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Basic boat building question


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#1 Neil

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Posted 15 August 2019 - 10:55 AM

Some basic boat building advice needed here. 
 
I have a 50L tank (Polyethylene? I think) which is required to “hang” from under a thick sheet of ply as per the photos. 
 
The question is how to attach it? The options I’ve considered are: 
 
1) Get some brackets fabricated which will go around the tank and then can be through bolted to the ply – Not sure who would make these and how much it might cost? 
 
2) Build a ply “box” under the sheet of ply that the tank can slide in to. For this I would made the box and reinforce the seams with fibre glass tape (round off edges etc etc) – Probably my current thinking is this option
 
3) Epoxy the tank directly to the ply sheet and then reinforce the join with fibreglass tape – Not sure this is even possible with this plastic or not? 
 
Any ideas on which of these is a good idea? Or any other options? 
 
Attached File  20190815_093212.jpg   329.19KB   1 downloadsAttached File  20190815_093236.jpg   305.75KB   0 downloads
 
PS. The ply sheet is symmetrical but it’s amazing how a phone camera close up makes it all look distorted!

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#2 Island Time

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Posted 15 August 2019 - 11:23 AM

Nothing really stick to cross link polyethylene. Repairs are normally made by plastic welding. 

If it were me, I'd use a sheet of ply under it and two bearers to support that, with rods and nuts with large washers through the bearers.  Do it up tight, any movement will break it, that tank will be heavy when full. Remember the shock loading that can occur, and the hydraulic ram effect of the free surface. I'd also make a frame on the ply to prevent ANY movement fore and aft or athwart ship.

 

Where will it go, and what will hold up the ply? It will have to be strong...


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#3 Neil

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Posted 15 August 2019 - 12:09 PM

Nothing really stick to cross link polyethylene. Repairs are normally made by plastic welding. 

If it were me, I'd use a sheet of ply under it and two bearers to support that, with rods and nuts with large washers through the bearers.  Do it up tight, any movement will break it, that tank will be heavy when full. Remember the shock loading that can occur, and the hydraulic ram effect of the free surface. I'd also make a frame on the ply to prevent ANY movement fore and aft or athwart ship.

 

Where will it go, and what will hold up the ply? It will have to be strong...

 

This tank is replacing a similar sized old one that was held in the same way. Bolted to the fibreglass mouldings that form the underside of the forwards V-berth. If you look at the pic of the old tank you can see that the piece that was the attachment was also the top of the tank itself (sealed and bolted to it). The old tank was glass and the seal with the top was failing so decided to bin it and start again. This one never moved and the new one is the same size to am happy the fixings to the boat are strong enough. 

 

I like your idea of just a bottom piece and then bearers with rods holding it up, I'll have a play in the shed later. 

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#4 Marshy

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Posted 15 August 2019 - 12:58 PM

Webbing Strap?


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#5 Neil

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Posted 30 August 2019 - 12:02 PM

Probably somewhat over engineered. However, as testing consisted of me and my 100(and some)kgs jumping up and down on it I'm now happy it will be ok with a few litres of waste in it.

 

There is still another piece to go on to stop any movement of the the tank backwards but had to plumb the pipes in before I can bolt that on.

 

Now just need to put the boat back together again.

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#6 Jon

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Posted 30 August 2019 - 03:03 PM

Nice Neil
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#7 Priscilla II

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Posted 30 August 2019 - 05:13 PM


Standen in the Concourse Henderson will make up a couple of stainless ratchet straps to support tank off the plywood.
Anzor also stock ratchets and pad eyes in stainless.
Cable tie to secure ratchet arm
Attached File  17DAE430-9F0B-4E8D-A163-391E5267E980.jpeg   145.16KB   0 downloads
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#8 Myjane

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Posted 30 August 2019 - 09:07 PM

Nice job how do you get on in the middle of the night with the water slurping about under the bunk
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#9 Frank

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Posted 31 August 2019 - 05:12 AM

Tidy workmanship there

Probably somewhat over engineered. However, as testing consisted of me and my 100(and some)kgs jumping up and down on it I'm now happy it will be ok with a few litres of waste in it.

 

There is still another piece to go on to stop any movement of the the tank backwards but had to plumb the pipes in before I can bolt that on.

 

Now just need to put the boat back together again.


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#10 ScottiE

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Posted 31 August 2019 - 06:20 PM

Probably somewhat over engineered. However, as testing consisted of me and my 100(and some)kgs jumping up and down on it I'm now happy it will be ok with a few litres of waste in it.

There is still another piece to go on to stop any movement of the the tank backwards but had to plumb the pipes in before I can bolt that on.

Now just need to put the boat back together again.


That's some heavy sh*t!
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