Re: [Paddlewise] Holding On

Brian wrote;

(SNIP)
:
> 
> Wouldn't providing enough initial stability to enable  reentering 
require
> increasing the beam so much as to reduce final stability to the point
that
> capsize in the first place could conceivably be more likely? 
> >

Not necessarily. Stability is obtained in four basic ways.

1. Lowering the CG.

2. Increasing displacement

3. Increasing waterplane area.

4.Increasing beam.


The first and second do not  increase the capsizing moments in rough water
and favorably increase the stability range. The third does not have to
increase the capsizing moments so much as increasing beam since it can be
done while retaining narrow beam.

In addition it is also possible to shape the hull in such a way as to
increase the stability range (secondary stability)  without increasing
initial stability. Usually this is accomplished through flared topsides.

Dan wrote;

> How would this make sponsons redundant?  Forgive me if I am a bit slow,
> but I really do not understand your point.  Of course one could design a
> boat which, due to it's substantial beam, always has the same stability
> as Boat X with sponsons deployed.  But the problem with such an approach
> is that you cannot reduce the beam for those times when a less beamy
> boat is desired.  With sponsons you can increase the beam *temporarily*
> for the purpose of taking a crap or a nap (or whatever), and then reduce
> the beam once it is time to paddle. How do you intend to achieve this if
> the boat is beamy to begin with?  Personally, I do not like the feel of
> beamy boats, but I do like the option of temporarily increasing the
> beam.  As always, this is just my humble opinion.  

You are not slow. Stability takes up a large portion of most naval
architecture books and is an extremely complicated topic. The nature of
stability changes as the boat heels beyond seven to ten degrees and what
seems good at low angles of heel is not good at high angles of heel.  More
importantly the nature of stability provided by form differs from that
provided by displacement and CG location. I hope the response to Brian's
question clears that up a bit.

My suggestion was not that everyone should have any type of boat. It was
that there are other ways of skinning this cat. They will not please
everyone just as no one boat will please everyone. Sponsons are one method
of solving certain problems but they aren't the only solution or maybe not
even the best solution for some types of paddling or paddlers. The
introduction of another solution should not be construed as a criticism of
any solution but rather the introduction of another possibility that may be
"better" for some one. 

We have heard here from people who do wet re-entries into narrow boats
without any assist. Some might prefer to put ashore for a nap. Some have
clever methods of handling bodily functions. Some use paddle floats .
If one likes sponsons and finds them useful then that is good. My concern
has always been that most people do not understand or are unaware of the
downside of things. I know of no rescue device or technique that is fool
proof or 100% reliable or does not have some aspect that will turn off at
least one paddler. 

I have attended SNAME (Society of Naval Architects and Marine Engineers)
symposia where people with more letters behind their names than I have in
mine argue over these things. :-)

Cheers
John Winters
Redwing Designs
Specialists in Human Powered Watercraft
http://home.ican.net/~735769/

 


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