Another prop question.

[reelapeelin]

Before the motor I have now, I was running a 150...it propped out to red line at 6 grand at 42 mph w/a 17p x 15 1/4"d...

Now w/a 200 Merc, the right prop seems to be a 19p...it's a smaller diameter, but works fine...I think yer gonna need closer to a 19p...

Keep in mind although you aren't planning to run around at WOT, the correct prop for all speeds will allow your motor to max out at the mfgr's recommended max rpm level...THEN you find your optimum cruising speed gauging speed, rpms and fuel consumption...

[BuilderFL]

Gill, check this prop selector from Mercury. Hope it helps
http://www.mercurymarine.com/propellers/prop-selector/#

[THEFERMANATOR]

Originally Posted by reelapeelin

Before the motor I have now, I was running a 150...it propped out to red line at 6 grand at 42 mph w/a 17p x 15 1/4"d...

Now w/a 200 Merc, the right prop seems to be a 19p...it's a smaller diameter, but works fine...I think yer gonna need closer to a 19p...

Keep in mind although you aren't planning to run around at WOT, the correct prop for all speeds will allow your motor to max out at the mfgr's recommended max rpm level...THEN you find your optimum cruising speed gauging speed, rpms and fuel consumption...

Your 150 was a 2:1 gear ratio most likely, so that changes your prop selection quite a bit whereas the 2.4L+ will have a 1.87:1. Either a large diamtere 17 pitch for cruising with a heavy load, or a 19 pitch small diamter for lighter loads would be my reccomendation.

[Destroyer]

Originally Posted by THEFERMANATOR

Your 150 was a 2:1 gear ratio most likely, so that changes your prop selection quite a bit whereas the 2.4L+ will have a 1.87:1. Either a large diamtere 17 pitch for cruising with a heavy load, or a 19 pitch small diamter for lighter loads would be my reccomendation.

Which is exactly why I suggested the 19p x 14 1/2 dia ss. I'm thinking that with 225 horses he'd have no problem swinging a 21, so I moved down a notch for better hole shots.

[THEFERMANATOR]

Personally I like the large diameter and 4 bladed props for better cruising speed and efficiency as offshore boats rarely get to use the top end much that a small diamter prop can deliver.

[spareparts]

based on Ridge Runners boat, I'd say start with a 19 Mirage(or Mirage copy Thunderbolt ) you may change up to a 21. The 225 3.0L is a torquie motor, You don't need to rev it up 5500 is plenty

[GillV20]

I greatly appreciate the advice thus far. It sounds more and more I am going with a 19 mirage or it's like. On the motor though there is already a 4 bladed prop, I have not gotten the numbers off of it yet, but I really do not think the 4 blade is going to help.

[Destroyer]

Well, the number of blades on a prop is a compromise between vibration and efficiency. In theory, a one bladed prop would be the most efficient, but it would also create a lot of vibration. As blades are added, the vibration decreases, but so also does the efficiency because of the added resistance. Most props use 3 blades, because it's a practical trade off between efficiency and vibration. So if you're using a 4 blade prop on your engine already, then you'll get less vibration, so your engine will be smoother, but your efficiency will also decrease. Again, it all depends on what you want your engine to do in what kind of conditions. 4 blade props give you better hole shots due to more blades biting the water, but your top end will suffer because of the reduced efficency. 3 blade props will give you less of a hole shot, but you'll have a higher top end due to increased efficency. This is, of course, assuming that all other factors like prop material, rake and cupping are equal between the props.
Each of them plays a role, which is why it's possible to have two19 pitch props of the same diameter but one performs better than the other. This is where a knowledgeable marina prop shop comes in. They can advise you better than anyone else as to what is right for your boat.

[reelapeelin]

Originally Posted by GillV20

On the motor though there is already a 4 bladed prop, I have not gotten the numbers off of it yet, but I really do not think the 4 blade is going to help.

What numbers are you getting from the existing prop......if it is getting the max rpms your motor's specs allow, and not causing any difficulties, you may already have the right one...

Post up some numbers rpms/speed @ increasing rpm range 2000, 2500, 3000, 3500, up to mfg's max rpm for us if you can...top down, light load, slick water, etc...

If you haven't gone through this test w/existing, you may not need to change props...