Underdeck tank

Chanchan168 · 26 February 2018, 14:09

Hi all,

Managed to cut the deck up to the stringers and all looks good. No rot in the deck and stringers look ok.

Tank is a lot bigger than I thought, but I need some advice as to how to lift it out. It doesn’t look foamed in as it’s resting on the stringers with a clear gap underneath for the bilge drain.

It looks like it’s just fibreglassed and resined in at each corner with some more resin placed in between the forward stringer and tank.

Any ideas on how to lift it out would be gratefully appreciated.

Chanchan168 · 26 February 2018, 14:11

Sorry peeps, it keeps on coming up as invalid file when I try to upload the pics.

Any idea as to why?

Chanchan168 · 27 February 2018, 22:02

willk · 27 February 2018, 22:13

Quote:

Originally Posted by Chanchan168

Sorry peeps, it keeps on coming up as invalid file when I try to upload the pics.

Any idea as to why?

Gonna guess yer doing it wrong

Use the paperclip icon to attach pics resident on your device. If using an existing web image use the yellow Insert Image box.

Chanchan168 · 27 February 2018, 22:18

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Chanchan168 · 27 February 2018, 22:19

Quote:

Originally Posted by willk

Gonna guess yer doing it wrong

Use the paperclip icon to attach pics resident on your device. If using an existing web image use the yellow Insert Image box.

Thanks,

How weird won’t work using safari, but fine using the app.

Now it’s working, has anyone got any ideas please how best to lift it out??

Last Tango · 28 February 2018, 09:23

If the leak is near the top and the tank's empty you could try filling the void around it with water and see if it'll float out? There'll be a lot of bouyancy there.

mhb100 · 28 February 2018, 18:46

Have a look on YouTube and some of the USA boat forums and see a few videos on mako boats. You should be able to use the inspection hatch to attach too, to raise initially. Can you see the fixings without removing more deck?

Chanchan168 · 28 February 2018, 20:53

Quote:

Originally Posted by mhb100

Have a look on YouTube and some of the USA boat forums and see a few videos on mako boats. You should be able to use the inspection hatch to attach too, to raise initially. Can you see the fixings without removing more deck?

There isn’t any fixings by the look of it. I’ve cut all the way around the tank right up to the stringers.

The tank is right up against the front bulkhead and a few inches short of the rear bulkhead. There’s about the same around the sides but all I can see so far is a bit of fb and resin at each Corner.

My mate had a Compton rib that apparently has the same kind of hull and his tank just sat in the chines on small pieces or neoprene.

His tank though is a lot smaller than mine. Mine was a coded boat, therefore the tank is circa 300l with a main and reserve split by baffles in the tank. I have two pickups at the front.

I’m hopeful it will just lift out with a bit of encouragement

GuyC · 28 February 2018, 22:19

Quote:

Originally Posted by Last Tango

If the leak is near the top and the tank's empty you could try filling the void around it with water and see if it'll float out? There'll be a lot of bouyancy there.

That's a very good idea.

Even a third of the way up the tank will give you around 100kg of lifting force.

Chanchan168 · 28 February 2018, 22:45

Quote:

Originally Posted by GuyC

That's a very good idea.

Even a third of the way up the tank will give you around 100kg of lifting force.

Gonna try it as soon as I thaw out

Chanchan168 · 01 March 2018, 10:41

Whilst I’ve got the floor up and the console moved, this gives me a chance to re evaluate options for fuel storage.

I know threads like his have been bantered around before, but if the tank is split and beyond repair, is there any benefit of replacing the deck in it’s entirety and putting an above deck tank in instead??

I’ve got the option of either putting a 140l tank in the rear bench and the batteries and switch in the console or putting the tank in the console and putting the batteries in the bench seat.

Would transfer of weight be an issue in either of these locations??

Chanchan168 · 02 March 2018, 15:48

Ok. Got the tank out. It’s huge and was a messy job. If I decide to put a new tank in the console instead and just replace the deck, would I have to put in a new stringer for support or as it’s a closed cell, would it be ok to just replace the deck??

