prop slip
 

so i calculated my prop slip, (http://go-fast.com/Prop_Slip_Calculator.htm) and i came up with 18%, is that good or bad. Its a deep-v, 30' boat single engine. Is there anyway to adjust the slip to lower it if 18% is too high. Thanks

What boat ? what drive hight ? what drive ? what prop?

And yes there is .........but do u need that ????.......
mypoint is some boats like higher slip and some don't !

Mine is 21%:eek:

Big single engine boats generally have higher prop slip numbers. Higher propslip also puts less stress on the drive.
18% is high, but not not so high that you should make any extreme changes, IMO.

What prop are you running?????

i have a bravo XR with imco 2" shorty, and a 28p bravo 1. Its a 1994 conquest enforcer 30'

What can I do? I have a 28' Pantera with speedmaster IIIA with 1.50. I don't know the drive hight, but I was told it was conservitive. According to the prop. calc. I have a 28% slip. 33"pitch, 1.50, 5700RPM, GPS 86mph; prop is merc. 4 blade. I don't know the degree of rake?

mine are at 14%

What is the drive?

I am at 15%, 100mph, 6000RPM

Imco SC Extreme -1
Bravo 1, 32" Labbed (assuming 1" less, so 31")

The rake is more likley around 13 degree.
I would actually stick a #4 on your boat with a 2 inch spacer ,,that will raise the drive up by 4 inches and give u better speed,,then ofcoarse u need to find the right prop .
But maybe yours would work too ?!
U can get the prop worked,,,,more cup and thin it ,,that would give u more bite ,,,in most cases less slip.
also if it is a stamped 33 merc, its more likeley a 35 pitch ,what diameter is it,,u can play with that as well and loose some slip. the single engine boats like around 17-17.5 diameter, my guess is u run a ~16 with that pitch so u burn holes in the water?! Mine is a 17 X 29.5 @ 6800 with a #4 ( 1:68 gear ratio ) .
Hope that helps.

I take it the prop is working good for you Phil...


I am about 5% on the stinger, even though nobody believes me about it.... 18 isn't too too bad, but i think the 15 16% is where people like to sit...
John jr

Thanks for the info., you are close on the diameter, it is 16.5. I have a pair of 5 blade mercury props I bought a while back. I think they are 17" X 29. I guess it is time to try a few different props. I will keep you posted. By the way, I drag race once in a while over there at Desoto - Love that track. Yea, I know, they changed the name. Also: I attended a couple of SBI races last year as a spectator, and I think one of them was Marathon. I think I remember seeing your boat at that race.

Yeah man, the prop changed the whole ride of the boat. That P-5 Hydromotive made the boat so unstable it was crazy. with this Bravo 1, I dont even have to steer at 100+, it just flat out goes. Rides softer, airs out a little more, increased cruise speed by 10mph, just completely changed the boat. Best money I have spent on the boat by far.
:ernaehrung004:

Here's my take on prop slip,I think that single engine boats,especially big ones with big power,can actually benefit from prop slip. I used to get all worked up over the fact my prop slip numbers are astronomical. At first glance everyone thinks your giving something up but if your boat performs good who cares. For the sake of discussion,lets assume you have tried several labbed and std props. Your boat has a decent balance of overall driveability,acceleration,top end and handling (kinda like my boat with a 30 pitch merc labbed). But lo and behold,your prop slip is 18% cruising and 25% at wot (this is about what mine is). We are also going to assume for the sake of this example that your boat rev's exactly where it is supposed to at wot.
We got this "terrible" slip problem though,although boat runs 90 mph at 5800.
what's the solutiuon, you try a 30 non-labbed,now boat has slightly better speed vs rpm's light cruising but only revs 5400 at wot and is a dog plus starts getting a little transon lift.
you bolt on a 5 blade 28 pitch,man,part throttle cruising is great but acceleration is dead,slip is down to 12% cruising/15% at wot,rpm's are down 100-200 rpm's at wot,top speed is down and now boat transom lifts,bow steers and out and out handles like crap.
The thing you have to realize is if a boat runs 90 mph at a motors peak hp point and 25% slip, there usually isn't some extra speed to be had by lowering the slip like you would think,it's not that simple if you are reaching peak power,instead you lose rpm's,lose top speed and are pulled away from the power band. If you could pull a prop the same rpm's with less slip/same pitch of course boat is going to be faster but that usually takes MORE hp. I'm not saying not to try every prop you possibly can and not to experiment with x dimesion,I'm just saying don't expect alot,Smitty

Thanks you for your example. I bought this boat with less than 40hrs, it previously belonged to a well known world champion. The factory told me the boat was tested twice by them, and that it ran 95mph on GPS. I know for a fact I do not have the original prop they used to achieve that speed, because the person (who was not the world champion), who had the prop disapeared with it. You must agree, 28% slip is a little bit to high. I will post results of some future testing. Thanks for your imput.

sorry just got back on, that was with a b1 with a 2''shortie 1.50 gear and 670hp. I would of gone faster I think with a 28 or 30 p bravo 4 blade I was at 6000 rpm so a 28 might of pulled to 5700 and give me a mile or 2, it got there quick with the 26. does the factory know what the old prop was for size?

Hey, what length Baja, what speed, and you did'nt mention what prop was at 6000?

What kind of power do you run to achieve that speed?

Do you have a blower and what is your weight?

I ran my current numbers thru the slip calculator adjusting for the fact its a merc prop and its labbed and my slip is 18%-19% (currently 98.5-99 mph w/32 pitch merc labbed at 6100-6200 rpm's) but still the same I have lowered the wot slip and never had any kind of gain on top of trying a stellings box with neg results and a imco 2" shorty with neg results,Smitty
28% would be pretty high,I would be trying drive spacers and different props until you get the best overall balance of speed and driveability.

Nice I am at 15% slip , 122MPH, 6000RPM

I am running a JC Performance 598/800hp N/A, dynoed a bit over 800 lb/ft. A 29' Kryptonite weighs in around 5000lbs, or so I have been told.

That boat runs hard. Is it a step bottom?

Yes, single step. Pad bottom, full length lifting chines.

A stock 525hp will get it into the low 80's.

I have a boss hammer 21'6" I JUST PUT IN A 502 WITH 500HP
WHAT PROP WOULD WORK FOR MAX SPEED, WHEN I HAD MY 454 310 HP MOTOR THE BOAT RAN 64 GPS WITH 4 PEOPLE AND A HALF FULL TANK OF GAS. tHE PROP I HAVE IS A 23P.

I came up with 11% for my setup. Would this be too hard on my drive or motor. the boat is a 98 25 Active Tunder, with estimated 500hp, 489ci, 1.5 bravo one on a Stellings box with 1" lower spacer, 26 B1 wheel. Prop shaft is 2" below boat. 73mph at 5000 rpm. Im not real sure on the drive ratio, could it be something else?

An interesting observation on slip... Gary Taylors TPI Howard Bullet, which is extremely fast, has prop slip right around 20%.

I have done an extreme amount of testing and data recording on different drive depths, and different props on my 28' Nordic Heat, and have determined that it runs faster and handles better with slip numbers in the 14%-18% range.

After spending literally hundreds of hours fretting over attaining low slip numbers (got them as low as 5.2%), I deciced to let those numbers go, and concentrate on overall speed and boat handling. As a result, my boat is now faster, and handles better than ever before.

91-92 mph consistantly. 730hp out of a Whipple upgraded Mercury 600sci

Best speed to date: 94.1 mph, 1.504 gear ratio, 5900 rpm, 30 pitch p5-x labbed by Herring, 15.5% slip

Just my observations,

Chris