Adding Under Belly Fuel Tank

[Gone Postal]

Hey Guys need some Input.
I have a 2105 Cottage. Currently it has 2 Portable Tanks Mounted on Rear Deck.
I want to add a Larger Under Belly Tank.
Looking at the Moeller design with the flat top and rounded bottom.
what should I look out for in doing this.
Thanks Tim

 

[rickdb1boat]

Re: Adding Under Belly Fuel Tank

Here's where a guy used an undermounted tank..

http://www.pontoonstuff.com/psforum...title=country-dave-1986-stardust-24ft-rebuild

 

[5150abf]

Re: Adding Under Belly Fuel Tank

There is alot of water splashing around under a boat so make sure it is attached really well and make sure you don't get water in the tank obviously.

My biggest worry would be just the force of the water ripping it off, maybe have someone run your oat and take a peek over the front of the boat to see where the water isn't so bad.

We do this at Bennington and the tank goes in an enclosure, I have made the enclosure but I have never seen one on a boat, no I can't get you pictures.

 

[EGlideRider]

Re: Adding Under Belly Fuel Tank

+1 for 5150. No doubt that the tank can be secured well enough to prevent it from being ripped off but it is bound to create lots of drag at high speeds.

 

[Blank-N-Ship]

Re: Adding Under Belly Fuel Tank

Here's where a guy used an undermounted tank..

http://www.pontoonstuff.com/psforum...title=country-dave-1986-stardust-24ft-rebuild

I love the concept of this under-mount for the fuel tank. I just worry that it will change the flow under and past the bottom of the transom, negatively affecting performance.

If you watch water in a river setting and how it flows around rocks you'll see how any obstruction forms interesting eddies/vortices in the flow. An under-deck tank will be an obstruction. Water will take interesting paths around that tank to eventually form back into a stream. Until it does though, what you've managed to do is to reform a clean channel of water (directed at your prop) into something that's now not.

 

[jjohnson120]

Re: Adding Under Belly Fuel Tank

Are toons gravity fed or do they have fuel pumps? Just curious if there is any effect on that from where they are traditionally mounted.

 

[EGlideRider]

Re: Adding Under Belly Fuel Tank

Toon or not, marine engines are equipped with fuel pumps.

 

[Blank-N-Ship]

Re: Adding Under Belly Fuel Tank

The higher the fuel tank in relation to the engine the higher the pressure there will be on the intake. There's a fuel pump but there will likely be a performance difference between pumping already-pressured fuel in the line versus fuel that needs to be lifted.

Another issue is that a 35-gallon tank weighs over 200 lbs from just the fuel weight alone. It should be properly balanced within the design.

 

[EGlideRider]

Re: Adding Under Belly Fuel Tank

The higher the fuel tank in relation to the engine the higher the pressure there will be on the intake. There's a fuel pump but there will likely be a performance difference between pumping already-pressured fuel in the line versus fuel that needs to be lifted.

Another issue is that a 35-gallon tank weighs over 200 lbs from just the fuel weight alone. It should be properly balanced within the design.

I must respectfully disagree that a performance difference will be noticed. There should be less than 10 extra vertical inches to pump the fuel so I don't think any detectable performance will be realized. Practically all fuel pumps are designed to pump more fuel than is required by the engine, and a fuel regulator controls the actual amount delivered to the carbs or injectors.

 

[Water logged]

Re: Adding Under Belly Fuel Tank

On my SunTracker the tank is mounted below deck level ahead of the transom and it seems to be able to pump lots of fuel. I'm just going by how often I have to fill It..

Glenn

 

[5150abf]

Re: Adding Under Belly Fuel Tank

I'm with Eglide on this one, I am sure there are limits to how far a fuel pump can lift fuel but the 12'' or so from under the deck to the engine can't make a difference and I have never seen a boat with the fuel tank above the engine.

