Reply
 
Thread Tools Display Modes
 
Old 12-25-2013, 08:22 AM   #1
Guru
 
Portuguese's Avatar
 
City: Salvador - BA
Country: Brazil
Vessel Name: Rainha Jannota
Vessel Model: Curruira 46
Join Date: Jun 2011
Posts: 662
Send a message via MSN to Portuguese
Mileage vs Consumption

Merry Christmas Sailors:
Many ideas and opinions have been written in this forum about consumption, cruising speed, engine RPM, etc.
I am yet to find out what is economical and what is not for a specific boat size and weight. When I project the behavior of my boat, which is one of a kind because it is the first one in its size and design and there’s no brother vessel to compare, the best I can get is 2.4 miles/gallon at 7 knots cruising speed. According to the same calculations max speed will be 8.5 knots where the performance would be at its best 1.45 miles/gallon.
Anyway, having in mind that the cruising speed of 7 knots, in a 55 Klbs displacement hull sliding in 40.2’ of LWL, are 2.39 miles/gallon an economical number or could the it be better?
For you guys with boats ranging the same size and weight, is this a good number?
Thank you for your answers.
Portuguese
__________________
Advertisement

__________________
Now retired and cruising in calm waters
https://www.flickr.com/photos/rainha_jannota/
Portuguese is offline   Reply With Quote
Old 12-25-2013, 08:53 AM   #2
Guru
 
cardude01's Avatar
 
City: Victoria TX
Country: USA
Vessel Name: Bijou
Vessel Model: 2008 Island Packet steadysailer
Join Date: Nov 2012
Posts: 3,170
I'm looking at a 44' powercat that allegedly burns 2.5 GPH at 8 knots, which is 9.2 mph, so that's what, 3.68 mpg?

Is that how you figure that?
__________________

cardude01 is offline   Reply With Quote
Old 12-25-2013, 08:57 AM   #3
Guru
 
Portuguese's Avatar
 
City: Salvador - BA
Country: Brazil
Vessel Name: Rainha Jannota
Vessel Model: Curruira 46
Join Date: Jun 2011
Posts: 662
Send a message via MSN to Portuguese
My miles reflect nautical miles. Nautical miles/hour are Knots.

Basicaly what you burn in 0n2 hour divided by what you run in the same period.

It's about that. There's a diference between road miles and nautical miles.
__________________
Now retired and cruising in calm waters
https://www.flickr.com/photos/rainha_jannota/
Portuguese is offline   Reply With Quote
Old 12-25-2013, 09:08 AM   #4
Guru
 
cardude01's Avatar
 
City: Victoria TX
Country: USA
Vessel Name: Bijou
Vessel Model: 2008 Island Packet steadysailer
Join Date: Nov 2012
Posts: 3,170
If one knot = 1 NMPH, just divide 8 knots per hour by 2.5 GPH is 3.2 NMPH?
cardude01 is offline   Reply With Quote
Old 12-25-2013, 09:55 AM   #5
Senior Member
 
Join Date: Oct 2007
Posts: 158
My sweet spot for cruisin is determined usually by rpm's. However actual speed/distance traveled can be greatly altered by the wind and current. Therefore I have always referred to gph, regardless.
El Sea is offline   Reply With Quote
Old 12-25-2013, 10:06 AM   #6
Senior Member
 
magicbus's Avatar
 
Join Date: Nov 2010
Posts: 460
According to my engine electronic monitor our current trip is at an average of 7 mph getting an average of 2.3 mpg. Don't know why the monitor is in statute miles.



Dave
__________________
Barnegat Light NJ or Nantucket MA
magicbus is offline   Reply With Quote
Old 12-25-2013, 10:19 AM   #7
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,707
That's an easy one for me. I got a boat w such low consumption it dosn't matter. Haven't got the time to go far enough for mileage to be worth thinking about.

What .. me worry ... who cares.

But I've always thought of fuel consumption on a boat as GPH. Never been able to relate to MPG. Since we burn 1GPH I instantly convert that to 6MPG as we go 6 knots whenever you guys start talking about MPG.

I had a Cadillac that burned 6 GPH at 60 mph.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 12-25-2013, 10:24 AM   #8
Guru
 
Moonstruck's Avatar
 
City: Hailing Port: Charleston, SC
Country: USA
Vessel Name: Moonstruck
Vessel Model: Sabre 42 Hardtop Express
Join Date: Nov 2008
Posts: 7,848
Quote:
Originally Posted by magicbus View Post
According to my engine electronic monitor our current trip is at an average of 7 mph getting an average of 2.3 mpg. Don't know why the monitor is in statute miles.



