Aux fuel tank on H50

artboas · Feb 7, 2022

Gianni65 said:
Hello.

I've an Hunter 50 2007 equipped with 3 water tanks, two port and one starboard, this latter of 67 gallons capacity.

By reading around I come under the impression that there are Hunter 49/50 with tank configuration where the starboard tank has been turned to aux fuel tank, and also looking at the aux tank layout (here attached) might point to that idea.

My intention is to do the same, using the stb tank to aux fuel and the question are:

1) such layout is that the standard use Hunter recommended for aux fuel tank, I mean same tank either for water or fuel?
2) material the tank is make for water is also suitable for diesel?

Thanks in advance any consideration on my question.

G

Hi,
Firstly, if you have a 2007, I believe it’s a 49; not a 50
Not that there’s a huge difference where this is concerned.
Hunter did not use the water tank as a fuel tank
They installed an extra tank forward
Then, they had an electric transfer pump arrangement, to fill the main tank from the aux tank.
I’ve never seen this firsthand, but I’m aware of it.
Of course this makes sense that they needed a transfer pump, as there is no way the 2 tanks would level
To the best of my knowledge, the additional tank was in the bow under the bunk, and they had an extra deck fill for this tank.
This isn’t all that complicated, but I believe their drw. Is incorrect. There is no logic to a fuel return to the aux tank. In fact, this would cause issues. The engine and genset both draw fuel from the main tank, and have their returns accordingly. The function of the aux tank (according to my information), was to act as a storage tank that you could dump into the main tank ; hence the electric pump.
I believe this was meant as a one way transfer. Also, the absence of any filters in this drw confirms this.
If, by any chance, you pump more fuel into the main tank than what it will hold, it will flow out of the air breather. Certainly, one has to monitor main tank level before pumping the aux tank into it. This is no different than putting 5 gallons from a Gerry tank into a full fuel tank. It’s going to spill somewhere .

ice breaker · Feb 8, 2022

Artboas:

The reason that you need the return line is incase you walk away while transferring fuel. Trying to put 35 gallons into a tank that only has space for 20 is the reason. It needs a return path else it is going to get pumped out the vent line.

In 2004 when they launched the 41AC, standard tankage was one 33 gal tank. If you added the genset then they added a second 19 gal tank with the transfer system. I believe that the 2005's all went to a single 50+ gallon tank to simplify things.

The return line has saved my butt a few times when distracted. My current SOP, is never leave the NAV station when transferring fuel.

artboas · Feb 10, 2022

ice breaker said:
Artboas:

The reason that you need the return line is incase you walk away while transferring fuel. Trying to put 35 gallons into a tank that only has space for 20 is the reason. It needs a return path else it is going to get pumped out the vent line.

In 2004 when they launched the 41AC, standard tankage was one 33 gal tank. If you added the genset then they added a second 19 gal tank with the transfer system. I believe that the 2005's all went to a single 50+ gallon tank to simplify things.

The return line has saved my butt a few times when distracted. My current SOP, is never leave the NAV station when transferring fuel.

Yes, I thought about this, but I think you’d still get fuel out the vent line. The fuel line is only 5/8”, and the vent is probably 5/8 or 3/4.
But, you clearly have more experience with this.
I think the idea of removing the water tank & replacing with fuel is not feasible. You’d have to pull up the floor, cabinetry, etc. major ripup
There’s room in the fore peak, so that is only logical

artboas · Feb 11, 2022

artboas said:
Yes, I thought about this, but I think you’d still get fuel out the vent line. The fuel line is only 5/8”, and the vent is probably 5/8 or 3/4.
But, you clearly have more experience with this.
I think the idea of removing the water tank & replacing with fuel is not feasible. You’d have to pull up the floor, cabinetry, etc. major ripup
There’s room in the fore peak, so that is only logical

artboas · Feb 11, 2022

After racking my brain, I now recall a 49 that had the aux fuel tank installed. It was definitely in the forward cabin under the bunk, I also recall the fuel hose, and it was nominal diameter. Likely 3/8” as used for the engine.
When I did my “filter project” this summer, I found that the engine used 3/8” hose, and the genset 1/4”
The overflow vent fittings that Hunter used for their tanks all had 5/8” hose.
So, I agree that a return line would, in theory, provide a return path for an overflowing main tank.
But, it would have to travel through approx 40 feet of hose, versus a much shorter run to the rear vent, with lower restriction.
I don’t believe there was a fuel guage on the aux tank. The way that the h49 / 50 sensed fuel was through the Teleflex engine system. The tank sensor fed into the Teleflex 5600 unit, which then converted it to N2K data.
This was visible (if you want to call a useless monochrome quirky display visible) on the Teleflex display in the cockpit.
Of course, the smart thing to do was pipe this into the raymarine plotters, which had a full Color engine page display. I never even took the plastic cover off the Teleflex after I did this upgrade.
So, all I’m saying is that I wouldn’t place a huge bet that the return line would keep fuel from exiting the vent. My specialty is electronics; not hydrostatics. There are clear cut formulas that would prove this one way or another.

