Walking Sideways

About a week or so ago, someone posted a link to this great website that I find very informative – http://www.captainhugenot.com. I can't find the post now, so whoever recommended this, thank you.


At any rate, there is one article that I don't understand. It's regarding walking your boat sideways and there's either a mistake, or I'm missing something. I would like the great TF members opinions.


It states the following -




Suppose we have dock off our starboard side, and we want to “parallel park” our boat between two other boats on that same dock. We would simply turn our helm hard to starboard (or toward the dock when landing). Then, with the engines at idle, we would shift our outboard engine (the one farthest from the dock) to provide reverse propulsion, and shift our inboard (the one closest to the dock) to provide forward propulsion.


The astern thrust of the outboard engine and the forward thrust of the inboard engine will tend to turn our bow away from the dock. However, the thrust from the inboard engine impinging upon the rudder surface will tend to push the bow toward the dock – and these two effects will cancel each other out, leaving the boat idle.


Since both propellers are now turning clockwise ( port is left handed, starboard is right handed) this provides a “paddlewheel effect” of moving the boat to the right. The net effect is a movement sideways to starboard toward the dock.


Of course, if it were that simple, everyone would find it easy.


However, the opposing thrust of the two propellers has a greater turning force that the prop wash against only one rudder, and so our bow may head in slightly quicker that our stern. If we don't stop this turning, we will soon be headed straight for the dock – bow first. . . . .




Everything makes sense to me except the last paragraph. It states that the opposing thrusts have the greatest effect, yet it says the bow will be turning into the dock. It makes sense to me that the bow will still be turning away from the dock as stated in the second paragraph.


Here is the link to the article that also has diagrams - http://www.captainhugenot.com/images/TWIN-SCREW_06-2004.pdf


Is this a mistake in the article or am I missing something?

I have tried this technique with our boat, I have had a couple of REALLY experienced ex-professional boat handlers (one of them ex-USCG) try this technique on our boat. And I can assure you that with our boat, at any rate, it doesn't work if the objective is to move the boat straight sideways, as if you had a bow and stern thruster.

I have had people swear up and down that it works and then when they've actually tried it on their own boats while we watched, it didn't.

It might if your props are really far apart. Like on a Great Harbor or a power cat.

But on GB where the props are tucked in real close to the keel and each other, it won't work. It will work for a moment but after that moment one end of the boat will move farther than the other one.

Anyway, I don't think this is actually "walking" a boat. Walking a boat, as it's always been explained and demonstrated to me, is moving the bow in, then the stern in, then the bow in, then the stern in, in small increments until you arrive next to the dock. Assuming the wind and current leave you alone long enough to do this, this is quite easy to do with our GB.

But we don't dock using this technique, so other than proving to ourselves that it works, we never do it as a matter of practice. But the helm toward the dock, opposing thrust pivoting the boat away from it (so the stern toward it), straight sideways thing has never been anything we've seen anyone be able to demonstrate even remotely successfully with a boat like ours.

Thanks for your reply Marin.

I have doubts whether this will work on my boat as well, but I do want to experiment with it. However, before I do, I want to at least understand the theory and this article confuses me.

Any thought on whether the writer made a mistake, or am I missing something?

Neal

Nsail:
Good catch. I can't make sense of that article either. Maybe his boat is different from mine. His diagrams would have the towards the dock arrow switched with the away arrow, if he was operating my boat. Maybe the size of the rudder surface makes his description correct for his boat and the opposite work on mine. His explanation of both propellors turning clockwise to generate turning forces ignores the rudders. On my boat I rely on propwash and propwalk, not the direction of rotation.

That is a technique that I use frequently. I keep my boat in a shelter, so if I turn towards the opening of my shelter and find my bow too far to port, I walk to starboard to correct that and then slide in without touching anything. Other guys let the shelter supports deflect their bows as they slide in. I have varnish on my rails, which would touch first, so I don't like to have the rail touch and had to learn this technique to save my varnish.

I find his terminology confusing. I will call the engine away from the dock "offside" and the other "nearside".

