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Old 06-26-2017, 09:06 PM   #1
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Fuel Capacity

Moving along the path towards 'wholeness in fuel tankage', the question turns to 'how much capacity should we try to have aboard?' My calculation shows that the original tanks could each contain 176.9 gallons or by another approximation, 177 gallons. The boat's listing stated that she had 200 gallons. Given that I cannot get that much capacity in the proposed three-linked-tank replacements, what should I be willing to accept? Bear in mind that we really have no idea after two seasons and about 100 hours on the hourmeters and some unknown leakage loss, what out burn rate is on this 38' 26000 lb boat is at 8 knots/1800 rpm on the Perkins 6.354s.

I've made a plywood mock-up of a three-linked-tank setup and I'll find out whether I can get 'em in, tomorrow. Pics (and perhaps screams, if I have to modify the models) to follow on the morrow!
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Old 06-26-2017, 09:13 PM   #2
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My take on tank-age is Sea boat that crosses big water big tanks. Typical family boat don't overdo the tank-age otherwise you have a lot of fuel lying around looking for some water and unwanted growth of gunk. I think most trawler types are over tanked relative to their use patterns.
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Old 06-26-2017, 09:46 PM   #3
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150 gallons should get you around 500 miles.
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Old 06-26-2017, 11:46 PM   #4
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Quote:
Originally Posted by DHeckrotte View Post
we really have no idea after two seasons and about 100 hours on the hour meters and some unknown leakage loss, what out burn rate is on this 38' 26000 lb boat is at 8 knots/1800 rpm on the Perkins 6.354s.
We have somewhat similar boat's, size and power. I'm 15 tons scale weight, twin 6.354, 130hp. I carry 500 gals in 4 tanks.

We Have gone from Anacortes, Wa to Ketchican, Ak without refueling, that's about 700 miles and still had a good reserve. We ran 2100 rpm's going North and made a lot of stops in between. Coming back we were tight for time, ran a more direct route and 2500 rpm all the way. Definitely burned more fuel, but still made it back without refueling.

I figure 6 gph as an estimated fuel burn at 2500 rpm's. At your 1800 rpm's 8 knots, which sounds about right, you're probably in the 4 - 5 gph range.
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Old 06-27-2017, 05:47 AM   #5
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Under 5 GPH would be my guess for fuel burn , so figure tankage for your intended use .

150 gal would be at least 30 hours , about 240 NM, no reserve

slowing to 6K should lower fuel burn by half so 400- 500 miles , no reserve.
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Old 06-27-2017, 06:10 AM   #6
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I replaced my 2-200 gallon tanks with 2-58 gallon plastic tanks when my steel tanks became worrysome.

My single burns 2 gph at 6.3 knots so my range is around 300 miles if the last leg or so is cslm enough to take the fuel down low in the tank. Easy to do now that I can see into the tank.

For me, thats about a weeks cruising time before refueling. So fueling isnt intrusive into my schedule, and stopping at a marina for fuel, water, pumpout and groceries usually falls into place.

In the big scheme of things, 150 gallons woukd be nice, but there weren't any off the shelf tanks that fit the way these did.

I really enjoy all the extra storage in the engine room, and my fuel is always fresh as even when I dont cruise for the summer, i have burned it down to just a few gallons. Just enough to get to fuel docks if a hurricane heads my way.
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Old 06-27-2017, 06:27 AM   #7
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I have 660 gallons in 2 tanks. Burn 2GH at 7 knots (3.5 MPG). Have a theoretical range of 2,000 miles. Rarely use the capacity, but it was nice to fill up at $1.48 per gallon. Usually run between 1/3 and 2/3. Putting in the biggest tanks doesn't obligate you to fill them full all the time.

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Old 06-27-2017, 07:14 AM   #8
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When we had our single engine 38' Fu Hwa with a 135hp Perkins, we burned between 1.5-2 an hour at mostly 1650 rpms which was good for almost 7 knots. I think the previously posted estimate of 4 gph at 1800 rpms seems reasonable for twins. We could have easily gotten by with 150 gallons of tankage.
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Old 06-27-2017, 08:30 AM   #9
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It depends on how you plan to use the boat. Very few people do multi day runs away from fuel sources and fresh fuel is always great to have. As said above a week's cruising will probably take you to a fuel area at least once. IMO you don't want fuel that lasts into the next year of cruising.

An alternative if you go for maximum capacity is to not fill the tanks but run low so that you keep fresher fuel. In that case you have options not provided by small tanks.
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Old 06-27-2017, 11:19 AM   #10
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I have the Perkins 6.354s with a flow scan on the starboard engine. At 7 knots I'm at about 4.4 GPH. I just double the amount on the flow scan. That's with an almost full load of fuel (approx. 350 gallons) and a full water tank (approx. 100 gallons).

