Dual Tank Flow Issues

[TheBronze]

Fuel tank questions.

Last night I ran out to Apple Tree Cove to test out fishing gear and try and find fish. No luck there. Before going I dropped around 3 gallons in each tank to top them a bit. According to my gauges, I had 5 gallons in each. We ran up to the cove, played around, then ran back to Poulsbo. I noticed that the stbd fuel tank appeared to be draining down faster than normal and the port tank looked like nothing was happening. Well, around Keyport the engine stalled out and the bulb wouldn't prime. I had run the stbd tank dry (I think) and it was sucking enough air to cause the port tank to not feed. After disconnecting the stbd tank and re-priming, we were on our way.

Question is: How do the rest of you run dual tanks? I would prefer to have both tanks feeding at the same time, but perhaps that isn't realistic? I can certainly switch them out with my quick disconnects, but would rather not. Wondering why both tanks fed for a while and then the port one stopped.

Another question. Tank sending unit calibration. When I installed the sending units I thought I did it right. First fill of 5 gallons put the needles at 1/4 tank. 2nd 5 gallons brought them to 1/2. As I ran last night, the stbd gauge was showing above 1/2 when I set out and then 1/4 tank after it ran out, but obviously was in error. I am using Moller sending units and they are brand new. Anyone have issues with these units? Calibration tips?

The good news in all of this is that it looks like I went to Apple Cove and back on a little more than 3 gallons. Not bad!

Thanks guys!

[Skagitguy]

John, I can talk only about your first question. I personally like to run on one tank at a time as that way i know exactly how much i have burn in the 12 gal tank #1 and 12 gals tank #2 i know is still full. I do have a 4 way fuel switch for the three 12 gals tanks and the off position . If this is going to be a long journey ( Alaska ? ) i place the extra 12 gal tank #3 into the boat as a back up but most of the time i only use two 12 gals tanks.Some people like to run their tanks dry and then it is hard to start when that Jumbo ferry is bearing down on a person after switching their discounted line to the other tank quickly i feel is hard on the motor as well. I have heard it is hard on a motor running it out of gas. That's why i just have the other person who is with me go back and flip the fuel switch to the other tank when it looks like it is getting low. As far as calibration tips i have found out you can't trust ANY of the gauge on the market. Back in 1999 i had a brand new boat with a 454 I/O that even that you could not trust the gauges. You might look into a electronic febelflector unit. Those work every time !

I fill the 12 gals tanks to about 10 gals only as i don't want any spillage. As far as the balance of the boat being you are emptying one of the tanks first, i just trim it out a little bit with the T&T from the motor.....no problem. That's my 4 cents worth.

[GregJ]

John, I do what Chuck has been doing. I can carry 5 12 gal. tanks if I want but usually I run with 2. I tend to use the weight of the fuel as ballast when I am alone. My whole thing about my boat is to keep everything as simple as possible that is one of the reasons there are no side tanks with sending units.

[TheBronze]

Thanks guys. I'll start running tanks individually. I'll probably have to get a 3 way valve, but for now, I can use my quick disconnects. I'm confident in this now because I figured out the issue with the gauge yesterday. Part of the main harness had come off and was causing the gauge to read incorrectly. After running around and getting potentiometers, resistors and fiddling with it, I caught the issue towards the end of the day yesterday. It's all back together and reading correctly for the fuel I have in it. Yay!

Good news is, I ran the boat 7 times on 13 gallons. Not bad! Just a 2-4 gallon usage depending on the trip. I'm pretty happy with that consumption.

[Helmar]

I have mine set up with a valve to switch from saddle tank to saddle tank. I also got tired of the fuel sending units not being accurate so I just poured in enough gas until it started coming out the fuel line.
Put the fuel Stick in, filed a notch and called it Empty. It was to hold 20 gallons but I lost a little in the bottom of the tank. I put in 5 gallons, called it 1/4 of a tank, put in another 5 gallons, called it 1/2 full and up to the top.
That fuel checking device has never failed me either.
I knew what she used for fuel (Volvo B-18 with dual webers) and as long as I kept her down under 3k (right at about 16mph cruising speed) she just sips fuel like my Bearcat.
I filled both tanks, left Port Townsend, went up and though the cut to LaConner for the 50th, down around the other side, waved at Everett, came around the lower side of Whidey and all the way back up to Port Townsend.
I still had at least 9 gallons of fuel left.

Here is the kicker. I had the old Glass tanks. Fuel Out was down on the bottom of both tanks. That fuel line ran back along the floor and into a filter that was down low, over the the Volvo fuel pump.
I never had to use that switch, my fuel went down evenly.

So, big question, does your tanks have the fuel outlets on Top or bottom ?

[TheBronze]

Fuel siphons off the bottom of the tank with fittings up top. They have to go up, along the gn'l, and then to the center of the transom to a fuel filter, then back up and out to the engine. There really isn't any way to keep the lines above the top of the feed tube either. I may need to re-run the lines though. Can't remember if I used the same diameter line on both. That will be a check for later in the season at this point though. She runs fine off of one or the other, so switching will be acceptable until then.

[Skagitguy]

John, Look at the line and it should say what size the lines are Coast Guard reg's. Mine are 5/16 for the forwards 12 gal's tanks and i had about 15 feet of 3/8 line that was left over from another boat project for the third 12 gal and i will use about 5 feet of that line for the back up third tank if i need one about once a year....maybe. Being i had a four way fuel switch in my box of things i decided to use it on this boat instead of a three way one i have as well. I like to leave the quick disconnects alone as one time i did switch a line and the quick disconnect unit ( Merc ) came apart. So when i'am out on the high seas i just like to turn a switch.

[TheBronze]

A switch will definitely be easier. Fancy would be an electric one so I wouldn't have to get down under the seat. But fancy is spendy, so it will be a manual.

[Bflaherty]

As cool and handy as electric would be... It is really just one more electronic to corrode and ultimately fail... I have always followed he "KISS" methodology...

[Skagitguy]

Here's some pictures of my fuel lines going back to the fuel switch and on to the fuel / water separator unit and then to the motor. I have had this setup on about 5 boats and never a problem going kind of up hill to start with the fuel hose thru the pvc pipe back to the outboard motor or I/O .In this case it's going over to the starboard in the stern to hook up to the fuel switch and on to the motor.

[McSkagit Tim Jones]

The reason the fuel draws off one tank when the valve is set to both is due to the heel of the hull. Pretty difficult to keep the boat perfectly trimmed so that the height of each tank is the same. If one tank is higher than the other it will draw from the higher tank.

I use Wema senders in my fuel, water and holding tanks. Only one moving part. The first ones I bought ten- fifteen years ago were made in Norway. Recent ones I bought are made in China. Very accurate and very dependable. Never had one fail. Work with most common instruments. The best! Not the cheapest, but not expensive either. One of the more important components of your boat, especially if you have built-in tanks....

Cheers,

Tim

[TheBronze]

Ya, it is all making sense to me now. I'm just running off of a single tank at a time. They are big tanks for this size of a boat, so I'm not too worried about getting stuck in a bad spot.