Dave
Dave, it was probably set for statute mpg because the ICW id denoted in statute miles.
__________________
Don on Moonstruck
Sabre 42 Hardtop Express & Blackfin 25 CC
When cruising life is simpler, but on a grander scale (author unknown)
http://moonstruckblog.wordpress.com/
Moonstruck is online now   Reply With Quote
Old 12-25-2013, 10:28 AM   #9
Guru
 
Alemao's Avatar
 
City: Fort Myers - FL
Country: Brazil
Vessel Name: ORIGINAL
Vessel Model: Hi Star 55
Join Date: Jul 2011
Posts: 629
With a 22 tons vessel, I can do 3.5gph at 7 knots, it means 2 mm/gal. I think thats good
Alemao is offline   Reply With Quote
Old 12-25-2013, 10:38 AM   #10
Guru
 
O C Diver's Avatar
 
City: Fort Myers, FL... Summers in Crisfield, MD
Country: USA
Vessel Name: Slow Hand
Vessel Model: Cherubini Independence 45
Join Date: Dec 2010
Posts: 4,813
A great deal of fuel consuption efficiency will depend on drive train setup. My guess is that your miles per gallon could be over 3. A lot will depend on what engine rpm you run at 7 knotts. Engine size will also be a consideration. At 7 knotts you may be under 40 HP. If you are generating that 40 HP out of a 450 HP motor, you won't get the efficiency you would get generating the same HP out of a 130 HP motor. Time will tell.

Ted
__________________
Blog: mvslowhand.com
I'm tired of fast moves, I've got a slow groove, on my mind.....
I want to spend some time, Not come and go in a heated rush.....
"Slow Hand" by The Pointer Sisters
O C Diver is online now   Reply With Quote
Old 12-25-2013, 10:48 AM   #11
Guru
 
Alemao's Avatar
 
City: Fort Myers - FL
Country: Brazil
Vessel Name: ORIGINAL
Vessel Model: Hi Star 55
Join Date: Jul 2011
Posts: 629
I have 2 turbo cats 3208, 375 HP each one. I think that I don't need 750 HP, the maximum speed that I cruise is 9.5 at 1,800 rpm. To cruise at 7 knots, i run at 1,200 rpm.
Alemao is offline   Reply With Quote
Old 12-25-2013, 11:04 AM   #12
Guru
 
twistedtree's Avatar
 
City: Gloucester, MA
Country: USA
Join Date: Jan 2013
Posts: 3,187
When looking at efficiency, which is Nautical Miles Per Gallon, not GPH, there are several factors that come into play. Some of those factors are really big, some are medium impact, and some have a small impact. In order of importance, they are:

1) Speed. The HP, and hence fuel burn, required to move a boat varies as the square of the speed. If you double the speed, you quadruple the fuel burn. This is by far the dominant factor in fuel burn and efficiency, and is why comparing numbers between boats is almost always a useless and misleading exercise.

2) Displacement. The HP, and hence fuel burn required to move a boat varies proportionally to the displacements. In this case, displacement is the actual weight of the boat, fuel, and gear, not the calculated displacement used by registries. The size of your boat matters, but not nearly as much as the speed you are trying to move.

3) Engine size, type of running gear, and hull form. This makes very little difference. The fuel burn of an engine, regarless of it's size, depends on how much HP it is generating, and that depends on the two factors above. A 100HP engine and a 400HP engine, both putting out 70HP to move a boat at a particular speed, will burn just about the same amount of fuel. Yes, there will be some difference, but it's the least important factor. Changing speed by 1/10th of a knot will make much more of a difference. Also, there will be slight differences between old engines and newer, common rail engines, but that too is small compared to the other factors. Hull shapes can make a difference, but that too is comparatively small.

There are lots of calculators that will estimate fuel burn, and they tend to be pretty accurate. It's the same calculators that are used to size a prop, which in turn determines the HP.

We tend to focus on things like "the most efficient RPM for my engine", and "4 vs 5 blade props". This can make a difference, but they are the small things, not the bog thing. The big thing is speed.
__________________
www.MVTanglewood.com
twistedtree is offline   Reply With Quote
Old 12-25-2013, 11:20 AM   #13
Senior Member
 
magicbus's Avatar
 
Join Date: Nov 2010
Posts: 460
Quote:
Originally Posted by Moonstruck View Post
Dave, it was probably set for statute mpg because the ICW id denoted in statute miles.
Yes my wife plans our day by the ICW books and I think in terms of knots, which actually works out well because we end up with a cushion factor that - knock fiberglass - has so far managed to get us to a stopping point before dark!

