View Full Version : 22zx prop

12-05-2011, 08:09 AM
I recently rebuilt my alpha one 1:47 out drive on my 22zx, powered by a 350 magnum (300hp)

top RPM is around 5300, I was looking to get a new prop. one that performs well and possibly gain a little more top speed.

I bought the vessel with a 4 blade stainless steel prop. and thought a 3 blade might be a better performing prop.

Any help on what would be an ideal prop for this set up would be greatly appreciated. (diameter/pitch ect.)

Thank you,


Dr. David Fleming
12-05-2011, 12:41 PM
Several years ago I had a chance to talk to Chris C. the Donzi chief engineer about the 22ZX. Among other things he said the boat was designed around the Mercury Bravo I four blade prop. I did not ask if he ment the hydroplane hull version before 1999 but we were talking about the step hull.

Tyler Crockett talked me into trying to rake the blades back on a Bravo I four blade to change the bow lift and trim the drive in farther. All this did was kill the top speed of the 22ZX.

Would think Donzi had a pretty good reason for the prop the boat came with. I would start with getting that prop "lab finished."

Some of the other ZX Donzi models expecially those with duel engines used a Mercury Mirage three blade prop.

This prop change thing can be an expensive game to play with a large investment in props you don't use. Would check out what other folks are having success with first. I do have a Mercury Bravo I lab finshed 26p if your looking for one. Only seem to use my 28p and 30p.

12-05-2011, 01:33 PM
Thanks for the responce. I do have the step hull design. If I were to get my four blade "lab finished" what does this entail and the average cost? Also, is a 26p to large for a 22zx? I have a decent knowledge of the Alpha out drive, but not very savy on prop. types, basically I'm in the market to purchase a prop, I just dont want to waste money on little or no changes in performance.

Thanks again,

12-05-2011, 03:15 PM
Let's start with what prop are you running now? Brand and size. What speed are you getting @ 5300. You will need at least 2" of prop to get you down to about 4900-5k where you want to be. With my Scarab I ran a 23" and at 5k she was running low 60's(no GPS back then). But a 23" Mirage is way different than a 23" Quicksilver Elephant ear style or a...so lets try and not compare apples & oranges.

Yes a 26 will be too big for your setup. I amthinking a 23 mirage or maybe even a 21". Not sure how that would translate ina 4 blade B1.

Dr. David Fleming
12-05-2011, 04:23 PM
Ok this is the basics of props. They are measured by Diameter in inches and pitch which is the imaginary amount of distance they would screw through in one revolution. Your boat has say Bravo I or Mirage prop it is a certain diameter - then they make five or ten sister props that look exactly the same that have increasing pitch. The pitch is needed on each more powerful engine.

Donzi made three basic engines for the 22ZX a 310 horsepower, a 385 horsepower and a 415 horsepower. Each more powerful engine uses a larger pitch to put the power to work. 310 horse used 24 inch pitch. 385 horsepower used 26 inch pitch and 415 horsepower used 28 inch pitch. This are rough requirements and each boat must be tested for the prop that keeps the engine speed at the 4,800 rpm to 5000 rpm range and boat speeds go up with pitch.

It is entirely possible to get the wrong pitch prop on your boat. Usually the engine will not hit its power peak or will be over reving past the power peak. The boat performance will vary from aggressive to slugish - to undrivable.

Start with the manufacturer recomended prop and then adjust for any hot rodding or load increases.

Lab Finish is having the propeller finely tuned by having the blades made perfect in shape - these props are sold by Mercury or can be done by a professional propeller rebuilding business. Costs $600 for regular prop $ 800 - 1000 for labed prop.

The Hedgehog
12-05-2011, 05:41 PM
A 24" B one is the same effective pitch as a 23" Mirage Plus.

I would listen to D on this one. The hull likes a Bravo I.

It is always worth trying different props but I would not waste money on them without trying first. I don't really waste money on labbing heavier V-hulls. You may want to blueprint it but I doubt you would see much by thinning the blades. You will probably pick up a tiny bit of high end and give up 3 mph of cruise.