Always remember that the offside (Port if you want to move to Starboard) engine should be in forward, and the wheel should be turned in that direction. That gives you wash against the offside rudder, pushing the stern in the direction you want to go. With forward power being applied from one side the bow will want to go towards the other, and the whole boat will want to move ahead, so counter that with reverse of the nearside engine. It takes a bit of practice to get the balance just right.

Should your bow get going towards the nearside too quickly, shift both engines. Leave the rudders set as they were. Now you have wash against the nearside rudder, pushing the stern to the nearside together with propwalk of the offside engine, pulling the stern towards the nearside as well, so only a little of that correction is needed, before shifting both engines back to the walking sideways manouvre.

My reading of the paragraph leads me to believe as you do, Neal, that the writer is either wrong or didn't say what he meant to say. If the thrust against the rudder is less than the pivoting force from the opposed thrust the stern will yaw in the direction dictated by the propwalk and the leverage from the opposed thrust, Which in this case will be toward the dock, thus aiming the bow away from it.

Nsail, are you reading the second sentence of para 2, which I read as modifying the first? Makes sense if you do.
I`ve yet to experiment with this method but intend to. I once saw a Riviera 35 moved sideways to a dock without bowthruster, wondering how it was done. Noting Marin`s experience, maybe it works better for Rivs with planing hulls than for for trawlers with semi displacement.

walking a boat..

Nsail said:

Thanks for your reply Marin.

I have doubts whether this will work on my boat as well, but I do want to experiment with it. However, before I do, I want to at least understand the theory and this article confuses me.

Any thought on whether the writer made a mistake, or am I missing something?

Neal

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Neal,
The bottom of the boat determines if they will walk sideways or not. I occasionally drive a 80' fast ferry that will walk quite well. She has no keel like most " trawlers ".What is interesting is that for this boat to walk to Starboard the helm goes hard to port, starboard engine in reverse, port forward at idle. As the boat starts to go sideways you control the position forward and astern with the starboard engine with additional throttle. Angle to the dock is controlled with changes to rudder.
Exactly opposite of the article suggests.The ferry has about 1000 hp, big props and no keel. It is a bit hard to get used to but the 80' boat fits into a 90' space.. and there is no view of the stern from the bridge.
The SeaRay I currently own is 45', has 700hp with props in partial tunnels and I have found it impossible to walk. My bud that owns the ferries was aboard the SeaRay and razzed me about not walking it to a parallel dock.. I felt a touch of chagrin when he gave up after 30 minutes with no luck when he tried. Some will.. some wont.. give it a shot, if it works on your boat it is a fantastic too to get you into tight spots.
HOLLYWOOD

Whew... Thanks for the replys. I thought I was losing it. I've read the article over and over and played out the scenerio hundreds of times in my mind, and I just couldn't make sense of it.

I'll experiment next weekend and sleep better tonight!

Neal

When the previous owner brought my boat into our Marina ( condition of purchase ) he went to the wrong area for haul-out area ( to the left in this picture ). The doc master told him he needed to move over to the next area and he walked it sideways. My brother-in-law thought he must have used the thrusters. There are no thrusters on my boat. The previous owner was a 35+yr fisherman and made it look easy to move sideways.

I have tried it several times but no luck in total sideways walking but have lots of times maneuver the bow or stern the way I needed it to move by just using both motors as the article states in the first part of it.

This summer I am going to take time to see if I can actually do this..

Nsail said:

Whew... Thanks for the replys. I thought I was losing it. I've read the article over and over and played out the scenerio hundreds of times, and I just couldn't make sense of it.

I'll experiment next weekend and sleep better tonight!

Neal

Click to expand...

think of it this way.. the outside prop is pushing the stern of the boat in the direction of walk, the inside prop ( dock side ) keeps you from going forward and pulls the bow in the direction of the walk

HOLLYWOOD

Elwin:
Don't give up on it. I have found that a little adverse wind will negate any chance of walking, as would current. Fortunately, there are at least aas many times that the wind or current will help, or not be a hindrance.
Marin:
I believe my keel to be a lot deeper and longer than yours, so I expect the factors making mine easier than yours, are more to do with rudder size than keel size. Of course there could be other factors too.