Dave
__________________
Barnegat Light NJ or Nantucket MA
magicbus is offline   Reply With Quote
Old 12-25-2013, 11:52 AM   #14
Scraping Paint
 
City: Fort Lauderdale
Vessel Model: CHB 48 Zodiac YL 4.2
Join Date: Oct 2007
Posts: 3,804
Quote:
Originally Posted by twistedtree View Post
When looking at efficiency, which is Nautical Miles Per Gallon, not GPH, there are several factors that come into play.
Most of which are not even mentioned after that introduction.

Nautical miles per gallon is pretty much a useless measure except for ballpark comparison of trips from one day to the next and has zero to do with efficiency - of which type of efficiency never seems to be mentioned in these voodoo engineering threads.

If you count the shaft turns, the distance traveled over the ground, the distance traveled through the water, the weight of fuel burned, and the horsepower hours produced, then you might have a number which makes some sense or has a useful meaning.

Otherwise it is equivalent to looking at a photo of a transom and telling the world what kind of engines are best suited for the boat.
RickB is offline   Reply With Quote
Old 12-25-2013, 12:08 PM   #15
Guru
 
twistedtree's Avatar
 
City: Gloucester, MA
Country: USA
Join Date: Jan 2013
Posts: 3,187
Quote:
Originally Posted by RickB View Post
Most of which are not even mentioned after that introduction.
True, I left the division out, assuming it's not hard to do.

Quote:
Nautical miles per gallon is pretty much a useless measure except for ballpark comparison of trips from one day to the next and has zero to do with efficiency - of which type of efficiency never seems to be mentioned in these voodoo engineering threads.
huhh? Efficiency is a comparison of work done per unit of energy. In this case NM moved per gallon of fuel burned. GPH is energy per hour, but leaves out the work accomplished, i.e. the distance traveled. Comparison of GPH is meaningless unless you also consider the distance traveled, ie the work done. One boat burning 10 GPH moving 10 kts is the same efficiency as a boat burning 5 GPH moving 5 kts. Both are getting work done at 1 NM/G

Quote:
If you count the shaft turns, the distance traveled over the ground, the distance traveled through the water, the weight of fuel burned, and the horsepower hours produced, then you might have a number which makes some sense or has a useful meaning.
Yes, and it distills down to NM/G
__________________
www.MVTanglewood.com
twistedtree is offline   Reply With Quote
Old 12-25-2013, 01:24 PM   #16
Guru
 
O C Diver's Avatar
 
City: Fort Myers, FL... Summers in Crisfield, MD
Country: USA
Vessel Name: Slow Hand
Vessel Model: Cherubini Independence 45
Join Date: Dec 2010
Posts: 4,813
Quote:
Originally Posted by twistedtree View Post

3) Engine size, type of running gear, and hull form. This makes very little difference. The fuel burn of an engine, regarless of it's size, depends on how much HP it is generating, and that depends on the two factors above. A 100HP engine and a 400HP engine, both putting out 70HP to move a boat at a particular speed, will burn just about the same amount of fuel. Yes, there will be some difference, but it's the least important factor. Changing speed by 1/10th of a knot will make much more of a difference. Also, there will be slight differences between old engines and newer, common rail engines, but that too is small compared to the other factors. Hull shapes can make a difference, but that too is comparatively small.
This isn't really true. A DD 8-71 will burn significantly more fuel to generate 70 HP as compared to a John Deere 4045T (4 cyl). You may not see as much of a difference between 2 engines of the same series such as a Cummins 6BT 220 HP and 6BTA 375 HP. When Willard switched from the Cummins 6B 135 HP (6 cyl. ) to the John Deere 4045T (4cyl. ) for there last 40' trawler, they realized a 20% fuel savings at 7 knotts. Same hull, same speed, different engine. While speed is likely the biggest factor, engine size can make a significat difference. At $4 a gallon, fuel savings could be substantial to an active cruiser.

Ted
__________________
Blog: mvslowhand.com
I'm tired of fast moves, I've got a slow groove, on my mind.....
I want to spend some time, Not come and go in a heated rush.....
"Slow Hand" by The Pointer Sisters
O C Diver is online now   Reply With Quote
Old 12-25-2013, 03:15 PM   #17
Guru
 
Portuguese's Avatar
 
City: Salvador - BA
Country: Brazil
Vessel Name: Rainha Jannota
Vessel Model: Curruira 46
Join Date: Jun 2011
Posts: 662
Send a message via MSN to Portuguese
Thank you all guys

Ted, thank you for your comments in particular.

