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Helm Seat pedestal base installation.

On my Bertram 20, I am ready to install the helm and companion seats. The pedestal bases would typically be through bolted to a backing plate under the sole.

With the closed cell foam and the fact that the seat bases were an original and notorious source of water intrusion I do not want to repeat.

THe pedestals have a 9" Diameter. I was thinking of making a 15" diameter "pad" to mount them on.

Would it be sufficient to make a pad with 3/4" coosa or even just ply have these tee nuts secured with the proper hole pattern into the bottom of the pad, then plexus the whole thing to the sole.



Thanks in advance.

Ian.

Ian - I love that Seashell Green!

Personally, I would not use a blind tapped hole to mount the pedestals, which is essentailly what you have sketched. Difficult to repair and not a secure mounting. You'll have a high of bending moment on the base with a weak attachement to the deck. I think you will pull out the T-nuts in short order.

I would use thru-bolts with an aluminum backer plate sealed/bonded to the underside of the coosa deck. Seal the bolt holes, torque them down and forget about it for the next 30 years.

Cam

I just hate to drill a hole in that perfectly sealed compartment.

So you think the leverage on the pedestal would eventually delaminate the fiberglass on the coosa sole?

Anyone else care to weigh in?

Ian.

I agree. Too much leverage to be fooling around with......especially when you've got some beer drinker sitting in the other seat with his feet on the dashboard and you're doing 40 over the whoops. Drill through and back with 3/8" aluminum plate (which is probably overkill but why cheap out over the last $20). Slather the holes with 4200 and make a 4200 'gasket' under the pedestal base. It shouldn't leak during your lifetime.

Ian,

I agree with Cam on this... The amount of torque and torture that pedistal base to deck mount will get is tremendous and seriously needs a heavy backing plate.

Here's how I've done it using a blind and perfectly hidden backing plate below the deck:

First pencil mark your position for the pedistal base. Mark 1/2" inside of the pedistal base mark. Cut out along the inside mark.

Get a plate of 3/8" aluminum cut into a circle 20% larger than the pedistal base. Cut the aluminum circle into three pieces. Dig out just enough deck foam and coring to slide each section of the aluminum into place through the hole and under the deck.

Clean up the area, mix a large amount of thickened epoxy and pack it into the hole. Slide in and position the aluminum pieces. Adjust as necessary, carefully clean the excess epoxy off of the top of the aluminum and allow the epoxy to cure.

Now, epoxy the deck cutout back into the hole and on top of the aluminum. Smooth it down, wipe up the excess epoxy and allow it to cure.

Position the pedistal, mark and drill undersized holes to match the pedistal bolts. Tap the holes to the appropriate size. Apply TefGel to the bolts and bolt the pedistal down.

OK... I am Convinced.

Captain Patrick's method it is.

Just a clarification question though.

"Mix a large batch of epoxy and..." I assume the intent is to have the aluminum plate snug against the sole or is that not overly important? Also should there be enough epoxy that the foam will effectively be sealed from any potential water?

As always, thank you.

Ian.

Ian,

Enough epoxy to fill back up everything that the aluminum doesn't... It'd be a great time to use vermiculite as a real bulk filler. And, yes, try to have the plate as flush to the underside of the deck as possible.

Got it. Just have to think a bit more on this. Seems that the stringer, which the sole rests on is under the inboard 1/3 of where the pedestal will sit.

For those that are not aware, I used Prisma stringers which are 3" wide foam filled. Not sure I will be able to (or want to) undercut that.

Should have, could have planned better.

Ian.

Ian, I don't have any pictures of it and have not made it to the boat this week, but I built up my mounting pad above the sole and embedded stainless bolts and secured my seat bases to that. Perhaps you could do that and have a larger stainless apron or bell housing fabricated to finish it nicely. Having said that, they are not pedestals and the raised section does not effect drainage or aesthetics and does not present a toe stubbing hazard. After the wet foam removal all of us 20 owners have had to do, I completely understand your reluctance to make a hole in the deck skin.