Trouble getting on plane

[95cajun]

I have a 95 Cajun 19.5 foot fish and ski with a 115 hp evinrude with a 3 blade 12.75 dia x 21 pitch prop. Boat is rated for 195 hp I believe it originally had a 150 fast strike v6 engine.

Problem: I gun it out of the hole and it struggles (motor trimmed in) start trimming out and on slick water I can hit the sweet spot and the rpm's will start to rise up to 3600 and the back of the boat will come up and the nose will fall then I will continue trimming the motor up then the rpm's will either run away or start to fall off. I call it cavitation but some call it ventalation, I don't care I just know it falls flat and I have to back out of it and jump back into it. Sometimes it feels like a motor performance issue but it never comes up on plane without me trimming up and down the feathering the throttle to keep the prop grabbing water. The motor is a little high, about 3 inches above the bottom of the hull but the bottom of the hull end about a foot before the transom. I have tried the doel fin the motor is all the way down. I don't know the top speed but I can achieve 4900 to 5300 rpm's depending on motor tilt, but at max rpm it is shooting a 6 to 10 foot roster tail so it seems like i'm spinning my wheels so to speak. I will try to remember the gps next time. I have been doing nothing but fishing but when it's right we will try tubing agian.

It seems as if my blades on my prop are narrow but they do have a cup. Does it sound like a 4 blade prop would help my hole shot (or lack ther of) and give me a decent top speed? It feels like I'm moving across the water at 40 mph or so, but I can't bring the front of the boat up to keep from getting pounded in rough water.

Please give me your recomendations.

 

[Reel Kahuna]

Re: Trouble getting on plane

Sounds like a Jack Plate would help you quite a bit.

 

[steelespike]

Re: Trouble getting on plane

Without getting to crazy about details I think a 19" 4 blade Like a Solas Amita
should solve your problems.Better hole shot less ventilation.Lose the fin.
If you still need more help smart tabs are a better solution.

 

[95cajun]

Re: Trouble getting on plane

Smart tabs....is that like the perma trim plate? A 4 blade with a 19 pitch right? Thank you for y'alls input. I'm checking if I can do the jack plate, I found one with a 10 inch back set but it seems like it's too much. I have to make sure it's not going to put the steering cable in a bind.

 

[95cajun]

Re: Trouble getting on plane

does this picture make sense? this notched transom is what I have. Taking a yard stick and putting it even with the bottom of the boat I measure 3 inches. if this setup is correct the ventalation problem is with the prop and not the height. I really want to try a 19 pitch prop before I buy. I need a decent hole shot and good top speed. Does the little holes drilled help? I see some listed for sale with these options

 

[95cajun]

Re: Trouble getting on plane

Okay put new spark plugs in the motor. Help a little. I believe that a 19" prop would pay dividends on this motor. Still slow to plane, once it planes I can get 36 mph (gps) about 52 to 5500 rpm can trim the motor up to increase rpm's but not speed. I lowered the throttle a little to about 34 mph then trimmed the motor down and actuall picked up speed back to 36 mph at 4600 rpm's. This tells me I'm loosing my bite on the water and not gaining any more speed, do you think a 19" is enough?

 

[steelespike]

Re: Trouble getting on plane

These things aren't carved in stone.Your present prop
has issues a 4 blade will eliminate most or all of them and I think could add 2 or 300
rpm.It will also allow you to run at maximum height possibly adding some rpm there.
Thats real rpm not from slip.
Slip numbers should be lots better.

 

[95cajun]

Re: Trouble getting on plane

Thanks I'm learning more and more every day. I am thinking for a 4 blade as you suggested probably in aluminum for financial reasons. DO you think the 19 is enough?

 

[northernmerc]

Re: Trouble getting on plane

Based on that diagram, it looks as if the prop is not far enough into the water. Is it possible that you have a short shaft motor on a boat that requires a long shaft motor? What is the height of the transom - from the lowest point to where the motor clamps on? And what does your motor measure at?

 

[steelespike]

Re: Trouble getting on plane

Thanks I'm learning more and more every day. I am thinking for a 4 blade as you suggested probably in aluminum for financial reasons. DO you think the 19 is enough?

If I was my boat I'd be getting a Solas amita 19" 4 blade.I'm not a real expert on prop selection but I have seen many excellent results with the solas 4 blade.
Especially when dealing with problems like yours.Generally all 4 blade have similar results
but the Solas seems to be more predictable. Its a more consertive solution than some other props but really effective. I also like the Turning point Hustler but their results seem to be all over the place.

 

[Reel Kahuna]

Re: Trouble getting on plane

...I'd be getting a Solas amita 19" 4 blade....

I have a 20' Reinell Cuddy Hardtop. I bought a used Yami 150hp that had a 14-1/2 x 20 3 blade SS prop. At WOT the tach registered 3K rpm. I bought a 14.8 x 17 Solas Aluminum 3 blade prop which brought my WOT to 4900-5100 rpm but this Yami should be turning 5500-5600 WOT so I exchanged the prop for a 15 x 15. I'll try that out either tomorrow or Wedsnday.
My point is that one has to try different prop pitch to achieve the factory's WOT specific to the motor.

 

[95cajun]

Re: Trouble getting on plane

I forgot to tell u that I took a body hammer, a dolly and a file. I worked the blades on the prop until I could feel the blades smooth. I know it could still be out of ballance but i figured it couldn't hurt. I took the fin off the motor is mounted all the way down. I went to a more secluded part of the lake where the water is much calmer. I never vented the motor! it still took days to get up on plane but jacking with the tilt I could get it there. I have ordered the 4 blade 19 pitch prop. it will be here Friday. cant wait to try it. Im not ignoring the post about the long shaft motor but impretty sure that the boat is supposed to have the shorter shaft. I sure hope that the 19 is enough pitch but its too late now bought and paid for.

 

[95cajun]

Re: Trouble getting on plane

I have a 20' Reinell Cuddy Hardtop. I bought a used Yami 150hp that had a 14-1/2 x 20 3 blade SS prop. At WOT the tach registered 3K rpm. I bought a 14.8 x 17 Solas Aluminum 3 blade prop which brought my WOT to 4900-5100 rpm but this Yami should be turning 5500-5600 WOT so I exchanged the prop for a 15 x 15. I'll try that out either tomorrow or Wedsnday.
My point is that one has to try different prop pitch to achieve the factory's WOT specific to the motor.

wow this is a big change in pitch.....what motor did you pull off when you put the 150 on? what pitch was you old prop. are you adjusting the trim of the motor? did you loose alot of speed?

 

[Reel Kahuna]

Re: Trouble getting on plane

wow this is a big change in pitch.....what motor did you pull off when you put the 150 on? what pitch was you old prop. are you adjusting the trim of the motor? did you loose alot of speed?

LOL..I converted the boat from 4.3L I/O to the Yami 150hp that was on a 17' Bass boat. My conversion included a 25" set back Gil Bracket with a power CMC jack plate. Trim and jack plate both trimmed to the achieve the optimum speed. When shopping for a prop, both mechanic who serviced the motor and the prop shop's owner suggested either a 17 to start and may need a 15...both were correct.

 

[95cajun]

Re: Trouble getting on plane

I forget what the horsepower is on a 4.3 but it seems like it's in the 175 range. So tell me...speed about the same. The boat must be alot lighter.

 

[Reel Kahuna]

Re: Trouble getting on plane

...So tell me...speed about the same. The boat must be alot lighter.

When the 4.5L was in, I didn't have my GPS installed so the dash speedo read 36 mph. Yesterday with the 15 x 15 prop on the Yami, the dash speedo registered 42 mph at 5600 rpm WOT. It gets up on plane quick, I'm quite pleased with the performance.

 

[95cajun]

Re: Trouble getting on plane

Well the new prop is installed! Hope it is enough pitch! I can't wait to try it. I want it to get up out of the water and hopfully give me close to 40 mph. Reel, I'm glad your conversion worked out. That's a bold move, you must like that boat.

 

[skibrain]

Re: Trouble getting on plane

I don't know how this compares on a boat with a notched transom, but a fairly standard mounting height for an outboard is so the cavitation plate above the motor aligns with the bottom of the hull. If you had a standard hull, you motor would appear to be mounted 3" above this standard mount height.

That would yield a crazy, unacceptable amount of ventilation on ANY boat. you have multiple holes in your motor bracket correct? Do you have room to LOWER the height that your motor is mounted on the transom? I would start there.

 

[95cajun]

Re: Trouble getting on plane

Well I have an update...it comes up on plane alot quicker...with the motor tilted all the way in. Then I only get about 4500 rpm's about 34 mph tilting it up very slowly I can get up to 37 mph around 5000. It begins to ventilate if you tilt it up much more. Ski, I have lowered the motor as far as I can. I might have to get the chapperal type brackets and drop it 2-3inches. I'm afraid to push it back much because of the steering cable. I let my son drive so I could look at the motor while running at WOT. The cavitation plate is right at the top of the water. I know the motor is under sized. Could I expect more or am I about right for 115 hp?