I didn't mean to start a major discussion about the subject. It is obvious that we are far from a conceptual consensus about the issue.
I have no doubts whatsoever that fuel efficiency for a given vessel has to be translated in miles per gallon, distance traveled per volume of fuel burnt, which translates in work done/energy spent in the process. It does not matter if it considers speed over ground, speed made good, shaft rpm engine brand etc. This is just desk engineering technicalities which I am tired off after 33 years of deep water sub-sea engineering in the oil drilling industry.
What I would like to see here, is an arrow straight answer based on the boat data below, from your experience, assuming that the boat sails, with a 1.1 times the hull speed, 7 knots, in normal quite conditions of sea, current, wind etc, covering 2.4 miles per gallon, is this specific hull performing good or bad in terms of fuel efficiency? That is all I want to know.

Pertinent data of M/V “Rainha Jannota”
LOA 46’
LWL 40.2’
Hull Weight @ 75% 55000 lbs
Main Engine Deutz Turbo 145 HP @ 2500 RPM
Gear ZFW220 3.96:1
Propeller 4 Blade Bronze 34” x 26”
Shaft 2.25” 304 SS

Thank you all
__________________
Now retired and cruising in calm waters
https://www.flickr.com/photos/rainha_jannota/
Portuguese is offline   Reply With Quote
Old 12-25-2013, 03:21 PM   #18
Guru
 
Brooksie's Avatar
 
City: Cape Cod, MA
Country: USA
Vessel Name: Island Seeker
Vessel Model: Willard 36 Sedan
Join Date: Oct 2007
Posts: 954
Quote This isn't really true. A DD 8-71 will burn significantly more fuel to generate 70 HP as compared to a John Deere 4045T (4 cyl).

This would be true be true because the DD is way oversize & 2 cycle.

Quote When Willard switched from the Cummins 6B 135 HP (6 cyl. ) to the John Deere 4045T (4cyl. ) for there last 40' trawler, they realized a 20% fuel savings at 7 knotts. Same hull, same speed, different engine. While speed is likely the biggest factor, engine size can make a significat difference.

Really, 20%?
Brooksie is offline   Reply With Quote
Old 12-25-2013, 04:15 PM   #19
Scraping Paint
 
City: Fort Lauderdale
Vessel Model: CHB 48 Zodiac YL 4.2
Join Date: Oct 2007
Posts: 3,804
Quote:
Originally Posted by twistedtree View Post
Yes, and it distills down to NM/G
Which is a number that may vary radically within hours and miles. It depends on the wind, current, waves, and ability of the driver to steer straight.

When the term "efficiency" is tossed in just for effect, it becomes even more of a gratuitous expression since the power and time to move an unknown weight that distance is not expressed or probably even known.
RickB is offline   Reply With Quote
Old 12-25-2013, 04:22 PM   #20
Guru
 
O C Diver's Avatar
 
City: Fort Myers, FL... Summers in Crisfield, MD
Country: USA
Vessel Name: Slow Hand
Vessel Model: Cherubini Independence 45
Join Date: Dec 2010
Posts: 4,813
Quote:
Originally Posted by Brooksie View Post
Quote When Willard switched from the Cummins 6B 135 HP (6 cyl. ) to the John Deere 4045T (4cyl. ) for there last 40' trawler, they realized a 20% fuel savings at 7 knotts. Same hull, same speed, different engine. While speed is likely the biggest factor, engine size can make a significat difference.

Really, 20%?
Willard's last 40' (Aloha) was custom built for Patrick Gerety a principle in the trawler division of Willard. At the time of it's building, it wasn't expected to be the last 40'. It was built with the JD 4045T and according to Patrick from the testing at Willard, " Expect to burn about 1.3 GPH @ 7.5 knotts in Aloha and 1.7 GPH @ 7.5 knotts in Annabelle (Willard 40 with Cummins 6BT)."

Ted
__________________

__________________
Blog: mvslowhand.com
I'm tired of fast moves, I've got a slow groove, on my mind.....
I want to spend some time, Not come and go in a heated rush.....
"Slow Hand" by The Pointer Sisters
O C Diver is online now   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not 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 Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





All times are GMT -5. The time now is 06:28 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012