[PUP] PPM- Stability & Comfort

[Tad Roberts]

  Lots of good points here, too much for me to reply to it all.  But I'll
stick a couple of thoughts up.

 

The Flanders, cruising on Egret.

Statistics are tricky, pay attention when someone starts posting numbers.

2639 days is indeed 7+ years, but I don't believe they didn't stop (tie up,
anchor, etc.) at least a few times for food and fuel.  Thus they could not
have spent 2600 days at sea.  If we believe 41,000 miles and the 5.8 knot
average, we get roughly 7069 hours on the engine. This might be 294 full (24
hour) days at sea, or 589 half-days at sea.  Probably it's somewhere in
between, say 450 partial days underway at sea.

 

Ken mentions he "can't imagine a passagemaker that doesn't have a wing
engine or twin engines."  How about one with sails and a single engine?

 

Hannu mentions many points, they come across as statements of facts when
they are really opinion.

Regarding motion and comfort.  I disagree that draft in itself is a key
component of the relative comfort of a particular vessel.  I would say that
a vital component of seagoing comfort is displacement (weight), of which
draft can be a result.  The relative comfort and motion of any vessel at sea
is an extremely complex problem.  Today we are still some distance from
developing useful computer models that deal realistically with all the
variables. A couple of the really important factors are a vessel's weight
and her waterplane.  Waterplane is a cut through the ship at her waterline,
this area (in square ft) and it's distribution, will give some hint of how a
vessel might react to a given wave.  Of course in a sea the waterplane is
highly dynamic, changing size and shape constantly.

 

Some years ago Yacht Designer Ted Brewer published what he called a
tongue-in-cheek "Motion Comfort Ratio". This relates the vessel size and
weight and assigns a numeral, roughly from 5 up into the 70's, higher being
representative of more comfortable boats.  You can find this ratio with
google.  Brewer called it tongue-in-cheek because it is only a rough
indication of relative comfort, he well knew there would be exceptions and
that there are many more factors involved. Running though some available
numbers I find Idlewild and Windhorse rate an identical 50 on the motion
comfort scale.  A Nordhavn 55 is 72, an N40 is 58, a Diesel Duck 462 is
67.8, and my own PL46+ (at half load) is 40.

 

Regarding the motion of Idlewild, I would submit her crew were inexperienced
and had never been to sea on any other boat.  Her voyage was a stunt, far
from a typical pleasure cruise. Their course across the southern ocean was
an extreme one, no other typical passagemakers are going that way, of course
the motion was uncomfortable.

 

The photo of a rolling N40 that keeps popping up.  The actual roll angle is
difficult to ascertain, but in the picture I doubt it's more than 25
degrees.  This is not in itself dangerous, but I suspect the quickness of
that rolling was what scared people.  Motion is magnified by distance above
the waterline, and a great deal of the N40 is quite high.  Again this points
out the complexity of motion at sea, the perception of the observers is a
huge factor in determining the comfort of a particular ship.  The Dashew's
state Windhorse is far more comfortable that their previous sailing vessels,
much (perhaps all) of this has to do with the oversize active stabilizers.
Yet they have harness built in to strap themselves down when the going gets
rough, some would look on this with horror.      

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