pitch?

Mr.Kitch'nPass · 05-07-2003, 09:54 AM

Im trying to figure out what pitch to go on a stainless prop. :whazzup: The boat came with an aluminum 14.25x21 but at max the rpm is about 2200. The owners man says motor should be 4600 max rpm.Sounds like I need to go down a bunch? Any opinions? [img]graemlins/1zhelp.gif[/img]
Thanks Dave

Pilar · 05-07-2003, 09:59 AM

Dave, that sounds like your motor is sick. Or you forgot to put the plug in before you launched. :grin: It should do better than 1/2 redline.

Cascade Marine on 149th and Stark can help you out with a loaner prop. Then you can try it before you buy it.

Miss B Haven · 05-07-2003, 10:05 AM

Pilar is right Dave- the prop would not pull you down to 50% rpm. Rule of thumb is 200 rpm for 1 inch pitch (or 1 inch diameter- but don't go messing with the diameter). You would have to drop to about a 10 inch pitch to gain those r's back. :shocked:

You got other issues. Speaking of which. Is this a brand new motor? (remember running in to me at Channel Marine?). You sure the tach is right? Does the motor sound like it's lugging or really reving up? :whazzup:

Myles · 05-07-2003, 10:06 AM

I agree with Pilar, something other than the prop is wrong. How fast will the boat go? Did you leave the trailor attached? :shocked: Take it back to NR and get them to look at it.

myles

id. painter · 05-07-2003, 10:09 AM

The H.P. of a motor is directly related to the r.p.m. of your prop. I have been told that to get the most out of any motor you want close to max R.P.M.when throttled up. . A flatter prop will turn more freely and there for give you better performance from your motor. id. p.

Mr.Kitch'nPass · 05-07-2003, 12:12 PM

It is a new motor,The guys that put the motor in said when they tested it with there equipment thats what they had for r's and it matched my tack :whazzup: . I have not had the boat out yet, maybe thats what I need to do next to see myself. As far as North River goes...lets just say at this point I have not had good luck with them wanting to help me with numerous problems

Thats a whole nother story.
Thanks for your help guys

Mr.Kitch'nPass · 05-07-2003, 12:27 PM

Im an idiot [img]graemlins/stupid.gif[/img] I just read my original post. I typed 2200rpm I should have typed 4400rpm duh (does this make a diff?) :grin:

Miss B Haven · 05-07-2003, 12:45 PM

Yes - A lot of difference. THat is very close to max. I would not change anything until you get the boat in the water and run it a few times under various loading (how much stuff and how many people). You're max rpm should have a range (not just a single value) in the mamual (Merc right?) anyway. Within 200 of your max is pretty close. If you get the boat loaded up with gear and people and you max drops further you may want to prop it down. As I stated above - it's about 200 rpm per inch of pitch and DO NOT reduce the diameter. You will lose some top end as you pitch down (when you are lightly loaded) but the motor will not be working as hard getting on plane.
If you drop to far you can actually over rev. Too much pitch and you are "lugging" the engine. This is almost exactly the same as changing rear end gear ratio in a truck for pulling loads (or not). You should know all about that right? :grin:
Good luck Dave- glad to se you are back in the water!

Myles · 05-07-2003, 01:18 PM

Disconnected the trailor huh??

myles