1983 Montauk 17 Re-fastening RPS to Deck

[Crusty the Clam]

The reversible pilot seat (RPS) fasteners on my recently purchased 1983 Montauk 17 had loosened over time and the plywood substrate rotted. A 4-foot by 4-foot area of the deck was replaced where the RPS sits. Now I need to re-fasten the RPS to the deck.

On my boat, the RPS is fastened to the deck with two screws at each end on each side of the base. That’s it. When sitting and leaning back on the RPS, this puts upward leverage on the screws. The screws are only bedded into the half inch plywood substrate. Eventually they will loosen.

This forum has info on creating a void in the foam and filling it with epoxy below the fastener hole so as to provide a thicker substrate and to distribute upward force on the screw over a larger area of the plywood floor. Basically creating an epoxy “backer” for the screw on the underside of the deck. Very good idea. I think of it as the Hockey Puck Backer.

After further thought, I consulted my West Systems Wooden Boat Restoration and Repair manual. It cost a few bucks years back, but the info may be free now. In Chapter 6, West describes installing hardware to wood by using epoxy. I recommend reading it for its information. It describes over drilling a fastener hole for most of the depth of the fastener and finishing the hole with a narrower hole appropriate to the fastener so it has something to grab. The purpose of the wider portion is to have the epoxy bond to a larger area of wood. Because epoxy is stronger than wood, this large “plug” of epoxy holding the fastener effectively spreads upward shear forces over a larger surface area of the wood. It’s a stronger connection than just screwing into the deck and plywood.

The second method is even stronger. West instructs to also bond the base of the hardware by coating it with epoxy so that upward forces on the hardware (tensile) and shear forces are distributed over a larger area--the epoxy glued contact area of the hardware--rather than the forces acting only on the relatively small contact area of the screw fastener.

I plan to use the Hockey Puck Backer combined with 7/8-inch mahogany bases that have a larger contact area with the deck than the footprint of the RPS. The RPS will be screwed only to the base. The bases will be attached to the deck, raise the RPS up a bit, and lengthen the lever force thus reducing the force on the screws. In addition, I will epoxy the fore and aft ends of the mahogany base to the deck surface. This will further increase the strength of the attachment and form an additional barrier to water reaching the plywood.

I’ll report back on how the install goes, but welcome any thoughts.

Crusty T. Clam

[Tomtep]

I would use caution when creating these epoxy "pucks". Epoxy generates heat as part of the curing process. The larger the amount of epoxy, the more heat generated. In your application, there is no place for this heat to dissipate, there is a possibility that this heat could cause problems with the surrounding foam, in an extreme case if enough heat is generated there is a possibility of the foam igniting.

[Phil T]

Typically, a failure of the fastening of the RPS or the console to the deck of a 16'7 or 17' hull is due to either a) the plywood backing material rotting as a result of moisture due to the lack of, or failure of, the marine sealant or 2) shear forces that exceed the rating of the fastener and substrate.

In my case, the fasteners attaching the RPS on my 1987 Montauk failed due to excessive sheer. I fell against it hard as a result of loosing my balance while transiting in breaking waves on top of swells under small craft advisory conditions. I also had bow locker hinge screws fail.

Given the construction of the hull, the hockey puck method you describe will not be effective given the backing material. Using the hockey puck method is recommended in locations were there is no backing material.

I would use the factory method of using stainless screws into the backing material. I would insert marine sealant into the hole as well as in the fastener hole of the RPS and under the screw.

[NLA01]

When you replaced the 4 by 4 foot section did you put in marine grade wood or foam?

If wood then screw it down like factory and use 5200 on the bases. The WEST System method is used when there is no wood backing.

I would not epoxy the wood to the deck either' use 3M5200. They make a chemical that dissolves 5200 for removal. You will have to destroy the wood and floor to get the epoxy up.

Not sure why you are reinventing the installation a RPS.

Archie

[Crusty the Clam]

Thanks for he replies and thoughts. A couple answers to your comments.

1. The puck method is described here and is used where there is a backer. The problem with the plywood backer is that it is thin--only 1/2-inch and plywood has poor holding strength compared to wood and much poorer compared to epoxy with 404 filler.

http://continuouswave.com/forum/viewtopic.php?f=6&t=3224

2. Heat is a concern. I need to be careful. That is avoided by using small amounts at a time, adding as layers finish their reaction and cool, using 404 filler material and using a slow hardener. Good point and thanks for the reminder about the foam.

3. Expanding the hole in the plywood and filling it with epoxy is far stronger than the plywood and the plywood to epoxy contact area is greater. West’s manual speaks directly to that technique.

4. The forces on the seat base can be quite large if two people are sitting back. Further with use over time, the plywood is going to loose its grip starting the path for water to intrude and cause rot, further exacerbating the fastener loosening.

5. Whaler did not use marine plywood as far as I could tell. The replacement of the four by four section was done with regular plywood and using the original cut out of the deck over top. Two part expanding foam was added beneath to fill some voids that were created on cutting out the deck and ensuring support for the wood.

