Reply
 
Thread Tools Display Modes
 
Old 03-15-2016, 11:58 AM   #1
Veteran Member
 
City: Naperville
Country: us
Join Date: Dec 2015
Posts: 44
Fuel consumption at low speed?

I've read on line that sailboats can get 8MPG under power(no sail) ~ at low speed like 5-6knots.

Obviously power boats have very different engine, hull design etc. I wonder in general what kind of MPG can a power boat get at low speed? Or could you tell me for your boat, what max MPG can you extract? At what speed and what kind of engine? Thanks!
__________________
Advertisement

chicagoq is offline   Reply With Quote
Old 03-15-2016, 12:37 PM   #2
Guru
 
City: gulf coast
Country: pinellas
Join Date: Jun 2014
Posts: 1,846
greatly depends on the size of the boat
__________________

bayview is offline   Reply With Quote
Old 03-15-2016, 01:05 PM   #3
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: 3,752
45' semi displacement 40,000 lbs.
John Deere 4045TFM75 135 HP
6 knots at 1,200 RPM 1.2 GPH 5.0 MPG

Not a significant improvement below 6 knotts. Also feel the engine needs to run at or above 1,200 RPM when cruising for hours.

Ted
__________________
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 offline   Reply With Quote
Old 03-15-2016, 01:12 PM   #4
Guru
 
City: Satsuma FL
Country: United States
Vessel Name: No Mo Trawla
Vessel Model: Hurricane SS188
Join Date: Jul 2014
Posts: 1,383
I have looked at the fuel consumption tables for on a Mercury Verado 200 hp gas outboard and on a Sun Tracker 24' pontoon boat, and at 2.8 knots, it gets 9.3 miles per gallon. At 13 knots, it gets 4.8 MPGs.
Donsan is online now   Reply With Quote
Old 03-15-2016, 01:30 PM   #5
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 2,948
38' 15000lb single Cummins 450- consistently gets 1.9gph at 7.5kts, 950rpm, just under 4nmpg.

Not happy running engine at that low of a load, but it does not seem to hurt it. Often run it 2000rpm/20kts/12gph to clean it up.
Ski in NC is online now   Reply With Quote
Old 03-15-2016, 02:27 PM   #6
Guru
 
dhays's Avatar
 
City: Gig Harbor
Country: United States
Vessel Name: Kinship
Vessel Model: North Pacific 43
Join Date: May 2015
Posts: 2,808
You can take a look at this thread . Lots of information on there.

Sailboats have a full displacement hull and small engine. They burn very little fuel to get to just below hull speed. Full displacement power boats with smaller engines will do the same. Other hull shapes will not get anywhere near those fuel burn numbers.

So as other have said, "it depends"
__________________
Regards,

Dave
SPOT page
dhays is online now   Reply With Quote
Old 03-15-2016, 02:46 PM   #7
Dauntless Award
 
Wxx3's Avatar
 
City: New York, NY
Country: USA
Vessel Name: Dauntless
Vessel Model: Kadey Krogen 42 - 148
Join Date: Jan 2013
Posts: 1,953
Kadey Krogen 42, 44,000 lbs. Lehman SP135

1400 rpm 1.2 gph, 5.8 knots
1600 rpm 1.6 6.8

I can go 1200 to 1300 and keep it at 1 gph, at about 5 knots, but engine stays too cool.
__________________
M/Y Dauntless, New York
a Kadey Krogen 42 Currently https://share.delorme.com/dauntless
Blog: https://dauntlessatsea.com
Find us: https://share.delorme.com/dauntless
Wxx3 is offline   Reply With Quote
Old 03-15-2016, 02:48 PM   #8
Veteran Member
 
City: Naperville
Country: us
Join Date: Dec 2015
Posts: 44
Thank you guys! So actually the numbers are comparable with sailboats. That gives me more confidence. I have seen so many 1MPG, 2MPG for power boats on boattest.com, have been wondering with most boats have only a few hundred gallon fuel, how do these boats go long distance at all? Now I understand those 1MPG, 2MPG are at higher speed, the fuel consumption drops significantly at lower speed, and this applies to power boats too, not just sailboats.
chicagoq is offline   Reply With Quote
Old 03-15-2016, 04:48 PM   #9
Guru
 
TDunn's Avatar
 
City: Maine Coast
Country: USA
Vessel Name: Tortuga
Vessel Model: Nunes Brothers Raised Deck Cruiser
Join Date: Feb 2015
Posts: 607
My 32'8", 10,000 lb, pure displacement cruiser (see avatar pic) burns about 0.2-0.25 gph at 5 knots or 20-25 nmpg. My 36', 15,000 lb sailboat burns 0.45 gph at 6 knots for 13.3 nmpg.
TDunn is offline   Reply With Quote
Old 03-15-2016, 05:01 PM   #10
Senior Member
 
