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  SPORT 15, 90-HP, Powered Jack Plate

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Author Topic:   SPORT 15, 90-HP, Powered Jack Plate
mdono posted 04-03-2014 06:57 AM ET (US)   Profile for mdono   Send Email to mdono  
In setting up a Sport15 with power provided by a Mercury 90-HP carburetor engines weighting 300-lbs, the steering is to be hydraulic, probably Seastar. I am going to install a powered jack plate, and am in process of selecting a unit with the best combination of performance, weight (very important), and cost. All the powered jack plates I have looked at have similar up and down travel and can be adjusted on the transom so all equal enough in that respect. The lightest powered jack plate for my needs has 5-1/2-inch setback as opposed to heavier powered jack plates with 4-inch set back.

How will a powered jack plate weighing 45-lbs with 5-1/2-inch setback perform as opposed to a 61-lbs unit with 4-inch setback?

Keep in mind the 300-lbs beast is levered further out with the lighter jack plate. The fuel tank to be mounted under front thwart seat. The battery possibly under console. [Your] thoughts and or experiences [will be] welcomed.



bloller posted 04-03-2014 08:44 AM ET (US)     Profile for bloller  Send Email to bloller     
I don't see the need for a jack plate on a 15-footer if your putting on a 90-HP. More than enough performance with a 90-HP. Just get the motor height right bolting it directly tithe transom.
Teak Oil posted 04-03-2014 08:55 AM ET (US)     Profile for Teak Oil  Send Email to Teak Oil     
I had a 6-inch set back jack plate on a Montauk and it helped, since that motor could not be raised on the transom in the usual fashion. I would go with a 4-inch set back; if you go too far back the boat will tend to porpoise.

I agree, unless you plan to run the boat on shallow flats the gains will probably not justify the expense. With the right prop and engine height you will get 50-MPH with a 90-HP Mercury directly bolted on the transom.

bloller posted 04-03-2014 09:18 AM ET (US)     Profile for bloller  Send Email to bloller     
If you must do a jack plate than I would reccomend the Vance manual jack plate with only 3-inch setback. It is a lot lighter
dgoodhue posted 04-04-2014 07:10 AM ET (US)     Profile for dgoodhue  Send Email to dgoodhue     
I disagree with a jackplate being a waste on 15-foot Boston Whaler with 90-HP. Someone who is putting a 90 on a 15-foot Boston Whaler wants to go fast. Jack plates are worth easily 2- to 3-MPH. My 15-footer with a 70-HP two-stroke-power-cycle engine and 5-inch set back can do 48-MPH, but I have it setup to do 47-MPH. Why put on a 90 hp motor and only do 49 to maybe 50-MPH with the engine on the transom?

I, personally would think about modifying the hull to cut down on chine walking if I were going to use a 90-HP engine. If it were me, I would probably try the 5.5-inch set back, if you thought it was a quality piece. A few years ago someone here put a 90-HP E-TEC, 320-lbs, and used a hydraulic jackplate. You should be OK on weight. The weight isn't going to be perfect, meaning I would expect you take some water over the transom if you slow down fast. I would play around with the weight distribution of moving the battery and fuel tank. I notice in my Boston Whaler boat that more rearward weight cuts down the chine walking, but my motor only weights 260-lbs.

My boat has manual jackplate. The reason I have my boat is setup to run 47 instead of 48-MPH: the engine height require to do 48-MPH and not uncontrollably chine walk drives like crap at lower speeds. I can definitely see the advantages of using a hydraulic jack plates.

sosmerc posted 04-04-2014 10:06 AM ET (US)     Profile for sosmerc  Send Email to sosmerc     
I wonder which 90hp Mercury two-stroke is going to be used? The 6-cylinder or 3-cylinder? Big difference between the two, but, either way, it's going to be fast and fun. And a challenge to drive!
mdono posted 04-04-2014 04:20 PM ET (US)     Profile for mdono  Send Email to mdono     
Thanks for all the knowledgeable replies.

I might bolt-on straight to the transom. If I feel like there is a need, I can later add a jackplate. (I probably will) Need to throw money at the interior right now anyway.

The motor is a 1998, 3-cylinder with 182 hours that really looks good. Prevoius owner went to four-stroke for trolling. The dealer that swapped out the motors put my 90-HP on the four-stroke engine's shipping pallet "because it would be a shame to put a motor looking this good on her side".

Almost can't wait to complete the rig. I'll let you know how it turns out. Thanks again.


sosmerc posted 04-05-2014 12:24 AM ET (US)     Profile for sosmerc  Send Email to sosmerc     
You can mount that engine quite high on the transom as long as you are using a good stainless performance prop like the Laser II, HighFive, Trophy Sport, Michigan Rapture, etc. That lower unit design has a very large anti-cavitation plate and likes to be mounted high. The choice of propeller will be the factor that limits engine height.
jharrell posted 04-05-2014 07:26 AM ET (US)     Profile for jharrell    
Bob's ultra-light 4-inch hydraulic jack plate is only 33-lbs, but only rated to 115-HP---fine for this application. You will have to find a place for the external pump, which is part of the reason for its light weight: 4-Setback-Standard-Series-LIGHTWEIGHT-Jack-Plate-115hp-100-104000.htm

I went with the 45-lbs CMC jackplate on my Montauk only because the pump is self contained. I have been happy with it, but doing it over I might try and find room for the pump in my console and go with the lighter Bob's.

Teak Oil posted 04-05-2014 09:01 AM ET (US)     Profile for Teak Oil  Send Email to Teak Oil     
If you bolt to the transom, try starting four holes up, or one set from as high as it will go.

Get a good prop like an Enertia or similar

Tom W Clark posted 04-08-2014 10:28 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
The Enertia is not made for intermediate size gearcases. Try a Laser II or Stiletto Advantage.
Tom W Clark posted 04-09-2014 12:30 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
The ATLAS Micro Jacker weighs only 25 pounds and has self-contained hydraulics. Hydraulic-Jack-Plates/ATLAS-hydraulic-jack-plates/Atlas-Micro-Jacker

mdono posted 08-12-2015 04:32 PM ET (US)     Profile for mdono  Send Email to mdono     
With Atlas Micro-Jacker, a Lazer II 22-pitch, and a plastic fuel tank plastic mounted under front thwart seat, [after] an hour on a Chesapeake tributary, [the boat] seems fast to me, and I will dial it in [next] week and let you know how it works out. Thanks for your input, which was much appreciated.

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