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View Full Version : Prop Choice....I know my RPMs now!



Stix Magill
09-03-2001, 08:57 PM
Stix Magill here. I asked last week about the best prop for my 20 Minx and I didn't have my RPM info. Well, here it is. My Donzi 20 Minx was repowered in 1997 with a new Mercury 350 Mag. 270 hp. It has a Alpha One drive. The boat came with two props when I bought it a couple of months ago. The Mirage 23" pitch is installed, and a spare 21" pitch Mirage thrown in. On glassy water, I am hitting about 4700 RPMs with the 23 Mirage with a near full tank and only the driver. This shows on the VDO as 61 mph.

How will going to the 21 affect my performance? What would the Revolution IV do for my performance?

Tomahawk recommended the Revolution IV and I am concidering selling both of these and buying on of those. Thanks for the input!

Happy Labor Day!!

Stix Magill :) http://stixmagill.homestead.com/files/donzislow.jpg

Moody Blu'
09-03-2001, 09:57 PM
if you go to a lower pitch prop then you will slow down.

I dont know all the glamour about the differnet props but, if your gonna change props and want more speed then go to a higher pitched prop, (25-27p)

you could probably hit 65-70 mph.

does your boat max out at 4700 rpms, or do you have a couple rpms in your pocket?

dont forget when you trim the boat out trim it out until the prop starts to cavitate and then tuck it back in a bit!

BigGrizzly
09-03-2001, 10:23 PM
Sky your wrong. This is not always the case. This weekend. I hit 82+ with a 28 pitch prototype laser, at 5000 than 83+ with a 26 inch Vector at 5200. These are GPS readings.
Stix, the 21 will probably put your revs about 5,000. this will probably give you the same mph. since you have them try them you will get your answer in 10 minutes after changing it. All boats react differently to prop swaps.
Your engine will not pull a 25 or a 27 inch pitch prop. Sky is wrong here too. That trim untill it cavitates then trim in a bit is not true either.. All three of my current Donzis can be trimed and slow down before they cavitate. I speak from experience since I have had Donzis since 1966.


Randy

Tomahawk
09-03-2001, 10:45 PM
Oh Man!!- Stix - now it depends upon what rpm you want your engine to achieve at full throttle. You are actually pretty close with your Mirage 23. The 21 would increase your rpm to about 5000. Your speed would be about the same as with your 23 but acceleration would improve a bit. You need to test the 21 now. The only way to tell for sure is to go out and try it with a similar load and note your rpm and speed. I wouldn't get rid of your Mirage props just yet. They are very good props. The Rev 4 works great on a lot of boats, but not all. Try not to spend the money until you try a prop on your own boat- it's expensive if you guess wrong. A Rev 4, 21 would probably put you rpm at about 4800.

Stix Magill
09-06-2001, 12:49 AM
Thanks Ya'll. I'm new to this and you don't know how much I appreciate the input! I will try to compare the two props I have "side by side" in the next few weeks and post the results. Do I just need a prop tool from Overtons? Maybe others will benefit from my prop tool purchase!

Thanks again,

Stix

Stix Magill
09-06-2001, 12:58 AM
One little Labor Day picture.......... http://stixmagill.homestead.com/files/donzifast.jpg