Fuel Tank Size

[redcobra]

I am repowering and this also requires a new diesel fuel tank. The old tank is a 30 gallon tank. The engine will burn about 1-1.25gph at 7 knots. My initial thought was to go with a 30 gal tank again, however I have room for up to 50 gal. Previously I used about 25- 40 gallons a year.
I mainly cruise the Chesapeake Bay, but may venture into the Delaware Bay. Possible circum nav around the DelMarVa, remote possibility of a trip to Bermuda (dream dream).
Whadda u tink? 30, 40, 50?
Thanks

ps: 39 ft Pearson Yawl with a 4 cyl 38hp diesel.

[David M]

There are two things you need to consider but in your case it probably wont matter much at all.

The first is your change in trim. This is calculated by getting the MT1 figure for your boat. MT1 is the moment it takes to change your trim one inch. The further you put the increased weight away from the LCB, or location of center of buoyancy, the greater the weight will affect your trim.

The second item is moment of inertia. The greater the mass is placed away from the boats center of gravity, the greater the tendency your boat will have to pitch.

In your case you are only adding 7 pounds per gallon times 20 gallons or a weight of 140 pounds plus the weight difference of a larger tank. As I said, its pretty much not worrying about for a 39 foot boat.

I say go for for the 50 gallon tank.

[thinwater]

Originally Posted by redcobra

I am repowering and this also requires a new diesel fuel tank. The old tank is a 30 gallon tank. The engine will burn about 1-1.25gph at 7 knots. My initial thought was to go with a 30 gal tank again, however I have room for up to 50 gal. Previously I used about 25- 40 gallons a year.
I mainly cruise the Chesapeake Bay, but may venture into the Delaware Bay. Possible circum nav around the DelMarVa, remote possibility of a trip to Bermuda (dream dream).
Whadda u tink? 30, 40, 50?
Thanks

ps: 39 ft Pearson Yawl with a 4 cyl 38hp diesel.

You can sail. You can motor everything. I've done the Delmarva trip 4 times now (some discussion on my blog, below) and I found that the ability to motor as much as 100 miles really cuts down on the need for marina hopping, should the wind die. The longest run between fuel stops can be Cape Charles to Lewis to Cape May, depending on draft and weather, which is over 150 miles. So, perhaps 30 gallons is a good minimum. More likely, you can fuel in Ocean City or Chincoteague if the wind is lacking.

The counter argument, you mentioned; your fuel is going to get very old, which can bring its own pain. You cannot leave the tank 1/2 full, unless you really want polymerization/oxidation sludge and biological contamination issues.

Clearly, the best answer is more tankage and more trips!

PS. I am looking at uping the tankage on my new boat - Bermuda is calling... loudly!

[Pblais]

The fuel tank can't be too big. It's why you are a cruiser. You do have to be practical as far as space and displacement. We used to have 60 gallons on the last boat with a 35 HP engine. I think if you can handle the extra weight then go for it. No one ever ran out of fuel because the tank was too big. The engine side of things is not unimportant. Hope to be heading up the Bay mid month in June so look for Bright Eyes.

[Paul L]

How about installing a 35 gal tank and 15 gal tank. You can use the 15 gal tank for your normal sailing and avoid stale fuel. When you plan on longer trip, fill them both.

Paul L

[markpj23]

I'd opt for the bigger tank - and since you're doing a new installation add a polishing loop!

[redcobra]

polishing loop?

Just looked it up. Is that really necessary for a sailboat with a new tank? The old tank was 33 years old and I never had a fuel problem.

Always used a Racor external filter/separator

[Formosa46AK]

To: MarkPJ23
Join Date: Nov 2005
Location: Black Hills, SD
Boat: Now Boatless
Posts: 1,148

"Boatless" ... so sad

[FSMike]

A larger tank might be more desirable to a prospective buyer should you decide to sell.
Or, of course, if you were to change your sailing area/habits.