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Old 12-29-2005, 07:25 PM
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Default Jack Plate?

I have a 21ft center console 2005 Sea Fox with a 2005 150 Mercury. I was thinking of putting a jack plate on it to get the motor back off the boat a little, and also maybe get the boat on plane a little quicker (at a lower speed). It doesnt seem to plane off until about 30 mph. I would like it to plain at about 25mph, and make the bow ride a little lower (seems to ride up all the time no matter where you have the motor trimmed at). Any one have any suggestions?
Thanks, CV
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Old 12-29-2005, 10:06 PM
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Default Re: Jack Plate?

Your hull should plane a a lot lower speed than 25; I would say closer to 10-14 mph. Sounds like she is set up wrong, and/or there is too much weight in the stern. And mounting the motor further back will only accentuate this problem as you leverage the bow up higher.

I would get this looked at before spending more $$ on a jp. Motor height, weight distribution, prop type, trim tabs, doel fin and finally a jack plate would be my order of execution in trouble shooting this problem.

A simple permanent height adjustment may do wonders to start.
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Old 12-29-2005, 10:22 PM
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Default RE: Jack Plate?

I agree with Bullshipper - the rear of the boat is the crucial hull region for initiating planing - dynamic lift is lowest there, and yet it typically carries the most weight.

Try to increase lift at the rear - e.g., by using motor trim or trim tabs... ; or reduce downforce there - e.g., by shifting weight forward. Increasing lift or decreasing downforce at the rear of course do the same thing - they will raise the stern out of the water.
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Old 12-29-2005, 10:37 PM
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Default RE: Jack Plate?

I have lenco trim tabs on it, but when I use them to lower the bow it kills the speed. I usually leave them all the way picked up. The boat rides pretty good, I just wanted it to plane a little quicker. The weight seems to be distributed OK. The battery is in the rear, but I only have 1 (for now). Someone told me with a jack plate I could trim the motor down lower to start with, and get up on plane quicker at a lower speed.
CV
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Old 12-29-2005, 10:47 PM
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Default RE: Jack Plate?

Quote:
cvnobles - 12/29/2005 11:37 PM

I have lenco trim tabs on it, but when I use them to lower the bow it kills the speed. I usually leave them all the way picked up. The boat rides pretty good, I just wanted it to plane a little quicker. The weight seems to be distributed OK. The battery is in the rear, but I only have 1 (for now). Someone told me with a jack plate I could trim the motor down lower to start with, and get up on plane quicker at a lower speed.
CV
Hmmm - ideally there should be some intermediate setting you can tune them to where the increased lift of the trim tabs will beat their increased drag. Trimming the motor lower than it can go now would be another way to increase lift at the stern. Of course, even if you can do that, you will necessarily also lose some forward speed, as you are changing the thrust angle, directing more of it up, and so less of it forward - as with the trim tabs, a useful compromise may result though. I have never had a jack plate - but I have heard that they don't affect the range of motor trim?
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Old 12-29-2005, 11:25 PM
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Default Re: Jack Plate?

those hulls ride bow proud no matter what you do.
put the tabs and engine trim all the way down to get on plane, and bring them up once there, and "play" with the tabs and motor trim together to see if you can get a slower plane speed.
add a little tab down, and a little engine trim up.
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Old 12-30-2005, 06:07 AM
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Default Re: Jack Plate?

You could consider a prop change, perhaps to a 4 blade, to assist with getting up on plane and staying there at slower speeds.
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Old 12-30-2005, 07:09 AM
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Default Re: Jack Plate?

How low is the motor mounted on the transom? The motor should be roughly an inch to an inch and a half above the lowest portion of the V of the hull closest to the motor. Quite often the manufacturers will mount the motor on the highest(top) holes of the motor bracket for simplicity. I had to raise my motor up on the transom to acheive better results because my boat felt like it was squatting in the water while at moderate speeds. It now shoots up on plane much sooner and I get more speed out of it at lower rpm's. Using the trim makes it even better.
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Old 12-30-2005, 08:14 AM
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Default RE: Jack Plate?

