tired cleaver???

[N2DEEP]

My 27 pitch cleaver for the 330 TRS 18 had been cut down several times before I got the boat. Could this actually cause revs and speed to drop since a cleaver is suppose to "surface"? I have a 25 Hydromotive mounted on for this spring and it looks a lot bigger, taller whatever..

[Rootsy]

have you run the numbers through a prop slip calculator to get a general idea of how the cleaver is working... if it is just slipping all to hell you're just wasting all of those ponies.... all of the cleavers i have run on the 16 have come in at 14 - 16% slip... the hydromotive quad IV is a semi cleaver 4 blade with a big honkin diameter (15 1/2 inches)... i ran a 25 all last year on the 16 / SS... 9% across the board above 2500 rpm topping at 5500... but the big diameter in a submerged kinda environment kills some WOT rpm so expect to give up 2 - 3 mph over a good running cleaver... i spun a labbed 25 cleaver to the rev limiter which was set at 6000 rpm...

i'm going back to a quad IV O/T this spring, albiet in 27 or 28 pitch (to bring my rpm to a more comfortable level).. after removing the blowout ring on the sterndrive i had exceptional results with a 25 O/T last fall... rivaling the quad IV in slip and 2 1/2 mph faster plus 300 rpm gain... it's smaller in diameter at 14 3/4... handling wasn't noticably worse but i could definitely get the nose up more and feed it a bit moer trim...

From talking to tom and gary at hydromotive, on smaller hulls with the quad IV they like to take some diameter off of the prop which essentially will turn it into a quad IV O/T...

happy running with the big Quad... she's stable as all get out... midrange will rock vs the cleaver but expect to give up a little on top if the cleaver is in fact running efficiently...

[BLACKIE]

have you run the numbers through a prop slip calculator to get a general idea of how the cleaver is working... if it is just slipping all to hell you're just wasting all of those ponies....

Rootsy & N2Deep,
I just purchsed a 14.5 23'' pitch turbo three blade stainless from Dr. Dan. I've been reading your posts about slippage. I'm not sure I understand the term. Can you guys explain?

On my BBC 18' (Nervous Energy) I'm currently running a 22' Raker. I just bought a 23' turbo for a spare. I was curious as to what I can expect from the 23' turbo. RedDog told me that with the Raker I could expect 73.4 GPS @ 5,300 RPM. Should the 23' bring the RPM down a bit, how about speed?

PS N2Deep, are you planning to come to the MADCOW get together in July on Lake St. Clair here in Michigan? I don't want to be the only BBC 18' there. We could compare notes. I probabaly will only be there one of the days (Saturday hopefully). I have to schedule my boating around my other passion of flying the Yankee Airforce's B-25D Mitchell bomber at airshows & flyins. I'm on the number 2 crew and the plane can't fly without both a pilot & co-pilot. Not sure of our flight schedule yet though.

Thanks for you input.

[Ranman]

How to find your propeller slip

This type of testing requires an experienced driver, good water conditions and enough room to not be a hazard to others or yourself. Take the time to become familiar with the handling characteristics of your boat before attempting a full speed run.
Where do you start? First, it is important to have accurate speed and RPM information. This is critical for the best results! If you are serious about getting the most performance out of your boat, invest in accurate instruments. We have found Gaffrig speedometers to be the most accurate. We prefer digital tachometers, especially for testing.

Think of a prop as screw. The pitch is the theoretical distance the prop should move through the water in 1 revolution. A 24" pitch prop would move 2 feet. The theoretical speed is figured by multiplying the pitch x engine rpm and dividing by (gear reduction x 12) = feet per minute. Divide by 5280 = Miles per minute, multiply x 60 = miles per hour. This can be shortened to (Pitch x RPM) / (Reduction x 1056) = MPH.

Slip is figured by comparing this theoretical speed to the actual measured speed. By the way, for these calculations, add 1" to the pitch if your prop is cupped. (Just about all hi-performance props are)

PITCH X RPM / GEAR RATIO X 1056 - THEORETICAL SPEED

THEO SPEED - ACTUAL SPEED / ACTUAL SPEED = SLIP

For the purpose of this test, we are looking for the absolute fastest boat speed. So trim the boat by the speedo! Assuming we are in the ball park, and do not have to worry about over revving the engines, ignore the tachs for the moment.

If this is your first test of a new package you do need to watch the RPM, and you might not be able to test at full throttle. DO NOT over rev. Check with your engine manufacturer for maximum RPM.

Without getting the boat so loose you lose control, open the throttle to full speed. Try increasing and lowering the trim until you find the fastest mph on your GPS or Speedo. Now look at the tach, and make notes of the trim position, rpm and speed. You can repeat this at any throttle setting or speed. In fact you may be more interested in your cruising speed than top end. The highest RPM is not necessarily the fastest speed !

