Prop Walk

woodster · Apr 6, 2016

rvoigt40 said:
Hi all I just bought a 37c 1979 in September I haven't been out on it to much this winter but spring is here in PNW.
my question is, Dose anybody else have a problem backing up? the boat goes to the port and i have go to the starboard no matter what i do, Tried hard burst of power then neutral but there's really not enough room for all that.
Its getting to the point where i don't even want to go out, I'm afraid I'm going to hit another boat.
Is it me or the boat? I've had a boat most of my adult life, mostly power though but i never had this problem.
Is it so under powered that there's no control? I guess i should have ask that before i bought it i mean who puts a 20 horse power motor in a 17k lbs boat.

you have to have motion in the water in order to have steerage you also always hold the wheel when backing up never let it go .....find you a buddy to help you through the learning curve on your sailboat ...there are days when i question what i have learned ....just sunday i was backing out of the slip at low tide and it finally hit me my keel was in the muck...thought i was never going to get it right ......as far as the 20hp thing way before axillary power they sailed in an out of slips and morings ...so don't feel alone ...in time you will become proficient with practice

Kings Gambit · Apr 6, 2016

RV,
Here's a good explanation of the prop-walk "phenomenon" from Sail magazine, and advice on how to handle it.

http://www.sailmagazine.com/cruising/cruising-tips/walking-the-prop/

JohnVTX · Apr 6, 2016

Have a dock line that you can adjust from the boat while backing up attached to the Starboard cleat at the stern. As you start backing up keep tension on it until the boat begins to pivot to starboard, then release and let line fall into water.

frankies56 · Apr 6, 2016

RV. this is something that all boats have. the best thin to do is use it to your advantage . its just a mater of practice and getting used to. as for me I dock on the port side so when I come in when its time to stop full reverse and the aft end goes right to the dock,it make for an easy landing. now on the other haned when leaving the slip she wants to rub all the way out my fix was to put a fender roller on the and of the dock, if the wind will push you back thats a good thing when its at your back its a chore. but the storie is we all have to deal with it one time or another, dont let it bother you just learn her ways. my best Frank

Dave602 · Apr 6, 2016

We have a couple of tricks for backing out of our slip as we have cross winds most of the time. One is a line running the length of our long finger pier. we loop a line around it and the wife holds us close to the dock as we back out. The finger pier is on our port side by the way. I usually take a boat hook and give the stern a little push off the pier and that gets our direction going until the momentum catches up. I also use short burst of power, seldom more than idle as more power is more prop walk. But prop walk is handy when we have a strong wind on the port side when coming back in. We nose in and then hit reverse hard and the stern pull right up to the dock. The line on the finger pier is also good to grab with a hook coming in and keeping the boat up to the dock in the wind.

Good luck, learn to use the prop walk to your advantage.

Capt jgw · Apr 6, 2016

You could consider backing into the slip. Most power boaters and some sailors do that. That way the prop walk will be working for you as you back in instead of against you backing out. The only real downside is privacy, anyone walking down the dock can see into the boat if the companionway is open.

Kings Gambit · Apr 6, 2016

You avoid "prop walk" altogether in a boat with sail drive. In sail drive, the thrusts from the up and down strokes of the prop are equal b/c its blade axis is always vertical relative (i.e., normal) to the direction of the pull. There is never asymmetry in the respective orientations of the blades. Forward and reverse thrusts are the same. It's great to be able to back-up straight!

Stu Jackson · Apr 6, 2016

1. Do a search here on this forum for prop walk and read the answers.

2. Do a Google search on the topic.

3. Search on "spring lines" which is what these folks are suggesting you learn.

4. Use more throttle, not less. Prop walk ONLY occurs when the boat is motionless.

Good luck, we've all BTDT.

Alctel · Apr 6, 2016

Also, don't be afraid of hand bombing to get the initial motion going!

Roland5048 · Apr 6, 2016

Stu Jackson said:
4. Use more throttle, not less. Prop walk ONLY occurs when the boat is motionless.

