Sweet spot in diesel

Jan 12, 2010
5
Catalina 30 Lake Murray, SC
At what RPMs does your diesel tend to have less vibration? 800 RPMs, 1200 RPMs, 2000 RPMs 2,800 RPMs?

While lazily motoring on, where is your diesel's "sweet spot" and at what RPMs?

Do RPMs, vibration, noise, rattles and shakes coienside? If so, what would you tackle first to rid your boat of the annoyances?

If responding and applicable, could you add the motor manufacturer, motoe model, propeller a two blade or three blade and length of your Catalina?

Thanks for reading and I hope to get a good response as I am always trying to get the best performance from my 1987 Catalina 30.

Lew
 
Nov 8, 2010
11,386
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
If you are looking at the life of the engine, the 'sweet spot' of any marine diesel is 80% of its max RPM. Down to 60% on occasion, but it long-term will be better served running at 80%.
 

Tom J

.
Sep 30, 2008
2,301
Catalina 310 Quincy, MA
I call my diesel's sweet spot 2,400 to 2,500 RPM's. That's cruising speed, and she is smooth and quiet. On the other hand, from 1,400 to 1,800 she vibrates noticeably. She is a 3 cylinder, so what are you going to do? M25-xpb engine, Universal. Catalina 310. Three bladed prop.
 
Sep 25, 2008
30
Catalina 30 Lake Murray Sailing Club
Two things:
Install new motor mounts for vibration reduction
Install air filter system that Aaron discussed in previous thread to reduce engine noise

I plan on going on the hard to bottom paint early next Spring. Will review shaft and propeller then.

My Cat 30 gets the shakes around 1800,too!

Lew
 
Jun 29, 2011
142
Catalina 30 Mk II Gibsons
Unshackled;
Top sweet spot, and cruising rpm is on my m25 xp is 2100 , it can go up from there, but with increase in noise, vibration and steering difficulties.
Typically we cruise at the next lower harmonic, you can feel it when you throttle down, let it settle there when you are not in a hurry.
Aaron is on the same dock as we are, I will be modifying my intake to his setup this spring.
CBC
 
Sep 25, 2008
30
Catalina 30 Lake Murray Sailing Club
Are you on Salt, or fresh water?
I am on fresh water. Lake Murray in Columbia, SC. The lake has 500 miles of shoreline. It's 13 miles long and 3.5 miles wide at the widest part.

We typically raft up with four other sailboats at a cove named hurricane hole, 4 miles from my marina. Usually sail there and stay as long as possible, then motor back at dusk.

Is there a significant difference? I haven't given that much thought.

Lew
 
Jun 29, 2011
142
Catalina 30 Mk II Gibsons
Yes, fresh water will make a difference, there is a formula for hull speed, and another for prop efficiency that will affect performance, I do not have those figures at my fingertips right now, however you can google the formulas.