Hollywood brings up a really good point and that is the effect of a boat's keel on the ability to "walk." Boats of the general configuration of a GB have a keel that's quite deep at the aft end and doesn't exist at the front end. So the very act of pushing the boat sideways through the water generates asymmetrical drag that will help defeat the attempt.

I believe that is the correct way of visualizing it, Marin. I have tried the maneuver countless times, even varying throttle and rudder position, with no luck. Our deep keel aft with virtually no keel forward is the problem.

My DF walks sideways pretty good, but get a current and it goes goofy. That is why I had a bow thruster installed, slack water is not too common for us. Rudder size really makes a difference too, bigger is better if you want to move sideways in a twin, no pun intended.

I have done this with my single screw when I blew it coming up to a lock wall (finished up too far away). Putting the helm full over to starboard and using alternating reverse prop walk and forward thrusts to bring the bow in. Remember this is at the bottom of a lock so there is no wind and no current and no audience. We are also only talking about a foot or so. Just so my wife could grab a line dangling on the wall.

Large rudders and inboard rotating props will walk straight sideways. Unfortunately most of our recreational boats have neither.

The "H" maneuver works best with planing hulls. My 30' Tolly responded immediately but my Nova Sundeck with a 4' keel is somewhat slower to perform this maneuver.

Vyndance said:

Large rudders and inboard rotating props will walk straight sideways. Unfortunately most of our recreational boats have neither.

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I'd like to know why inboard turning props would do that????

The whole reason they turn outboard on rec boats as well as commercial boats is to make maneuvering easier...

I played with this a little bit last summer going up against lock walls. I think the drawings are exactly opposite. I had a little bit of success doing what's shown in the right side drawing, but to move the boat towards the wall/dock, not away from it.

With a centered rudder, the opposing thrust of the engines wants to rotate the boat clockwise pushing the bow towards the dock and the stern away. But by adding in a hard-port rudder, the prop wash counteracts the rotation and pushes the stern towards the dock too. I found that by playing with the forward and reverse, and using the bow thruster to help compensate one way or another, it worked. But I wouldn't say I mastered it, not even close.

psneeld said:

I'd like to know why inboard turning props would do that????

The whole reason they turn outboard on rec boats as well as commercial boats is to make maneuvering easier...

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True story. But what part of manuvering? It makes twisting easier. It makes going fast easier. It also doesn't squat as much. Inboard props are hard to handle which is why our boats have outboard props. A boat that needs to work sideways as part of it's job will have inboard props.

This is a new one on me. The direction the props turn doesn't seem to make any difference to the ability to pivot the boat. The PT boats of WWII had all three of their props turning the same direction, yet they had no problem pivoting the boat with the two wing engines although it probably wasn't as quick a pivot since the propwalk from one was counteracting the propwalk from the other with the thrust opposed. So all they had going for them was the twisting or yawing moment. Their rudders were so small as to not really be much of a factor although the Higgins was better than the Elco in this regard.

If counter-rotating props turn inboard, you still get the combined propwalk of both props turning the same direction when you oppose the thrust, same as you do with a pair of props that turn outboard. The only difference is the inboard turning props will propwalk the other direction as the ouboard turning props.

The rudders will still have the same effect if they are put over in the direction of the pivot. The only difference will be which rudder is being struck by the propwash.

In fact I've been told that outboard turning props actually do a better job of pivioting the boat because when you oppose the thrust the wash off the prop turning in reverse, which would be turning inboard, corkscrews forward where it curls up and strikes the side of the hull, helping to push the hull sideways even more.

I don't know if this is anything that's been tank tested and proven to be a hard and fast fact, but when I've looked over the side of the boat when we've had opposing thrust in to pivot the boat I can see the water from the prop in reverse bubbling and boiling against the side of the hull forward of the prop's location. So perhaps there is something to it.

Vyndance said:

True story. But what part of manuvering? It makes twisting easier. It makes going fast easier. It also doesn't squat as much. Inboard props are hard to handle which is why our boats have outboard props. A boat that needs to work sideways as part of it's job will have inboard props.

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explain how that works...I have always seen the opposite because prop walk works WITH outboard turning props...

Tugs have outboard turning props...so what boats are "made" to walk sideways????

psneeld said:

explain how that works...I have always seen the opposite because prop walk works WITH outboard turning props...

