Reply
 
Thread Tools Display Modes
 
Old 04-11-2010, 06:28 AM   #1
Guru
 
Daddyo's Avatar


 
City: Cruising East Coast US
Country: USA
Vessel Name: Grace
Vessel Model: DeFever 48
Join Date: Apr 2008
Posts: 2,441
prop calculation

Does anyone have access to a prop calculator that can figure out the following prop pitching? My engine will make 2200 of 2500rpms with the following:
23x21 4 blade prop. 120hp 1.5" shaft. 2.5 reduction. 24,000lbs semi displacement. 33' waterline.
I'm thinking about reducing the pitch to get a flatter wheel and the ability to make some more rpms at the top end. The boat is for sale and surveys will require the higher rpms.
Attached Thumbnails
Click image for larger version

Name:	s5000674.jpg
Views:	92
Size:	212.4 KB
ID:	1955  
__________________
Advertisement

Daddyo is offline   Reply With Quote
Old 04-11-2010, 09:33 AM   #2
Guru
 
Codger2's Avatar
 
City: San Diego
Country: US
Vessel Name: "Sandpiper"
Vessel Model: 2006 42' Ocean Alexander Sedan
Join Date: Oct 2007
Posts: 5,421
RE: prop calculation

A subscription to BoatDiesel.com will result in a one year use of their prop calculator. $25 well spent.
__________________

Codger2 is offline   Reply With Quote
Old 04-11-2010, 09:34 AM   #3
Guru
 
koliver's Avatar
 
City: Saltspring Island
Country: BC, canada
Vessel Name: Retreat
Vessel Model: C&L 44
Join Date: Nov 2007
Posts: 2,170
RE: prop calculation

boatdiesel.com
I used their prop calculator to verify my guesses, they agreed, I did the change and it worked exactly as predicted.
May cost you the $25.00US membership fee, but worth it to get all the wisdom about engines and systems on that site for a year.
koliver is offline   Reply With Quote
Old 04-11-2010, 09:40 AM   #4
Scraping Paint
 
City: Fort Lauderdale
Vessel Model: CHB 48 Zodiac YL 4.2
Join Date: Oct 2007
Posts: 3,804
RE: prop calculation

Quote:
Daddyo wrote:

The boat is for sale and surveys will require the higher rpms.
I would suggest talking to a good prop shop.

*

As far as the survey goes, a legitimate surveyor will simply note that the boat goes X speed at 2200 rpms.

Unless you are classed by Lloyds or ABS and the class rules require a certain engine performance spec be maintained, tell the little hammer wielder to go pound sand if he tells you that you have to meet some spec he has decided to apply.

If the surveyor is known for applying bizarre "requirements" to the boats he attends, don't let him onboard. If you do, make him document his findings and reference the "rule" that applies.

*

*
RickB is offline   Reply With Quote
Old 04-11-2010, 09:49 AM   #5
Guru
 
koliver's Avatar
 
City: Saltspring Island
Country: BC, canada
Vessel Name: Retreat
Vessel Model: C&L 44
Join Date: Nov 2007
Posts: 2,170
RE: prop calculation

DO
you could try dumping 1/2 of your load of water and using 1/2 of your supply of fuel. or dump all the water. A lighter boat may get you those extra rpm.
koliver is offline   Reply With Quote
Old 04-11-2010, 01:50 PM   #6
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,530
RE: prop calculation

First check is that the engine will reach WOT of 2500 or whatever the gov speed is supposed to be.

Would be a shame to haul and do a prop change , because a cable is not properly set.

30 seconds at WOT for the test will do no harm , as long as 10% over the required gov speed is not exceeded.
FF is offline   Reply With Quote
Old 04-11-2010, 01:57 PM   #7
Guru
 
Daddyo's Avatar


 
City: Cruising East Coast US
Country: USA
Vessel Name: Grace
Vessel Model: DeFever 48
Join Date: Apr 2008
Posts: 2,441
RE: prop calculation

Engine made 2500rpm* @WOT no problem with prior undersized prop.
Daddyo is offline   Reply With Quote
Old 04-12-2010, 04:47 AM   #8
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,530
RE: prop calculation

Engine made 2500rpm @WOT no problem with prior undersized prop.


