Max Speed Attainable with These Fgures

[fs5]

or over pitched from whats stamped on it,sometimes tacko's are out to.even the old gps can tell a porky sometimes...

[pdt]

That's the thing with most tall stories of speed on water, the facts that are given are wrong, in many cases impossible speeds are given for the goods they are running.
I know some don't know the difference between knots kms per hour and miles per hour .

[zul8tr]

This is getting long in the tooth. Speed issue resolved.

If you want your rig to be fast just read the mph on the gps or water pickup speedo and report the value as knots and it will going about 15% faster.

[omcstratos]

This speed calculation stuff is beginning to get redundant...

[R Pierson]

Been watching your thread....

Couple of observations. I have found over the last 30 years of doing this that what is stamped on the prop is kind of irrelevant. With these new progressive pitch props, the part of the blade that does the most work at the trim setting and rpm you are evaluating is the most relevant info. Crab angle ( the more you have the less active pitch you have to work with) and trim angle ( tucked under vs trim past parallel Under adds and trim out takes away) effects the pitch as it is attacking the water. Ron Hill showed me 20 years back using lipstick, of all things, that we could find the part of the blade doing the most work. Then you could accurately find the slip numbers based on the pitch that was on that part of the blade. The part of the blade toward the leading edge and near the hub does the most work on initial take off. As rpm increases, centrifical force causes it to move out toward the tips and the faster you go...same result. I found out many years ago that all the calculations are kind of moot. I'd rather have a prop with 30% slip than one with 10% if the 30% one was faster. We also found that the prop swing from about 2-3 o-clock to about 7 o-clock did the most work ( on right hand rotation stuff). Some of this came from guys like Dave Bostic of Hoss props. Dave even showed Mercury that when they take off the rear prop on the ill fated Blackhawk twin prop drive...not much happened. But...putting on a prop with 20% more pitch than the front prop, it started to work. Then they sh&% canned the drive..so much for that.

Also, I never understood why everyone thought slip was a bad thing. Slip is thrust. If an airplane prop had no slip....the plane would fall out of the sky. Dennis Cavanaugh from Merc High perf ( before he passed away) was brilliant on this subject.

So...when we set up any boat at my shop, crab angle of the motor and getting a prop to run without much positive trim is the first priority. That tell us we have a good set up..prop included. If you are running a ton of positive trim or the engine is crabbed a bunch the prop or set up in general are not doing the job.

Hope that gets you guys thinking out of the box a bit..

I've wrecked a ton of props in my day modifying them...but I've also have some wonder-props come from that experimentation.

[pdt]

This is great, I have not laughed this much for ages, please keep it up, its cold and boring on tv, this is fantastic entertainment .

and there was me thinking that nobody here has a sense of humour, then along comes a brilliant comedian,, great stuff.

[pdt]

admin please lock this topic, my ribs are killing me, I cant take much more.

just incase I die laughing merry xmas guys

[Ron Hill]

Randy made the point that he'd rather have a prop with 30% slip, if it went faster than a prop with 10% slip. Looks at these pictures:1. The Prop Scan cost $27,000 and you can make a 4 million measurements on one prop blade, the next prop blade might be different. Propellers that are CNC's are perfect, because it is really very hard to get "PERFECT". Look at this three blade: At the leading edge it is 22 1/12 or such, 24 in the middle, and m26 or 27 on the out pitch. This is an OLD mechanical gauge, and we only use it to measure ONE radius on props. It really is just a "GOOD GUESS", as I measure a new Mercury propeller yesterday, it was supposed to be an 18....It went 16-19 1/2 20 on the three spots I measured it. Mercury calls it an 18. I'd call it an 18.5 at where I measure it. This five blade, is like the one Randy ran at Parker on the 250 Yamaha 4 Stroke. We call it a 15 5/8 X 32. It would go about 94, unless you wanted to "PUCKER" and then 100 was right there. Is it a 32, how fast will it go????As Greg Foster says, "Give me a happy prop" and I'll win the race. "Happy" meaning something that doesn't require a bunch of trim, something that will push the boat on an even keel!

[MWhite]

That's the thing with most tall stories of speed on water, the facts that are given are wrong, in many cases impossible speeds are given for the goods they are running.
I know some don't know the difference between knots kms per hour and miles per hour .

What tall stories u refuring to?? facts are what they are and there not wrong, and the gps don't lie. your calculations and figures are only good on paper, that's it, on the water it a different story and u can throw all that away...If u don't believe it,,,, that's your problem.

[Ron Hill]

My Mark 30-H would turn 7,200 RPM's on a good day. My Mark 55-H would also turn 7,200 on a good day. We were at Modesto Reservoir in Waterford, California for the APBA Stock Nationals. Weather was dry and borderline 90 plus. My first run in my C Runabout was 60 MPH but over the old record. My dad said, "For the second run put your D Hydro wheel on." I did and I broke the C Runabout UIM record at 64.661. It may still be a record. I then, took the same prop off my "C" (30-H) and put it on my D Runabout (55-H). I broke the D Runabout record (I think the speed was 70.456). Both flat bottoms, both 7,200 RPM motors, one a 30 cubic inch, one a 40 cubic inch....One with an A-B-C Quickie, one with a "D" Quickie...One at 425 pounds, one at 550 pounds. The same prop would go 76 MPH on my brother Sid Craft Sid Hydro. The motor only turned 7,200 RPM's....In 1966, I ran this same prop on my Quincy "A" Looper for a Kilo Record of 71 MPH....The Looper was probably turning 8,000 but with has 16:21 gears...How fast will a prop go?????? Check the GPS!!