How much fuel?

[stillbuilding]

Originally Posted by robert sailor

Often the size of the fuel tanks will give you some insight into the light air sailing ability of the sailboat. If the boat is 40 feet or less and comes with a 100 gallons of fuel chances are it needs a breeze to get it moving.
Our first offshore cruising boat had 25 gallons of fuel and the little atomic bomb motor burned close to a gallon an hour. On long crossings motoring was not an option as the fuel was used only for charging batteries. We got used to sailing no matter the speed and we were also becalmed for a couple of days. Make sure you have good light air sails, one of the most important things on an offshore boat.

Sometimes has more to do with where you are cruising, ready availability of fuel, variability of fuel cost and other non-sailing parameters.

I have a 60' yacht and cruise Asia - Pacific with varying supply, quality, price and occasional need for schedule. I carry 4000 litres in three big tanks, filter carefully and fill when economical or desirable!


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[donradcliffe]

Given your emphasis on sailing vs motoring performance, I reckon you would be happy with a 45-50 gallon tank. This will give more than enough range except in the doldrum areas, where you might want to carry an extra 20 gallons in jerry jugs.

[El Pinguino]

Never mind the doldrums... it does happen that you can find you have zero wind for a day or two in the 'Roaring ( titter) Forties' . Usually with a confused but heavy ( by some standards ) swell. Crash bang thud roll crash wallop bugger me there goes my dinner....oops.. make a note to self buy more fine bone china tea cups...

The ability to motor and reduce the pain is rather nice... and means you are still knocking off the miles towards destination...

And you can be stuck in the middle of highs like that for a few days at a time

[micah719]

Is there a metric for fuel capacity that makes comparisons easier? Consumption per hour, range at most economical speed, for instance? How about taking an arbitrary 100nm unit and calculating the fuel needed for that, like how we compare cars with litres per 100km highway vs. city driving? We could then compare that with the carrying capacity of the boat.

[colemj]

Originally Posted by Delancey

Peter, you directly articulate through your experiences something I couldn't quite sum up in my own words.

For the advocates of more is better when it comes to tankage, I have to ask do you ever use it? Really? What the hell do you do with 130 gallons of diesel on a sailboat? A thousand pounds? Really?

For the life of me I just can't imagine. I've crossed an ocean and only used ten gallons and I'd do it again. Maybe I am too comfortable with depravity or maybe you people are too comfortable conspicuous consumption.

If the extra space where the tank will be located is unusable otherwise (like on our boat), then why not make the tank as large as possible? You don't have to fill it full if you don't want.

We have a 120 gal fuel tank. This allows us to never have to jug fuel or go out of our way just for a fuel run. Many of the cruising grounds you are contemplating are unsafe sailing at night, so without motoring, you will be limiting/constraining your day passages more than necessary.

Take the Bahamas, for example. They are filled with wonderful areas that have no fuel available at all. Additionally, to get fuel, you may have to beat to windward 60 miles and must make it in daylight or even by the afternoon to get good sunlight. And even then have to jug the fuel.

Then there are places you may want to cruise that are notorious for bad fuel. Fill up with good fuel before heading off to those areas and don't worry while there.

With a large tank, you have the option to keep it 1/4 full when around fuel and full when you are fully off-grid for 6 months.

Mark

[micah719]

Another thought....keeping a large tank partially full, what is the downside to condensation from the airspace, and stability effects from free-surface effect? Could one build a pressurised bladder to fill in the airspace?

[colemj]

We have never had a condensation problem with a partially full tank, and our tank spends long periods of time partially full. If out cruising in warm weather, condensation will never be a problem, even if it isn't a wive's tale.

If one is still fretting over condensation, just fit a drier on the vent line - that is the only possible air ingress point.

We have also never had problems with "old" diesel. I also think that the necessity of "fresh" diesel is a bit of a wive's tale.

Mark

[Jon Eisberg]

As always, my first reactions to questions of this sort is, 'It Depends...' ;-)

As others have already noted, largely on the kind of boat you sail, and where you intend to sail it...

For example, if you're cruising a region like Labrador, and are blessed with some beautiful, but often calm weather that will accompany a high pressure system, you will wind up doing a LOT of motoring if you want to keep on the move, and see what's around the next bend...





And, with there being no such thing as a fuel dock anywhere along that coast, and the spots to obtain fuel being very few and far between, coupled with the inconvenience of schlepping fuel to the boat one container at a time, you definitely want to be able to carry more, as opposed to less...





I carry 50 gallons - plus one jerry can for transporting or emergency - on my little tub, which is quite a bit for a 30-footer... That seems just about right, for me - thought there have certainly been times I've wished for more, I don't want to impinge on the storage space for my light air sails, after all ;-) I think the guiding principle re fuel capacity on a cruising boat should always be, 'However much it takes to avoid the risky and typically unnecessary practice of carrying additional fuel on deck...'

