Prop Slip Test

Handymans342

@Randy56. I am not trying to get more speed. I am just trying to figure out how boat manufactures figure out everything ratio wise. Why is my prop slip test so high at 33? Most others are half that or less. 

zaverin1

Give your drives a handy real quick 
it might excite them and give you less slip.

Handymans342

zaverin1 said:

Give your drives a handy real quick 
it might excite them and give you less slip.

What???????????

zaverin1

Make love to the diesels and ur drives 
I heard it gets you 100 extra torque and  5mph

randy56

See if this link helps. How did you determine 33 percent. 
http://www.go-fast.com/prop_slip.htm

wm61356

I have B2 drives on my 320 and it performs well. I am also happy with the responsiveness at slow speeds and when docking. I've often wondered about switching to 4 blade props though. I've heard that 4 blade props provide better efficiency at cruise speeds. I've inquired about this in the past but have not found anyone who has switched to 4 blade props, so I've been unable to get any "real world" data. If anyone is running 4 blade props on B2s in a Rinker cruiser I'd like to hear how they work and if they offer any improvement over the stock 3 blade props. (I apologize for hijacking this discussion)

Handymans342

@randy56, I came up with the same slip of 31. B2s have more slip than B3s so not much I can do. 
@wm61356  I have a call in to a prop shop down here and I am waiting to see what he says about the 4 blade B2 prop. 
I went to a local prop shop yesterday and the guy couldn't believe the figures either. 

wm61356

Thanks Handy, let me know what you find out please.

jmichels

Handy you ever have your props checked to see if they are inline and balanced , cupped properly etc?

Handymans342

Yes 

Handymans342

I may take them off this weekend

raybo3

Handy are you saying if you reduce your slippage you will get more speed?

Handymans342

Don't know Ray. Think of it like this: my boat is only operating at 70 percent effientcy

Handymans342

Everyone should do this test

wm61356

Handy, were you able to get an opinion on 4 blade versus 3 blade props for B2 drives from you prop shop?

Handymans342

I will call the guy again. How do people stay in business?

reneechris14

I think you'll like the SS 4 blade,19x23 ?? ,that should get you up over the 80%.also 28mph should be more efficient.To bad you can't just borrow to fine out.maybe 19x24???.

Dream_Inn

I'd love to play with a couple 4 blade and SS.  I'd spend the money once I knew what worked!

Handymans342

Dream, do you know what props you have now?

Dream_Inn

Mine are 17.5 X 23

captpaul

learned in the military that hull design and hardware can make a difference up to about 20-25 mph...after that it is horsepower to make additional speed....

Michael T

@captpaul. agree 100% and for 20 to at least 30 foot boats the rule of thumb (for normal engines as not turbo or super charged) was 12 HP for every 1 MPH. On a twin that was 12 HP per engine. 

Handymans342

Ok, so I have seeked out advice from Al and Prop tech and Prop tech said i should go to an 18.5 by 21 pitch 4 blade prop and that i should get me to 36 mph and increase my slip to 86 % which should keep me on plane at 25 mph if desired. You can return the props for a fee of $150 each. So I will soak this in. 

jmichels

I would hope that you could stay on plane at speeds lower then 25 mph.

Whats your current prop and pitch Handy?

wm61356

@Handymans342 - that is interesting. I wonder if they could make a recommendation for my application. I've spoken to a dealer in my area about props but they wouldn't commit to any improvement with 4 blade props and, with the shop I spoke with, once the props have been mounted they wouldn't take them back. The shop you are working with sounds much more reasonable.

Handymans342

jmichels said:

I would hope that you could stay on plane at speeds lower then 25 mph.

Whats your current prop and pitch Handy?

19 by 23 pitch

Handymans342

This is all theory though.

jmichels

Some interesting info from another forum with a Chapparal. They were comparing 4x3 and 4x4 props. WM61356. For the record that I had a 4 x3 prop on my Rinker Fiesta Vee 270 and it rode and planed very nicely. 

So I have tried cupped 3x3 26p, non cupped 3x3 26p, Merc 4x3 non cupped, 4x4 cupped 26p, 4x4 cupped 24p and 4x3 cupped XR  25p all on my boat as an experiment. Here is the summary.

 

8.1 with b3 drive. Painted bottom. Tests were done when the bottom was a bit slimey reducing the rpm and top speed, but was about the same for all tests. When the bottom is cleaner, it is 300 rpm higher and top end around 50 for the faster props.

3x3 26p OEM props with 'L" option
hole shot is fine, smooth. Mid range is acceptable. WOT is 4400 at a speed of 45. 30 mph is 3200 and a fuel burn of 13.0

4x3 26p Mercruiser props
nice hole shot, bow lifts a little more than the 3x3. Very smooth and quick to 3000 rpm. Almost feels like it is slipping with how quickly it gets to 3000 but I don't think it is. Mid range is strong. WOT is 4550 at a speed of 46-47 or so. 30 mph is 3200 with a fuel burn of 12.6.  This set would lose the bite in hard turns and slow down.

Hill marine 4x4 24p
explosive holeshot. Quick to plane with little bow rise. Amazing mid range. WOT is 4650 but the top speed was around 43 or so. 30 mph is 3400 at a fuel burn of 14.1. Slight vibration at low rpm maybe.

Hill marine 4x4 26p
strong hole shot with minimal bow rise. Reasonably quick to plane. Nice mid range punch. WOT was 4300ish or so at a speed of 46. 30 mph is 2900 rpm at a fuel burn of 12.6 
this set had a bit of vibration at 900-1300 rpm if the drive was down all the way. Might be an out of balance set, or cup not even on all blades, not sure.

4x3 Merc XR props 25P
nice hole shot, strong. Minimal bow lift. Quick to plane. Nice mid range punch. WOT was 4500 at a speed of 42 or so. 30 mph was 3300 rpm at a fuel burn of 13.5. This set also had what felt like a small vibration at low rpm.

Handymans342

Thanks Josh, But that dont help me any LOL

Handymans342

wm61356 said:

@Handymans342 - that is interesting. I wonder if they could make a recommendation for my application. I've spoken to a dealer in my area about props but they wouldn't commit to any improvement with 4 blade props and, with the shop I spoke with, once the props have been mounted they wouldn't take them back. The shop you are working with sounds much more reasonable.

Call Jerry or it may be Jeremy at 318-688-1970