jack plate

sinkunit0

Seaman Apprentice
Joined
Feb 28, 2004
Messages
33
i have a 18ft vee hulled speedboat called a phantom.on it i have a mariner200efi with sportsmaster gearcase.can any boby advise me on how much set back on a jack plate i would need or is it the more the better? at the minute i am pulling 71 mph using a laser2 23 pitch on a 25 inch transom
 

walleyehed

Admiral
Joined
Jun 29, 2003
Messages
6,767
Re: jack plate

sinkunit0, what RPM are you turning???<br />Looks like your speedo may be off unless you are turning above 6500 with the 23....<br />Is the gear ratio different than 1.75:1???
 

sinkunit0

Seaman Apprentice
Joined
Feb 28, 2004
Messages
33
Re: jack plate

i,m reving at about 6400. the speed was clocked on my gps and speedo on boat. the gear ratio i,m running is 1.87:1
 

Hooty

Rear Admiral
Joined
Oct 2, 2001
Messages
4,496
Re: jack plate

Sounds to me like you've found the sweet spot.<br /><br />c/6<br />Hooty
 

walleyehed

Admiral
Joined
Jun 29, 2003
Messages
6,767
Re: jack plate

I'm with Hooty on the sweet spot, and I also believe your prop is more than 23", as that would equate to only 3-1/2% slip, which I'm not sure is possible. I bet if your prop was checked, it would be closer to an actual 25".<br />As for adding set-back, or any other change, I would advise against it due to your numbers showing near perfect efficiency.
 

sinkunit0

Seaman Apprentice
Joined
Feb 28, 2004
Messages
33
Re: jack plate

thanks for taking the time to work this out. i may have my prop checked because its nice to know.
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: jack plate

With a progressive pitch prop like that, the given number -- 23 in this case -- is the average across the blade. Thats why with todays props its really hard to compare one brand to another.<br /><br />If you wanted to try a jackplate, I would suggest a Bob's Machine manual. It has 6" of set back and can be turned inside out for 3 1/2". With a set of his 2" spacers you can test at 2", 3 1/2", 5 1/2", 6" and 8". Plus all the different heights. <br /><br />That ought to keep ya busy for a few hours!
 

walleyehed

Admiral
Joined
Jun 29, 2003
Messages
6,767
Re: jack plate

sinkunit0, If Dhadley says it's OK to add to your set-up, that's reason to try it.<br />He knows quite well what will work and what doesn't work. :)
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: jack plate

Well, the numbers look pretty good as is. But if I was goning to try a jackplate thats the one I would use. I've never set up this particular brand hull. The Phantoms built here are 30' and completely different I'm sure.
 
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