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Old 24-08-2016, 03:21 PM   #1
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Country: gibraltar/spain
Location: gibraltar
Boat name: sexy girl
Boat make: phantom 25/ring ranger 25
Engines: evinrude 250 ho
Cruising area: costa del sol

Join Date: Feb 2015
Location: gibraltar
Posts: 84
jackplate equation ?????

hi guys

i own a ring ranger 25 which is a front heavyboat

i have mounted a single outboard instead of dual outboard set up like many come with.

with the weight of 2 motors the boat would have a better balance but where i live the authoritys don't permit it.

now i have mounted a evinrude 250 ho ..25" gearbox

the actual transom of thew boat measures 28 "

the boat handles well but i think i need to lower engine 1 to 3 inch more a when i cruise in big waves she's want to nose dive but at w.o.t i have no problem..she just fly over them lol

another downside i have is motor steering touches transom when i want to tilt up in mooring
and leaves some of the motor in water which is not ideal.


I'm thinking of putting a 6" inch jackplate on the back of ring

what is the exact "equation" of each of every
1" of offset?

what difference will a 6 " backplate make and how much lower will it be in the water?

plz plz plz i need some serious advice ......

thanks guys
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Old 24-08-2016, 05:59 PM   #2
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Country: UK
Location: Coventry (but from Lee on Solent)
Occupation: Sales Director
Interests: My Boat of course
Boat make: Extreme 21
Engines: Merc V8
Cruising area: Solent

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Location: Coventry (but from Lee on Solent)
Posts: 578
Where does the gearbox bullet sit in relation to bottom of hull? Maybe you need to go up and try different prop and trim.

Typical is 1 inch up for every 12 inch setback according to merc at least.
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Old 24-08-2016, 09:35 PM   #3
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Country: gibraltar/spain
Location: gibraltar
Boat name: sexy girl
Boat make: phantom 25/ring ranger 25
Engines: evinrude 250 ho
Cruising area: costa del sol

Join Date: Feb 2015
Location: gibraltar
Posts: 84
Cool

hi doc

so if if have a 6" setback backplate i will only gain 1\2 " lower leg in the water?
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Old 24-08-2016, 09:41 PM   #4
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Country: gibraltar/spain
Location: gibraltar
Boat name: sexy girl
Boat make: phantom 25/ring ranger 25
Engines: evinrude 250 ho
Cruising area: costa del sol

Join Date: Feb 2015
Location: gibraltar
Posts: 84
so i got a 28 inch transom ,,,and a 25 inch gearbox.....im trying to "lower "between 1 to 3 inches of more leg in the water when there is chop without cutting the transom down ....thats why i asked about the equation of the setback as I'm not sure if u can lower the jackplate ..only higher it i think.........also the jackplate i will use is gonna be hydraulic from sea star solutions.....boats in water so i can't check exactly where bullets sits still...any other tips or info?
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Old 24-08-2016, 09:42 PM   #5
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Country: england
Location: southampton
Occupation: engineer
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Boat make: scorpion 8.1
Engines: 250HO
Cruising area: solent

Join Date: Mar 2004
Location: southampton
Posts: 1,334
I have put a 6 inch jack plate on mine and the steering still impacts transom. 8-10" I reckon to get the steering to not touch transom. Mine only touches in last 1/4 ish so I am going to live with it
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Old 24-08-2016, 09:45 PM   #6
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Country: gibraltar/spain
Location: gibraltar
Boat name: sexy girl
Boat make: phantom 25/ring ranger 25
Engines: evinrude 250 ho
Cruising area: costa del sol

Join Date: Feb 2015
Location: gibraltar
Posts: 84
hi glen what make is your jack plate ?

seastar solution say there jackplate go up 6 inches?

do u have any pics?
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Old 25-08-2016, 08:15 AM   #7
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Location: IOW
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My jack plate has a 8" lift and have different set backs of your choice, rated to 300hp and made by Detwiller which i think is part of seastar now!
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Old 25-08-2016, 10:24 PM   #8
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Country: england
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Sorry I was wrong mine is 5.5". But with this clearance it still will hit when tilted.
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