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Old 02-06-2016, 12:43 PM   #61
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@ Marin: Do you have a right hand wheel on Port shaft and left hand wheel on Stbd? Got a pic?

Here's a quote from a prop shop on prop descriptions for all.
Rotation

The Direction a prop rotates when viewed from the stern facing forward.
Right-hand propellers rotate clockwise to provide forward thrust.
Left-hand propellers rotate counter-clockwise to provide forward thrust.
Note: Left-Hand Propellers are primarily used on twin engine boats to cancel the steering torque that would be caused if both propellers spun in the same direction.

In this case these are outboard turning props that will NEVER walk sideways But are really good at twisting.
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Old 02-06-2016, 12:48 PM   #62
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We have a single engine which is of course very different from a twin. With our old single engine boat we just used springs but when we bought another single engine boat we fitted a bow thruster.
The best thing I ever did (after the bow thruster) was to fit one of the 1700 series Morse single lever controls and used the rocker switch (normally used on outboards to raise/lower the engine) to operate the bow thruster giving completely single handed control over the 3 functions making the whole manoeuvrability child's play and even with a long keel make the boat move sideways.
But as we all know it takes practice, practice and yet more practice to avoid a red face at the wrong moment.
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Old 02-06-2016, 02:19 PM   #63
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@ Marin: Do you have a right hand wheel on Port shaft and left hand wheel on Stbd?
Our prop arrangement viewed from behind is the same as in your illustration. So far as I know, all twin-engine GBs have this arrangement.

When both props are providing forward thrust, or both are providing reverse thrust, the prop walk from each prop cancels out the propwalk of the other prop.

When the thrust is opposed with one prop providing forward thrust and the other providing reverse thrust, both props will be turning the same direction so the prop walk from one prop is doubled by the other one.

This is exactly what one wants while executing some maneuvers and is why we elected to retain the four-bladed props that were installed by a previous owner in place of the boat's original three-bladed props. As a general rule more blades produce more propwalk while fewer blades produce better efficiency.

So betwee our two, counter-rotating, four-bladed props and the boat's two large-ish rudders we can swing the stern very rapidly to one side or the other if we want to.
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Old 02-06-2016, 02:40 PM   #64
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With twins people seem to think they need to use both engines all the time. A twin boat is two singles with opposite rotating props so you can use each independently to get special thrusts. Try using each of your twins with different rudder setting and as you shift into and out of gear and you will find some interesting possibilities.
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Old 02-06-2016, 05:28 PM   #65
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Ok, so unless that picture is a flipped image, you have OUTboard turning props. So indeed your boat will never walk.

The references to INboard turning props does not apply to your boat (or other boats propped like yours.)

Your boat inherently twists better than inboard turning props, but will never walk like my earlier description shows.
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Old 02-06-2016, 05:58 PM   #66
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Ok, so unless that picture is a flipped image, you have OUTboard turning props. So indeed your boat will never walk.
Again, as psneeld has written several tines, walking sideways and sliding sideways are two different things. We can walk our boat into a dock just fine although we never do in practice but instead put the bow in and then walk the stern in to the dock.

What we can't do with this boat is slide it straight sideways as though using a bow and stern thruster together.

So which maneuver are you referring to above? Walking the boat sideways or sliding it sideways?
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Old 02-06-2016, 06:23 PM   #67
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I do believe that twisting is the more official name for turning while staying in place (opposing prop thrust).


I haven't heard that walking and sliding sideways are same in all boating/shipdriving circles but I could definitely see it.


I was just using 2 terms that are layman friendly to make sure people were trying to discuss the same maneuver.
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Old 02-06-2016, 06:33 PM   #68
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I do believe that twisting is the more official name for turning while staying in place (opposing prop thrust).

Okay. Well, our boat definitely "twists" (what I have been calling pivoting) very, very well. One in forward, one in reverse and the rudders hard over in the direction of the pivot and the boat spins around very impressively. It will do it just fine without the use of the rudders but the rudders make the maneuver much, much quicker.
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Old 02-06-2016, 06:41 PM   #69
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I do believe that twisting is the more official name for turning while staying in place (opposing prop thrust).

