Prop for 2008 115 Mercury 4 stroke

[EricD]

I have a lund 1750 with a 115 Mercury 4 stroke on it. I need a new prop. The damaged one is a 13.25x17 but when I went to the Mercury prop selector, none of the props they recommend spec out like that. It generally recommends a pitch of 20 or 21. I wonder why the stock prop isn't recommended anywhere. Any thoughts?

[marine_man]

Any idea what you were turning for RPM's at Wide Open Throttle? How is your performance for holeshot & top end?

What kind of 1750 do you run? Fisherman, Tyee, etc?

If it's that bigger type of boat, I don't think a 17 is out of line.

marine_man

[EricD]

It's a 1750 Lund Explorer SS. I wish I could say more about performance but this is the first boat of this sort I have owned. I've been a pick-it-up-cheap tiller guy until I paddled back to the dock one too many times. It's been a dream boat for me but anything that actually ran under it's own power would be a dream boat for me. I thought I might split the difference - keep the diameter the same and move to a 19 pitch. That would drop the rpm some but I'm a bit afraid of deviating from the stock too much even if the manufacturer's own chooser says to move to a 21 pitch.

[boatfixer]

They're suggested prop is only a reference point. Not all boats perform the same, unfortunately it may be trial and error. As MM eluded to, its going to depend on performance. 115 4strokes may be a little slower out of the hole and that may be the reason for the lower pitch. I would want to know the max RPM at wide open before suggesting a deviation in pitch.

[EricD]

I wish I had paid more attention to performance last year. We chewed up the prop in the sand at a rather undeveloped access last fall just as we were taking it out. Each of the prop choosers I've used on line seemed to settle on 17 and 19 inch pitches as recommended with a wide margin on either side as options. It's interesting how only the Mercury site gave recommendations of 3 or 4 inches higher. You'd think they'd recommend their own stock props specs as an option. I don't think I can do much damage going up a couple of inches to 19 and I'll see if I can have the 17 inch repaired and then compare them.

[marine_man]

Since you don't have the performance data available... can you describe what your performance has been like? Has your holeshot been pretty good? Any idea what you're getting for speed?

If you can provide your speed your RPM's can be closely approximated to get your RPM's.

With respect to risk; the risk is that you'll pickup additional speed, but your holeshot will be poor.

marine_man

[EricD]

I generally top out at around 37mph and (I'm guessing here) at about 6000 rpm. That's with two people, fishing gear and a livewell full (of water, not fish)so it's pretty lightly loaded. I went fishing with 4 people once and didn't notice any real slip in performance. Hole shot seems pretty good to me but I don't have a lot of experience. I'm up on plane in less than 5 seconds.

[marine_man]

Sounds like it performs pretty close to where it should. Understand that if you're running where you think you are right now, going to a 19 will increase your speed slightly, but will make your holeshot worse.

marine_man

[EricD]

Thanks for the info. I ordered a 3.23x19 inch prop. I thought I'd simply have the 17 inch repaired but I found out today repairing it comes close to the price of a new one ($70 - ouch!). I'll try the 19 and see how it goes. Then I might buy another 17 to replace the one I have or repair the old one.

[delcecchi]

I don't think there is such a thing as a "stock prop" for a 115 merc. There is only the prop the dealer includes, since it depends so much on the boat. Not like a 10 horse that comes with a standard prop.