245 Osprey repower issues

[flounderpounder225]

It's been a while since I have been on here, my 97' 245 Osprey project has been slow going, work busy, and now the Oil Spill threatening our beautiful emerald waters.  I have finally got an engine on the back of the boat, the original Johnson 225 Ocean Runner turned out to be too expensive for a rebuild after dis-assembly and inspection, so I purchased a used 2003 Yamaha 250 HPDI, had some ethanol issue from the motor sitting up too long, but have that corrected.  I could use some advice on prop size, and engine height on the transom as I will explain.  SeaBob... I'll buy you a cold one...

The dealer mounted the engine (25" shaft of course) where the cavitation plate on full down trim sits about 2" below the bottom of the step-up (euro-transom), on plane it APPEARS to be dragging a lot of water.  My question is: should the cavitation plate on the engine sit even with the bottom of the step-up portion of the hull? I can move the engine up one bolt hole, which would put the Cav plate even with the step?

PROP SIZE:  After water testing the boat today, I used the prop that came with the engine, 14.25 X 17 and achieved 30 KNOTS @ 4900 RPM WOT.  I have a 15.25 X 17 that I took from my last Yami before selling, and I am going to try that this weekend, it feels like the boat should be going faster than it is at WOT.  I know dropping in pitch is an increase of about 200 RPM per inch of pitch, then throwing in the different diameter...so thinking of 15.25 X 15 pitch maybe, but more later after the next water test, with the bigger diameter wheel.  I guess what would be interesting is, what do some of the other 245 Osprey owners with a 250 HP motor run??  

Thanks for the help
Marc
Pensacola FL

[seabob4]

FP,
You want your cav plate to be basically level with the keel at neutral trim (forward and aft areas of the cav plate equidistant from the keel).  +/-1/2".  When at speed, the plate should be just below the waters surface, or right at it.  Typically, we mounted the engines 2nd hole down, which is where yours is at.

Have you thought about talking to your dealer as far as borrowing some test props to get you where you need to be?  You should be seeing around 5500-5700 RPM WOT, and you should be seeing mid 40s WOT.  First thing is to get the HPDI into her max RPM at WOT, then work on getting the speed numbers correct...

But remember, with max speed you will suffer holeshot, and maybe cruise speed issues...

JMHO

[flounderpounder225]

Thanks Bob, I will work with the prop issue, figured you might know about the engine height issue.. more later