Mounting Hardware

I have decided the best way for me to mount my propane tank is on the lower cabin roof. I have also decided I don't want to drill through the cored roof to mount it, so I have a plan with no holes.

After reading articles on backing plates for through hulls made of G-10, I think if I drill and tap 6"X6" 5/8" plates for 3/8" all thread and glue them to the cabin roof with 3M5200 (at four points) that I can mount a pair of 1 1/2"X3" teak rails to bolt my horizontal 7 gallon aluminum bottle to.

I figure the bolts would be loaded in shear, and the primary motion is port and starboard, which is the longest dimension in the base (most stable). I also figured I could wind a set of heli-coils into the G-10 for extra strength, route the edges for a nice contour, and color matched finish them with gel coat before glueing them down.

See any obvious flaws with this plan? Looking for some opinions here...

I would think I would go with West System and fiberglass cloth to make the connection of the mounting plate to the roof. This would be much stronger, but not so neat.

A larger plate with holes to go over your threaded rod as a decorative finish. Kind of like a wall plate for a light switch to cover the ugly.

The beauty being I can try out the arrangement before committing to WEST. The threaded rod would run up through the teak rail and cap with more bronze, it looks good when it gets weathered Otherwise it would be invisible. The hardware through the tank bracket into the teak rail would probably be more bronze, perhaps carriage bolts up from the bottom with a lock washer and nut. No vibration to speak of to loosen things up, nautical looking...

If 5200 was suitable for the purpose I think we would see it used in production boats. Just because I haven't does not mean it is not. (triple negative, wow)

Might be worth checking with 3M for the application. Would be lovely if it worked.

Plan sounds good to me Doug.

If it were me I'd use something easier to take appart than 5200. Perhaps SikaFlex 291. Even it would probably be way overkill it terms of tank security and the ability to keep your hardware stuck to the cabin top. Six by 6" is a lot of surface area. RE UV damage 5200 may not be the best adhesive either.

I think all you need is a better adhesive. 3M 4200 is specially made for UV performance. Seems to me it's had some bad "press" here on the forum and it too is probably too good of an adhesive w that much surface area. Using 5200 would be like using a 125lb anchor.

Keep those opinions coming! I am in the formative thought process now, and have the same doubts I have heard expressed. Before committing to WEST I would like to try a more temporary attachment. I would not think UV would be an issue since the adhesive would be under the G-10 plate, and there is 144 inches of contact area in 4 6"X6" plates. The size of the plates are intended to distribute the load over more of the cabin roof area and increase the bonding area. I agree 5200 might be too much adhesion... The teak mounting rail would only be the thickness of the G-10 plate above the cabin roof, the tank through bolted into the rails. Winter is here.

Propane tank project

Here's how the project looks now. $100 worth of G10 1" thick plate cut into fourth's, with the rear plates cut to allow the outboard fuel tank and a 2 1/2 gallon gas can to sit securely between the teak rails. The front plate is the full 6" X 6" and the rear plate is cut so the fuel cans don't rub on sharp corners.

I routed the corners and sanded the G10, next is color matched get coat and securing bronze bolts. The plates were drilled and tapped for 3/8" hardware, with brass hardwood inserts screwed into the backside of the teak mounting rails for the propane tank.

The teak rail was recessed to fit over the G10 plates, leaving just enough room to wash underneath.

Now let's see if this posts

Rethink your fasteners - brass, bronze, aluminum and stainless. The tank will corrode where the fasteners go through. Just use 316 fasteners and large washers, you will have some corrosion at the tank but as long as you don't thread stainless into aluminum it will be manageable.

Personally, I would toss the teak and use aluminum bar stock and probably aluminum pads. The teak will turn black or green, will look like hell and will need attention.

That S/S hardware is what I had in the tupperware used for fitting my construction together, and will all be replaced with bronze, which shouldn't overly react to the brass inserts. The rails are bolted into fiberglass pads tapped for the thread, no other metal there. I can think of no way to completely isolate an aluminum tank from the through bolts, but plan on a little anti-seize where I am brass to bronze. The bolts passing through the tank mount brackets will just have to corrode a little. The holes are oversized enough in the tank mount brackets to be a loose fit.

The teak on my Bayliner is 29 years old, minor brushing with a bristle brush seems to keep the wood looking good. Wood has class, aluminum not so much... That's the great thing about boats, we all get to do it to our personal satisfaction! I am SO happy we all don't like things the same way! I also have $100 in two teak 2"X3"x24", not going to toss

Use Tef-Gel for wherever you have dissimilar metals meeting. Great stuff made for exactly that purpose, S/S fasteners into aluminum being the biggest application. Brass to bronze being another. Pricey, but a little goes along ways.

My propane tank got a temporary installation and it works so well it may stay in place for some time. It's a FG tank so I can see how full it is. Didn't like the industrial look of the greenish FG tank so I covered it w a green fender sock. Turned black real fast. It's very handy and quite secure but definitely looks a bit shabby.

You're on the right track Doug. How are things coming along?

Howdy Eric,

I have things pretty much demolished for the winter, almost time to start putting it back together. I have a new aluminum mast coming this week, complete with a boom to support a rain cover, and I have a nice Lewmar hatch hidden under my bed that will be a skylight in the pilothouse roof. Once on the mast, I wanted an anemometer up there, along with a new anchor/mast light (LED, low RF interference) and I added spreader bars to open up the lower cabin roof for storage space. New Dickinson propane oven/stove to feed off my propane tank installation, so I have the lines to plumb for that as well as tearing out the electric stove top and microwave.

My electrical is being completely upgraded with new house batteries, switches, and a high output (100A) alternator with external regulator to keep them up. I am feeling in a bit over my head currently, but it will all come together quickly once the weather lets me go to work.

Then there are the maintenance projects, pulling all the hatches and ports and re-bedding them. I have boxes and piles of "not crap" stuff around here to put on board once the weather warms up a bit.

Did that answer the question?

Doug,
If you stay hot on your maintenance chores fall will come and you will not have slipped your lines. That was one of my big boating problems w Alaska. There's a reason there are so many aluminum boats in AK.

But when I look at my north pictures .......

We have a new propane cook stove too. Chris really likes it. We got batteries recently while. Still in AK from Boat Electric in Seattle (on Westlake). Highly recommendable. Got ______ River AGM batts

I have been boating here all my life, so I know well the danger of maintenance during the summer I am deferring a lot until fall (like bottom paint) when I can expect the weather to start blowing and not quit until the snow falls. I am planning on a May 1st launch date. Most of the work is done down to "kit" form so it's mostly installation. I will hire a carpenter who knows about boats to help me cut in the counter top for the new range and frame it in.