swim platform installation

[Bertramp]

I'm installing a swim platform. I need to use something as a backing plate on the inside of the transom. What have folks used and how large ? My thoughs were 4"-5" stainless squares for each bolt. Someone else has suggested using
3/4" starboard ..... any thoughts or recommendations ? The platform has 4 brackets and each has 2 bolts.
thanks

[SKYCHENEY]

My backing plates are OEM and are glassed in to the transom. They are threaded which is nice since you don't have to get access to them to install or remove the bolts. I think I would go with the stainless plates. I would weld the nuts to the plates and then 5200 them to the inside of the hull. That would essentially be an OEM install.

[OldHatt45]

When I had my Swim Platform put on, the Guy that made the brackets, etc. made up 5 stainless plates, one for each exterior bracket. Drilled the holes for the brackets, used a center punch from the outside to mark the plates.
Drilled the plates, checked for fit/alignment, then welded on stainless nuts on the inside. Told me I could glass over the plates if I wanted. But did caution me that the plates should be attached to the bonding system. He even drilled and tapped a hole in each plate for a number 12 screw for the bonding wire. Haven't gotten around to glassing the plates in though....

OldHatt45

[solanderi]

I was told by Sam's that my Hat has built in reinforcement in the transom for a dive platform. I'm not sure exactly how to find it or of your boat has it too.

The previous owner on my 1985 45 had flimsy one piece stanchions on an aftermarket platform. The platform was lagged into the transom. Needless to say, it was a substandard setup. One little sailfish in reverse against 2 foot seas was all that was needed to end that arrangement. The fix was heavy duty Hatteras style stainless steel bracket replacements with the help of Sam's, including 5 inch stainless backing plates (unbonded) and some starboard to adjust for the curvature of the transom. Nine months and many fish later, it's still there.

If I break this one off I might go for an oem platform....costly...if that becomes artificial reef, the answer is those little swim step gizmos which actually are not that bad of an idea if you have a transom door.

[Genesis]

My backing plates and platform brackets were NOT bonded, and as evidence that its not necessary I cite the 20 years of service with nary a sign of corrosion anywhere on the hardware.

The key is that no part of it can touch ANY OTHER METAL ON THE BOAT.

Its all stainless, no connection to any other metal, no problem. No different metals in contact, no galvanic corrosion.

[SKYCHENEY]

Mine were not bonded either. But, get this, they were bronze brackets with stainless bolts and I have no idea what they thread into as that is all fiberglassed in. I assume that the plates are stainless too since the bolts came out without much effort. Luckily my boat is a fresh water boat, so no corrosion in 20 years either. My new brackets, however, will be SS.

[Traveler 45C]

Genesis, were your backing plates glassed in?

[Genesis]

Nope - not on my boat....