The handbooks for marine diesel engines often say that you change the oil and filter every 50 hours or once a year?
Then some may add that if you use a higher grade oil (Shell Rotella is one) you can change the oil every 100 hours and once a year?
So what is the truth, can we go further than the 100 hours?
On my last cruise and to St Helena Isle, Brasil, Trinidad and Tobago, Venezuela and the return to Cape Town in South Africa, the oil was changed every 250 hours.
This worked out fine and when that boat was later sold the BMW Hatz 30hp twin cylinder had some 3600 hours on the clock.
The issue is that the oil in a cruising boats engine hardly ever gets cold, this means there is less chance of an acid building up from condensed moisture in the engine.
A comment from a marine engineer follows:
Purely on appearance as depicted in your photo, I would suggest it can be returned to service. It is running hours that matters - age in years is not significant - of course provided it's suffered no corrosion through moisture in the oil during extended periods of cold idleness. In ships' generator engines, which run continuously for weeks or months at a time, bearing renewals at under 25,000 hours would be unusual. A year of continuous running equals only 8,760 hours, and I doubt your Perkins hasn't seen that in its 30 years' life!!
Think about my recently traded-in Toyota Hilux with 270,000 kms on the odometer. In running hours, that equates to:
7,700 hrs at 35 km/hr average speed, or
3,800 hrs at 70 km/hr average speed,
and involves lots of cold starts, hot stops, crawling in traffic and high-speed cruising. I think that engine has worked longer and harder than your yacht engine. It's been resold by the dealer without any opening-up and with a guarantee.
Unless your engine has suffered abuse in use, poor maintenance or some other calamity, I would suggest a head overhaul and a crankcase / sump clean is all that's justified, plus possibly injectors and fuel pump to clean / service. Or maybe nothing at all!
If it aint broke don't fix it!