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Old 06 September 2014, 14:19   #1
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Why don't outboards/sterndrives have multiple gears?

I remember reading about an Arctic Blue 29 or 37 which had two selectable gears and did 86 knots with a single Ilmor as a result. Why isn't this more common, surely selectable gears would increase fuel economy by allowing a higher gearing when cruising and increase holeshot with a faster ratio?
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Old 06 September 2014, 14:25   #2
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Cost, weight, complexity...

???

Cars/trucks etc are the exception lots of stuff doesn't have variable gearing.
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Old 06 September 2014, 14:33   #3
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I remember reading about an Arctic Blue 29 or 37 which had two selectable gears and did 86 knots with a single Ilmor as a result. Why isn't this more common, surely selectable gears would increase fuel economy by allowing a higher gearing when cruising and increase holeshot with a faster ratio?
Cos it's not as simple as that! my understanding is that prop grip and cavitation (in its true sense) becomes the issue. there was a variable pitch prop around which achieved something similar not sure why it wasn't a commercial success.you'd have extra weight, maintainence and drag issues to offset against any gain.
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Old 06 September 2014, 14:48   #4
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It doesent take much variation in load to totally stall your motor you can see that when fitting a slightly larger prop
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Old 06 September 2014, 17:20   #5
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Sunseeker had a dabble at a two speed box. The problem is torque. As soon as it changed you went below the optimum power band and used to bog down. We had a go at putting a Motorbyke engine in a boat. Sad results on that
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Old 06 September 2014, 18:33   #6
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We had a go at putting a Motorbyke engine in a boat. Sad results on that

I think I can remember seeing that episode of Scrapheap Challenge..?

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Old 06 September 2014, 18:36   #7
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Would have been a better result to just hang the back tyre over the back
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Old 06 September 2014, 20:11   #8
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Where's Kitten these days anyhow?
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Old 07 September 2014, 03:30   #9
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Very common in flat bottom V-drives to use a Turbo 400 or Powerglide transmission. Ironically it is only used at low speed, and often to give a usable reverse. When drag racing they all throw it in the top gear for launching. Of course most of those boats are running highly modified BIG blocks with goobs of horsepower and torque. Nothing like American Muscle

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Old 07 September 2014, 04:56   #10
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I can see how it'd work if you could use a Constantly Variable Transmission, as a CVT can be dialled into the 'powerband' and the whole HP of the motor used.
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