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Old 02-06-2015, 18:04   #31
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Re: Cruisers: How Much Fuel?

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so you were able to drive a 12.8m yacht at 4.7 knots on .75 litres per hour?

That seems extremely hard to believe. Double that consumption and it would be impressive and believable, but that simply seems impossible.
How about .75 gallons per hour?
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Old 02-06-2015, 18:25   #32
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Re: Cruisers: How Much Fuel?

Duckwheat,

When we crossed the Pacific in our first Insatiable (36' OA, 29' WL), we had a 45 gal. fuel tank. We planned on 1/2 gal/hr. flat water fuel consumption. We never motored for long, were able to sail almost the whole way. It was quite slow through the ITCZ, but no problem. How many hours of motoring will your present tankage give you?

Base your calculations on that, and plan on sailing when you can--the course does not have to be the ideal rhumb line course, just keep the boat moving, and adjust the course when the wind direction allows.

Ann
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Old 02-06-2015, 19:57   #33
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Re: Cruisers: How Much Fuel?

We motor in perfect conditions at 7.5 Knots. About 2 gallons/hour. We have 380 gallons in 5 tanks. 280 gallons of water in 4 tanks. Water maker & Generator; 660 name-plate watts solar. Water gathering tent ducted to the tanks. I also carry jerry cans on deck - never leave with empty containers. On-deck stuff gets transferred to the main tanks ASAP.
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Old 02-06-2015, 22:37   #34
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Re: Cruisers: How Much Fuel?

Is the 3/4gal per hour at normal cruise speed? We get about 6mpg at our normal 6kt cruise speed. If we drop back to 4-5kts, that jumps up to around 10mpg (slower might be even better but never had the patience to test it out). Assuming you have a simlar scenario, that would give you around 500mile range. Are you comfortable with that?

Another consideration: If you get a huge tank and then keep the purist sailing approach, you are asking for a mess as your fuel gets old and "grows" stuff.

Always baffled me why people are still using gal/hr to measure fuel efficency.
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Old 02-06-2015, 22:48   #35
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Re: Cruisers: How Much Fuel?

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...Always baffled me why people are still using gal/hr to measure fuel efficency.
They're using it to manage fuel, as mpg varies so much due to wind, current, course, etc. A skipper needs to know how much he is burning per hour, so he can anticipate when he'll need to refuel.
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Old 03-06-2015, 02:19   #36
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Re: Cruisers: How Much Fuel?

All the above pontificating emphasizes that for normal cruising routes, light air capabilities are really more important than the ability to withstand the ultimate storm.. something all you "heavy and slow is what you need for "blue water" sailing" guys to contemplate.

IMO, a decent SA figure and some good light air sails make the fuel worries less of an issue.

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Old 03-06-2015, 05:06   #37
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Re: Cruisers: How Much Fuel?

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They're using it to manage fuel, as mpg varies so much due to wind, current, course, etc. A skipper needs to know how much he is burning per hour, so he can anticipate when he'll need to refuel.
So you are 100miles from your destination with 15gal of fuel. You burn 1 gal per hour.

Can you make it or do you need more fuel?

It's insufficent data. It in no way helps account for wind, current, course. You always have to adjust for those. If you are fighting a strong head wind, you probably just throttled up to maintain your speed but now you gal/hr number is wrong or if you didnt' throttle up your speed just dropped so it will take more hours. The end product that you need is can you cover the distance, not how long will you be able to keep motoring.

For more typical scenarios, what people will say is they assume X kts cruise speed assumed, which is effectively giving you MPG. No one says thier car burns 2gal/hr and calcualte distance to destination in terms of gallons used. With MPG, it's realtively easy to add or subract to account for current.

It's not bad to have a feel for gal/hr but for most situations, it's not the best measure of can you make your destination.
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Old 03-06-2015, 05:12   #38
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Re: Cruisers: How Much Fuel?

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IMO, a decent SA figure and some good light air sails make the fuel worries less of an issue.

Jim
Until your mast falls down...

Motored for 7 days after mine fell down... across the wx.... and in last year's puddlejump someone lost their rig and motored for a good few days and miles back - up weather - to Galapagos.

Me? Typically carry 200 + 300 = 500 litres. Economic motoring uses 2.5l/h so thats about 200 hours worth.

Just gunshy I guess
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Old 03-06-2015, 05:15   #39
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Re: Cruisers: How Much Fuel?

Oh... and don't forget plenty lube oil as well.... all the diesel in the world wont help you when you run out of lube oil....
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Old 03-06-2015, 09:51   #40
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Re: Cruisers: How Much Fuel?

