Fuel Consumption Question

[jgwinks]

Agree with Comodave. He's given you a workable number, with the caveat, your mileage may differ.

Just be careful when reading quoted gallons per hour; under identical conditions, a US boat will burn 20% more per hour than a Canadian boat.

5 quarts in a Canadian gallon, right?

 

[smitty477]

A twin won't burn twice the fuel of a single at the same speed. It just doesn't work that way. The 2 - 4 nmpg range at around a knot below hull speed is a reasonable estimate though (depending on the hull, engines, etc.)

Exactly

 

[smitty477]

In theory, my AT34 and 400 gallons of fuel, I should be able to go from Miami to about some place in NY. Most definitely if I jump into the Gulf Stream.
Of course, if I traveled in the ICW I would see many interesting things.
I cant figure out why I would want to end up in NY. LOL

"I cant figure out why I would want to end up in NY. LOL"
Because there are fantastic cruising grounds with a huge number of spots to see in Long Island Sound, Block Island, between the forks, in Ct and RI , the Ct river, the Hudson River, etc, and a bunch of lakes if you want to cruise that far.

 

[rslifkin]

"I cant figure out why I would want to end up in NY. LOL"
Because there are fantastic cruising grounds with a huge number of spots to see in Long Island Sound, Block Island, between the forks, in Ct and RI , the Ct river, the Hudson River, etc, and a bunch of lakes if you want to cruise that far.

And it's a good escape from the oppressive heat down south in the summer. It only gets hot up here, not nuclear hot.

 

[jgwinks]

I'm in the same situation. Moving from a 36' sailboat, 21hp, .25 to .33 GPH. Now on a 41' MY, twin Perkins T6.354's at 175HP each. On the hard in Michigan now so I won't even be able run the boat til April or May. I'm estimating 4-8 times the burn and that doesn't even count the rare times we could actually sail to a destination.

 

[smitty477]

I'm in the same situation. Moving from a 36' sailboat, 21hp, .25 to .33 GPH. Now on a 41' MY, twin Perkins T6.354's at 175HP each. On the hard in Michigan now so I won't even be able run the boat til April or May. I'm estimating 4-8 times the burn and that doesn't even count the rare times we could actually sail to a destination.

Will you be traveling at the same speed as the past sailboat with your newer 41' boat? What was the % of time and/or distance you sailed without power in the past? Are your planned cruising distances significant?

 

[jgwinks]

Will you be traveling at the same speed as the past sailboat with your newer 41' boat? What was the % of time and/or distance you sailed without power in the past? Are your planned cruising distances significant?

A little faster, 6kn in the sailboat, probably 7kn in the MY. It's capable of 18-20, but only plan on that in emergencies. I'll have to see where the sweet spot is. Didn't get to sail much, maybe 10% when travelling, we daysailed some, but that's not what I'm talking about. Yes, we're going to be cruising, Great Loop or at least half of it, need to get away from Michigan winters.

 

[smitty477]

A little faster, 6kn in the sailboat, probably 7kn in the MY. It's capable of 18-20, but only plan on that in emergencies. I'll have to see where the sweet spot is. Didn't get to sail much, maybe 10% when travelling, we daysailed some, but that's not what I'm talking about. Yes, we're going to be cruising, Great Loop or at least half of it, need to get away from Michigan winters.

Then the fuel use will not be near your high estimate that you had posted per mile cruised.

 

[jgwinks]

Then the fuel use will not be near your high estimate that you had posted per mile cruised.

Well 4-8 times was a wild guess. 4 x .25 is only 1gph, and at a slightly higher speed so not that bad per mile which is all that counts. Even 8x is 2gph which I've read people say they're getting. It could end up being more than that. And of course I would do 60-80 miles per day at 6kn because I couldn't go any faster. Knowing I can go faster might change my tolerance. I'm not known for massive will power.

 

[smitty477]

Well 4-8 times was a wild guess. 4 x .25 is only 1gph, and at a slightly higher speed so not that bad per mile which is all that counts. Even 8x is 2gph which I've read people say they're getting. It could end up being more than that. And of course I would do 60-80 miles per day at 6kn because I couldn't go any faster. Knowing I can go faster might change my tolerance. I'm not known for massive will power.

