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Old 12-27-2008, 04:51 PM   #1
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Why don't boats have multiple gears or at least a high and low like cars?
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Old 12-27-2008, 05:50 PM   #2
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RE: Transmissions?

The ones with controllable pitch props do. But I expect simplicity and reliability are the main reasons most marine gears have only forward, neutral, and reverse. And since a boat is "pulling" all the time, as opposed to a car which uses lots of power to get going but very little power to stay going, having several gears in a boat probably wouldn't accomplish much. That's my guess, anyway....
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Old 12-27-2008, 06:45 PM   #3
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RE: Transmissions?

Marin, Daddyo,
For semi displacement boats another gear wouldn't do much or any good depending on the boat because at any reasonable cruising speed resistance and drag would be rather high. With a FD boat, however, resistance drops dramatically with a slight ( 1 - 1 1/2 knot ) reduction in speed ( where most FD boats run ) and engine loading could be more optimised. I forsee one problem though .. high and low gear equates to high and low speed in cars ( there lies our famillarity ) and high gear on the boat would be for low speed and low gear would be for high speed. I think the answer lies in the fact that few if any boats that are simmilar to our yachts have such a feature. One would think fish boats and other commercial craft would have multiple gears if there was much benifit. They don't.

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Old 12-28-2008, 12:43 AM   #4
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RE: Transmissions?

A controllable pitch prop is a more efficient means of tailoring the engine's output to the boat's speed than multiple fixed gears in a transmission.* The controllable pitch prop will accomplish what Eric describes, allowing a degree of overpitch (coarse) for cruise speeds, ideal pitch for proper engine loading at maximum speed, and underpitch (fine) for the times you want the boat to go really slow.
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Old 12-28-2008, 05:30 AM   #5
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There made , check out the 2 speeds by ZF.

The few boats that need them are go fasts , and there not cheap.

If we finally get a box boat done it will have BOTH 2 speed and CP.

Only by allowing the engine to work really hard ,( not doable except at a single speed with a fixed tranny & prop,) will real economy be achieved.

The question of course is still the hour number of use , $25K of fancy prop , tranny vs $8K of OTS, takes a lot of hours to ammortize.

But should the boat generate enough interest to cookie, the world wide magazine articles* about its economy would pay as add bucks.

FF

-- Edited by FF at 06:32, 2008-12-28
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Old 12-28-2008, 02:08 PM   #6
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There is only one way to " real economy " as FF puts it, and that is to get a FD boat, power it with 3 to 4 hp per ton and run it about one knot slower than hull speed. All the other roads to increased efficency have been or result in fly stuff. Anybody serious about economy or even range will embrace the FD hull. It dosn't really matter if you guys buy into what I'm saying because almost all of you don't feel efficency is that important. If you did you'd be looking for a FD boat. And what if you'all suddenly went balls out for efficency, economy and range ? That would be a problem as there wouldn't be nearly enough FD boats to buy .. there just aren't that many. Other than Willard, Fisher and the little Albin 25, name some FD boats 30 to 40 feet. On second thought don't bother .. I'd just get a long list of SD boats.

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Old 12-28-2008, 04:44 PM   #7
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RE: Transmissions?

Yo Willy, you forgot about the FD catamarans! They be awfully efficient as well.
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Old 12-29-2008, 03:59 AM   #8
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"get a FD boat, power it with 3 to 4 hp per ton and run it about one knot slower than hull speed. "

Hull speed is SL 1.34 or so , economy is at SL.9 for most FD.

The question we are working on is weather a box keel , reverse deadrise hull can be ALMOST as efficient at SL 2.1 to 2.8 as a FD at .9 .

A radio controlled power model shows miniscule wake , and the hull remaining flat , but a real test tank would be required to optomize the 50 year old concept.

EG how much of the boats displacement should the box keel float?

Here is one attempt,

http://www.alsphere.at/




-- Edited by FF at 05:30, 2008-12-29
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