4 mile rock numbers? - FryingPanTower.Com

Posted: Wed Sep 02, 2009 10:46 am Post subject: props

i recently bought another cc which i put the motor off the old cc on. the new cc is heavier than the old one and the motor is stuggling to keep up. the boat runs out about the same speed as the old one but has a harder and longer time getting on plane & more than three people forget it. i would like to up the hp but $$$ is an issue right now. i am wondering if i go to a 4-blade prop would it help. it has a 17 pitch 3-blade now. 17 pitch 4-blade help it get out the water better??

Posted: Wed Sep 02, 2009 11:33 am Post subject:

what about the rpm's. did they go down and if so by how many.
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Posted: Wed Sep 02, 2009 11:43 am Post subject: props

now iam by no means an expert on this matter but when i had a 17.5' sunbird with a 3.0 cobra.with OMC outdrive i was told if i went to a 4 blade i would get more top in speed but i would loose it on take off as it was at WOT the boat ran 44mph on plane but if i had more than 2 people on board it would take off bow up and take a long way before it would plane out it was suggested to move some weight forward to the bow and by gosh it worked i could get on plane but on the down side if you put to mush forward the boat wants to bow plow at low speed so you are haveing to move stuff back and forth. my self iam trying to figure out witch way to go to get more speed out of the boat i have now WOT on plane 31mph is what the gps says. i know someone on here can tell what is you best way to go and good luck and be safe!!![/b]

Posted: Wed Sep 02, 2009 12:08 pm Post subject:

i do not have a tach on either boat. the old boat ran out at 32mph and the new one runs out about 29mph. its a 75hp merc. im not looking for more speed just get it out the water better. i have used the trim to help it. i just did not know what the "advantages" of going to a 4- blade would be, never had one.

Posted: Wed Sep 02, 2009 1:56 pm Post subject:

to simplify the ??? what is the advantage to a 4-blade prop??

Posted: Wed Sep 02, 2009 2:31 pm Post subject:

on that smal an engine I don't think it will make alot of difference, 3 or 4 blade. You may have to drop down to a 15 pitch to get you out of the hole.
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Ol'Salt Joined: Jun 12, 2008 Posts: 110

If it is as slow getting out of the hole as it sounds, you can almost bet it is over propped, but without knowing your WOT RPM's it is hard to say. You really need to know what rpm it is running at WOT to be sure you are not lugging your engine. This will shorten it's life. Good luck with it.

Posted: Wed Sep 02, 2009 7:17 pm Post subject: props

for the all important ???? you said the new boat is heaver!! how big was your old boat are both boats the same footage you also said the old boat wasn't all that great on getting on plane could be under powered from the start

Posted: Wed Sep 02, 2009 10:43 pm Post subject:

All of these guys are correct. Sounds like a lower pitch prop is the course of action. However, without knowing the rpm's that the motor is currently turning it is hard to guess. Don't want to over rev the engine on top end. A cheap option to try is a whale tail for your cavitation plate. Buy a good size one. It will help push that bow down.
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Posted: Wed Sep 02, 2009 10:49 pm Post subject:

Go to a lower pitch,it'll give you more tourque for take off,a 4 blade 13 pitch maybe?but like everyone else says rpm's?get a tach!don't want to blow it.also don't want to lag it either.

Posted: Thu Sep 03, 2009 12:40 am Post subject: props

seen it harbor freight. a rpm gauge that works on 4-8 cyl engines. i think it was about $19 small , about the size of a fuel gauge. bets the heck out of paying big bucks to see what your Rs are or check and see if some one in a shop can check it for you. and yes that fin does work i have it on mine. i have a angler 21.5 w/a cabin with a 120 force and the specs say this boat is 2200lb empty, add motor ,55gal fuel ,all the tac, 3 people, 40lb ice, drinks and with that fin she picks up pretty good and goes on plane, at WOT 4800rpm it runs 31mphand at 4000rpm it crueses 28mph that makes a nice ride or me and the motor don't sound like its straning.

Posted: Thu Sep 03, 2009 7:45 am Post subject:

The folks at Chatlee told me that a 4 blade is the only way to go on my 18' Seapro with 90 Johnson. My problem was different than yours though. I was running over 6K RPM's at only 30 MPH with a 4 blade 17 pitch. Switched it to a 19 pitch and it helped greatly. Reduced the RPM's to 5400 and picked up to 34 MPH, but it slowed down my out of the hole plane time a little. Small sacrifice for getting the correct engine RPM's. I'm thinking I'd try the whale tail first also.....but I ain't no expert. Good luck!
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Posted: Thu Sep 03, 2009 8:31 am Post subject:

Check out the below links. They have some good info on props and prop sizing. What I have been told is that a 4 blade prop will give you a better hole shot but you will loose rpm and speed at the top end. I also know that there are some prop suppliers that will let you try a prop and if it doesn't perform the way you want you can exchange it for a different pitch or size for no charge. You just have to pay shipping. Good luck.

http://www.westmarine.com/webapp/wcs/stores/servlet/westadvisor/10001/-1/10001/Propellers.htm

http://turningpointpropellers.com/propellers_101_cm.htm
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Posted: Thu Sep 03, 2009 9:48 am Post subject:

ok thanks to all. i think i have it figured out. i think its just going to boil down to a bigger motor 115hp to 135hp. for now i may try a 15 pitch 3-blade, already has a whale tail on it. the boat is the same size as the old one just lot heavier b/c it wider. went from a seaway to a proline both 17'
again thanks!!

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