Thanks for your question! Here’s the short answer:
(1) Get steerageway
(2) Throttle down, shifting into neutral if it’s bad
(3) Coast through your turn and make it a little (not much!) tighter than you normally would
(4) Bursts of speed where needed and then coast backwards, in neutral
When prop walk is really strong, the boat doesn’t back up at all, turning in place in one direction, regardless of how much you accelerate. You have an implicit question as well: “How do I back up my boat when it has strong prop walk?” Please note that I am assuming a single-screw (propeller) boat. Twin-screw powerboats have opposite engine rotations and are properly driven at slow speed by the engines, with only occasional wheel, so this doesn’t apply to them.
Boat propellers, with a couple exceptions, are designed to go forward efficiently and provide some reverse functionality but not much. As a result, they push water behind them (in forward gear) very well, with only a little being thrown out along the axis of the blades – You can see this with the wake in calm conditions when the prop’s not going too fast or slow – Sharp lines of water on the surface perpendicular to the thrust, if your prop is behind the boat.
In reverse, the prop throws most of the water aside with only a little forward. Due to the shape of the propeller blade, the water is thrown in one direction, so it hits, for instance, the port side of your boat but not the starboard and the water being diverted along the hull affects the direction your boat’s going in reverse in two ways: It pushes the boat to one side and creates a flow of water that’s not in the direction the boat’s going in. The same problems exist for the rudder, if mounted ahead of the prop, as in an outboard mounted on a transom and while the uneven deflection of the water on the rudder’s surface is not so much of a problem here, the force of the water can uncontrollably slam the rudder to one side or the other, causing serious damage, injury and an out of control boat. Things are made worse by the position of the rudder in relation to the prop and on tiller boats, it’s often almost impossible to keep the tiller from slamming to one side or the other, completely losing control in reverse! With this uneven force of heavily swirling water, there’s not much control and what control there is, is very lopsided.
There are propellers that are reversing and they have greatly reduced prop walk but are also much less efficient going forward, which is almost all the time. Once you’ve learned what I’m showing you here, prop walk is an annoying but relatively small price to pay. There are fancy outdrives that have two propellers spinning in opposite directions on the same shaft and they don’t have appreciable prop walk and are really, really cool! But we’re helping out the average Joe powerboater and the sailor, here.
There are two techniques and one principle that will get you past the worst of prop walk. Here’s the principle: Steerageway. You’ve got to go a minimum speed for your rudder and keel to be able to steer. Usually that’s about 1.5 knots. If you don’t go that fast, no amount of steering will have any effect. The first thing to do is get up to speed, so you can turn. once you’ve got steerageway, your boat will glide for a good fifty yards if there’s no wind, so you’ll be fine.
To effectively and quickly gain speed, I gradually increase engine revolutions so the prop is thrusting water and not bubbles. At the same time, counter the prop walk with the rudder only enough to get the boat going straight back – Don’t worry about turning. When the docklines are cast off, shift into reverse at idle and then accelerate to 1500 revolutions per minute (RPMs), glancing at the wash on one side or the other of the rear of the hull to make sure you’re not blowing bubbles but are pushing strongly. Increase to 2000 if possible, over a period of perhaps five seconds – You ought to now have steerageway and you’ll know it because the rudder will suddenly feel alive and direct the boat, pulling in the direction you’ve turned it. Congratulations – You’ve got steerageway!
At this time, you’ll need to ease your correction, throttle down and if the prop walk’s bad, shift into neutral, keeping the boat going straight out of the slip until the curve of the bow starts clearing the slip (On a powerboat, this is usually halfway between the windshield and the bow and on a sailboat it’s just forward of the mast.). If the propeller is behind the rudder, the propwalk will probably throw the rudder to one side if you try steering anything but straight back, so once you’ve got steerageway, throttle down to idle (It will help pull the boat just a little and that really helps!) and steer through the turn normally. When your boat’s through the turn and pointing straight, you can increase the throttle to just the bare minimum needed to maintain steerageway if your prop walk isn’t that bad or if it is, keep going in bursts and coasting in neutral. You’ll know if your prop walk is bad because you’ll have to correct a lot for it and your boat will be “crabbing” (traveling at an angle) as you back down the channel.
Finally, make sure you’re giving yourself plenty of room at the end of your turn if you’re reversing direction because as you stop the boat by engaging the engine in forward (ease the throttle into no more than the proper engine rpm’s!), you will force her to slower than her steerageway, both in reverse and in forward. This doesn’t stop her initial backwards movement, though and you’ll find yourself skidding sideways. You’ll therefore need more space on the outside of your turn, so you end up in the center of the lane and not banging against the boats on the next dock. Remember that the leading end (stern if you’re reversing and bow if you’re going forward) of a sailboat and to some extent, of a single-screw powerboat, cuts inside the turn, so you can cut your turn a little tight and you’ll end up drifting into your ideal center path.
To summarize:
(1) Get steerageway
(2) Throttle down, shifting into neutral if it’s bad
(3) Coast through your turn and make it a little (not much!) tighter than you normally would
(4) Bursts of speed where needed and then coast backwards, in neutral
That’s it! Happy sailing!
