gas tank building

[bushbunny]

Hello Everyone
I'm not sure if this is the right forum to post this in but he goes. I'm building a sorenson runabout and I have a question concerning gas tanks. I'm going to build two gallon and a half tanks to hang off each side of the transom.I'm going to connect both tanks with a hose, what I need to know is. The tank on the starboard side will have the fill tube (1 1/2inches) and the other on the port side will just have a hose from the fill tank connecting it and a breather tube. My question is should the hose connecting the two tanks come out of the botom of the fill tank and go into the top of the other tank?... Or should it also go into the bottom of the other tank? I'm thinking of using a 1/2 inch hose to connect the two tanks so they will fill faster. Or should the hose go into the middle of the tank?

Thanks
BB

[Timm]

I don't know what the rules are in Canada, but here in the US we aren't allowed to put any fittings in gasoline tanks other than in the top. I would put fills in both tanks and some type of 3-way valve that will allow you to switch tanks. I have done this before using shut off valves on each tank. The owners would play with the two valves until they found a "sweet spot" where fuel would flow equally from each tank. Thus it worked the same as if they only had one tank.

[bushbunny]

Hello Timm
Fills in both tanks just wouldn't work for this application, I need to fill both tanks at the sametime while on the fly. Thats why I'm thinking of the balancing hose connecting the two tanks. I want both tanks to drain at the sametime and when filling I want both to fill quickly.This is for a racing application and I need to refuel without stopping or passing a tank between boats. I need to be able to fill both tanks in a hurry. It will be like when a fighter plane refuels in the air, same idea as that. Thanks for your idea about the valve but that just wouldn't work for me.

Thanks
BB

[bushbunny]

Someone must have some thoughts on this subject?
Please help with your ideas.

Thanks
BB

[mmd]

Timm is correct about fittings on the bottom of the tank. Fuelling up whilst underway is certainly not reccommended, but racing tends to eschew safe practices. I would suggest finding a positive-connection fuel spigot for your re-fuel hose so that wind will not siphon a spray of fuel out of the open fill pipe - in such close proximity to the hot, running motor might this might lead to your becoming a very large marker flare. Possibly to overcome the bottom-fittings problem you could fabricate a fixed pipe between the two tanks effectively making them structurally one tank. Aluminum for both tanks and connector pipe would be my choice. Be sure to pressure test the completed unit to DoT regs.

[bushbunny]

Howdy MMD
I like the idea of the positive gas fill connection but th solid pipe wouldn't work unless it was small. But then it makes me wonder about flexing.If my boat flexes from hitting waves hard that solid pipe might break. Thats why I was thinking steelbraided hose. The part that really has me stumped is where the hose should exit the fill tank and enter the other tank. The outboard will be between both tanks so that will determine what size of hose I can run between the tanks.
Thanks for your suggestions.

BB

[Timm]

I have no idea what your boat looks like, but could the fuel tanks actually be one tank that is shaped to fit around the aft end of the engine? I am thinking of a U-shape when viewed from above, with the bottom of the U connecting the two tanks into one. Then you would eliminate all the plumbing. Just a thought!

[bushbunny]

Timm
That wouldn't work because that U-shaped tank would be huge in order for it to wrap around the outboard. The reason I'm going this route is because the boat I'm building requires alot of air under the hull to make it go fast. That is why I want the tanks hanging off the back of the transom on each side of the outboard. That will put the added weight behind the pivot point and should allow for better weight transfer so the bow will ride higher out of the water.

I hope this links works so you can see what the boat looks like.

Thanks
BB

[Willallison]

Leaving aside awkward issues like legality for a moment....
How do you intend to draw fuel from the two tanks? 2 Fuel lines with a valve that you change over when one tank's nearly empty?
One problem I see is that if the 2nd tank fills from the top, then it won't begin to fill until the 1st tank overflows into it. Similarly if you hope to draw off only one tank (say #1) then you will have to have #2 filled from the bottom. And they won't 'balance' unless the tube runs from the bottom of one tank to another.

This might be a simpler, safer and better solution - a small tank that clips onto the transom....
http://www.westmarine.com/webapp/wcs...=78&storeNum=6

[bushbunny]

Hello Willallison
I will draw fuel from both tanks at the same time with single hose going into the fill tank. I want the two tanks to balance each other as the gas is burned off. Now I'm beginning to get a handle on this set up. From what I now gather both tanks have to have the hose connecting them in the bottom so they will fill equally and drain off equally. Correct me if I'm wrong on that? What I'd trying to accomplish is to fill both tanks fast while on the fly. That transom mounted tank is a great idea but filling it behind my back might prove to be dangerous while going 35mph in a river laced with curves and gravelbars. Not to mention the 20foot riverboat beside me going the same speed and only 6 feet away. The fill pipe (1 1/2") will be near my left hand so I can still drive and look where I'm going as I refuel. I hope that info helps more Will?
So the balance tube should be on the bottom edge of both tanks but when filling will both tanks fill to the maximum?
*banging my head on my desk* laughs
How can something that sounds so simple become so difficult and hard for me to get a handle on. I'm guessing now that the weight of the fuel entering the fill tank (#1) will force tank (#2) to fill providing tank (#2) has a vent to release the air?

Gawd I won't be working for NASA anytime in the near future *laughs*

Thanks for your input Will
Your words of wisdom opened my eyes on a few good points *smiles*

Thanks
BB

If you are filling with a pressure feed, the transfer pipe best be large enough to transfer the fuel from one tank to the other fast enough.

Bunny,
Looking at your boat, it seems to me that you might be better off building one long (laterally) tank atttached to teh forward side of teh transom, with baffles, of course. Your trim aggle should be about 5 degrees for minimum drag and you should be to achieve this angle just as easily with the one inside tank as with the two small tanks on the transom and the rest of the fuel and the pump stored further forward.

Methinks you may be too busy driving to do the tricky transfer anyway, not to mention the safety and polution problems..

Before you go to all the trouble of the hanging tanks and pump rig, diagram the longitudinal moments of the weight distribution of both schemes. Do this for full tanks and as the fuel is used up. My guess is that you may be chasing small returns with great effort. Loss of concentration while you are making the necessary fuel transfer could easily lose more than the gain, if any, achieved by having the small tanks aft of the transom.

Since you may be heavier than the boat plus fuel and engine, moving your weight slightly will affect the trim more than the fuel placement.

Tom Lathrop

[gonzo]

If you fill one tank with a 1 1/2" hose and the transfer hose is 1/2", the second tank will be about 1/8 full when the first one overflows. I think two 1 1/2" fills would work better. Run the fills over the transom and tee them together. Both tanks should fill aproximately at the same time.