Jack Plate Adjustment Question

[SeaDawg]

I'm installing a 6" manual jack plate, and I am wondering what adjustment height that I start with.<br /><br />I'm figuring on making my first run with the motor cavitation plate about 1" higher than the bottom of my boat.

 

[evin300]

Re: Jack Plate Adjustment Question

Sounds good to me. What is your boat motor combination? More importantly, do you have a prop that can run at elevated settings? This would be the other approx. 50% of the equation. Keep an eye on water pressure as you raise the engine.

 

[SeaDawg]

Re: Jack Plate Adjustment Question

Sorry for the delay in responding back, went to WV for the holiday. Now, back to getting the boat ready for spring (or a calm winter day).<br /><br />Evin300, I'm putting a 50 HP 4-stroke Mariner onto a 17 ft. Lowe Roughneck (MT1760). I'm replacing a 25 HP Honda, which would push the boat at about 20 mph with the factory prop.<br /><br />I have not bought a proper prop yet, most people are telling me to go with an aluminum cupped 14 pitch 3-blade. (The motor has a 12 pitch prop which I'm pretty sure will overrev if I open it up and trim it out. Do you have a prop recommendation?<br /><br />I'll mostly be using the boat in long narrow tidal creeks (very smooth water), so I would like to have as steep of a pitch as possible. I don't know if the motor will do it, but I'm hoping for 32 - 34 mph on calm water and no wind in my face.<br /><br />Total normal weight for everything (boat, motor, gas, battery, tackle, me, passenger, etc.) is about 1,500 lbs. max.<br /><br />Got some questions on water pressure. What pressure range should I be looking for with this engine? where is the proper place to install the water pressure fitting?

 

[evin300]

Re: Jack Plate Adjustment Question

SeaDawg, I dont know where to hook up the pressure gauge on your particular motor, A local dealer should be able to supply this info. <br /><br />I believe 15 psi at high speed is the minimum, but I would read your pressure at a low jack setting and then raise the motor as to not compromise your best readings.<br /><br />As far as props go, stainless is more efficient than aluminum, high rake - high cup stainless seems to perform well at elevated settings, If you want the most of everything out of this combination, then stainless is the only way to go. A cupped aluminum will work ok, it just depends on your goals. <br /><br />There are some good aftermarket stainless props out there that perform well, and are quite a bit cheaper than OEM. As far as pitch goes, you need to know the RPM and top speed with a normal load in your boat, and the highest jack setting. Then you can make a better choice. <br /><br />It always nice if you can borrow a prop from your dealer for trial purposes, many of the bigger ones will do this. Good Luck

 

[DP]

Re: Jack Plate Adjustment Question

SeaDawg<br /><br />I am running a Merc 50 hp 4 stk on my Whaler Montauk and loaded I weigh about the same as you. I have the cavitation plate set 1 1/2" above the boat bottom and am running the stock Merc 13 pitch aluminum prop. I can turn 5700 rpm and 33 mph. With a Vengence 13 pitch SS I can only get 5200 rpm and can't crack 30 mph. Try it with an aluminum prop befor wasting your money on SS, I don't feel like these small gear cases like the extra weight of the SS prop.<br />****

 

[evin300]

Re: Jack Plate Adjustment Question

As far as my experience goes, the only money wasted on a stainless prop, is buying the wrong pitch and style for your set-up, If memory serves me, in general, you want to drop 2" of pitch when going from aluminum to stainless.

 

[SeaDawg]

Re: Jack Plate Adjustment Question

Thanks BW and Evin. Actually, I've decided to take one step back further.<br /><br />I'm going to mount the motor with no jack plate and try her with the Mercury 12 pitch prop first, to set a baseline and get all the kinks out the motor. I drilled my motor mount holes so that the cavitation plate is exactly even with the hull bottom. A water pressure guage is going in now too.<br /><br />Then, I'll install the jackplate and and start playing with heights and props.<br /><br />I found that there is a local shop called the "Propeller Feller", and they loan props to try. Once I see my power and RPMs, I'll borrow an appropriate prop and test it out. <br /><br />Protected water is nearby the shop, so I can test several in one nice winter day.<br /><br />I do prefer stainless, because I have found that the extra weight lets it act like a flywheel and they really smooth out low speed trolling vibrations.<br /><br />At least it did on the last boat I put one on.<br /><br />If anyone else has a 17 ft. boat with a 50 HP motor, please post your prop style and pitch.<br /><br />Otherwize, I'll post what I end up going with, to help someone else in the future.<br /><br />Later.....

 

[evin300]

Re: Jack Plate Adjustment Question

Seadawg, I for one, certainly agree with your stategy.

 

[Richard RG]

Re: Jack Plate Adjustment Question

Your prop is the most important consideration. As you raise the cavitation plate above the bottom of the transom you will begin sucking air. What you need is a double cupped or surface piercing prop. A company in LA. makes a couple of good one. The name of the company is Power Tech. or Propulsion Technologies. Sorry I don't have a phone number for them.<br />Richard RG

 

[Richard RG]

Re: Jack Plate Adjustment Question

Add this note. I've taken off with my cavitation plate four inch above the top of my tunnell and run the boat with the plate six inches above the tunnel.<br />Richard RG