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mhb100 · 02 March 2018, 19:39

How did you get it out in the end, how was it held in? What state is the deck in? Did I read somewhere this had sank at some point or flooded?. My personal view is as the boat is all stripped down then put another under deck tank back and do it properly plus the boat will have more value. Cost can vary massively if you need a custom tank.

Have you found what is wrong with the tank itself, split seam or corrosion?

Chanchan168 · 02 March 2018, 19:44

Quote:

Originally Posted by mhb100

How did you get it out in the end, how was it held in? What state is the deck in? Did I read somewhere this had sank at some point or flooded?. My personal view is as the boat is all stripped down then put another under deck tank back and do it properly plus the boat will have more value. Cost can vary massively if you need a custom tank.

Have you found what is wrong with the tank itself, split seam or corrosion?

I used a drop in saw set to the depth of the deck and managed to cut straight along all of the stringers. The tank was foamed in all the way around but the tank recess looks like a closed cell.

Managed to chip around the foam with a screwdriver and hammer and then prize the tank out. The oily substance in the ottom of the well looks like old seawater mixed with fuel, as when she sunk on her mooring water got in through the deck hatches that weren’t even hatches, merely flat fibreglass.

Tank looks to be in good order. Just gonna clean up the space and reset tank after inspection, clean out and pressure test.

mhb100 · 03 March 2018, 06:44

Seems wrong to put that +15yr old tank back. Still a bit confused why you didn't clean tank out and pressure test before removing floor, but now you have its got to be better to put something new back in and not consider any above the deck tank options.

Last Tango · 03 March 2018, 08:05

Now the tanks out your going to have to think about that space if you don't put the tank back there.
If it's a sealed space water shouldn't get into it but it if it does it won't get out again and you could be running around with 300+ litres of water under the deck and blissfully unaware.
I'm not a fan of under-deck tanks for the reasons you'll be all to familiar with now but "the worst is over" and I'd say it makes sense to put the new tank back in that hole. It might also be worth considering a deck fitting near the back end of the cell so as you can stick a hose through to "mop out" any water that might have got in.

Chanchan168 · 03 March 2018, 08:46

Quote:

Originally Posted by mhb100

Seems wrong to put that +15yr old tank back. Still a bit confused why you didn't clean tank out and pressure test before removing floor, but now you have its got to be better to put something new back in and not consider any above the deck tank options.

The main reason for lifting it out was due to the fact that when I cut a little of the deck out to fit the new rear inspection hatch, there was water present, so I wasn’t sure if it the area was full or just a bit of rain water sitting on top of the foam.

As it had been under, I had no idea what state the underdeck was in, so it was niggling me and I didn’t want to redo the floor, put the new seats in and have it bug me for ever. The previous owner hadn’t a clue about anything.

Chanchan168 · 03 March 2018, 08:48

Quote:

Originally Posted by Last Tango

Now the tanks out your going to have to think about that space if you don't put the tank back there.
If it's a sealed space water shouldn't get into it but it if it does it won't get out again and you could be running around with 300+ litres of water under the deck and blissfully unaware.
I'm not a fan of under-deck tanks for the reasons you'll be all to familiar with now but "the worst is over" and I'd say it makes sense to put the new tank back in that hole. It might also be worth considering a deck fitting near the back end of the cell so as you can stick a hose through to "mop out" any water that might have got in.

That’s why I suppose I was gonna just put the deck back, but install two hatches to mop up anything that got in there.

Thanks for your comments guys. Appreciated

matata · 03 March 2018, 17:34

When we bought our rib (Delta) we were disappointed that the tank wasn't below deck. Now five years later our four tank system under seat system is great!. Each tank can be lifted out and filled at the local petrol station which is very handy if your up in Scotland where we Safari a lot. WE have a manifold with taps to select each tank. You always know how much you have rather than using a fuel gauge. Just my thoughts! Nik