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The Volvo TMD 22 as installed by Amel in the SM has a design max rpm under load of 2800. Many of us suffered untold grief trying to get more. It will rev cheerfully to 4000 no load. Ie in neutral. If you get higher revs under load it is likely the turbo wastegate is frozen. This causes the engine to get excessive turbo boost pressure which over time will do serious harm to pistons and rings. The wastegate opens progressively as rpm increases to prevent this. Carbon build up causes them to freeze (stick) and periodic maintenance is to remove the exhaust mixer elbow to access the wastegate and free it.
On 07 June 2021 at 11:35 Germain Jean-Pierre <jp.germain45@...> wrote:
Hello 2 X Bills,
My previous boat had an identical TDM22. It was setup to reach 4200 rpm.
Was very noisy with lots of vibes... but the 46 footer reached 9.5 at full power.
I’ve noted exacty the symptoms described by Bill K too but given the torque curve of the engine, I understand why Amel decided to keep the max revs down at 3000. Though 3350 is still well into the good range.
Jean-Pierre Germain, Eleuthera SM007, NZ
On 7 Jun 2021, at 09:28, Bill Kinney <cruisingconsulting@...> wrote:
When we got our Amel (SM #160) it came with what was then the standard 22” diameter MaxProp. All of our documentation pointed to using a setting of 20 degrees (15” Pitch) With the boat set up like this, it checked all of the standard performance boxes. Maximum engine RPM 3000: Check. Boat speed with a clean bottom: 8.0 knots, Check. Should be perfect...
Except... under some conditions, the boat was just not happy. Motoring into a strong headwind, or steep chop, and the engine RPM could not QUITE climb up high enough that the turbo boost come up enough to continue up the power curve. It would “get stuck” at 1800 RPM and the boat would really struggle. In flat water, this never happened, it worked just as expected.
This might have been due to an aging powerplant (she’s up to 8200 hours) or some other quirk unique to our boat, but just in case anybody else is left with one of these engine/propeller combinations and has had some of the same issues, here is what we did.
It seemed the engine needed to be un-loaded just a tiny bit. The next lower setting on the MaxProp is 18 degrees with gives a 13.5” Pitch. All other things being equal, I calculated this as bringing the engine speed at any given boat speed up by about 8%. I knew from observations if the engine reached 2100 that was more than enough to get the boost pressure up and let it generate full power. After consulting people who know a lot more about turbochargers than I do, we made the change.
Maximum engine RPM is now about 3350RPM (still way below the engine makers recommended maximum) Highest boat speed is still just about 8.0 knots, maybe just a hair faster. So that was all as expected. The performance against headwinds and seas has dramatically improved. We haven’t yet found any conditions where the boat gets “stuck.” Unless we find something dramatic, I expect this to be a change we will stick with.