 

[san diego flyer]

Re: Adding Under Belly Fuel Tank

It seems like strange stuff happens on pontoons. Personally I would not want an add-on fuel tank, couplers, lines, and fasteners where I could not physically get to it on the water---but instead would have to pull it out of the water to inspect/fix an issue. Where, and how long, is the filler tube for this under center mount?

 

[Silver Eagle]

Re: Adding Under Belly Fuel Tank

It must be me ,I have my fuel tank above my engine. It's an 2007 StarCraft and I don't have a fuel pump.Tthe fuel is feed by was of a rubber hose that goes into a hand Squeezy to a clear gas filter to the engine. If I don't prime the ball the motor won't run.Just like on an out board.

 

[EGlideRider]

Re: Adding Under Belly Fuel Tank

Sorry Silver Eagle, but you have a fuel pump even though it may not be obvious. If your tank is above the engine, then the pump won't have to work hard and the regulator will control the fuel flow to the carbs or injectors.
Priming the ball is often necessary to remove air from the fuel line.

 

[EGlideRider]

Re: Adding Under Belly Fuel Tank

It must be me ,I have my fuel tank above my engine. It's an 2007 StarCraft and I don't have a fuel pump.Tthe fuel is feed by was of a rubber hose that goes into a hand Squeezy to a clear gas filter to the engine. If I don't prime the ball the motor won't run.Just like on an out board.

I've just realized that I've never seen a fuel tank above the engine of a pontoon during my many years of pontoon ownership. It seems like it would elevate the center of gravity to a point of concern.

Pictures would be appreciated.

 

[Bamaman1]

Re: Adding Under Belly Fuel Tank

I see where so many pontoons have large built in fuel tanks--24 gallons to 50 gallons. I don't go through that much fuel in a year.

Modern 90/10 gasoline is very susceptible to deterioration over time, and all the gasoline companies change their fuel formulations (additives) according to the time of the year. Fuel problems cause deterioration in fuel lines and carbs--and will often rot rubber items fuel is in contact with. Gasoline separation will also cause needle valves to stick, and the resulting drip, drip drip can cause rough engine performance and fouled plugs.

I use two 12 gallon plastic portable gas tanks and a 6 gallon metal factory fuel tank. I can easily drain any of the three, and have never had any fuel related problems of any kind. All 3 tanks are above the level of my engine, and they don't negatively affect the boat's center of gravity in any way.

Answering the question: The only under belly fuel tank I would want would be built into the rear of a center toon or in an aluminum motor mount. I wouldn't want one hanging under the deck of my boat. I prefer to be able to easily manipulate my boat's gasoline.

 

[Silver Eagle]

Re: Adding Under Belly Fuel Tank

If I have a fuel pump where is it, I know it's not before the Engine.

 

[Silver Eagle]

Re: Adding Under Belly Fuel Tank

I have a 30 gallon fuel tank on the left rear and I sit on the right rear So I balance out the tank. Gasoloine wieghs in at around 12 .lbs per gallon. so we are an equal match.My tank is the new anti fouling plastic and the hoses are ethenol safe.

 

[EGlideRider]

Re: Adding Under Belly Fuel Tank

If I have a fuel pump where is it, I know it's not before the Engine.

It's in the engine... With the cowl off, follow the fuel line and you'll locate it.

 

[san diego flyer]

Re: Adding Under Belly Fuel Tank

We have two 25 gallon tanks opposite each other in the rear for balance. We try to use them equally as much as possible. Since our primary use is skiing, tubing, kneeboard, we are on and off the throttle most of the time. We go through 40 gallons in a weekend, probably using it two weekends a month in the summer. Fuel consumption is pretty much dependent upon your chosen use. I can certainly see if one parties, swims, fish that a tank of gas could be stretched much longer.


PS- gas does not weigh 12 lbs/gallon:

"The weight of gasoline is dependent on the temperature, but it also depends on how much alcohol has been added. Today, that's sometimes a lot. So we come up with
1 gallon of water equals 8.33 lbs.
1 gallon of gasoline equals 5.8 to 6.5 lbs.
1 gallon of ethanol equals 6.59 lbs."