ZF Tranny thoughts

Please forgive both the length of this post and also any mechanical terms/ concepts that I may mangle.

I am running a 1996 60' Viking Motoryacht w/ 820 MAN's (2200 hrs) and ZF gears. I am into my 2nd summer with the boat. Usually, I run at 1950 RPM's. 7 weeks ago, pulling out of the marina, as I went to throttle up, my stbd engine rev'd up to 2500 rpm's with no power transferring to the prop. I saw a cloud of black smoke off the stern (usually only the smallest amount of grey smoke at start up that dissipates after 5-10 seconds). No noises of having hit anything. I immediately pulled the throttle back and, thinking perhaps it was transitory, I tried to power up again - same thing (no black smoke). I tried to throttle up, this time with 'sync engines' on in case that might 'fix' the problem but no luck. One more time (w/o the sync) and I headed back to my slip. The boat was maneuverable at idle.

I had a diesel mechanic to the boat. He checked the tranny oil (cooked) and determined that it was more than clutch plates. (I also checked the shaft/prop, which were in good order). Over the course of the next few days, he disconnected the tranny, removed it from the boat and sent it to a well-known rebuilder in NJ.

The mechanic commented that he suspected that I hit something or wrapped something around the prop. The rebuilder expressed his opinion, after disassembling the tranny, that I had probably hit something or gotten something wrapped around the prop. He mentioned that there were 'imprints' on the gears, which would be indicative of the tranny having been 'shocked' into stopping abruptly and I believe his opinion of what happened was based on this.

I made an insurance claim and the insurance company 1) surveyed the tranny before uncoupling from the engine 2) took oil samples 3) visited the repair shop to examine the tranny after disassembly 4) took another oil sample. The forensic engineer for the insurance company is now suggesting either:

regular wear and tear
lack of maintenance (all maintenance since I own the boat is per MAN
guidelines)
improper pitch on the prop (I do not know the numbers on the prop or even
if they are the original spec'd by Viking).

I would appreciate any thoughts / comments to help formulate my thinking in dealing with the insurance company.

Thanks in advance. jack

Yachtjocky: sure, boat was surveyed prior to purchase (2 surveys - boat and engine) both were OK. I had a diver check the shaft/prop the day of the incident as I thought possibly the prop fell off or was spinning loose - everything was OK. Props are listed on my survey as 31 x 41 (4 blade). I always ran the boat at 1950 rpm's but top s/b 2300. (when this incident happened, the rpms shot to 2500). Re ZF maintenance - noted - thank you.

DTW Viking60: I have no idea what shafts are on the boat but I will check when it is hauled this winter. Thanks for the heads up. Yeah, it's a great boat. Best combo I have found for size, space, handling, seakeeping, etc that I can drive myself. Sorry to hear about your past problems and good luck in the future. Keep the shiny (dry) side up.

Jack

I am talking about the shafts INSIDE the gear boxes, not prop shafts. There are 3 shafts inside the gear box that are input, transfer and output. I would make sure that your re-builder manga flux tests these shafts before re-assembly. The shafts can have very small longitudinal cracks in them that will allow the high pressure oil in the internal passage in the shaft to leak out into gearcase and allow the high pressure side of the oil circuit to leak into the gear case. When this happens you lose high pressure to the entire oil circuit, which will cause the problems you have. Low "high side" pressure will create a failure on the clutches and gears. You should have transmission pressure gauges both up on the bridge and below in the ER, did you note the pressure readings? Should be above 325 psi.

Wow - OK. Unfortunately, the tranny is reinstalled. At this point, I cannot imagine that I can check for the internal shaft cracks you mentioned (this would hardly be considered normal/routine maintenance). Yes, I have gauges up and down. I did note that all analog readings on the bridge were within operating range (at idle as I did not even have a chance to get to higher operating ranges). Thanks. Jack

Pleased to advise that my insurance company called and said they are covering. Jack.

not yet but I'm heading out to buy grease.