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Old 10-06-2012, 15:02   #1
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Holding Tank Holding Tank

No I'm not stuttering, I'm replacing my old aluminium holding tank that had a paper thin bottom. I, of course, couldn't find a replacement that was an exact match to the old one so I bought an appropriately sized rectangular poly tank. Now I'm faced with installing this tank in the same location as the old which was shaped to match the hull shape. This means the rectangular tank need to have a platform built to raise the inside edge. It is located aft of the head bulkhead in the cockpit locker and spans the width of the locker. This means raising it to at least eight inches above the present location so that I still have a three degree slope on the tank to send contents towards the dip tube outlet.

Any ideas on how to raise and secure this tank.

I've been reading posts to this forum and would like to hear from so many people who have done some amazing work on their boats. Sailboats have to be the ultimate DIY project. So many thing affect its performance in the most hostile environments that it seems every detail of its construction has to be thought out.

Thanks in advance for your help.

Gilles
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Old 10-06-2012, 15:37   #2
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Re: Holding tank holding tank

You might get a response if you tell what make, size, model etc boat you have and some photos of the new tank, old tank and proposed location.
Without that info, everyone will just be guessing or not bother to reply.
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Old 10-06-2012, 15:39   #3
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Can you not glass in a frame using pressure treated wood as the frame? I used pressure treated wood as stringers and simply covered them in glass before installing.
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Old 10-06-2012, 15:55   #4
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To those interested, the boat is an Aloha 30 the new tank dimensions are 30l x 12w x 20h. I don't have pictures yet. The tank sit along it's 12" side on the hull and it's length (30") is along the bulkhead towards the centre thus the large drop.

I was think just to build a wooden frame with some Bolshevik paint but it would be necessary to glass it in place? Also attached to the bulkhead or on a stand? Don't know.
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Old 10-06-2012, 16:30   #5
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I mean bilge paint darn spell check
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Old 10-06-2012, 16:55   #6
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Re: Holding tank holding tank

I put a holding tank into Boracay a few years ago. A few thoughts:-
* Assuming your dimensions are in inches that's about a 120 litre holding tank. Going on 6 litres/person/day it could hold for 10 days of careful use by two.
* You don't mention emptying the tank or any method of gauging the contents. My experience suggests that both of these are more important than getting the last few drops out. The pumpout needs to be fool proof. I use the pumpout tube for a dipstick - not the best way of doing this.
* I also found that locating the plumbing in a convenient manner is also a mission critical matter. I put an additional stop cock on the outlet hose and a quick disconnect. I should have done more.
* If the bottom of the tank can be located just above the waterline then the surge of seawater can assist in clearing the tank where this is allowed. This also would make it easier to pump into the tank.
* I used 45x90 and 35x70 (2'x4' and 1.5"x2.5" dressed?) epoxy coated pine as the supports, bolted to the steel frames.
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Old 10-06-2012, 17:30   #7
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Re: Holding tank holding tank

Building a plywood shelf, glassed to the hull on that side isnt that difficult. However, if you must, styro foam (noisy) or that blue, white or gray semi rigid (nylon?) foam will support huge weight. You could build up a platform with that. You still should belt the tank down somehow.
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Old 10-06-2012, 18:31   #8
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Now that's an idea. Use foam to build up then maybe frame it with wood.

It seems that I'll need to either glass it or epoxy the construction. Any preferences.
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Old 11-06-2012, 11:41   #9
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Re: Holding tank holding tank

If you are going to get out the glass and epoxy... just build a shelf.... or use Urethane foam as the resin wont melt it!
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Old 11-06-2012, 18:32   #10
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Chechaco,

You've gone beyond my knowledge level. Are you saying to use foam with Urethane paint. How will this hold the tank in place or are you just talking about raising the bottom and then build something on top?
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Old 22-06-2012, 08:47   #11
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Here is a picture of the area the holding tank will occupy.
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Old 30-06-2012, 17:59   #12
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Download the holland marine catalogue. They have plastic tanks that may fit this. Can you return the other tank? Holland marine is located in Mississauga....I think. I downloaded their catalogue and they have curved tanks listed that are from C&C.
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Old 30-06-2012, 19:25   #13
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Re: Holding tank holding tank

Thanks for the tip but the Holland tanks had the same problem as many other tanks I've looked at. They are too wide. I could have gone with a wider tank but I would have been putting gear on top of the tank and didn't want to do that so it was make a shelf or make a floor for the cockpit locker and I just chose the shelf because the tank was closer to the connections and it offered more room in the locker.

I bought my tank at Ronco who have good prices and the largest selection I've ever seen then and since.

I think I've decided to go the easy route since I have no experience glass wise. I will just build a wooden platform and paint it with poly paint and screw it into the bulkhead and floor. I will also screw into the bulkhead a painted wooden brace to hold the tank down. If the wood doesn't stand up to the experience, I will have to take a fibreglass course or something. Will be using scraps of wood so it won't cost me much and if it doesn't work not much lost. The old platform that lasted twenty five years was painted plywood.
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Old 30-06-2012, 20:13   #14
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Re: Holding tank holding tank

We are in the process of installing a holding tank into our Beneteau 40 behind the aft head bulkhead. The advice that we have been given by the local experts that we rely on in the BVI's is to install the holding tank as high as possible, within reason, above the waterline. Then you plumb it to a 2" sea cock / through hull just below the waterline so that it will gravity flush when well offshore with the seacock open. Needless to say, you still have to have a pump out fitting and a vent on deck. You eliminate all other plumbing by routing the toilet straight to the elevated holding tank and controlling it with the seacock. All of the charter companies are now ordering their boats with this system as it is troublefree and effective. It might not hurt to consider a toilet exhaust check valve as redundant protection against backflow should the toilet valve fail. You can add deodorizer and/or flushing water through the deck fitting. gts1544
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Old 30-06-2012, 20:20   #15
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I'd love to take your advise from the BVI, if it were not for the fact that in the waters I sail in, it is illegal and I would have to pay hefty fine if ever I were found out.
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