More Prop Questions

[KRE]

Sorry so long on the reply, I'm done fencing for another week. The wife's horse hobby always seems to be more important than my boat hobby, imagine that

The Stiletto prop was a dud. First, I question the quality. After pressing the hub kit into place I noticed that the splined fit at the exhaust end of the prop appeared to be off center. So I pressed it out, rotated it, and tried it again. Same results. It’s the prop, not the hub kit. I installed it anyway, cause I wanted to test the pitch. The runout was .075”. A little too much for my liking. But…I used it anyway.

Max RPM achieved was 5200 (same test parameters) and 30.9 mph. Seemed considerably slower out of the hole. In any case I did’nt keep it in the water long cause it is going back!

I talked with Dan, he wants me to go straight to the Performance people for a trade out. I’ll be looking for the 13 pitch on the trade out plan. I also plan on raising the motor another 1/2" to 3/4". Gotta drill two new holes, dooogh! We'll see what happens next.

[TomW]

Kurt did you test with or without the water. This is a crucial part of the testing and one that was throwing our calcs off but we tried to make do with. Sorry the prop was bad, they have always been a quality company when I have dealt with them and other guys here that have used them have had no problems and like the product. The Stiletto should get you up on plane faster, give you some bow lift, a higher top end and better mid range. I would not do any more raising of the engine if you have to drill holes until you do testing without the water back there, you won't always have it will you and the weight will be more evenly distributed.

Tom

[KRE]

Tom,

Actually, this trip (test) was was more of a joy ride than a "Real Test". I had a buddy show up that had not been on the water here in Crystal River, so we went for a tour. The boat was empty except for he and I. He weighs considerably more than my wife. I had about 1/2 tank of fuel, no water in the wells and the cooler well was empty (not even a beer in it). I figure the load was marginally less than the original test given his extra weight and the absence of water in the wells.

One thing has been bugging me. The old aluminum prop has a flat profile at the trailing edges of the blades. I want to refer to is as a semi-cleaver only because I dont know how else to identify it. The steletto has a more traditional "prop" shape to it. Can this be causing the difference in the calculations?

[KRE]

Here's some pictures of the old prop and the current elevation of the motor.

[TomW]

Yes your old prop was a semi-cleaver, that is very complimentary of the low torque of the Yamaha's. Yes you need to raise your motor. I assume your holding a level there. If you are, go up all the way to the 4th hole, on my Yammi specs that is 55.5mm or 2.19", if your not level go to the third hole. I don't know why you need to drill new holes as the motor should just lift up and the bolts go right back into the old transom holes at the new motor height. Unless the dealer mounted it wrong. Oh, well. I'm guessing they put the bottom holes at the bottom of the slot instead of at the top.

Tom

[KRE]

I mounted the motor. This was a home-build! I wasnt provided any templates, only advice. For which some of it may have been poor. That's not a level, just a piece of straight bar to project the vee bottom out to the cavitation plate. I have room at the bottom slots, but am in the bottom hole at the top. No big deal. After drilling the first few holes in the hull when it was new, I am now numb to the fear of the drill! I'll epoxy puddy the old holes and cover them with a decorative backing plate.

OK, Ok, OK...How far up should the cavitation plate be above the lowest point on the vee? In other words, from where it is now.

Ya still think the "Q" at 13 pitch is the way to go? The 15 goes back in the mail on Monday.

[TomW]

Go up 2" on the motor from where your at. On the prop I think you probably need a flatter one now. Call Dan and see if he will exchange since that one was bad, go for the Powertec SCD3 15" for your motor. This was the other prop we were thinking of. It is a semi'-cleaver like you have, but should turn easier than the aluminum. If you have rpm's left with this prop then we can change it for the 17" for the best match. We are both shaking our heads at how little torque these small Yamaha's have.

Sorry I didn't get back to you yesterday.

Tom

[KRE]

Tom,

Too late to change the prop to a Powertec SCD3 15. Here's the readers digest version of a long story. Performance Propeller is upgrading me at no cost to their Turbo Line in a Q13-1/8" X 13 pitch. I got lucky because either they dont make one, or dont have, a 13 pitch in the Stelleto line. I talked to Dan and he says the Turbo at 13p is virtually identical to the Powertec SCD3 15. At this point I'm preparing to throw shamon bones on the beach to see which prop the spirits suggest. I think airline math is easier to figure. I expect the new prop next week. I'll keep you posted.

[TomW]

Yea know how you feel prop selection is more black art than science. To do it right we need all sorts of info to work with our calcs and then it may take two or three times to get it right. Don't give up you should get there eventually.

Tom

[ThistleDewDayDreamin]

OK you guys, how did this end up !?!? Did the performance ever get to where Kurt wants it? What was the solution? What were the final numbers? Geeze, string people along for five pages of thread and no closure? I hope u guys were able to figure it out!
It sounds like poor Kurt had a frustrating time of it. Hope all ended well.