According to the handy-dandy wire sizing chart in the West Marine
catalog:

1. Sprokkie asks if 35 sq. mm. wire is adequate, and the chart shows
that AWG (American Wire Guage, for Sprokkie's benefit) number 2 is 33.62
sq. mm. So, lets see what AWG 2 wire will do.

2. Again, according to the chart, AWG 2 will carry 210 Amps a maximum of
34 feet, or approximatley 10 meters, with a 10 percent voltage drop. The
10 meter figure is "ROUND TRIP" distance. That means the TOTAL distance
from the battery, through any disconnect switches, to the starter, and
from the engine block (the starter is grounded to the engine block) back
to the battery. Sprokkie says the battery is 5 meters from the starter,
so the "round trip" should not be over 10 meters.

3. A 10 percent voltage drop is not unreasonable for a starter circuit.
That would provide 10.8 volts (12 volts minus 1.2 volts) at the starter,
assuming the 210 Amp load. It also assumes that the battery is pretty
low since the battery would normally provide about 13.7 volts or so if
it were in good condition and freshly charged.

So what is the conclusion? I don't know how much current the the
Farrymann (sp?) starter draws. If I remember correctly, that engine is a
pretty small diesel and the starter would not likely draw more than 210
amps, so 35 sq. mm. wire should be more than adequate. I think 50 sq.
mm. would be overkill,
but not undesirable if cost of the wire is not a factor.

Hope this helps a bit...

Ed Greeley