2002 115 mercury 2+2

Coldwave600

Cadet
Joined
Jun 22, 2018
Messages
7
Right now I have a qa2038x 19p prop. Boat is a 16.5 Baja converted to a “fish and ski” built a front deck, bow mount trolling motor,batteries.... wife me 2 kids and dog (Golden) holeshot is AWESOME mid range good top end trimmed out is about 40-45ish at 5200-5300 rpms. ? Is will I gain much top end with a higher pitched prop? I’m willing to sacrifice some holeshot for top end.
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
I doubt you will gain any speed just by adding Pitch, just lower top RPM and slower holeshot. Your engine has a WOT RPM range of 4750 - 5250, so you are propped about right for your load.
If you run with less load, ie: just yourself, then the engine will likely over rev, and an extra inch in pitch will be of benefit.

What is your prop? Mercury or 3rd Party? AL or SS? A higher performance prop, combined with higher engine heights can add an extra mph, but there is no free ride, higher engine heights can often increase ventilation and slippage. Good Prop design can help a lot regarding that. At 45mph you are at lower end of where there is any advantage of higher engine heights, usually 50+ is where it starts to make any noticeable difference.
 

gbrowne9

Petty Officer 2nd Class
Joined
Jan 1, 2010
Messages
102
I have a 1989 115 2+2 on a 1973 crestliner Apollo 660 ,1100 lbs and I am running a 23p turning point or a 24 lazer 2. RPM,s are about the same.your boat should be lighter than mine.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
You could stand to come up in pitch like 200 rpm per inch as I recall is the rule of thumb. Whether or not it buys you anything really depends on whether or not the prop is apples and apples, not better or worse in thrust/performance efficiency, and how your boat reacts to the change. On 2 strokers I liked to run at or just above the recommended upper limit. On 4 strokers I doubt it matters that much.....but that's a swag, not having had one but usually they are cubic inch rich meaning they don't have to have the RPMs to get the HP number: HP simple equation is: [(Torque in Ft-Lbs) x RPM]/5252. On a 1 hp per cubic inch 2 stroker you aren't very cube rich!

Having trim is a plus as you can now find a different sweet spot and in doing so, you may get more boat out of the water, or your thrust efficiency may improve (prop slip number decreasing) and you wind up with more speed and more rpms to boot.

Usually however, lower speeds are adversely affected, in particular cruising just above the planing speed. Boats tend to cycle from dropping back off plane, operator applies power to get back on plane.....but as boat gets on plane losses are reduced and it's now going faster than desired etc.
 
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