| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 1328.1 | sounds reasonable | MSCSSE::BERENS | Alan Berens | Fri Sep 01 1989 13:21 | 14 |
| A displacement-length ratio of 320 is only heavy by the standards of the
racer and racer/cruiser crowd. It is certainly moderate and reasonable
for a cruising boat. Typically, the lower the displacement-length
ratio, the quicker the motion of the boat (the higher the accelerations).
See Marchaj's book "Seaworthiness, the Forgotton Factor" and also note
1098.9 (among others). Our Valiant 32 (11800 lbs displacement if you
believe the specifications) has a displacement-length ratio in
the range of 300 to 330 and is an extremely seakindly boat that still
sails reasonably well, even compared to many larger cruising boats.
Wetted hull area is more of a problem than weight in light air. Lighter
boats accelerate out of a tack faster, to be sure, but a heavy boat is
not necessarily slow in light winds when cruising, assuming, of course,
reasonable sail area.
|
| 1328.2 | Heavy but comfortable | SNOC01::SMITHPETER | | Wed Sep 06 1989 09:52 | 4 |
| My boat has a dl ratio of over 600..,if my calculations are correct.
And is very comfortable. Particularly when the wind gets above 18k.
Must admit we are slow in light airs.
|
| 1328.3 | | STEREO::HO | | Fri Sep 08 1989 16:41 | 29 |
| Boats with long overhangs suffer unfairly with the normal D/L
calculation becuase it fails to account for the immersion of the
overhangs as the boat speeds up and/or heels.
One naval architect suggests using the average of the LOA and LWL
as a more realistic input to the metric.
Using this algorithm "Gypsy's" D/L is 216. As a benchmark, a Hinckley
38's D/L is 207. I've sailed a short rigged version of this boat
often. It's a responsive boat in both light and heavy air. And
my regular boat is an Etchells with a D/L of 84. Displacement is
not an impediment to light air performance if there is adequate
sail area. I'm reminded of this on light air Saturdays when the
International One design fleet, which starts 5 minutes after the
E-22's, sail through our fleet. The IOD's weigh twice as much but
carry much more sail area.
It's interesting to compare the D/L' s for an E-22 (84) and a J-24
(138). Despite what the ratios tell us, the J-24 is universally
acknowledged to be the more responsive and quicker accelerating
of the two. And they weigh about the same and have comparable sail
areas. About the only thing D/L does accurately predict is the
higher speed of the E-22 due to the longer "L".
One test sail is worth a bazillion metrics.
- gene
is adequate sai
|
| 1328.4 | | MOOV01::KEENAN | PAUL KEENAN DTN 297-7332 | Fri Sep 08 1989 17:53 | 9 |
| Gene,
It's my understanding that the E-22 & J/24 both have a 22' waterline.
If they weigh about the same, shouldn't the D/L ratio be the same?
How are you calculating L, is it LWL or (LWL+LOA)/2 ?
-Paul
|
| 1328.5 | | STEREO::HO | | Fri Sep 08 1989 18:00 | 9 |
| Paul:
I'm using the alternate algorithm: L = (LWL + LOA)/2.
An E-22 is 30.5 ft long. Putting that into the formula really lowers
the D/L.
- gene
|
| 1328.6 | Still waiting... | RIPPLE::KOWALSKI_MA | | Sat Sep 09 1989 16:52 | 14 |
|
Re: 1328.3 by stereo::HO
Thanks, Gene, I hadn't considered that. Still waiting to get out
on Gypsy for a test sail. But this is an interesting discussion
of metrics.
BTW, I did get to go through her log the other day at the dock.
Turns out she's a C&C design. Still have no SA, as there were no
builder's specs about. She appears to be a bit worn, maybe 10-12
years old...hard to say, really, with my limited experience.
Regards/Mark
|