Of course the wife hasn't fully loaded the boat for cruising yet, so that number may go up a little.
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Old 06-27-2017, 12:10 PM   #11
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Put in what you are comfortable with from an installation prespective.

The reason I say that is because there are few places that a coastal cruiser needs allot of fuel capacity.

The furthest place that I have been able to find in North America that you NEED to traverse without taking on fuel is 280 NM between Yakutat Alaska and Cordova, or Valdez, or Whittier Alaska.

So...

You need what you need for your geographic area. You of course want more fuel capacity to give you choices, but your wants are dictated by the realities of your boat and how difficult it is to have larger capacity.
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Old 06-27-2017, 12:52 PM   #12
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I have 2 x 180 = 360 gallons for a single FL 120.
That's too much fuel for 2 gph consumption.
Half that would be more than adequate.
That said, I was able to cruise in Canada for almost 4 weeks without buying diesel. That was nice.
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Old 06-27-2017, 01:00 PM   #13
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When I built my 38, I put in two 160gal tanks. At hull speed of 7.5kt/2gph that is a range of over 1000nm. At planing speed of 20kts/11gph range is over 500nm. Longest leg I have run port-to-port was about 160gal, and had 200 loaded to start the leg.

I could have put in smaller tanks for sure.

I only once had a full load, and that was after taking a friend on a gulfstream trip and he insisted on filling the tanks. Boat felt a little piggy with the load. So once on the dock I pumped out two barrels and got it back down to about 200. With that load it sits nice on its lines and does not feel piggy.

For local goofing around I keep about 100-200 on board. Same for most trips, but more if a long leg.
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Old 06-27-2017, 09:29 PM   #14
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Oh, the good life in south New Jersey! My mock-up replacement three-fer tanks (on each side) would fit if I were to remove the exhaust hoses and we'd get most of the installed capacity. Or, we could get betw. 75 and 90 gallons in a single replacement tank (on each side). (The quickie mock-up has no top and the inboard side extends down to the white-painted stick.) Lots of access, vastly improved access to the port side of the port engine!

Given we have no need to travel such great distances w/o refueling, the lesser, cheaper, simpler, smaller tanks seem pretty reasonable. Lovely sunset this evening; one of the three mock-up three-fer tanks; a quickie mock-up of the single tank.
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Old 06-27-2017, 10:37 PM   #15
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I have 400 gallon capacity and a range at typical cruising speeds of between 1,000 to 1,200 nm. I have only filled the tanks a few times. Normally, I have been filling to full. I have realized that that is silly. From now on I am going to fill to about 1/2 way unless we are going to head out on a long trip. That means the next fill will probably be from about 1/4 full (hopefully) to full before we head North. Then for the rest of the time I'll keep the full level lower to save the fuel in weight. Plus, it will keep me from having fuel that is as old.
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Old 06-28-2017, 08:06 AM   #16
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I'd go for the 75 gallon tanks on each side. Simpler, cheaper and actually more in line with the use of the vessel. Don't believe it would affect resale in any way.

Just check the trim. Maybe move some other jammed up equipment around.
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Old 06-28-2017, 08:18 AM   #17
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If your fuel tanks are not leaking or otherwise defective, my suggestion is to leave well enough alone until you determine that you need more capacity. You don't even know your fuel usage at this point so you can't determine any potential need for more capacity.

Remember that fuel has weight and carrying more fuel than you need increases fuel burn (to move that weight). Also, the more fuel you carry, the older it will get before you use it (unless you are actively cruising).

If you will be crossing oceans you will need a lot of capacity. Cruising the AICW, you will have plenty of opportunities to purchase fuel.
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Old 06-28-2017, 09:02 AM   #18
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Greetings,
Mr. WK. I'm pretty sure Mr. DH's tank IS leaking Rock Hall, MD, to Ottawa, ON, CA, and back post #24. Additionally, the tank(s) are already removed.
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Old 06-28-2017, 09:43 AM   #19
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Quote:
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Remember that fuel has weight and carrying more fuel than you need increases fuel burn (to move that weight).
That depends on whether you're planing or in displacement mode. The difference for my boat (only displacement vessel) between full and reserve is about 4,500 pounds or 10% of the vessel's weight. I see no difference in speed or fuel consumption. I think the draft in the stern changes 2 to 3" and the bow, maybe 2".

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Old 06-28-2017, 11:50 AM   #20
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True on both accounts.

My fuel burn with 400 gallons aboard was impossible to see the difference when nearly empty.

Plus based on the photos like RTF said, I think the tanks are already out if mockups were tried.
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