Plz help me pick the right prop.

Hey guys...I managed to hit a rock this weekend which tore up the prop bad. So, looks like its time to bite the bullet and get a different one. First on all, its an 85 crestliner crusader 2105 with a 3.8 v6. I've only had the boat on the water for a couple of weeks. It seemed to only pull 3600 rpms and about 36 miles an hour. It should be pulling around 44-4500 rpms right? The prop that was on there was a 15x17. I wanted to hook up a different tach to make sure the guage was reading right..but never got the chance. What do you guys think? Sound like a bad tach reading, or the wrong prop? Thanks in advance for the replies guys

Forgot to mention...Right now I'm thinking i'll go with a 15 pitch prop, however I've only been able to find them in a 15/1/4X15 and 15/1/2x15. What will this change over using a 15x15 which is what I was thinking about going with. Thanks again guys.

I'd first get your tachometer working correctly.
Without a working tach, you have NO means of checking WOT RPM that will allow you to see if you are geared/propped correctly.

Without this, you risk engine damage if indeed you are on the low side of your WOT RPM.

To do a WOT RPM test, engine must be in full tune, prop in tune, hull clean!
Keep the horse in front of the cart... not behind it!


See OEM specs for this WOT RPM range!

Are you willing to call in the experts? Around here (Chesapeake/Annapolis) there are several propeller services. They will bring several propellers along and do the in water testing to find the best one. You may be surprised to find that the prop you thought would be the best is actually not, so it pays to have several to test.
In addition, your interest may not actually be to have the engine top out at 4500. Maybe you would like lower cruise speed or hole shot for skiing or whatever and again, having a half dozen or so to compare side by side will show vast differences in how they perform.
Or, just get a 14.5x17 and be done with it.

The tach works...I just wanted to hook up another to be sure that it was accurate. It seems to work right, it shows around 550 rpms at idle and it sounds spot on. I was just hoping to hook another up to be double sure since i just got this boat. It comes out of the hole good now with the 17..I know that this motor should turn 42-4600 rpms. So I would like to get into that range. Like you said Ricardo..if its only turning 3600 it will eventually hurt the motor. I know it'd be nice to test a few different props, but I wont be able to return what I order. So I hope I get it right the first time. I looked in all three of my service manuals (clymer, Seloc, and OMC) and none them really cover the 3.8 . Sorry for the novel, just want to fully explain myself.

Both Rick and 02batsea have given you excellent advice, first make sure that the RPM's are correct and the engine performance is the best you can get it. Second you need to decide what the boat is primarily used for, there is no perfect prop for all applications, the smaller the pitch the higher the RPM's (better hole shot but top end suffers), higher pitch gives lower RPM's (hole shot is like a dog but top end picks up)


Some marinas (especially if you deal with them) will lend you used props to test providing they are sure you will buy a new one from them.

Mine is a 20ft 4.3 4200-4600 wot went from a 15x17 to a 14.25x21 much nicer to plane the 15x17 is used on my bigger boat 24ft 5.7 the 21fter with the 15x17 took longer to plane and rpms woudnt go to max though I only run 75% or less

http://www.turningpointpropellers.com/ try this worked for me you have to no your boat specs to get it right

I will not name names, please don't ever post that recommended wot does not have to be attained.

The motor MUST reach recommended wot. Doesn't mean you have to run it at wot all the time. Actually 2/3 of wot is recommended for cruising and wot for a emergency, such as getting out of the way of a giant tanker.

I always run wot at the beginning of the season, mine is 4500 then i know it's running in peak condition. Say i lost rpm then i know that compression is down for some reason. Or some other problem. I also run wot one time in the middle of the season, and again at the end of the season. 3-4 minutes at wot is all it takes.

Lugging the motor with a too much pitched prop that will not allow you to reach recommended wot will blow your motor, maybe not today or tomorrow but sooner then latter.

I had my trashed Prop re-built by a fellow near me. $85. Canadian, and it looked BRAND NEW. He even re-pitched it to a 14.25 by 18, from a 16 pitch. WOT is now 4000, and I'm quite happy.
The Boat goes like stink , for a 20 footer that weighs #2750.

S.

Chief, there are many instances in which one wants their engine to be running at RPMs way higher than 4500. ***** runners and race boats in particular. I am certain that you understand this. I did not put out wrong advice. Propping is not a science, it's an art.

i agree if the motor is set up for it.

And then again the recommended wot for those motors i'm sure are being followed.

If not then they blow up and they have to rebuild it again.