Seacast for a gast tank cover? 1979 246 CCP

[kaptainkoz]

Hello,
Just wondering if anyone has any information or experience on using seacast "pourable transom" in place of the typical plywood and glass restoration for a rotted out fuel tank cover core. Is the stuff at 3/4's of an inch going to have the same stiffness as ply? Also I guess this would save a bit a weight as it is lighter than ply and I would not have to glass over it, just fill and go. lastly, I want to slightly recess the round inspection hatch so it is totally flush and not raised. The problem with this contouring the plywood to match the recess without having large gaps to fill. I had two of them that I had to fit on my buddies' Grady and I was not happy with the trial and error grinding to make it fit. Then when it fit the inaccuracies had to be filled. I would love to think I can modify the cover as needed, pour it and done. What do you think?

[RickK]

Koz, do a search on "Seacast" and you'll find what you're looking for.

[kaptainkoz]

Thanks Rick!

[kaptainkoz]

Rick,
I did a search for 'seacast" and yes, 57 hits came up but they seemed to all be about transom applications.  I have an email out to seacast to see how they rate the product against plywood, and/or what they think about it in that application. I would be thrilled if I could pour it!

[gman 82 aquasport]

If you can't find an answer, my take would be to do a test piece, maybe 12 inches wide by 18 inches long to the thickness you would need for the cover , let it harden all the way then support the ends and stand on it, you would think that it would be strong enough because it takes the stress of the motor on the transom, but the transom also has all the fiberglass reinforcement with it, and being tied to the stringers worst casse you are out a little bit of seacast, best case you discovered a new way to re-do coffin covers

[RickK]

Rick,
I did a search for 'seacast" and yes, 57 hits came up but they seemed to all be about transom applications.  I have an email out to seacast to see how they rate the product against plywood, and/or what they think about it in that application. I would be thrilled if I could pour it!

In those 57 hits I think I remember reading that the compression of the seacast is nil vs that of a wood transom. Rock solid.

[bondobill]

I used Seacast for my transom.
Had about a 1 1/2 gl left over in a 5 gl bucket.
Couple days later I took a 5 lb maul to it to see how tough it was, couldn't bust it apart. Tough stuff.
Probably would want to lay a layer of fiberglass on the bottom side after the pour cured.
I think I read they recommend the pour be sandwiched between glass.

Bill

[slvrlng]

My bet is it won't work. It will be too thin and crack. I would think Seacast would have a minimum thickness recommendation. Putting a layer of glass on the bottom side would help, but my thinking is it will be too thin. I used Divinycell 5/8 H80 3 lb and my hatch went from weighing ~120 lbs with the wet ply in it to 33 lbs with one layer of 1708 on the bottom. It now reminds me of a diving board with just a little spring in it. Zero problems since I repaired this. My lid is 92 inches by 27 wide.

[wingtime]

I used okoume marine plywood when I redid my tank cover and covered the bottom of it with a few layers of glass mat.  Whatever material you use you have to glass the bottom of it.  The bottom layer is placed in tension when you stand on the deck much like the bottom flange of an I beam.  The sea cast may work but a strong bottom layer of glass would be the key.  I would think it would be too expensive and heavy to make it worth it if you ask me.

[Capt. Bob]

Give that man a cigar.

The casting material works great in compression (that's what is occurring when used on a transom) and poorly in tension. Concrete acts the same way and that weakness is overcome with the installation of a supporting structure to allow it to act in tension. With concrete it's steel reinforcing bars.

While wood in its natural state also acts better in compression than tension, you can increase its ability to perform by increasing dimension along the lines of tension or......
Construct it so the grains run perpendicular to each other... aka plywood.
I would think, as Lewis stated, modern coring material will perform well also with a weight advantage offset with a higher cost.

Whatever you choose, be sure to have a lot of anvils when you glue it all together.

Good luck.

[kaptainkoz]

Wow great information and angles everyone. I really appreciate the think tank. You are correct with the compression and "sandwiching" of the seacast as this is the response I got from their tech:

Yes Seacast™ would be a very good material for the hatches or covers. What we do here at the shop is to remove all the wood from the backside of the covers and then after pouring Self leveling Seacast™ we then cover the Seacast™ with 2 or 3 thin layers of fiberglass and resin 3/4's of an inch will make the cover strong enough to walk on without any problems. Stop by our Facebook page for some examples off hatches and deck we have done for our customers. Thanks for your interest in Seacast™ it will be the last time you have to fix the wood core on any part of your boat it is used on.

So they do reccomend to sandwich it. I am even invisioning taking a piece of woven roving, pulling out every 3rd strand or so to create a mesh, pouring half the sea cast, laying in the roving, then pouring the rest... somewhat like rebar in concrete. Wow, I wish it were spring and I could get started on my wild ideas!

I know im making more of it than it deserves being a gas tank cover, but the 2 that I have done I wasnt 100% happy with the fit of the plywood, If the skin were perfectly flat with perfect right angles at the edges (horizontal to vertical, im not talking about the rounded corners) Then it would be easy to tight fit ply. But its not. The edges are rounded. There is residual resin that has the skin uneven with various thicknesses. I was hesitant to belt sand them out as there is no way to ensure accuracy. Sure you can round plywood and mix a sludge of resin and filler to fill it all in and it would be better than new, but im just thinking of different ways of doing things that may be easier, better, lighter and stronger. Obviously I cannot say "cheaper" as this stuff is expensive.

well, its one more thing on my list to think about for my project boat.

[kaptainkoz]

Thanks Slvrlng,
I will look into Divinycell as well. Very interesting. Thanks!

[kaptainkoz]

Divinycell... looks similar to Coosa on the websites. Does it have the same issues holding screws as Coosa? I will have a swing back cooler seat bolted to the tank cover which I dont think would need all that much holding power anyway. What is the cost like for 5/8's Divinycell? I take it it comes in 4x8 sheets only?

[Capt. Bob]

Answer to the Divinycell/Coosa holding power is simple.
The tank cover is removable, so just lay out the cooler frame before you install the cover and thru bolt with plates to the cover.
Need to remove the frame, just remove the cover.

All my hatches/pie plates are thru bolted on my WAC tank cover. All but one, tank cover fasteners are also thru bolted.

No worries.

[kaptainkoz]

Thanks Capt Bob, thats the way to go. I try to thru-bolt as often as possible as well. To be continued as to which way i will go. Its going to be an interesting project!