"Wayne.B" wrote in message
...
On Fri, 16 Apr 2010 23:07:17 -0700, "nom=de=plume"
wrote:

My understanding is that the engine on a cruising type boat would be able
to
bring the boat to "hull" speed. You can't really go faster than that, so I
suppose the appropriate engine would be one that could do that (or nearly
so)? 1.34 x sq. rt of water line? So, assuming there's overhang on a 42'
boat, say the water line is 40' the max speed would be about 8.5. Of
course,
if it were not pushing all the water, skimming, then you could go faster.

As I stated previously it doesn't take a lot of power to get a
sailboat moving at close to hull speed in flat water and no wind. It
takes a lot more power however, and a large prop, to get the same boat
moving against 25 kts of wind and 6 ft seas. You have to decide what
kind of conditions you are likely to encounter. There is nothing
worse than being caught out in a raging wind squall with an under
powered boat, and a lee shore close at hand.


I can imagine. Our thinking is that with a fairly new sailboat in the
40-foot range, it would likely have a decent engine. I'm sure that would be
part of the go/no-go decision for buying. I can imagine it would be fairly
expensive to repower if it wasn't sized properly. My friends in Santa Cruz
have a sailboat with a fairly small engine (30ish foot boat). I think the hp
was maybe 15... something like that. A larger boat.. maybe 50 hp? I think
that's what I saw at the boat show.

--
Nom=de=Plume