Prop for 4.3l merc I/O 22.2 ff aquasport

[Capt. Bob]

Hey John, The guy is new and has some questions. Just like I had in the beginning. Your answer and advice was indepth and professional. Lets not try and scare him off the web.

I don't think anyone is trying to "scare him" but let's be fair.

What does he REALLY want to know?
How fast he can run his engine or what size prop should he be using?
Reread his first post then each one after that. I'm assuming he wants to know how to get the best performance from his boat/engine/prop combination. Very reasonable question and the place to start is here... What is the current size of his prop? With that information, one can ascertain which direction he should go. What would be of even more help is what he is looking for in the way of performance. Is he an avid waterskier, offshore guy, lake runner or a Sunday cruiser? He has, if I remember correctly, four (4) other props to choose from. So in conclusion, tell us the current size of the screw attached to the drive now and the sizes of the remaining props. Give us something to work with and I'm pretty sure we can help. :)

[sebas54]

Thanks for the reply.

No, I don't think that the previous owner set the RPM's to 3900 because of the bent prop.  I bent the prop while driving there was some rope drifting and it got tangled.   The engine will go past 3900RPM's but I was told not to. I  once ran it at 4200 RPM's but when noticed turned it back down to 3900 and still then it was not at WOT.  I will try to take a pic but it is in the water.  Thanks again.  I am sorry that I am such a neophyte.  Thanks for all your patience.

[Capt. Bob]

 I am sorry that I am such a neophyte.  Thanks for all your patience.

That's quite alright. I'm a drunkard myself.  No apology necessary.

Let's start here.....
Since you stated you had additional props (that are not, I assume ) in the water, could you tell us the pitch and diameter of those props? Look on the inside of the hub where the mounting nut (that holds the prop on the shaft) mates with the hub. There should be two (2) numbers there that indicate prop size and pitch. If you don't see something there then try the back of the hub or the side of the prop itself.

[GoneFission]

If the boat was not at WOT at 4200, it might be propped correctly.  You could run it up to WOT and see where she runs out - if she runs above 4800, you want to reprop with a higher pitch prop.  

If you never intend to run it over 3900 to 4000 RPM, you could prop it to max out at that engine speed.  That would be a higher pitch prop than you are using now.  The prop you have now probably has some numbers on the hub or somewhere that lists something like 14 x 17 or maybe 14 x 15.  That means 14 inch diameter and a 15 or 17 inch pitch.  Most V6 outboard props and Mercruiser Alpha drives use a propeller with a diameter somewhere around 14 inches.  

Pitch is the distance the prop travels through the water in one revolution.  Pitch is like transmission gears - higher gives more speed, but lower gives better acceleration.  The best prop balances top speed with acceleration.  Typically you want the boat to run out of power and reach top speed at the recommended maximum continous RPM.  In the case of the 4.3 Vortec V6, that's 4500 to 4800 RPM.  However, if you only intend to run it at a max of 4000, you can select a propeller with a higher pitch and the RPMs will come down.  Say you are running a 14 x 17 now - you could go to a 14 x 19.  You will give up some acceleration (hole shot) and some top speed, but will not have to worry about over-revving the engine and may get some improvement in fuel economy.  

Again, trial and error might be the easiest - take all the props with you along with a screwdriver and a 1-1/16" prop wrench and try them until you get what you want.  It only takes a few minutes to change a prop - you can do it at the dock, so you don't have to take the boat out of the water.  Just don't drop the nut, washer, or propeller in deep water - they don't float!  However, some of the plastic prop wrenches do!  

If you need instructions on how to replace the prop or more info, go to:

http://www.boatsville.com/boating_how_to.cfm?tipID=212

http://www.wikihow.com/Install-Your-Mer ... -Propeller

You can use any 1-1/16" socket to remove the nut, or you can buy a special (even floating) wrench made for prop nuts for about $10.  And don't overtighten when replacing!  Bass Pro Shops plastic prop wrench is less than $10:
http://www.basspro.com/webapp/wcs/store ... rchResults

Good luck!!