Reply
 
Thread Tools Display Modes
 
Old 09-12-2012, 08:17 PM   #1
Senior Member
 
honeybadger's Avatar
 
City: Hampstead,NC
Country: USA
Vessel Name: HoneyBadger
Vessel Model: 1990 Harkers Island Trawler Typical wooden hull with a Carolina flare and no deadrise at the stern
Join Date: May 2012
Posts: 194
Why Commerical boats around here use L/H props

i have a R/H diesel engine but a Transmission that turns L/H and a L/H prop, When i ask i was told since it was a shrimp boat the commerical guys like the L/H props ? Anyone even heard anything like that, i don't see the advantage between left or right if its a single screw. However i did walk the local boat yard and i would say 75% of the larger commerical boats are L/H props.
__________________
Advertisement

honeybadger is offline   Reply With Quote
Old 09-12-2012, 09:40 PM   #2
Senior Member
 
jeffnick's Avatar
 
City: Spartanburg, SC
Country: USA
Vessel Name: Big Duck
Vessel Model: '72 Land-N-Sea
Join Date: Feb 2012
Posts: 425
My 40 yr old Volvo outdrive came standard w/ LH prop...could it be that it 'walks' in the preferred direction?
__________________

jeffnick is offline   Reply With Quote
Old 09-13-2012, 12:37 AM   #3
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,707
With a LH prop the boat pulls to stbd. in reverse.

Boats to your right have the right of way and need to be seen better. So helms are usually on the stbd side.

When landing on the stbd side as you reverse to stop the propwalk pulls your stern nicely.

Most engines are CCW rotating and most gearboxes reverse rotational direction to CW in fwd gear ... CCW in reverse and that produces prop walk to the port side in reverse. Not as described as ideal above. Most modern gears have 2 shafts and 2 sets of gears but the very popular Brog Warner Velvet Drive planetary drive gears rotate their output shaft the same way as the input shaft. Skippers w modern 2 shaft gears will prefer landing on the port side so reversing dosn't leave the stern hanging out away from the float, however the helm is still usually on the stbd side so they haven't got an optimal view of vessels approaching that have the right of way. Hope I got all those directions right.

jeffnick,
Yes

Honey,
Most of those commercial boats are probably quite old and have BWVD gears. Like my Willy. Preferred. But if you have a RH prop and your'e more concerned about graceful landings than legal matters and have a port helm you would consider the RH prop and port helm preferable.
Nomad Willy is offline   Reply With Quote
Old 09-13-2012, 08:44 AM   #4
Guru
 
City: North Charleston, SC
Country: USA
Join Date: Sep 2010
Posts: 4,390
I suspect the designer/manufacturer/builder of the boat puts an engine and transmission (Volvo calls it a "reverse gear") in it and then uses whatever prop causes it to go forward in "forward gear".
rwidman is offline   Reply With Quote
Old 09-13-2012, 09:22 AM   #5
Guru
 
City: Carefree, Arizona
Country: usa
Vessel Name: sunchaser V
Vessel Model: DeFever 48
Join Date: Apr 2008
Posts: 6,361
Eric X2
sunchaser is online now   Reply With Quote
Old 09-13-2012, 10:02 AM   #6
Guru
 
City: Georgia
Country: USA
Join Date: Jul 2012
Posts: 952
On some outboards and I/O's they have dual counter rotating props. I suppose that eliminates prop-walk. I suppose it'd be difficult to do with an inboard, shaft issues I suspect. On a pod drive it could be done, I think.

Oh wait, it's been done on a Zues:


Prop walk gone? But at what cost?
Rambler is offline   Reply With Quote
Old 09-13-2012, 10:54 AM   #7
Guru
 
Phil Fill's Avatar
 
City: Everett Wa
Country: US
Vessel Name: Eagle
Vessel Model: Roughwater 58 pilot house
Join Date: Oct 2007
Posts: 2,919


What ever the reason for the starboard prop walk and I am grateful as they usually ask for a starboard tie, which leaves more port ties for ME!
Phil Fill is offline   Reply With Quote
Old 09-13-2012, 01:48 PM   #8
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,707
Thanks Tom ... that makes me feel like I just aced a Bio101 test.

Ram,
Who cares about prop walk when the prop rotates. But it would be nice if a boat went straight in fwd gear w/o rudder correction.

There's so much P factor on my 40hp OB skiff that when alone sitting on the stbd side is'nt enough to compensate. The boat still rides high on the stbd side. And I'm sure prop walk plays a part too.

I wonder what those things cost ... not the Zues drive but the counter rotating leg like the Volvo. Do they have a patent or do others not offer it because of the expense. Do some outboards have CR props?
Nomad Willy is offline   Reply With Quote
Old 09-14-2012, 06:18 AM   #9
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,518
The boat will be created with the engine off center to angle the prop 4 or 5 deg so it will run straight at cruise with no rudder input.

They did it in the 1920's , so todays NA should have a good idea if you ask for it.
FF is offline   Reply With Quote
Old 09-14-2012, 01:59 PM   #10
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,707
Yes FF,
I've seen quite a number of boats w off ctr prop shafts and some w shafts not parallel w the keel. My Willy is on CL and requires port rudder to go straight w/o hydraulic steering. I got hydraulic steering and it's fine except it's not as light as I was expecting.
Nomad Willy is offline   Reply With Quote
Old 09-14-2012, 02:51 PM   #11
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: 10,254
A three-degree left rudder is necessary on my boat to keep a straight course in powered forward motion. The hydraulic steering makes it unnoticeable, and with hands off the wheel the rudder remains in the same position. The angle is only apparent with the rudder indicator.
__________________
Kar-KEEN-ez Koot
markpierce is offline   Reply With Quote
Old 09-14-2012, 07:45 PM   #12
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,707
Mark,
Exactly.
So if the manufacturer spent a little more effort and put in an offset shaft you'd go straight w a dead ahead rudder. Your 3 degree rudder creates drag ... drag that wouldn't be there if you had a twin w CR propellers. And I think it would reduce prop walk too. As it should be. Same w an Aqua Drive type drive system. As it should be but if they made the perfect boat we couldn't afford it. Each type of build has it's drawbacks.
Nomad Willy is offline   Reply With Quote
Old 09-15-2012, 06:27 AM   #13
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,518
Most boats would profit from a CPP setup, but who would pay for it?
FF is offline   Reply With Quote
Old 09-16-2012, 09:46 AM   #14
Guru
 
City: North Charleston, SC
Country: USA
Join Date: Sep 2010
Posts: 4,390
Quote:
Originally Posted by markpierce View Post
A three-degree left rudder is necessary on my boat to keep a straight course in powered forward motion. The hydraulic steering makes it unnoticeable, and with hands off the wheel the rudder remains in the same position. The angle is only apparent with the rudder indicator.
But you don't know if the rudder indicator is accurate.
rwidman is offline   Reply With Quote
Old 09-16-2012, 12:47 PM   #15
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,707
It could be 2 degrees 4 degrees or whatever but it is unquestionably there. Just like wing tip vortices will always be at the wing tip w an angle of attack. It's a given. To what extent it exists varies from boat to boat but it is always there. Mark's indicator is probably right but if the rudder input was in the wrong direction then I'd question his indicator.
__________________

Nomad Willy 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 06:58 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