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Old 09-01-2015, 09:37 AM   #41
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Am I misunderstanding something in those two conflicting statements?
Why not throw in making retractable rudders. Then he'd have the best of both worlds. Or the worst, depending on how you look at it.
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Old 09-01-2015, 11:33 AM   #42
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So w a rudderless boat what would one do to make a right hand turn?

A. Increase the rpm of the port engine?
B. Decrease the rpm of the stbd engine?
C. Increase the rpm of the port engine and decrease the rpm of the stbd engine?
D. Increase the one engine more than one would decrease the other.

D of course would obviously give one much greater latitude in the range of turn radius and speed so for much or most of the turning both throttles would be involved. Then perhaps more rpm increase on one side and less on the other the difference of rpm would vary also. But this differential would probably not be linear. Would a good helmsman familar w the rudderless boat be able to keep up w all the variables?

Sounds like it would need to be computer controlled.

The Bismark battleship was sunk because they lost their steering. If you damaged a prop or the computer decided to mix up the program a bit you'd be sunk .... almost literally.
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Old 09-01-2015, 11:54 AM   #43
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Having the engines rev up and down constantly would drive me nuts. It would sound like weedwhackers, leaf blowers, dirt bikes and jet skis. All infernal machines based on their sound note always changing pitch.
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Old 09-01-2015, 11:59 AM   #44
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Eric-- When we got our old GB we had never run a twin engine boat before. The GB we'd been chartering is a single w/ thruster. We had friends with a lot of boating experience including Bob Munro, the founder of Kenmore Air Harbor who for years until his death in 2000 had a steel hull/wood topsides deFever, one of three (I think) made.

We talked to these folks at length about twin engine maneuvering but the best advice cane from Bob who said the most effctive way to learn twin engine maneuvering was simply to take the boat out and do it. Which we did.

One of the things we practiced so we could take advantage of it was maneuvering and steering using differential thrust alone. No rudders. Now the props on a GB are positioned fairly close in to the keel so they don't exert nearly as much leverage on the boat as the widely spaced props on something like a Great Harbor.

And what we found is that while the boat can very definitely be steered with differential thrust the rate of turn is very slow. It's fine for making a course correction at cruising speed. But it's far too gradual for making a swerve to avoid a piece of debris in the water.

And it's an unnecessary effort. You split the power, muck around with the differential to try to get the best rate of turn, then you have to put the power back to balanced cruise rpm and sync the engines.... It's all easy enough to do but why bother when you can accomplish the same thing and instantly get whatever turn rate you want by turning a wheel one way or the other?

Bottom line is that it's nice to know the boat can be steered with differential thrust alone but I view it as a last resort technique, as when the steering system screws up.

In fact it is so imprecise that we would be inclined to steer with our boat's emergency tiller rather than differential thrust particularly in a following sea condition where quick and precise steering control can be very important. I've had plenty of experience steering sailboats so driving our boat from the aft deck with a tiller would be relatively familiar.
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Old 09-01-2015, 12:09 PM   #45
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Yes Marin I mentioned the following sea scenairo awhile back. One would clearly be out of control much earlier. Like you say just much less control.

Ski,
Agree and something I hadn't considered in post #42 is the "rum rum rum" harmonics. Harmonic vibration noise cascading up and down would be awful ....... well many quite entertaining for a very short time.
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Old 09-01-2015, 12:25 PM   #46
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" So we know how long to pause in neutral before shifting into into gear again."
AS I have previously posted, with electronic shifters/throttles, the time it takes to engage/disengage the transmission is important. In my case it's 1.5 seconds which is an eternity when maneuvering close in. It all boils down to a "management" problem, like almost everything in boating.
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Old 09-01-2015, 01:13 PM   #47
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So w a rudderless boat what would one do to make a right hand turn?

A. Increase the rpm of the port engine?
B. Decrease the rpm of the stbd engine?
C. Increase the rpm of the port engine and decrease the rpm of the stbd engine?
D. Increase the one engine more than one would decrease the other.

D of course would obviously give one much greater latitude in the range of turn radius and speed so for much or most of the turning both throttles would be involved. Then perhaps more rpm increase on one side and less on the other the difference of rpm would vary also. But this differential would probably not be linear. Would a good helmsman familar w the rudderless boat be able to keep up w all the variables?

Sounds like it would need to be computer controlled.

