Thanks for all the feedback. I anticipate there might be one more round of replies from the weekdays only crowd.

The original question was "How thick"? There was of course the anticipated far east diversion. No, I am not going to build a solid glass core. (Fiberglass is still black magic to me. Wood/Aluminum/steel...anything solid that doesn't come in a jar...that I understand! Building a steel boat would be up my alley!)

General consensus based on the replies seems to be a core in the 2"-2.25" range. The only thing I have to put thru the transom are the drain plugs and splash well drains so I should be able to accommodate any thickness.

What is the general consensus on these drain plugs? Gimmick? Angled Drain Plug

I'll look into the Trevira Mat. I did have a couple of dry spots on the exterior layup that I ground out so I'll need to fill those in.

(Did a marathon 8.5 hour grinding session on the transom today. Glad that is mostly done.)

Old 02-10-2019, 09:26 PM
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Originally Posted by Docked Wage View Post
I did.

It was misleading and different from your followup post. You said, "solid fiberglass (which sinks in water) instead of wood (which floats in water)" and then followed up with the correct logic of buoyancy in a subsequent post.

Either way your questioning of the weight difference in your next sentence is valid since FRP (Fiberglass and Polyester resin only with no core) has a higher density than most plywoods.
doesn’t matter, but you’re still not reading it in the context of the original post. The part about the relative density, (using the density of water to show the comparison), was to demonstrate the impossibility of Tunnles wanting more total transom volume (he recommended the thicker option) made out of denser material, to yield 2/3 weight reduction. Nothing in my post had anything to do with whether the boat would float. You’re inferring that incorrectly from the density comparison.

If we curve the transom to follow his later posts and make it thicker and make it out of solid FRP, we can increase the volume even a bit more, making the weight savings that much more impossible unless he’s got a secret beyond, “I can’t be wrong so I’ll call Americans stupid.”

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