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Old 08-31-2015, 07:10 PM   #21
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Years ago, the chain gear for turning the rudders on our old Trojan broke while cruising in the San Juans, 5 hours from our home port. Dad cruised all the way back turning with just the throttles. Not ideal, but worked in a pinch.
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Old 08-31-2015, 07:14 PM   #22
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Psneeld-- On our boat, assuming the boat is operating at idle and is moving through the water at idle speed, not decelerating from a higher speed, it takes about 3 seconds for the shafts to stop. A major factor in this is the cutless bearings--- how tight or loose they happen to be. Ours are pretty tight.

However, most of our shifting is done with the boat not moving through the water much at all. So the shafts stop a wee bit sooner than they do with the boat established at idle speed which for us is just under 3 knots indicated.

So we allow at least 3 seconds in neutral when going from one gear to the other.

The reality is, however, that we almost never find ourselves having to shift all that quickly from one gear to the other. So the transmissions generally remain in neutral for a lot longer than 3 seconds between a shift out of gear and the next shift into it. In fact during a docking or whatever the shifters are in neutral probably 90 percent of the time and we just "nudge" it with thrust and rudder as necessary and let inertia do most of the work.
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Old 08-31-2015, 07:25 PM   #23
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I appreciate the many thoughtful comments.

Some responses:

I am thinking about a power catamaran. The most I'll need is perhaps 125 hp per hull.

I started out looking at pods, but can't find any that small. I don't want a science project trying to cobble together something.

Steering will not involve shifting; just small amounts of differential will accomplish most turns. I don't really turn very much until I get where I'm going. Go straight for a while, maybe make a little correction, then straight again.

The AP will have nothing to do but adjust throttle; nowadays this is an electronic function. I appreciate that programming here might be a science project. Maybe no AP is needed.

I think getting rid of all the disadvantages adds up pretty big. There are lots of threads about steering issues and the occasional thread about rudder disasters. I can say that I am frequently being told, "That's where the rudder post has to go, that's where the AP mounts, that's the space for the cross bar, " etc.

And this way, I never have to sort out the spade rudder debate.
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Old 08-31-2015, 07:33 PM   #24
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Marin- It's not a big deal to shift before shafts stop windmilling. The clutch plates engage from relative motion, and some shaft rotation just means more relative motion. It's oil that gets sheared to engage the clutch, no significant wear.

Still it's good to let the shaft stop, but it is not a big deal. No different than shifting with idle 100rpm higher.

On my boat I can stall the engine if I jerk it straght from fwd to rev. That's why I pause!!!
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Old 08-31-2015, 07:35 PM   #25
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Quote:
Originally Posted by Cottontop View Post
Disadvantages of rudders:
Heavy
Expensive
Drag
Potential big hole in boat
Linkages, etc. clutter up spaces
Maintenance
Fouling
Hard working AP

Let's stipulate two things:
Both engines are used all the time
If an engine goes down, there will be a way to steer (get home rudder?)
As I reread through the OP's first post and, considering each of his listed disadvantages both separately and then as a whole, I fine I'm questioning several things:
Heavy--really? The bigger the boat the bigger the rudder but, comparatively as a percentage of the overall weight of the boat, the weight of the rudders is tiny.
Expensive--same thing here. Really? When compared to the cost of a boat?
Drag--similar thing here. We're on a trawler forum where they move slowly through the water and we're even considering the drag caused by rudders? Really? It's that drag through the water that makes them work.
Big hole in the boat--yup. I'll give you that one. Probably two big holes.
Linkages--aren't those usually tucked way back in some inaccessible space in the stern? What else would you use that space for, 'cause on most boats you can't really get to it easily.
Maintenance--yup. Just one more thing to check on and lube when doing routine maintenance.
Fouling--if whatever is going to foul on the rudders makes it past the prop(s) I guess it might foul on the rudders, but all it's going to do is drag through the water and possibly make the rudders a little harder to turn.
Hard Working AP--maybe, but how are you going to use an AP if you don't have rudders. Is your AP going to adjust your throttles to keep you on course. If you didn't have rudders you probably wouldn't have an AP.

I recently had one set of hydraulic shifters go out and that prop (starboard side) was stuck in reverse. Because I do have rudders on the boat I was able to go into a lock and get tied up, then exit the lock and make it about 15 miles back to the marina. Without rudders I'd have been stuck with one engine and no way to use differential anything to get anywhere.

Thanks OP, but I'll keep my rudders.
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Old 08-31-2015, 07:38 PM   #26
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Quote:
Originally Posted by Cottontop View Post
I appreciate the many thoughtful comments.

Some responses:

I am thinking about a power catamaran. The most I'll need is perhaps 125 hp per hull.

I started out looking at pods, but can't find any that small. I don't want a science project trying to cobble together something.

Steering will not involve shifting; just small amounts of differential will accomplish most turns. I don't really turn very much until I get where I'm going. Go straight for a while, maybe make a little correction, then straight again.

