Securing seat post base to plywood/fiberglass deck

[Dtruedog]

I need to restore my captain's chair seatpost base to the fiberglass deck of my boat. A previous owner had mounted the round base to a slightly larger 3/4" thick piece of plywood and then secured that to the deck with ss sheet metal screws and what appears to be epoxy. It rotted and basically failed. After removing the leftover residue via cutting/grinding, the fiberglass deck seems to be pretty sound in the immediate area under which the plywood had been bonded although there a numerous screw holes left behind.

I am looking for advice on two different repair options I am considering for securing the seat post mount to the deck. I plan to use a rectangular 3/4" piece of fiberglass wrapped plywood, about 4" larger than the round post base on each dimension and edge beveled to blend better with the deck under carpeting, that will have ss t-nuts installed on the underside and glassed in place to match the post base mounting hole pattern.
Once plywood is wrapped and cured, the post base can then be secured using the t-nuts with six 1/4" oval head ss machine screws .

Options I am considering for securing the plywood base plate to the deck are:
1. Epoxy it to the fiberglass decking and reinforce top and around the perimeter with two or three layers of cut glass/epoxy, or
2. Use 3M 5200 adhesive between the decking and the fiberglass wrapped plywood base.

Which do you believe would provide greatest rigidity and strength? Any other suggestions I might consider in lieu of my two ideas?

I want to fix it right and not have to go back to redo it for many years to come.

Thank you for your feedback!

 

[jigngrub]

Re: Securing seat post base to plywood/fiberglass deck

Option #1 will best your best/strongest build.

 

[Woodonglass]

Re: Securing seat post base to plywood/fiberglass deck

#1 but something like this...

 

[Dtruedog]

Re: Securing seat post base to plywood/fiberglass deck

Looks great. Just what I have in mind, Thanks.

 

[Georgesalmon]

Re: Securing seat post base to plywood/fiberglass deck

When your glassing around those T nuts coat them with a lot of vasilene to protect from resin getting in the threads. Just sayin'

 

[tazrig]

Re: Securing seat post base to plywood/fiberglass deck

If you really wanted to strengthen it further you could cut a small hole in the floor, Just big enough to get your hand through. Take 6 pieces of 2 inch by 4 inch stainless plate with a hole drilled through the center of each. Use "T" bolts to "through bolt" mount your chair to the floor with the stainless plates obviously being on the underside of the floor. You can lag it down good and tight. Seal under the pedestal base with 5200 to lock out any moisture. The pyramids will fall before that chair will. Your option #1 will work well too If you don't want to go through the extra work. On my boat I had everything from cleats to grab handles to seats (basically anything that was attached to the boat through bolted) so I never had to worry about stuff pulling out. Just presenting another option for you. Either way good luck with you installation.

 

[JASinIL2006]

Re: Securing seat post base to plywood/fiberglass deck

When your glassing around those T nuts coat them with a lot of vasilene to protect from resin getting in the threads. Just sayin'

This is a very good idea. I did NOT do that, and I had a couple of T-nuts that got a bit of resin in them. Not much, but enough that I had to basically tap threads thru the dried resin. Not fun and could easily have been avoided.

Aside from that, I mounted my bases by using thickened fiberglass resin as an adhesive and then covering everything with 2-3 layers of 1708. They are quite sturdy and the T-nuts really let you crank down on the pedestal bases for very solid attachment.

Good luck!

Jim