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Old 06-09-2015, 19:27   #1
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How Much Diesel is Enough?

Hi all,

I hope that I'm not running out of 'ask the audience' lifelines.

I'm searching for a reasonably priced sailboat, with which to circumnavigate and my top contender is an IP38. Unfortunately, it only has 57 gallons of diesel in its tank. I realize that I can supplement this with jerry jugs, but even this has a limit. I also realize there are those that have done this without an engine.

Is the 57 gallons adequate or should I be looking for a different vehicle?

Thank you for your replies.
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Old 06-09-2015, 19:40   #2
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Re: How Much Diesel is Enough?

Well... in round numbers you are probably talking 400-500 miles on that tank of diesel.
So it depends. I think most of my boats I felt like I had too much diesel at 100+ gallons. The fuel gets old. But if I was crossing the Pacific I would want a lot. It's usually easy enough to add some additional tank capacity that you could fill before a 3 week crossing and leave empty the rest of the time.
I added two additional smaller tanks to my catamaran and ended up emptying them and not refilling after all that work!
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Old 06-09-2015, 19:56   #3
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Re: How Much Diesel is Enough?

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Originally Posted by Sevi View Post
Is the 57 gallons adequate or should I be looking for a different vehicle?
In my opinion, it's certainly adequate...

But as this recent thread posing the identical question illustrates, not everyone agrees...

;-)

Cruisers: How Much Fuel?
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Old 06-09-2015, 20:09   #4
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Re: How Much Diesel is Enough?

With my sailing habits 57 would be adequate. Each person needs to make that decision based on what they normally do. If you fire up your engine if you are going less than 4 knots you might need more.
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Old 06-09-2015, 21:56   #5
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Re: How Much Diesel is Enough?

We had 70 gallons when we left for French Polynesia and brought most of it home with us after a years cruising. Currently have 25 gallons and it was enough to power 200 miles back to start port to effect repairs without getting into the Gerry Jugs stashed on deck. Based on consumption at a comfortable cruising speed would be happy with fuel for 48 hours of powering.

If you are a frustrated power boat owner and will turn on the engine every time the speed sailing drops below 7K, or will run the generator 24/7 at anchor, 57 gallons may not be enough.
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Old 06-09-2015, 22:15   #6
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Re: How Much Diesel is Enough?

I have a ten gallon tank and three jerrycans. But I am a frustrated power boat owner that likes to turn the motor on when the wind dies.
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Old 06-09-2015, 22:18   #7
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Re: How Much Diesel is Enough?

Our boat came with a 55 gallon diesel fuel tank and two 85-gallon water tanks. Used it that way for 5-years cruising in Puget Sound.

Converted one 85-gallon water tank to fuel in 2000 when we installed a big water maker. After the conversion; we had 140-gallons of diesel or about 1,200 NM range with about 100 NM reserve.

At the same time I converted the water to fuel tank I added a big Code 0 sail for light air use. We already had an even bigger fairly light asymetrical spinaker that we loved to fly and used anytime it was possible. We sail anytime we can make 3 knots and that is much of the time.

We also have 500-watts of solar power and never, ever, use the propulsion diesel for battery charging.

We burn 0.7 GPH at about 6.3 knots with a Yanmar 4JH2E and an 18" Maxprop. The engine turns 2300 - 2400 RPM at 6.4 knots.

We've cruised off and on since then including a 4,000 NM trip from Seattle to SW Mexico and then several years in the Sea of Cortez and another 1,200 NM trip from Seattle to San Diego.

My big problem now is old stale fuel - the original 55-gallon tank would have been plenty of fuel. That tank would give us a 405 NM range with a 130 NM reserve. Our longest non-stop motoring experience was 36-hours at 6.4 knots or about 25 gallons.

If you have the sails and are willing to be patient and sail - then 50-some gallons of fuel should be plenty.

Even for oceanic passages a 50-gallon capacity should allow you to motor for at least 75-hours with an 8-hour reserve to get into harbor when you arrive at your destination.

Our big fuel tanks allow me to purchase a lot of fuel when it is cheap but it also requires I work hard to keep it clean and useable.
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Old 06-09-2015, 22:50   #8
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Re: How Much Diesel is Enough?

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Is the 57 gallons adequate or should I be looking for a different vehicle?
When planning our circumnavigation, my wife and I decided that we never wanted to worry about fuel. Then again, we tend to over-provision.
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Old 06-09-2015, 23:25   #9
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Re: How Much Diesel is Enough?

Quote:
Originally Posted by Cheechako View Post
Well... in round numbers you are probably talking 400-500 miles on that tank of diesel.
So it depends. I think most of my boats I felt like I had too much diesel at 100+ gallons. The fuel gets old. But if I was crossing the Pacific I would want a lot. It's usually easy enough to add some additional tank capacity that you could fill before a 3 week crossing and leave empty the rest of the time.
I added two additional smaller tanks to my catamaran and ended up emptying them and not refilling after all that work!
Why in the world would you leave your fuel tanks empty all the time? If you're worried about the fuel going bad, then simply install a good fuel polishing system. Is the diesel quality that bad where you sail?
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Old 07-09-2015, 07:30   #10
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Re: How Much Diesel is Enough?

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Originally Posted by Kenomac View Post
Why in the world would you leave your fuel tanks empty all the time?
Weight. Catamaran.

