new prop ?s and results

[cornholio]

1989 Evinrude 225, 23' Powercat Sabalo 232.<br />First Prop<br />Old, stainless 14.75x 19 (prop shop said it was so worn it was more like an 18 pitch)<br />Max rpm 5000, max speed unknown maybe 35mph<br />Boat planes so slowly.<br /><br />New stainless 15x17<br />Max rpm 4800 (whoops I wanted higher rpms, didn't realize the diameter would drop them so much)<br />Max speed 33 mph.<br />Planes very quickly now and seems much more responsive to throttle.<br /><br />Question is, is there a prop that will give me a higher top end speed, more rpms, and still let me plane fast?<br />Also is it bad if my engine maxes out at 4800 rpms ?

 

[walleyehed]

Re: new prop ?s and results

First, Yes, 4800 will kill the engine by coking up internal parts from high combustion temps..simular to high manifold pressure, low RPM destruction.<br />Don't know what brand of 15X17 you bought, but I do have data on OMC/BRP that shows that particular prop is very efficient, usually fater than most 17's and bites hard.<br />What I would recommend is "If you know the engine is good and healthy", start raising the engine on it's mounting platform 1 hole at a time and test. That's a big boat, and it may even require some serious setback for best performance, but let's look at engine height first.. On the large V6's, I see about 100RPM gain with each hole, depending on hull style, sometimes maybe 75 per hole, but we need to get it up as high as it will run without consistant venting problems. At that point, we need to determine RPM, and make a decision as to what route to go...we have several choices.<br />As you raise it, we should see a slight increase in hole-shot, and chances are, the 15X17 you have is not a vented hub prop, I'm guessing.<br />I wouls also guess that boat is rated for a max HP a bit bigger than what you have on it..????

 

[cornholio]

Re: new prop ?s and results

The prop non-vented and is a michigan wheel. The engine is at its maximum height.<br />The prop was recommended by a knowledgable local prop shop, thats why I was disappointed in the rpm drop. <br />I don't have the dough currently to invest in a jackplate or bracket. A bracket with twin 115s or 130s is what I would ideally get.<br />The boat is rated for 280 hp.

 

[walleyehed]

Re: new prop ?s and results

Well, lemme start with this...Michigan wheel has only 1 SS prop that has shown real decent performance numbers and 1993 was the last year it was built...the MWC EdgeII.<br />Unless you have a Rapture or Ballistic, for an Outboard application it should be painted black.<br />If it is NOT a Ballistic or Rapture, and is polished, it's a sterndrive prop with more blade area than you can use...<br />Can you give a number or Model?????<br />Should be a number like 013044 or something like that....niether ballistic or Rapture are 15" diameter, so it's about gotta be the std black prop.

 

[cornholio]

Re: new prop ?s and results

Michigan Match SS<br />013044 OMC 15R17 SS 3 BLADE MI MATCH<br />Its shiny stainless with no coating.

 

[walleyehed]

Re: new prop ?s and results

OK, that's a decent design, as it says "Michigan match", it's real close to the OMC 15X17.<br />Let's assume the 19 was worn @5000RPM, and maybe pulled 4800 when new. That engine really should be turning 5600+ with a normal load. But, the new 17 only pulls 4800, right where the 19 should have been new..Hummmm????

 

[walleyehed]

Re: new prop ?s and results

My thoughts are leading me to think we may want to do a compression check.<br />When you say the engine is at max heigth, are you saying it's mounted to the transom in the 4th set of holes???? yours may have 5...anyway, the bottom most holes for the top bolts???