Tally Ho · Feb 11, 2022

In theory, but if the other tank is full, where is the return line going to go?
Maybe I am not understanding…

A fuel return is used to take unused fuel from the engine back to the tank. It is not an overflow line. The vent line is also not an overflow line.

Having a good idea what is in the tank, and much to fill it is critical to not overflowing the fuel tank.

Greg

artboas · Feb 12, 2022

Tally Ho said:
In theory, but if the other tank is full, where is the return line going to go?
Maybe I am not understanding…

A fuel return is used to take unused fuel from the engine back to the tank. It is not an overflow line. The vent line is also not an overflow line.

Having a good idea what is in the tank, and much to fill it is critical to not overflowing the fuel tank.

Greg

Greg,
I think everyone has been guilty at one point or another of pumping a bit too much fuel only their diesel tank, and having some come out of the vent. Same as water tanks, but not as messy.
I agree, of course that the return from the engine and genset is used to capture unused fuel running in the fuel galley during normal running operation. That’s how diesels work.
But, specifically, the question here was the rationale and efficiency of having the return line on the aux tank used as a pumping overflow relief.
Clearly, the vent on the main tank is used as the vent for the aux tank as well.
When I’m rinsing my head tanks, I’ll get “leakage” out of the vent before it starts coming out of the deck fitting. Same thing with my water tanks, On that subject, I’ve got 3 tanks. They are all connected together at a manifold in the bilge. When I’m filling one, it is cross feeding to the other ones, but is limited by the 5/16 whale pipe size.
So, I’ll definitely see water out of the vent from the tank I’m filling long before all 3 tanks are full. Once again, it’s all about hydrostatics, line loss, feed pressure and filling speed.
I know one of the “gurus” who used to work at Hunter. I’m going to reach out to him, and get his opinion.
I believe the aux tank option was very rare on the 49/50. On all of the listings I’ve seen over the years, I’ve never seen one with this specified.
Lastly, it’s curious that on the Drw for the aux tank it’s marked “preliminary”, and no other drw are listed on file.
I believe that the actual implementation of the tank would have included it’s own vent line, as you clearly needed to have a fill fitting as well.

ice breaker · Feb 13, 2022

On our 41 with two tanks, there are two separate fills and two separate vent lines. I can not comment on a 40 foot return line as my tanks sit side by side.

Tally Ho · Feb 13, 2022

artboas said:
Greg,
I think everyone has been guilty at one point or another of pumping a bit too much fuel only their diesel tank, and having some come out of the vent. Same as water tanks, but not as messy.
I agree, of course that the return from the engine and genset is used to capture unused fuel running in the fuel galley during normal running operation. That’s how diesels work.
But, specifically, the question here was the rationale and efficiency of having the return line on the aux tank used as a pumping overflow relief.
Clearly, the vent on the main tank is used as the vent for the aux tank as well.
When I’m rinsing my head tanks, I’ll get “leakage” out of the vent before it starts coming out of the deck fitting. Same thing with my water tanks, On that subject, I’ve got 3 tanks. They are all connected together at a manifold in the bilge. When I’m filling one, it is cross feeding to the other ones, but is limited by the 5/16 whale pipe size.
So, I’ll definitely see water out of the vent from the tank I’m filling long before all 3 tanks are full. Once again, it’s all about hydrostatics, line loss, feed pressure and filling speed.
I know one of the “gurus” who used to work at Hunter. I’m going to reach out to him, and get his opinion.
I believe the aux tank option was very rare on the 49/50. On all of the listings I’ve seen over the years, I’ve never seen one with this specified.
Lastly, it’s curious that on the Drw for the aux tank it’s marked “preliminary”, and no other drw are listed on file.
I believe that the actual implementation of the tank would have included it’s own vent line, as you clearly needed to have a fill fitting as well.

I guess I just don’t see a “return line” preventing an overflow (if that is what you are suggesting). The flow from the pump will easily be more volume than the return line can take away (even if it does have a place to go). It doesn’t work that way on an “individual” tank.

Fueling up can make a mess, but with care, it shouldn’t cause a spill.

Greg

CliveCollett · Nov 23, 2022

I own a 49 with the extra fuel tank!!
It is on the starboard side under the floor in the galley instead of the third water tank. It is a 200ltr stainless steel tank with a level sensor connected to the Werma multiple tank system.
There is a separate deck filler and vent for this tank.
The transfer pump on my boat goes through a large Racor filter before going to the main tank. If I leave the return line open it will circulate between the 2 tanks. I assume this was done to provide a small volume polishing system. So far I have only used it once as the boat came with full tanks and I have not refilled yet as we have been fixing and upgrading.
All of this was fitted as part of the original build. The PO added just about every optional extra there was.

Aux fuel tank on H50

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