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Old 01-03-2011, 01:04   #1
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To Re-Pitch a Folding Prop, or No ?

I am sharing my old boat again this year. It's a Viking 33, largely stripped out, with a direct-drive Atomic 4, in good working order.

I started with the "stock" 12 x 6 two-blade fixed prop. I switched a few years ago to an 11 x 8 two-blade Gori folding prop, which with I have been very happy for the most part.



The main differences between the props is that I have a far lower "dead slow" now, which makes docking easier. I also have a more aggressive reverse, seemingly, because I can stop better, likely due to the pitch.

The folding action means less drag, faster sailing. A definite plus.

What I do not have, however, is a really good top speed now. I can make six to six point one knots in light chop. I used to make 6.5. The engine seems to rev so far and no farther (yes, it's tuned properly).

So my question is should I bother to flatten the pitch of this prop, and if so, to what degree, and what would be a reasonable price? I launch in seven or eight weeks.
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Old 01-03-2011, 09:02   #2
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Re: To Re-Pitch a Folding Prop, or No ?

Before you touch the prop do three things:

1. Calibrate your tach with a photo tach, either electronically by adjusting a pot on some or making an adjustment table.

2. Determine how fast the engine will rev in neutral at wot. The governor will limit engine speed and do no damage. The engine should reve to the rated wot speed plus about 200 rpm.

3. Determine how fast you can go in gear at wot.

If you can't hit rated rpm in gear then you can think about flattening pitch. If you can "rev so far and no farther" then it may be limited by the governor doing its job as in #2 and you are underpitched.

Most prop shops are leary about working on feathering/folding props. I suspect that they know that they can cause more problems than they can solve. You may have to work with Gori to get this done. But the results of #3 will give them some data to work with.
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Old 01-03-2011, 09:42   #3
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Re: To Re-Pitch a Folding Prop, or No ?

Good advice. I should install a tach anyway, and a timing light I can borrow. I rebuilt this engine and frankly, I've always worked on sound. With the fixed prop, I was able to get a "roar" and you could feel the push. Now, the engine maxes out with the throttle advanced less than half its full "throw". I estimate neutral idle to be about 800 rpm and "dead slow" forward to be about 700 RPM.

This is useful in docking and crawling along with minimum way on. Maneuvering is easy and almost pinpoint. So I am on the bubble about going from a pitch of eight to a pitch of six, for instance, except I'd like to access the right of the power band.
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Old 01-03-2011, 09:45   #4
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Re: To Re-Pitch a Folding Prop, or No ?

[QUOTE=djmarchand;631710]Before you touch the prop do three things:


"2. Determine how fast the engine will rev in neutral at wot. The governor will limit engine speed and do no damage. The engine should reve to the rated wot speed plus about 200 rpm."

Atomic 4 engines are not equiped with a governor. I would strongly recomend NOT to run the engine at wide open throtlle in neutral.

Regards

Daniel
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Old 01-03-2011, 09:56   #5
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Re: To Re-Pitch a Folding Prop, or No ?

Thanks. I wouldn't do that, anyway. I rebuilt the thing, and no parts were left on the bench.
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Old 01-03-2011, 10:13   #6
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Re: To Re-Pitch a Folding Prop, or No ?

Call someone who does this for a living. The owner I totally trust and have been doing business with him for over 20 years. He will probably give you advice over the phone for free.

San Francisco Bay Boating: The Prop Shop
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Old 01-03-2011, 10:28   #7
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Re: To Re-Pitch a Folding Prop, or No ?

Alchemy,
When you took the motor appart, did the exhaust valve seats need replacement with hardened inserts?

Thanks

Daniel
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Old 01-03-2011, 10:41   #8
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Re: To Re-Pitch a Folding Prop, or No ?

I had the same problem on my Pearson Vanguard. It seems that the A4 is really picky about pitch, if it doesn't get it's rated rpm it's not doing all it should. I changed to the indigo prop and it made a world of difference. I know that doesn't help you, but if you could match the pitch of the indigo prop it might help.
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Old 01-03-2011, 11:02   #9
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Re: To Re-Pitch a Folding Prop, or No ?

Quote:
Originally Posted by Dangen View Post
Alchemy,
When you took the motor appart, did the exhaust valve seats need replacement with hardened inserts?

Thanks

Daniel
No, they did not, if you're talking about what I think you are. The springs and valves themselves were replaced (and the valves kept for spares as they weren't in bad shape) along with new pistons (as I recall, they were .010 oversized), rings, a head hone and other bits and pieces. The block was throughly flushed and peered at.

Here in Toronto, if you get 20 hours a season on the A4, it's 60 trips to and from "head to wind". I have difficulty draining even the gas tank I installed that was 2/3rds the size of the original Monel tank.

I take a couple of trips per season of the weekend/overnight variety, and that's when 75% of my hours are put on, so basically, stuff doesn't wear out if you winterize properly and relube properly. More A4s are damaged from crappy winterization and dissolving water mufflers than through actual hours run around here.

More diesels, too, come to think of it.
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Old 01-03-2011, 11:05   #10
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Re: To Re-Pitch a Folding Prop, or No ?

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Originally Posted by Sailmonkey View Post
I had the same problem on my Pearson Vanguard. It seems that the A4 is really picky about pitch, if it doesn't get it's rated rpm it's not doing all it should. I changed to the indigo prop and it made a world of difference. I know that doesn't help you, but if you could match the pitch of the indigo prop it might help.
Good suggestion. I am getting information that this is a job that will cost me more than the prop did (I got it used for $300, which is 1/4 its cost new), so I think I will shelf it as an idea UNLESS I encounter someone looking to trade an 11 x 7 or 11 x 6 folder with a 7/8" shaft...but the odds against that are long!

Thanks for all the suggestions. Discussion of this sort influences how I am going to pitch my feathering VariProp when I finally bolt that on.
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Old 01-03-2011, 12:00   #11
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Re: To Re-Pitch a Folding Prop, or No ?

Whoops, missed the A4 reference. Yes the A4 has no governor, so skip #2. But do check rpm at wot in gear. The ear can be deceiving.

David
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Old 01-03-2011, 13:35   #12
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Re: To Re-Pitch a Folding Prop, or No ?

Good counsel. Roll on, launch!
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