And now in the slip?


Have you borrowed a portable tach to check yours is accurate?
FF is offline   Reply With Quote
Old 04-12-2010, 12:09 PM   #9
Senior Member
 
Join Date: Oct 2007
Posts: 272
RE: prop calculation

Quote:
Daddyo wrote:

Does anyone have access to a prop calculator that can figure out the following prop pitching? My engine will make 2200 of 2500rpms with the following:
23x21 4 blade prop. 120hp 1.5" shaft. 2.5 reduction. 24,000lbs semi displacement. 33' waterline.
I'm thinking about reducing the pitch to get a flatter wheel and the ability to make some more rpms at the top end. The boat is for sale and surveys will require the higher rpms.
Reducing your pitch by one inch will raise your RPM's about 200, so taking two inches out would be a little more than you need but it will get you to 2500. Is the Lehman 120 max RPM 2500 or 2550? Seems like the manual says 2600 RPM unloaded and 2550 RPM loaded for the max RPM???

I had a spreadsheet that I found online called propcalc.xls, you might try searching on Google for it. It worked pretty well, if i can find a link again I will post it.
troy994719 is offline   Reply With Quote
Old 04-12-2010, 06:48 PM   #10
Scraping Paint
 
City: -
Country: -
Join Date: Oct 2007
Posts: 13,748
RE: prop calculation

The manual for our boat (1973) calls out the horsepower rating of the FL120 as 120 hp @ 2,500 rpm.
Marin is offline   Reply With Quote
Old 04-13-2010, 03:48 AM   #11
Senior Member
 
AllanY's Avatar
 
City: Tin Can Bay, Queensland, Australia
Country: Australia
Vessel Model: Cheoy Lee, Trawler
Join Date: Apr 2010
Posts: 171
RE: prop calculation

Try this one
http://www.alberg30.org/.../Mechanic...r/propcalc.xls

Allan
AllanY is offline   Reply With Quote
Old 04-13-2010, 03:54 AM   #12
Senior Member
 
AllanY's Avatar
 
City: Tin Can Bay, Queensland, Australia
Country: Australia
Vessel Model: Cheoy Lee, Trawler
Join Date: Apr 2010
Posts: 171
RE: prop calculation

This might help

http://www.google.com/custom?q=prop+...h=alberg30.org

Allan
AllanY is offline   Reply With Quote
Old 04-13-2010, 07:16 AM   #13
Guru
 
Daddyo's Avatar


 
City: Cruising East Coast US
Country: USA
Vessel Name: Grace
Vessel Model: DeFever 48
Join Date: Apr 2008
Posts: 2,441
RE: prop calculation

Quote:
FF wrote:

Engine made 2500rpm @WOT no problem with prior undersized prop.


And now in the slip?


Have you borrowed a portable tach to check yours is accurate?
Don't know what you mean by now in the slip? I have an infrared tach. I was thinking the one to two degrees as the way to go.

*
Daddyo is offline   Reply With Quote
Old 04-13-2010, 09:03 AM   #14
Senior Member
 
Join Date: Oct 2007
Posts: 272
RE: prop calculation

Are you getting black smoke in the exhaust at WOT now? If you only go one degree then it will probably still have smoke at WOT. I would go for two inches if youre looking to make sure the boat turns the full RPMs and doesnt smoke. *
troy994719 is offline   Reply With Quote
Old 04-14-2010, 04:30 AM   #15
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,530
RE: prop calculation

By in the slip I mean in neutral not underway ,


just advancing the throttle OUT of gear ,to find out where the top of the gov is set
__________________

FF is offline   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


Similar Threads
Thread Thread Starter Forum Replies Last Post
help with prop # olesouth Power Systems 4 03-01-2012 12:54 AM
Prop fouling SOMERS General Discussion 11 03-11-2011 06:20 PM
Four blade prop awpptdt Power Systems 2 12-14-2010 06:20 PM
Prop...... dwhatty Power Systems 24 05-08-2010 12:24 PM
New prop Phuket Custom Builds & Refit Projects 1 03-09-2009 08:42 PM




All times are GMT -5. The time now is 03:05 PM.


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