Mercury Prop question

[Jsparks987]

Hi new to the Forum and have a problem Identifying the prop on my engine It's 1998 150xl off shore mercury serial 06740017. The existing prop is a 4 blade alum prop with the only #'s I can find are QA6186 20. I have no idea of pitch or dia. I'm thinking of replacing it to gain more top speed the boat is a 1982 20' Chappall walk around. The hole shot is good but seem to taper off at top wot. I'm not sure the MPH as the GPS recently took a dive..

 

[rndn]

Re: Mercury Prop question

The experts, not me, will need to know your current rpm's at WOT and the speed you are attaining. Your current four blade prop is a 20 inch pitch. I googled your part number.

 

[Jsparks987]

Re: Mercury Prop question

Thank you !!the RPM at WOT is 5600 but will have to get a friends GPS to clock the speed. Did you happen to get the Dia. Thank you again

 

[Silvertip]

Re: Mercury Prop question

Measure the diameter. Blade tip to prop shaft center x 2 = diameter. If a four blade, measure from blade tip to opposite blade tip. Sounds like 5600 is the correct WOT RPM. Slapping a prop with more pitch does not guarantee more speed. You also need the power to twist that prop. Since you are already at 5600, increasing pitch will drop RPM and potentially decrease speed at the same time since the engine may no longer be able to reach 5600 RPM. Maximum speed it what you get when you are propped at the top of the recommended WOT RPM band.

 

[stevens]

Re: Mercury Prop question

Your current prop seems to be a 14x20, judging from the part number.

But, don't be too concerned with the diameter, concentrate on getting the pitch right.

 

[Jsparks987]

Re: Mercury Prop question

Thank you for the information any suggestions on switching to 3 blade SS prop as far as pitch?

 

[stevens]

Re: Mercury Prop question

It's hard to predict exactly; there are too many variables changing at once (alu to steel, limited cupping to more, 4 blades to 3, one brand/style to another).

Personally, I'd try some decent brand 21 pitch 3-blade first, such as a Stiletto, Turbo (or maybe an Enertia if you can find one at an affordable rate). There's no guarantee you'll hit it right on the first try, though. Perhaps a good idea to find a prop shop where you can try before you commit to buy.