Newbie question re range

[Hartstukke]

Please advise - How do I calculate the range of a 2012 27’ Ranger tug Yanmar 180 turbo (100 gallon tank) at 4.5 gph at 10-12 knots? The very basic idiot version please [emoji2957]


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[BradOwens]

I believe the formula is gallons of fuel available, divided by gallons per hour, times speed in knots.
So in your case 100/4.5 = 22.2 × 10 = 222 miles.

 

[bob daily]

Part-time
This is how I would figure it:
100 gal divided by 4.5 gpu =22.2 hrs of burn!
22.2 hrs times 11 knots = 244.5 nautical miles

 

[Hartstukke]

I believe the formula is gallons of fuel available divided by gallons per hour times speed in knots.
So in your case 100/4.5 = 22.2 × 10 = 222 miles.

Many thanks Brad!


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[Hydraulicjump]

and on that boat, if you drop your RPMs to about 1600, you will be burning a gallon per hour AND going pretty much the displacement hull speed of the boat which, assuming 27' on the waterline and a super clean bottom and prop is 6.9 kts. Imagine, as much as 700 miles on a tank. But...

before anyone else weighs in, the calculated range is not your range, of course, because it is crazy to put yourself in a position of running out of fuel given the consequences of getting your diesel restarted. The rule of thumb I like is to not let it drop below 1/3 of a tank just to cover contingencies. 1/4 tank in developed areas.

We always found that early mornings were for displacement speeds when you are feeling mellow and have a cup of coffee in your hand (6-7 knots) and afternoons with deadlines were for putting the boat up on plane (14+ kts). You will notice, by the way, that your burn rate at 10-12 kts is about the same as your planing speed (14-16 kts). Just the hydrodynamics of a semi-displacement hull.

Enjoy! Spring is here!

Jeff

 

[Hartstukke]

and on that boat, if you drop your RPMs to about 1600, you will be burning a gallon per hour AND going pretty much the displacement hull speed of the boat which, assuming 27' on the waterline and a super clean bottom and prop is 6.9 kts. Imagine, as much as 700 miles on a tank. But...

before anyone else weighs in, the calculated range is not your range, of course, because it is crazy to put yourself in a position of running out of fuel given the consequences of getting your diesel restarted. The rule of thumb I like is to not let it drop below 1/3 of a tank just to cover contingencies. 1/4 tank in developed areas.

We always found that early mornings were for displacement speeds when you are feeling mellow and have a cup of coffee in your hand (6-7 knots) and afternoons with deadlines were for putting the boat up on plane (14+ kts). You will notice, by the way, that your burn rate at 10-12 kts is about the same as your planing speed (14-16 kts). Just the hydrodynamics of a semi-displacement hull.

Enjoy! Spring is here!

Jeff

Yes Spring is here at last! Many thanks Jeff, I will definitely abide by the 1/3 tank rule, thanks for pointing that out!
Enjoy right back at ya!


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[Hartstukke]

Part-time
This is how I would figure it:
100 gal divided by 4.5 gpu =22.2 hrs of burn!
22.2 hrs times 11 knots = 244.5 nautical miles

Thanks Bob, this helps tremendously.


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[Crewdog]

I think your numbers might be a little off;
Even accounting for individual boat differences.

Here's my fuel burn chart - 80 gal fuel, full water, one person aboard, no food or long trip gear:
no wind, fresh water lake, altitude about 800 ft msl.

• RPM SPEED NMPG
  800 3.6 8.4
  900 3.7 8.3
  1000 4.3 8.2
  1100 4.6 7.6
  1200 4.9 7.8
  1300 5.1 6.9
  1400 5.3 6.1
  1500 5.5 5.8
  1600 5.9 5.3
  1700 6.0 5.0
  1800 6.4 4.6
  1900 6.6 4.4
  2000 6.8 4.0
  2100 7.1 3.7
  2200 7.3 3.0
  2300 7.5 2.9
  2400 7.7 2.9
  2500 7.9 2.5
  2600 8.2 2.4
  2700 8.5 2.2
  2800 8.8 2.2
  2900 9.2 2.1
  3000 9.6 2.0
  3100 10.3 2.0
  3200 11.1 2.0
  3300 11.8 2.0
  3400 12.4 1.9
  3500 13.2 1.9
  3600 13.6 1.8
  3700 13.9 1.8
  3800 14.3 1.7
  3950 15.2 1.6

I can send this as a msword docx if u pm your email address.
I'd suggest you make your own one calm day.

Good luck,
Bill

 

[Hartstukke]

I think your numbers might be a little off;
Even accounting for individual boat differences.

Here's my fuel burn chart - 80 gal fuel, full water, one person aboard, no food or long trip gear:
no wind, fresh water lake, altitude about 800 ft msl.

