Two fuel tanks or one?

[danshat]

This is probably a pretty stupid question, most of mine are. Since I need to remove the fiberglass gas tanks and replace them with aluminum tanks I wondered about some changes. I would like to put a queen size berth in the aft cabin of my 34DC. The original has two berths with 100 gallon tanks below each. If I put a single 200 gallon tank centered on the keel will their be any negative reprocussions? I'm not sure if the tanks on each side add to the stability or if it was just designed to give my wife a reason to sleep in a seperate bed.

[UNIQUE_NAME]

one thing i would look for is to make sure the strut bolts are accessable

[Brian Degulis]

I don't see how one large tank on the centerline would change anything at all as far as stability bouyancy. As long as the weight is about the same and it's sitting in about the same spot for and aft I don't see a problem.

Brian

[SKYCHENEY]

One larger tank should not be a problem. Just make sure that you have proper baffling so that the fuel does not move around too much. The only other negative to one tank over two is that if you run out of fuel in one, you may be able to make it home on the remaining fuel in the other. Or.... you could just put one pick-up tube a little lower that the other. That kind of creates a "reserve" tank.

[nyrussell]

We have the 40 DC. We have a centerline main tank holding 285 gallons of fuel and a keel tank in front of it that holds 75 gallons. Might consider that...

[akintosyali]

STOP!!!
I have 41 DC, and I had them make me a single aluminum tank with all the baffles, etc, only to receive the tank and realize that the tank would not fit through the main door!!! The tank was turned on its side, and the problem was not the height of the tank (width of the door) but width of the tank (the space between where the stairs start and the hatch rests...
Even if I cut the hatch housing, the tank would have been too long and wide to pass through the stairs to the main cabin without taking out some of the flooring.

SO DO NOT order anything until you build a darn box the size of the tank you want, and see if you can move the tank from the outside to inside the boat without having to take anything out.
Trust me.
The tank cost me 3k, and I was lucky to sell it for $600.

[Trojan]

Wow! So much for the big single tank. I don't think I would ever own a boat with just a single tank. The safety features of having 2 tanks would out weigh any reason to have only one. The though of contamination of one tank and not having a chance of switching over to another. The amount of fuel moving around in the single tank even with baffles would be greater. The same amount of fuel in 2 tanks would have less movement and would have less effect on stability and balance over just one. Plus the center of gravity would be lower with 2 tanks when full. 2 tanks of smaller size can be made stronger with less weight and material than one big one. But this is just my opinion.

BILL

[Boatsb]

Also the ability to get them in is a major consideration. remember to take into account any protrusions like the fill and vent pipes and pickups when sizing. I would look at 2 or even 3 tanks ( generator and emergency tank ) and also make sure you have access to the items that may need service on the tanks and below them.

[REBrueckner]

A properly baffled large tank should be as stable as a pair of small tanks...but if not baffled properly, you'll potentially have twice the surge forces in rough weather. You won't be able to trim your boat by drawing fuel from one tank or the other. A large tank must be very securely fastened to the hull. It also means that with twice the weight it must be properly padded to prevent abrasion wear from inevitable vibration. Whichever way you go, be sure to pay a LOT of attention to the "padding" used to protect the tank. In general, many tanks would, I think, tend to be more expensive than a few larger ones.

The shape of a tank, low profile versus high, can affect stability to some extent, but in general it's minor since the tanks are usually low in the bilge anyway. Be sure that any tanks do NOT sit in bilge water as that is never helpful.
As Trojan noted, separate tanks are nice in case of potential contamination from a load of dirty fuel. In practice, I always end up adding fuel to all three of my tanks when I take on fuel, so I've concluded for me it's a minor issue. Related, if you ever lose a fuel line or connection, with multiple tanks and proper plumbing you can turn off the leaky line and get home on a good one.

Finally, depending on the trim of your vessel and cruise speed, you might choose to put a tank way forward and another aft to permit better load balancing fore and aft. A final consideration: Can you fit in a standard size, off the shelf, tank or tanks? That might be potentially less expensive if you can get the material you desire. And don't forget to ground water tanks and fills you add to your bonding system.

[gpellissier]

Another suggestion, if it fits, would be to leave the tankage as built, and modify one of the berths into an athwartships full or queen. Did this on my 44 ft, and it worked like a charm...except for a few curse words getting a regular firm queen mattress down into the aft cabin. On the 44, the result is a queen bed you can still walk all the way around, and use the original bureau.