Prop suggestions

[Mybiggles]

Hey guys. I have a 92 Larson senza 170lx that I swapped an old 1982 merc 115 onto. boat is roughly 1300lbs, when fully loaded its probably around 1800-1900lbs 90% of the time. The prop I have on it now is pretty rough, it has a bent blade and another blade has a pretty decent chunk out of it. Its not marked and the 3 times ive used the boat the tach wasn't working. The tach is fixed now but I havnt had a chance to take it out yet. Anyways I was wondering if anyone had any suggestions on what size and pitch I should try? The turning point prop wizard spits out anything from a 13.25x17 to a 13.25x25 just by changing the type of boat. ski boat was a 17 or 19 pitch and a high performance boat was a 19 or 21 pitch, and a runabout was 23 and 25 pitch. I emailed turning point and they suggested to start with a 19 and go from there.

Now for what kind of prop, used locally in really good shape there is a mercury laser 2 20 pitch, a stiletto 13X19 and 20, A ballistic 13.125x21, a solas 13x21. all of these would end up around the same price as buying a new turning point hustler 3.

The boat will mainly be used for cruising but would like to retain good pulling power for skiers or tubers, or the odd time I have it loaded up with 5 big guys.


heres a pic of what the hull looks like

 

[Sea Rider]

Anyone can suggest any prop they're currently running but only a water tesr will determine if any good or not, variable deck load is a killer to any equation, to each boat his own prop. Did you had a chance to tach current prop on a wot run before being damaged and tach entering kaput world ?

Happy Boating

 

[Mybiggles]

no I grabbed the boat around Christmas time and pulled the motor from an old cobra ski boat. It topped out about 47mph on the cobra (according to the onboard speedo). the cobra was quite a bit lighter, so if It was properly propped for that boat its pretty far from ideal now. On the current hull it averages mid 30's and I had it to about 42mph with just myself on board. I think the prop has been damaged since the beginning. Theres an old merc aluminum 13x17 prop on craigslist for $15 I might pickup just to get a starting point for pitch.

I also just played with the mercury prop selector and its suggesting a 13x24 or 25 pitch for the same info as the turning point wizard lol

 

[Mybiggles]

I just ordered a turning point hustler 13.25x17 pitch prop from amazon. The good thing about amazon is I can return it if it over revs and go with the 19 pitch lol. or maybe even try a 4 blade.

 

[jimmbo]

I doubt it will over rev with the 17

 

[Mybiggles]

I doubt it will over rev with the 17

So I finally got a chance to bring the boat out today. it was fairly choppy and long story short the boat was taking on water, all the electrical shorted out and I was probably 10min away from sinking by the time someone rescued us.

Before all that happened I got a chance to test the new prop. I had 3 adults and 3 small children with a full cooler and a bunch of gear on board. Hole shot was a bit better and it got on plane a bit quicker and was able to keep plane at a bit lower speeds then before. The new prop is a turning point 13.25x17 3 blade, the old prop was also a 13.25x 17 pitch stock mercury 3 blade aluminum prop. Top speed was still around 35mph and I finally had a working tach this time and I was topping out at 5000rpm. I was able to pull a tube fairly well so its decent for what it is but I feel like it could be faster and perform better overall

I checked turning points website and the 13.25 x 17 is the lowest pitch that make in that diameter They have 14x11, 14x13 13.75x15 and a 4 blade 13.5 x15

I guess my question is how would the larger diameter and lower pitch affect rpm? I read 200rpm for every inch of pitch but havnt seen mention of how diameter affects it

 

[jimmbo]

The rpms will go up. I don’t know why the last couple of years there has been a fixation about Diameter, Leave that to the prop engineers to worry about, as it is only one of many things in prop design. As pitch drops Dia gets bigger on a lot of prop lines
@5000 you are at the bottom of the WOT range for that engine(5000-5500) so a 15 may be a better choice

 

[wahlejim]

I had 3 adults and 3 small children with a full cooler and a bunch of gear on board. Hole shot was a bit better and it got on plane a bit quicker and was able to keep plane at a bit lower speeds then before. The new prop is a turning point 13.25x17 3 blade, the old prop was also a 13.25x 17 pitch stock mercury 3 blade aluminum prop.

That statement could easily account for 500 RPM, and then some.