[C38] Universal M30/5424 reduction ratio -- Prop size

[Steve Smolinske]

Good question, it seems to me when I had the diver switch out my two
blade martec to the three blade max prop he had to come back and adjust
the pitch, At the end of this month after the Van Isle 360 Im putting
the max prop back on, Ill check with him on the pitch setting he has on
record.  With the max prop we run higher rpm 2400 or so to get the same
speed as the two blade martech at 2000. 

-----Original Message-----
From: listserve-bounces at catalina38.org
[mailto:listserve-bounces at catalina38.org] On Behalf Of Jon Whitney
Sent: Tuesday, June 04, 2013 7:12 PM
To: listserve at catalina38.org
Subject: [C38] Universal M30/5424 reduction ratio -- Prop size

Hi All,
I was just researching the proper prop size and pitch to match the
Universal M30/5424 on our Cat38's (as I'm sure many of you have done).  
I just got off the phone with Catalina Direct and we stumbled upon an
interesting question that you may know the answer to.  We were looking
up the gear reduction ratio on the transmission for the original
M30/5424  and found a discrepancy in the ratios reported by Catalina and
Universal.

The Universal Maintenance Manual for models 5411/5416/5424/5432 states
that the transmission reduction ratio is 2.14:1  (with an HBW-10 Hurth
Transmission) on the 5424 (24 hp, 3 cylinder, 2800 max rpm).  However
the Catalina factory specs state that the gear reduction ratio is 2:1 
(for the same engine).   Does anyone know which is accurate and why the 
discrepancy?

The difference doesn't seem like much, but when they punched all the
numbers to determine ideal prop size it changes the pitch ~ 1 inch.  
E.g., using the 2-blade fixed prop a ratio of 2:1 gives 15" x 13" pitch
(13.3" to be exact), whereas the ratio of 2.14:1 gives 15" x 14".

 From what I could gather the older S&S C38's with the Universal
M30/5424 came standard with a 2-blade 15"x13" and an optional 3-blade
15"x12". Obviously, the 15"x13" is fine as thats probably what most of
us have had, but just wondering which ratio/pitch is more accurate and
if anyone has used the larger (15"x14") prop size. As always, I'm
grateful for any advice.

Best,

Jon Whitney
1979 Hull #54
"Eye Whitness"
Honolulu, Hawaii

ps. Thanks to everyone for their comments on thru-hulls sizes
(especially Max, Les, and Steve).


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