Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 01-09-2010, 15:22   #1
Registered User
 
markpierce's Avatar

Join Date: Aug 2010
Location: Central California
Boat: M/V Carquinez Coot
Posts: 3,782
Matching Engine, Prop and Boat

For example, John Deere makes a diesel marine 84-horsepower engine model 4045D with a rated r.p.m. of 2400 with peak torque delivered at 1400 r.p.m.

In regards to a displacement hull, would the ideal be to match a propeller and boat with this engine so that cruising speed is reached at 1400 r.p.m.? What is the "rule-of-thumb" competent boat makers use in matching engine and boat to be operated at displacement speeds? Thanks.
markpierce is offline   Reply With Quote
Old 01-09-2010, 16:20   #2
Registered User

Join Date: Jun 2005
Posts: 1,901
Quote:
Originally Posted by markpierce View Post
For example, John Deere makes a diesel marine 84-horsepower engine model 4045D with a rated r.p.m. of 2400 with peak torque delivered at 1400 r.p.m.

In regards to a displacement hull, would the ideal be to match a propeller and boat with this engine so that cruising speed is reached at 1400 r.p.m.? What is the "rule-of-thumb" competent boat makers use in matching engine and boat to be operated at displacement speeds? Thanks.
you want to put full load on the engine at half RPM. I doubt JD will ok that warranty.
never monday is offline   Reply With Quote
Old 01-09-2010, 18:01   #3
Registered User
 
Ziggy's Avatar

Join Date: Apr 2008
Location: U.S., Northeast
Boat: Currently boatless
Posts: 1,643
Images: 2
I think peak torque rpm is a good choice for cruising speed. You should still prop it so it can just get to the rated max rpm.
__________________
... He knows the chart is not the sea.
-- Philip Booth, Chart 1203
Ziggy is offline   Reply With Quote
Old 01-09-2010, 18:19   #4
Registered User
 
Ziggy's Avatar

Join Date: Apr 2008
Location: U.S., Northeast
Boat: Currently boatless
Posts: 1,643
Images: 2
Quote:
Originally Posted by markpierce View Post
What is the "rule-of-thumb" competent boat makers use in matching engine and boat to be operated at displacement speeds?
One rough rule of thumb is 1 hp per 550 lbs of displacement.
Note: you should use fully loaded displacement, including all tanks full, max crew, stores, etc.

To get a more accurate figure for horsepower needed, calculate your boat's resistance at hull speed, divide by the prop efficiency, and add some reasonable reserve. You really need to get a copy of Dave Gerr propeller handbook, if you're serious.
__________________
... He knows the chart is not the sea.
-- Philip Booth, Chart 1203
Ziggy is offline   Reply With Quote
Old 01-09-2010, 20:02   #5
Moderator Emeritus
 
Boracay's Avatar

Cruisers Forum Supporter

Join Date: Feb 2004
Location: Sunshine Coast, Qld, Australia
Boat: CyberYacht 43
Posts: 5,174
Images: 19
35' Seahorse Coot?

I'm assuming you are posting about a 35' Seahorse Coot, 28,000lb and 13' beam.

I put a John Deere 4045D into Boracay, a Roberts Offshore 44 that's about the same weight as the Coot.

With a (from memory) 22"x15" prop I got a maximum of 1700rpm and 8 knots with everything clean. From memory 1400rpm gave me 5-6 knots with everything clean.

I had the prop repitched and cut down to 20"x12.5" and I can now get 8 knots and 2500rpm with everything clean. However the engine does not sound happy.

At the moment I'm using 1700rpm to cruise at 6 knots with good fuel consumption. With the boat half dirty I now only get 2300rpm and 7 knots.

My prop man said that if I brought a new prop he'd go for less pitch and slightly more diameter.

I'm thinking I'd like 10" pitch, but this is less than most "tables" suggest.
Boracay is offline   Reply With Quote
Old 01-09-2010, 20:28   #6
Registered User
 
markpierce's Avatar

Join Date: Aug 2010
Location: Central California
Boat: M/V Carquinez Coot
Posts: 3,782
Thanks! I'm a self-admitted ignoramus concerning engines.

My philosophies for engine running are (1) don't operate beyond 66% of maximum engine rpm except for very-short-term emergency conditions, and (2) cruise between 40-50% of max rpm. Feedback?
markpierce is offline   Reply With Quote
Old 01-09-2010, 23:32   #7
Moderator Emeritus
 
Boracay's Avatar

Cruisers Forum Supporter

Join Date: Feb 2004
Location: Sunshine Coast, Qld, Australia
Boat: CyberYacht 43
Posts: 5,174
Images: 19
OK on a John Deere...

What you're suggesting sounds OK for a John Deere 4045D. I have found that there is a power setting where the engine sort off "digs in", things stop rattling (Problem with DIY install...), and I'm sort of moving faster than other boats. Engine is loaded but not overloaded.

The higher reving engines may need a different technique.
Boracay is offline   Reply With Quote
Old 02-09-2010, 03:35   #8
Registered User

Join Date: Jun 2005
Posts: 1,901
Quote:
Originally Posted by markpierce View Post
Thanks! I'm a self-admitted ignoramus concerning engines.

My philosophies for engine running are (1) don't operate beyond 66% of maximum engine rpm except for very-short-term emergency conditions, and (2) cruise between 40-50% of max rpm. Feedback?
if you had a gas engine I could go with your running philosophies.
You have a high torque diesel. Running it like that will be killing it with kindness. Akin to running your 5 speed car in 5th gear all the time.
Prop for 110% of hull speed at max RPM. then you get what ever speed you get. AS you pull off the power.

Diesels are rated differently than gas engines. The will have a 1 hr rting. This is a power setting that can be run for 1 hr out of 12 hrs. Then they will have a slightly lower setting know as the continuous rating. You can run at the continuous rating until the cows come home. the engine won't care.
Over loading will exacerbate cylinder wall wear.
never monday is offline   Reply With Quote
Old 02-09-2010, 09:05   #9
Registered User
 
markpierce's Avatar

Join Date: Aug 2010
Location: Central California
Boat: M/V Carquinez Coot
Posts: 3,782
Quote:
Originally Posted by never monday View Post
if you had a gas engine I could go with your running philosophies. ...
How perceptive! My only experience has been with gas engines. Thanks!
markpierce is offline   Reply With Quote
Reply

Tags
engine

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
How Much Protection Does Prop Zinc Offer Engine Cooling System ? yamaha30c Engines and Propulsion Systems 4 07-06-2010 13:28
Looking for Matching Hawse Pipe snorskyp Anchoring & Mooring 6 23-12-2009 12:19
Propeller Noise! New Engine, Old Prop Paolo Propellers & Drive Systems 9 05-10-2009 19:29
Best combination of Prop to Gear Ratio & Engine ribbony Propellers & Drive Systems 25 17-01-2009 11:28
Matching prop to engine Weyalan Engines and Propulsion Systems 15 19-03-2008 09:19

Advertise Here


All times are GMT -7. The time now is 04:05.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.