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Old 07-09-2015, 07:43   #11
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Re: How Much Diesel is Enough?

I fill my tank immediately when I arrive at a destination so I can always go in an emergency, or if the heart desires.

I have 38 gals in the tank and have circumnavigated but I think the OP should buy a boat with at least 10,000 gallons, plus extra gerrys. And some packets of Instant Diesel - just add water (free steak knifes included).
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Old 07-09-2015, 07:53   #12
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Re: How Much Diesel is Enough?

Need to know how much fuel to carry in order to meet the range required? An easy calculation is:


For petrol engines fuel consumption can be estimated as:

Litres/hr = 0.508 x KWprop

For diesel engines fuel consumption can be estimated as:

Litres/hr = 0.274 x KWprop



Where: KWprop = Kilowatts from propeller power curve

------------------------------------------------------------

correct rule of thumb for diesel engines is 1 gal per 20 horsepower per hour,

1/2 gallon per hour per 10hp. So 100hp diesel would use 5 gal per hour.
------------------------------------------------------------

To convert g/kWh to Liter/h

Multiply g/kWh by the power output, then divide by the density of the fuel. (0.85 for diesel)

---------------------------------------------------------------------------------------

example....



Fuel consumption 215 g/kWh

Rated power is 100 kW.


At 100 kW, fuel consumptuion is

215 g/kWh x 100kW = 21500 g/h or 21.500 kg/h

Diesel varies, but 0.85 kg/l is a good typical figure for diesel, so (1Lit diesel = 0.85kg)

21.500 kg/h : 1 L/0.85 kg = 25.3 L/h ( 5.56 Imperial gallons or 6.68 US gallons)
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Old 07-09-2015, 08:06   #13
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Re: How Much Diesel is Enough?

Quote:
Originally Posted by blackcrow View Post
Need to know how much fuel to carry in order to meet the range required? An easy calculation is:


For petrol engines fuel consumption can be estimated as:

Litres/hr = 0.508 x KWprop

For diesel engines fuel consumption can be estimated as:

Litres/hr = 0.274 x KWprop



Where: KWprop = Kilowatts from propeller power curve

------------------------------------------------------------

correct rule of thumb for diesel engines is 1 gal per 20 horsepower per hour,

1/2 gallon per hour per 10hp. So 100hp diesel would use 5 gal per hour.
------------------------------------------------------------

To convert g/kWh to Liter/h

Multiply g/kWh by the power output, then divide by the density of the fuel. (0.85 for diesel)

---------------------------------------------------------------------------------------

example....



Fuel consumption 215 g/kWh

Rated power is 100 kW.


At 100 kW, fuel consumptuion is

215 g/kWh x 100kW = 21500 g/h or 21.500 kg/h

Diesel varies, but 0.85 kg/l is a good typical figure for diesel, so (1Lit diesel = 0.85kg)

21.500 kg/h : 1 L/0.85 kg = 25.3 L/h ( 5.56 Imperial gallons or 6.68 US gallons)
Mark,

'Curious... then why does my Yanmar 100hp turbo diesel only consume 1 gallon per hour at 1800-2000rpms? Enough to drive our 25 ton boat at 6 knots in relatively calm seas <15 knot winds.

What am I doing wrong?
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Old 07-09-2015, 08:22   #14
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Re: How Much Diesel is Enough?

Quote:
Originally Posted by Kenomac View Post
'Curious... then why does my Yanmar 100hp turbo diesel only consume 1 gallon per hour at 1800-2000rpms? Enough to drive our 25 ton boat at 6 knots in relatively calm seas <15 knot winds.

What am I doing wrong?
IMO, nothing. Your Yanmar can develop 100HP but if you are only burning 1 gallon per hour then your engine is only developing about 20HP or 0.055 gallons per HP.
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Old 07-09-2015, 09:26   #15
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Re: How Much Diesel is Enough?

Diesel capacity and motoring range is often a concern to those new to cruising under sail. Depending on where you intend to sail, IMHO 57 gallons of fuel is plenty. Having said that, I can imagine (and have experience) scenarios where 57 gallons is too little, depending on how dedicated you are to sailing upwind. As an example, there are a number of options for getting from Cabo San Lucas to California. It can and has been done taking some long off-shore tacks, basically following the Clipper route. However, for some cruisers the more direct route up the coast is more appealing. In the absence of a favorable tropical depression developing from the south, one is more likely to encounter wind, waves and current all on the nose for the entire trip north along the Baja Peninsula making for a long upwind motor-sailing slog (the notorious Baja-bash). Fuel consumption is generally higher than expected (motoring the entire way against the forces of Mother Nature). The preferred fuel stops along the route are at Bahia de Tortugas (~450nm) and Ensenada (~800 nm). Under these circumstances, 57 gallons of fuel capacity may be inadequate. For these special cases, rather than selecting a boat or modifying an existing vessels fuel capacity to meet these unusual conditions (we all know 'gentlemen do not dine to weather') this would be one of the few cases where you might want to consider supplementing your capacity with jerry jugs on deck. Otherwise, as has been shared by most here, 57 gallons is adequate. Slow down and enjoy sailing. Hone your light air skills by leaving your engine off and sailing. Good luck and fair winds!
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