Prop for Merc 115 4 stroke

[TilleryTom]

Hey guys,
I need some expert prop advice.
Re-engined with a new Mercury 115 4-stroke engine on my old 1995 Smoker-craft deckboat.
(Old Force 120 seized under power). Marina guy tried the 21p stainless off the Force engine - no good.
3 blade alum 19p very little improvement in either holeshot or top end, and way under rpms. 17p 3 blade alum
much better, but still under 28mph by boat speedo at top end, and very sluggish holeshot. I was thinking of going with a 4 blade Solas Amita alum 15p. Hoping to keep or slightly increase top end, greatly improve holeshot and be able to get on plane and stay there at lower speeds. Open to any suggestions.
: Engine 2011 Mercury 115 4-stroke
: WOT 5800-6400 recommended, actually getting 5800-6000 with the 17p
: At sealevel
: Boat 1995 Smoker-craft Sunship 21ft deckboat. Fiberglass semivee hull. 2000lbs dry wt + engine wt +200lbs gas
+ 200lbs batteries and stuff + 6 people. Approx 4000lbs total. Used mostly for cruising and tubing. Would like to be able to pull up a 200 lb skier. Am I looking in the right direction?
Thanks
TilleryTom

 

[Bondo]

Re: Prop for Merc 115 4 stroke

actually getting 5800-6000 with the 17p

Ayuh,... A 15" oughta work, but it may need smaller....

 

[Bamaman1]

Re: Prop for Merc 115 4 stroke

If you're going to have to buy a new prop anyway, why not go to a prop shop, where they're experts in propellers?

Chances are their advice will not cost you any more than buying a prop from a dealership. Many will allow you to swap props immediately if they don't do the job.

 

[steelespike]

Re: Prop for Merc 115 4 stroke

Prop calculator says at 5800 a 17" should get about 38 mph at 15% slip.
Guessing slip a little high at 15% due to the load your pushing.
Your figures 5800 at 28 mph indicates 37% slip high normal is 10-12%.
A gps is better for accurate speed.
I think your asking a lot of a 115 what HP is the boat rated for?
I have seen some good results with the Solas Amita 4 blades. And the 15" may be what you need.
Calculator undicates a 15 at 6000 would run about 36.@ 12% slip( a guess)

 

[TilleryTom]

Re: Prop for Merc 115 4 stroke

Prop calculator says at 5800 a 17" should get about 38 mph at 15% slip.
Guessing slip a little high at 15% due to the load your pushing.
Your figures 5800 at 28 mph indicates 37% slip high normal is 10-12%.
A gps is better for accurate speed.
I think your asking a lot of a 115 what HP is the boat rated for?
I have seen some good results with the Solas Amita 4 blades. And the 15" may be what you need.
Calculator undicates a 15 at 6000 would run about 36.@ 12% slip( a guess)

Thanks Steelespike,
Sounds like sage advice. I'm leaning towards the Amita 4 blade 15p to get max holeshot and low speed control.

 

[TilleryTom]

Re: Prop for Merc 115 4 stroke

Thanks Steelespike,
Sounds like sage advice. I'm leaning towards the Amita 4 blade 15p to get max holeshot and low speed control.

The boat is rated for 200hp, but is a little tail-heavy with just the 115.

 

[steelespike]

Re: Prop for Merc 115 4 stroke

They usually reccomend to set up a boat with 3/4 of the rated hp.
Also it's hard to believe a 120 Force with a 21" prop could handle that boat at the load you described.