The Bismark battleship was sunk because they lost their steering. If you damaged a prop or the computer decided to mix up the program a bit you'd be sunk .... almost literally.
You forget put the starboard engine in reverse.
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Old 09-01-2015, 01:13 PM   #48
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AS I have previously posted, with electronic shifters/throttles, the time it takes to engage/disengage the transmission is important. In my case it's 1.5 seconds which is an eternity when maneuvering close in. It all boils down to a "management" problem, like almost everything in boating.
You go bow in?
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Old 09-01-2015, 01:43 PM   #49
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You go bow in?
Yes...Too much lack of privacy when going stern in.
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Old 09-01-2015, 03:56 PM   #50
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Yes...Too much lack of privacy when going stern in.
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Old 09-01-2015, 04:11 PM   #51
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What are you up to Walt ..... or down to?
With all those windows in the aft salon I wouldn't think you were too worried about that.

menzies,
Didn't even think about or addressing going in reverse. If you steered in reverse w no rudders you'd really need a bow thruster ... even w no wind. Inertia would rule the bow otherwise.
Of course he's going bow in ... didn't you see the pics? I have shoved the shift lever straight into reverse w my BW and know they can take quite a lot of that but I shift almost like Marin most of the time.
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Old 09-01-2015, 04:18 PM   #52
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What are you up to Walt ..... or down to?
With all those windows in the aft salon I wouldn't think you were too worried about that.

menzies,
Didn't even think about or addressing going in reverse. If you steered in reverse w no rudders you'd really need a bow thruster ... even w no wind. Inertia would rule the bow otherwise.
Of course he's going bow in ... didn't you see the pics? I have shoved the shift lever straight into reverse w my BW and know they can take quite a lot of that but I shift almost like Marin most of the time.
I meant, in your example, to turn - port in forward, starboard in reverse.
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Old 09-02-2015, 12:22 AM   #53
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I wonder what happened to old Cottonhead, errr, I mean Cottontop. Maybe he didn't get the positive feedback he expected so he left.
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Old 09-02-2015, 01:28 AM   #54
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I wonder what happened to old Cottonhead, errr, I mean Cottontop. Maybe he didn't get the positive feedback he expected so he left.
Still here, learning.

I expected skepticism, as I too am skeptical.

Why the hostility?
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Old 09-02-2015, 04:16 AM   #55
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I shift almost like Marin most of the time.
Eric-- We try to dock using a minimum number of shifts. From when we start our (port) turn into our slip from the fairway we can generally get the boat in and stopped on a light wind day in three quick shifts in and out of gear; two into forward on the starboard engine and one into reverse on the port. Ninety percent of the time on the way in the boat is coasting in neutral. What we do with the rudders is a big part of why this works so well.

If it's windy or the current is stronger it can take a shift or two more sometimes.

Most of our maneuvering is done this way. A brief shot of thrust to overcome inertia and then just waiting in neutral while what happens is happening, and then another brief shot and another wait.

Things just don't happen that fast in a heavy boat unless it's blowing hard. I've never really understood the need a lot of boaters have to be hauling back and forth on the shifters and revving engines up and down during a normal docking. We found early on that a couple of little nudges with thrust at the right time and the proper use of the rudders and the boat pretty much docks itself. I imagine you do the same thing.
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Old 09-02-2015, 05:33 AM   #56
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I hope you and I don't meet in a narrow curving channel some night with you needing to make a quick course change.

Bad idea.

Want to get rid of your rudders, get pods.

Just finishing running the Erie Canal. There have been at least two boats with PODS that will give you $16,000 reasons they may not be as protected as keel/shaft drive vessels.
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Old 09-02-2015, 07:01 AM   #57
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Didn't even think about or addressing going in reverse. If you steered in reverse w no rudders you'd really need a bow thruster ... even w no wind. Inertia would rule the bow otherwise. .
Eric, backing in reverse with our twin is quite controllable. Generally do it with rudders neutral and little if any bow thruster activity. Just did a few hundred feet slip change in Snug Cove a few days ago in reverse all the way. Important to remember the pivot point is about 1/3 forward of transom.

But if any current on this deep draft vessel then rudders and thruster are used. Wind doesn't affect our boat much when docking. Over half a century ago used to back sailboats in reverse quite easily when working in a boat yard on LI, big rudders worked well for steerage.
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Old 09-02-2015, 09:44 AM   #58
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Ok here's a challenge then for all those who think rudders are unnecessary. I'll be in the Bahamas tomorrow and I'll leave a hundred dollar bill at the big game club bar for the first captain who can get to it by crossing the stream on a twin engine inboard boat running only on one engine without using any rudders. I don't care which engine you use and you don't have to remove the rudders but you do need to remove the steering wheel and disable the autopilot.


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Old 09-02-2015, 10:32 AM   #59
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Tom,
I back up fine w little or no wind. I can go about 2.5 to 3 knots holding on to the quick helm tightly making small corrections I can steer fine all over the place. But go slower w a bit of wind and there's no telling where I'm going to go. Going slow w no wind I usually set the rudder hard over (and leave it there) and give a blip of prop wash over the rudder at times to handle the propwalk.

Marin,
No we're quite different on that one. I don't limit the number of shifts at all. I'll have to ask Mike at Harbor Marine how often I should shift. For now though I shift as often as I need to or want to. Like a car it's how you use the clutch not how often. My 87 Nissan clutch is the original and she's gone 280K. Not perfect but I'm not replacing it yet. It's not surprising this old truck driver likes to shift. But I get your message. Years ago you had the notion that an engine had "X" number of revolutions for it's life. I think it's much more a matter of things like working an engine hard before it's warmed up ... not changing the coolant ect than number of revolutions. Same applies to gears. With some obvious differences.
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Old 09-02-2015, 11:22 AM   #60
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Naughty!
Don't I wish!
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