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Agreed. It's true that propwalk works with opposed thrust props no matter which way they normally turn as long as they are counter-rotating when both are in forward (or reverse).

A. If props are outboard turning in forward and you put the port prop in forward and the starboard prop in reverse, both props will be turning the same direction (counterclockwise) and you will get combined propwalk to port, thus pivoting the boat to starboard. The pivoting or twisting force from the opposed props is pivoting the boat to starboard and the combined propwalk is also pivoting the boat to starboard. So the two pivoting forces work together.

B. If both props are inboard turning turning and you put the port prop in forward and the starboard prop in reverse both props will be turning the same direction but the other way (clockwise) and the combined propwalk will be to starboard thus pivoting the boat to port. So the opposed thrust is still trying to pivot the boat to starboard as in A but the combined propwalk is now trying to pivot the boat to port. So the speed of the pivot--- and the maneuverability of the boat--- will be reduced.

Therefore, if you want the maximum effect from opposing thrust, you want a counter-rotating twin with outboard turning props, not inboard turning props.

I agree that outboard turning props are desirable..inboard for high speed craft that don't worry about docking.

Without typing way more than I can handle right now....many pro skippers I work with worry less about twisting and more about single engine maneuvering in tight quarters.

Here's the most basic example I can come up with right now. Coming to a dock starboard side to. Approach at 30 degrees...about 50-25 feet away...both to neutral...then port in reverse. It slows you to a stop and now the outboard engine starts to pull the bow parallel and the stern towards the dock...AND the prop walk from an outboard turning prop (now helping because it's in reverse) further pulls you to the dock..

Simple, clean, effective, etc...no muss no fuss and done tens of thousands of times a day by about every commercial twin operator I've ever driven with. (at least on craft under 100 feet/100 tons of conventional design.

That's exactly how we do it although once the forward way has been stopped by the outboard (from the dock) prop in reverse we will often put the inboard engine in forward and the rudders hard over away from the dock to speed up the pivot and get the aft part of the hull right up against the dock quickly so the land handler can get to the dock right away with the spring line. Particularly if the wind wants to blow us off the dock or forwards.

All tugs have outboard props? Really? Ever seen a crew or workboat move sideways up to a dock or platform? Why won't your boat do this? I don't know why, I am not a hydraulics engineer. Maybe Mr Roberts will chime in.

Vyndance said:

All tugs have outboard props? Really? Ever seen a crew or workboat move sideways up to a dock or platform? Why won't your boat do this? I don't know why, I am not a hydraulics engineer. Maybe Mr Roberts will chime in.

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Having run tugs and crewboats with outboard turning props...I don't know where you got your info and all I did was ask you to explain the basics like Marin and I have.

My sportfish would most certainly walk sideways as well as any tug or any other boat without flanking rudders/nozzels.

Even after 14 years I continue to be surprised at how fast our GB pivots when opposing thrust is put in. Like every twin-engine boat in the boatyard in our marina that I've paid attention to the props on, our boat has outboard turning props. This fast-response pivot plus the use of rudder and my more recent addition of the use of power on one, the other, or both, has "saved" many a docking situation particularly on windy days.

If the props were inboard turning I cannot see how the pivoting performance of the boat would be improved but I can see how it would be reduced.

Vyndance said:

True story. But what part of manuvering? It makes twisting easier. It makes going fast easier. It also doesn't squat as much. Inboard props are hard to handle which is why our boats have outboard props. A boat that needs to work sideways as part of it's job will have inboard props.

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Marin, please reread the post. I am agreeing that outboard props make all those things easier. Inboard will not twist or pivot like outboard props but it will walk dead sideways. My information comes from 2 real tug captains who live on my dock who both tried to walk my boat. Different times and they both said the same thing. It has something to do with the turbulance at the keel which helps produce side thrust off the rudder and overcoming pivot. As this topic is about walking sideways and not outboard vs inboard I think we have beat it up pretty good.

The move-straight-sideways-ability described by your tug captains sounds to me like a characteristic that is very specific to a very specific type of hull configuration. So perhaps not a broad attribute of inward-turning props in general.

But it would be interesting to know how their props on their boats act to make a straight sideways move possible.