The AP will have nothing to do but adjust throttle; nowadays this is an electronic function. I appreciate that programming here might be a science project. Maybe no AP is needed.

I think getting rid of all the disadvantages adds up pretty big. There are lots of threads about steering issues and the occasional thread about rudder disasters. I can say that I am frequently being told, "That's where the rudder post has to go, that's where the AP mounts, that's the space for the cross bar, " etc.

And this way, I never have to sort out the spade rudder debate.
If you build this boat, leave provisions available to add rudders later if needed. You might not like the way it runs without them.
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Old 08-31-2015, 07:40 PM   #27
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Originally Posted by Ski in NC View Post
Marin- It's not a big deal to shift before shafts stop windmilling. The clutch plates engage from relative motion, and some shaft rotation just means more relative motion. It's oil that gets sheared to engage the clutch, no significant wear.

Still it's good to let the shaft stop, but it is not a big deal. No different than shifting with idle 100rpm higher.

On my boat I can stall the engine if I jerk it straght from fwd to rev. That's why I pause!!!
Especially with the BWers...on the assistance tow boat my tranny sees a workout in one day that the trawler guys give them in a lifetime.

I am only on the second tranny in 13 seasons with no end in sight on this one.
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Old 08-31-2015, 08:25 PM   #28
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Especially with the BWers...on the assistance tow boat my tranny sees a workout in one day that the trawler guys give them in a lifetime.
Like most everything else to do with boating, it all depends on which "expert" one believes has the most credibility.

Transmissions are like all mechanical things--- the easier you make their lives the longer their lives tend to be.
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Old 08-31-2015, 09:36 PM   #29
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Like most everything else to do with boating, it all depends on which "expert" one believes has the most credibility.

Transmissions are like all mechanical things--- the easier you make their lives the longer their lives tend to be.
So which "expert" is telling you that you will damage your gear by shifting with shaft still rotating?
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Old 08-31-2015, 09:40 PM   #30
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Think of following seas and possible broaching.

Rudders are essential.
At least until the following seas over run the rudders and then the only way to save the boat from broaching is with the engines.
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Old 08-31-2015, 10:06 PM   #31
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Just when I thought I heard it all....
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Old 08-31-2015, 10:13 PM   #32
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Lose one engine, and meet yourself running in circles.
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Old 08-31-2015, 10:17 PM   #33
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Try selling a boat without rudders. Not going to be easy.
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Old 08-31-2015, 10:22 PM   #34
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Try selling a boat without rudders. Not going to be easy.
Jet boat.
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Old 08-31-2015, 10:37 PM   #35
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Ditch the props and install jet drives. No more rudders then.
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Old 08-31-2015, 11:33 PM   #36
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Quote:
Originally Posted by Cottontop View Post
I appreciate the many thoughtful comments.

Some responses:

I am thinking about a power catamaran. The most I'll need is perhaps 125 hp per hull.

I started out looking at pods, but can't find any that small. I don't want a science project trying to cobble together something.

Steering will not involve shifting; just small amounts of differential will accomplish most turns. I don't really turn very much until I get where I'm going. Go straight for a while, maybe make a little correction, then straight again.

The AP will have nothing to do but adjust throttle; nowadays this is an electronic function. I appreciate that programming here might be a science project. Maybe no AP is needed.

I think getting rid of all the disadvantages adds up pretty big. There are lots of threads about steering issues and the occasional thread about rudder disasters. I can say that I am frequently being told, "That's where the rudder post has to go, that's where the AP mounts, that's the space for the cross bar, " etc.

And this way, I never have to sort out the spade rudder debate.
You are a funny man!!!
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Old 08-31-2015, 11:56 PM   #37
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A twin screw straight drives with no rudders is the worst of both worlds. You couldn't take advantage of the redundancy of twin screws.
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Old 09-01-2015, 01:19 AM   #38
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Quote:
Originally Posted by Cottontop View Post
I started out looking at pods, but can't find any that small. I don't want a science project trying to cobble together something.

The AP will have nothing to do but adjust throttle; nowadays this is an electronic function. I appreciate that programming here might be a science project. Maybe no AP is needed.
Am I misunderstanding something in those two conflicting statements?
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Old 09-01-2015, 05:24 AM   #39
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A little late but....Rudders? We don't need no stinkin' rudders!

Seriously though, when I was in the guard, I was (again) taught throttle steering. Not my first rodeo, but this time on a bigger boat.

My training coxswain on the 41 was a real stickler about throttles and control...smoothness and "finesse."

He had us walking a 41 out of a marina in pinwheels using throttles to demonstrate control.

Obviously though, if I have a rudder(s), I'd prefer to use them in tighter places.

OD
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Old 09-01-2015, 07:15 AM   #40
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The problem is not that it woyld not work , the hassle is it would need constant attention.

I did a delivery where the steering failed , and was able to steer , but it was constant work , 100% of the time.

Ocean City MD was calm in the entrance,
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