Proper prop pitch???

[nortana]

I have a new 115hp mercury 4 stroke. It came with a 4 blade 19 pitch blade. The boat is also a new 1750 fish hawk by crestliner.
If the boat only has 2 guys in it, it takes a while to get up on plane.........but once there I can skoot right along about 38mph. Now.......if the rear live well is full..........there is no way I can get up on plane.
Do I need, or can I get better get up and go with maybe a 17 pitch blade and should I go with a 3 blade instead of a 4 blade.
What do I need????

 

[Georgesalmon]

Re: Proper prop pitch???

what you need is a prop that will allow your engine to run WOT in the RPM range the manufacturer recommends with your average load.

 

[nortana]

Re: Proper prop pitch???

I forgot to add that I was told my engine should run 5800rpm and the best I'm getting now is 5400rpm.

 

[Georgesalmon]

Re: Proper prop pitch???

sounds like you could go down to a 17 pitch. you will get a better hole shot and likely get closer to 5800. might lose a tiny bit of top end but might not.

 

[phillnjack2]

Re: Proper prop pitch???

go back to shop where you got boat and engine and tell him he gave you the wrong prop .
you need to go down a size for sure, the engine needs to be able to get to max revs or it will be lugging and
wear itself out much too fast.
your wasting fuel as well and just not getting the engine releasing its true power.
youl probably see same speed or maybe 1mph more but with far better holeshot.


phill

 

[nortana]

Re: Proper prop pitch???

Ok??? Should I go with a 4 blade like it came with..........or drop down to a 3 blade???? What is the advantage/disadvantage of each.

 

[QC]

Re: Proper prop pitch???

Simplistic explanation is that a 4 blade typically is a little better on hole shot, and a three blade is a little better top speed. 4 blades usually lose 100 RPM with same pitch. As long as you are getting good performance all around with a 4 blade, it might be best to go down to the 17 with the exact same prop. It is not just about blades, it is about rake, shape of the blades, cupping, and a whole bunch of Voodoo. If you really want to know more read Walleyehed's Sticky at the top. Read all the stickies, and read a bunch of threads in this section. There is a TON to know about props, and then of course there are the trips to the Witch Doctor.

 

[jestor68]

Re: Proper prop pitch???

I forgot to add that I was told my engine should run 5800rpm and the best I'm getting now is 5400rpm.

With a WOT rpm range of 5800-6400 rpm, that's the reason your motor can't perform like it should. It needs to turn at 6100 rpm in order to develop full power.

If I were to recommend a prop; it would be the Solas HR Titan 4 ( 4 blade SS ) in a 15 pitch.

 

[QC]

Re: Proper prop pitch???

With a WOT rpm range of 5800-6400 rpm

Missed that. Agree 15". That far off, and I never say this, but I do think you have a discussion with the dealer. They missed this. Of course that assumes that they made these decisions . . .

 

[nortana]

Re: Proper prop pitch???

Thanks for the feed back. I'll be talking to my dealer this week about swapping props.

 

[Georgesalmon]

Re: Proper prop pitch???

For what its worth I have three props I change for different conditions. I have one 3 blade I use for two guys and a few rods to fish inland lakes, I have another I use for fishing lake Michigan with four downriggers, lead balls, three people, a 150 qt cooler with ice for fish another cooler for lunch and a pile of tackle. I have a third 4 blade for water sports with 4 to 5 people in the boat. All my props will run the engine in the power band for the motor during each condition. Maybe overkill but I feel good about running my motor with out any lugging. The dealer can't know how each boat owner will use/load his boat and can only make a good guess about the prop he supplies. A good dealer should also swap the prop for free. You don't have to be at the top of the motors RPM range to protect your motor, you just have to be somewhere in the range.