Thread: Jackplate Set Up

Hole shot is about venting and proper pitch. You want enough venting to spin the RPMs up to around 3500 RPMs while coming out of the hole. Think of it kinda like a torque converter on a truck. Not enough venting and it will bog, too much venting and it will spin up and not bite or take forever to bite. You would be well served trying a Mercury Trophy or Tempest on that rig. Either one will have the PVS holes which will allow you to play with the venting until you find just the right recipe for the correct hole shot. If you have a decent prop shop around they might have some you could test before buying and you can probably trade the ones you have as partial payment on something better suited for your rig.

Originally Posted by Slab Junkie

Hole shot is about venting and proper pitch. You want enough venting to spin the RPMs up to around 3500 RPMs while coming out of the hole. Think of it kinda like a torque converter on a truck. Not enough venting and it will bog, too much venting and it will spin up and not bite or take forever to bite. You would be well served trying a Mercury Trophy or Tempest on that rig. Either one will have the PVS holes which will allow you to play with the venting until you find just the right recipe for the correct hole shot. If you have a decent prop shop around they might have some you could test before buying and you can probably trade the ones you have as partial payment on something better suited for your rig.

Funny you say that, the 4 blade has some small holes in it to vent, wonder if I can get away with drilling them out some more and try it?

sent you a PM

no,,,don't drill the prop

Got it, thanks

You have to be real careful drilling out the holes. If you get them too big you will have to have them welded shut and start over. I did it on one once but I only increased the hole size a little. What is the prop doing now, bogging down or just spinning and not biting? If it is bogging down it might be too much pitch, or not enough venting. A 26p might be just a little stout for your set-up. Since it's a four blade it is going to turn about the same as a 27p three blade. The rule of thumb is if you add a blade you want to drop one degree of pitch to achieve the same RPMs as a comparable three blade. Can you get it out of the hole at all? If so what is the top RPM at wide open throttle? If it were me I would find a buddy or prop shop and borrow a 25p Trophy or 26p Tempest to try. You could also try a Powertech TR04 in 25p or a Turbo TXP 26p. Those are all good props for bass boat style hulls with aggressive rake and cup. I used to tinker around with props and jack plates quite a bit. I've ran quite a few of different brands and types. The trading post area on Bass Boat Central is a great place to find good deals on used props by the way. I'm not familiar with the prop you say you are running now so I can't say anything specific about it other than something ain't right with your set-up. Hope you get it worked out. If I can be of any assistance just shout.

Prop is bogging bad, like 2000 rpms wide open trying to get out of the hole. It will get out of the hole and once out runs good, lowered the motor to 5" below pad trying to help the porpoising to no avail. While I had it lower the 4 blade was unning 60 MPH at 5200 pms WOT.
Took it off and put the other one on, good hole shot no top end, too small.
Today I drill the vent holes in the 4 blade out some and raised the motor back to 3 3/4" below pad but the weather here was not favorable for a boat ride, wind already here and thunderstoms on the way.
Hopefully the additional venting will help the hole shot, tomorrow will tell I hope. Would like to stay with the 4 blade Mach if I can get a hole shot and then have it worked and some cup added to help the popoising in the midrange.

Sounds like too much pitch to start with. 5200 is not near enough RPM on the top end. You'll gain some RPM by not running it so deep but not enough to make that motor happy. You need less pitch. Try a different four blade in 24p or a three blade in 25p. Surely you can find one to borrow. Just make sure it has the right hub. One that is hubbed for a OMC won't work. Yamaha has the same spline count and configuration but is not set up for the tab washer that Mercury uses. So, find one from another Merc, beg and/or borrow but don't steal they will lock you up for that. I would rather run a motor right up near the rev limiter than bog one down. Lugging a motor down is not good for it at all.