Re: [Amel Yacht Owners] Re: Volvo D2-75 for a SuperMaramu


greatketch@...
 

Graham,

Like you I think a lot of sailboats are significantly overpowered because that is what people think they want.  

Your thoughts on the Beta 60 are interesting, and I'll follow carefully what you end up doing and how it works for you. None-electric and non-turbo is nice.  The weight is also a good match.  Just a couple things to be sure of... 

The Volvo specifications I have are rated at the output shaft of the transmission, be sure that the Beta HP ratings are the same.  You can easily lose 5% in the transmission. and another 3-4% in the C-drive.

The Beta 60 lists its HO at 2700 as 56HP, the Volvo graph I have shows theTMD22 as about 62 at 2800.  That's enough difference that it is starting to matter.

For what is is worth (and it's not all that much) using standard sizing calculations, and assuming a fully loaded displacement of 38,000 lbs and a LWL of 41.25ft, the HP needed AT THE PROPELLER for a SM looks like this:

6.4 kts 31.3HP
7.0 kts 40.6HP
7.4 kts 47.6HP
7.7 kts 54.1HP
8.0 kts 61.2HP
8.5 kts 72.0HP

I'd add 4% to account for loss in the C-drive if the engine is rated for  transmission output.  If the engine was rated for output from its shaft, I'd add 10%.

My thinking is I'd start to worry that the Beta60 might be cutting it a bit close on the lower end... depending on exactly what you want your engine to do.

Bill Kinney
SM160, Harmonie
Fort Lauderdale, FL, USA


---In amelyachtowners@..., <crwggb@...> wrote :

The answer to all this is in the torque curves. As you say Danny 2800 is the max on the Amel TMD22A installation. This effectively limits its max OP to approx 60HP. I have been very happy with this performance for the past 14 years as are many other owners. Looking at the torque curve for the TMD you will see max torque is at around 2500 RPM, hence  its susceptibility to a fowled prop/bottom. Compare that to the hugely bigger torque at similar RPM on the D2-75 and that is why it will push through to its advertised rpm despite the fowling.

Amel should really have rebadged the TMD22A with a 60HP label.... but of course thats not what sells boats! Given that I've been very happy with a "60HP" engine for all these years its the main reason I'm looking at the BETA 60. It has no turbo and no electronic control boxes and will fit very comfortably in the space. At cruising RPM (2000 to 2100) that will give 7kts it produces 170nm torque compared to the TMD22A...same RPM but153nm torque. The beta tops out at 2700 rpm. So essentially it does exactly what the tmd22a has been doing all these years...but without the turbo.

The BETA man is coming to the boat on Monday I'll keep you posted on how it all goes.

Graham

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