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Old 09 November 2010, 23:52   #1
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high thrust motor on zodiac GR

I just bought a yamaha 50hp, yeah me. The problem is I didn't know that it is a high thrust motor designed for pushing pontoon boats and barges, neither that plane.

Has anyone reproped one of these motors to push a zodiac GR MKIII??
I will be using it to fish by myself and fully loaded for scuba diving.

thank you for thoughts and experiances
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Old 10 November 2010, 00:37   #2
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I just looked up the specs. Your gearcase is 2.33 to 1 vs 1.85 to one for a standard motor. Your prop is going to turn 25% slower than a non high-thrust engine.

I have no direct experience but I would think that you will have a hard time finding a prop in that size pitched high enough for your use. If you do, it may be somewhat inefficient. Try using one of the online prop calculators to compare what prop you would need versus the pitch that would be recommended for standard 50hp four stroke.
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Old 10 November 2010, 00:42   #3
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It turns out that your bottom end is the same as the merc 70-115 so finding a prop may not be a problem after all.
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Old 11 November 2010, 00:06   #4
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prop for a T50 up thru 130hp should fit is what one boat shop told me

thank you
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Old 20 November 2010, 23:39   #5
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I got the carbs put back together and back on the boat
mounted a water seperator/filter on the transom and fabricated new fuel lines
sunday i'm off to the lake to see if this thing will push my zodiac
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Old 25 November 2010, 11:38   #6
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If you got the geared down bottom end you may be easier finding a standard engine that someone has managed to sieze, and take the whole bottom end?

...and could then sell the high thrust one to a pontoon / barge owner who met a big rock so it's a low / no cost change!
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Old 25 November 2010, 14:51   #7
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Zodiac GR mk3
2800 pound gross
50 hp high thrust
300 pound boat with gas
200 pound me and camera
no tachometer
26 mph (garmin GPS)

13 3/8 X 13 high thrust prop

what should I try to get more speed

thank you
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Old 25 November 2010, 17:14   #8
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Quote:
Originally Posted by nice.diver View Post
Zodiac GR mk3
2800 pound gross
50 hp high thrust
300 pound boat with gas
200 pound me and camera
no tachometer
26 mph (garmin GPS)

13 3/8 X 13 high thrust prop

what should I try to get more speed

thank you
Without a tach you'll just have to use trial and error... I'd try a 15 if I was paying for it (I doubt you'll be over pitched). If you're feeling lucky try a 17 pitch.

Just checked a prop calculator. It says that you're turning right around 5500 rpm. which is the suggested wot (5500-6000). A 15 pitch would be your best bet. It says you should do 27-28 mph with that prop. A friend here has the same engine (non high thrust) on a 14 Boston Whaler... he says he gets arund 26 mph out of it.
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Old 28 November 2010, 23:31   #9
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D80nov10 544 by nice-diver, on Flickr


D80nov10 515 by nice-diver, on Flickr

its got some power and does 25 mph
would like to get some speed out of it...how fast could it go??
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