They should be grounded.

In a typical generator. The user would run a cord to say a power tool. If
the tool shorts out to the case you want the easiest path to ground through
the ground wire back to the generator's GFI. The GFI would sense the short
and open. Without the ground the user may provide the path bypassing the
GFI. The GFI would not sense the short and this could be a shocking
experience.

In a boat with the generator connected as shore power you run through the
boats distribution panel and that panel provides the protection. In the
strictest electrical terms the generator should be grounded and if you want
to do this I would use a zinc "Guppy" overboard. However, if your AC system
is grounded to the boats motor or the through hulls then due to stray
currents I would not ground. Electrolysis may cause damage to the
underwater metal parts of your boat. If the boat's AC system is not
grounded then the "Guppy" is a reasonable approach.

"Doug Dotson" wrote in message
...
Every portable generator I have seen has this situation. I have
2 portable generators and never setup the ground as they say.
Just visit a construction site and see haw many generators
are grounded. I've also seen many portable generators on
boats. None have an earth ground. Just plug it in and go.

Doug
s/v Callista

wrote in message
...
Please help me understand. MyYamaha manual says" be sure to ground (
earth) the generator" and the picture is showing a wire connected to the
generator and the other end is a nail burried to the earth ground. How
to I do that on a boat?
I have a 26 foot Monterey with shore power.I purchased a boat shore
power adapter to regular household plug ( 3 prong) and I was thingking
of pluging that to the generator. I am confuse about grounding of the
generator to the earth ground ( the nailing to ground thing) ????