6. The idea of using 5200 is a good one for glueing the wood base to the deck. I’m more familiar with epoxy so that’s why my original thought was thickened structural epoxy. My goal is to avoid ever having this recur. The RPS could be removed by unscrewing it from the mahogany boards, but it’s true the boards wouldn’t be removable without destroying then if they are glued to the deck with epoxy. Then again, they cost me $20 and 30 minutes time to make.

Thanks again. I’ll think through this and the feedback more.

Also, "hockey puck" was probably a bad term. I’m aiming more for an Oreo cookie size. Which is making me hungry.

[MarkCz]

It's too late now but you could have used T nuts made from stainless on the plywood section you made before you put it back in.

[Crusty the Clam]

It's too late now but you could have used T nuts made from stainless on the plywood section you made before you put it back in.

In hindsight that is so obvious and elegant and simple, it is brilliant. Hopefully it helps the next person avoid a “palm to forehead” slap moment.

All these ideas and observations have been helpful and thought provoking. Thanks for taking the time to offer them up.

Crusty T Clam (real name Rod btw)

[NLA01]

Your plan makes more since now.

Are you planning to put the puck under the 1/2 wood?

If you did that, it work work very well and would be very strong.

Also attaching the wood to the deck and then the RPS to the wood is how I did that on my last boat. I made a riser with 2-inch Teak. I glued and screwed the teak to the deck using 3M5200 and then screws on the RPS to the teak. This makes a clean install and the teak riser were not much bigger than the feet of the RPS.

I have never made pucks before like you describe. I would like to see your progress if you don't mind posting some pictures of the install.

Archie

[Acseatsri]

I used 2 layers of 2" polyethylene to raise the rps on a 1982 Montauk. By layering it, I was able to double up on the screws holding the seat to the deck. Pretty sure your seat is only 15" high for that year as well, but they also made 18" high legs as well. It's a lot more comfortable not chewing on your knees when driving. I raised it 6" at the owners' request, but 4" would have been ideal for most people.

[Crusty the Clam]

Thanks all. Im revising my thoughts thanks to the feedback. 5200 for the riser to deck. Instead of creating a void in the foam immediately under the plywood, I’m going to go with a 1” forstener through the plywood and fill it with 404 thickened epoxy (peanut butter consistency). Maybe a small void in the foam so the epoxy forms an upside down mushroom but am thinking that won’t really add much. I think the larger hole will add sufficient strength along with the 5200.

That helps solve excess heat problems and I won’t be having to mix multiple batches.

Also I’m really digging the taller riser ideas. It would allow for making a sub-seat space for tackle, maps, pfd’s...

I will take some photos and see if I can figure out how to post them.

Great forum. Thanks again and also to Jim for hosting and monitoring it.

[Phil T]

I think you may be going a bit too heavy handed.

If the backing material is new and adhered to to the deck skin, no special measures are necessary.

On my Montauk I built 6" risers based on the design by Finnegan, aka, LHG using composite lumber. I screwed the first blocks into the floor using the existing holes with fasteners that were 2" longer, the second block and top plank were screwed into the first block. There was no adhesive needed.

The new owner was not very tall and removed the risers returning the RPS to its factory height without any bother.

[NLA01]

I think I am going to agree with Phil here on this one. I really think if you have new laminate on 1/2" wood plus 5200 liberally on the risers, that really would be plenty to hold the seat in place. 5200 is a very strong adhesive.

One thing to think about is that if the punks are made with a mushroom shape. What is to keep them from spinning from the shear forces of screwing the risers down with big screws

Also what about installing stainless toggle wing anchor nuts. They are a one time use in most cases and you would need to make a big hole and dig out some foam under the hole. And then just seal it all up when you put the riser on.
Archie

[Crusty the Clam]

Phil and Archie,

Wow, I just had an epiphany. What if you guys are right? I think that I may finally be old enough to accept that someone else could be right... getting this weird out-of-body floating feeling...

Archie, to your question about the plug spinning, the first step in the bonding is wetting out the sides of the hole with unthickened epoxy to coat and soak into the grain, then the thickened epoxy plug fills the void. Once it cures, there's no way it can spin. The wood fibers will fail long before the epoxy - wood bond does.

Phil, do you recall what diameter/ pitch (roughly) that you selected for the screws? did you go all the way through the underlayment plywood?

Here's a final question: if the laminate deck is well glued to the new plywood, do you ( or I, or the Royal "We") really need screws in the first place? It would be great to avoid creating pathways for water to intrude.

For grins, here's a link to the West System info on bonding hardware. One difference in the Montauk situation is that the plywood is not thick enough to create the two step hole depicted. But in lieu of that, the same effect can be created by letting the thickened epoxy cure with the screws covered in release agent and set in place. The remove the screws and set the RPS or base in place and drive the screws in.

https://www.westsystem.com/instruction-2/epoxy-basics/bonding-fasteners-hardware/

Despite the back and forth on ideas and tips for everyone, hopefully this info is helpful to someone else. My searches found some info, but this discussion has really helped. That said, I won't take up any more bandwidth on the forum with this topic. I'll save my chits for The Great Electrical Re-Wire Debacle that is coming as soon as we get some cool air and the mosquitos die off!

Best regards and thank you again.

Crusty T. Clam (Rod)

[Phil T]

I used the same diameter screw, just added length. #14 (1/4") flat head stainless screws with a fender washer on the top for a clean look.