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Old 14 December 2015, 03:00   #11
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Country: Poland
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Quote:
Originally Posted by Valiant Knight View Post
I had a Solas Rubex 3*13.25*17 aluminium propeller on my 5.2 m Valiant PT520 RIB. When I bought the boat, used, in 2011, it was already equipped with that propeller.
Since one of the blades got damaged, I bought a Solas Amita 3*13.875*19 aluminium propeller.
With the Rubex 17 propeller, the engine, at WOT, exceeded 5500 rpm and went into plane easily, even if heavily loaded.
Now, with the Amita 19 propeller, the engine runs slower: at WOT, under light load, stays between 4500 and 5000 rpm (maximum recommended for the engine is 5500), but will not go into plane with 5 people on board.
Should I go back to a pitch of 17?
Don't you have any boat service who can lend you some prop to test ?
If not I would suggest go back to 17" and 4 blades.

You have mentioned that you damaged prev. prop. Are you sure that everything is OK with gear case ?

Please find mentioned below guide (this one is for Evinrude but rules are common):


http://www.evinrude.com/Content/Pdf/...ide_766315.pdf

Usually one pitch more is 200-300 RPM less so I do expect 5400 as minimum when you jump into 19".

I do have 19" (3 Blades) and 20" (4 blades)
I do have 100-200 RPM less on WOT (normal load)
but better consumption in average range.

I do suggest to check again 17" and RPM.
If you have much lower RPM than before go and check gear case.

They suggest to test RPM use load which you usually have.
If you go always alone, test it with single person.
If you go with family test it with family.
Hope it helps
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Old 14 December 2015, 04:01   #12
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Country: UK - Scotland
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I can't imagine the gearbox is damaged causing your loss of rpm but if you continue to use the boat as is you are in danger of damaging the power head , valves etc can burn out due to overloading
If the engine can't make max revs it's overloaded not just at wot but through the entire rev range.
You need it prop so the engine can make just over max rpm with moderate load (during testing but don't run over max rpm) this can be achieved in various ways ss props 4/5 blade combinations different diameters etc there are dozens of prop combinations available.
The important thing is to let the engine rev to max rpm or its overloaded through the entire rev range with the potential for engine damage
A good dealer will often loan you several props for testing purposes to get the correct combination for your boat
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Old 14 December 2015, 17:54   #13
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Country: Other
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Dear all:

Thanks for the hints.
I am going to try a Solas Amita 3*13.875*17 (17 instead of 19).
I will let you know the results as soon as I am able to test the solution.

Regards

Antonio Manuel Carrapatoso
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Old 16 December 2015, 02:58   #14
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Country: Poland
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Hope it helps:

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Old 27 November 2016, 12:12   #15
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ECU malfunction

After a long struggle with the performance of the engine, I decided to change the shop I did the maintenance of the engine.
After an ECU replacement, I got back to 6.2 k rpm and 32 knots with just the driver or 6.0 k rpm and 30 knots with 2 on board, with a 17*13.875 propeller.
Should I go back to a 19 inch propeller?

Antonio Manuel Carrapstoso
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Old 27 November 2016, 12:20   #16
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ECU malfunction (2)

Apparently the engine was running on 2 cylinders instead of 4...
Hard to understand how that was not noticed in the yearly maintenance.
:-(

Antonio Manuel Carrapatoso
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Old 27 November 2016, 13:15   #17
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On my 5.85 rib with a Df 90 I had a 14x 19 Ali prop and a 13.5 x 21 SS prop both doing around 45 mph at WOT perfect conditions
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Old 27 November 2016, 13:32   #18
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Thanks for the info.
Just a few extra questions:
When you state 45 mph, do you mean 45 knots?
What RPM did you get at WOT? Under what load?

Antonio Manuel Carrapatoso
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Old 27 November 2016, 14:20   #19
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I think it was 45 miles so it be about 39 knots.

Based on this website Suzuki Marine - Product Lines - Outboard Motors - Products - DF90 - 2012 - DF90A
RPM range is 5300 - 6300 so you do not exceed it.
If you plan to make fast trips with 2 people you can try to use 19"

But if you plan to go with more people and max is not so important maybe you can stay at this prop
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Old 27 November 2016, 14:33   #20
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RPM range

Thanks for the info.

My engine is from 2006. DF 90 and not DF 90 A.
Recommended max. RPM range is 4.5 k - 5.5 k (Suzuki manual)

Antonio Manuel Carrapatoso
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