Mercury 40hp Prop specification

[glenlyn]

Hi,

I would like to know what size/pitch prop is required.

I have a Mercury 40hp 2 stroke thunderbolt start, serial number 9185219.

I beleive the engine is late 70's?

My boat is a 14.4ft cathedral hull.

Can anyone help?

 

[Sean-Nos]

Re: Mercury 40hp Prop specification

You will need to find the rpm of your engine,the weight of your boat with everything in it and what passengers you would normally carry.

 

[Silvertip]

Re: Mercury 40hp Prop specification

There is no such thing as a standard prop. What's on it now? Next -- read the sticky at the top of this forum. It tells you what we need to know in order to make an educated guess as to what you need.

 

[glenlyn]

Re: Mercury 40hp Prop specification

Hi,

I have the following info:

length at water line 13.4 ft/4.02m
displacement 500kg/1100lbs/.49t
single outboard engine
40hp
5300 max rpm
gear box ratio 1.7

I have used some software that calculates a 10.60 prop diameter with 11.15 pitch.

The pitch alters depending on what you input for the hull type ie full displacement, semi displacement, ski boat

I am unsure what to class the boat as???

 

[Silvertip]

Re: Mercury 40hp Prop specification

You are still missing some important information. You state the engine RPM is 5300 max. Is that what the manufacturer states as the maximum recommended wide open throttle rpm or is that what you actually observe on the tach? There is a big difference in those numbers. 5300 is where you actually want the engine rpm to be. What you observe may be more or less than that which is where prop pitch enters the equation. We need to know what rpm you actually see on the tach. We also need to know what speed you currently observe at wide open throttle. Use a GPS, locator, or the speedometer but the more accurate the speed reading is the better our recommendation will be. Without this data, anything will be just a guess.

 

[steelespike]

Re: Mercury 40hp Prop specification

Your boat is a planing hull intended to get up on the water and go.Not a speed hull.
Displacement and semi displacement hulls are harder to get on plane thus would be likely to require less pitch.Not an expert but from my experience your 11" pitch result is close.Try to get the other info to refine things more.