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Old 01-27-2013, 08:57 PM   #1
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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?
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Old 01-27-2013, 09:22 PM   #2
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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.
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Old 01-27-2013, 09:41 PM   #3
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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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Old 01-27-2013, 09:53 PM   #4
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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.
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Old 01-27-2013, 09:58 PM   #5
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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.
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Old 01-27-2013, 10:06 PM   #6
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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.
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Old 01-27-2013, 10:11 PM   #7
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walking a boat..

Quote:
Originally Posted by Nsail View Post
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
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.
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Old 01-27-2013, 10:15 PM   #8
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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
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Old 01-27-2013, 10:24 PM   #9
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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..
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Old 01-27-2013, 10:24 PM   #10
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Quote:
Originally Posted by Nsail View Post
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
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

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Old 01-27-2013, 10:33 PM   #11
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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.
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Old 01-27-2013, 10:33 PM   #12
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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.
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Old 01-27-2013, 10:51 PM   #13
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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.
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Old 01-28-2013, 12:04 AM   #14
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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.
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Old 01-28-2013, 08:18 AM   #15
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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.
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Old 01-28-2013, 10:32 AM   #16
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Large rudders and inboard rotating props will walk straight sideways. Unfortunately most of our recreational boats have neither.
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Old 01-28-2013, 12:45 PM   #17
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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.
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Old 01-28-2013, 12:55 PM   #18
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Quote:
Originally Posted by Vyndance View Post
Large rudders and inboard rotating props will walk straight sideways. Unfortunately most of our recreational boats have neither.
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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Old 01-28-2013, 07:21 PM   #19
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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.
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Old 01-28-2013, 08:23 PM   #20
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Quote:
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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...
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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