Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 15-04-2005, 13:27   #1
Registered User
 
Wahoo Sails's Avatar

Join Date: Jul 2004
Location: Marathon, Florida
Boat: Cape Dory 28, "Night Wind"
Posts: 353
Images: 16
Doin' Da prop walk Boogie

Our "new to us" Nomade has a 2 bladed prop, and prop walks worse than anything I've ever been on. Obviously, a 3 bladed prop will help the sutuation, but in the meantime are there any techniques to help minimize the situation?

L S/V Love Nest
Bob & Lynn
__________________

__________________
Wahoo Sails is offline   Reply With Quote
Old 15-04-2005, 15:24   #2
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,586
Images: 240
Prop' Walk is GOOD !

Boat Handling advice: http://cruisersforum.com/showthread....&threadid=1462
__________________

__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 15-04-2005, 20:30   #3
Senior Cruiser
 
Alan Wheeler's Avatar

Cruisers Forum Supporter

Join Date: Dec 2003
Location: Marlborough Sounds. New Zealand
Boat: Hartley Tahitian 45ft. Leisure Lady
Posts: 8,038
Images: 102
It's not so much the number of blades, but the surface area and pitch that causes the prop walk. In other words, the amount of rotational friction the prop has in the water. This can be improved with Propellor design. However, the most important thing you can do, is ensure you have the correct size and pitch to match your boat. Oh and boat hull can an an effect. If it has little lateral resistance at the point that effort placed on the hull, it will cause the hull to pivot easier than a design that has greater lateral resistance at that point. ie. large rudder/keel.
__________________
Wheels

For God so loved the world..........He didn't send a committee.
Alan Wheeler is offline   Reply With Quote
Old 15-04-2005, 23:12   #4
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,586
Images: 240
What Wheels said, and the basic standards for propí and pitch could be stated:
Slow Displacement Hulls (Sailboats): Bigger Diameter, Less Pitch = Power
Fast Planing Hulls: More Pitch, Smaller Diameter = Speed
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 16-04-2005, 00:24   #5
Registered User
 
BC Mike's Avatar

Join Date: Jun 2003
Location: Gabriola BC
Boat: Viking 33 Tanzer 8.5m Tanzer 22
Posts: 1,034
Images: 5
Prop

I keep hearing about this prop walk thing and feel like I am missing something. Why don't I get it. I bung it in reverse and give it some throttle and we go backwards. The steering is no good until we hit about two knots and then everything is fine. If you do not give it enough throttle to get the required speed then the steering will be no good. I have been backing out of my stall for a long time in all conditions and it works every time. What am I doing wrong?
Michael
__________________
BC Mike is offline   Reply With Quote
Old 16-04-2005, 01:23   #6
Registered User
 
Wahoo Sails's Avatar

Join Date: Jul 2004
Location: Marathon, Florida
Boat: Cape Dory 28, "Night Wind"
Posts: 353
Images: 16
Thanks guys!
Gordy, you bet prop walk can be a good thing! When we went to leave the dock she was tied to, I used it to good advantage, she was in a 50' wide canal (36' boat) and the prop walk turned us so smartly that friends aboard accused me of having practiced the night before
Wheels, Hull design you say? This is s swing keel boat, and we had her cranked all the way up (wind had driven the water out of the river we were in) ... duh ... ya think that could have anything to do with it?
BC Mike, Count yer blessings! Have never yet ben aboard a sailboat that backed down "nicely" ... but this one really takes the cake ... put her in reverse & for every foot that you go astern, you go 3 to port!
As for planning to depart before you tie up ... that's why we tie stern into our slip ... departure is a piece of cake that way. Once knew a guy that used to hang a trolling motor over the port stern quarter to counteract the effect of prop walk ... not ready to go to that extreme ... but I sure understand why he did it

L S/V Love Nest
Bob & Lynn
__________________
Wahoo Sails is offline   Reply With Quote
Old 16-04-2005, 09:59   #7
Senior Cruiser
 