"4 x .25 is only 1gph"
Yes - exactly.
And 0.33 X 8 is 2.64

 

[DDW]

I think you could plan on 2 or 2.5 g/h. It might be a little less. On the AT34, I plan on 2 g/h at 7 knots, long term averages are about 1.9. On my sailboat motoring, 1.3 g/h at 6.5 knots (but it is bigger too).

 

[jgwinks]

"4 x .25 is only 1gph"
Yes - exactly.
And 0.33 X 8 is 2.64

Right. But still a wild guess. Time will tell...

Thanks!

 

[backinblue]

I am thinking about purchasing a trawler having put my sloop up for sale. (I am "a gentleman of a certain age"). But I have no idea of what fuel consumption is on a trawler. One 36 footer for sale has two Cummins 6BT5.9M engines rated at 210HP. Can anyone educate me as to fuel consumption of such a vessel? Thank you in advance for your input.


Ron

Welcome. As a former sailboat owner until recently I understand your fuel concerns. You should be able to find online info for your boat or something similar in size and shape and power to get a ballpark. In my experience after a couple seasons, fuel costs are really not as bad as you imagine. Of course it depends a lot on how far and especially how fast you want to cruise. Coming from sailing, you probably think that if you can go 7 knots in a straight line all day, you are flying! You'll be surprised how quickly you wish you could go faster. Unless you are buying a true displacement boat and expect to go no faster than hull speed, don't trivialize the cruising and top speeds (although probably reduce them by 10% from what's advertised). You might might not care much about 10 knts vs. 15 knts of cruise speed now, but you will once you get used to it. Lots of knowledge on this site so feel free to ask anything. Good luck!

 

[Salish Nomad]

I forgot, I am ignoring the prop pitch and cupping.

According to factory sea trials, running a know distance two ways,
American Tug 34, net 12ton
A single Cummins QSB 5.9 QSB 380hp
1000rpm, 6.5knts, 1gph.
1200rpm, 7.4knts, 1.4gph
1400rpm, 8knts, 2.1gph
The point is, the above is the theory of an empty boat, pretty much flat water, no or little wind no current or tidal effect.
So these numbers do not equate to the real world.

Yes, exactly. I run 1380, 1.7, @7kn. Real World.?

 

[Salish Nomad]

Here is a more complete consumption curve, taken by me for the AT34 (which is about the size you are talking). Actual numbers slightly better as this was about 0.5 kn foul tide and 5 knots headwind. Note that there is a big knee in the curve at around 8 knots. How fast can you afford to go?

RPM %load G/H Boost SOG
1300 33 1.9 1.1 6.5
1400 34 2.3 1.4 6.9
1500 35 2.7 1.7 7.2
1600 35 3.6 2.3 7.7
1700 36 4.1 2.9 8.1
1800 36 5.0 3.7 8.5
1900 5.8 4.9 8.9
2000 43 7.4 6.6 9.3
2100 7.9 7.8 9.6
2200 51 9.0 10.4 10.4
2300 10.0 12.4 11.0
2400 11.2 15 12.3
2500 12.1 16.8 13.3
2800 80 15.8 22.3 15.7
3050 99 19.2 26.8 17.4

That's close to my numbers as well.

 

[Salish Nomad]

In theory, my AT34 and 400 gallons of fuel, I should be able to go from Miami to about some place in NY. Most definitely if I jump into the Gulf Stream.
Of course, if I traveled in the ICW I would see many interesting things.
I cant figure out why I would want to end up in NY. LOL

I can go Anacortes to Ketchikan, and have a good reserve margin.

 

[markpierce]

80 horsepower is sufficient for the typical recreational cruiser. should be 1.5 to 2 gallons per hour unless operating in wide-open throttle where consumption will double for a gain of one knot.

 

[Art]

No body can exactly predict what fuel use numbers you will get, at any particular time, with any boat you purchase.

