Paging Dr. dhadley

Strider

Cadet
Joined
Jun 25, 2004
Messages
12
Hi there, I'm the guy with the 25 Hydra Sport with the single 300 Johnson on it. You were kind enough to answer some questions posted by my fishing buddy (suprise). I've gone out and checked out the setup and this is what I've found.<br /><br /> The transom measures 27 1/4 inches to the bottom of the V. The cavitation plate is about 1/2 or 3/4 inch above the bottom of the V. I can move the motor up one hole and it looks like that would move it up about 1 1/2 inches. (there's only two holes?!) With the current setup I get some cavitation with the motor trimmed up. I get 27MPH at 4500 and 36 MPH at 5700. I like the idea of getting up into 6500 or so to get the rest of the power as suggested. Not because I want to go faster but I'd like to get that HP when I need it. <br /> <br /> Can I move the engine up 1 1/2 inches ( which would put the cavitation plate up about 2 inches above the bottom of the v)? Or with this setup am I limited to prop experimentation?<br /><br /> The symptom we've noticed the most is that in rough seas when climbing a wave the boat slows way down while the rpms don't drop much. This leads us to believe the prop is slipping.<br /><br /> Many thanks for all your help.<br /><br />Ken
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: Paging Dr. dhadley

OK, good info. The motor is probably sitting pretty good as far as height goes for the prop you have. What pitch is it? What brand and style? (3 blade, 4 blade, aluminum, stainless, Stiletto, 17, 19 etc?)
 

Strider

Cadet
Joined
Jun 25, 2004
Messages
12
Re: Paging Dr. dhadley

I'm not sure of the model but it's a 14 1/2 x 19 three blade stainless. A prop guy I was refered to said a 15 1/2 x 17 mirage might do the trick. what do you think? He also offered to keep supplying props till I got what I want. Do you think I'd gain the extra rpms I'm looking for with that prop?
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: Paging Dr. dhadley

#1 -- lock on to the prop guy!<br /><br />I would have guessed you had a 19 but the question is -- how much of the cup is worn off? My guess -- strictly a guess -- that the cup ends somewhere just before the middle of the tip. Probably some diameter gone too. No problem. <br /><br />Before we test props we have to make darn sure the motor is healthy. Make sure the timing is right, the carbs are all synced etc. A real easy test is after the visual (sync & link) and timing check run it on a test wheel. The rpms will come to a certian level (the service manual will give you the test wheel number and rpms). Once we know the motor is indeed running correctly then we can test. A V8 sounds real good at 3/4 throttle or on 7 cylinders.<br /><br />I like the large diameter props. The large Mirage should be a good prop. Here's the deal, and I'm sure your prop guy knows, a Merc prop will fit on an OMC but he has to shorten the splines in the hub. No big deal. Its done all the time. Since he offered, I'm sure he knows and its probably already done. Thats good.<br /><br />Try it. But dont move the motor until after youve tried it. Make one change at a time. Keep good written records of top rpm and speed. And water pressure.
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: Paging Dr. dhadley

Youre very welcome. Keep us up on the progress!
 
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