CONTINUOUSWAVE

Q1: how can screw fasteners that hold the plywood seat base of a Reversible Pilot Seat to the top of the Z-legs be removed when the wood has rotted and the T-nut fasteners in the plywood just spin?



BACKSTORY
The reversible pilot seat on my 1990 Montauk 17 is sagging enough to rub on the fuel tank below the reversible pilot seat on the starboard side. The seam in the seat upholstery has opened to reveal rotting plywood. The upholstery and padding itself are in decent shape for a boat its age, and I would like to simply replace the plywood; however, the screws that attach the seat to the Z-legs are just spinning in place when I try to remove them.

I removed enough staples holding the vinyl upholstery to the plywood to allow me to feel around above the plywood. I think there are T-nuts frozen to the machine screws, and the T-nuts are just spinning in the wood; the wood is too solid to pry off. And, I can't pull back the upholstery enough to get a purchase on the T-nuts with pliers, and the screws appear too beefy to just drill out.

At this point, I am contemplating cutting up the plywood from underneath with an oscillating saw to get enough room to grab the frozen T-nuts.

Q2: what trick I am missing for removing these fasteners?

I went through this similar problem last year. What I ended up doing was adding some upward pressure to the seat base while spinning the screw head with a drill driver. This made the T-nuts spin into the wood and act like a router bit. When enough of the wood was removed by this process, then there was a gap between the Z-leg and seat base into which I could fit an oscillating tool blade to cut through the bolt.

On a few occasions while doing this pull-up-and-spin-the-screw procedure a few of the T-nuts were able to bite into the wood and the screws came out.

Give that a try.

Mark, thanks for the suggestion. Despite considerable upward pressure on the seat, I couldn't get the T-nuts to bite. Under these circumstances, I thought the best way to remove the seat would be to pull the upholstery staples and remove the cushion so that the T-nuts could be grabbed with locking pliers. The problem was that the staples on the ends were covered by the Z-legs. In preparation for cutting the screws, I managed to get enough clearance to pull the staples on one end, allowing the cushion to be pulled over to the other side, exposing all the T-nuts. Here are some photos of the process.





Note that the T-nuts appear to be bronze and were installed using a flaring tool; thus, it became impossible to remove the machine screw once corrosion had set in. I'll probably replace the T-nuts with stainless steel ones that bite into the wood, and use some anti-seizing compound.

M

I used stainless steel T-nuts when rebuilding my reversible pilot seat. Mcmaster Carr carries the good 316 stainless steel hardware.

Also, when you replace the foam use a higher density foam,, which will give enough cushion without squishing down and bottoming out.

Q3: what type of wood was used as the seat base of the Reversible Pilot Seat?

It looks like some sort of mahogany or teak.

Q4: is [the method of attachment of fasteners shown above the way that] Boston Whaler built their RPS?

On the RPS on [my unidentified boat] the Z-legs are attached with wood screws straight into the board.

Q5: were those (threaded T-nut] inserts glued in?

Q6: [did Boston Whaler] just trust that [the threaded T-nuts would be fastened with enough tension that they] wouldn't spin in the wood?

If you are going to stick with [machine screw fasteners] I recommend using a stainless steel T-nut that has three prongs that digs into the wood and are hammered into the pre-drilled hole in the board on the top side of the board.

Q3: what type of wood was used as the seat base of the Reversible Pilot Seat?

It looked like ordinary plywood. I suspect it was discolored due to age and contact with the overlying foam rubber, but I can’t rule out that it was treated with something before installation.

Q4: is [the method of attachment of fasteners shown above the way that] Boston Whaler built their RPS?

It was in 1990 when my boat was built.

On the RPS on [my unidentified boat] the Z-legs are attached with wood screws straight into the board.

Not surprising, as that would have been a much easier way to install the seat. If you purchase an aftermarket replacement seat now, that is how it is installed.

Q5: were those (threaded T-nut] inserts glued in?

They did not appear to be glued. That might have been a good idea, though. And not using dissimilar metals would have been a good idea as well.

Q6: [did Boston Whaler] just trust that [the threaded T-nuts would be fastened with enough tension that they] wouldn't spin in the wood?

Apparently so.

If you are going to stick with [machine screw fasteners] I recommend using a stainless steel T-nut that has three prongs that digs into the wood and are hammered into the pre-drilled hole in the board on the top side of the board.

That is what I did. I also fiberglassed the replacement plywood before I reassembled the seat.

M