what prop?

[meatyb]

hi all
i have a 1997 sea ray 175 br ob 115 mercury 2 stroke seems slow tried 3 diffrent props 17 pitch gets me up out of hole fast!! no top end maybe 30mph?? could easily rev to 6k 19 pitch ok holeshot about 34mph @5500 wot and a 21 pitch not so good hole shot but maybe 36 mph top end @ 5000 wot is that it for this boat? max wot stamped on motor is 5250. would a 23 pitch be too much? i wanna go fast


just me and one other adult 20 gals fuel and no extra gear just the required stuff. water was semi calm but not glass? any help would be great anyone have this same setup and what speeds are you getting? thanks

P.S all props are aluminum 3 blades

 

[Barnacle_Bill]

Re: what prop?

5500 RPM is the top of your recommended WOT range. I would stick with the 19. If you want a better hole shot go with a 4 bladed 19

 

[Sea Rider]

Re: what prop?

Try a prop that gives near 5500 rpm at wot for that boat/engine/weight combo, the faster you go the guzzler an engine will be, on the other hand bad hole shot with best top speed, you decide. Or stick with 2 best props for different boating applications.

Happy Boating

 

[meatyb]

Re: what prop?

thansk for the input guys hey bhilewhat would the 4 prop do besides better hole shot? will it slow my top end down or speed it up?

 

[steelespike]

Re: what prop?

Something isn't adding up. Using 2.15 gear ratio and guessing a 9%slip 21" prop I get about 42
at 5000. Same specs with a 19 at 5500 I get about 38. Are your speeds by gps?

 

[meatyb]

Re: what prop?

Something isn't adding up. Using 2.15 gear ratio and guessing a 9%slip 21" prop I get about 42
at 5000. Same specs with a 19 at 5500 I get about 38. Are your speeds by gps?

yeah im using a iphone with speedo app. checked in car and its dead nuts on with car speedo. and surprisingly enough 98% of the time gps (phone app lol) is right on with boat speedo its weird lol cause i know boat speedos are unreliable at best

 

[steelespike]

Re: what prop?

Either my figures are wrong or you have excessive prop slip or your tach is off.
My figures say that with a 19" prop at 34 mph and 9% slip your rpm would be about 4500. a 21" prop at 36 and 9% slip would be at about 4300. 9% is a guess slightly on the high side.
The antivent plate (just above the prop) should be even with the bottom or slightly above. This could help the speed and improve the slip numbers slightly.
But I think the tach may be high.You could check the switch on the back is set right and operate it a few times to clean the contacts.You could varify it against another tach.

 

[meatyb]

Re: what prop?

i will clean all contacts on tach and get better numbers. what would cause excessive slip? the 17p and 21p props are used but good shape just some paint missing. the 19 is brand new

 

[steelespike]

Re: what prop?

A number of things could affect slip.a disturbance in the water ahead of the prop.
poor prop design or condition.A prop poorly matched to the application.
Under powered or a difficult to push boat.
I don't think you have slip issues its much more likely the tach.