A lot depends on: How much weight you have loaded aboard. How clean your boat's bottom is. What size/shape/#-of-blades prop are spinning. Power/condition of engine. Tail wind or head wind. Following sea or head sea or beam or 3/4 angle. Direction of current. Speed of current. etc... etc... etc

Soooo... In generality: You can pretty much bet on getting 1 nmpg [or less] if you push your boat over hull speed. And you can pretty much bet on getting from 2 to 3 nmpg if you cruise a bit below hull speed.

When you travel in a boat I recommend tail winds and going with the current!

Good luck in your search and choice!

Art

 

[Mike Potter]

Cummins engines has a great public sight. Go to it, look up the 210 6b. There is propellor horsepower, fuel burn, heat rejection all the stuff you need

 

[MVDarlin]

I have twin 120 Ford Lehman's in my OA 43, 52 ft overall. I burn less than 5 gph at 80% power, 8.2 knot's.

 

[jgtrucking]

I have twin 120 Ford Lehman's in my OA 43, 52 ft overall. I burn less than 5 gph at 80% power, 8.2 knot's.

44' Island gypsy, twin fl120's, 8.75 mph, 1550 rpm, 2.75 gph over 1500 miles average.

 

[catalinajack]

DeFever 44, 56,000#, 1,600 RPM, 8.5 MPH, 3.5 GPH over 1,400 miles including some generator time.

44' Island gypsy, twin fl120's, 8.75 mph, 1550 rpm, 2.75 gph over 1500 miles average.

 

[boathealer]

GH N37. 50,000#, Twin 54hp Yannis, 7.5mph, ~2200rpm, 2.2gph average over 2000nm

 

[fryedaze]

42' 30000 lb, twin 1989 6BT5.9M, 210 HP, 9 mph at 1500 rpm. 3.5 gph

 

[JohnP]

36' boat 210 Cummins 2.55 nmpg Average Florida to New Jersey-- Between 7 and 7.5 knots Speed Approx 1200 rpm. Boat loaded 400gallons fuel 200 water and lots of stuff.

 

[JohnP]

If You look at Daves post above you will notice the 210 cummins are better suited to a longer boat. 42' works well. Friends have a 42' Grandbanks with the 210s and also travel faster than me. With better mpgs.

 

[OldDan1943]

IMO, the two reasons we worry about fuel consumption are, do we have enough to get there and the other is, unlike a car and buying maybe 15 or 20 gallons at a time, a boat fill up might be 100 - 2000 at a time aka big bucks.

 

[backinblue]

IMO, the two reasons we worry about fuel consumption are, do we have enough to get there and the other is, unlike a car and buying maybe 15 or 20 gallons at a time, a boat fill up might be 100 - 2000 at a time aka big bucks.

It may seem like big bucks but the size of the tank doesn't affect the price of the fuel. (I know I am being capt obvious). My boat only holds 180 gal, so I am probably unlikely to be buying more than 100 gal at a time. Once full it lasts quite a while so the few hundred spent is not a big deal. If your car had 100 gal tank it would be similar. Getting back to sailing, the wind is not free. If you own a sailboat long enough to replace sails and running and/or standing rigging, that's more painful than filling up on fuel.

 

[Nomad Willy]

44' Island gypsy, twin fl120's, 8.75 mph, 1550 rpm, 2.75 gph over 1500 miles average.

MV Darlin wrote;
“ I have twin 120 Ford Lehman's in my OA 43, 52 ft overall. I burn less than 5 gph at 80% power, 8.2 knot's.”

An FL burns 6gph at WOT.
That would be 12 gph w two engines.
“Less that 5gph” .. no way

 

[rslifkin]

MV Darlin wrote;
“ I have twin 120 Ford Lehman's in my OA 43, 52 ft overall. I burn less than 5 gph at 80% power, 8.2 knot's.”

An FL burns 6gph at WOT.
That would be 12 gph w two engines.
“Less that 5gph” .. no way

I expect he means 80% of max RPM, not actually 80% power. 80% of max RPM is more like 60% power on a typical prop curve, so it's much more reasonable sounding in that case.