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Old 20-11-2021, 17:11   #1
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How to mount water maker pressure vessels to hull

I've just purchased a modular water maker. I've got a 40 foot cat, and am thinking of placing the high pressure vessels (the membranes) in my starboard forepeak birth. The boat is foam cored glass.

I picked up a Seawater Pro dual membrane system. I'm guessing I'l use 8 screws per membrane to hold the pressure vessels in place.

What are my options for mounting hardware?

My thoughts were:

* Drill over sized holes into hull for each screw, fill with epoxy, and then sink a screw into this epoxy to hold the membranes. Would be the "cleanest" install, but would require drilling 16 holes into my hull, quite a bit of work, and one mistake and you now have an above water through hole. Not ideal.

* Glass in a piece of marine ply that is a bit bigger than the 2 membranes. Decent amount of work (and I've never glassed before), but would be plenty strong and waterproof. Con is I might crack my glass job if there is ever any flexing in the bow (not sure if this is a concern or not). Also, this is pretty permanent and never coming out. Ever.

* Adhere (glue/epoxy/magic sauce) a piece of marine ply like above, but don't worry about glassing it. Now flexing sounds like more of a danger and what about water proofing?

* Adhere several smaller blocks of wood directly where I want to sink the screws. A bit more work than the above solution, but flexing of the bow shouldn't be too much a concern, as the wood would be 50 mm wide by 100 mm tall. Same concern about water proofing though.

I'm trying to balance out skill required vs finished look and strong enough to hold vs impossible to correct a mistake.

I'm planning on gluing a rubber mat to the floor and mounting the motor to that mat to aid in vibration/noise reduction. I'm not overly concerned with that mounting approach for the motor, because I am not fighting gravity.

Thanks for any idea or tips!
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Old 20-11-2021, 17:43   #2
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Re: How to mount water maker pressure vessels to hull

I'd Sikaflex a piece of ply and just use that. If you use one of the polyurethane construction adhesives (221?) and prepare the surface well, it will hold. Just cover as much areas as you can.The reason for using Sika instead of epoxy is that it can fill gaps, flex and will be removable without destroying the substrate (as much!) if that is ever required.

Rather than drill through the hull, I'd make a mounting plate from aluminium, stainless or even just painted steel with the prerequisite mounting points and then screw this to the ply using as many screws as required for the job.

Not sure of the factory mounting system in your case, but if it's a standard tube pressure vessel than stauf clamps should work as an alternative and require only 2 clamps/4 bolts per cylinder.
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Old 20-11-2021, 17:50   #3
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Re: How to mount water maker pressure vessels to hull

#3, definitely.

Just use a nice big surface area for that piece of wood so that the load is distributed over a big surface area. That will keep any delamination forces to a minimum.

Screw right to the wood. For extra measure, you could use marine ply. You could also paint the wood. Or seal the wood in someway so that water doesn’t get into it.
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Old 20-11-2021, 20:18   #4
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Re: How to mount water maker pressure vessels to hull

Don't drill into the hull!!!!
The area of your hull that you want to mount to probably?/maybe?, has a decent amount of curvature in both directions.
A flat piece of plywood has a good chance of touching the hull only at the corners, (maybe only 3 corners,) and in the middle their might be quite a gap.
Under that scenario using gobs of Sika, or other "stuff in a tube" is more-or-less a "Rube Goldberg" approach.
A more "Pro" way is to shape a couple of little "ribs", that have a curvature to fit the hull, and have their inboard faces straight.
Now, your plywood part can be fastened to the ribs, and that assembly can be "glued" to the hull with thickened epoxy "mush".
If the loads/weights are not too much you're good-to-go.
If you think the weight is too much, you can unscrew the plywood from the ribs and add glass reinforcement over them, and then fasten the plywood back down to them.
Of course, making sure that the hull is clean, and free of anything that would compromise the bond.
Simply "mashing" a piece of plywood against the hull with goop or epoxy is really a "farmer" way, and precludes later changes or removal without large efforts.
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Old 21-11-2021, 00:32   #5
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Re: How to mount water maker pressure vessels to hull

Reefmagnet - thanks for the pointers. A couple clarification points:

Quote:
Originally Posted by Reefmagnet View Post
Rather than drill through the hull, I'd make a mounting plate from aluminium, stainless or even just painted steel with the prerequisite mounting points and then screw this to the ply using as many screws as required for the job.
Is there a reason for making a metal mounting plate rather than just putting a couple screws directly into the wood from the pressure vessel mounting brackets? Are you thinking the wood might not be strong enough?

Quote:
Originally Posted by Reefmagnet View Post
Not sure of the factory mounting system in your case, but if it's a standard tube pressure vessel than stauf clamps should work as an alternative and require only 2 clamps/4 bolts per cylinder.
These clamps aren't to scale, but hopefully this gives an idea about how the pressure vessel is mounted to the hull.

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Old 21-11-2021, 00:37   #6
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Re: How to mount water maker pressure vessels to hull

Thanks for the rib idea Bowdrie!

