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Old 04 January 2015, 15:27   #11
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Originally Posted by rusty McCaw View Post
I am thinking a new 13p with some cup to have as a spare and surf prop?? Any advice would be appreciated
Don't over look the fact that you were using a shagged 13" prop before, so a new 13" should really show an improvement.
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Old 04 January 2015, 22:02   #12
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Agreed, might possibly have to go to a 12sst with cup, all will be reviewed when the tacho arrives. Anybody know what the surf boats lifeguards use?? Usually 30hp mercs here in NZ but no stamps on their props
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Old 23 January 2015, 22:52   #13
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Upped the pitch and Baffled buy the results

Prop geniuses please chime in, sorry I know it's been awhile since I last posted, but the tacho took longer than expected and well the surfs been pumping....any hoo..... Out on the water today with a little ruffle and a lightish load...top revs achieved were 5280rpm while flying over little lumps and normal top revs in the flats were around the 5180....

I don't know the exact top revs required for my donkey but am sure it's around 5500/5600rpm so would down pitching back to the 10/13p be on the money?? And would a sst option mean I would have to drop another " in pitch?? Or not due to cupping?

Evinrude 25hp
1998
2cyc single carb
Omc prop 10/15p
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Old 24 January 2015, 12:20   #14
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You'll lose a few revs (100 or so) just by going stainless (added weight to turn.) That assumes the props are otherwise identical (which they won't be.) Figure on losing more revs if there's cupping on the SS prop.

jky
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Old 24 January 2015, 14:00   #15
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[QUOTE That assumes the props are otherwise identical (which they won't be.)

jky[/QUOTE]

So right, its sometimes frustrating when testing props and the results is not logical, one of the challenges is that the pitch can be pretty much off compared to what is reported... And even if the pitch is right, still different diameter, cupping, thickness of blades can make unexpected results. So what looks good on paper might not work so well in reality. So real word testing is only way to make sure.
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Old 27 January 2015, 09:00   #16
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What's the gear ratio in that engine? In the surf there's not really any facts or figures you can go by when prop tuning, it's just how it feels.
If you're into top speed prop tuning you can use speed, revs, engine height, trim etc. Have you got a GPS you can use for speed readings? you might end up going faster with the 13p
You should check out boatracingfacts, they know a lot about tuning. If you're not on the rev limiter (if there is one) then going down in pitch is a good idea for the surf, better acceleration and not much loss in top end if you're still revving. Definitely go stainless though, better performance all round
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Old 27 January 2015, 17:27   #17
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Thanx guys, yea I'm chewing things over and I'm leaning towards a SS prop due to my uses with the boat.., I'm not to worried about losing a tad up top but definitely can't afford to struggle down low when heading out to spots in bigger swell, playing in the surf , or pulling kids on toys....

My mech told me that my max Rpm,s for this engine are 5200-5500 so I'm not far off the mark, I think 13p SST with cup will be the ducks nuts...

I'm toying up between the Solas Saturn and the Michigan ballistic 3blade,,,,what way would you lean??

Sorry I don't know the gear ratio for this engine? It's short shaft
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Old 27 January 2015, 17:37   #18
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2.15 gear ratio??
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Old 29 January 2015, 11:24   #19
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Really depends on your boat and what you use it for, I only really know about thundercats.
SOLAS make good allround props, not so many people have tried ballistic but apparently they're pretty decent. Maybe even better in the surf due to the cut on them, more like a semi-cleaver. Mercury props are just about the best out there if they fit your engine. They make a prop called a vengeance which is great in the surf.
the order I'd put them in
1: Mercury vengeance 10.5 x 13p
2: SOLAS 13p
3: Ballistic 13p

Whichever you get cup is usually a good idea for more grip, but try it out the box first. this is all just my opinion
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