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gpeacock · 30-05-2016, 01:49

Hi all
We have just removed one of our holding tanks and are considering installing a flexible diesel bladder to increase our motoring range offshore. This tank would only be used a couple of times a year so Im not too worried about chafe from constant use. Flexible is looking like the way to go because we need the space for storage as well. The main issue is how to plumb it.
Nauta says It can be plumbed without a vent because it expands as filled and collapses as emptied. With 50Gal of fuel though do I need to worry about too much pressure from daily thermal expansion? What about pressure from it being tossed around at sea?
I plan to fill it via some sort of transfer pump plumbed from my main tank. Once the main tank is drawn down enough I'd pump the bladder empty. The solid state pumps are way cheaper(albeit way slower) but I cant figure out if they can be reversed by changing the polarity... If I spend the big bucks and buy a real reversing transfer pump do I need to worry about pressure blowing up the tank if I forget to keep an eye on the transfer?
Who's set up something like this?
Thanks
Gary

Paul L · 30-05-2016, 02:41

I used a stock fuel pump. Hooked it up with quick release hydraulic lines. To reverse I unhooked the pump and reattached the other direction using the quick releases.

gpeacock · 30-05-2016, 05:08

Quote:

Originally Posted by Paul L

I used a stock fuel pump. Hooked it up with quick release hydraulic lines. To reverse I unhooked the pump and reattached the other direction using the quick releases.

Hey good idea... I didnt know that quick release fittings also had shutoff valves built into them... Not much fuel mess I guess.
Just one fitting on your bladder? No air vent?
Thanks
Gary

SteveSails · 30-05-2016, 05:22

I installed a 25gal Nauta bladder last year. Sprung for the Groco reversible transfer pump and I'm glad I did, makes quick work of filling or emptying the bladder. I did installed a vent line T'eed to the main tank vent, if the bladder overfills then it would just run out the vent and back to the main tank. From what I remember of the Nauta instructions they require a vent for diesel but not for water use.

If you do install a transfer pump add a T with a hose so you can transfer from or to a jerry can. Very handy when it's too rough and wet on deck to open the fuel fill.

Steve

Chuck Hawley · 30-05-2016, 09:13

I added two 100 liter (26 gallon) Vetus tanks to a race boat that I was bringing home from Hawaii. The bladders sat on the inside of the hull with no permanent plumbing. I think there was a fuel fill inlet on the top center of the tank, which was not ideal, but also not used very often. The fuel outlet was a 5/8" barbed fitting to which I attached a few feet of hose, and then corked off the bitter end.

I used an impeller pump from Jabsco that pumped about 5gpm to pump the fuel into the main tank, using a longer piece of small diameter fuel hose. There was no vent, no permanent plumbing, no spillage, etc. Very simple. When I had pumped the tank dry, the transfer pump made a different sound and I turned it off, plugged up the discharge line, and waited until I would need the other bladder (several days later). No vent required.

I could roll up the empty bladders and store them off the boat. They want to assume a pillow shape, so you need to have enough space so they can "fluff out" to their normal shape.

As a cautionary note, the only time I did this was in 1983 when the 67' boat I was captain of lost her 10,400# keel in 12,000' of water, about 300 miles north of Kauai. The boat did not capsize, thankfully, and we were able to power back to Waikiki, although we came close to rolling over on a number of occasions. Had we rolled over with the unrestrained bladders full of fuel, it would have made a terrible situation just that much more terrible, but it's not easy to restrain a full bladder of fuel, unless you have a securely bolted "top" to it's containment area.

Chuck Hawley
Former boat captain of "Charley", Holland 67
Winner of the First to Finish, Transpac, 1983.

exMaggieDrum · 30-05-2016, 09:38

I looked into bladder tanks as an option for increasing my fuel capacity on my sailboat. I remember that every manufacturer specifically said not to put a bladder tank inside of any boat. I would be very cautious. The fellow who did it one time on a special case basis is one thing. Doing it permanently is quite another. I know it wouldn't pass a competent survey.

bongo · 30-05-2016, 10:28

Our boat has a rigid bladder mounted inside the original metal fuel tank. It fits the tank perfectly. We have never found any sign of any condensation inside this tank. It has been in the boat at least 12 ywEA. SO FAR SO GOOD.

Paul L · 30-05-2016, 13:03

Quote:

Originally Posted by gpeacock

Hey good idea... I didnt know that quick release fittings also had shutoff valves built into them... Not much fuel mess I guess.
Just one fitting on your bladder? No air vent?
Thanks
Gary

One bladder fitting and no vent. The bladder was in a somewhat vertical area surrounded by anti-chafe outdoor carpet. In this configuration it would only fill to about 85 or 90% of Max spec, so I didn't feel it needed venting.
T