[C320-list] Gori-Prop buyer question -Notapropmanufacturerdebate

[bruceheyman at cox.net]

Jeff,
Since that is only 1/40th of a boat buck I don't have to wait for the tool box.  I'm off to the hobby store, hope I don't also come home with an RC sail boat. Dock neighbor was sailing one and it looke like fun.
Bruce
Somerset 671 SoCal
Sent via BlackBerry from Cingular Wireless  

-----Original Message-----
From: "Jeff Church" <jjemail at comcast.net>
Date: Fri, 13 Oct 2006 17:53:03 
To:"C320-List" <c320-list at catalina320.org>
Subject: Re: [C320-list] Gori-Prop buyer question -
	Notapropmanufacturerdebate

Bruce,

If you don't want to wait for the toolbox, you can buy an optical tach at a 
hobby shop for about $25. They use them to tune the prop speed of radio 
control airplanes and helicopters. I picked one up this summer and it works 
very well.

Jeff
----- Original Message ----- 
From: "Bruce Heyman" <BruceHeyman at cox.net>
To: "'C320-List'" <c320-list at catalina320.org>
Sent: Friday, October 13, 2006 5:30 PM
Subject: Re: [C320-list] Gori-Prop buyer question - 
Notapropmanufacturerdebate


> Warren,
> Excellent research and analysis - thanks!
>
> I took the boat out (we have the Autoprop) last weekend and ran it maxed 
> out
> for about three minutes.  The engine settled in at about 3350.  That says
> I'm down by about 6.9% which is in your "concerned" ranged.  I still have 
> to
> verify that the tach is accurate at these RPM's. When do we get the group
> tool box so I can barrow the hand held tachometer.
> Bruce
> Somerset 671 SoCal
>
> -----Original Message-----
> From: c320-list-bounces at catalina320.org
> [mailto:c320-list-bounces at catalina320.org] On Behalf Of Warren Updike
> Sent: Friday, October 13, 2006 3:10 PM
> To: c320-list at catalina320.org
> Subject: Re: [C320-list] Gori-Prop buyer question - Not
> apropmanufacturerdebate
>
> I recommend: "Propeller Handbook," by Dave Gerr, International Marine
> Publishing Company, 1989, as a reference for understanding propeller
> selection.  In the introduction he states, "Actually, all propeller
> selection is a process of approximation and estimation."  If you have the
> engine manfacturer's power curves, they can be useful in understanding the
> operation of your engine, and in selecting a proper propeller.
>
> On the matter of top RPM, on page 6, he says, "If your engine is reaching 
> 95
>
> percent or more of its top RPM, the propeller is probably sized quite 
> well.
> If you are unable to reach 90 to 95 percent of the top RPM, there is 
> reason
> to be concerned."  The reason for this being that the engine mfgr.s top
> rated RPM is based on ideal conditions.  It is more likely than not that
> your engine will not attain the stated or specified max. rated HP in 
> actual
> use.  Therefore, it is better that your propeller power curve cross the
> engine power curve below the max.rated RPM.
>
> The following are my own observations:
> I have a two blade 15 X 11 on my 1994 C320 with the Perkins M30 engine and
> Hurth 2:1 reduction reverse gear.  To my eye, it appears that the blade 
> area
>
> of a 3-blade prop (i.e. Catalina stock unit,) is somewhat greater than 
> that
> of my two blade prop.  That being the case, to keep the same power 
> function
> as the two blade prop relative to engine power, it would seem logical to 
> me
> that I would need something smaller than 15 X 11 when changing to a three
> blade prop.  Infact, Gerr includes the measurement of "blade area" with
> pitch and diameter:  "Choosing the correct propeller pitch, diameter, and
> blade area will insure that power requirements of the propeller match the
> engine correctly."
>
> Before making the selection, I would want to conduct a few trials with my
> current configuration to determine speed at various RPM levels and under
> various sea conditions.  Then, compare this to the same trials with the 
> new
> prop to be confident that it is correctly sized.  The new prop should 
> allow
> you to attain the same max. RPM as the old, and give you more speed and
> better acceleration in flat water as well as in rough.
>
> Other factors you may want to consider are degree of prop "walk," and
> performance in reverse.
>
> Warren & Pattie Updike
> C320, #62, 1994, "Warr De Mar"
> Frog Mortar Creek, Middle River
> Chesapeake Bay
>
>
>
>
>