RE: [Paddlewise] Hull Shape & Stability

Commenting on Nick's and Marks comments about stability and shape, I
have a simple approach that seems to work pretty well.

Right now I am working on a plug for an 18 foot 22 inch boat and have
been looking into what I want the boat to do.

When the boat is placed on edge, the amount of volume increase under
water  by the side that  enters, will contribute to the restoring force.
A round hull will not add any volume in the water when placed on edge. A
wide flat hull will add a lot of volume and will displace so much water
and create a large restoring force. A V hull will be somewhere in
between, as well as a combination of shapes between the totally round
and the totally square.

Extremes are: round to give zero support, and square to give maximum
support.
On the other hand a round hull will be faster since it has the minimum
wetted surface. The square hull will be the slowest. 

So the compromise is always in between. 

Round means less stable, less maneuverable by edging.
Sharp on extremes and flat at mid ship seems the best compromise for
cutting water but obtaining stability and maneuverability.

Epic 18, has pretty round hull, almost olympic shaped, is very fast, but
needs a rudder for sure, and feels tippier.

Silhouette is very fast, with almost rounded bow and stern, both ending
sharp, and with some widening and flattening in the middle, and hard
chines. It is very fast but hard to maneuver.

Then the Legend, the Greenlander Pro or the Point Bennet, keep a sharp
bow and stern, V continuation bending to become quite flat a mid ship
with almost vertical side walls and hard chines. They are fast, but very
maneuverable and more stable.

The same trend can be seen in some of the Current Design boats, like the
Slipstream and the later models.

I have two boats with the same seam width. One has the hull with higher
angle walls, soft chines and slight V. It is reasonably stable, very
good maneuverability, good tracking and reasonable speed.

The other, with the same bow and stern, and seam shape, but with
vertical walls, hard chine and almost flat bottom is tremendously
stable, slower, but very easy to turn with the slightest edging. 

This is in agreement with the concept of rounder is faster, less stable
and less maneuverable. 

Just my observations.

Best Regards,

Rafael
Mexico.
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