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Prop Settings for older SM with Volvo/MaxProp
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Bill Kinney
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. Bill Kinney SM160, Harmonie Eleuthera, BS |
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Bill, Very interesting. You may be on to something. When I checked with MaxProp, I was told 22° 
On Sun, Jun 6, 2021 at 4:28 PM 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... |
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Germain Jean-Pierre
Hello 2 X Bills,
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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:
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Danny and Yvonne SIMMS
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. Kind Regards Danny SM 299 Ocean Pearl On 07 June 2021 at 11:35 Germain Jean-Pierre <jp.germain45@...> wrote:
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Bill Kinney
Danny, I hear you, except… the turbo is new. The exhaust elbow is new, and clean. The boost pressure is spot on Volvo’s spec (I measured it) the waste gate opening is in spec. When going upwind, the engine will NOT climb up into the turbo boost zone if the RPM is limited to 2800. Yet it generates full power and speed if I allow the max RPM to climb to 3350.
What problems would you predict I’ll see by running at this prop setting? Bill Kinney SM160, Harmonie Great Guiana Cay, Exumas, Bahamas |
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Danny and Yvonne SIMMS
Hi Bill, my experience was to ruin a perfectly good engine because the waste gate was stuck causing over pressuring at higher revs. Check for freedom of movement of the operating flap. You can do this by applying air pressure to the bellows by removing the outer end of the small air hose. This will check the bellows at the same time. Or remove the circlip holding the operating rod to the waste gate arm and check for free movement of the arm. You should be able to flick it back and forth with your finger tip. If that is OK I would not see how higher revs would cause any damage. However I would never run my engine constantly at peak revs. My diesel utility vehicle does 1500 rpm at 100 kmh, our legal speed limit Kind Regards Danny SM 299 Ocean Pearl On 09 June 2021 at 10:56 Bill Kinney <cruisingconsulting@...> wrote: |
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