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Old 09-08-2012, 10:45 AM   #1
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Help with single screw inboard.

My wife and I are looking to buy a single screw trawler. We took her for a sea trial and I was surprised about the amount of prop walk she had. In reverse, the stern would go to starboard and the bow to port. She had a bow thruster, but would not compensate for the prop walk. Iíve been sailing for twenty years on quite a few inboard sailboats, but have never experienced this amount of prop walk before. This is our first time on a trawler.

Is there any way to compensate or correct this situation, or should I be looking for a twin screw boat?

This boat is in the Great Lakes.
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Old 09-08-2012, 11:03 AM   #2
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Yes .. If you have a left hand prop that pulls to stbd and you want to make a landing on your port side ........ approach at a wider angle and before you would normally reverse apply full right rudder, get the stern swinging toward the float and then reverse to a stop. The boat's stern swing toward the float will be stopped by the prop walk when you reverse but then you'll be parallel alongside the float.
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Old 09-08-2012, 11:11 AM   #3
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Greetings,
Welcome aboard Mr. jj. I've found the learning curve for a single prop to be fairly steep. You'd be surprised what some practice will do. Don't be put off by what you perceive as a LOT of prop walk compared to a sailing vessel with a large keel and a small prop/motor. Go out on a LOT of boats, both singles and twins and enjoy the search.
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Old 09-08-2012, 11:36 AM   #4
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Quote:
Originally Posted by jjsemo1 View Post
My wife and I are looking to buy a single screw trawler. We took her for a sea trial and I was surprised about the amount of prop walk she had. In reverse, the stern would go to starboard and the bow to port. She had a bow thruster, but would not compensate for the prop walk. I’ve been sailing for twenty years on quite a few inboard sailboats, but have never experienced this amount of prop walk before. This is our first time on a trawler.

Is there any way to compensate or correct this situation, or should I be looking for a twin screw boat?

This boat is in the Great Lakes.
If this is the first single screw boat besides and outboard/IO, I strongly suggest you find a single screw boater willng to ride along a couple times or spend a couple hundred for a few hours with a capt who is well know in your area with single experience. Most say it's the best money spent on the water for them.

If that's not your cup of tea, there are hundreds of articles on just the prop walk issue, and hundreds of articles describing the use of a spring line/planning ahead to compensate. The trouble with trying to explain it here, is everytime you do it, the conditions are just a hair different and people may start the process a little different or finish it a little different...so in a forum..it's is hard to think the process from start to finish if between on Capts posts, there are 20 more saying something slightly different.

Don't think that singles are hard to manuever, especially if you have even an underpowered thruster, it'll just take time or some lessons. Most singles have good rudder control and are quite maneuverable.

Sometimes adjusting approach speed is all it will take to help negate the prop walk. I have found that in most docking situations, a strong influence by something, either wind, current, prop walk etc is a great help or hurt depending which way you need to be. Someimes all it takes is thinking outside the box to make that hurt and major help in docking.
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Old 09-08-2012, 11:38 AM   #5
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While I understand the propwalk issue, I do not understand why a properly functioning bow thruster would not more than compensate. Your thruster should be capable of delivering much more side thrust than a prop (at idle) in reverse. If this is truly the situation I would check out your thruster because it does not sound as though it will be much use when you really need it!!
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Old 09-08-2012, 11:56 AM   #6
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15 years ago I went from a Nonsuch 30 which backed up anytime following the rudder position, you could drive the boat the same in reverse as you could in forward! Our new to us PT38 Sedan has a single Perkins (no thrusters bow or stern) with a huge amount of prop-walk to starboard. When I first bought the boat the previous owner told me on sea-trials when I asked him about the need for thrusters said "just don't try and put her someplace she doesn't belong". Prop-walk is now my best friend and it only took a few outings to figure it out. If you give me the choice (I always ask) my docking will always be on the starboard side which is our preferred side for boarding, if I have to dock to port I do as Eric says. She goes into our boathouse(90 degree turn) without touching either side, you should hear my neighbours on both sides with twins scrape the entrance ways. They cannot figure out how we do it, easy put the bow in the middle of the entrance slowly, put her in reverse till the stern centers with prop-walk and then straight in.
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Old 09-08-2012, 12:48 PM   #7
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My single-propellered boat requires a 3-degree rudder to go straight while in forward gear.

Prop-walk in reverse can be your friend if one plans ahead to take advantage (as explained in previous posts).

When backing out of my berth, I use the bow thruster (very short burst) to angle the boat so the to-the-starboard prop-walk is effectively countered, repeating burst if needed.
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Old 09-08-2012, 01:54 PM   #8
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Use reverse to get her moving backward and then coast in neutral - no prop walk in neutral. Keep the rudder hard over to the prop-walk direction (you're moving slow enough that the rudder has no effect). When the stern gets too far in that direction, put the transmission in forward and give it a short burst to bump the stern in the other direction. Repeat.
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Old 09-08-2012, 03:11 PM   #9
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I do just as Gary said.
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Old 09-08-2012, 03:17 PM   #10
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Old 09-08-2012, 05:22 PM   #11
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Propwalk moves the stern. A bow thruster moves the bow. The propwalk is not moving the bow even though it may look like that to you. You are simply seeing the results of the stern swinging to starboard which obviously (I hope) makes the bow point to port.

