Fuel Tank Mounting

[drewpster]

Ok I came up with an idea on how to go about mounting my fuel tank and batteries to ballast the way I want it to. I want to mount the tank in the middle and the batteries to either side of the hull under the splashwell of my tri-hull. The problem I have is that the deck drain in the transom is in the traditional location in the middle/ bottom of the transom. If the tank is in the middle it will block access to the drain.
Here is what I want to do.

Moeller makes a 19 gallon tank that is longer than it is wide.

I want to build a shelf a few inches off the deck to mount this tank on. It will allow access to the drain under the tank. Then it will be a simple matter of mounting my battery boxes in front of the tank to either side. walla equal lateral ballast.

I have some concerns. First, I will have to make sure it will fit. Next I am concerned about elevating the weight of the full tank off the deck. It will be heavy when its full. You think maybe four inches or so would be to high? I am also concerned about the design of the tank itself. I assume the pickup in the tank drops in the middle. Is the engine going to starve for fuel as the boat rolls through turns when the fuel gets low?

This is all moot if the tape measure wont allow me to mount it this way. And I am not looking forward to building the shelf. But it is an answer.

What do you think?

 

[Greg Mrozinski]

Re: Fuel Tank Mounting

Drew,

Raising the tank will elevate your center of gravity/bouancy but I don't think it will matter much. Securing the tank is a valid concern. If you plan to secure it to the shelf than you have to make sure the shelf itself is well secured to handle the shifting weight. As far as the pick-up goes I don't think you need to worry too much about that. The fuel pump will keep the pressure up to the carbs even if the pump draws a few bubbles of air. Go and take some measurements.

 

[Mark42]

Re: Fuel Tank Mounting

Having mounted a 17 gallon permanent tank under the splash well last year, I have to say that the weight of the tank & fuel (about 133 lbs) plus two 800 cca batteries will come to 200 lbs. If you were running with a single battery and 6 gallon tanks before, the added weight to the stern will be a big issue.

For example, my 16' cuddy cabin had a 9 gallon "portable" tank that had to be removed and re-fit into its "cubby hole" under the splash well every time we went boating. The boat has one 800 cca marine battery. Its big and heavy. could easily get away with a much smaller batter for starting purposes.

The result of the 17 gallon tank was that when the tank is full, and the boat is full to its capacity, the boat would just not get on plane easily. Ended up adding Smart Tabs that were not needed when running on a 9 gallon tank. That small difference in load made the boat handle much differently.

I have plans to move the battery up to under the cuddy v-birth, as well as add a second battery to run the kids video screens and stereo, pc plugins, etc. Believe me, we had all this stuff running earlier this week, but I had a spare battery to swap in if needed.

My suggestion is to plan on mounting the batteries in the bow, or somewhere farther fore than the transom. Use 6 or 4 gauge wire, and make the run. Using dual batteries, you need a battery switch, ($40 or so) plus the extra 12 - 14 feet of battery cable to make the 8-10 foot run up front.

Regarding my personal experience with raising the tank, the fuel tank I added is much taller than what came in the boat, and that added height of fuel does affect the way the boat handles, especially in turns. The higher the center of gravity, the farther over the boat leans in turns.

Just something to think about.


Good luck!

Mark

 

[Greg Mrozinski]

Re: Fuel Tank Mounting

That is how I am going to set-up my boat. Tank in the back and batteries up front.

 

[drewpster]

Re: Fuel Tank Mounting

Actually, other than the additional battery and a couple of extra gallons of gas, the weight will be close to the same as original. Originally the boat came with a 12 gallon tank. Sounds like allot I know, but this boat came from Florida. I assume that is why it had a larger tank. Most of the boats I have seen from the coast have larger tanks. Guessing? It is a concern however given the larger engine. The new cores should be ok because even after all the work I could lift the stern by hand. It is heavy, but lighter than I thought.
I plan on floating the boat once the engine is mounted to be sure before getting too far along.