Stu, I don't quite understand the last sentence. I have tremendous prop walk to port when backing. When I have enough astern speed, I go to neutral and let the rudder take over.

Capt jgw · Apr 6, 2016

I disagree that prop walk only occurs when you're standing still. Your rudder is ineffective unless you have way on, and the faster you're moving the more effective it is. This makes prop walk more pronounced when moving slowly or not at all, bit it is present to some extent at all speeds. This is readily seen on displacement power vessels with small rudders, they will back to port (or starboard if its a left hand prop), no matter how much throttle you apply.

Kings Gambit · Apr 6, 2016

From the article cited above in post #3. Emphasis added below.

"Prop walk is much more noticeable in reverse and is more pronounced at slow speeds and at high RPMs. It is less pronounced when a prop is in shallow water (i.e., on a boat with shoal draft), as this reduces upward water flow from beneath the vessel. The amount of clearance between the propeller and hull has an impact, as does the hull’s shape. Increased wheel diameter or blade pitch increases prop walk. Two-blade props walk less than 3-blade props; folding and feathering props walk less still. A moving vessel’s yaw rate can negate or augment prop walk, as can the wind, depending on its direction and strength. An offset shaft may alter the effect, and when a shaft is parallel to the water’s surface, as in a saildrive, its prop doesn’t walk at all.

When driving forward you can easily compensate for prop walk with your rudder, so you hardly notice it. In reverse your rudder is much less effective, so prop walk is more obvious and more difficult to control. To compensate, or to take advantage of it, you must anticipate its force and direction."

Capt jgw · Apr 6, 2016

That's exactly the way we present it in my Master License course, and the way the relevant exam questions are written.

kito · Apr 6, 2016

The OP says he has a H37C (Hunter Cherubini), does this boat have a spade rudder? My H30C has a skeg mounted rudder and was wondering if the skeg helps or hinders prop walk. I haven't launched mine yet so don't know. Also, I always heard 3 blade props like the Campbell Sailor actually reduce prop walk, that's why I bought one. Now I hear 2 blades reduce prop walk...........? Anyway, after years of driving inboard ski boats I kind of got used to prop walk anyway. Most of the time it came in handy.

Kings Gambit · Apr 6, 2016

Prop-walk under high RPMs was, I believe, the impetus for the mounting of counter-rotation outboards on twin-outboard fishing boats. The engine rotation on one side is LH, on the other, it's RH. The respective effects of prop walk are supposed to cancel each other.

frankies56 · Apr 6, 2016

You know RV. 20 hp is bearly enough for your boat I have a 33 hp yanmar and feel like I wish I had 50 hp. but at least I can get to hull speed. but every one is right prop walk it is what it is, just learn it and you will !!!

Johnb · Apr 6, 2016

rvoigt40 said:
Its getting to the point where i don't even want to go out, I'm afraid I'm going to hit another boat.
Is it me or the boat? I guess i should have ask that before i bought it i mean who puts a 20 horse power motor in a 17k lbs boat.

Ouch!

This is a little off topic but give it a chance and you hopefully will love your HC37, as we still do after 17 years of ownership.

On topic. We also have prop walk to port in reverse, most noticeable at the instant you put her in gear before she starts moving. I turn the steering hard to starboard before departure and I keep a boat hook handy and pull the stern to starboard as we are leaving. Generally this is enough to counter the prop walk until enough movement has built up for the rudder to have effect, which comes soon enough to usually leave the berth in pretty much a straight line. Goose it to get going (while you can hook to the dock) and then back off or go into neutral once you have momentum built up.

Capt jgw · Apr 6, 2016

Kings Gambit said:
Prop-walk under high RPMs was, I believe, the impetus for the mounting of counter-rotation outboards on twin-outboard fishing boats. The engine rotation on one side is LH, on the other, it's RH. The respective effects of prop walk are supposed to cancel each other.

On high hp boats torque also tends to "twist" the boat in the opposite direction of the prop. Happens on single engine airplanes, and is why helicopters have tail rotors. Counter rotating twins cancel this out.