Write your numbers down, maybe include notes as to weather, number of passengers, amount of fuel, etc. When you get back to the dock, pull out your trusty (or rusty if you are like me) calculator and do the following: Figure your theoretical speed from above, subtract you actual speed. Divide this difference by the actual speed. The number you get is your slip percentage.

Slip is never a negative number, and will range from 5% on a light cat to 25% on a heavy workboat. Most hi performance applications will be between 7 and 12 percent.

Mercury has a handy slide rule type calculator available to do the math. Contact us for the part number and availability if you are interested.

Now that you know the slip, what does it mean? Less is not necessarily better. Prop slip is not the same as efficiency.

HELPFUL LINKS:

Speed Calculator (http://www.go-fast.com/boat_speed_predictions.htm)

Find Your Prop Slip (http://www.go-fast.com/prop_slip.htm)

Sterndrive Gear Ratios (http://www.go-fast.com/sterndrive_gear_ratios.htm)

[BLACKIE]

Thanks Ranman for the great explanation. That is a cool web site. It will give me something to think about. I'm going to try to compare the props when I get the boat into the water.

[Ranman]

BAM's explanation, not mine. This is why when someone quotes a bodacious speed number from a seemingly stock package, I ask about prop pitch and gear ratios. Some people can't grasp the concept that negative slip numbers are impossible.



Can't tell you how many 80MPH boats I've outrun. :biggrin: :biggrin:

[Rootsy]

props such as cleavers and the hydromotives don't have a very NOTICABLE cup unless someone took the time to work it in.. therefore i do not add an inch for cup and neither do any of the prop manufacturers i've spoke with such as hydromotive and turbo, etc... these props have a very straight backbone and just a bit of a flare... if you look at a round ear such as a mirage + or a turbo you'll then see what CUP really looks like...

gotta love BAM eh Randy ;)


so in summary... theoretically a prop would act as a screw in wood.. whatever you turn it in one revolution it moves the pitch distance... water though is a fluid not a solid and cannot resist shear... this leads to inefficiency because the prop will actually NOT move it's pitch distance but rather will "slip"..... pretty much the same analogy as SPINNING YOUR TIRES...

A GPS and an accurate tach are essential... as well as a good memory cause it is hard to run 70 and write... at least in a 16... :rolleyes:

[olredalert]

------So Blackie,if you arent at MADCOW on Sunday you WILL do a fly-over,right? Man, flying a B-25D or a fast Classic DONZI. There are some serious decisions going on there. Sounds like a great gig,Blackie. Cant wait to hear more about it!.............Bill S

[BLACKIE]

Yes, it is fun to fly the bird. Here's a picture taken last Fall at Monroe/Custer Airport in Southeast Michigan. The plane is based at Willow Run Airport near Ypsilanti, MI. It's the only flying "D" model in the world. It's very similar to the "B" model that the "Doolittle Raiders" used in the famous raid on Japan in 1942. This plane just completed a total restoration that took almost 5 years. We will be flying it regularly this summer at airshows, flyins, & flex rides. Yes a flex ride, you will be able to ride in it on Thursday evenings for a trip around the Detroit metropolitan area (approx 40 minutes). This will cost approx. $375 per person. I will be flying on most of those flights. We don't have the final schedule yet but I will post it here if anyone is interested when it's finalized. If you guys want more info, let me know.

PS I attached a photo to this post but I'm not sure if I did it correctly.

[N2DEEP]

....Blackie, I am not sure about the MADCOW BIG BLOCKATHON yet, but I would like to try if my turkeys let me. I will stay in touch.
....Can someone shoot me some idea of the weight of my 18 with a 330 TRS so I can run some prop calc.
... have been told this boat ran a wild 78 on radar some years back at 5500... unknown cleaver prop.
I want to guess HP for that speed.
....68 at 4800 was best last fall on the tired cleaver...I hope the cleaver is
tired and not my RAT!!!

[Rootsy]

Blackie,

that is totally awesome! i've seen a few of you yankee airforce guys crusiing overhead on occasion. My parents live about 15 miles from monroe. Last summer i was working on a tractor and a B17 came overhead and circled for a while... i can only imagine what 100 of those things sounded like in formation... I've also had a few trainers or fighters appear overhead from time to time... you can't mistake the sound of a performance engine... even in an old warbird ;)

I hear they are working on a messerschmit in monroe at the custer airport????

you better make st. clair one way or another!

JR

[N2DEEP]

If I pushed the right buttons, I think I am getting 21-24% slip with the cleaver. So....it looks tired , right??? Rootsy? Ranman?

PS NOTE TO SELF... Get batteries for GPS and learn how to use it before Spring!!

[olredalert]

Blackie,

------I for one really want to see that schedule when its available. I will do that trip in a heartbeat! And thanks for the offer. Come on guys lets get together for a whole MADCOW B-25D group trip How bad would that be???????...............Bill S