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Author Topic:   Adding a fuel tank
JJN3 posted 08-08-2005 02:17 PM ET (US)   Profile for JJN3   Send Email to JJN3  
I seem fixated on the topic of fuel....however....

Has anyone ever heard of anyone who has added additional fuel capacity to a Conquest? Our 275 is about 25 gallons less than I am comfortable with for a canyon run from the Cape May area. Based on an average of about 1.3 NM/Gallon, I can make Wilmington and troll for six hours, returning with about 38 gallons. There seems to be adequate room under the floor of the Conquest for an additional fuel cell; was wondering if it has ever been done (and who would do the install for something like that).


LHG posted 08-08-2005 06:12 PM ET (US)     Profile for LHG    
Although I have no familiarity with the 275, my recommendation would be to use the red on-deck Tempo or Moeller portable fuel tanks, which range in size from 12 to 27 gallons. They make sizes which will fit under stern seats, etc., or just sit in a corner of the boat.

You will have to decide how you want to use it/them and what sizes make sense. One tank for each engine, or just one tank feeding only one engine. In the latter case, the portable tank is used up first on one of the engines, then it, too, draws from the main tank. If you do one tank for each engine, a nice safety factor is to run the main tank dry, and then switch the engines to the portable tanks. This way you will know EXACTLY how much fuel you have left.

To incorporate into the boat's fuel system, all you need to do is insert a Tempo 3-way selector valve (about $15 bought right) into the fuel line AFTER the water sep filter, and BEFORE the primer bulb. The you can select the source of the fuel. On my boat, I have the fuel hose for the aux tank(s) permanently rigged and coiled up, for aux tank use if being carried on board for extended range. The end of the fuel hose has the tank connecting barb. All you do is plug it in to the aux tank and flip the selector

JJN3 posted 08-09-2005 07:19 AM ET (US)     Profile for JJN3  Send Email to JJN3     
I was looking at the Tempo tanks yesterday, trying to decide if I could rig something up with one of them under the deck. I was not sure how to best set them up in the fuel line; an interesting solution though, thanks!
handn posted 08-09-2005 09:21 AM ET (US)     Profile for handn  Send Email to handn     
On a cruise, we carried 50 gallons additional fuel in our 305 Conquest by carrying plastic cans in the stern. When it was time to add fuel, we siphoned fuel into the mains. This involved lifting the cans onto the gunnels at calm anchorage. In rough water, fuel could be pumped into the mains without moving the tanks.
When the cans were empty, we lashed them to the bow rails to get them out of the way.
I didn't want to alter the factory fuel system by adding connections for Tempo tanks.
Try trolling with one engine. With one engine powered at 2100 rpm, speed was about 7 kts. With two engines powered at the same rpm speed was 8 kts. Gallon per hour fuel consumption is cut in half and the boat averages 2 nautical miles per gallon while trolling.
Conventional wisdom says the higher speed is better for blue water trolling but we do at least as well at the slower speed because the flat lines run in blue water and are visable to the fish. The boat produces much less white water at 7 kts with one engine powered.
JJN3 posted 08-09-2005 12:22 PM ET (US)     Profile for JJN3  Send Email to JJN3     
Handn, were those numbers from four strokes or two strokes?
Plotman posted 08-09-2005 01:55 PM ET (US)     Profile for Plotman  Send Email to Plotman     
Larry - why wouldn't you splice in an auxiliary line ahead of the water separating filters? I realized that the likelihood of water accumulating in a portable, on deck tank is fairly low, but you never really know when you will get a bad load of fuel from a marina tank. Is there a downside to running it through the filters?

John - I would not put a standard on-deck tank below decks, or if you did, you would need to make absoluetly sure that the vents were closed tight while it was below deck and bring it up on deck before you use the fuel. I think you run too great a risk of accumulating fumes below deck if you tank vents into the bilge. You then have an explosive vapor in an enclosed space, which is a bad thing.

The way I see it, you have two safe options. 1) use on-deck tanks 2) If you put anything below decks, use a take made for this purpose that is properly vented overboard and has a deck or gunwale fill.

You do NOT want to be messing with trying to get gas from jerry cans into a deck or gunwale fill offshore - too easy to spill fuel or get water into the tank.


LHG posted 08-09-2005 03:57 PM ET (US)     Profile for LHG    
There is no downside to running the aux fuel through the filter. Wherever it is easiest to splice in the 3 way valve is all that counts. Above deck tanks need no water separating filter.
fishin mission posted 08-09-2005 04:16 PM ET (US)     Profile for fishin mission  Send Email to fishin mission     
JJN3, What is your total fuel burn? What kind of engines are you running?
JJN3 posted 08-09-2005 07:21 PM ET (US)     Profile for JJN3  Send Email to JJN3     
I have a 2003 275 Conquest with twin four stroke 225's (Yamaha blocks). I run most economical at 4100-4300 RPM at 25-26 knots (tabs full up) at abot 1.5 NM/gal. That said, if it gets a bit snotty I need to run down to 3800-4000 RPM with the tabs full down (assuming head sea) and I drop to about 1.3-1.35 NM/gal.


handn posted 08-10-2005 03:26 PM ET (US)     Profile for handn  Send Email to handn     
I have YamaMerc 225 4-strokes. At 2100 rpm fuel burn is between 3 to 3 1/2 gph per engine. Troll with one engine at 2100 rpm and the fuel burn is a little more than half, the speed drops only a little more than a nautical mile per gallon, the fuel economy goes up about 70% compared to trolling with two engines at the same rpm and the fishing is surprisingly good because the fish can see the flat line lures in the clean blue water wake.
Certain lures such as slant heads and concave heads such as Aliens and Pakulas perform well at slow trolling speeds. Other lures such as jet heads and bullet heads need greater trolling speeds to perform well.
With rigged dead bait, I cut the trolling speed down even more to 6 1/2 knots.
Slow down on your next canyon trip, you might not need to carry extra fuel.
JJN3 posted 08-11-2005 07:09 AM ET (US)     Profile for JJN3  Send Email to JJN3     
Thanks Handn! That is exactly what I was looking for! We ar eheaded to the 50 fathom line (about 10 miles short of Wilmington Canyon) this weekend to test overall fuel use and tweak the calibration of our NavMan 3100. If everything works out we will hit the 100 fathom line next weekend!


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