swim platform holes

[Jimmy]

I am in the process of building a new swim platform for the 11 meter. There was one on there at one time from PO. The holes in the transom were sealed ok with the bolts and nuts straight through and just caulked with some rubber washers to help seal it. I want to re-use the original holes, however, I am thinking of drilling the holes out slightly to 1/2" for the 3/8" bolts. Once the 1/2" holes are drilled, the plan is to fill the holes with west system to fill the area around the hole. Then push a Tube through the hole to allow the epoxy to cure around the tube. Then I will put my bolts through the cured in place tubes for the platform. My hope is this removes any possible water intrusion into the transom itself. Has anyone done this? Good idea? Bad idea?

[The Dog House]

Most people just drill through the epoxy once it has cured. I'm not sure what the purpose of the tubes is.

[prowlersfish]

Most people just drill through the epoxy once it has cured. I'm not sure what the purpose of the tubes is.

Agreed

[Big D]

Most people just drill through the epoxy once it has cured. I'm not sure what the purpose of the tubes is.

+1
If you're dealing with a cored transom, you should also dig out about 1/4" to 1/2" of core all around the hole, then fill the cavity and hole with epoxy. After it's cured, drill holes.

[Jimmy]

The thought was once the epoxy was set, the holes are already there. Yes, alreay dug out the core a bit and letting it sit in heated storage for a few more weeks to make sure it is fully dry. I suppose drilling through the cured epoxy should also work, just worried if I drilled off a bit on center, it would not be sealed. Thus the tubes.

[comodave]

When I am working with a cored deck or transom, I drill the hole oversize and then take an allen wrench that I cut down to about 3/8" and chuck the allen wrench into a drill. Putting the allen wrench in the hole and running the drill reams out the core surrounding the hole. If I an working on a horizontal surface, I just drill through the top glass and the core leaving the bottom glass intact to hold the epoxy. After reaming the core out, I put in liquid epoxy to soak into the core edges. Then suck out the liquid epoxy and fill the hole entirely with thickened epoxy and let it harden. After the thickened epoxy has gone off, I drill the correct size hole for the bolt. This process seals the core with the liquid epoxy and gives you a solid epoxy "tube" so that you do not crush the core around the bolt.

[Jimmy]

Great idea with the allen wrench, i actually did the same with a cheap bent screwdriver, since I have holes through already, ill need to tape off the backside, also going to put a slight champher on outside for extra cover on the hole. Second thinking on the tubes.... If I do not have them aligned correctly, I could add more stress on the area. I think, ill go with the fill it up and drill it out. Thanks for the excellent advice. Ill post pics of the build and install. The platform is 30" wide, 103" long. Last coat of epoxy is curing, then wash, wet sand, then paint with non-skid LP.

[Big D]

.....also going to put a slight champher on outside for extra cover on the hole......

This is critical. Not only does reaming the top edge of the hole prevent the gel from radiating cracks, it also leaves a gap for caulking to collect in and around the bolt/top of hole that can't be squeezed out by overtightening. This is good practice anytime a hole is drilled in gel coated glass whether it's going to be sealed or not.

Make sure the bolts go through decent sized backer blocks to spread the load as much as possible.

[Jimmy]

There is plenty of backing wood on the inside, should be good to go.

[Jimmy]

Next question: I will have solid welded aluminum brackets for the platform. I was not planning on running grounding wires to them, or, should I, and add a zinc to each one?

[P-Dogg]

Why aluminum? Where do you boat? I am practically in fresh water, and use aluminum anodes....

I would walk around boatyards looking for boats that have aluminum underwater fittings and see how they look, and how they are protected. Powder coating would delay the inevitable. I believe I have seen clear.

[P-Dogg]

See also Big D's comments regarding aluminum in the underwater lights thread.

[url][/http://www.trojanboats.net/wforum/viewt ... &t=9505url]

[Big D]

I wouldn't go with aluminum. Look into heavy stainless steel round tubing. A lot of people use them for swim platforms, even extended ones. One need only work on stern drives all the time to experience the downfalls of having aluminum in the water in close proximity to SS and having to constantly deal with worrying about corrosion. I've also worked on several TNT hydraulic swim platforms where most of the system is aluminum and under water. As a result I've seen some units in pretty bad shape requiring some major work to remove and replace major support and operational hardware. Same goes for aluminum UW LED lights. Powder coated or anodized, eventually they will corrode. Heck, I've seen anodized and powder coated aluminum corrode topsides, and they are not in an electrolyte (in this case water).

Any time you put dissimilar metals in the water with differences in potential like aluminum and stainless steel, the aluminum is going to give up metal. Just ask anybody that owns or has woked on stern drives. Especially units like Merc Bravo III or Volvo DP with dual SS props. That's a huge mass of SS not including the drive shafts. All making for a constant battle to keep the casing from giving itself up. Hense they have anodes and electronic corrosion mitigation systems like Mercathode. Even then, casings corrode. Your shafts and aluminum supports will act the same way. Conditions play a large roll in determining how quickly things happen but happen they will.

If you are in fresh water, you could try adding a lot of magnesium anodes to help but you have to be carfull as too much magnesium is not desirable in fiberglass hull applications. Be prepared to replace the anodes every year, and magnesium is not cheap. This is what's done every year for stern drives and I'm currently keeping an eye on a couple of TNT units that magnesium has been added to in hopes of delaying the inevitable.

Your call but I wouldn't be using a material that is also used as an anode meant to "sacrifice" itself to protect other metals! Sure some special alloys are also incorporated in aluminum anodes because they have to protect aluminum casings but it's aluminum just the same IMO.

[Jimmy]

The reason I was considering aluminum was the was the Proper SS was hard to find, and our previous boat had cast aluminum brackets on it (with no grounding wires), so figured, should be Ok. The zinc on the aluminum ( or, Mg which I have easy access to all I need), was to keep the aluminum somewhat protected.

And, i have seen other components on other boats in storage where ours is, ladders, power lifts for digys etc, that are aluminum. Given the low cost and east to replace, I'll give it a go and see how they handle it (fresh water). They will have an epoxy coating prior to installation, so that should help. That will buy me time to find the right SS. Which I'm sure to need long term. Stay tuned. All good advice.