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Old 20 October 2014, 15:05   #1
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Prop cavitation

Hi I have just bought a ring 6.50 rib with a mariner 90 four stroke. The bow seems to be a bit low in the water but if I try to trim up it cavitates very easily it is running on a 15 pitch aluminium prop was wondering if increasing the pitch may stop the cavitation and make it possible to lift the bow on trimming rather than cavitating any ideas welcome


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Old 20 October 2014, 15:23   #2
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15 pitch seems a little on the low side. What size prop??
I would hazard a guess at 13 x 17 ...!
Need to look at trim cavitation plate on the out board. ideally half an inch above V on hull
which links in to engine height so could be too high.
I'm also thinking engine a bit light for that hull. i personally don't know that hull at all but the engine comes in at 155kgs i think..
Check the engine cav plate fisrt. Maybe post a pic of the rear
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Old 20 October 2014, 15:43   #3
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I think the engine height is pretty much right between 1/2" to an inch max but will check at the weekend and get a pic if I can. I think 15" pitch is low aswell but talking to the broker I bought from he thinks a 17" would cure the cavitation but I was thinking 19" maybe. I need to get the boat back out and see what it is revving at at full throttle with a bit of grin I guess.


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Old 21 October 2014, 09:46   #4
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I have put a straight edge on the cavitation plate so as you can see the height. The prop number is 48 77342A45 15p not sure what diameter it is . Anyone know what a good stainless option would be to give better bow lift ?? Or anyone have a stainless prop available for this motor ??


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Old 21 October 2014, 09:55   #5
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That engine looks a bit high to me? Any chance of dropping it lower on the transom? We run a 15 inch pitch but have to haul heavy divers & kit out to dive sites. A 17 pitch would be ok though, but I still think you should try to lower the engine. Regards-John
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Old 21 October 2014, 10:01   #6
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The engine would go down one hole on the transom Brkt but any lower would need new holes drilling in the transom which I don't fancy . Would one hole make much difference ??


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Old 21 October 2014, 10:43   #7
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I have a Ring 18 with a 200 HP 2 stroke on it, I have my engine up as high as it will go, the cavitation plate is roughly 3" above the bottom of the hull, it sits great in the water at all speeds.
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Old 21 October 2014, 13:34   #8
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I run a Suzuki 90 four stroke with Ali 14x19 s/s 13.5x 21 and a s/s 14x20 all work well the 14x20 drops the revs by approx 500revs

Regards Jeff
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Old 21 October 2014, 17:08   #9
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The 1" above the transom stuff is a good guide but read this article as well.

Propping correctly & how to test props.....
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Old 21 October 2014, 19:53   #10
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Quote:
Originally Posted by Oscarguitar View Post
The 1" above the transom stuff is a good guide but read this article as well.

[url=http://www.veradoclub.com/smf/index.php?topic=137.0]Propping correctly & how to test props.....[
/url]
Hi all.

I saw this awhile ago and thought it was very informative and logical mmm that sweet spot.
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