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Towbarman

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Reply with quote  #1 
Hi
We want to fit a jack plate to our small 15ft speed boat around 500 kilos plus etec 90hp
Boat speed is 35knots @ 5000rpm
what does the set back distance, altar between a 4inch 6 inch or 12inch apart from the attack angle off the nose with the trim being faster
And the deeper water is the further it's set back so engine can be higher ?in cleaner water
Need it for
River shallows and sand bank shifts
RandyLinden

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Reply with quote  #2 
Hi
I don't know if there is a formula or a rule of thumb to go by for this but from my experience there are some boats that do not work better with a jack plate but at the same time most boats can benefit from being able to run the engine further back and higher. You might try to contact the manufacturer of your particular boat and ask if they or any other owners have experience with a JP on that particular hull. I have also found that there are some boats that you should not mount a plate on due to the extra stress on the transom so checking with the manufacturer would be the best first step. Another resource might be to find other boats like yours and see what they are using. You may need to alter or lengthen the steering and control cables on the boat to work with a JP. If your boat runs really well without a JP and you want one to provide better shallow running I would suggest trying a smaller setback such as a T&H Marine Atlas 4" Jack Plate. This would have the least change from your stock set up. On some smaller boats the added weight of the JP can be a factor that is often overlooked causing the boat to sit stern heavy. In the end this is a bit like props testing and trying them is the only real way to find what works. A new SS prop might be required as well.
Cheers
Randy

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Towbarman

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Reply with quote  #3 
Hi randy
Thanks for that unfortunately the manufacturer closed down years ago , and I have never seen a jack plate on any boat in the UK other than the racing boys
They do not know what they are lol

Kind regards carl

Must be some expert who knows on here ?
Megalodon

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Reply with quote  #4 
A very general rule of thumb is that 3" of setback allows you to run 1" higher. The bigger the setback the less trim you will need to lift the bow, but the higher you run the motor will reduce the effect of any trim.
Yeah
For a small boat like yours I'd suggest using a 4" setback, and bear in mind you're shifting a large percentage of your overall weight back, so it may feel more 'flighty'. What kind of boat is it?

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Towbarman

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Reply with quote  #5 
Hi
Thanks for your reply it's a fletcher gto 15ft arrowflash going to fit a etec 90 hp to it with ballistic prop
There is confusing data on this subject
Some say 1 inch for 12 inch set back ?

Kind regards carl
Towbarman

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Reply with quote  #6 

We have had a 75 yam on this hull and it was slow out the hole but got going eventually

We tied different props best was 17
Had the etec on a arrowsport hull 15 ft
but 100kilos heavier went well perfect set up!
with cav plate set 1 inch above hull
but the angle off arrowsport transom angle is steeper which let's you trim back too hole shot better then trim out at speed nearly to top off gauge before blow out
The arrowflash transom in not as steep angle for hole shot and the yam blew out with half the trim
The etec has a lot more power than the yam can a 4inch jack plate let me increase the angle off the transom as well
Towbarman

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Reply with quote  #7 
Hi
Thanks for your reply it's a fletcher gto 15ft arrowflash going to fit a etec 90 hp to it with ballistic prop
There is confusing data on this subject
Some say 1 inch for 12 inch set back ?

Kind regards carl
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