How to Determine Auxiliary Diesel Range? - SailNet Community
Reply
 
LinkBack Thread Tools
post #1 of Old 01-30-2009 Thread Starter
Senior Member
 
Join Date: Jan 2009
Posts: 134
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 7
 
Question How to Determine Auxiliary Diesel Range?

Is there a rule of thumb that I can use to estimate auxiliary diesel range. If I know the cruising speed and engine horse power, can I get a reasonable burn rate (mpg). In Yachtworld they usually mention tank capacity, so with mpg I can get range. I assume the miles in mpg, for a cruiser, is in nautical miles. I tried searching old threads but gave up on that.
Winderlust is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
Advertisement
 
post #2 of Old 01-30-2009
Senior Member
 
Join Date: Jun 2007
Posts: 166
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
 
For my boat I figure 1/2 gallon/hr at 5 knots with a 20 gallon tank that gives a range of 200 miles. This is a conservative estimate. My boat is 32' 12500#s with a 20 hp diesel. Of course everything changes depending upon conditions. That is why I use conservative estimates. Speed is a huge factor as speed really sucks up the fuel.
MoonSailer is offline  
Quote Quick Reply Share with Facebook
post #3 of Old 01-30-2009
Wandering Aimlessly
 
PBzeer's Avatar
 
Join Date: Nov 2002
Location: Cruising
Posts: 20,889
Thanks: 0
Thanked 91 Times in 88 Posts
Rep Power: 15
     
Marine fuel is generally determined in gallons per hour, rather than miles per gallon. This link should get you on the right track: All About Fuel and Your Boat - Nautical Know How

John
Ontario 32 - Aria

Free, is the heart, that lives not, in fear.
Full, is the spirit, that thinks not, of falling.
True, is the soul, that hesitates not, to give.
Alive, is the one, that believes, in love.
JCP


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
- Website & Blog

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
PBzeer is online now  
Quote Quick Reply Share with Facebook
post #4 of Old 01-31-2009
Glad I found Sailnet
 
Bene505's Avatar
 
Join Date: Jul 2008
Posts: 3,807
Thanks: 14
Thanked 51 Times in 50 Posts
Rep Power: 8
   
Great post. Thanks. Rep to you.

Quote:
Originally Posted by PBzeer View Post
Marine fuel is generally determined in gallons per hour, rather than miles per gallon. This link should get you on the right track: All About Fuel and Your Boat - Nautical Know How
Bene505 is offline  
Quote Quick Reply Share with Facebook
post #5 of Old 01-31-2009 Thread Starter
Senior Member
 
Join Date: Jan 2009
Posts: 134
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 7
 
Smile This I can use

PBzeer this is a good answer; thanks.

Quote from your link:

"Diesel engines consume about 1 gallon per hour for every 18 hp used. You can estimate the number of gallons consumed per hour by multiplying horsepower used by 0.055.

Note: An engine at cruising speed usually uses only about two-thirds of its maximum available horsepower. Most marine engines are designed to run continuously at between 60 and 75 percent of maximum speed. Diesels tend to be more toward the top of the range."

So the horsepower factor is .055.

Can I say that, in calm/flat, a 54 hp diesel running at 75% rpm cruising speed ((54*.75=40.5)*.055), burns 2.23 gph. And if the boat's cruising speed is 8nts and its fuel capacity is 50 gallons, then its range should be ((50/ 2.23)*8) or 179 nautical miles!?

I think I got it.
Winderlust is offline  
Quote Quick Reply Share with Facebook
post #6 of Old 01-31-2009
Senior Member
 
Join Date: Sep 2006
Location: Scotland
Posts: 2,364
Thanks: 0
Thanked 11 Times in 11 Posts
Rep Power: 9
 
My 10 ton ship, long-keeled, driven at about 5.5 kt has a consumption of about 9 nautical miles per UK gallon, or about 7.5 nautical miles per US gal, in flat calm.

The motor is a 35 hp diesel, when used flat out, can reach 8.5 kt. It's a while since I did that.

Work the engine hard, and you'll think there is another hole in the tank.

Get someone to help you. Choose a flat-calm day, with no tide. Pull the fuel hose off the tank fitting. Get a wee calibrated jug and fill it up with diesel.
Get your stopwatch and your calculator. Run your motor at various speeds and calculate the fuel consumption yourself.

It must be flat calm. Into a headwind it will alter. Into a chop the ship really drinks fuel. That 5.5 kt can become 1 kt into a wicked chop.

Write your figures down, and you can plot a wee graph to work out your optimum cruise.

To save fuel, run the ship slowly. It can save enormous amounts of fuel. The state of the hull surface also matters. In a wee sea trial about a decade ago, at Stonehaven Scotland, 1700 rpm with a wee thin weed growth meant a speed of 5.5 kt. Next morning, same conditions, with the weed film removed, that 1700 rpm became 6.6 kt.

That's quite a hit.

I simply cannot keep all the weed off the ship all the time though. It's nothing like the same problem in fresh water though, well, here at least.
.

