Bilge pump pad wet

[Rustygaff]

Greetings,

Yesterday I began to install a new thru-hull transducer Garmin GT51-TH). My plan was to keel mount the TD. The location I chose was the flat area where the bilge pump & switch were located. My plan was to move the switch a few inches to make room for the thru-hull wire stem and studs. I unscrewed the switch from the pad and also temporarily removed the pump and base.

I then drilled out my thru-hull stem/bolt holes and discovered the glassed in plywood bilge pump mounting pad was a bit wet. GW did a crappy job sealing the screw holes when they installed this equipment. I realize that the pad is not structural but my concern is securing the transducer nut(s) & washers to a piece of wood that could fail in the future.

What are my options? Create a backing plate to go on the topside of the pad and secure the transducer to that? Remove the plywood pad and replace with starboard? If so, how difficult is the pad to remove with an oscillating muli-tool? Or, simply fill the screw holes around the stem/studs with 4200 or Life Caulk and install oversize washers over the pad?

 

[Rustygaff]

I ended cutting out the pad with the multi-tool. The plywood was completely saturated and will be replaced with starboard embedded in epoxy.

 

[DennisG01]

I wouldn't embed the SB in epoxy. Epoxy (actually, pretty much everything) doesn't make a great bond with HDPE. There's a chance that, over time, the HDPE will pop off the epoxy down the road. Granted, you'd still have the mechanical connections, but still. Personally, I'd use marine ply that's been pre-coated with epoxy a few times and then secured with thickened epoxy to the hull. Then drill oversize holes and fill with epoxy. Once that cures, come back and drill your correct-sized holes. That will be a 100% permanent, rot-free installation.

But, if I was to use HDPE, I'd use something like LifeCaulk between the hull bottom and HDPE. I'd weight it down slightly (after aggressively roughing up the surface of the HDPE), but not so much to squeeze out all the LifeCaulk. The idea would be to create a rubbery layer between the hull and HDPE. Then, I'd roughen up the top surface, making sure to round all your top edges/corners well (and possibly fair the edge) and put a layer of 1708 over it to keep it in place.

 

[SkunkBoat]

"then drill oversize holes and fill with epoxy." I'm sure he meant not thru the hull, just thru the wood to the hull.

You already drilled the hull so you just need to put bigger holes in the plywood

 

[Rustygaff]

I wouldn't embed the SB in epoxy. Epoxy (actually, pretty much everything) doesn't make a great bond with HDPE. There's a chance that, over time, the HDPE will pop off the epoxy down the road. Granted, you'd still have the mechanical connections, but still. Personally, I'd use marine ply that's been pre-coated with epoxy a few times and then secured with thickened epoxy to the hull. Then drill oversize holes and fill with epoxy. Once that cures, come back and drill your correct-sized holes. That will be a 100% permanent, rot-free installation.

But, if I was to use HDPE, I'd use something like LifeCaulk between the hull bottom and HDPE. I'd weight it down slightly (after aggressively roughing up the surface of the HDPE), but not so much to squeeze out all the LifeCaulk. The idea would be to create a rubbery layer between the hull and HDPE. Then, I'd roughen up the top surface, making sure to round all your top edges/corners well (and possibly fair the edge) and put a layer of 1708 over it to keep it in place.

Thanks for the help on this. If I use HDPE bedded in Life Caulk, would it create a more mechanical bond if I drilled out some small holes that the caulk would get pressed into? I have never worked with glass so wetting out and installing 1708 on top would be a new experience for me.

Also, the 2 transducer studs are (if my memory is good) 5/16 diameter. I was a bit off when originally drilling them out with a 3/8 bit so ended up enlarging them to 1/2 so the TD would not bind when pushing up against the hull. How best to seal the gap between the stud and the hole itself? Life Caulk?

At the rate I am going here, the boat may not see the water until June. After the TD and new Garmin install, I will be diving into the new windlass project. :-|

 

[DennisG01]

"then drill oversize holes and fill with epoxy." I'm sure he meant not thru the hull, just thru the wood to the hull.

Actually, I did mean to oversize the hull holes, as well. The reason being is this allows the inside, cut edge, of the glass and gel to be encapsulated with epoxy. In essence, what you end up with, is a plastic tube from the outside of the boat to the inside of the boat. IF water, should ever get past the sealant used for the transducer on the outside of the hull or the mounting bolts, water would NEVER touch the bare fiberglass or the gelcoat. Although Grady's aren't particularly known for blisters (water getting between the gel and the glass), and doing this isn't completely necessary, it is best practice.

One thing I didn't mention, but honestly assumed it was a given, is to countersink the hole on the outside of the hull. This, again, is a best practice thing. It helps to prevent spider cracking of the gel and also allows for a larger area for sealant to be placed.

 

[DennisG01]

Thanks for the help on this. If I use HDPE bedded in Life Caulk, would it create a more mechanical bond if I drilled out some small holes that the caulk would get pressed into? I have never worked with glass so wetting out and installing 1708 on top would be a new experience for me.

Also, the 2 transducer studs are (if my memory is good) 5/16 diameter. I was a bit off when originally drilling them out with a 3/8 bit so ended up enlarging them to 1/2 so the TD would not bind when pushing up against the hull. How best to seal the gap between the stud and the hole itself? Life Caulk?

At the rate I am going here, the boat may not see the water until June. After the TD and new Garmin install, I will be diving into the new windlass project. :-|

Yes, drilling the holes for the caulk is a good idea. If you want, slightly countersink the top of the hole to create a half-hour glass look. That will further help to lock it in place by creating a "key", of sorts.

West Systems (not West Marine... although it may be available there) used to sell small packets of epoxy and resin. These would be ideal for those larger screw holes and give you an easy introduction to working with epoxy.... countersink the hole on the outside of the hull... place a piece of tape over the hole... fill with epoxy from the inside. When it cures, redrill the proper hole with a countersink and finish off with LifeCaulk.

But, yes, another way to do it would be to simply use LifeCaulk to fill the void.

 

[Rustygaff]

I dug out all of the wet wood and now I am down to the glass hull material. It looks to be about 3/4" thick in that particular spot. I will put some Six10 into the holes and re-drill. As far as a backing goes, still not sure what I am going to do. I probably could get away with simply installing the transducer without backing but still need to figure something out for the pump and switch and cleaning up the rough edges.

 

[blindmullet]

When I did my Mako I made a little mold and layered glass. Bonded it to the hull with an epoxy mix and a final piece over the block. Working down below on a boat that you can't really get down into sucks. I'll do this once and move on. The easier way would be ply glued/glassed to the hull and over size drill the holes filling with epoxy.

 

[ROBERTH]

I cut out my pads also. Black and nasty smell. Cleaned up good and cut a piece of PVC board instead of wood or Starboard and it came out great. I glassed over it with Epoxy and the PVC board holds screws well and epoxy bonds to it very well also. So far, I think it has been the best material to use and is cheap. Can pick it up at the local Lowes/Home Depot.