The "theoretical" nature of the calculator relates to hull shape/wetted
surface, which it doesn't account for, and waterline length, which changes.
It doesn't consider if a boat can plane, which is an entirely different
ballgame. It does offer a pretty close estimate of how fast a displacement
boat can travel, power or sail. If the calculator wasn't fairly accurate, it
would be pointless, wouldn't it? Are you saying a CR38 can plane upwind? I
would find that extremely hard to believe, considering hull shape and
displacement. Now I have seen the calculator with the addendum that it
applied to boats with D/L ratios of over 150, but again the author was
referring to the ability to plane. The CR38 has a ratio of 359, which makes
it well over 150. I think if you quiz any NA they'll agree. Not my ideas,
just passing them along. Will a CR38 exceed it's theoretical hull speed?
Sure. Will it exceed it's theoretical hull speed by 50%. I don't think so.
" The slowest the CR is, is into the wind in heavy chop, 4 to 8 ft seas
close together. The boat does not ride up and down them, it kind of goes
through
them, EACH WAVE SLOWING THE BOAT DOWN. I find it best to fall off some and
power up the sails, it gives a nicer ride but slows your vmg to 3 kts or
so.
Remember gentleman never sail upwind."
My caps for emphasis.
And another personal response:
"No we don't normally need to reduce sail until the gets around 25kts. I
recently left Lemmington in Canada in 25 gusts to 35. We had one reef in the
main and staysail. We averaged 6.8 kts for 6 hours to Huron,OH and were very
comfortable."
Now I don't know what direction the wind was coming from, but even if the
wind was on his nose, he wasn't doing 11 kts. Could he have done 11 kts. in
a planing hull? Probably, but I don't think he would have been very
comfortable, either. And considering the probable sea state-by the time he
reached the half-way point the lake would have been fairly choppy regardless
of the wind direction-6.8 kts. is a pretty good speed.
John Cairns
"Capt. Mooron" wrote in message
...
"John Cairns" wrote in message
m...
| Have no idea how fast a Nordica 30 is, don't recall seeing phrf #'s.
Never
| attempted to do any reverse calculations, ie., how fast is a particular
boat
| based on it's phrf #, but I feel it is a useful tool when comparing
boats
of
| similar length. BTW, more than one responder on the CR list told me they
| didn't consider their CR38 to be a fast boat, no one, including the lake
| sailors, claimed their boat would do 11 kts.
It's not supposed to be fast.... look at the stats on SailCalc. Never the
less I often have the boat exceeding her theoretical hull speed. I have
raced boats that are supossedly faster according to both phrf and hull
speed
calcs.... unfortunately the realities of extraneous inputs on the vessel
can throw a spanner into the works and those supposedly faster boats are
not
performing to their stated potential..
Now seriously... are you claiming that a 38 foot cutter with a full keel
and
cut-away forefoot cannot achieve 11 knots of speed because her theoretical
hull speed is rated at 7.3?
The thing about the numbers is that they are general benches for
estimation.
To state flat out that a vessel can not exceed her calculated hull speed
is
erroneous. My 30 footer has attained speeds well in excess of her
theoretical hull speed.... 10+ knots over a nautical mile... mind you we
were flying all the laundry and the wind was dead astern at 36 kts gusting
to 42 kts. You've seen her hull shape John... surfing isn't an option
here.... she was pushing water hard with the bow biting down.!
CM
|