It could be an oil build up that causes a runaway in a yacht. But it's very very rare. It's usually a governor issue that causes a runaway.

Cost is because of access, it takes a lot more time. 12v71s because you have 4 cylinder heads, on yachts you also have a lot of stuff that has to be sent to be cleaned. Heat exchangers and other things necessary to cool them (oil cooler, fuel cooler, transmission cooler), on TI's intercoolers, etc. Also, all of the stuff on the yacht that has to be padded and carrying all of the stuff out of the yacht.

To the OP, they have a reduction gear (transmission) it is a single gear that does forward, neutral, and reverse. It will be around 3:1 reduction, engine turns 999 rpms, shaft turns 333. Generally you'll see twin disc in that era, but could also be Borg Warner or ZF. Generally you don't have an issue with the gear and it's rare they need to be rebuilt, but figure $10k if does need to be rebuilt and re-installed. On a rare occasion you could also have an oil seal fail and it's probably $3-4k to fix it....

This message has been edited. Last edited by: jimmy123x,

When looking for an overhaul find a commercial marine diesel specialist and save some money over the "yacht" guys. Any competent commercial mechanic should be able to in-frame a 12v71 in under a week for under $10K. Back in the ancient times (when we still ran 2 strokes) we would do a complete main engine swap on a 12 or 16 cylinder diesel in under 48 hours with just the vessel crew.

I had a Cat C280-16 (about a $900,000 6500HP engine) run away on me last year (in gear with transfer hose hooked to a drill ship) 2nd Mate had the Conn and he panicked. I gave him about 30 seconds to try to sort it out before I stepped in and hit the E-stop and took manual control of the remaining 3 engines/thrusters before we put a strain on the transfer hose.
The cause was an unsecured electrical cabinet door banging against a Dynamic Positioning primary thruster control interface board and shorting it out.

Thread drift aside, definitely find an excellent surveyor to look over the boat before committing to a 46 year old boat, even in FW that is a lot of years on the equipment.

quote:

Originally posted by CaptainMike:
When looking for an overhaul find a commercial marine diesel specialist and save some money over the "yacht" guys. Any competent commercial mechanic should be able to in-frame a 12v71 in under a week for under $10K. Back in the ancient times (when we still ran 2 strokes) we would do a complete main engine swap on a 12 or 16 cylinder diesel in under 48 hours with just the vessel crew.

I had a Cat C280-16 (about a $900,000 6500HP engine) run away on me last year (in gear with transfer hose hooked to a drill ship) 2nd Mate had the Conn and he panicked. I gave him about 30 seconds to try to sort it out before I stepped in and hit the E-stop and took manual control of the remaining 3 engines/thrusters before we put a strain on the transfer hose.
The cause was an unsecured electrical cabinet door banging against a Dynamic Positioning primary thruster control interface board and shorting it out.

Thread drift aside, definitely find an excellent surveyor to look over the boat before committing to a 46 year old boat, even in FW that is a lot of years on the equipment.

One old Oil rig Captain told me they had a crew boat right when the first 12v92's came out. All 3 engines were from a different marinizer....one was J+T, one Covington and another S+S. He told me they were always grenading one of them and majoring them in a couple of days.......

For those that don't know......whoever marinized an engine spec'ed the turbo's, spec'ed the injectors, and a bunch of other parts. So a J+T 12v92 TI might be 1165HP, a covington 1050HP, etc. But you put props on a boat so they're all matched.....so imagine the mess with each engines load factors that created.

What labor rate are the commercial diesel engine guys at? Here in South Florida the dealers are $116hr and charge drive time, mileage, etc.. Good independant marine Diesel guys are around $75-85hr. But the hours still really add up when you look at the configuration of a 12v71 in a yacht like a hatteras......you're torqueing connecting rods and main bearing caps upside down and with mirrors.

Also a major in a yacht engine really adds to the cost because you're sending out the 2 heat exchangers, oil cooler, intercooler, tranny cooler all to be professionally ultrasonically cleaned, injectors to be rebuilt, ordering rebuilt heads from DD, have the blower checked/rebuilt,starter and alternator rebuilt,and on and on. Usually everything on the motor gets done because of access and it has to come off anyways.

A full service on 12v71s- oil change, fuel filters,zincs and raw water impellors will take a mechanic a full day with a helper usually just because of access and carrying all of the stuff through the yacht. And that's considered fast.