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Old 08-19-2015, 03:57 PM   #1
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Moving boat sideways

It seems a while ago I ran across a U-Tube video about moving a twin screw boat sideways. But I can't find it anymore. I seem to recall it involves moving one engine back and forth between forward and reverse. Maybe both? Can any of the experts on TF explain the maneuver?

Thanks,

Bob
(Still trying to learn how to drive this twin engine boat. Seems our single screw sailboat was easier to maneuver.)
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Old 08-19-2015, 04:01 PM   #2
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Turn the rudder the opposite of the way you want to go, then alternate between port in fwd, stbd in reverse and vice versa. Depending on the boat, that may not be enough to overcome wind and current.

There is a more advanced technique in which engine rpm are varied.
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Old 08-19-2015, 04:06 PM   #3
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Is it always port in forward and starboard in reverse or does it change to move in the opposite direction?
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Old 08-19-2015, 04:08 PM   #4
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Is it always port in forward and starboard in reverse or does it change to move in the opposite direction?
The way I do it, you have to switch back and forth between port forward, starboard reverse. The only changes with direction is rudder position.
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Old 08-19-2015, 04:13 PM   #5
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I'm trying to visualize this. If the rudder is hard over to starboard and I put the port engine in forward, the bow will turn to starboard. Then, I put the starboard engine in reverse and the stern will move to port. Seems to me I'd be making a circle?
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Old 08-19-2015, 04:20 PM   #6
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As far as twin screws I've only had experience in sportfishers but to "walk" the boat to starboard I would put the rudders hard to port...and leave them there. I then put the port engine in forward (if the stbd is kept out of gear the bow would move forward and to port while the stbd aft quarter moves to stbd and fwd) and the stbd engine in reverse. The stbd engine halts fwd motion and the port prop walks the back of the boat to stb. If the bow wants to move to port I would add/drop stbd throttle (or fuel lever for you pedantic purists) to control the bow. Of the half dozen different boats I have done this on they all seem to react differently so practice with your boat in windless conditions in a safe area. Also the heavier the boat the easier it seemed to me.
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Old 08-19-2015, 04:27 PM   #7
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If you keep the rudders centered, the boat will start to pivot to starboard (port gear forward, starbord reverse), and when you switch (to port reverse/starboard forward), it will pivot back to port. By putting the rudder hard to starboard, the bow of boat will pivot more to port when the starboard engine is in gear. The net effect would be to walk to port.
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Old 08-19-2015, 04:32 PM   #8
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I can't wait to try this. I'll try it out when nobody is around to watch. If it works, I will win many a bet.
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Old 08-19-2015, 04:43 PM   #9
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I'm more confused than ever. It's the windless conditions I have problems with. There never seem to be any. This boat with the full enclosures seems to have more windage than the sailboat we had with the sails up.

Seems to me to move to port, rudders to port, port engine forward will move the bow to port, stern to starboard. Then port in neutral and starboard in reverse, the starboard propwalk will move the stern to port. Not so?
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Old 08-19-2015, 04:44 PM   #10
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While this may work with some twins, it's been our experience with ours that it doesn't work at all. Not if what's being talked about is moving the boat straight sideways as though it had bow and stern thrusters. The boat can be "walked" sideways easy enough, but not moved straight sideways. (This is assuming that the boat does not have a bow thruster but is being moved and directed by the props and rudders alone.

This came up in a discussion years ago with friends at an island we used to visit a lot. The husband had been a fantastic boat handler in the USCG (he is still the best boat handler I have ever met) and he was sure that a twin could be moved straight sideways using the techniques described earlier in this thread. I'd tried them with no success but he is far better at maneuvering than I was then.

No luck at all. He tried everything he could think of and in the end he said it's impossible. The boat can be made to move straight sideways for couple of feet, but that's just until the forces at play take over and one end or the other starts moving to the side faster than the other.

Now in a twin with very widely spaced props like a Great Harbor it might be possible because of the leverage that can be exerted by the props. But in a boat like ours, with the props fairly close-in to the keel, not gonna happen.

Again, it can be walked sideways very easily: move the bow over, then move the stern over, then the bow, and so on. My dog can do that. Blindfolded. But straight sideways? No way. The physics simply aren't conducive to it.

And FWIW, I have yet to meet a twin operator who has claimed and demonstrated he/she could do it, either, at least not with their boat.
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Old 08-19-2015, 04:51 PM   #11
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Marin, I have tried and tried with my GB and could not make it happen either, all though I must say I haven't tried in a long time and may have done it wrong. I'll try again.

