trying to get my combo dialed in and think I am back to the prop

[ditchen]

Have a 1548 modified V tinny JON. Running a 1980 50hp Johnson on a jack plate 6" set back with a omc 11 1/4x21 SST prop. total weight 700lbs.

The best results is with ventilation plate aprox 3 3/4 above bottom, if I lower the motor it get a wicked porpoising when starting to trim it up from all the way in. I raise the motor (big mph gain) and the proposing will go away and I can trim it up a little over half way and then slipping, ventilation will result (not cavitation) water pressure still in the safe zone. It will start to over rev and need to lower the throttle.

I tried to redistribute the wait, no difference.

Will a bigger dia prop help, more cupping or more of a surface prop?

 

[NHGuy]

Re: trying to get my combo dialed in and think I am back to the prop

So can you run it 3.75" above bottom and trim a bit below halfway for max speed? What are your rpms at this setup? Do you get desired WOT RPMs? Or can it run a little less jack with more trim? I hear jack plates and porpoising are an "experiment til it's right" kind of thing. Sounds like it!

 

[ditchen]

Re: trying to get my combo dialed in and think I am back to the prop

RPM is on the high side. If I lower the motor is when I get the porpoising with trying to trim. With the motor at the current height I can trim but I get the ventilation.
I was going to try a larger diameter and more cupping. Was trying to make a decision on the manufacturer. With this small gear case it limits my options

 

[NHGuy]

Re: trying to get my combo dialed in and think I am back to the prop

Would it be worth a try without the jack plate?

 

[ditchen]

Re: trying to get my combo dialed in and think I am back to the prop

yes, started out without. Jack was added later. jack plate made a big improvement.