School me on Jack Plates please

[Wilfong9]

I haven't been able to find a thread that explains advantages and disadvantages of different size jackplates. I have a descent understanding of hydraulic vs manual but 6" vs 12" I'm not so sure.

Currently have a 12" rapid jack on a 2001 Triton Tr-20 and 225 Merc EFI. The boat runs pretty well (mid 70s in the winter) but the bow is tough to elevate in the summer.eveb with a balanced and cup added Croxton 26 Tempest.

Well one of the bolts on the Rapid Jack broke and I can't get it out without mangling the plate so I'll be in the market for a new one now. Just needed an education on what the advantages of different setbacks do for my setup. Thanks!

[gehol]

Jack plate has two main purposes. 1. Allow easy way to change motor height. 2. Allows the prop to be moved back to better water. The higher you run the motor the farther back you have to be to get good water. However, there is trade off. As you move the motor back you make the effective length of the boat longer making it harder for the prop to carry the bow.
Your boat likely runs the prop 3-4 inches below pad. Generally speaking you could run less set back than perhaps a 20 foot Bullet that may run the prop 1.5 inches above the pad.
You likely do not need more than 12 inches and my personal opinion is a little less than 12 might be better. Something like 8-10 inches perhaps would be better.

Edit: I am adding a BBC link. The link shows two videos that Hagen made of his boat. He is running 1.5 inches above pad. Notice if he used any less set back he likely would not get enough water in his low water pick up to cool the engine and likely too much of the prop would be out of the water. Now imagine he run the motor 4 inches lower you can see he could run the motor closer to the transom, less set back, and still be plenty deep for the prop to be in the water.

http://www.bbcboards.net/showthread.php?t=916941

[gehol]

I will add if you are getting mid 70's GPS with fishing load I would not change the set up one bit.

[Bassmeister]

I will add if you are getting mid 70's GPS with fishing load I would not change the set up one bit.

[greenfshrmn]

Gehol, I had always assumed a jack plate (or set back plate) would make it easier to lift the bow....I undertstand that it is making the entire boat longer, but isn't the motor acting like a lever with the pivot point being the pad of the boat?

[1Holeshot]

Gehol, I had always assumed a jack plate (or set back plate) would make it easier to lift the bow....I undertstand that it is making the entire boat longer, but isn't the motor acting like a lever with the pivot point being the pad of the boat?

^
This is my understanding. Somewhat like a see saw with one person at the very end and the opposite person sitting somewhat forward. With equal weight the person sitting closer to the end will lift the person sitting closer to the pivot point.

[gehol]

Common misconception, pushing the back of the boat down into the water is not the same as lifting the boat out of the water. Place a 2x4 on a flat surface. Pinch the sides about a foot from the end and pick up the long end (bow) keeping the short end (stern) on the table. Now move back to the end and do it again. It will be harder to pick it up. Boat lift is like that 2x4, you want to lift it off the table with the back end still on the table.

[Wilfong9]

Thanks for the responses! Very insightful. And that video, I would have never imagined so much of the cone was out of the water. I can't really see how he is getting any water pressure.

Two things I did forget to mention.. Since day one my boat has had zero rooster, which has always bewildered me. I even added trim extenders (which I hate) but did pick up noticeable speed doing so becuase they helped get the bow up considerably. This alone has been what made me question the jack plate. Second thing was I just added a second power pole, extra AGM battery (88 lbs) and new 112 Fortrex on the front. So my average very light load of fishing has recently put on a healthy few pounds, the Fortrex on the front being the worst culprit I think. I've dropped 3 mph in a week with these additions and now really struggle to get the bow up.

I do run close to 3" below pad, maybe slightly higher and get good water pressure. When I raised the motor up to the next setting there was no change but it actually felt like I could notice a little more prop slip so I dropped it back down and called it good enough for me. The power pole mounts I guess actually add even another inch of setback as they are mounted between the motor and jackplate.

[gehol]

Ya, the sportsmaster is designed to run high. The water pick up is on bottom of gear case a few inches back from the point of the case. Point being, as you can see, set back is partially a function of lower unit height. If Hagen had any less set back or motor higher, water pressure could be a problem. OP has to consider this also since his water intake is in a different place.
As far as your trim that is odd. Generally one trims for best speed. Hard to believe it takes that much trim. In my boat ( same as Hagen's in the video) I have 2 degree shims to give more negative trim allowing better take off. Best speed for me is still in the 80% of available trim, of course two different boats. Anyway, your speed shows the set up is close.