Quote:
Originally Posted by Bowdrie View Post
A more "Pro" way is to shape a couple of little "ribs", that have a curvature to fit the hull, and have their inboard faces straight.
Is there any reason to not just screw into these ribs directly and instead put a sheet of ply on the ribs and then mount to the sheet of ply? I don't think these vessels will weigh very much (in the videos, people pick them up single handed). There shouldn't be too much flexing or sheer force, I would hope. I wasn't sure if there was another advantage to having the whole sheet of ply.
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Old 21-11-2021, 00:37   #7
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Re: How to mount water maker pressure vessels to hull

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#3, definitely.
Or seal the wood in someway so that water doesn’t get into it.
Do you have a method you like for sealing wood?
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Old 21-11-2021, 01:22   #8
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Re: How to mount water maker pressure vessels to hull

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Originally Posted by workmaster2n View Post
Do you have a method you like for sealing wood?
Obviously epoxy is the best, but this is just a vertically mounted indoor mounting surface. Some paint is probably good for the next 30 years to be honest.

I do agree with bowdrie depending on the gap size. Anything over a cm and I’d probably find a solid filler to put in there first.

Another simple way to do the solid filler would be to use a piece of foam such as the stuff the hull is made out of. Or another piece of wood shaped with an angle grinder. Or something of that nature.

I’m not sure I’d go through all the trouble of glassing ribs in there just to hang up a pressure vessel, which is a utility look in itself.
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Old 21-11-2021, 02:27   #9
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Re: How to mount water maker pressure vessels to hull

Have you considered mounting them vertically on the bulkhead where the fixings can be bolted right through. No pads less weight, less work, less everything.
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Old 21-11-2021, 08:07   #10
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Re: How to mount water maker pressure vessels to hull

When mounting my water maker high pressure gear I chose a location where a potential leak would be of no consequence. The forepeak berth was rejected because this is high value dry storage on my boat. A leak could ruin a lot of stuff. But your call on your boat. After much deliberation I found an unused zone in my cross beam locker, which has its own overboard drains.

I glued small PVC boards to the foam core using Goop marine adhesive. I find Goop amply strong, but easily removed once cured (if I ever want to move stuff later). PVC because it will never rot. If I want fancy I install stainless Tnuts in the PVC to match the mounting screws before gluing the PVC to the hull.
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Old 21-11-2021, 08:55   #11
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Re: How to mount water maker pressure vessels to hull

Quote:
Originally Posted by Sparx View Post
When mounting my water maker high pressure gear I chose a location where a potential leak would be of no consequence. The forepeak berth was rejected because this is high value dry storage on my boat. A leak could ruin a lot of stuff. But your call on your boat. After much deliberation I found an unused zone in my cross beam locker, which has its own overboard drains.

I glued small PVC boards to the foam core using Goop marine adhesive. I find Goop amply strong, but easily removed once cured (if I ever want to move stuff later). PVC because it will never rot. If I want fancy I install stainless Tnuts in the PVC to match the mounting screws before gluing the PVC to the hull.

Agree maintenance and or leaks from WM's can result in a big salty mess. Moved mine from an engine room to behind the shower, any mess can be easily washed away.
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Old 21-11-2021, 21:33   #12
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Re: How to mount water maker pressure vessels to hull

i used a thick plasic called polymer hdpe sea sold by dibe r plastic supply on ebay. i ruffen up one side so that 3m 5200 can sick to it and put it down. now you can drill and screw through that. dont have to waterproof since it is a plastic. that is what i used as a base for my bilge pump and switch
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Old 21-11-2021, 21:46   #13
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Re: How to mount water maker pressure vessels to hull

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Originally Posted by workmaster2n View Post
Thanks for the rib idea Bowdrie!
Is there any reason to not just screw into these ribs directly and instead put a sheet of ply on the ribs and then mount to the sheet of ply?
Not really, it's just that a piece of ply gives a measure of "leeway" in the mounting with screw locations, especially if any changes are made.
And the plywood, being spaced from the hull a bit, allows the use of bolts for any reason you may have at a later date.
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Old 22-11-2021, 09:32   #14
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Re: How to mount water maker pressure vessels to hull

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Originally Posted by workmaster2n View Post
Do you have a method you like for sealing wood?
If it's in a relatively dry place (not wet or damp all the time only sometimes, like everything on a boat) and if I'm not going to be painting it and just want to seal it, I mix up one part PVA glue with four parts water and paint it on. Very cheap and non-toxic which means you can splash it around in tight spaces without worrying about your health or your wallet! Even in wet paces (I've used it on the inside of a fresh water tank) it seems to last nearly forever if allowed to dry out fully before putting more water on it.
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Old 22-11-2021, 09:51   #15
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Re: How to mount water maker pressure vessels to hull

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Originally Posted by workmaster2n View Post
Do you have a method you like for sealing wood?
CPES - epoxy sealer
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