AKDoug's Avatar
 
City: Kenai, Alaska
Country: USA
Vessel Name: Melanie Rose
Vessel Model: 1999 Willard PH
Join Date: Feb 2013
Posts: 444
I burn .42 gph at 5.5 knots, 1 gph at 7 knots. I usually cruise at 4.5 to 5.5 knots and use 7 knots for bucking an opposing current or hurrying across a large open stretch, since the hull doesn't really like it. I get 14 mpg at my 5.5 knot speed and more than that if I slow down, above 6 knots my hull starts digging a hole in the water and pulls the exhaust under. 50 hp Yanmar 3JH with a 3 bladed prop.
AKDoug is offline   Reply With Quote
Old 03-15-2016, 07:33 PM   #11
TF Site Team
 
Baker's Avatar
 
City: League City, Tx
Country: Texas
Vessel Model: Carver 356
Join Date: Oct 2007
Posts: 5,120
Quote:
Originally Posted by chicagoq View Post
Thank you guys! So actually the numbers are comparable with sailboats. That gives me more confidence. I have seen so many 1MPG, 2MPG for power boats on boattest.com, have been wondering with most boats have only a few hundred gallon fuel, how do these boats go long distance at all? Now I understand those 1MPG, 2MPG are at higher speed, the fuel consumption drops significantly at lower speed, and this applies to power boats too, not just sailboats.
I am one of those 1mpg folks(18kts). Range is not really an issue when you do the type of boating I do. To get more range, I just stop for more fuel. It seems you are in the research mode on powerboat cruising. My biggest advice to you is to be absolutely honest with yourself on how you are gonna use your boat. Sailboaters are the worst about this...no offense and I used to be one(had 3 sailboats). Sailboaters have this impassioned perception of what it is all about. They feel guilty if they are too comfortable...or burning too much fuel. They feel the need to have extremely complex and expensive charging systems..... Heaven forbid they start the generator!!!! Anyway, you have perception and you have reality. Hopefully those two "visions" are very close to one another!!! If not, the boat sits and/or is sold.
__________________
Prairie 29...Perkins 4236...Sold
Mainship Pilot 30...Yanmar 4LHA-STP...Sold
Carver 356...T-Cummins 330B
Baker is offline   Reply With Quote
Old 03-15-2016, 08:57 PM   #12
Veteran Member
 
2dboat's Avatar
 
City: Northwest Basin, Penetanguishene, ON.
Country: canada
Vessel Name: SAN-BAR
Vessel Model: 1981 CHEER MEN PT 38 EUROPA
Join Date: Mar 2016
Posts: 27
We sold her last summer but our 1963 34ft Chris Craft Constellation with original twin 283V8's consistently burned 4 gallons per hour at 8mph when we river cruised. So at a "trawler like" speed we got 2mpg. For fairly antiquated technology I always thought that was reasonable. Of course at 25mph all bets were off...
2dboat is offline   Reply With Quote
Old 03-16-2016, 08:58 AM   #13
Guru
 
boatpoker's Avatar
 
City: Port Credit
Country: Ontario
Vessel Name: DIRT FREE
Vessel Model: Benford Fantail 38
Join Date: Sep 2012
Posts: 1,958
38' full displacement (34' waterline)
Westerbeke 55A
.75gph at 6.5 nautical miles per hour
1.5gph at 8.0 nautical miles per hour (bow thruster visible)
__________________
If you can live with the consequences, go for it - wg
Y'am what I y'am an' thats' all that y'am - Popeye
As God is my witness, I thought turkey's could fly. Mr.C
boatpoker is offline   Reply With Quote
Old 03-16-2016, 09:19 AM   #14
Senior Member
 
tallswede's Avatar
 
City: Baytown, Texas
Country: USA
Vessel Name: Islander
Vessel Model: Prairie 36
Join Date: May 2013
Posts: 206
I haven't had my boat long enough to know what the fuel burn rates are yet but doing research I expect about 2 gpm(2 x 4-236 80 hp Perkins) at 1500 rpm which is about 7mph on the GPS in calm conditions. We'll see how it goes this summer. My little Hunter 23.5 sailboat with an 8 hp Tohatsu 4 stroke got about 14 mpg at 5.5-6 mph unless fighting into a heavy chop. Motorsailing I once got 30 mpg at the same speed.

