pitch pitch pitch

[tbone999]

so simple facts 3.0 merc with 4 blade 17p prop wot 4800/4900rpm at around 32mph with only me and my dog and half tank of fuel, ive installed tabs on a boat that is under powered so getting up hasnt been a problem, looking to trade hole shot for a little more speed thinking 19p anyone see a problem here?

cheers

 

[alldodge]

If your tabs are powered ok, but if there smart tabs remove them.

19 pitch 3 blade ok

 

[tbone999]

Power tabs! Can i not stay with 4 blades sounds weird but i liked its performance better at low speeds, docking etc

 

[alldodge]

Can i not stay with 4 blades sounds weird but i liked its performance better at low speeds, docking etc

Sure, but it takes more power to turn a 4 then 3 blade and your wanting more top end. Rule of thumb is 2 inch of pitch for the extra blade (4 blade 17 = 3 blade 19). Since your reaching just past the rpm limit now, could have your current prop cupped just slightly. This gives it more bit and might reduce slip if (the big IF) your not just trimming up a tad to much at WOT. That said cupping works for forward but reverse gets worst (less bite)

 

[jimmbo]

Ditch the 4 blade. The 3L being small usually has a high gear reduction, so a 19" or 21" 3 blade is likely the best choice

 

[tbone999]

K thanks guys ill look into a 3 blade asap so if im getting what ive seen on other post for every time i go up pitch i lose 300/400 and gain 3/5 mph on the top end assuming the engine has the power? I never want to run at wot im looking for a little higher cruising speed at the 3500/3700 ish range

 

[jimmbo]

You have to choose a prop that allows the engine to run in the WOT throttle range. You can't go choosing a prop that gives a higher mph for a particular rpm, if the engine can't get to the WOT rpm range.
If you want a higher cruising speed but are not willing to run the rpms needed, you need a bigger engine, with more torque

 

[tbone999]

Am i right on this? Last question before i order a new prop

 

[alldodge]

I'll put it this way, increasing the pitch will lower your rpm and increase the speed for cruise speed. It will not increase the WOT speed. While the boat may have 2 to 3 mph increase for lets say 3500 rpm (example may not be real world), it will be burning more gas at that rpm because the motor is being lugged. The hole shot will be reduced and lugging a motor makes it work harder and over time can create more wear