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Old 07 April 2010, 12:13   #1
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Jack plates and set back plates

I can understand the need for a jack plate, as i am in need of making one for my longshaft engine to fit my shortshaft boat transom.

But what exactly is the benefit of the setback plates ?

Apart from it giving extra room inside at the back of the boat !

Is there a performance increase /decrease ?




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Old 07 April 2010, 14:00   #2
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I'm no real expert, but I believe it allows the engine to run in cleaner water not immediately behind the hull. Of course the higher the engine is mounted the more reason to locate cleaner water.

Somebody will probably be along to call me a plonker in a minute and correct me.

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Old 07 April 2010, 14:38   #3
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Plonker

No, really I think you're about right. When you increase the effective waterline it has some effect on the overall hull speed, and the cleaner water for the prop is of help too.
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Old 08 April 2010, 04:49   #4
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Quote:
Originally Posted by Erin View Post
Plonker

No, really I think you're about right. When you increase the effective waterline it has some effect on the overall hull speed, and the cleaner water for the prop is of help too.
You're not increasing the waterline if you don't fill in the gap - by moving the outboard back you can raise the engine higher, this in turn reduces drag and as Nasher and Erin say the water is cleaner higher up further back.
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Old 08 April 2010, 07:43   #5
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Cookee

I have to own up to the fact that I only have an understanding of the principle from reading posts you've made in the past.

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Old 08 April 2010, 14:38   #6
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So being as i am going to be making a jack plate for my 30hp suzuki, would it benefit me
to make it a setback plate at the same time ?

And what would be suitable amount of setback ?
Remember i need 5 inch of lift just to make it a normal ride height , so any setback will
need to be raised even more ! just how high do you go.

And also what is the cons to it, there must be some bad side effects or they
would be much more widely used !


Or is a 30hp not worth talking about as far as setback is concerned ?



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Old 08 April 2010, 15:29   #7
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No expert either, but with a setback You will have more torque on the transom, and also the weight distribution will slightly be changed. Are these significant issues, that I don't know.

I have a 56 cm(long rig) on a 50 cm transom, have been thinking about the same issue but decided only to extend the transom with a fixed plywood "Jackplate". Hope to post some pictures when completed.
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Old 08 April 2010, 17:22   #8
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The more i think about the more im inclined to agree with C-NUMB and just
put on a simple bit of wood to raise it up.

If you use wood to raise the transom do you put it inside or outside ?

I need 5 inch lift (12.5cm), and thats a fair bit if lift for wood so might use steel plate.

If the weekend is nice ill also have pics to show , even if it dont work ha ha



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Old 09 April 2010, 07:00   #9
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Just to chuck a thought in here, and not knowing what age your engine is, for the sake of buying a new leg / shaft / water toob and a couple of gaskets, might it be easier to convert the engine to short shaft? If it;s a 2-0 stroke I'll bet theres a few bits kicking about in the usual haunts.....
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Old 09 April 2010, 07:36   #10
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i.m.h.o and i am only speaking from my own past experences if your only using your boat as a runabout and dont want optimum speed out of it i dont see what all the fuss is about ,i have run numerous boats with short transoms with longshaft engines and with only minimal drop in speed perhaps a couple of knots ,and with some types of engine a bit more spray getting kicked up , down side is that your draught is increased by 5 inches or so and changing or clearing a prop from weed or a plaggy bag you will have to stretch out a bit more and with some older engines with a small pressure relife hole it may have a bit more back pressure on the exhaust when at rest ,plus side is that in lumpy /choppy water conditions you dont lose power as the prop never airates as its always in the water ,and up to now i have never twisted a transom off a boat or sommersaulted one when setting off as in some of the myths .
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