J/30 Class Association

Transom Thickness - ?

Posted By: AndyR

Transom Thickness - ? - 05/22/19 04:49 AM

Anyone know the thickness of the J/30 transom?

Am installing a fold-down swim ladder, am sizing the bolts that will attach. It's a four solid post folding ladder with a bottom hinge, built solidly and folding well into the water to accommodate my special needs fellow that can't work with a less rigid installation.

Bolts holding the ladder have to go through the skin, core, skin, backing plate, and have enough threads for a nut, but I'd rather not too much stick into the lazarette. I'm missing the thickness of the transom and not near the boat at the moment so I am hoping someone knows.

Also, am sharing my build plan in case there's any holes in said plan, things I should consider or do better. Please post concerns if you have any, I'm all ears.

Plan is to determine ladder's final location and clamp it to the outside of the transom. Some adjustment will be needed moving it around to make the location outboard enough to not interfere with the rudder going hard over, and miss everything that needs missed on the transom inside and out.

Then transfer drill one of the three holes in each post to locate everything precisely enough on the inside and provisionally attach it to the boat to be worked.

Going inside, I'll mix up some west system epoxy to a peanut butter, one by one attach the backing plates with (no holes yet) to the inside wall of the transom over the bolt pattern-to-be.

Then I'll transfer drill everything else out from the outside in, locating the holes. Removing everything for the moment, I'll remove just a little core from each hole and inject some more epoxy to seal those holes from the core.

Once the epoxy cures and I've redrilled those holes out, I'll bolt it up with 316 stainless hardware, making sure I isolate the aluminum backing plates.

It's a plan at the moment - any holes, better ways at this? Thanks to all.

Andy Radcliffe
Lady J #365


Posted By: Russ Atkinson

Re: Transom Thickness - ? - 05/23/19 06:58 PM

Nobody can ever accuse you of not designing and planning your project. That said, and not trying to skip steps here but why not do all your precision layout, drill your transom holes, determine their depth and then buy the screws?
Posted By: Rhapsody #348

Re: Transom Thickness - ? - 05/24/19 12:28 PM

Having done this on Rhapsody, I agree with Russ.

The Balsa core is 3/4" thick. The inner and outer skin is approx 3/8" combined, with an irregular surface on the inside. Use a non water absorbing material for backing plates and you'll never have an issue. Since you selected aluminum and have stainless hardware, put tefgel on the interface so you don't create a battery that corrodes. Better yet - make the backing plates from G10 and that issue disappears!
Posted By: AndyR

Re: Transom Thickness - ? - 05/24/19 04:26 PM

Thanks for the info - much appreciated!

As far as the iterative process vs. buying ahead of time, I'm just trying to get everything together to knock it out in one shot - I work an hour away from the boat and the fastener specialty store we have in town isn't open on the weekends - so I like to show up fully equipped for the full project if at all possible.

From Bill's comments it seems my guess (had to purchase the hardware a day or so ago) should work out fine, maybe a touch long but the solid part of the screw should be short enough. If it interferes with anything on the inside I can swap in a couple slightly shorter 316 fasteners and finish it next trip - I'll be isolating core through the mount holes ( instead of using 5200 lol) so I'll have that option.

Thanks again!
Posted By: Chris623

Re: Transom Thickness - ? - 05/25/19 03:09 PM

... and of course, be ready for surprises! Bill's comment about the thickness being irregular is both true as well as tricky to deal with. Though the bulk of the transom on my boat has a 3/4" core, there are triangle doublers in the upper corners to support the backstay chainplates as well as a vertical one along the center for the rudder. There are also some thinner spots, notably where the fuel tank vent is. These areas taper to the new thickness at about 45 degrees, and where my ladder is mounted, hit both the vent and the triangular doubler areas. The original installation had fasteners in these 45 degree areas that were weak enough to allow the mounting weldments to move just enough to cause premature caulking failure. My solution was to use thickened epoxy to add G10 / FR4 tube with a slant cut on one end to bring the surface that mates with the washer up to level.

Good luck!

-Chris
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