How many hours is too many?

[wsmurdoch]

Originally Posted by David Mathis

Only 4000 hours on a diesel is low. It matters little if it’s generator hours or propulsion hours. The only catch is maintenance. Check the maintenance log. How often was the oil changed? Every 100-150 hours, you’re ok, every500 hours, not so good. Was the filter changed with the oil? Take an oil sample and have it analyzed. It will tell much about the condition of the engine and specifically the bearings. It’s a cost effective measure for boat buyers.

What do you think of this engine?

[capt jgw]

Originally Posted by mvweebles

In OP, states M25, which is a Universal 20hp 3 cylinder. These engines do not have duty ratings the way that larger engines do. It was made for sailboats of this size and was quite ubiquitous during the 1970s through early 1990s when Yanmar dethroned Universal at the small end, and Perkins at the medium end (say, under 100 hp). They were a very popular replacement g and upgrade for Atomic 4 gas engines. Another post on this thread said Universal used Kubota power plants. I have no idea.

It's a Kubota D850, designed for small tractors and other light equipment. Used all over the world in that application. Marinized by Universal, also I believe Nanni and Beta used the same or very similar block.

[capt jgw]

Originally Posted by Cowpoos

Are you guys sure? I would be almost certain its a Shibaura 653, that Perkins rebadged into its 100 series small diesel range and the Perama series of marine diesels. They look similar, obvious give away is the different side of the engine of the oil filters.

Nope, Universal only used Kubota on all their models. Westerbeke, who now owns Universal does use other makes, but that's pretty recent.

[capt jgw]

Originally Posted by kenbo

The M-25 is a good engine, the weakest link on that engine is the Rube Goldberg manner in which the alternator is mounted and tensioned. If the alternator mounting modification has not been done that's what I would focus on. The mod is available from Catalina Direct. Change the oil and coolant enjoy the boat.

Right. Universal used the stock tractor alt mount that came with the block. Fine for the 15 amp alt in the tractor but no way adequate for the 55 amp unit they used. It will break the timing gear housing, and that is no longer available from Universal or Kubota. The reworked mount bolts to the exhaust manifold and is strong enough for 100 amps or more. It doesn't touch the gear housing at all.
The engine the OP is asking about must have had this upgrade, unlikely to have made 4k without it.

[kenbo]

Since I'm in lockdown I thought I'd play with some numbers in regards to the OP's situation.

Using Frank Butler's design displacement (light ship???) of 10,200 lbs., LWL of 25' with a theoretical hull speed of 6.7 kts and 21 hp at 3200 with a 2:1 reduction: the Catalina 30 needs all 21 hp to drive the hull to 6.7 kts. It works out to be 501 lbs. per hp. In my opinion that's at the very top end of satisfactory weight to hp ratio, some would differ. Loaded with fuel, water, stores and 2 souls the displacement could easily go to 11,500 lbs. or higher. At 11,500 lbs. the hull needs 23 hp to reach 6.7 kts and 565 lbs to hp.

My point with this exercise is to say it's probable the engine was worked very high in its power range during it's usage. At 11,500 lbs, using 75% of the engines power would drive the hull to 5.8 kts in calm, low wind conditions. Some owners would be tempted to over prop the engine to bring the rpm down at cruising speed making a marginally sized engine work even harder in a high exhaust temp condition. How bored am I???

On edit, Kubota, the manufacturer of that diesel, rates the D850 at 15.5 hp at 3000 continuous and 19.8 hp at 3000 Gross intermittent. And that's without taking into account hp lost at the 2 shaft bearings on that boat but they do rate their engines spinning a fan so maybe a wash.

[donradcliffe]

Originally Posted by a64pilot

Most people run their boat motors harder than they realize, average 3600 RPM max motor run at 2500 RPM is often at least 50% power, and I think you will find many people run them that hard, or harder.

If the propeller is matched to the engine (the engine is putting out rated hp at 3600 rpm), the hp at 2500 rpm will be more like 30% or less of rated hp. Take a look at the propeller law curves for marine applications.

[kenbo]

Originally Posted by donradcliffe

If the propeller is matched to the engine (the engine is putting out rated hp at 3600 rpm), the hp at 2500 rpm will be more like 30% or less of rated hp. Take a look at the propeller law curves for marine applications.

Of course that all depends on how well the engine was matched to the hull.