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Here is a link to the spec sheet for a MD21A in case you don't have it.http://www.volvo.com/NR/rdonlyres/D31B4531-5ABF-48D2-A08A-8104E5946F2A/0/MD21A_RB_BW_19741_en.pdf
As you can see you are getting about 40hp at 2200rpm. Maximum cruising should be 2800rpm giving you about 50hp. Replacing new I expect you would consider yanamr 4jh5 at 54hp. (Not as much choice here as Europe.)
I have a Maramu in Port Douglas, Australia with a Perkins M60 (same as volvo MD22). I do 7 knots in flat water at 2600rpm equivalent to about 50hp. I don't go above that but engine revs up to 4000rpm.
I am planning on selling this engine as I already own a nearly new Perkins M65 which is 67hp at 2600rpm. The engine is still on board and runs very well.
--- In amelyachtowners@..., "rotormaneuros41" <rotormail@...> wrote:
recently I started a small project - painting the engine. I had small leaks here and there so I removed some of the aux. things from the engine. And then I found a long crack on the exhaust maniford. I removed it and found that the tube inside the maniford is so corroded that when I touched it it fall apart.
The cost of a new maniford is approx 7000 NZD plus I would need quite a few other parts (including a new raw water pump) so this repair is getting quite expensive.
So instead of repairing the old engine I am thingking about buying a new one. I already got information from Amel about the prop size (FYI 19x13 C7 LH 35).
Now the dealer is asking me about the max RPM of my old engine. The max rev I ever had was about 3000 (entering an atoll against strong currect).
My old eninge is the Volvo Penta MD21A with Borg Warner Transmission (ratio 2.91)
So question #1: what was the max RPM you were using your engine?
Whenever I was motoring I was always running the engine at 2000 rpm which gave me 5.5 knots or at 2200 around 6 knots, so I have no idea about speed at higher rpms. What about you?
Question#2: RPM vs Speed on flat sea?