Handling Question:moving sideways w/twins

@ 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.

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.

cappy208 said:

@ Marin: Do you have a right hand wheel on Port shaft and left hand wheel on Stbd?

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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.

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.

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.

cappy208 said:

Ok, so unless that picture is a flipped image, you have OUTboard turning props. So indeed your boat will never walk.

Click to expand...

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?

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.

psneeld said:

I do believe that twisting is the more official name for turning while staying in place (opposing prop thrust).

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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.

psneeld said:

I do believe that twisting is the more official name for turning while staying in place (opposing prop thrust).

Click to expand...

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.

cappy208 said:

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.

Click to expand...

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.

"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.

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!

cappy208 said:

I am trying to find animated videos of this two methods but am having a difficult time.

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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.

Xlantic said:

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.

Click to expand...

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.

The diagram:

cappy208 said:

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.

Click to expand...

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.

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.

kulas44 said:

I have only ever seen outboard turning props on any twin engine v-hull boat, but I aint seen em all.

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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.

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.

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.

If you visualize the prop as an automobile tire turning with its blades touching the "ground," you will immediately know in which direction the stern will move using that prop.

Dramamine is recommended!

All these examples are only to twist or walk to port. I am not going to changing directions so as to try to make it clear how prop torque works, leaving it as a 'one sided example'. All of the prop torque comes from the bottom half of the blades. (as noted by an earlier poster who made the comment about the 'tires on the bottom'.)

Here is why boats with outboard turning wheels can't walk sideways. (without some outside force or help)

via Imgflip GIF Maker

In the above examples, the top video is both ahead, outboard turning.
via Imgflip GIF Maker
the second is backing the port, ahead on the stbd. the stern is being twisted to the starboard. The intent is to lift the bow to port, but you have to accept some stern slew the "wrong" way
All the prop torque is pushing the stern of the boat away from the dock.
The only way an outboard turning vessel can 'walk' sideways is using an outside force (bow/spring line, thruster, wind, current) to twist against to go sideways. But that is not walking, it is twisting, warping, springing, or breasting (depending upon which part of the world you learned your vocabulary from.)

The only thing that can be attempted (depending upon rudder size and horsepower) is to walk an outboard turning vessel by slewing it diagonally overpowering the backing engine with the ahead engine, but it is really influenced by wind and current more than an inboard turning vessel. And the progress is about at a 45 degree angle to the dock, making it impractical to dock in tight spaces as has been described earlier.



However, inboard turning wheels have two distinct attributes. Here is one of them.


Inboard turning wheels.

This is an example of inboard turning wheels, ahead propulsion.
via Imgflip GIF Maker


Now, here is the 'walk' laterally sideways.
via Imgflip GIF Maker


This is while walking to port, with approximately 10 to 20 degrees Stbd rudder. (the amount varies with wind, vessel characteristics, and rudder size.)

port backing, stbd ahead. Note direction of bottom of wheels, both are walking the stern to port. On a good walking vessel the stern will walk faster with the rudders used to balance the walk out to be even and in control.

This has little to do with space between wheels, depth of keel, or other physical attributes. It is all about the prop torque and how to harness it (or realize that you have NO prop torque to benefit from to walk sideways)



Sorry if the GIFs make you sick. They sort of all blend together after a while as I was making them!

"The only way an outboard turning vessel can 'walk' sideways is using an outside force (bow/spring line, thruster, wind, current) to twist against to go sideways. But that is not walking, it is twisting, warping, springing, or breasting (depending upon which part of the world you learned your vocabulary from.)"

Sorry to bust your bubble, but in the last 21 years of driving my outboard turning (in fwd) boat, I have never needed anything but the shifters, to get my boat to spin on its helm, or to move the stern where ever I wanted it to go by applying a little reverse of the appropriate side. Using the rubber on the road analogy, if ever I want the stern to move to port, I apply a little starboard reverse, or if I want to move the stern to starboard, I apply a little port reverse. Always works. Never need a line to the dock.

The key is, in reverse, each side will always move the stern to the other side. When backing down the fairway, with both in reverse, steer by putting one side or the other into neutral until the boat staightens out, then both in reverse, with throttles at idle. Always works.

To get off the dock, put the side nearest the dock in reverse, the side away in fwd. twists the boat until the stern is outboard of the boat tied close behind, then both in reverse and away you go.

You're not bursting anyone's bubble. I'm just trying to clear up the reasons 'why' inboard and outboard turning wheels perform differently.

Often (sometimes even in this particular thread) people who 'think' they know whether they have inboard or outboard turning wheels when they actually have the opposite! Then again, the concept of moving a boat laterally sideways (without a bow thruster or spring line) is an anathema to others. There is a difference between twisting the stern off, and walking the entire boat. Sometimes people want to actually know the 'how and why' (as the OP asked) of why their boat 'does this' when I back, or twin screw.

My intention is to share this info with others, not to seemingly contradict how you feel about running your particular vessel. You will not find this info anywhere in a yacht forum, because as you have so eloquently put it, "NO yachts have inboard turning wheels". This is not true. However, certainly the majority of yachts do have outboard turning wheels. But for those people who see 'something' done on another boat, and wonder: "Gee, why can't I do that with my boat?' This explanation may help them see the why.


The 'walking' of inboard turning wheel does not require twisting. The entire boat moves laterally (sideways) away from (or towards) the intended destination. Your comment only reinforces my explanation about how outboard turning wheels affect maneuvering.

Closing with an observation: If you have never operated a vessel with inboard turning propellers, don't knock that there are maneuvering characteristic differences between inboard and outboard turning vessels.

What you don't know isn't necessarily bad, or wrong. Just unknown.

We used this technique on Crew Boats in the Gulf of Mex. 135 footers with 4 engines. We left the inside engines in neutral and just used the outside engines. Docking was so tight.
Boats would all be backed in. They were tied with 2 stern lines and then to each other. If you left. someone else would come right in. Basically bumping the boats on each side as you slid in. If you couldnt walk the boat, you would never be able to back in because the river current would spin you around.

It would be easier to explain how to do this if you had the space to lay up against the dock. Start by pulling parallel to the dock and come to a stop. Then turn wheel away from the dock (turn in opposite direction than you want to walk). Cross the shifters in Clutch (the detent position on the shifter which is idle speed and in gear) as if you were going to pivot toward the dock. It will take a few seconds before the boat actually reacts. it will then move sideways toward the dock. It will take some fine tuning adjusting the engine speed or taking one of the engines out of gear for a moment or two to keep the boat from going forward or backward.

This usually will only work with boats that do not have a real keel, so to speak. That is - a relatively flat bottom.

It works on my Mainship 36 on not so windy days. Problem is, I have separate throttles and shifters. The oil field boats all had one throttle/shifter for each engine. So much easier to control. Dont know why all boats aren't that way.

The single lever throttles are the way to go. I don't know why so many companies installed them in he 80's. I want to change mine to single lever but the cost is too much to justify. Maybe next Christmas. I am looking at two consignment shops to see if I can find two used ones.

I am not a fan of single control levers...but like many things...what you get used to can become a favorite.

When referring to a running diesel engine I was under the impression that idle meant the transmission was not engaged which is how you get definitions of high and low idle on a Diesel engine.
So you can run your Engine at wide open throttle at Idle

To me "idle" refers to to the minimum throttle setting, whether the transmission is engaged or not.