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...If you are fighting a strong head wind, you probably just throttled up to maintain your speed but now you gal/hr number is wrong...
Does anyone actually do this? Over-rev their engine just because the wind is blowing? No. Except when idling, boat engines are normally operated at "cruise" rpm. This does not change, like driving a car in traffic, shifting through the gears, constantly varying rpm to maintain position in traffic, and as required by stop lights.
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Old 03-06-2015, 10:08   #41
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Re: Cruisers: How Much Fuel?

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so you were able to drive a 12.8m yacht at 4.7 knots on .75 litres per hour?

That seems extremely hard to believe. Double that consumption and it would be impressive and believable, but that simply seems impossible.
My 44 ft cutter/39 waterline had a perkins 4-108. I kept track of fuel usage over the life of the boat (my ownership) The usage was .65 gal/hour. The boat would do 8.5k + in flat water.
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Old 03-06-2015, 10:33   #42
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Re: Cruisers: How Much Fuel?

You need enough fuel not to worry about it, to put it simply. How much that is is not subject to a simple calculation. For one thing, liters per mile varies enormously depending on conditions. Downwind or in a dead calm motoring slowly or motor-sailing, we consume from nearly zero to a maybe .5 liters per mile. That's at 1200 -- 1600 rpm. Faster motoring (2300 rpm) will use about a liter per mile. Fighting headwinds or currents, this can go up manyfold -- up to perhaps 5 or 6 liters per mile or even more. Dirty bottom or clean also makes an enormous different in fuel consumption.

We have 678 liters on board, which could be enough for a couple thousand miles or only enough for a couple hundred -- depending on the conditions.

We also heat and generate electrical power with diesel fuel, so that also needs to be taken into account. And making water, if you have a watermaker.

I'm about 900 miles from Helgoland, where we last filled the tanks. We've got about half a tank left, so we've used maybe 300 to 350 liters. We've done some motoring (including 65 miles of mandatory motoring through the Kiel Canal), but we've had no headwinds, so almost no motoring over 2000 RPM. We've made a lot of electrical power and done some heating. YMMV, literally, and to say the least. This amount of fuel would be ok for a tradewinds Transat, since there will be less than usual motoring, but I wouldn't actually want any less. And I would certainly have some jerry cans in the lazarette or behind the transom platform. At least 100 liters, I would say.

Equipment run on diesel fuel: 100hp Yanmar main engine, 6.5kW Kohler generator, 10kW Eberspaecher central heating system.


One thing which I would really hate would be to have to conserve electrical power because I don't have enough fuel to generate. This is misery. I would never want to be on any boat where you don't just fire up the generator or main engine and generate all the power you need.
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Old 03-06-2015, 10:40   #43
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Re: Cruisers: How Much Fuel?

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Does anyone actually do this? Over-rev their engine just because the wind is blowing? No. Except when idling, boat engines are normally operated at "cruise" rpm. This does not change, like driving a car in traffic, shifting through the gears, constantly varying rpm to maintain position in traffic, and as required by stop lights.
If your assumption is you always cruise with the engine running flat out, you have a point about over revving your engine. I don't know any cruisers who do that. Bumping up the throttle a bit to compensate for conditions is hardly overr reving.

We normally run closer to 1/2 throttle but if we are fighting a strong head wind or more commonly a strong current, we will throttle up to keep up speed. Likewise if we have a strong tail current, we will throttle back to enjoy the efficency while not costing us time. Maybe we are the only cruisers smart enough to adjust to conditions.

The same arguement could be made for a car. When you are on the freeway, do you just set the throttle and leave it...of course not. City driving is more akin to going in and out of a port.
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Old 03-06-2015, 10:48   #44
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Re: Cruisers: How Much Fuel?

I used to carry lots of fuel and found i simply wasn't using it. As you say, it's a sail boat. If you're crossing oceans, carrying jerry cans isn't going to give you that much more range under power. A day here or there doesn't make much difference when you're dealing with thousands of miles. However much fuel you carry, if you lose your mast half way across the Indian Ocean you're still in the brown sticky stuff. Now I just fill up the tank, which is 40 gallons, and call it a day.

The one exception to this is if i pass through somewhere that has really cheap fuel. Then i fill up the 4 extra jerry cans and save a few bucks in the long run.
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Old 03-06-2015, 12:25   #45
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Re: Cruisers: How Much Fuel?

i seem to never carry enough and end up drifting in ocean for a coupla days until i am close enough to leapfrog into harbor. once i even had 3 gallons remaining iin tank. zihuatenejo i had less than an ounce, and that was in return line. ok.....so
figger out your gph and figger out how many hours at a speed over ground less than reality so you know that you will mebbe have almost enough to make port without drifting, and then add one more jerry jug to the mix so you are ok. mebbe--it also depends on uphill or down hill sailing .....
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