I think your concern about keeping fuel "fresh" is overblown, there are several ways of mitigating that risk... As already mentioned, any cruising boat really going places should have an on-board polishing setup, for starters... I certainly hope your new fuel tank will have a large inspection port to facilitate any cleaning, 8" diameter or so at a minimum might pay huge dividends over time... And, I'd also recommend the installation of an indicating silica gel 'moisture blocker/absorber' in your vent line to inhibit the possibility of condensation in the air space of your tank, especially for a boat that lives in a region like the NE that will see a wide fluctuation of climactic conditions over the course of different seasons... There's a product called H2Out currently available:

h2out

...but you can save yourself some $ by building an equivalent yourself, for about $40 using materials scrounged from eBay... ;-)

[micah719]

Thanks Mark! Cool blog btw...

[Stu Jackson]

Originally Posted by Panope

1. This will alleviate many of the concerns about having a perpetually 1/2 full tank and the condensation this condition is believed to produce. I personally have never filled my tanks (because they are large) and have found only a few drops of water in my sumps during the last 15 years.

2. I also believe that diesel has a very long shelf life. I foolishly gave away a batch of 10 year old diesel that looked, smelled, and worked perfectly - in an engine.

1. Doesn't this "prove" that the condensation nonsense is really an urban myth?

2. Yup. So what's the issue with a large tank with fuel that'll last forever again?

Seems to me that 53 foot boat with 225 gallons balances well with a 35 footer with anywhere from 25 to 40 gallons.

Cruise range being based on hourly fuel consumption based on YOUR engine is pretty much a reasonable way to size a tank, plus where you plan to be going.

[Stu Jackson]

Originally Posted by micah719

Is there a metric for fuel capacity that makes comparisons easier? Consumption per hour, range at most economical speed, for instance? How about taking an arbitrary 100nm unit and calculating the fuel needed for that, like how we compare cars with litres per 100km highway vs. city driving? We could then compare that with the carrying capacity of the boat.

While your goal is laudable, what others do on their boat is meaningless, all I care about is what MY range is. Therefore, I keep fuel logs and can confidently state that my engine uses 0.493 gallons per hour, for the past 17 years.

That said, most folks will also know, from reading many of these fuel/range discussions that low 20 hp engines get 0.5 gph, 30-35 get 1.0+ gph, and larger engines use more fuel per hour. It's based on manufacturers data and real world record keeping.

gph times speed = distance (range)

[sailorboy1]

The day comes when sailing slow isn't as important as making happy hour


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[Jim Cate]

Originally Posted by colemj

If the extra space where the tank will be located is unusable otherwise (like on our boat), then why not make the tank as large as possible? You don't have to fill it full if you don't want.

We have a 120 gal fuel tank. This allows us to never have to jug fuel or go out of our way just for a fuel run. Many of the cruising grounds you are contemplating are unsafe sailing at night, so without motoring, you will be limiting/constraining your day passages more than necessary.

Take the Bahamas, for example. They are filled with wonderful areas that have no fuel available at all. Additionally, to get fuel, you may have to beat to windward 60 miles and must make it in daylight or even by the afternoon to get good sunlight. And even then have to jug the fuel.

Then there are places you may want to cruise that are notorious for bad fuel. Fill up with good fuel before heading off to those areas and don't worry while there.

With a large tank, you have the option to keep it 1/4 full when around fuel and full when you are fully off-grid for 6 months.

Mark

The above is good, real world cruising advice. Anyone with long range cruising aspirations should pay attention.

Our experience over the past years of cruising in the South Pacific supports Mark's opinions. Once you have paid an exorbitant price for dirty diesel, syphoned from a rusty drum with an open bung in an area with heavy rainfalls (ie the Solomons) you will understand the joy of a large fuel capacity!

Sure you can cross oceans with sparse engine usage... we have done so more than once. But cruising is more than ocean crossing, and the needs change with the cruising grounds. If you are worried about the weight slowing the boat, don't fill to capacity when not needed... that's a no brainer IMO, and in the non-US world where normal diesel is available, fuel age isn't an issue.

And the joys of engineless cruising may be there for some, but most cruisers prefer the ability to use an engine judiciously, for safety, convenience and the need to make the occasional bar crossing at the right state of the tide.

Jim

[Delancey]

Yeah, Mark's comment has stuck with me more than any of the others. The space above my fuel tank is where the life raft locker was, and I was planning on using that space for something else but it might end up as empty space when it is not full of fuel.

[jcapo]

Originally Posted by sailorboy1

The day comes when sailing slow isn't as important as making happy hour

Or getting through a cut while you still have good light.