3 vs 4 blade props

[walleyehed]

Re: 3 vs 4 blade props

225HP on an 18ft'r swingin' a 19 pitch wheel doesn't add up...?????<br />42MPH equates to 20% slip (very inefficient) at 5500...Did you say what RPM he's getting??

 

[markvan]

Re: 3 vs 4 blade props

sorry walleyehed i called him last night to make sure i got all the details correct......here is what he said, 1981 Sunset 19ft, 225 evinrude (1988) 19 pitch and 42 mph at 5750 rpm. any suggestions

 

[walleyehed]

Re: 3 vs 4 blade props

That's 24% slip...something is not right there.<br />several possibilities and it's gonna be hard to pin it down...<br />#1-lots a drag<br />#2-speedo off<br />#3-tach off<br />#4-EXTREMELY heavy boat<br />#5-incorrect engine-to-boat set-up<br />#6-combination of all of the above.....heck a bad prop can cause some strange data, so I would hate to guess blindly at this without more info.

 

[markvan]

Re: 3 vs 4 blade props

what other info would would you like, i am heading there tomorrow so i can get it from my neightbor. as far as his spedo its gps and i have checked it to mine and its right on....tach not sure he said sometimes it seems like a wire is loose as it stops working for a few seconds in rough water. He did say that his mechanic told him that it is a very heavy boat as it is a 24 yr old fiberglass and they tend to get almost water logged ? i kow that a few years ago he replaced the floor, the stringers, and the transom it does seem to sit lower than it should in the water, if there is a bit of chop on the water the back sits down so low that the exhaust goes in and out of the water.......let me know if there is any info that would help you out.

 

[walleyehed]

Re: 3 vs 4 blade props

Verify the pitch of the prop first. If we know both of your GPS units are reading the same, we can eliminate that.<br />This may be a long-shot, but depending on how he jigged the boat for stringer lay-up, the hull may no longer be true.<br />The 5750RPM just doesn't match-up with a 19 pitch prop at 42 MPH..The numbers DO, however, compute to acceptable efficiency if he has a 17 pitch prop.<br />See if you can get some numbers off of the prop..we'll try and determine something from that.

 

[markvan]

Re: 3 vs 4 blade props

ok - i know he has has that prop repaired before and also last year he had some cracks on the front of his hull so he had them fixed and got the boat repainted from the gunnels down.

 

[walleyehed]

Re: 3 vs 4 blade props

If the prop has been worked or repaired, we really don't have a leg to stand on without him trying a different prop.<br />Some prop shops have a hard time keeping the original shape and contour. I see fresh repairs come in here alot that scare me into paying the gurus the big-bucks for PROPER prop work.<br />I guess we really don't know the condition of the hull for sure, so here's what I recommend...Test the boat with a prop of known size and collect some data from that...we gotta have a base-line of some sort.

 

[markvan]

Re: 3 vs 4 blade props

just got back from the lake and did some testing, we put a 3 blade quick silver prop that is vented, 14.5" x 19" pitch, never dinged or worked on....it gave him about 5 mph extra and really didnt loose much as far as time to plane. We also weighed his boat on a portable truck scale....his boat weighs 3265lbs and thats with nobody in it, not much gear and about 20 gal of fuel...needless to say it is much heavier that he thought.

 

[walleyehed]

Re: 3 vs 4 blade props

OK, if you're showing 46-47MPH at that weight, I'd say you made a drastic improvement!<br />How did the rpm turn out???<br />Still get 5700 or so???<br />You just showed (and proved) to your self that no 2 props are alike even when valued the same pitch, and by testing, you verified that fact. Good job!<br />p.s. There are a few other items that can possibly "fine-tune" his set-up even farther if he'd like to play with it, but looks as though you're in the 15-16% slip ratio now, and for the HP/weight, that's not out of line by any means.