Prop pitch too steep?

[alcodiesel]

Hello Y'all. I get 1900 rpm and a tad over 5 kts no wind or current with a clean prop, ok bottom and 1500 rpm when the prop is barnacled up and 4 kts, same conditions. Wide open throttle.

This prop is a Maxprop and has two adjustable blades.

Knowing the power curve of the A4

I am wondering, when we haul out this spring, if I should flatten out the pitch a notch or two. I would like to get 2500 rpm WOT clean prop. The purpose is to get into a higher horse power range and not to lug the engine.

The photo is from the pre purchase haul out Oct '15. I see not a lot of pitch but big Dumbo ear blades making what pitch there is do a lot of pushing.

Observations and comments are appreciated

[Nanook]

Indigo 3 blade prop and call it good?

[Marian Claire]

You may have already read it but this http://www.moyermarine.com/faq/12.1.html has some good info.
When I repropped the info provided by a vacuum gauge helped in determining how hard the A-4 was working. Also make sure your tach is accurate. Mine was off and caused a bit of confusion.
How is the prop set now, size and pitch.
Dan S/V Marian Claire

[JDK]

I'm very happy with my Indigo upgrade propeller, I'd say go that route since he's the only one to actually put research and development into the subject.....

[sastanley]

alco...those max props are nice! It does sound like you might be overpropped, if all the other things mentioned are true, but unless you've heard another Atomic 4 run, you have no 'gauge' to tell if the tach is accurate.

You can get a cheap photo tach that reads a piece of reflective tape on the prop shaft/flywheel, etc. to confirm.

I might give the Max Prop people a ring and see if they can help you out...maybe they know what settings = what pitch? I have no idea how blade size/diameter compares to a visual on the pitch, or if it changes based on diameter, etc.

I like my Indigo, but I really wish I had a folding prop to help with sailing performance. I think when I was researching that, Martec recommended something like a 12" prop with a 5" to 6" pitch. It was also WAY more $$$ than the Indigo so I sacrificed sailing performance to make the motor happier.

I also don't think it would hurt anything to go one less notch on the pitch if you are only getting 1,900 WOT, and see how it goes. I think you can even adjust those in the water, but I am all thumbs and have to tie all my tools and everything to me so I don't lose them to Davey Jones' locker.

If you decide to switch out props (and that is a 1" shaft) maybe I can help you out by taking the max prop off your hands!

Edit - If you don't already have it, here is a link to the manual if that is the 2-blade "classic"...It looks like you should be able to determine the present pitch if you disassemble the prop and check out the chart and letters and stuff on the parts inside.

http://www.pyiinc.com/downloads/max-prop/max-prop-2-blade-classic-instructions.pdf

[alcodiesel]

Thanks guys. Thanks Shawn for your ideas. I never thought of call the maxprop guys. I have no reason to believe the tach is off, it's new and correctly installed and sounds like the A4 is turning the indicated rpms. But I'll ask around to borrow the rpm thingy mentioned.

No I don't want to change a feathering for a fixed prop. but you're the first to contact if I change my mind. The prop came with the boat and at first I thought it was a gimmick till I looked it up. Besides low drag it presents full blades in reverse.

I have a manual but not the one you linked. Tks.

One notch less is what I was thinking if I got no other info.

[sastanley]

Bill, I totally understand.. and agree with all the positives of the prop. I am too cheap to buy my boat a new Max Prop, so I was just putting it out there if you decided to sell a used one some day. They are extremely popular on higher end race boats.

Good luck and let us know what you find when you disassemble!

[joe_db]

Step 1 - get a vacuum gauge. You really learn a lot from them regarding prop pitch. Airplanes where you can adjust the prop pitch while flying all have these gauges
Step 2 - If you are getting a low vacuum reading at your max RPM, like say 2" or less, you are definitely pitched too high. Looking at that blade area, you likely are anyway.

I would shoot for around 2200-2300 static RPM, which should give you about 2400-2500 underway.



RPM = how fast am I working
Vacuum = how hard am I working