So a bow thruster cannot counter propwalk. You can make the boat go backwards in a sideways crab by using the bow thruster and propwalk together. But the bow thruster will never "stop" the propwalk.
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Old 09-08-2012, 07:14 PM   #12
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Surely the propwalk is simply applying a turning moment to the stern, so consequently you should be able to correct the turning motion by applying an opposite force to the bow. -- ie if propwalk is turning boat to starboard at the stern, then thrusting the bow to starboard will help straighten the boat out. The boat may be moved laterally to starboard by the combined effect but you should be able to compensate for the starboard propwalk turning moment. I agree with others that propwalk can be used to your advantage as when intentionally turning the boat in a small distance.
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Old 09-09-2012, 06:55 AM   #13
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The propwalk is not moving the bow even though it may look like that to you.

The bow does move, it moves more than the stern when backing.

When a boat is moving ahead, the point around which the hull yaws from the turning force of the rudder - the pivot point - is about 1/4 hull length back from the bow at the water line.

When going ahead the stern moves much more to the outside of the turn than the bow moves inside, it may appear that the bow is always pointing in the direction of movement but it is not. To show this, wait for a calm day and start a moderate turn, or even a sharp turn, and watch the water close inboard on the turn. You will see a "slick" caused by the hull moving sideways behind the pivot point. This is easily seen by looking a the wake, it is wider inside the turning circle than outside.

When backing, the pivot point moves to about 1/4 waterline length ahead of the stern, the greater length of the hull is ahead of the pivot point now and the bow moves in a larger radius than the stern. So the OP is correct, the bow moves opposite of the stern and to a greater degree. Try the same experiment going astern and you will see the slick and the bow tracking well outside the turning circle.

When the boat
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Old 09-09-2012, 07:07 AM   #14
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Here is how it's done.



Some boats have more prop walk than others. It's something you learn to deal with as evidenced by the guys in the video.

In reality, you will spend a very small percentage of your operating time in reverse so prop walk shouldn't be something that keeps you from buying a boat you otherwise like.
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Old 09-09-2012, 08:45 AM   #15
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In reality, you will spend a very small percentage of your operating time in reverse so prop walk shouldn't be something that keeps you from buying a boat you otherwise like.
Prop walk in reverse will occur with most all single screw boats. Not only should you not fear it, but embrace it. When you learn the characteristics of your boat, prop walk can be used to your advantage. If you want to back in a nearly straight line Gary P offered good advice.

Most all boats have their handling characteristics. Pivot points vary some, and the pitch of the prop can have its own effect. Find a place to work with your boat even if you have to put out some temporary floating markers to back around. It will give you a target. Find and empty dock or slip to practice on. You will catch on soon enough. It is not rocket science. Then you can move on to using spring lines to help in certain situations.
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Old 09-10-2012, 06:00 AM   #16
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"Prop walk in reverse will occur with most all single screw boats. Not only should you not fear it, but embrace it. When you learn the characteristics of your boat, prop walk can be used to your advantage."

You bet , prop walk is your friend if you ever do the big mud run aka,,"The Loop" with perhaps 100 locks to transit.

Just be sure to dock on the proper side to work the stern movement.
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Old 09-10-2012, 05:43 PM   #17
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I agree, be sure to dock on the side of the prop walk. The Eagle prop walk is to port so we try to dock on the port side and when maneuvering to turn to starboard. If we have a starboard tie and have to maneuver to port that is where the bow thruster, plenty of funders and lines come in handy. Its like using the wind/current to your advantage or disadvantage?

Actually, the best is to call and beg/plead for dock help, so when you get there you toss them a line and they pull you in. Works for me!
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Old 09-10-2012, 08:14 PM   #18
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If you have to go in reverse for any kind of distance you can have an issue. i never back down a fairway. Just go down the fairway in forward, stop when your midship point is just past the center of your slip. steer with your thruster to line up the boat with the slip. about three seconds of reverse, then neutral. Use your thuster when in neutral and the boat will go where you want it to go. I can make my boat go completely sideways either port or starboard using the thruster and back and fill with the shifter.
I watch a lot of sailors during the wednesday night races in Annapolis and they all back completely down the fairway when docking. if I tried to do that I would bounce off the pilings on each side.
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Old 09-16-2012, 09:06 PM   #19
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Rudder straight .... good shot of throttle in reverse ... quickly back off throttle and back to neutral. repeat as required. the boat will back down in a (mostly)straight line (wind/current excepted).

If the throttle is pushed hard and quick enough, the thrust overcomes the walk. You have to go back to neutral because the walk is more prominent at idle when there is little thrust to counteract it. Keep in mind it is thrust you need to overcome the walk NOT speed. "Walk" is your friend.
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Old 09-16-2012, 09:11 PM   #20
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most single screw boats have a mind of their own...they are reasonably predictable but using one technique for all single screw boats in all situations is a recipe for disaster.
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