fuel tanks 86 46'

As fuel is metered into the engines it is replaced by fuel that is stored in the tank(s). That process eventually lowers the level of the tank(s).

Is that what you wanted to know?

Depends on the boat. Some have one tank feeding each motor. Others have a connection between the tanks that then goes to each motor. The best system is for the cross-over to have a valve so you can seperate the systems; run them together or all out of one. Look near the bulkhead in your engine room for a cross over pipe or follow the fuel line from a tank.

Sounds like you have a single main tank with a reserve. Again, it could be one to the other or you could have to switch tanks manually. Used to work on a 440 Carver that had 2 main and 2 reserve tanks. There were no cross over valves and each tank fed one engine. There was a valve for switching to reserves. I once moved a 36 Carver with just enough fuel to get to the dealer. About 1/3 of the way there the port tranny blew leaving one engine pushing the whole boat and sucking fuel fast. There was no way to transfer fuel from one tank to the other (not even a garden hose for syphoning).
The best thing is to just follow the fuel lines to figure out what kind of system you have. What kind of boat is it?

It sounds like these tanks are fore and aft rather than one on each side, is that correct? Generally, when there are two engines the two tanks are the same size and mounted to each side of the boat. They are often valved so they can be cross connected to feed both engines from one tank, an engine from the tank on its side of the boat, or both engines from both tanks at the same time. This arrangement allows you to manage list or leaning toward one side or the other by using fuel to balance the boat.

If your tanks are fore and aft, they are probably sized to fit the available space and one may well be much larger than the other. You should still be able to feed both engines from one tank and may be able to feed separately. If you have diesels you will have a fuel return line from each engine to a tank. You may or may not be able to switch the return from one tank to the other. This could create spillage problems if both engines are drawing from one tank and the returns are going to the other (full) tank.

It is important that you trace the fuel system and understand how the fuel lines are valved and what options you have available to feed fuel to each engine and generator and where the returns are routed. It is not a difficult as it may first appear and knowing the system well will make your boating a lot more pleasant and much safer.

I have a 1984 43' so they should be the same setup. The rear tank feeds the starboard engine as well as the generator. It is slightly larger because of the generator (20-30 gal?). The front tank feeds the port engine. You should be able to follow the fuel pickup line into each primary fuel filter as well as the fuel return line from each engine's fuel cooler to confirm this.

You probably also have a transfer pump plumbed between the two tanks with a switch on the bridge helm and a breaker on the main electrical panel you want to leave off unless using it. This allows you to transfer fuel between the two tanks in either direction. Because the rear tank is taller than the front tank to fill the space under the cockpit, there is no manual valve to transfer fuel because it could overfill the lower front tank. The pump allows the transfer while also preventing the natural syphon from the rear tank to the front tank because of the physical fuel level difference in the tanks.

Hope this helps.

Finally a Post owner giving advice about a POST! I have an 85 47' Ditto on what this guy just said. Also, mounted on the rear of the aft tank is the transfer pump to get more fuel from that tank if you wish.

Hi,

It is good to have participation from those with intimate knowledge for sure but in the absence of such as appeared to be the case when the thread was started 3 weeks ago any sensible advice is better than none.

I don't see anywhere that you added your own experiences to the thread before just agreeing with another poster.

If you take the time to read the first posts you will see that Marmot has actually posted a reasonably accurate description of the system without claiming to have owned or seen one, this was done soon after the original question which should have been sufficient to help out the person who asked the question.

so someone please tell me how many gallons does the rear tank hold. Have a 46 Post I am delivering and lost both fuel guages. It would be helpful to know how many gallons are in the rear tank. It just took on 137 gallons in the rear tank after a 7 hour run. Like to know how long I should run the transfer pump from fwd to rear on a 10 hour cruise. I'll go through 150 gallons in like 8 hours of run time, be good to know how much fuel to transfer so I dont run the rear tank dry. Many Thanks in advance.

300 front and 350 rear tank

The newer 46/47 has a smaller aft fuel thank. I believe that is to allow for cockpit ER access

Thanks Much. This is a 1985. I believe the difference in capacity is much greater possibly 420 to 200 ? Total capcity from owners book is 620? Very noticible difference in size from the engine room. Any post owners out there that can help.

FOLLOW THE HOSES, from the tanks to where they go. It shouldn't be too difficult to trace them. First figure out if everything draws off of one tank, then you may have a transfer pump to pump from the fwd tank to the aft or a set of valves or vice versa. But should be easy to figure out just following the 1/2"-5/8" hoses from the tanks to wherever they go to. As for the size of the tanks, look on the tops for a capacity plate, or measure them and calculate it.

I carry 300 forward and 350 aft. The genset runs from the aft. The engines are plummed separately. Port to forward and Starboard to aft with genset. Looks like your burning around 20 GPH/engine.

I have the same tankage and fuel draw

Thanks for your assistance. Very much appreciated and helpful