I have owned a few twin screw diesels over the last 20 years so I have a lot to say, bare with the long thread.
Nothing is ever clear cut when it comes to a diesel engine especially when you don’t know its history or the way it was operated during its life. A 700 hour diesel engine is no good to you if it’s been sitting for a few years (common with live-a-boards) as most of the internals would have corroded over that time. Hence a diesel that has been consistently run to the manufacturers spec sheet can see a lot more than 4000 hours and on many forums you will see people saying this. But the engines that seem to get to the higher hours are generally the low revving / low HP engines. High revving / high Hp diesels don’t have much of a life as they run hotter and faster. Most High RPM/Revving Diesels need an overhaul after 1500 hours.Diesels got there reputation for being bullet proof when they were revving at 1000rpm and pushing out 100 Hp running at 1 specific speed (which it was designed for) and never being turned off to sit for long periods of time. Mainly in commercial applications 80years ago.
Generally you can bank on 2000 USD per cylinder, but that is just the engine itself. If the engine has not been overhauled in 4000 hrs and needs one, then generally most of the other components won’t be too far behind as well. No point in only doing a partial overhaul only to find that 200hrs later the heat exchanger or another major component fails and you over temp the engine then your back to square 1. If you are going to do an overhaul do it properly, and get the whole system overhauled that way you will have a fresh new start, longevity and peace of mind. Below are some of the other components that you will need to scrutinise before you can say it’s a full overhaul and not just a partial. By all means these components will last but they will all need an overhaul/ new fit eventually and that is the cost you really have to focus on as well. Note the other components that make a diesel engine reliable.
· Crankshaft seals
· Gear box
· Injection pump
· Fuel cooler
· Turbo chargers
· Exhaust riser or elbows
· Sea water pump
· Circulating pump
· Oil cooler
· Heat exchanger
· Senders & sensors
· Drive plate adaptor & dampner
Have you considered what it will cost to get the vessel on a slip to pull out the engines? I spent nearly 2000USD before the engines were even out of my vessel before the overhaul begun, and if you are not there to supervise they will surely scratch up your boat in the process. They drove the forks ofthe forklift into my saloon wall when I did my last overhaul 3 years ago.
I have seen full overhauls cost as much as 40K to get the whole system done, and if you come in under all that the better, but do not underestimate repair costs. Quite simply an overhauled engine is never the same as a new engine, which is why it is cheaper to overhaul.
Now that’s the engine, what about the gen/set, that must be running high in hours also.
What about the electrics in the vessel, battery bank.( 4 large batteries could set you back $$$$) fuel tank pressure checks, hull condition, props and prop shafts and the steering and throttle control. What about the bilge pumps??????????????????????/
Get it all on paper and see when the last Survey was done, all the repairs completed over the years, when was the last overhaul, electrical re-fit, gen set etc. etc.
If you are unsure about larger motor yachts and the costs involved, all I can suggest is get a well reputable marine surveyor and marine diesel mechanic and have them do a static inspection on a slip and then an open water test, otherwise you will never know what you’re dealing with. Better to spend 1000 USD now to save 150K USD later.
I good rule of thumb is there is no such thing as a free lunch. If something looks too good to be true be aware or be willing to have deep pockets. If a boat is normally on the market for 400K and you can get it for 250K for sure you will need to spend 200K to get it up to spec, but if you just want to keep repairing her as she breaks that’s an option too. Band-Aid on top of a Band aid will show when you come to sell her yourself so think of the re-sale in years to come. The only people who make money on boats are the brokers.
Too many times I have been invited out on fishing trips never to leave the berth, or broken down whilst fishing, only because people think they can get away with a cheap fix. But that’s just my opinion. Over my years I have learnt to keep 10-20% of the cost of the vessel when in tip top shape to keep her that way. Every year I put her up on the slip for a good clean up even when the antifoul looks good. If you’re in Dubai, surely the sun will mean lots of polishing the gel coat to stop it from wearing away. And I also have someone employed part-time to maintain my 55’.
Now saying that, basically I spend 20-25K a year in pro-active/active maintenance which has never seen me break down or turn back from a trip. I know I can steam in one direction for days knowing the reliability in the core of the old girl. Spending that money on maintenance and upkeep keeps it looking new even though it 15+ years old, but it is worth it.
Nothing like turning a key whenever you feel like it, grabbing an ice cold beer out of the fridge, listening to some good music, and heading out of the marina. The money I spend each year does not out weight the enjoyment I get from boating. And most of the guys I know feel the same. The money only becomes an issue when you don’t have it.
I hope the sale goes well for you and never be too shy to offer half of what they are advertising, it doesn’t hurt. A friend of mine is selling his yacht advertised for 1.3 million, but he would sell it to me for 800K. What a wonderful world.
Hope some of the info helps