• RPM SPEED NMPG
  800 3.6 8.4
  900 3.7 8.3
  1000 4.3 8.2
  1100 4.6 7.6
  1200 4.9 7.8
  1300 5.1 6.9
  1400 5.3 6.1
  1500 5.5 5.8
  1600 5.9 5.3
  1700 6.0 5.0
  1800 6.4 4.6
  1900 6.6 4.4
  2000 6.8 4.0
  2100 7.1 3.7
  2200 7.3 3.0
  2300 7.5 2.9
  2400 7.7 2.9
  2500 7.9 2.5
  2600 8.2 2.4
  2700 8.5 2.2
  2800 8.8 2.2
  2900 9.2 2.1
  3000 9.6 2.0
  3100 10.3 2.0
  3200 11.1 2.0
  3300 11.8 2.0
  3400 12.4 1.9
  3500 13.2 1.9
  3600 13.6 1.8
  3700 13.9 1.8
  3800 14.3 1.7
  3950 15.2 1.6

I can send this as a msword docx if u pm your email address.
I'd suggest you make your own one calm day.

Good luck,
Bill

Thanks Bill, I sent you my email as a Private Message. Much appreciated.


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[TexasEye]

Fuel burn is normally .5 pounds per HP with a slight increase with TC engines

SO:

180 HP divided by 2 is 90 pounds of fuel per hour divided by 7 pounds per gallon equals 12.857 (13) gallons per hour at wide open throttle (plus a TC factor of a gallon or two more)

Most of us cruise at 50 to 75% power 90 to 135 HP is your case

as you approach 50% and less power the specific fuel burn goes slightly above .5 pounds per HP

This is a pretty good rule of thumb approach is you don't have the charts for that boat.

Each boat and engine is different, so what you really need to do is run a chart for your boat.

Tex

 

[Hartstukke]

Fuel burn is normally .5 pounds per HP with a slight increase with TC engines

SO:

180 HP divided by 2 is 90 pounds of fuel per hour divided by 7 pounds per gallon equals 12.857 (13) gallons per hour at wide open throttle (plus a TC factor of a gallon or two more)

Most of us cruise at 50 to 75% power 90 to 135 HP is your case

as you approach 50% and less power the specific fuel burn goes slightly above .5 pounds per HP

This is a pretty good rule of thumb approach is you don't have the charts for that boat.

Each boat and engine is different, so what you really need to do is run a chart for your boat.

Tex

Thanks Tx - I will run a chart, will be a worthwhile exercise. Many thanks for the info.


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[bob daily]

Well Hartstukke so much for the idiot version you requested!
So I have a 30 hp yanmar, at .5 lp of fuel per hp at max rpm =15 lp or a little over 2 gal. At 50% it would consume about a gallon an hour according to the math. Which is about 4 times what I put in the fuel tank! I have a 35 hp and a 65 hp tractor that I use for farming and get better fuel economy than the .5 lp per hrs at max rpm consumption. Every situation is different so you'll need to calculate your fuel consumption per you boat.
It wouldn't hurt to have the knowledge of how to prime the system just incase your calculation is wrong. Good luck and be safe! Bob

 

[TexasEye]

Well Hartstukke so much for the idiot version you requested!
So I have a 30 hp yanmar, at .5 lp of fuel per hp at max rpm =15 lp or a little over 2 gal. At 50% it would consume about a gallon an hour according to the math. Which is about 4 times what I put in the fuel tank! I have a 35 hp and a 65 hp tractor that I use for farming and get better fuel economy than the .5 lp per hrs at max rpm consumption. Every situation is different so you'll need to calculate your fuel consumption per you boat.
It wouldn't hurt to have the knowledge of how to prime the system just incase your calculation is wrong. Good luck and be safe! Bob

Rule of Thumb planning isn't supposed to be exact math but a plan that is easy to calculate and provides a good answer leaning towards safe operations where the actual numbers are not available.

The estimated math is .38 to .42/HP if that helps. This puts the 180HP example at WOT burning between 9.5 and 10.8 GPH and the Rule of Thumb at 13 GPH.

Now if you have a boat that you are operating for the first time, or ferrying a unknown vessel on a long trip the Rule of Thumb is probably the number you need to plan until the first fuel stop where you can adjust your numbers, even then I use the Rule of Thumb until I have confirmed the fuel flow three times, unless the actual numbers are greater than the Rule of Thumb which has happened.

The Rule of Thumb is based on the unknown factors and safe operations.

Every boat is different as is every adventure.

Tex

 

[bob daily]

Tex
You are correct and every situation/vessel is different prior to adventuring out in any condition one needs to know what their capabilities are! I would recommend that every diesel owner knows how to prime his engine and know the limitations. Thanks for your thoughts !

 

[TexasEye]

Yep!