Need Prop Advice for Merc 115 Four Stroke Pro XS

[Bad Boy]

I have a new Merc 115 Four Stoke Pro XS Tiller Handle on a 20'x45" Homemade Flat bottom. I have Tried several Props and none of them are performing the way I think they should. Can someone offer some prop advice?

[Juciy]

You have to provide some info. What props did you use? # of blades, pitch, rpm at wide open throttle. I am assuming since you have a tiller handle that you did not instal a tach.


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[Bad Boy]

Yes I have a Tach.
I ran a 13.25x21P 3 Blade Michigan Ballistic 6300 RPM at 53 MPH Handled crappy.
I ran a 13x21P 3 blade Power Tech SCD Semicleaver 6300 RPM at 52MPH Handled Better.
I am running a 12.7x21P 4 blade Mercury Spitfire X7 6000RPM at 53 MPH Handles Great.

[Juciy]

You are getting 12% slip which is normal, I am guessing but the larger prop are giving you more feedback in the tiller?

There is only so much you can do with a flat hull, they have no natural now lift. The hull geometry just does not offer any performance attributes.




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[Bad Boy]

How did you calculate my Slippage with out knowing my Gear Ratio?

[Bad Boy]

It just seems like I should be able to get more out of this set up. From everyone I have spoke with it feels like I am chasing something that is not there. I guess there is no more speed to be found.

[redaddiction]

Originally Posted by Bad Boy

It just seems like I should be able to get more out of this set up. From everyone I have spoke with it feels like I am chasing something that is not there. I guess there is no more speed to be found.

Dang! 53 isn't fast enough? Especially driving a tiller handle.

[dphung1]

Is your boat a true flat bottom ?


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[Bad Boy]

No it is cut 1" from 10' forward to the back.

[Rjrobin2002]

53mph is all my 18x54 custom 1/8" aluminum runs with a 115 Yamaha, just cant expect bass boat speeds out of these thick commercial hulls that are not hyperlift. No torque steer and ability to turn without blowing out is the most important thing I look for when prop hunting cause it is what makes driving a boat enjoyable. Why not try a 23 pitch Spitfire since you say it handles great and your hitting 6000 and see if you can keep 5800 RPMs when your are on step and get your motor jacked up with that hydraulic jack plate?

[netmkr]

I run a 21pitch 4 blade power-tech RDS Getting 48mph with a Mercury 90 HP 2 stroke. One hell of a hole shot with a 29'x48" bottom

[netmkr]

I run a power-tech RDS 21p 4 blade on a 20'x48" flat with a 2 stroke 90 Mercury. Getting 48mph with one hell of a hole shot. And can run motor jacked up without blowing out in turns.