Reply
 
Thread Tools Display Modes
 
Old 08-28-2014, 03:08 PM   #1
Newbie
 
baycoaster's Avatar
 
Join Date: Feb 2014
Posts: 2
prop size for Marine trader?

Looking for info on proper prop size for my 40' sedan trawler
With single 120 HP lehman
__________________
Advertisement

baycoaster is offline   Reply With Quote
Old 09-03-2014, 12:38 AM   #2
Guru
 
C lectric's Avatar
 
City: Somewhere
Country: , Canada
Vessel Name: Island Pride
Vessel Model: Palmer sedan 32'
Join Date: Oct 2007
Posts: 1,872
This would best be asked of the Marine Trader Forum.
Note however that what was on the boat when new will NOT be suitable now without doing some serious checking to ensure you do not overload the engine with too much prop.

You will need a handheld laser pointer digital phototachometer along with some of the reflective tape. E-bay for ~ $50.00. Put a piece of Tape on the crankshaft dampener and when out on a run use the tach to shoot the tape on the dampener. Put one stripe of tape on the whole width of the dampener so it is easy to aim at. Not a tiny little dot of tape.

With a helper to run the boat take it out for a run and push it to wide open throttle [WOT] only for long enough to get a stable rpm reading and a boat speed reading. If you are bucking current or a lot of wind you will have to reverse course to average out the boat speeds. While reversing course, if needed, slow down untill ready again.

These tachs are accurate to a few rpms. Your dash tach is likely accurate to a few hundred rpm. Accurate readings are important for good results.

You will also need:
- the boat weight fully loaded as you will cruise
-boat length at water line, approx.
-the gear ratio
-engine hp and rated rpm
-existing propellor, diameter, pitch and #of blades
-boat speed now with the existing prop


Then a good prop shop can come up with a good recommendation. Otherwise you are flying totally blind and it could be expensive.

There are also online calculators which can guide you.
-Boatdiesel has one although you will need to join for $25.00 - well worth it
-http://rbbi.com/folders/prop/propcalc.htm
-http://www.vicprop.com/calculator.htm

Keep in mind though that good as calculators are they are a guide only and must have good info.

So to start get the tach and test your boat as it is now.
C lectric 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





All times are GMT -5. The time now is 05:31 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