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View Full Version : 4 blades on an 18 with a Stock X?



The Hedgehog
10-11-2010, 09:27 AM
Has this been a good combo for anyone? I tried a labbed B-1 on my 18 for while. The boat hated it. I did not really think it was a good idea, but it was what I had laying around.

Well it was not exactly horrible, but no fun to drive at speed. It would chine walk pretty good around 65, had a 45mpp hop, ran ok at 55mph and liked to torque into waves. I was always either messing with the trim or throttle when I either turned or encountered wakes.

I have found the Turbo and the M+ both to be better all around and on top.

Like I said, I was just wondering if anyone has pulled this off successfully.

Ranman
10-11-2010, 09:58 AM
I have a Hydromotive Quad IV that I run occasionally. The QIV has less bow lift and is about 2MPH slower, but the boat handles like it's on rails. A very good handling rough(er) water prop. Try one of those if you can find one.

Step down an inch of pitch. I turn a 25P Mirage+ at about 5200 PM the QIV is a 24P nd I turn it right around 5000 PM

axelkloehn
10-11-2010, 10:01 AM
I have a Hydromotive Quad IV that I run occasionally. The QIV has less bow lift and is about 2MPH slower, but the boat handles like it's on rails. A very good handling rough(er) water prop. Try one of those if you can find one.

Step down an inch of pitch. I turn a 25P Mirage+ at about 5200 PM the QIV is a 24P nd I turn it right around 5000 PM

doesn't rpm usually increase when you step down in pitch? Or is it the difference between 3 and 4 blade? just wondering

VetteLT193
10-11-2010, 10:29 AM
doesn't rpm usually increase when you step down in pitch? Or is it the difference between 3 and 4 blade? just wondering

if you go down in pitch on the same prop RPM goes up. adding the extra blade though changes things. usually an extra blade drops the rpm. all that is contingent on the different prop types though.

Ranman
10-11-2010, 12:56 PM
doesn't rpm usually increase when you step down in pitch? Or is it the difference between 3 and 4 blade? just wondering

Vette is correct. Generally speaking as you add blades (i.e. surface area) to a prop the more it will "bite" and the more power you'll need to turn it. Mirage Plus's and Hydro Quad IV's are popular props for Donzis. A one inch drop in pitch is perfect when goiong from the M+ to the QIV.

axelkloehn
10-11-2010, 02:04 PM
means for when you drop pitch and drop rpm you loose speed with the 4 blade, right?

Ranman
10-11-2010, 03:01 PM
means for when you drop pitch and drop rpm you loose speed with the 4 blade, right?

Generally, yes. You have to account foer prop slip as well.

You might lower RPM's and pitch, but still go faster because of less prop slip.

A theoretical example:

25P X 5200 RPM / 1.65 Gear Ratio X 1056 = Theo Speed of 74.60

Theo Speed 74.60 - Actual Speed 66.4 / Theo Speed 74.60 = 10.99% slip

Note "Actual Speed" of 66.4 MPH

24P x 5100 RPM / 1.65 Gear Ration X 1056 Theo Speed of 70.24

Theo speed 70.24 - Actual Speed 67.1 / Theo speed 70.24 = 4.5% slip

Note "Actual speed of 67.1 (faster than the 25P)


While I made up the actual speeds and a slip number of 4.5% is low, you can see by the example that it IS POSSIBE for a really bad prop (high slip %) that has a higher pitch and is spun faster can ACTUALLY be slower than a lower pitch prop spun slower but is more efficient (less slip)

In the case of my M+ 25P and QIV 24P four blade, my actual speeds are ;ike 66.5 for the 4 blade and 68.7 for the M+ everything else being equal.

axelkloehn
10-11-2010, 03:56 PM
this is quite interesting. 10 days ago I pushed 57 mph with a OMC 21" Alu-prop at 4600 rpm, theoretical speed is 68- means 16% spin!!
Yesterday I had a 23" Mirage and pushed 63 mph at 4200 rpm in bad conditions, theoretical speed would have been also 68- means a lot less spin (8%).... is the stainless so much better than the alu?? Or did I calculate something wrong?

RickSE
10-11-2010, 04:15 PM
I had good luck with a Merc. Rev-4 on my old 18C. It was a little slower then the M+ and I had to go down to a 19P but it worked pretty good with no ill handling; up to 60-MPH.

VetteLT193
10-11-2010, 04:17 PM
this is quite interesting. 10 days ago I pushed 57 mph with a OMC 21" Alu-prop at 4600 rpm, theoretical speed is 68- means 16% spin!!
Yesterday I had a 23" Mirage and pushed 63 mph at 4200 rpm in bad conditions, theoretical speed would have been also 68- means a lot less spin (8%).... is the stainless so much better than the alu?? Or did I calculate something wrong?

If it is a Mirage Plus you have (more common that straight mirage) it is said to add 1" to the prop size because of the added cup. so plug 24" into your calculations.

Another note is there is top speed and cruise speed. Generally slip changes... That said, I picked up a ton of MPH on cruise with 4 blade props. Because I cruise more than I go top end I stuck with the 4 blade Bravo 1 over the 3 blade M+

jstokes8407
10-11-2010, 08:02 PM
I run a 23 pitch ballistic 4 blade around 4800 rpm and boat handles on rails and Gps somewhere around 72 - 74 depends on day and gas. i also run a alpha ss drive. the prop was a 24 or 25 before it was repitched

The Hedgehog
10-11-2010, 08:50 PM
I run a 23 pitch ballistic 4 blade around 4800 rpm and boat handles on rails and Gps somewhere around 72 - 74 depends on day and gas. i also run a alpha ss drive. the prop was a 24 or 25 before it was repitched

Did you run it before you ran the SS?

MOP
10-11-2010, 10:09 PM
John had the SS before he tried the Ballistic, it was my old Ballistic. Some say you lose top end with a 4b, just the opposite on my rig a 4b turned out to be the fastest prop. All rigs work different with different wheels, you need to try a bunch before you hit the right combo. The prop I ended up with is a Turbo Ultima 23, on a good day I hit 65.5 with my SB 22 not bad.

Phil

The Hedgehog
10-11-2010, 10:15 PM
John had the SS before he tried the Ballistic, it was my old Ballistic. Some say you lose top end with a 4b, just the opposite on my rig a 4b turned out to be the fastest prop. All rigs work different with different wheels, you need to try a bunch before you hit the right combo. The prop I ended up with is a Turbo Ultima 23, on a good day I hit 65.5 with my SB 22 not bad.

Phil

That is the kind of feedback I wanted.

Others? Anyone do well with the Bravo I

LKSD
10-12-2010, 08:40 AM
I had good luck with a Merc. Rev-4 on my old 18C. It was a little slower then the M+ and I had to go down to a 19P but it worked pretty good with no ill handling; up to 60-MPH.

I have had some good luck with that Rev 4 on some hulls too.. Kind of handles like a lightened B1, but a bit faster on some of these smaller boats.

I have also had good results with the 3 blade ballistics.. :) Other than that the M+ I have found to be pretty good..