Okay. Well, our boat definitely "twists" (what I have been calling pivoting) very, very well. One in forward, one in reverse and the rudders hard over in the direction of the pivot and the boat spins around very impressively. It will do it just fine without the use of the rudders but the rudders make the maneuver much, much quicker.
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Old 02-07-2016, 09:53 AM   #70
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Ok, so unless that picture is a flipped image, you have OUTboard turning props. So indeed your boat will never walk.

The references to INboard turning props does not apply to your boat (or other boats propped like yours.)

Your boat inherently twists better than inboard turning props, but will never walk like my earlier description shows.
I would agree with Cappy, but would say "seldom" rather than "never".

In the sideways moving manoeuvre described in this thread, in boats with OUTboard turning props the lateral force from the rudder and the one from the propwalk are in opposite directions. So the net lateral force will be small or even cancel out with little or no lateral motion.

In INboard turning props the lateral force from the rudder and the one from the propwalk are in the same direction so the combined sideways force can be significant and so would the sideways motion.

Most twin engined boats, though, have OUTboard turning props (starboard prop rotates clockwise and the port prop rotates counter-clockwise) so in most boats the manoeuvre would not work well.

In my previous boat, a Brand Banks 42, the manoeuvre would not work. My current boat though, a Grand Banks 50 with OUTboard turning props, will move laterally I believe because it has relatively large rudders close to the props and their sideways thrust are able to overcome the opposing propwalk force.

Well it's a theory.
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Old 02-07-2016, 10:55 AM   #71
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"Most twin engined boats, though, have OUTboard turning props (starboard prop rotates clockwise and the port prop rotates counter-clockwise) so in most boats the manoeuvre would not work well."

Make that ALL twins: I challenge you to find a boat that has its engines installed on the wrong sides of the boat. All twins are set up so that, in fwd, the prop blades are: port rotates counterclockwise, Starboard rotates clockwise.

In reverse the blade at the top of its travel is moving towards the centreline of the boat, pushing the hull in that direction (propwalk).

In the moving sideways maneuver, the prop turning in reverse is only holding the boat from moving forward. Its propwalk away from the dock is easily overcome by the prop in fwd that has its wash pushing against the rudder, turned so the stern is being pushed towards the dock.

If indeed this didn't work well on a previous boat, that is due to other factors, not to the engines turning the props opposite to universal practice.
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Old 02-07-2016, 11:45 AM   #72
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Inboard turning wheel Unicorn? Or not!

@ Koliver: You assume too much to think that twin screw vessels ONLY have outboard turning propellers. And you also assume incorrectly that vessels with inboard turning props are installed 'backwards'. There are reasons for both installations. Unfortunately there is a knowledge block from some who are having a difficult time understanding the differences between inboard and outboard turning wheels and how the prop walk is used when maneuvering. Then again, maybe for most it is superfluous.

Suffice it to say that the two methods for maneuvering to a dock (or away from) using either method (depending upon which your vessel has) 'look' similar to the uninformed. but in fact are completely different. Even on this forum people are routinely confusing, mixing up the two, and not understanding the terminology of prop torque, and how it is used between the two systems. It is not so much that 'walking' is being used here on this description, but that it is a specific description of a method of boat handling that IS used in one specific method of use, and is not the correct descriptor of the method(s) being described here by others.

I am trying to find animated videos of this two methods but am having a difficult time. I can find turning wheel animated, but Left handed animations are difficult to come by. And twin screw seems to be like a unicorn.

The end all is: Outboard wheels do NOT walk sideways. They twist using leverage (spring lines or bowthrusters). But bowthrusters help this 'look' like walking. This twisting everyone is referring to takes multiple changes, port ahead, stbd astern, and visa versa to accomplish the maneuver.

Inboard turning wheels walk. Walk the whole boat laterally sideways to the dock with or without bowthrusters, spring lines, or help. This can be accomplished usually without even taking the engines out of gear almost TOO the dock, and just finding the sweet spot on the rudders to keep the boat parallel to the dock.


If anyone finds a visual description about prop torque please post it for all to learn from. Especially Left handed wheels!!! Unfortunately I am not a C++ person and don't know how to make animations.

On outboard turning boats, when twisting the prop torque swings the stern in the direction of the ahead engine side.

