Merc 115 & 26P SS?

[iboatWayne]

I recently bought a 1978 17' witchcraft banshee with 115hp merc. Just curious what size prop this merc would be able to turn. Currently it has a Mercury Vengeance 16P SS prop. The guy I bought it from claims the boat does 60mph but I'm calling his bluff before I even get it in the water.
Anyone running a 115 merc with a 13.5" x 26P Quicksilver Lightspeed SS prop (or similar)?. It's the only one I could find on iboats.
This should *in theory* push the boat to 60.
I'm hoping for some warmer weather soon so I can get this thing out on the lake. I have a few minor things to fix before I take it out. The tach isn't working and there are a few odds & ends to fix.

 

[steelespike]

Re: Merc 115 & 26P SS?

60 is highly unlikely unless that is an extremely fast hull.
Assuming the the 16" is running within the motors rpm range
lets say 5,500 going to a 26 would knock off about 2,000 rpm.
About 200 rpm per inch.putting the rpm at about 3,500.
These figures are rough but I think you can see a 26" isn't feasable on that boat
If you read the stickies at the top of the page and the helps on the prop store page it may help you understand prop selection better.
If you get us your present rpm and speed Preferably by gps we can help determine what may be possible.

 

[junior1113]

Re: Merc 115 & 26P SS?

ditto u need to be 5600-6000 wot rpm. what ever prop lets this happen is the one you need. if the 16 is pushing it in this range its good. that much more pitch isnt going to make the boat go way faster its going to lug and kill the motor.
example
16p=6000rpm good long engine life
26p=3700rpm problobly wont get on plane and if it does it will blow up very soon

ive ran diferent prop sizes 17,18 ,19, 21 and all went close to same speed just rpms were different

 

[iboatWayne]

Re: Merc 115 & 26P SS?

The reason I came up with 26p in the first place is that the Mercury website recommended it based on the information I gave it. Assuming it would just be me and a half tank of gas. I'll know more this next week once my new water pump kit arrives. I have the lower off right now.

http://appcenter.mercurymarine.com/propSelector/home.do
Boat Type: Fish and Ski
Boat Weight With One Engine: 800
People & Gear: 500
Fuel Capacity: 13
Performance Goal: Top Speed
Altitude (ft. above sea level): 0

Engine Manufacturer: Mercury
Engine Type: Outboard
Year: 2000
Number of Drives: Single

Engine: 115
Drive: Mid Outboard 2.07 Gear Ratio
Gear Ratio: 2.07

The only difference is my outboard is a 78 115hp and 2:1 lower. They don't have an option for anything below 2000 yr model.
With those options, they recommended a trophy plus 28P!