volvo D6

[Bigfoot1]

I am building a 36 foot power boat that I am going to power with D6 volvo sterndrives. We do a lot of fishing, trolling at low speed, 1 - 2 knots.
I have been told that the duoprops cannot be used for that slow spped but I can build trolling brakes using the trim tabs so that is not my concern. I wish to use a single diesel at a time for trolling but some people have told me that the Volvos will carbon up and be ruined in short time.
Two boat builders have said that the engines will carbon up and the clutch needs a higher engine rpm to stay engaged without slipping. A volvo techy said the same. A salesmanager for volvo engines said no problem but run them a bit after trolling to clean them out and an experienced volvo mechanic said you can troll with them and there is no clutch issues.

So I am lost,
Anyone have experience with this situation
I do not want to have to mount a gas outboard on the swimgrid with redundant steering and controls to troll slow.

[Guest62110524]

hello
Before I started building in the late 70,s I was a qualified diesel fitter with Cummins,
I just fitted one of those D6 ,s to a boat
With any new diesel do not let it lo idle or high idle, high idle is full rpm no load
work the boat in the beginning, this is so the bores do not glaze , If you are say testing things at the dock, run the boat against spring lines, but do not let it idle for long periods
After the engine is bedded in you can then safely idle it,

[CDK]

I do not believe in clutch problems and the carbon quickly leaves the engines when the boat returns home at speed.
But there is something else:

With duoprops matched for the 36 ft boat, trolling at 1-2 knots will only be possible with something in tow that causes enough drag, otherwise even on one engine the boat does more than 2 knots at idle.

[FAST FRED]

"and the carbon quickly leaves the engines when the boat returns home at speed."

The problem with under loading is not some carbon in the exhaust.

At very light loading the combustion does not get behind the rings , forcing them to seal the cylinder bores .

This caused the cylinder walls to be burnished , a polishing action that removes the oil holding honeing (scratch pattern ) the engine requires.

This lack of sealing also causes blowby , which contaminates oil rapidly , the lube oil adative package is rapidly exhausted , requiring frequent oil changes.

When the cylinders become smooth , and the engine will start to really EAT oil .

Commercial fish harvesters have had this hassle for decades.
400hp to get there 20- 55 hp while there.

Some solutions are square cut piston rings , not trapizoidal, no Turbo .

FF

[CDK]

Originally Posted by FAST FRED

At very light loading the combustion does not get behind the rings , forcing them to seal the cylinder bores .

FF

FastFred, who wants combustion behind his rings?

For years I have had twin Mercruisers and when the old ones suffered from corrosion eaten manifolds, I replaced them with a new pair.
But because they tried to save a few cents there was only one idle screw for the whole carb. We were seldom in a hurry, so we coasted slowly but were embarrassed by the amount of sooth the engines expelled after starting and the comments from other boat-owners.

The problem was solved when we decided to do the last mile at full throttle whenever we returned from a days trip......

[FAST FRED]

"who wants combustion behind his rings?"

Anyone operating an engine , that wants full power , no blowby contaminating the oil.

The combustion PRESSURE behind the ring PUSHES the ring up against the cylinder wall, the requirement for a proper seal.

FF

[Karl2]

Not often I agree with Fast Fred but this time I do.

Fred is 100% correct: Combustion pressure behind the rings is what provides good and final seal.

Karl2

[Karl2]

Bigfoot,

I have fished for two years now on a boat with D6 engines. We troll for billfish 6-8 hours at the time at 650-700 rpm. I'm guessing we now have 250-300 hrs of trolling at that engine speed and have had zero issues.

When we are cruising we run somewhat hard, 3,100 - 3,250 depending on conditions.

Karl2