Message-Id: <199710081111.HAA34382@www.onlink.net>
From: "John Winters" <jwinters@onlink.net>
To: <baidarka@lists.intelenet.net>
Subject: Re: design+building -- Longish
Date: Wed, 8 Oct 1997 06:27:08 -0400
Carl wrote;
I have seen several people mention the degrees of V in their boats, but I
am
> not sure I understand what reference point the degrees are measured from
or
> how far they are measured to. Is there a standard? What I have been
> guessing is that it is the angle at which the hull curves upward away
from a
> plane on which the keelson is resting (with the boat held upright.) Is
the V
> measured only out to the first stringer from the keelson (i.e. to the
first
> chine up from the bottom) or is it measured out farther? The former
makes
> more sense to me...but then I thought hot water would make ice-cubes
faster
> when I was young.
>
> > It seems to me that the
> > fullness in the aft hull contributes to the stability.
(SNIP)
What some call a boat's "V" is called "deadrise" by naval architects. It is
the athwartship rise of the bottom measured with a tangent to the hull
surface that originates at the keel line exclusive of any appendages. Thus
even round bilge boats have deadrise. The deadrise can be measured at any
point along the boat's length and every station will have a certain amount
of deadrise. When discussing the boat as a whole one takes the deadrise at
the midship section.
It is easy to see that this doesn't really tell one much since a boat
could be flat bottomed for a short distance near the center so, to get a
better picture of what the section is like, another term, midships
coefficient, is used. This is the area of the section divided by the area
of a rectangle having the same beam and draft. This provides an excellent
measure of whether the section (or boat) is full or fine.
Any increase in the waterplane area or section coefficient will increase
stability but it need not necessarily be aft nor does is an increase aft
necessarily the most efficient way to achieve this. The problem with added
fullness (here I am assuming you mean higher section coefficient rather
than just wider) is that the boat will float higher and there may be a loss
in initial stability that might not be what you are after.
Hope that is clear.
Cheers
John Winters
Redwing Designs
Specialists in Human Powered Watercraft
http://www.onlink.net/~jwinters