Prop Pitch

[Ken Juul]

The recent discussions on prop pitch got me thinking.  So as we were motoring on Saturday I did some experimentation.  In neutral the engine maxes out at 3600, that is full throw, not sure if I've made the governer or not.  So I probably have some tach indicating issues to sort out.  In gear the max I can get is 2700-2800.  Even though the indicated rpm are probably not correct, the 800-900 rpm drop is about 1/4 of the available rpms.  Is this big a drop normal or am I overpitched? 

M25xp engine with about 1100 hours on it, seems to be making the same power as previous years so I don't think it is a lack of power issue.

[sedelange]

Depends.  Did you measure the RPM's with the boat sitting still, accelerating, or at steady state maximum speed?  It you waited until you speed stabilized, in smooth water, then I am guessing you are a little overpitched.

Steve DeLange

[David Sanner]

Sounds over pitched to me... or your engine isn't at the top of it's game.
Anything below 90% of maximum of your no-load RPM could be an
issue or something to investigate further.

Are you getting black smoke when you run @ 80-90% of your
max (in-gear, flat water, clean bottom) rpm?  (What's your
boat speed looking like?)

With my current 15x9x3 prop I get close to max no-load RPM but
not 100%.  Tied to the dock I get 90% . 

Some say your engine should always get 100% of its no-load RPM but
I don't know if that's a reality since we only have 23hp from the factory.

Having said all of that I think the most obvious way to tell if you're
overpitched is excessive black smoke... otherwise my thinking is the
more pitch the better.

[Ken Juul]

I took all the measurements at steady state moving about 5 kts.  I don't notice any black smoke while we are running, but notice alot of black residue around the exhaust after I've motored for a long while.

Plan on checking the dip switches this weekend and perhaps borrowing a mechanical rpm meter from a local boatyard to get the tach indicating correctly.  I remember reading about using a florescent light tube to set the rpm but can't find it.  Anybody have the details?

[Craig Illman]

Ken - I think the routine about using the florescent light was on the C36 site. I tried it without success. I must not have had the correct type of lamp or too much ambient light. David Sanner posted the Teleflex tach instructions on the Manuals page to fix the dip switches.

Craig

[Craig Illman]

Ken - Here it is: http://www.catalina36.org/articles/reference/dieselAndPropellerTutorial.htm

Craig

[Ken Juul]

Thanks Craig!

[Ron Hill]

Guys : I put that "TIP" in the C34 Mainsheet tech notes over 12 years ago (about checking RPM with a florescent light).  Because of the 60 cycle AC, I  recommended you check at 1200 and 2400 rpm. 
Maybe the C36 being 2 feet longer needs to check at a higher RPM??   
A thought ?? 

[Ken Juul]

Thanks Ron, 
I knew you had written it up but could not find it. 

Craig,
I too had problems seeing the tape.  As I played with the rpms I noticed that the pulley mounting bolts were doing the wagon wheel dance.  Played with the rpm, got them to stop moving.  Assuming that was 1200 I looked at the tach.  Read 1450.  Adjusted down to 1200.  Ran engine up until the bolts stopped the dance again.  Tach read 2550.  Again adjusted down to get 2400.  Did this a couple times to fine tune.  Now at the idle stop, tach reads 750 at full open 3150.  Not sure if it is exact, but I'm sure it is a whole lot closer to being right.

Tomorrow I'll get some new reading on the rpm in gear.

[Ron Hill]

Guys : I purchased a BorgWarner mechanical tack. for about $48 - 19 years ago.  It's been a great investment as I have taken readings at various points and know what the Teleflex says at 1000/1500/2000/2500 rpm and then know what the actual engine rpm really is at those settings!
A thought.   

[David Sanner]

Or they have fancy laser tachs... here's the cheapest I could find:
http://www.virtualvillage.com/items/item.aspx?itemid=3589880