downrigger mount reinforcement - transdeck or plywood?

[MiddlepointBight]

Hi all,

I'm re-mounting some hp scotty riggers (bailing on the 90 degree gunnel mounts that came with boat), and have two materials to chose from to reinforce the bolts/mount on underside of gunnel (standard 4 bolt mount).

I have an offcut of 3/4" ply, and in addition, an offcut of 1-1/4" transdeck. Trying to decide what to use, and don't have a ton of experience with transdeck, but it looks pretty bombproof!

thanks for any insights

 

[Foxsea]

Your choice. You are looking for compressive strength and there is plenty. When you mount either one, bed it in PL Premium to provide good contact with the fiberglass, then use flat washers on fender washers to back up the lock nuts.

 

[MiddlepointBight]

Your choice. You are looking for compressive strength and there is plenty. When you mount either one, bed it in PL Premium to provide good contact with the fiberglass, then use flat washers on fender washers to back up the lock nuts.

Thanks for that, good idea with adding a fender washer undernear the flat washer.

Haven't heard of using adhesive also - are you talking in between the reinforcing panel and fiberglass?

 

[gungadin]

Don't know about transdeck, but plywood. Sand the sharp edges, apply West System epoxy or other liquid epoxy that will soak in to all sides to seal the plywood. You could use thickened epoxy to secure it or the PL will work as well.

 

[Foxsea]

Thanks for that, good idea with adding a fender washer undernear the flat washer.

Haven't heard of using adhesive also - are you talking in between the reinforcing panel and fiberglass?

View attachment 60633

Yes, it will provide intimate contact with the potentially rough fiberglass underside. The PL Premium is a polyurethane adhesive and it sets up rock solid. The transdeck is a premium plywood used as transport trailer decking and as form ply. If you have it, use it. As another member said it may be a good idea to seal the edges. Put the finished face down. This will provide a bomb-proof attachment, especially nice under a trap puller.

 

[MiddlepointBight]

Yes, it will provide intimate contact with the potentially rough fiberglass underside. The PL Premium is a polyurethane adhesive and it sets up rock solid. The transdeck is a premium plywood used as transport trailer decking and as form ply. If you have it, use it. As another member said it may be a good idea to seal the edges. Put the finished face down. This will provide a bomb-proof attachment, especially nice under a trap puller.

nice one.. figure I might as well go with the transdeck - looks incredibly solid. good call with sealing the edges, even a couple coats of spray paint should do the trick. mounts will be for rigs and trap puller, so the stronger the better!

my one concern with using PL is that it's a rigid adhesive.. i'm considering picking up some sikaflex - might have a little more give?

from hazy memory, all the scotty bolts should be 1/4", correct? (same as the i-lock nut and fender washers...)

 

[MiddlepointBight]

Don't know about transdeck, but plywood. Sand the sharp edges, apply West System epoxy or other liquid epoxy that will soak in to all sides to seal the plywood. You could use thickened epoxy to secure it or the PL will work as well.

why do you sand the sharp edges?

 

[pescador]

I’ve got 3/4 ply as my reinforcing panel with large fender washers used on the bolts under the gunnel.Torque that down. It’ll never break. Ive never used adhesive. I don’t see the need. I’ve had the current boat 9 years and never had an issue..... even hanging up on reefs with a few cannon balls. The line will break first.

 

[Foxsea]

nice one.. figure I might as well go with the transdeck - looks incredibly solid. good call with sealing the edges, even a couple coats of spray paint should do the trick. mounts will be for rigs and trap puller, so the stronger the better!

my one concern with using PL is that it's a rigid adhesive.. i'm considering picking up some sikaflex - might have a little more give?

from hazy memory, all the scotty bolts should be 1/4", correct? (same as the i-lock nut and fender washers...)

You do not want flexible. You want a solid mount. Make sure your bolts are long enough. Yes, 1/4" stainless bolts have the same tensile strength as grade 5 mild steel - about 2000 pounds yield strength. The inside bolts have the most strain in use. As for the adhesive, it's more of a bedding function so things stay tight over time. But laminating is always superior to layering. Just my thoughts. YMMV.

 

[gungadin]

why do you sand the sharp edges?

Just to smoth out tearouts and splinters, appearance mostly

 

[Rayvon]

I've always used 1/4 "x1"x7" aluminum or 1/8"x1"x7" stainless strips ,when I have access to scrap metal.

 

[sly_karma]

I’ve got 3/4 ply as my reinforcing panel with large fender washers used on the bolts under the gunnel.Torque that down. It’ll never break. Ive never used adhesive. I don’t see the need. I’ve had the current boat 9 years and never had an issue..... even hanging up on reefs with a few cannon balls. The line will break first.

The plywood and washers protect against bolt pullout, but those aren't the only forces at play.There will be minute movement in the fibreglass as the downrigger or trap puller base flexes it relative to the plywood. Depending on the shape and uniformity of the underside of the gunwale, there could be sufficient movement over time to propagate small cracks radiating out from the boot holes. Bond the two together and you have a much stiffer assembly unlikely to flex at all.

 

[searun]

Only concern with wood backing is it will eventually rot. Aluminum plate is cheap alternative, and 1/4 inch plate won't flex.

 

[walleyes]

1/2” HDPE and done for life the boat will rot and fall apart before that material will. Don't be in a rush to do things, take the time and a little extra couple dollars and do it right. In the long run it will save you time and money and equipment.

 

[Foxsea]

Only concern with wood backing is it will eventually rot. Aluminum plate is cheap alternative, and 1/4 inch plate won't flex.

Wood only rots because moisture content is above 19% and it stays there - a condition for fungus growth and rot. Underside the gunnels never gets wet unless you have big problems. Aluminum plate also works very well.