Water tank bottom insulation

[Kristina]

I am refitting our boat and we have a new plastic watertank. we are planning on getting it spray foam insulated when we have our boat insulated. we are planning on removing a section of the subfloor and having the watertank sit on the ballasts/ girders there will be about 3 inch gap between the hull and watertank. Is there a danger or condensation trapped in this gap, should i insulate under aswell? 

[blackrose]

I would say yes, insulate the whole thing of you can. The top of the tank will attract more condensation but you'll also get some at the bottom. 

 

With a plastic tank there's also a danger of point loading stresses in areas where the tank is sitting on narrow supports when it's repeatedly filled with water. 

 

The other thing to think about is how to prevent the tank moving if you take the boat onto tidal water where it might bounce around a bit.

 

 

Edited November 26, 2020 by blackrose

[system 4-50]

Put the takeoff in the top  of the tank, there is no need to put it in the side. 

Insulate all round, bottom, top, sides.

[Onewheeler]

I'd put the tank on a sheet of ply to spread the load but not insulate underneath. The bottom plate will never freeze and you'll get some protection from frost, especially if the rest of the tank is insulated.

[IanD]

9 minutes ago, Onewheeler said:

I'd put the tank on a sheet of ply to spread the load but not insulate underneath. The bottom plate will never freeze and you'll get some protection from frost, especially if the rest of the tank is insulated.

Bottom plate will never get below 4C...