Kevin
tallswede is offline   Reply With Quote
Old 03-16-2016, 09:21 AM   #15
Senior Member
 
tallswede's Avatar
 
City: Baytown, Texas
Country: USA
Vessel Name: Islander
Vessel Model: Prairie 36
Join Date: May 2013
Posts: 206
Quote:
Originally Posted by 2dboat View Post
We sold her last summer but our 1963 34ft Chris Craft Constellation with original twin 283V8's consistently burned 4 gallons per hour at 8mph when we river cruised. So at a "trawler like" speed we got 2mpg. For fairly antiquated technology I always thought that was reasonable. Of course at 25mph all bets were off...
I had a 27' Constellation with the same power. Same year as yours. Loved that boat.

Kevin
tallswede is offline   Reply With Quote
Old 03-16-2016, 09:33 AM   #16
Guru
 
menzies's Avatar
 
City: Jacksonville
Country: USA
Vessel Name: SONAS
Vessel Model: Grand Alaskan 53
Join Date: May 2014
Posts: 1,427
Quote:
Originally Posted by tallswede View Post
I haven't had my boat long enough to know what the fuel burn rates are yet but doing research I expect about 2 gpm(2 x 4-236 80 hp Perkins) at 1500 rpm which is about 7mph on the GPS in calm conditions. We'll see how it goes this summer. My little Hunter 23.5 sailboat with an 8 hp Tohatsu 4 stroke got about 14 mpg at 5.5-6 mph unless fighting into a heavy chop. Motorsailing I once got 30 mpg at the same speed.

Kevin
Did you write that correctly?
menzies is online now   Reply With Quote
Old 03-16-2016, 10:45 AM   #17
Senior Member
 
tallswede's Avatar
 
City: Baytown, Texas
Country: USA
Vessel Name: Islander
Vessel Model: Prairie 36
Join Date: May 2013
Posts: 206
Whoops,, I meant 2 gph! I think I'll burn 1 gph per engine (conservatively) maybe a tad less at 1500 rpm. I will also test to see how running on just one engine works. My transmissions are supposed to be okay to freewheel in neutral.

Kevin
tallswede is offline   Reply With Quote
Old 03-16-2016, 11:32 AM   #18
Veteran Member
 
City: Naperville
Country: us
Join Date: Dec 2015
Posts: 44
I did some research on engine fuel consumption, I found at low rpm, bigger/smaller engines' fuel consumption are more or less similar. Take for example:
Yanmar 4JH5E, naturally aspirated, rated 53HP, burns about 3GPH at 3000RPM,
Yanmar 6LY3, turbo charged, 380HP, at 1600RPM it burns roughly 3.5GPH to produce 68HP
I read the data from the manufacture graph, so it's just a rough estimation

Is my above conclusion correct?

Also, I thought naturally aspirated engines are supposed to be less efficient, but from above data, it doesn't seem to have noticable difference? 6LY3 is more efficient by a small margin. I read somewhere turbo can get roughly 30% more power?
chicagoq is offline   Reply With Quote
Old 03-16-2016, 12:08 PM   #19
TF Site Team
 
Baker's Avatar
 
City: League City, Tx
Country: Texas
Vessel Model: Carver 356
Join Date: Oct 2007
Posts: 5,120
I asked a question a while back about using knots and mph. I was surprised when the majority of you said you used mph. And when a question like this is asked the vast majority of you used knots....?

Just an observation....carry on!!!!
__________________
Prairie 29...Perkins 4236...Sold
Mainship Pilot 30...Yanmar 4LHA-STP...Sold
Carver 356...T-Cummins 330B
Baker is offline   Reply With Quote
Old 03-16-2016, 01:47 PM   #20
Guru
 
dhays's Avatar
 
City: Gig Harbor
Country: United States
Vessel Name: Kinship
Vessel Model: North Pacific 43
Join Date: May 2015
Posts: 2,808
Quote:
Originally Posted by chicagoq View Post
I did some research on engine fuel consumption, I found at low rpm, bigger/smaller engines' fuel consumption are more or less similar. Take for example:
Yanmar 4JH5E, naturally aspirated, rated 53HP, burns about 3GPH at 3000RPM,
Yanmar 6LY3, turbo charged, 380HP, at 1600RPM it burns roughly 3.5GPH to produce 68HP
I read the data from the manufacture graph, so it's just a rough estimation

Is my above conclusion correct?

Also, I thought naturally aspirated engines are supposed to be less efficient, but from above data, it doesn't seem to have noticable difference? 6LY3 is more efficient by a small margin. I read somewhere turbo can get roughly 30% more power?
It seems to me that comparing those two engines is an apples and oranges type thing. It would be more helpful if you could compare two naturally aspirated engines. At what RPM does the turbocharger spool up for example? Turbocharged engines can deliver more power per liter displacement, but I don't know that they are inherently more efficient as far as fuel burn goes.
__________________

__________________
Regards,

Dave
SPOT page
dhays 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 11:22 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