Propeller 115hp 4 stroke 2008 Mercury

[HDBartman]

I have just bought a 115hp Merc 25" shaft and have it on a 1903 Trophy. We have just ben out to sea and found it very hard to get to the plane with 3 people and fuel. Went out with just driver and it got to the plane faster but still slow. The motor came with a 13 3/4" x 18" pitch prop. I have read some reveiws and with a similar boat to the trophy they were using 13? x 15" props. Anyone can maybe give me experience on this matter?

 

[steelespike]

Re: Propeller 115hp 4 stroke 2008 Mercury

Not an expert:: but its difficult to know exactly where your at without your max rpm and speed.After checking the 115 Etec(has lots of different boat performance reports) makes a great reference point.90% of their tests are running 17 in props planing times were between about 4 sec. and about 8 sec.
It would seem to me your over propped.Max rpm and speed will help figure.

 

[HDBartman]

Re: Propeller 115hp 4 stroke 2008 Mercury

3200-3400 RPM = 8 mph
4500 RPM = 20 mph takes about 30+ sec to get to here currently

 

[steelespike]

Re: Propeller 115hp 4 stroke 2008 Mercury

Is the bottom clean?
Check your manual my guess is your max rpm range is around 6,000.
If 4,500 is with just you aboard I think something is up with your setup.You better get your dealer to check things out.In order to get to 6,000 you would need something like a 11 inch pitch.Something you find on a pontoon boat.
Unless your boat is a real tub I would think you would end up with something like 15 to 17 inches.