Jim,

Finally, a dissenter from the Perkins crowd. I have been quite surprised at
the loyal Perkins support here. It has about convinced me that we should
stick with her.

I have had others comment elsewhere that the Yanmar is the rough running
engine and I don't understand why a three cylinder engine running at roughly
20% faster for a given power output, could be quieter and smoother than a 4
cylinder engine at that same power level. This is especially true if the
4-banger has greater displacement and would be running at, say, 3000 RPM at
max continuous rating of 37 SHP when the 3 banger is running at 3650 RPM at
a similar power level.

Of course, we would normally run much slower, say 2500 on the Perkins and
3000 on the Yanmar, easily reaching hull speed in most conditions.

I'm not sure I understand why having pistons at opposite ends of their
throws simultaneously would increase the vibration, but then, dynamics was
never one of my favorite courses. If you have a quick explanation, I am all
ears.

Thanks for your reply, the quest is interesting to say the least.

Keep on sailing,

Ken
S/V Parfait
Raleigh, NC



"Jim Woodward" wrote in message
...
I have lived with the 4-108 for about ten years (twenty years ago) and
took the Yanmar's big brother, a 4JH, around the world in our Swan 57,
Swee****er. I'd pick the Yanmar in a second.

Among other things, a 3 cylinder has inherently less vibration than a
4. (In a three, the pistons are 120 degrees apart, while in a four,
they are 90 degrees apart, so that when one hits top dead center, its
mate is at bottom dead center.)

Jim Woodward
www.mvfintry.com


"Ken Coit" wrote in message
.com...
Presuming you were looking to buy a used boat, which engine would you
rather
see in her:

Remanufactured Perkins 4-108
New BetaMarine 1505
New Yanmar 3JH3E

These are all adequate to the job of pushing a 16000 # boat at hull
speed,
so the question is one of your personal preference.

Thanks in advance,

Ken Coit
S/V Parfait
Raleigh, NC