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

Jon Whitney jonwhit23 at aol.com
Tue Jun 4 22:12:09 EDT 2013


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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