Alan Wheeler's Avatar

Cruisers Forum Supporter

Join Date: Dec 2003
Location: Marlborough Sounds. New Zealand
Boat: Hartley Tahitian 45ft. Leisure Lady
Posts: 8,038
Images: 102
Don't worry ya self Mike. I don't get any prop walk either. But then the boat is 26T, 46ft, and has a 7ft draft with full keel and a barn door for a rudder. As for steering in reverse, or I should say lack of it. Firstly, a Propellor is working in two ways. One, it is "propelling" itself through the water. The thrust is transfered via the shaft and to the hull and pushes it through the water. But a second energy source is the water moving away from the boat. This movment of water is used to move the boat in a different way. When in forward, the prop is delivering a fast moving volume of water over/around and past your rudder. When you turn the rudder, you deflect/direct this flow of water. The water pushing against one side of the rudder causes causes a high pressure side and the otherside is low pressure, thus the rudder moves to the low pressure. The Rudder being attached to the boat drags the hull along with it. This very reason of rudder being virtually sucked to the direction of low pressure and thus dragging the rear of the vessel around, is why the boat pivots around a point further along her hull. But thats a side track.
When the propeller is in reverse, the flow of water is no longer around the rudder. So the only time the rudder will have any influence on direction, is when the water is moving fast enough for a sufficient force to be formed against the rudder. This is why a vessel moving in reverse pivots at a different point than when it was moving forward.
You also have to be careful of vessels with very large barn door type rudders. The force exerted against a rudder when reversing is huge and very different than the propeller wash. It does require some speed, but the rudder or/and it's steering components can in fact be damaged in extreme situations.
__________________
Wheels

For God so loved the world..........He didn't send a committee.
Alan Wheeler is offline   Reply With Quote
Old 10-05-2005, 16:26   #8
Registered User
 
David W's Avatar

Join Date: Apr 2005
Location: Victoria BC, Canada
Posts: 41
Images: 10
I had to experiment

to figure out how much throttle in reverse would get me moving backwards enough to get steerage so I could use the rudder to counter steer. That said once I have enough momentum, I put her in neutral, steer and use occasional shots of reverse if I slow down too much.

I have a 34 ft tiller steered boat and I stand facing aft when backing to make sure I point the tiller the right way... there's enough going on without adding tiller direction confusion to the mix!

Cheers
David
__________________
David
S/V Cindino
Crown 34
Victoria BC
David W is offline   Reply With Quote
Old 30-06-2005, 05:03   #9
Sponsoring Vendor
 
harryrezz's Avatar

Community Sponsor
Cruisers Forum Supporter

Join Date: Aug 2004
Location: Southern Caribbean & Buffalo, NY
Boat: 44' CSY "Walkover" cutter, La Nostra
Posts: 220
Dave W made a very important point. You'll only experience than pull to port when the prop is turning fast enough to be "pulling" the boat backwards. As soon as you cut the throttle or shift into neutral the effect will stop and you can steer ... more or less, depending on other characteristics of your boat. So the key is to gun the throttle anough to get the boat moving sufficiently to generate a water flow past the rudder. Then cut her back and steer, giving occasional bursts of throttle as needed.
Another hint - if you plan ahead you can use that "walk" to you advantage sometimes. When docking go in portside to the dock when possible, and approach at a small angle. then, just as you reach the point where you want to stop, pop her into reverse and give her a good burst of power. This will stop the boat and the "walk" will pull the stern along side very nicely. Takes a little practice, but you can look like a real pro in no time.
The reverse can also sometimes be used. When leaving a dock when you are starboard to, leave in reverse and the "walk" will pull the stern away from the dock for you allowing you a nice, clean exit.
Of course, don't forget thefenders!
__________________
Cap'nHar
s/v La Nostra
CSY 44 W/O cutter
Located in the Sunny Caribbean
"Life's short ... Eat dessert first!"
harryrezz is offline   Reply With Quote
Reply

Thread Tools
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
Prop Walk irwinsailor Monohull Sailboats 27 04-02-2010 23:37



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 15:56.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.