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Old 19-11-2014, 16:19   #16
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Re: Fastening a heavy piece of equipment

Does the construction of the unit permit drilling additional holes for more screws?
Sheet metal screws have a better thread design than wood screws for resisting withdrawal.
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Old 20-11-2014, 06:34   #17
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Re: Fastening a heavy piece of equipment

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Originally Posted by Terra Nova View Post
Wherever you must mount heavy equipment to thin bulkheads, and through-fasteners must be avoided, simply screw and epoxy glue a large, thick, plywood doubler, first. This will provide adequate depth for the equipment mounting screws, and also help stiffen the bulkhead.

note: if the equipment produces vibration, the bulkhead can amplify this to a disturbing level.
Thanks, Terra,
the plywood is already doubled (two 1/2" sheets). I was thinking of adding a third. Does this make sense? What is an appropriate epoxy to use?
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Old 20-11-2014, 06:48   #18
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Re: Fastening a heavy piece of equipment

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Thanks, Terra,
the plywood is already doubled (two 1/2" sheets). I was thinking of adding a third. Does this make sense? What is an appropriate epoxy to use?
Water resistant wood glue will do just fine. There's no sense exceeding the strength of the glue that binds the plys in the plywood together. Besides, you're going to glue and screw it together so any stress is shared by the screws.
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Old 20-11-2014, 09:56   #19
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Re: Fastening a heavy piece of equipment

I use WEST System epoxy for virtually all glue joints. But 3M 5200 can be used for this kind of joint, if that's all you have.
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Old 21-11-2014, 01:55   #20
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Re: Fastening a heavy piece of equipment

Is it only me that bought a cheep inverter , that directions say DO NOT MOUNT VERTICALLY ? Or are others not reading the fine print ? I really had my heart set on mounting it to a wall. Anyway bought very nice strong white power coated brackets. Its still going on that wall , just horizontally . Steve.
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Old 21-11-2014, 02:30   #21
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Re: Fastening a heavy piece of equipment

My not cheap inverter says the same thing.
I don't agree with a lot of these comments though. Dynamic loads shouldn't be held in place with screws in most cases. And what's with trying to figure out the minimum needed?
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Old 21-11-2014, 04:31   #22
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Re: Fastening a heavy piece of equipment

I understand your concern….
My comfort level is that something that heavy should also be able to carry my own weight and momentum, if I ever fell on top of it in rough seas

Apart from being heavy, they go thru a lot of temperature changes (especially isolation transformer) if working hard and are very expensive.

My Victron units, (isolation transformer and multi system) come with a “wedge plate” for mounting on wall then hanging unit on, with 2 additional fasteners at base. (7 total)

I did not trust just that alone going into wood and since they want maximum cooling, I made a heavy open box 3” aluminum standoff to keep unit well away from bulkhead

I then used an alloy backing plate behind the plywood to mount the box with machine screws and stainless wood screws into additional hard timber

If you need to double up on plywood to get the backing plate and you have no internal studs, then you can also fashion a timber cleat to catch under the box so you are screwing both into bulkhead and down into cleat so that the cleat is also taking the weight as well

The wedge plate is thru bolted with back lock nuts onto box plate.
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Old 21-11-2014, 05:30   #23
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Re: Fastening a heavy piece of equipment

Screws are usually rated for depth into timber 7 x shank diameter. i.e. 7 x 0.25" = 1.75" embedment. The supplier won't take responsibility if you fix to something thinner.
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Old 21-11-2014, 06:17   #24
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Re: Fastening a heavy piece of equipment

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Originally Posted by sailersteve View Post
Is it only me that bought a cheep inverter , that directions say DO NOT MOUNT VERTICALLY ? Or are others not reading the fine print ? I really had my heart set on mounting it to a wall. Anyway bought very nice strong white power coated brackets. Its still going on that wall , just horizontally . Steve.
It doesn't matter if it's cheap or expensive, they pay people to write installation and operation instructions for a reason. If your inverter can't be mounted the way you intended and you can't figure out another way or place to mount it, return it and get one that can be mounted in the space you have.

Mine can be mounted vertically (with the connections on either end but not top or bottom).
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Old 21-11-2014, 06:20   #25
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Re: Fastening a heavy piece of equipment

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......... Dont obsess about a few boltheads showing in the cabin....
If you own a work boat or an old "not so nice" boat, your advice would be OK. I don't think it would be "obsessive" to not want a bunch of random bolt heads showing in the middle of a nice mahogany or teak panel in the saloon.
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Old 21-11-2014, 06:33   #26
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Re: Fastening a heavy piece of equipment

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Thanks, Terra,
the plywood is already doubled (two 1/2" sheets). I was thinking of adding a third. Does this make sense? What is an appropriate epoxy to use?
This brings up the question - How is this plywood fastened to the boat? How are the two plys fastened together? Nothing is going to be any stronger than these bonds.

Here is another idea - threaded inserts.

Drill the appropriate sized hole in the plywood, install the inserts and then install your device with machine screws.

The advantage here is it's all done from the front, the inserts provide a better grip in the plywood because they are larger, and you can remove and reinstall the device as often as necessary without compromising the integrity of the installation. If I were doing this I would use a little epoxy to make the inserts permanent. And lockwashers on the machine screws.
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Old 22-11-2014, 04:41   #27
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Re: Fastening a heavy piece of equipment

I have heard back from the manufacturer. They are saying that six 1/4 inch screws into 1 inch if plywood should be plenty. I am going to start with this and then see how things hold up over time. I can always try something else later if things begin to losen.
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