In terms of walking it sideways, just how does your dog do that maneuver,using 1 engine or both? ��

Thanks, Howard
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Old 08-19-2015, 04:58 PM   #12
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In terms of walking it sideways, just how does your dog do that maneuver,using 1 engine or both? ��

As I said, it's an extremely easy thing to do. He uses both engines and the rudders as well as differential power. The only thing he needs help with is turning the wheel from lock to lock because he is not a particularly large dog and the diameter of the wheel exceeds his reach. But he simply tilts his head in the direction he wants the wheel to go and one of us turns it around for him.

The photo below was taken while we were docking one day and he was watching the person at the helm, shaking his head in disgust at the inefficient manipulation of the controls.
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Old 08-19-2015, 05:12 PM   #13
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Then port in neutral and starboard in reverse, the starboard propwalk will move the stern to port. Not so?
Let's assume you want to walk the boat to starboard to a dock. In this case I put the rudders hard to port (opposite of direction I want to move toward), port engine in forward, idle speed. Typically I would not alter rudder or port engine throttle after that. Put the starboard engine in reverse and alter stbd throttle setting to keep bow straight ahead and usually boat moves to starboard with little forward or reverse motion. Some boats would require the stbd throttle to stay at idle and I would slip the gear in and out forward to keep all motion lateral. Like HMason wrote...find a spot all by your lonesome and practice. I learned on a 26 footer. My dad ran the boat out when on offshore trips and he would let me run it in. The most fun I had was pulling her up to the fuel dock and walking the boat like a pro...of course when things went textbook. When you get it figured out on your boat in ideal conditions then you'll be able to get the wind and current problem solved to...just takes practice.
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Old 08-19-2015, 05:15 PM   #14
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Marin...I thought he was just disturbed at my reference to throttles. Actually, in the case of the first twin I ran it had gasoline engines so it fits.
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Old 08-19-2015, 05:30 PM   #15
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Good idea!!

But don't expect the boat to just "jump sideways" to the dock, like a bow thruster. The effect on the bow is much less dramatic than the effect of moving the stern by counter shifting the port and starboard engines. In a perfect world, where there is no wind or tidal effect, the boat would glide to a stop parallel to the dock and allow you to take your time and walk it slowly in, but it's rare that you have those conditions.

Real world you're probably going to approach the dock at minimal speed, with a bow "in" angle and then reverse the outside engine, maybe a little forward thrust with the other, to move the stern to the dock as you come to a stop.

If you haven't already done so, before you practice docking you need to find the pivot point of your boat. It's probably a few feet somewhere behind your bow. (Mine is just ahead of the salon door.) Take your boat out on a calm day and find a buoy or a dolphin to use as a fixed reference point. Point your bow at it and put one engine in reverse and the other in forward. (The reverse engine will probably need a little more throttle to stop forward movement.) Note how your boat rotates around it's pivot point in relation to the reference point. That's your pivot point and knowing that will help you visualize how your boat will "probably" move when you approach a dock and apply different thrust techniques.

Now add wind and tide to that and all bets are off!!
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Old 08-19-2015, 05:47 PM   #16
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We dock our boat the same way we dock a floatplane. Angle in to the dock nose (bow) first at a 30 degree angle give or take.

In the case of the plane all one can do is put in (water) rudder when the tips of the floats are almost to the dock and straighten out parallel to the dock and then jump from the inside float to the dock as the plane slides along it and pull the plane to a stop with the forward mooring line.

With a boat we get the bow right up almost to the dock and then stop the boat and pull the stern in with the combined propwalk from opposing the thrust of the props. We also use the rudders to help move the stern in. Adding power on the appropriate engine will help counter the forces of an adverse current or wind up to a point. Beyond that point we start thinking about making more aggressive use of a spring line or using some other technique.

But we have never been in a position where moving the boat straight sideways up to a dock was something we actually needed to do. We have just played with it to see if it could or couldn't be done.
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Old 08-19-2015, 05:51 PM   #17
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Marin, do you figure a P-38 Lightning on floats could do the sideways shuffle with reversible pitch props? That would be a sight!
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Old 08-19-2015, 05:54 PM   #18
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Comparing a floatplane to a boat is a futile exercise because the forces acting on them in/on the water are very different.
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Old 08-19-2015, 06:03 PM   #19
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In my experience, the flatter the bottom the easier this is to do. I could do this on my Hatteras, but with its deep keel it is not nearly as easy on a Mainship: you could accomplish it by merely turning the rudders away from the dock and jockeying the engine farthest from the dock in and out of forward and reverse. Came in real handy once when we lost an engine.
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Old 08-19-2015, 06:07 PM   #20
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One item mentioned that affects ability to do this successfully is prop position another that I have experienced that can have a major impact on success is whether your props are recessed in a tunnel. The larger the prop tunnels the less successful you will be... Tunnels reduce the prop walk affect.

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