Dirona carries 1735 gallons of diesel for the main engine: 835 gallons in each side tank and 65 gallons in the day tank. (We also have a 10-gallon supply tank for the auxiliary engine). Although 1735 gallons would have been fine for the roughly 2,000nm trip between San Francisco and Hawaii, we added 532 gallons in cockpit bladder tanks for that run. We did this for two reasons: 1) it allowed us to run faster (at additional fuel cost) and 2) we wanted to test the practicality of fuel bladders for longer offshore runs.
We went with ATL FueLocker bladders. ATL bladders had a good reputation with other boat owners, and from his car-racing days, James knew they could smack the wall at 200 MPH without leaking. We bought two 300-gallon bladders with tie down-kits–these would come close to filling the cockpit, leaving space to walk around them, but little room for the bladders to shift should they come loose. The only question was how the extra weight would affect boat trim.
We air-filled the bladders with a vacuum cleaner so they would be roughly the right size and shape as when filled with fuel, but light and easy to move. Once we’d determined the positioning for them, we installed extra pad-eyes on the cockpit walls and on the floor under the barbeque console to attach the tie-down straps.
We also purchased SunShields for the bladders, mainly to protect them from UV rays. But they also provide abrasion and heat resistance. And on the trip across, the straps did wear the covers a bit, so we were glad to have them. The picture below shows the bladders ready to be filled in Oakland with the SunShields on. We filled the bladders with air first to get everything properly placed, then deflated them just prior to fueling. Our teak chairs and the flopper-stopper plate are secured against the aft cockpit wall. We normally secure these on either side of the cockpit, but the bladders filled that area. And the folding table, normally strapped-down by its base in the cockpit, is secured to the starboard walkway.
When we put the pad-eyes in for the bladder tie-downs, we also installed two in the ceiling above each bladder to support the fill standpipe when fueling. We tied a small line to the standpipe, ran it up and over the pad-eye to a cleat and adjusted the line as the bladders filled. The bladders are spec’d at 300 gallons but felt fairly full at 266, so we stopped there. It may have been possible to fit considerably more in, but we didn’t push it.
With the bladders full, the boat did go down a couple of inches at the stern, but the swimstep was still well above of the water. We were carrying 2,277 gallons of diesel: 835 in each supply tank, 65 in the day tank, 10 in the wing engine tank and 266 in each bladder. #2 diesel weighs 7.1 lbs/gallon so the total weight we carried in fuel when we sailed from Oakland was 16,167 lbs. That is more than half the weight of our previous boat, a 40’ coastal cruiser.
Below are shots taken underway. The bladders seemed quite secure, with no obvious impact on boat trim.
The bladders are not very stable when partially full, so we emptied them completely on the third day out when the main tanks had drained enough. To transfer fuel, we had installed a half-inch fuel hose from a Camlock quick-connect fitting at a bulkhead in the cockpit back to the fuel manifold. A short section of hose with Camlocks on either end connects the bladders to the bulkhead fitting, with a valve at each bladder end to control flow.
This way we can use our fuel transfer pump to pull fuel directly from the deck bladder tanks, through a filter and into one of the side tanks. This had several advantages over the more standard method of pumping from the bladder into the deck fill using an external pump:
- No-one had to be on-deck during the fuel transfer. All that was required was a quick step outside to open the valve on the tank to be drained.
- Our fuel-transfer pump can drain each bladder in about 80 minutes, limiting the time where a bladder is partially filled. One of our many factory upgrades was to replace the 43 GPH Walbro 6802 pump with a 822 GPH a Jabsco VR050-1122. Hose and plumbing restrictions take it down to an actual, but still respectable, rate of about 231 GPH.
- The fuel coming from the bladders is run through a 25-micron filter before entering the tank.
- We didn’t need to buy and store an additional pump, and likely a spare, to empty the bladders.
We left the empty bladders in place on deck for a few days, with the tie-downs tightened to hold them securely. On a calm day underway, we tilted them to drain the last 20 or so gallons out, hosed them down and stowed them in the flybridge brow.
When we arrived at Hilo, we had used 1,746 gallons so were 12,397 lbs lighter. Here are our fuel stats for trip:
- Duration: 296 hours (12.3 days)
- 12 hours less excluding Hilo offshore wait: 284 (11.8 days)
- Fuel: 1746 gallons consumed
- Distance: 2028 nm
- GPH: 5.90 gph
- MPG: 1.16 nm/gal
- MPH: 6.85 kts (7.14 kts not counting the Hilo wait)
- Fuel at Oakland:
- Main tanks: 1670 gal
- Supply: 65 gal
- Bladders: 532 gal
- Wing: 10 gal
- Total: 2277 gal
- Fuel at Hilo:
- Main tanks: 456 gal
- Supply: 65 gal
- Wing: 10 gal
- Total: 531 gal
Ironically, we arrived in Hilo with almost exactly the full bladders’ worth of fuel.
Update 2018/08/15: More detail on our fuel bladder system, including a third bladder forward, is at Fuel, Option Value, Speed, & Safety.