Subject: Re: [baidarka] new to forum
From: Peter Chopelas (pac@premier1.net)
Date: Fri Feb 25 2005 - 01:24:36 EST
Welcome Anne,
You wrote:
>I joined this list several weeks ago during a quiet time, evidently. Several
>years ago when I paddled regularly in the Gulf of Mexico and coastal lakes,
>bays, bayous, I preferred long, narrow Swede form kayaks. So I'm hoping to
>design and build a kayak, or just build an existing design, that will fit me
>and suit my paddling preferences. After online research, I've become
>fascinated with baidarkas.
>
>
"Swede form" is not terminology any native builder would have known or
understood. Unless you have tried a traditional baidarka hull it is
best you try to set aside whatever ideas you have about hull design
based on books and paddling factory kayaks. They behave very differnt
from a hard shell hull, and their performace in almost all aspects is
superior in every way.
You should also consider making (or buying from the few custom builders)
an Aleut paddle to go with your baidarka, they too are superior for long
distance sea kayaking than the fat "euro" paddles, and lots easier to
roll with than an EP, once you learn to use it properly.
>I haven't ordered nor read any books yet - just information online;
>
You might see if you local library system has either Brinik's,
Cunningham's or Morris' books available, they are all worth reading
since they describe different methods and details that can be used on
any design, some cover certain topics better than others. Not to worry
however, I built my first three skin on frame kayaks armed only with
internet information (there is much available out there, including the
archives of this forum).
>so I
>apologize if the following questions are too elementary for this forum. But
>I'd welcome guidance and feedback before I delve into my project.
>
The questions below are more advanced than most people get into, this
list is made of craftsmen (and women), and boat builders, not marine
architect's or engineers. Only a few on this this that I know of have
any kind of technical training (myself being one of them-and it does not
make me a better builder ;-) ).
>I'm not concerned about
>traditional construction methodology or reproducing an antique. Rather, I want
>a lightweight boat that fits me well and suits my style; and I can already
>imagine how a flexible keel baidarka might behave in the Gulf of Mexico.
>
I started out this way, and tried all kinds of modern 'innovations' to
speed and simplify construction, I have found I am going back toward
tradition construction methods, the hand forming of the frame parts are
simple and satisfying (versus power tools-the only two I use now are a
table saw to rip the stringers, and a router to make rib mortises-I
could never make clean ones with a hand chisel), the lashing is strong,
light, fast and rot/rust resistant, and steam forming of ribs fast and
easy (I actually boil the ribs, it is more reliable and less
sensitive). I do like nylon skin for it's lightweight and durability,
and I use one-part oil based polyurethane as a sealant (inexpensive and
reasonably durable).
> Also
>intriguing is the bifurcated bow and shape of the stern; and I haven't
>dismissed notions of possible functions of that form.
>
>
There is much modern debate on this, from the silly to the technical.
Much of the traditional design was developed in a long process of trial
and error, tradition and superstition. Some think, like us modern
humans, that the bow was designed for performance purposes, others think
it may have been done to make it look like the mouth of a sea mammal or
salmon, to attract more fish perhaps, or simply superstition. Who knows
now? They are as likely to stick with a certain detail because of a
legend of a man that caught a lot of fish who used one type of bow, and
another one drowned with a different style. One thing for certain, they
had many centuries and a very unforgiving climate to develop and perfect
their designs, with some pretty technically advanced details they
discovered that simply worked best. I have yet to build a traditional
bifed bow since with modern skin materials you can almost achieve the
same thing by pulling the fabric in under the bow plate with stitching,
without having to do all the tedious inside stitching around the
opening. I have used both types and there is not a lot of noticeable
difference in either bow shape in most conditions.
>
>First, the questions of terminology:
>
>My understanding of the Swede form kayaks (from paddling), is that the design
>entails higher buoyancy aft of the cockpit ... at least that's my perception
>onboard (with minimal gear in hatches) compared with paddling other kayaks of
>fish form. However, I'm confused by conflicting descriptions of the Swede form
>having maximum "volume" aft of midsection, or aft of cockpit, and other
>references that the cockpit, itself, coincides with maximum volume in any
>kayak. Which, if any, of those descriptions would be accurate? In my online
>research and in the general kayak market, I'm finding information and specs
>that seem counter-intuitive and at variance with each other as well as with my
>own experience.
>
>
Most kayak manufacturers carelessly throw around terminology for
marketing purposes. I have also met many designers of commercial kayak
builders here in the Pacific NW, it has been my observation that many
are technically incompetent anyway. Do not pay any attention to any of
the marketing BS (or anything else) you read about kayak design, much of
it is wrong.. People who should know better often spout nonsense. One
of the axioms I have found sometimes true in industry is that the job of
the engineering department is to keep up with the promises of the
marketing department.
