Using Seacast or similar with 5in" Tarnsom Increase

[DonV]

Hey we have all been where you are at....shoot I'm still there!!!! I did an Arjay transom and am very happy with the results, I learned a lot of things I wish I knew before I started, however the end result was good. I did not go up to a 30" transom, just like you going from a 20 to a 25, and in hind site I wish I had done it. I guess because I'm a "cheap bastard" and prefer to do things myself I tackled it on my own. I learned a few things on the "not to do list" and as luck would have it, most turned out actually like it was supposed to. One thing I would have done differently was to make a grid of fiberglass re-bar, suspend it between the front and back transom skin and poured the Arjay over that, think of it as pouring concrete with re-bar and wire to add structure. Oh yeah, if you go with Arjay.....NO leaks, NO leaks.....ask me how I know. Good luck!!

[Rybones]

Thanks DonV, funny thing is, I had the"rebar" thoughts too but coosa not fiberglass although I wasnt actually planning on doing. Why were you thinking 30"? I had considered that also because I was considering going with the porta bracket (that is no longer the case) and 30" would still allow me full tilt with that bracket. Also Arjay is a very strong consideration. But again, please tell me your thought s on going 30" and your misgivings for not doing so..

[77SceptreOB]

Originally Posted by DonV

One thing I would have done differently was to make a grid of fiberglass re-bar, suspend it between the front and back transom skin and poured the Arjay over that, think of it as pouring concrete with re-bar and wire to add structure.

Why do you feel this is necessary to add fiberglass rebar? Is Arjay not structurally sufficient? Were you not happy with the rigidity of the transom? Would Arjay bond to the fiberglass rebar to make a composite? Or would it create a cold joint and weaken the homogenious Arjay pour? Very curious...because I'm leaning toward this method of rebuilding my transom and have heard you speak about the fiberglass rebar concept before but never really had a chance to discuss it thoroughly with you.

Thanks,

Jim

[uncleboo]

Originally Posted by 77SceptreOB

Why do you feel this is necessary to add fiberglass rebar? Is Arjay not structurally sufficient? Were you not happy with the rigidity of the transom? Would Arjay bond to the fiberglass rebar to make a composite? Or would it create a cold joint and weaken the homogenious Arjay pour? Very curious...because I'm leaning toward this method of rebuilding my transom and have heard you speak about the fiberglass rebar concept before but never really had a chance to discuss it thoroughly with you.

Thanks,

Jim

My guess is peace of mind!

[FLexpat]

Please excuse me while I geek out here, just adding confusion of engineered structures without all the equations and tensile diagrams…
Rebar in concrete is for strength in tension because concrete is weak in tension but strong in compression. When it is in the middle of a concrete slab it really doesn’t help for flex. When a piece of concrete is designed for flex the rebar will be on the outer part, maybe an inch inside the concrete to protect it from the weather etc. That is why you see ‘cages’ of rebar in poured concrete columns.

A similar concept applies to reinforcing a pourable transom. The glass is there for tensile strength and should be on the outer edges; in the middle it just flexes. This is why a slab of Coosa just has a thin layer of glass embedded in both outer edges, not the middle (you can see it if you cut a piece).

A modern transom is cored construction with very high compressive strength (to keep bolts from crushing the core). The Elements of Boat Strength by Gerr has a very good discussion of cored construction – it is worth the read.

You can do what you want, but if I was doing this project I would lay up strong skins (scarfed to the old skins and finished smooth) around a temporary form of a core, pull the temp core and then pour Seacast in. A couple of additional layers of 1808 or 1708 could be added to the inside of the skins (covering the joint by about 3-4 inches) after the form was pulled. That way you would get a transom with construction similar to Coosa without having to completely remove one skin. Use peel ply on the layups. Since Seacrafts like the motor to run a bit high, I would make it either 26 or 31 inches, depending on what motor I was using.

Like others have said, practice on another part first; you don't want to realize you made a mistake by looking back at where the engine used to be. Good luck.

[Rybones]

Thanks All, now we are cooking with gas. Why do we want to lay up to the outside first/primarily and then to the inside? I figured there would be greater streanth (perhaps only maginaly) laying up the glass from the inside first. Also, I'm still trying to get my head around this 30" (or 31") inch transom thing. Wont 30" affect the overall ride greatly as I am currently at 20" and eleminating most ability to reverse? (I currently have a 25" shaft (insert joke here) and also have a hydraulic JackPlate with 5" of travel and 5.5" of setback). As it stands, my boat gets out of the hole instantly and I have a top-end of 45 plus it rides really nicely. I can see raising 5" or 6" but 30" or so is a 10" incrase that makes me think it will have a great affect on my hols-shot and ride. Please let me know the impact of going 30" and why, plus if it affects my rigging.

[flyingfrizzle]

Is porable transom a vaible option if done properly and bonded to new and old glass?

I would say its a viable option and would work if done right but me personally I wouldn't use it to raise a transom. I think what Flexpat says is the best word of advise. Long as you have the proper layups on each side you will be ok long as the core has the compressive strength for hardware. Make sure it is grafted to the old glass well. 12 to 1 and blend it in a ways with the inner and outer skins. I could see where this product would work well to fill voids vs cutting something open but I like the idea of wood or composite (dense enough) for transom cores. Especially if my motor is hanging off it or a bracket. There are a lot of loads from the outboard. Also just curious? What dose this stuff weigh? A 5 inch extension probably not so much but a full transom poured with this stuff would weigh a lot I would think.

Edit:
I really don't know much about these type of pourable products or have used them so I really shouldn't comment about them at all anyways. Those who have researched them and used it will tell you better than I. I would worry it could crack but with the technology today it may be a good product.

[Rybones]

I looked in to the weight of seacast, it is lighter than pywood and a little heavier than Coosa. I dont know what the weight of Arjay or Nida is, but I assume it is comperable.