3 blades are faster but will losen it up and slow planing time.

12-05-2011, 06:59 PM
I was told by my part number (48-825900-19) that this is a 4 blade mercury prop. I'm assuming this is a 19p prop and I probably need to go larger with the pitch to lower my RPM to the 4800-5000 range. If I go with the Bravo one over the Mirage plus how much pitch do you guys suggest? Also, in your opinion would it be a gamble to try the Mirage plus at a 21 pitch, or will I be wasting money and time.

I have recently dropped a lot of money into the boat and was hoping to gain speed at a well performing rate. I DONT want to create a lead sled that takes miles upon miles to plain out.......

All of your replies have been very helpful,

Thank you,

12-06-2011, 03:09 PM
That is a Mercury 4 blade Offshore model prop, not well suited for go-fasts. With a SBC I am thinking 23 Mirage. The 19 Offshore "should" be close to a 21" Mirage so 23 would drop you down to 4900-5k whih range which is low 60's. Dr D. What do you think on a 300hp SBC Alpha combo?

12-06-2011, 03:25 PM
I recommend the Bravo One 24 pitch . It is a 4 blade that will give you stern lift on the step hull .Should be the right RPM and all around great prop .

Dr. David Fleming
12-07-2011, 11:54 AM
As I mentioned earlier, talking to the Donzi Chief Engineer when the company was in business in Sarasota. The 22ZX owing to its step hull and the ventilation of the hull resulting from that step performed best with Bravo I.

What is a step hull - it is the large vent from side to side of the boat with the back part higher than the front. This is not a small engineering change from a completely flat bottom. It is a radical alteration of the hull from other designs.

Because of the step the prop runs in a great deal of water/air. This makes the boat fast because there is no drag from the water holding it back. Four blades like the Bravo I propeller give this prop a better grip on the water flow.

Donzi 22ZX standard prop with 300 horsepower is a Bravo I 24 pitch. Go with lab finish it is one of the few effective things you can do to increase the performance of the boat.

Your engine rpm should fall within the 4800 - 5000 rpm range to have the correct prop.

B-Blades propeller service in Wisconson is run by former Mercury Racing employees and they do all sort of propellor repairs. They have a loaner program where they will send you a prop to try out for a couple of weeks. Call them, talk to Brad.

12-08-2011, 11:23 AM
I spoke with Brad at B-Blades, he was very helpful and took the time to explain different props in detail. I am going to do the test program and test the Bravo 1 22p and the Rev 4 23p stock props. This is the suggested recommendations by Brad, giving my hp and WOT. He, Thinks a bravo 1 24p is the ideal prop for the 22zx step hull, however recommends the 22p giving my 310hp engine. Also, he said I can lab finish the prop to tweak the RPM if needed.

22zx info from B-Blades...
-Has a 10% slip on the prop.
-bravo 1 22p stock will produce 4900rpm
59mph 549.00
-bravo 1 24p stock will produce 4300rpm
suggests a bravo 1 lab finished to produce 4650rpm approx. Price 925.00

Thank you all for the replies and help with my prop issue, you all were very helpful and thank you DR. D. For the B-Blades recommendation.


12-08-2011, 12:25 PM
I'm not an engine expert, but propping a SBC down to 46-4700 rpm seems awful low. It doesn't seem to give any room to lose rpms for a hot day or bigger than normal load. I've allways thought they like a few more rpms. Around 4900-5000. The lower rpms sound like BBC numbers.

12-08-2011, 02:17 PM
I agree and hence why the 22B1 should do the trick. I don't however see the 24 losing 600rpm, more like 3-400.

12-08-2011, 02:25 PM
a stock 350-310 should be whelled to 4700-4800 WFO

12-09-2011, 04:29 PM
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Just FYI, a 23p Rev4 is way to much prop for that boat. When I was running a Rev4 23p, it acted more like the
25p Mirage+. In my opinion you need to start with a 23p Mirage + and then try the B1 24p.