Fuel delivery system question

[coyote454]

I'm presently in the process of purchasing a new (to me) Mainship 34. This has a fuel delivery system I haven't seen before and the broker wasn't familiar with it either. I plan on contacting the present owner before taking the vessel from Anacortes to the new port in Oregon, but has anyone seen this before? There's a valve for choosing the return diesel to go to the port or starboard fuel cells, with a timer for fuel transfer. There's also another valve for choosing which fuel cell will be drawn from. As there is only one fuel gauge on the instrument panel, I'm assuming you draw from one tank and then transfer fuel to that tank when the level gets low. But why do this? Seems odd. Ideas?

 

[SeaDogAK]

Lots of boats have a fuel manifold with one set of valves to close which tank to draw from and another set of valves to choose where the return fuel goes. Normally you’d have both the same but you could have them different if you want to transfer fuel from one tank to another. One reason to do that might be for weight balance.

It’s dangerous to draw from one and return to another because you could overfill a tank, which would result in the excess going out the vent, either in the water or in the bilge. I’m guessing that’s the reason for the timer, though I’ve never seen a timer on a fuel manifold. Fuel polishers have a timer.

It’s puzzling that you have only one fuel gauge but two tanks. You might locate the fuel gauge sending unit and see which tank it’s on.

 

[coyote454]

Thanks, SeaDogAK. I get the balancing of the boat but I would think both returns lines going back to both tanks, and both tanks being drawn from via a single feed line would be a lot simpler system. My last single engine, dual tank CHB was plumbed this way without problems. Thanks for the help.

 

[CharlieO.]

When I replaced my tanks I used a single valve (Groco six port) that directs pickup and return to the same tanks with one handle. I like simple. Both tanks have sending units, just haven't gotten the gauges yet.

Not that I'm really answering your question.

 

[SeaDogAK]

Thanks, SeaDogAK. I get the balancing of the boat but I would think both returns lines going back to both tanks, and both tanks being drawn from via a single feed line would be a lot simpler system. My last single engine, dual tank CHB was plumbed this way without problems. Thanks for the help.

Being able to just draw from one tank at a time allows you to use the oldest fuel first, for one thing.

 

[coyote454]

CharlieO, I'll look closely at the fuel delivery when I get the boat to the new port and make changes as necessary. Possibly a second gauge as suggested by SeaDog or rerouting the fuel into one line as you've done. I'd just never seen a setup like this one has, especially with the transfer transfer timer.

Thanks for the suggestions and insight.

 

[Jeff F]

As there is only one fuel gauge on the instrument panel, I'm assuming you draw from one tank and then transfer fuel to that tank when the level gets low. But why do this? Seems odd. Ideas?

Maybe there is a toggle switch to read between the two tanks with a single gauge? I had that arrangement on my old Mainship.

 

[coyote454]

Jeff F, I'll check for that when I see the boat next. Did you also have the fuel delivery as in the picture I attached? The fuel transfer timer kind of threw me. Hadn't seen that. Thanks.

 

[coyote454]

Jeff F, I just looked again at a picture of the control panel of the Mainship I'm purchasing and sure enough...there's a toggle switch right under the single fuel gauge. Never noticed it during sea trials.

Wish this vessel was closer to check out the systems, but I guess in the 600 mile trip down the coast a lot will be discovered. Thanks for waking me up!

 

[Bacchus]

Coyote454
Just a suggestion for future reference.
There are several Mainship 34 models with different systems.
I'm guessing you are referring to a MS 34P (Pilot). The 34T (Trawler) has some very different equip & systems. The same holds true for different mdel years as the 34T had several versions over the years.
There is some useful MS info in the Marlow-MS section.

 

[Lepke]

Letting the fuel decide which tank to return to can lead to listing and overfill problems. Running with the wind or waves on one side can induce a list that the fuel will follow, returning to the down side tank.
It also depends on how much fuel is returned. Small engines, not much. Detroits 30gph+. Bigger boats draw and return to a day tank, pumping from other tanks into the day tank as needed.