Effects of Long Term Displacement operation of 6V92TA

[bobk]

Since this is a subject that comes up periodically and I have a couple of data points, I thought I'd post them in a way that should be easy to retrieve in the future. The news is good.

The vessel is a 1981 48MY series I with 425 HP 6V92 TA's. The engines had inframe rebuilds, including turbo's at about 2000 hours a couple of years before I bought her. When I got her, she had about 300 hours on each engine post rebuild (I'm averaging here). I'm a trawler owner at heart and since this boat has a 'dual mode' hull, I have run it almost exclusively at 1000-1100 rpm/8.3 knots. I had some soot on the transom in my first 1000 mile trip and used Howes Meaner Power Cleaner in the fuel to clear it up and have used it exclusively since.

Two years ago, 2000 hrs SMOH I lost a seal on the starboard engine and had the engine majored in frame. The rings/pistons were not fouled and the hot side of the turbos were fine. The thermostats at this time were 160's and I changed both engines to 170's.

Last week at about 2500 hrs SMOH, I had the port transmission removed for service and again the turbos were dry and the exhaust manifolds were as well and just had a very light coat of soot.

My practice has been to run them hard every 20-30 hours just long enough for any blue smoke to clear, usually just a minute or two.

So for others considering operating as I have, It seems to have worked for me. BTW, somewhere along the line I increased the prop pitch from 23" to 23.5" just to load it a bit more. It still makes 2200 rpm at WOT with a clean bottom.

Bobk
1981 48MY
Chateau de Mer

 

[krush]

if you never go on plane, why not increase pitch or size of the props like Brian did and documented here a couple years ago/

 

[bobk]

if you never go on plane, why not increase pitch or size of the props like Brian did and documented here a couple years ago/

I've thought long and hard about it and agree it was a great post and way to improve operation..... but my prop guy doesn't think he can change the pitch that much and they ain't cheap to experiment with.

Bobk

 

[GJH]

I recall Brian's thesis revolved around de-rating the engines and increasing the diameter of the props. I cruise like Bob. OEM props are 30x29. I played with 30x31 for awhile, as that is what my spares are, and got a lot of soot on the transom where before I had none. So off they came. Life seems pretty good, other than I haven't figured out how to get the speed the boat should (JLR does) even though I get WOT easily when clean. Maybe we just have too much liveaboard stuff, though according to the travelift guys, we are only about a ton overweight.

 

[Jaxfishgyd]

I would be afraid of how much extra weight we have being liveaboards...
Know my top speed went from 18 kts at sea trial (boat completely empty) to a top speed of 14kts now even though we still turn 2450 rpm at WOT.
But I run ours at 1100-1200 rpm 90% of the time (8- 8.4 kts)

 

[bobk]

My boat was advertised as 44000 pounds. The last haul the marina owner estimated we are at 53000 pounds. Seems like a big diffderence but she is a liveaboard with multi season clothes, tools, heavy furniture, big dink, hard top etc so maybe. But when all is well, she still delivers 18 kt at WOT in deep water.

Bob