transom

[Ronbedard57]

Hello,
I've got the as-yet-unidentified small runabout, and I'm a bit concerned about the condition of the plywood at the transom. I figure that the boat often had a clogged scuttle and too much standing water, and the bottom of the transom plywood is a bit "mushy". I'd like to replace the whole piece, but it seems there'd be many rivets to drill out before a new one could go back in. I could get the old one out easily enough by cutting it up in place, but getting the new one in is problematic.
I'm sure someone has done this repair before, and I'd love to be directed to any related posts.
Also, is there a source for plywood of the appropriate thickness and water resistance out there? I can get a piece of LVL construction beam material that comes 1-3/4" thick and mill it down. Has anyone tried that?
Appreciate it,
Ron

 

[Ronbedard57]

Hi,
Been giving this a bit more thought, and I think I could cut out all of the old transom and remove all of the rivets that fastened the plywood to the boat. I could then "build up" a new transom in the largest possible pieces that wouldn't require removing any rivets that fasten metal to metal. Maybe three layers glued and screwed with epoxy glue would work. I could replace any rivets that went through the plywood and aluminum when all is said and done.
Hate to do too much disassembly when my riveting skills are still an unknown.
Thanks,
Ron

 

[CedarRiverScooter]

Welcome to the site. How about some pictures?

Replacing rivets is really not a big deal, You can do it. Just takes a cheap tool.

The plywood can be several layers, some guys will epoxy/ fiberglass between them, others don't bother.

An important step is to seal up the edges of the plywood.

Any new wood will be better than rotted stuff!

 

[Ronbedard57]

Hello,
I did some additional investigating, and it seems that the plywood must have frozen and expanded while saturated. The heads of all the rivets (8) that fastened the knee to the transom, and several other rivets in the area had popped off. There's no evidence of chisel marks that would make me think this was done on purpose. The knee was actually no longer fastened through to the exterior. Someone had fastened a piece of plywood to the outside of the transom with some hex head galvy screws. I found the plywood piece and a baggy of the screws in the boat.
The plywood transom was pretty mushy. So.. After playing around with a cardboard template, it seems pretty obvious that the original 1" thick plywood transom piece was in place pretty early in the assembly of the boat. It took two hours to drill and drive out all of the rivets holding the plywood to the transom and remove it. This includes the 8 rivets holding the carry-handles. There are four angle pieces that fasten through the transom and through the sides of the hull. I only removed the rivets that passed through the transom, since, even with these angle pieces removed, a single-piece 1" replacement can't be forced in. The knee (24 rivets through the keel), and the tumble-home shape of the hull prevent this.
My plan is to build up a new transom in place. I'll use four pieces of 1/2" plywood, and stagger the joints as far as possible from center to L and R.
I'll likely spread good silicone between the aluminum and the first layer, and use a marine grade adhesive between layers 1 and 2. I'll treat the edges with something before clamping, and then paint the whole thing when finished.
I'm actually a wood boat guy, so I really haven't got much (any) experience with solid rivets. I've sent for an air hammer and head, and the nice folks at Jay Cee are sending a bag of rivets. I'll need an assortment of sizes, so I bought them at 2" and will cut them to the lengths needed as I go.
Believe it or not, my wife has helped clench tacks during restorations of wood and canvas canoes, and on a 1949 W/C PennYan I've restored. I'll get another pair of earmuffs, and see how she does as "Rosie the riveter".
I'll attach some photos, and I hope they're self explanatory.
Any advice or critiques of the process are welcome.
Ron

 

[DaleH]

Watch the silicone use, as some silicone curing agents attack tin. All tin should be prepped and primed before sealing in any wood. A good wash/copper scrubbie clean with white vinegar, well rinsed, would suffice.

Honestly, if mine, a 1/2-gallon epoxy kit from www.raka.com and 2 pieces of ~5/8" plywood - using the techniques shown here: https://forum.tinboats.net/viewtopic.php?f=3&t=47405&p=474460 and you'd be done with it for $100 or less, although SS bolts/hardware would add to the overall co$t, yet eliminate any re-riveting.

 

[Ronbedard57]

Wow! That's some attention to detail on that StarCraft 15 transom. You dismantled the hull to quite an extent! I don't know whether I'll be setting epoxy plugs for the through-fasteners. I plan to use solid rivets (as original), and will depend on them to be water tight. The epoxy for laminating adhesive is probably how I'll go. It's a pretty small job, so the expense is manageable.
Thanks for the caveat re. the silicone/tin compatibility. What do you think of tile mastic in this application? I'll be sealing the plywood with the epoxy, but want to get something between the wood and tin.
Thanks,
Ron

 

[CedarRiverScooter]

Having just repaired a shower tile wall, I can tell you that tile mastic will absorb moisture over time. My preference to set the plywood would be to prime/paint the aluminium & use 3M5200. Others have their favorite stuff too.

 

[DaleH]

Goops like 3M 5200 can corrode/attack UNprimed tin, so just prep/prime it ahead of time. I've never put any goop between the tin and epoxied-wood, as the SS thru-bolts I use snug it up tight. But yes of course, I do seal it well up at at the transom cap, using BoatLife 'Life Caulk'.

 

[Ronbedard57]

Hi,
I guess I'll prep and prime/paint, and leave it up to all those rivets to snug it tight. About to start working on a mock-up so I can figure out getting a new piece in place in as few pieces as possible. I'm guessing four.
Thanks,
Ron

 

[DaleH]

Even a tube of construction/concrete adhesive would seal the tin-to-wood juncture at the top, whatever's handy; even epoxy mix. No need to over-think, just add something, but only to prepped/prime tin. The done deal will last a lifetime!

 

[Ronbedard57]

Just finished mocking up the four pieces I'll need to get this done. $83/sheet for the marine grade plywood!
Thanks for the help, I'll report in once this job is done. Going into storage soon so I'll be working on upholstery and other details after this.
Steering
Wiring harness
Lights
floorboards
horn
polish the windshield
Etc.

Ron

 

[Ronbedard57]

Hi,
Got the stuff for doing the riveting. (cheapy air hammer, rivet head for it, and some rivets and roves.) Got the rivets all 2" and will cut to fit. Tried it out on scrap, and am thrilled with the results.
Before I install any flotation, (looking into 2-part C.C. foam) I'll float the boat to check for any leaky rivets and tighten them. Don't want to find them only after insulation and hull paint.
Take care,
Ron