- Jerr
(1) Get steerageway
(2) Throttle down, shifting into neutral if it’s bad
(3) Coast through your turn and make it a little (not much!) tighter than you normally would
(4) Bursts of speed where needed and then coast backwards, in neutral
When prop walk is really strong, the boat doesn’t back up at all, turning in place in one direction, regardless of how much you accelerate. You have an implicit question as well: “How do I back up my boat when it has strong prop walk?” Please note that I am assuming a single-screw (propeller) boat. Twin-screw powerboats have opposite engine rotations and are properly driven at slow speed by the engines, with only occasional wheel, so this doesn’t apply to them.
Boat propellers, with a couple exceptions, are designed to go forward efficiently and provide some reverse functionality but not much. As a result, they push water behind them (in forward gear) very well, with only a little being thrown out along the axis of the blades – You can see this with the wake in calm conditions when the prop’s not going too fast or slow – Sharp lines of water on the surface perpendicular to the thrust, if your prop is behind the boat.
In reverse, the prop throws most of the water aside with only a little forward. Due to the shape of the propeller blade, the water is thrown in one direction, so it hits, for instance, the port side of your boat but not the starboard and the water being diverted along the hull affects the direction your boat’s going in reverse in two ways: It pushes the boat to one side and creates a flow of water that’s not in the direction the boat’s going in. The same problems exist for the rudder, if mounted ahead of the prop, as in an outboard mounted on a transom and while the uneven deflection of the water on the rudder’s surface is not so much of a problem here, the force of the water can uncontrollably slam the rudder to one side or the other, causing serious damage, injury and an out of control boat. Things are made worse by the position of the rudder in relation to the prop and on tiller boats, it’s often almost impossible to keep the tiller from slamming to one side or the other, completely losing control in reverse! With this uneven force of heavily swirling water, there’s not much control and what control there is, is very lopsided.
There are propellers that are reversing and they have greatly reduced prop walk but are also much less efficient going forward, which is almost all the time. Once you’ve learned what I’m showing you here, prop walk is an annoying but relatively small price to pay. There are fancy outdrives that have two propellers spinning in opposite directions on the same shaft and they don’t have appreciable prop walk and are really, really cool! But we’re helping out the average Joe powerboater and the sailor, here.
There are two techniques and one principle that will get you past the worst of prop walk. Here’s the principle: Steerageway. You’ve got to go a minimum speed for your rudder and keel to be able to steer. Usually that’s about 1.5 knots. If you don’t go that fast, no amount of steering will have any effect. The first thing to do is get up to speed, so you can turn. once you’ve got steerageway, your boat will glide for a good fifty yards if there’s no wind, so you’ll be fine.
To effectively and quickly gain speed, I gradually increase engine revolutions so the prop is thrusting water and not bubbles. At the same time, counter the prop walk with the rudder only enough to get the boat going straight back – Don’t worry about turning. When the docklines are cast off, shift into reverse at idle and then accelerate to 1500 revolutions per minute (RPMs), glancing at the wash on one side or the other of the rear of the hull to make sure you’re not blowing bubbles but are pushing strongly. Increase to 2000 if possible, over a period of perhaps five seconds – You ought to now have steerageway and you’ll know it because the rudder will suddenly feel alive and direct the boat, pulling in the direction you’ve turned it. Congratulations – You’ve got steerageway!
At this time, you’ll need to ease your correction, throttle down and if the prop walk’s bad, shift into neutral, keeping the boat going straight out of the slip until the curve of the bow starts clearing the slip (On a powerboat, this is usually halfway between the windshield and the bow and on a sailboat it’s just forward of the mast.). If the propeller is behind the rudder, the propwalk will probably throw the rudder to one side if you try steering anything but straight back, so once you’ve got steerageway, throttle down to idle (It will help pull the boat just a little and that really helps!) and steer through the turn normally. When your boat’s through the turn and pointing straight, you can increase the throttle to just the bare minimum needed to maintain steerageway if your prop walk isn’t that bad or if it is, keep going in bursts and coasting in neutral. You’ll know if your prop walk is bad because you’ll have to correct a lot for it and your boat will be “crabbing” (traveling at an angle) as you back down the channel.
Finally, make sure you’re giving yourself plenty of room at the end of your turn if you’re reversing direction because as you stop the boat by engaging the engine in forward (ease the throttle into no more than the proper engine rpm’s!), you will force her to slower than her steerageway, both in reverse and in forward. This doesn’t stop her initial backwards movement, though and you’ll find yourself skidding sideways. You’ll therefore need more space on the outside of your turn, so you end up in the center of the lane and not banging against the boats on the next dock. Remember that the leading end (stern if you’re reversing and bow if you’re going forward) of a sailboat and to some extent, of a single-screw powerboat, cuts inside the turn, so you can cut your turn a little tight and you’ll end up drifting into your ideal center path.
To summarize:
(1) Get steerageway
(2) Throttle down, shifting into neutral if it’s bad
(3) Coast through your turn and make it a little (not much!) tighter than you normally would
(4) Bursts of speed where needed and then coast backwards, in neutral
That’s it! Happy sailing!
- Jerr
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