jack plate advantages.

[andyxs]

what are the advantages of a jack plate, was thinking of geting one for my rib a 7m xs with 200 merc opti. and how dos the set back help? with the dollar so low there looking tempting from america

[Burty]

puts the prop in cleaner water and enables you to run the engine higher the downside is you loose handling but then i run with 8" setback and i've never pushed mine hard enough to notice any loss in handleing

[andyxs]

thanks for that how much of a difference performance wise dos it make? and how much of a difference dos the vertical motion help and or afect handeling? just trying to weigh up if its worth the cost and weight i have had 58-9 mph on a flat calm day hit a wake and nearly died lol still was fun.

[Jon Fuller]

Originally Posted by Burty

puts the prop in cleaner water

In what way is the water 'cleaner'? ..and how? can you explain.

[Captain Chaos]

i think the best jake plates are made by 'Brita' thus taking all the nasty gremlins out of the ole H2O.

keeps your prop nice 'n shiney too :well

[Burty]

Originally Posted by Jon Fuller

In what way is the water 'cleaner'? ..and how? can you explain.

I can't explain its what JBD told me

[Maxim Gibson]

"Cleaner water" actually means that the water is less "disturbed", I suppose is the best word to use.
Water that has come straight from underneath the boat will be more "messy", being all swirly and bubbly (such proffessional technical terms!), a prop will slip more and not give as much direct push in this kind of water. However the extra 5, 8, 10 or however many inches achieved by using a stand-off can give better prop performance by allowing it to run in "smoother" water.
Well that's what I think!

[FrenchPhil]

True, but considering the added strain on the transom I'd look at the Jackplate as a last resort for speed. Have you tried the other things like prop selection ?

[Jon Fuller]

Originally Posted by FrenchPhil

True

Is it?

[Matt]

I've always been suspicious of the "cleaner water" statement. And since we're discussing it, I'll come out all fluffed up and say I reckon it's bollocks.

Go and swirl some water round in a mug and time how quickly it slows down.
Compare that with the time for it to slow down appreciably with the time taken for a "piece" of water to travel an extra 18" at 70+mph. Feck all.

Ever tailed a boat - look how far behind it the water is still disturbed!

[floater]

go for the 5" one but tell all the laydees its a 12" works for me!!!!!!!

[Jon Fuller]

Originally Posted by Matt

I reckon it's bollocks.

BINGO!

JMHO

[TheOrs]

Not convinced of the 'cleaner water' argument either.

I would've thought any speed gained is more to do with a bit of extra leverage lifting more of the hull clear of the water. i.e. less drag & so more speed.

Maybe...

[Adam]

Originally Posted by Matt

I've always been suspicious of the "cleaner water" statement. And since we're discussing it, I'll come out all fluffed up and say I reckon it's bollocks.

You are probably totally correct if conditions are flat calm / perfect sea - However as soon as waves are introduced by running the engine further back the prop is more often in water that is less effected by the transom re-entering the water / breaking water flow. So in a dynamic situation there are gains to running the prop further back and I imagine that this is what has been called 'cleaner water'. Not a massive difference but one none the less.

As to other uses for using a lifter - they can vary from the obvious of different prop heights for different sea conditions, force and direction. (especially so with stepped hulls or multihulls) to shallow water use off the plane to protecting your skeg when trailering!

[MrRob]

I have a jackplate and the reason is it gives me a choice. Some times I am taking around 4 people out in my boat and I want a lower pitch prop lower in the water but when its just me + 1 mate then I like a larger pitch prop out the water for out and out speed. Plus they look cool.
I would recommend the Detwiler all in one.

[Cookee]

I honestly wouldn't put one on a pure leisure boat - My opinion is the less drag on the gearbox the faster you go! Gains of 2 - 3mph compared to the cost, maintenance etc osn't worth it ......................... IMHO!

[Jon Fuller]

Originally Posted by Adam

You are probably totally correct if conditions are flat calm / perfect sea - However as soon as waves are introduced by running the engine further back the prop is more often in water that is less effected by the transom re-entering the water / breaking water flow. So in a dynamic situation there are gains to running the prop further back and I imagine that this is what has been called 'cleaner water'. Not a massive difference but one none the less.

Having the lower unit further aft, would indeed have a different effect when it roughs up, the ability to control the height of the drive in the water flow, is non existant, and with a significan't amount of setback, every time the boat kites, or lands at all stern down, you dig a dirty great hole with ya lower unit out on limb, causing loads'a drag, and if the power aint kept on, a nice 'brake' to intiate rotation into a stuff. So appendage drag is gonna be all over the place, especially if you dip the drive low enough in the flow to to go above the streamlined portion of lower unit. I would think this would be far more of an issue with a traditional V bottom, as they're generally less stable in pitch than a stepped boat.

I believe, the further away from the transom, the messier the water (obviously up to a point where it begins to settle, but I reckon that 10's of meters behind the boat)

The only advantage I see of setback, is to increase the leverage for out trim, and moving the C of G aft, both of which will only benefit max speed in flat water.

It also means getting on plane will be easier, as the motor will dig deep at lower speed, so kinda automatically increase the drive height as speed increases, which I think was the thinking on the original 'Gill Brackets'.

I can see the advantage of being able to lift & drop the motor, but you can only usually have this, at the expense of having setback. again, this seems of more advantage with a pitch stable boat like the B23

So, for stepped bottoms, setback could be a good deal, but for non stepped V's, in an offshore situation, I reckon the advantages are hard to see, but the disadvantages are obvious.

JMHO and of course I aint a designer, so probably don't know jack.

[andyxs]

thanks every one was enlightening not sure what im going to do yet lol. might speak to barnet marine and ask them about the extra stress on it. but it is only a 200hp engine on a transom rated for 300hp.