[C320-list] Low speed under Load

[Jeff Hare]

Well... 

First, to be getting 5kts at 2000 rpm means you're well over pitched
regardless of which prop you have.  So, you'll be building up carbon in the
elbow like crazy this way.  Even if it seems ok it isn't.  So I'm guessing
your exhaust elbow is probably clogged unless you can rev to 3800 RPM easily
in neutral.  Since your diver says your prop is clean, there are really only
a few things I can think of that can keep you from getting over 2800 rpm
under way.

1:  Over pitched prop
2:  Clogged elbow
3:  Dirty prop  (ruled this one out)
4:  Dirty Primary or Secondary fuel filter

I think #1 caused #2.

-Jeff Hare
#809

-----Original Message-----
From: C320-list [mailto:c320-list-bounces at lists.catalina320.com] On Behalf
Of Donald Lawson
Sent: Monday, July 13, 2015 2:33 PM
To: C320-List at Catalina320.com
Subject: [C320-list] Low speed under Load

All
I have 2004 320 with a Yanmar 3YM30 fitted with a 15x9 MaxProp by PO.
Everything has worked well for 3 years. At last spring haulout I had the
prop serviced and bottom painted. Boat worked great. Recently I get 5 knots
at 2000 rpm, which is normal.  However there is no increase in boat speed
past 5 knots up to 2800rpm.  Cant' get above 2800 rpm. Rpm to 3000+ easily
in neutral.  No visible exhaust  at 2000rpm. 
Skipper says some minor black smoke at 2800 rpm. Seemed like a mist to me.
Recently serviced.  Got fuel and air OK. Had diver check MaxProp.  Seems OK.
Diver cleans bottom and prop once a month.
Anyone had a transmission trouble with a Yanmar? Starting to grasp at
straws.

Don Lawson
"Mandolin Wind"  
Ventura, CA