Reply
 
Thread Tools Search this Thread Display Modes
 
Old 03-09-2019, 12:59 AM   #1
Lt. JG
 
Join Date: Apr 2012
Location: Northern California
Posts: 22
Default Fuel Consumption at Cruising speed in 46 ft SCB

We have a Maxum 46 SCB with 2 x Cummins 450HP Diesel engines. Cruising at 1800 rpm's has anyone worked out estimated fuel consumption and speed?
Would really appreciate any input.
__________________

Thomtyler is offline   Reply With Quote
Old 03-09-2019, 05:33 AM   #2
Ensign
 
Join Date: Aug 2017
Posts: 14
Default 8.3 Cummins

If you are able to find out about the mileage, please let us know. Thanks
__________________

Scb46 is offline   Reply With Quote
Old 03-10-2019, 08:28 PM   #3
Lt. Commander
 
dbriceno's Avatar
 
Join Date: Apr 2010
Location: Huntington, NY
Posts: 175
Default

I was getting about 25g/hr combined at 19-20 knots. About .8 mpg
dbriceno is offline   Reply With Quote
Old 03-11-2019, 02:10 AM   #4
Ensign
 
Join Date: Aug 2017
Posts: 14
Default

Thanks
Very close to what I had figured.
Ron
Scb46 is offline   Reply With Quote
Old 03-11-2019, 03:49 PM   #5
Moderator

 
shrew's Avatar
 
Join Date: Apr 2008
Posts: 5,588
Default

Because speed (SOG) can vary for the same RPM due to sea state, tide, current and wind, fuel consumption over distance is not an accurate measurement. Only consumption at RPM over time is accurate.

Therefore MPG is not a relevant number when calculating fuel consumption. GPH based on a variable RPM is what is used.
shrew is offline   Reply With Quote
Old 03-11-2019, 04:27 PM   #6
Lt. Commander
 
dbriceno's Avatar
 
Join Date: Apr 2010
Location: Huntington, NY
Posts: 175
Default

You sound like you know it all. GPH doesn't tell you how much fuel you will need to get somewhere. And since time is spent in and out of 5mph zones at varied rpms GPH doesn't tell you squat. I know I need about 125 gallons to travel 100 miles. Of course that depends on tides and sea conditions. That is obvious.
dbriceno is offline   Reply With Quote
Old 03-11-2019, 07:08 PM   #7
Ensign
 
Join Date: Aug 2017
Posts: 14
Default

It’s all good. Condition of boat and props will figure in the too. I’m averaging a $100/hr on step, 20 hrs...ish. $60/hr @12kts
Thanks
Ron
Scb46 is offline   Reply With Quote
Old 03-13-2019, 12:45 PM   #8
Moderator

 
shrew's Avatar
 
Join Date: Apr 2008
Posts: 5,588
Default

Quote:
Originally Posted by dbriceno View Post
You sound like you know it all.
My apologies, that wasn't my intention. Do you have examples of consumption specs that rate based MPG? I'd like to make sure I'm clear on my oversight.
shrew is offline   Reply With Quote
Old 03-13-2019, 03:14 PM   #9
Moderator

 
shrew's Avatar
 
Join Date: Apr 2008
Posts: 5,588
Default

Incidentally, here is an example of my rationale which I strongly encourage anyone to correct my mistakes or oversights.

Distance: 30 Nautical Miles (NM)
RPM: 2400
Fuel Consumption/hr @ 2400: 2 Gallons
Tide/Current: 2kts
Speed @ 2400: 8 kts

Speed into Head Sea: 6 kts
Speed with Following Sea: 10 kts

(30 / 10) * 2 = 6 gallons (0.2 kmpg)
(30 / 6) * 2 = 10 gallons (0.33 kmpg)

This a 66% increase in fuel consumption. Obviously a planing boat would see a less dramatic impact, however, the difference is there. In this case, calculating kmpg will potentially lead to a significant miscalculation.
shrew is offline   Reply With Quote
Old 03-14-2019, 12:56 PM   #10
Moderator

 
shrew's Avatar
 
Join Date: Apr 2008
Posts: 5,588
Default

Quote:
Originally Posted by shrew View Post
In this case, calculating kmpg will potentially lead to a significant miscalculation.
Correction 'Calculating Nautical mile per gallon'.
shrew is offline   Reply With Quote
Old 07-04-2019, 08:35 PM   #11
Ensign
 
Join Date: Jul 2019
Posts: 1
Default

Were you ever able to track your miles MPG with the 4600 SCB. I know this is an old post and I know MPG can be a topic of debate but I am just looking for an estimated average if you have one? Thanks
BakesFam is offline   Reply With Quote
Old 11-04-2020, 12:25 PM   #12
Ensign
 
Join Date: Nov 2020
Posts: 6
Default Help with fuel consumption data

Quote:
Originally Posted by shrew View Post
Incidentally, here is an example of my rationale which I strongly encourage anyone to correct my mistakes or oversights.

Distance: 30 Nautical Miles (NM)
RPM: 2400
Fuel Consumption/hr @ 2400: 2 Gallons
Tide/Current: 2kts
Speed @ 2400: 8 kts

Speed into Head Sea: 6 kts
Speed with Following Sea: 10 kts

(30 / 10) * 2 = 6 gallons (0.2 kmpg)
(30 / 6) * 2 = 10 gallons (0.33 kmpg)

This a 66% increase in fuel consumption. Obviously a planing boat would see a less dramatic impact, however, the difference is there. In this case, calculating kmpg will potentially lead to a significant miscalculation.
Hi Shrew,

Can you help me with some data on your 4600?

I am looking to purchase and can't seem to find this info online. The boat I am looking at has the 450 Cummins. What I am looking for is what the fuel burn/speed curve is at different RPM's.

I don't know if you have this info - or if someone else does. It would be greatly appreciated!

Best,

David
Davestic is offline   Reply With Quote
Old 11-04-2020, 02:43 PM   #13
Moderator

 
shrew's Avatar
 
Join Date: Apr 2008
Posts: 5,588
Default

I dont have such a breakdown.
__________________

shrew is offline   Reply With Quote
Reply

Tags
cruising speed, cummins 450 hp, fuel consumption

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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


Powered by vBadvanced CMPS v3.2.3

All times are GMT. The time now is 12:51 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2024, vBulletin Solutions, Inc.