Prop Question

Anyone here with an I/O ever try a four blade prop. My father met some guy yesterday who owns a marina and he reccomended we try this.

Also what size props are you guys using on your I/O's?

Thanks,
John

[chumbucket]

I've used four bladed props in the past. What I found was that you'll shave a little off of your top end speed. What you'll gain is good out of the hole torque and also good bite when cornering. If you regularly have heavy loads, or like to waterski/tubing, the four bladed prop is a good option.

CB, I read somewhere that a 4 blade also causes more lift in the transom. Seems like a good thing to those of us with no tabs installed!
Anyone know what I'm talking about? ???

[macojoe]

It will get you out the hole fast!! But as far as the lift goes, I think it feels that way when you take off cause it lifts you up to get you on plain!
I think thats it for lift after up on plain its normal.
I was using a 15 pitch when I was I/O but was talked into a 17 went I went out board. I am going back to a 15 this year!

[chumbucket]

I never experienced any lift with the four bladed prop. But, it was a very heavy boat. You may be correct. I just wouldn't be able to say one way or the other.
For my use, I like a three bladed prop best.
The other question I would have is; Do they make them in aluminum? Most of the ones I've seen are either stainless or composite. Stainless is good, but expensive. Composite is cheap, but flexes too much. Believe it or not, aluminum will flex under load too but is a good compromise in material and strength. With stainless, if you're not careful and golf it off a rock, you risk breaking gears in your lower unit. Composite will snap (better have a spare). Aluminum will ding and still get ya home in most cases. Always a good idea to have a spare onboard no matter what even if it's not the best shape.
I know it's a lot to consider. Many people never think twice about the prop they put on their boats.

[macojoe]

I have 2 ;D

[Mac_Attack]

I have no idea what you guys are talking about when you mention lift. *The boat I just bought has a spare prop. *I'll have to check the pitch, this give me more to look into when I get the boat home. *

[chumbucket]

Mac, he's referring to stern vs. bow attitude. When a boat utilizes trim tabs and they are actuated in a downward motion, this downward force causes the stern of the boat to lift on either one side or the other or both depending on the operator selector switches. This will in effect make the boat level off to get on an even plane overcoming the natural tendency of the bow to lift when you trim out the motor.
Run the boat before you start worrying about the prop pitch and make sure that the top end RPM's fall within the manufacturers specification (usually somewhere between 5000-5600 RPM). If it falls below the mark, your motor is working too hard. Above the mark, not working enough and equally as bad as working too hard. Generally speaking, 1" of prop pitch equals 200-250 RPM's. That usually goes both ways whether increasing or decreasing pitch. Then you can get into diameter's which will also factor in but generally to a lesser extent.

[Mac_Attack]

CB I knew about trim tabs lifting the stern. Believe it or not my littlle 16' Gruman had fixed plastic trim tabs. What I had never heard of was that a certain type prop or pitch of prop could cause the stern to rise or create lift. As I just told the new member you guys are remarkable in your knowledge. I wonder how many years of boating experience are on this web site and how many of those years are with a V20 or V21?

What size four blade are you guys using? And what horsepower is your engine?

Thanks John