Last edited by Rockter; 01-31-2009 at 07:15 AM.
Rockter is offline  
Quote Quick Reply Share with Facebook
post #7 of Old 01-31-2009
Telstar 28
 
sailingdog's Avatar
 
Join Date: Mar 2006
Location: New England
Posts: 43,290
Thanks: 0
Thanked 14 Times in 12 Posts
Rep Power: 14
         
The only problem with this technique is that it won't work, since most diesel engines have a fuel return line, and unless your wee calibrated jug has the fuel return line run in to it as well, you'll just see how much the engine sucked up, but not what it actually USED.

Quote:
Originally Posted by Rockter View Post
My 10 ton ship, long-keeled, driven at about 5.5 kt has a consumption of about 9 nautical miles per UK gallon, or about 7.5 nautical miles per US gal, in flat calm.

The motor is a 35 hp diesel, when used flat out, can reach 8.5 kt. It's a while since I did that.

Work the engine hard, and you'll think there is another hole in the tank.

Get someone to help you. Choose a flat-calm day, with no tide. Pull the fuel hose off the tank fitting. Get a wee calibrated jug and fill it up with diesel.
Get your stopwatch and your calculator. Run your motor at various speeds and calculate the fuel consumption yourself.

It must be flat calm. Into a headwind it will alter. Into a chop the ship really drinks fuel. That 5.5 kt can become 1 kt into a wicked chop.

Write your figures down, and you can plot a wee graph to work out your optimum cruise.

To save fuel, run the ship slowly. It can save enormous amounts of fuel. The state of the hull surface also matters. In a wee sea trial about a decade ago, at Stonehaven Scotland, 1700 rpm with a wee thin weed growth meant a speed of 5.5 kt. Next morning, same conditions, with the weed film removed, that 1700 rpm became 6.6 kt.

That's quite a hit.

I simply cannot keep all the weed off the ship all the time though. It's nothing like the same problem in fresh water though, well, here at least.
.

Sailingdog

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
.

Still—DON'T READ THAT POST AGAIN.

Last edited by sailingdog; 01-31-2009 at 01:38 PM.
sailingdog is offline  
Quote Quick Reply Share with Facebook
post #8 of Old 01-31-2009
Senior Member
 
Join Date: Sep 2006
Location: Scotland
Posts: 2,364
Thanks: 0
Thanked 11 Times in 11 Posts
Rep Power: 9
 
My motor does not have a return line.

It has never had a return line.

Sailingdog, do you think that I spend my time making this stuff up? Does it ever occur to you that perhaps I have tried it and it works?

Does that ever enter your head?

Or do you just know that it doesn't work, from 3500 miles away? Did I make up the figures about the 5.5 and 6.6 kt too? Are they fiction also? Maybe Stonehaven is fiction too...?...

Stonehaven Harbour Webcam


If his motor has a return line... mine doesn't... then stick a wee rubber hose on the end of the return line and route it to the jug then (it does not even have to be the same jug, you can use another container, then pour it into the jug, or use two jugs and subtraction). Either way, with a tall jug, well calibrated, and a stopwatch it is very accurate indeed. A calculator helps, but it's not essential.

Oh, and warm the motor first.

.

Last edited by Rockter; 01-31-2009 at 10:33 AM.
Rockter is offline  
Quote Quick Reply Share with Facebook
post #9 of Old 01-31-2009
Dirt Free
 
boatpoker's Avatar
 
Join Date: Jul 2008
Location: Toronto
Posts: 1,154
Thanks: 9
Thanked 31 Times in 30 Posts
Rep Power: 7
 
I don't doubt your veracity but I have never heard of a diesel engine without a return fuel line (new common rail type excepted) and don't understand how that would work given the pressures involved. What make/model is it ? I'd love to learn about it.

Dirt People Scare me
boatpoker is offline  
Quote Quick Reply Share with Facebook
post #10 of Old 01-31-2009
Senior Member
 
Valiente's Avatar
 
Join Date: Jun 2006
Location: Toronto
Posts: 5,491
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 10
   
I haven't explored this methodically, but I know from the literature supplied in the manual and my own records of time run and speed attained that my 52 hp can push my boat at 7 knots expensively or 5 knots parsimoniously...so I do 5 knots and if there's nine-10 knots of wind from the right direction, setting all the sails can buy me another knot or so. With no engine and 10 knots of wind, I might do 4.5 knots of speed, so it's worth it to motorsail at times.

The point is that range is extremely hard to discern when chop, revs and speed are so interlinked. My solution is to add a third tank for "daytank" use, giving me 40 + 50 + 50 = 140 gallons. In a dead calm at 4 knots, that's nearly a week's worth of motoring or 600 NM of range...but when is it going to be a dead calm for nearly a week? Better I should sail!

Can't sleep? Read my countdown to voyaging blog @
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Valiente is offline  
Quote Quick Reply Share with Facebook
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.


User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
Rebuild 1980 Volvo MD11C Diesel Auxiliary ntheyer Gear & Maintenance 37 09-24-2006 10:33 AM
Diesel Fuel Essentials Tom Wood Gear and Maintenance Articles 0 03-22-2004 07:00 PM
Diesel Fuel Essentials Tom Wood Her Sailnet Articles 0 03-22-2004 07:00 PM
Light Lists, Lighthouses, and Visible Ranges Jim Sexton Seamanship Articles 0 06-19-2003 08:00 PM
Light Lists, Lighthouses, and Visible Ranges Jim Sexton Her Sailnet Articles 0 06-19-2003 08:00 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome