Bad hole shot, overrev WOT...

[shep247]

1991 Four Winns Horizon
4.3L OMC
SEI Mercruiser Alpha 1 Gen II Outdrive with 1.81 ratio (with SEI conversion kit)
14.5 x 18 4-blade prop

On the first test run of my OMC/Mercruiser conversion from SEI, I found that my hole shot was very slow, with the boat practically standing straight up in the process, porpoised anywhere below 28-30 mph, and at WOT the RPMs were still creeping up at 5300 (suggested for OMC 4.3 is 4500).

The first 2 symptoms tell me that I can't get the trim low enough, and I'm working that issue now, but I thought the 3rd symptom meant that I had too low of a pitch on my prop. The guy at the prop shop said that the trim could be the problem for all 3 of the symptoms, and the prop could be cavitating, causing my rpms to get too high. Is that right? The ride seemed geta lot smoother at around 30 mph, and the porpoising stopped, so I thought that meant the trim was about right for that speed. I don't have a hydrofoil or anything, but from what I read in other posts, I shouldn't need it, right?

I plan to fix the trim issue, and get the trim lower in time to try it out this weekend. Do you guys have any other suggestions of what I might look for?

 

[steelespike]

Re: Bad hole shot, overrev WOT...

I wouldn't make any decisions until you get the trim squared away.
It could very well solve your problems. There is a 20' and 18' Horizon
I'll assume yours is an 18.My feeling is you may need a little more prop.
The 4 blade should help your hole shot and resist venting(cavitation)

 

[shep247]

Re: Bad hole shot, overrev WOT...

I'm actually wondering how much I should have to trim that drive in. I can't really trust the gauge because its a conversion, and the gauge wasn't made to read this particular drive. Does anyone know at about what angle the prop shaft should be in relation to the bottom of the boat trimmed all the way down?

(and sorry for not specifying. Its an 18 footer)

 

[mlpaskett]

Re: Bad hole shot, overrev WOT...

Don't worry about what the trim gauge says. Trim the drive all the way down when starting from stopped. You can usually hear when the drive is all the way down when the whine of the hydraulic pump changes pitch. When boat is on plane you can adjust trim up until peak performance is reached. Then you can analyze prop performance.

--Mark

 

[marcortez]

Re: Bad hole shot, overrev WOT...

When you hit the throttle out of the hole, look back at the prop wash.
If you see a "tall" roostertail propwash, your not trimmed "in".

The prop is pointing upwards towards the surface of the water creating this roostertail affect.
Ideally, the prop should have a slight "down" angle into the water and not upwards.

Think of it as pushing water "up" vs pushing water "down"
"up breaks the surface of the water behind you, whereas "down" leaves a clean and flat propwash.

 

[ENSIGN]

Re: Bad hole shot, overrev WOT...

You can't trim the drive down to far for a hole shot.When you learn how to drive a boat you won't need that gauge anymore

 

[TilliamWe]

Re: Bad hole shot, overrev WOT...

I'm with the others, either fix the tilt/trim system so that the drive goes down all the way, or hold the button until the drive goes down all the way. With the outdrive trimmed up, you are creating ALL these problems. The poor holeshot and the over rev are all a function of the improper trim angle on the drive.

 

[bkwapisz]

Re: Bad hole shot, overrev WOT...

I'm with the others, either fix the tilt/trim system so that the drive goes down all the way, or hold the button until the drive goes down all the way. With the outdrive trimmed up, you are creating ALL these problems. The poor holeshot and the over rev are all a function of the improper trim angle on the drive.

Totally agree with this. When I first got my SeaRay I thought I needed new props till someone told me I had to trim the drives all the way down to get out of the hole. Once I learned how to properly launch all was set. And I had the same issues, not going anywhere, boat up in the air, engines screaming, etc.

Porpoising I understand is the drives trimmed up too high. I can actually induce this on my boat with the trims up too high. Like the other posters said, try trimming it all the way down and then see what happens. Once you plane out trim them up and back off the throttles as RPM's will come up as you trim up.

Good luck!