115 mercury optimax 2009 propeller problem

[sebaboscolo89]

Hello I am new to the forum, sorry for my english but i am italian.
I have a small boat 550x1.80m for 350Kg with a mercury optimax 115.
In this moment my propeller is a mercury laser II 23 but the speed is low, 47 mph/h.
What is the solution for raise the speed?? but without missing many copy.
Thank you very much

 

[Chris1956]

Re: 115 mercury optimax 2009 propeller problem

I put those numbers into a propeller calculator with a propeller slip of 10%. It shows your motor was turning 4795 RPM. Is that about right? Why do you think it should go faster?

 

[sebaboscolo89]

Re: 115 mercury optimax 2009 propeller problem

Yesterday i try a Mercury Laser II P.23, 5 people into my boat, 5850 RPM (sounds over the limiter) my speed is 50 mph/h.

 

[steelespike]

Re: 115 mercury optimax 2009 propeller problem

It appears your slip is high at about 18%.Typical slip on a setup like that is 6 to 10% maybe a touch more.
I suspect either the rpm or the speed is wrong.Is the speed by gps?
How was the hole shot with 5 people aboard?
It appears that the same prop in a 25 would put you at 5450.
With speed 52-55 You should verify your tach and speed
before buying a prop.

 

[sebaboscolo89]

Re: 115 mercury optimax 2009 propeller problem

Thanks for the help and sorry for my poor english
I measure the speed with a gps (android-samsung galaxy) it's very much accurate.
My tuchspeed mercury isn't accurate.
Last year i test a prop racing P.24 whit 4 blades and i touch 54 Mph at 5850 RPM but my copy (hole shot right??) is very very little and i go out maximum of two persons.
Where i found your prop calculator??? For "slip" you mean a margie error??
I question the need to install the Powerlift to increase the copy and the speed.

 

[steelespike]

Re: 115 mercury optimax 2009 propeller problem

For prop calculator I put in" propellor calculator" on google search
it is by Poison Enterprises. and the page is a green color. You'll need your gear ratio, 2.07.
The racing prop was designed specifically for speed so wouldn't do well in other performance aspects.
Slip is a number measuring a props actual efficiency moving through the water. It is based on the rpm,ratio,pitch and speed = slip.
Slip varies with rpm, boat weight, hull design and prop design.Very basically as rpm goes down slip goes up, as weight goes up slip goes up,As hull drag goes up slip goes up.For instance pontoon boats have high slip numbers .
In english "copy" as a noun is a duplicate of an item. Zerox copy machines make copies(duplicates) of pages of text or pictures.
If you suspect your tach isn't accurate you need to verify it. Perhaps borrow a shop tach or have a technician go with you
to test.