IMO, the 150 HP may be underpowered, 75% of maximum.I would talk with the manufacturer. I also agree that a jack plate will not solve the problem. What does the dealer say? Did you take a sea trial? What is max RPM at WOT? I'll bet the dealer took you for a test ride with 5 gallonsin the tank and just you aboard? Good luck. Welcome aboard.
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Old 12-30-2005, 08:30 AM
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Default Re: Jack Plate?

Not disagreeing with anyone here but a jack plate will improve a boats handling characteristics. Add the right prop and it's difficult to beat! His solution may be as simple as weight distribution.
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Old 12-30-2005, 09:23 AM
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Default RE: Jack Plate?

I am going to check the motor height today, and also prop size, but I think it is proped about right I can get about 5000rpm at WOT. I has also heard someone else say that the Sea Fox boats ride high in the bow. The boat probably does need the 200Hp motor (max rating), but the dealer had it as a package, and I got a real good deal on the boat the way it was already rigged. I have a stainless steel 3 blade prop will a 4 blade one help any?
Thanks for the welcome & all the info!!
CV
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Old 12-30-2005, 02:49 PM
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Default Re: Jack Plate?

My 4 blade prop has been my work horse. It runs the best, but just picking up any 4 blade prop may not work. Running different props is the only way to find the one that works best for you.
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Old 12-30-2005, 03:06 PM
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Default RE: Jack Plate?

I just checked mine. I have a 17 pitch 3 blade ss. I also looked at the height of my motor, and it looked about right (looks like the boat company or the dealer picked it up 1 hole before at some point). Sounds like prop trial and error could get expensive.
Thanks again, CV
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Old 12-30-2005, 03:56 PM
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Default Re: Jack Plate?

How much does the boat weigh? I have a 21' (see sig below). boat weighs 1425# w/o motor or fuel. My motor is a yam carb 150 add that, half tank of fuel=25 gal. me and average tackle load and I can plane in about the lenght of my boat and top out gps at 49 mph @ 5800 rpm's. My motor is in the bolt hole second down from the top.
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Old 12-30-2005, 04:33 PM
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Default Re: Jack Plate?

Sounds like your overpropped with too much pitch if you only get 5000 rpms at wot. This will slow your up on plane time and overall speed.

If the motor is too low, this will lengthen your up on plane time, and will knock down your top speed with more of the lower unit dragging in the water.

If your trim tabs have to be inclined so much that they cut your speed, you have a ways to go before thinking about a jp, as these are mostly used for real fast boats or if you fish in very shallow water.
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Old 12-31-2005, 05:39 AM
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Default Re: Jack Plate?

Try going up one more hole on the motor. I'll bet that will help: less drag and better hole shot! I believe that you should be getting 5400-5600 rpm's. For me, raising the motor up increased my rpm's 300-400 rpm's, gave me much better hole shot and better top end speed. You may want to try that before you start playing around with the props. BTW, any competent dealer shouldallow you to test props for a minimal, if none, fee.
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Old 12-31-2005, 02:12 PM
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Default Re: Jack Plate?

A 4 blade prop helped me plane at 750 rpm less while only taking away 3mph at WOT. Better hole shot also.

I recently added a Bob's manual jackplate for $210 and moved the motor back 5 inches. Raised it about 2 inches and am very pleased. Also picked up about 500 rpm WOT with the same prop after adding the jackplate.
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Old 12-31-2005, 10:31 PM
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Default Re: Jack Plate?

I would not buy a manual jack plate if you still have more holes on your OEM motor mount.
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Old 01-01-2006, 04:08 PM
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Default RE: Jack Plate?

Thanks for all of the input everyone. My motor is in the second hole from the top, so I still have a lot of adjustment that I can pick the motor up. (I will probably try that first). If that doesnt do the trick I may try a smaller pitched prop to get my RPMs up at WOT.

Rod H, it sounds like you & I have a simular boat & motor setup, what did the jack plate do for your hole shot, and the top end speed?
Thanks again, CV
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Old 01-02-2006, 12:33 AM
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Default Re: Jack Plate?

At the Mercury website. Checked the prop selector and for a Merc 150 Opti is was suggested that a 19 pitch prop be used. WOT specs are 5250-5750 range. You only getting 5000 at WOT IMO would effect your minimum playing speed. I would look into prop selection and better utilization of trim tabs and trim.
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