Reply
 
Thread Tools Display Modes
 
Old 06-26-2016, 11:57 PM   #21
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,714
Ski,
Did poorly on Willy. 2000rpm max. Not even smooth .. considerably more vibration than the three blade. Think it was sling's water off the skinny blade tips slamming into the bottom. A higher frequency vibe than would seem right. I maxed it out for pitch and got little improvement. If Willy was a trailer boat I'd cut her down till she got revs. But ....
__________________
Advertisement

__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 06-27-2016, 07:45 PM   #22
Guru
 
River Cruiser's Avatar
 
City: UMR MM283
Country: US
Vessel Name: Northern Lights II
Vessel Model: Bayliner 3870
Join Date: Jan 2013
Posts: 1,228
Quote:
Originally Posted by Nomad Willy View Post
RC,
What was your WOT rpm w both props? Does your 3 blade have very high blade area per blade? That's the only thing that would make them comparable IMO. Also IMO you should put the prop on that has the most rpm if it's less than 100 rpm over rated WOT rpm.

I lost 100 rpm near as I can tell by the tachs. I was at the spec rpm of 3000+ with the 4 blade. The blade area are very similar per blade, the gain in speed may be attributed to current speed, but it was checked in the same area of the river and the level gauge reading was within 10" of the 4 blade run. You are correct on using the props the give the proper wot rpm and that is the 4 blade pair.
__________________

__________________
Ron on Northern Lights II
I don't like making plans for the day because the word "premeditated" gets thrown around in the courtroom.
River Cruiser is offline   Reply With Quote
Old 06-27-2016, 09:46 PM   #23
Veteran Member
 
Paul Swanson's Avatar
 
City: Ventura CA
Country: USA
Vessel Name: Proud Mary
Vessel Model: Pacific Trawler
Join Date: Apr 2015
Posts: 77
I don’t think anyone really answered the OP’s question, “Why do some boats have 4 blade props and others have 3?” The fewer blades the more efficient the prop. (Racing airplanes have been known to use one-blade props.) However, the prop also has to be able to handle the power from the engine. For a given diameter more blades are able to transmit more power to the water, albeit at a somewhat lower efficiency. Two blades would be the first choice. With a bigger engine, if there is insufficient room for a larger diameter prop then add more blades. Blade pitch, shape and position are important details best left to the experts.

Paul
Paul Swanson is offline   Reply With Quote
Old 06-27-2016, 10:30 PM   #24
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,714
Paul .... Spot on
Yes the only reason for a trawler to increase the # of blades is to provide the necessary blade area for the power.
Of course the speed of the shaft and the boat get involved too.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 06-27-2016, 10:47 PM   #25
Guru
 
Mule's Avatar
 
City: Fort Pierce
Country: USA
Vessel Name: Florita Ann
Vessel Model: 1982 Present
Join Date: May 2014
Posts: 1,787
Proping

I have come to the hard learned conclusion that prop ing requires either a wizard or a witch, a voodoo consultant and likely all three an still it would not be right.
Mule is online now   Reply With Quote
Old 06-28-2016, 01:16 AM   #26
Master and Commander
 
markpierce's Avatar
 
City: Vallejo CA
Country: USA
Vessel Name: Carquinez Coot
Vessel Model: 2011 Seahorse Marine Coot hull #6
Join Date: Sep 2010
Posts: 10,265
Unless there is a significant problem, substituting the boat builder's propeller is probably a fool's game.
__________________
Kar-KEEN-ez Koot
markpierce is offline   Reply With Quote
Old 06-28-2016, 06:47 AM   #27
Guru
 
Mule's Avatar
 
City: Fort Pierce
Country: USA
Vessel Name: Florita Ann
Vessel Model: 1982 Present
Join Date: May 2014
Posts: 1,787
What he said!
__________________

Mule 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 10:09 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