On inboard turning boats, when walking (same prop directions as above) the stern will move to the backing engine side. Using rudder the bow can be kept in line, and the net result will be direct sideways travel with no appreciable ahead or astern movement.

Sort of mind boggling when first introduced. But true!
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Old 02-07-2016, 12:13 PM   #73
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I am trying to find animated videos of this two methods but am having a difficult time.
The diagram below is not an animation but it may help.

the boat on the left has the conventional OUTboard turning propellers and the one on the right has INboard turning propellers.

Both boats boats have the rudders steering the boat to port, the starboard engine going forward and the port engine in reverse.

As Cappy points out the boat on the right, with Inboard turning props, will easily move sideways as the lateral forces from propwalk and prop wash on the rudder combine to push the boat to starboard. The forward and backward forces of the props cancel and so are the torques acting on the boat.

In the boat on the left, with OUTboard turning propellers, the lateral forces from the propwalk and the prop wash on the rudder are in opposite directions. The relative strength of these forces, and hence how well the technique works, probably depends on many factors such including rudder size.

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Old 02-07-2016, 01:13 PM   #74
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The diagram below is not an animation but it may help.

the boat on the left has the conventional OUTboard turning propellers and the one on the right has INboard turning propellers.

Both boats boats have the rudders steering the boat to port, the starboard engine going forward and the port engine in reverse.

As Cappy points out the boat on the right, with Inboard turning props, will easily move sideways as the lateral forces from propwalk and prop wash on the rudder combine to push the boat to starboard. The forward and backward forces of the props cancel and so are the torques acting on the boat.

In the boat on the left, with OUTboard turning propellers, the lateral forces from the propwalk and the prop wash on the rudder are in opposite directions. The relative strength of these forces, and hence how well the technique works, probably depends on many factors such including rudder size.

Almost. The inboard turning example (on the right) will push the boat to the LEFT Port not stbd.

And, although counter intuitive, the left example will require HUGE amount of inordinate ahead thrust to counter the prop torque working against the desired effect (going to port) But the end result is more like a forward slew, crabbing at a 45 towards the dock.

Thanks for the examples. I was trying to get something end on, showing rotation and torque to show the lateral thrust, figuring people wouldn't 'take my word for it' as it were.
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Old 02-07-2016, 01:18 PM   #75
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The diagram:
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Old 02-07-2016, 01:22 PM   #76
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And, although counter intuitive, the left example will require HUGE amount of inordinate ahead thrust to counter the prop torque working against the desired effect (going to port) But the end result is more like a forward slew, crabbing at a 45 towards the dock.
Yes, this is sort of what I manage to do on my current boat with OUTboard turning props but large rudders. On my previous boat also with OUTboard turning props but small rudders it would not go anywhere.
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Old 02-07-2016, 01:38 PM   #77
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I have only ever seen outboard turning props on any twin engine v-hull boat, but I aint seen em all. Newish catamaran boats, like my Ameracat 31, use in board turning props.
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Old 02-07-2016, 02:31 PM   #78
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I have only ever seen outboard turning props on any twin engine v-hull boat, but I aint seen em all.
Unless i am very much mistaken, these are OUTboard turning props, the most common type (for some reason).

Propwalk pushes stern in direction of the engine in forward gear.
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Old 02-07-2016, 03:03 PM   #79
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Reading other forums Hatteras, and hull truth. There are reasons beyond conventional. Maneuvering, The desire to 'lift' a stern UP. Or push down a stern as needed to meet design specs. Some designs need the extra lift or squat to 'do' what the designer intended. The ability to walk sideways depending upon usual use of a vessel. Or the desire to increase speed or bollard thrust.

Of course, coming from the commercial industry the thrust and maneuverability is paramount.

But the term 'walking' is pretty specific to a set of circumstances that is only accomplished by inboard turning wheels.
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Old 02-07-2016, 03:08 PM   #80
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Because outboard turning generally give the best, least complicated maneuverability... not necessarily for specialty boats. Thus why you hardly ever see a rec boat with inboard turning.


I have heard that some high performance vessels will have inboard turning props...such as ocean racers...but don't have a link right now.
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