Also consider that the fineness ratio (max WL width to WL length) on
most native kayak designs is far superior to virtually all factory
hulls. As long as you have smooth transitions at the bow and stern, a
typical baidarka hull, built to traditional designs will always out
perform factory hardshells. When you optimize the hull shape, be it
fish form, swede form or symmetrical, there will be few identifiable
advantages to any of these shapes attributed their hull forms. Good
designs will always perform well no matter what the form, and a poor
design can not be over come with a better form selection. I think this
is marketing nonsense in a kayak, and I am not the only one with this
opinion. There are differences in certain aspects of performance in a
sail boat hull with these shapes going up wind,. down wind or on a
reach. These hulls are designed to resist lateral movement and the
heeling moment of the sail, but these are not considerations in a kayak
hull. And the extreme fineness ratio pretty much makes the difference
difficult to tell in a baidarka. The only reason you would alter the
below water line displacement is to balance the cockpit location. And
this balance would change depending on how your "design load" is
balanced out (day tripping, or a for fully loaded multi day trip).
>Also, doesn't "volume" refer to the volume of water displaced by the craft (or
>any portion of it) ... so volume would vary negatively or inversely with
>buoyancy? If that is accurate, could one define the Volume "V" of a kayak as a
>vector of "v's" representing the volume of water displaced by the
>appropriately loaded kayak (including paddler of a certain weight and buoyancy
>in the cockpit) along the keel from bow to stern, values which would optimize
>performance characteristics of the craft given the nature of fluid mechanics
>and the craft's other variables? Is that the actual starting point for
>designing?
>
>
Volume is usually short hand for displacement volume, which is what you
note above, but this could also refer to cargo volume, or cockpit volume
(roominess). No one that builds baidarkas ever thinks this way. A
baidarka used today is a recreational water craft that represents a
compromise between weight and strength, storage volume and size, comfort
and stability and width vs. skill level (narrower is better because it
is lower drag, and handles chop better, if you have the skill to use
it). If you want to optimize speed, you can buy a racing hardshell made
of carbon graphite and epoxy, for me this is too expensive, no fun to
use, too fragile and has no room for gear. If you want to optimize
storage capacity, get a big fat canoe.
Any design should start with a list of how you intend to use it (long
term gear hauler or week-end use), a list of which performace measures
are important to you, prioritized (speed vs. stability, enter/exit ease
vs.body fitting coaming, turning radius and maneuvarablity vs.
directional stability, etc.), and then you build appropriately. You
simply take the fluid mechanics as it falls out of your design
priorities. All design choices are compromises, by prioritizing them
you can make better choices based on what is most important to you.
So you start with your intended use, and which performance features are
most important to you.
>I may be splitting hairs here: but would the warmer waters and different
>salinity of the Gulf of Mexico also affect the design to optimize performance
>of a baidarka?
>
>
There could be some slight difference, but generally what works well in
cold water also works in warm water. It would be neglidgable at best.
Far more variable, and important is how the hull shape varies with how
much you intend to load it (a design that performs well lightly loaded
will not perform well heavily loaded, and visa versa), and the amount of
chop in the water. The best hull design for smooth water is not the
best for choppy water, and v.v. Again you simply make your best guess
at what you will most need it for, and live with it the way it comes
out. BTW, all of these considerations are way more than most commercial
manufacturers ever even think about.
>Obviously, I've never designed a boat before; but I perceive it as a dynamic
>optimization problem .. I just haven't identified the starting point in
>specifying the equations.
>
>
>
This is only done with large commercial freighter designs, where even a
small difference could mean millions of $ of fuel burned over long
periods of time. I have formal training and much experience in
computational fluid mechanics and I do not even go to this much trouble
(it would take more time optimizing a hull design on a computer than
actually building it!). Do not get caught up in such details, it will
only bog you down and fill your head with confusion. Pick a traditional
design that is popular (the fist tip off that it performs well, lots of
people are building it), adjust it to fit your size, and go build it.
Do not expect the first one to be your "ideal" hull, they build fast
enough and are inexpensive enough that you will shortly want to try
another design, or alteration to your design. Harvey Golden, after five
years and 40 different hull designs built (in his 'spare' time), quipped
"I bet you can not build just one". I am on my sixth one, with plans to
build at least several more to try out some ideas (including a couple of
folders, and at least two more non-folders).
Hint at your first one, keep the bottom fairly flat (see Cunningham's
book on an easy way to do this) and the hull not too deep, with a harder
turn of the bilge than shown in most books. A common mistake is to make
the hull too deep and round, making it have about as much initial
stability as a log (not much!).
I have found I like building them more than using them, it is nice break
from my desk job and it can be done year round in a relatively small
space (compared to most boat building). There are also few less
expensive ways to get a sea worthy craft on the water. Almost all of
the ones I have built have cost only $40 to $100 in materials each (I
try to salvage as much of the wood as possible from scrap piles and
construction sites, and rip the stringers on a table saw from larger
pieces). This is way less than you would spend on any other
construction method. The most expensive part is the fabric, typically
about $25-30 worth. Most of my tools I found at garage sales or flea
markets for only a few $ each.
Also do not over build, there is a tendency for most people to make the
frame parts much heavier than they need to be (especially if they follow
Morris' book). Take weight out where ever it is not needed. Most of
mine have weight between 15 and 35 lbs (the heavy one had deck hatches
and bulkheads!). My most recent one was a West Greenland style for my
daughter made of Doug fir with oak ribs and coaming, it has only 2-1/2 x
3/4 gunwales, 19" x 15' 8" LOA, 8 oz nylon skin with 3 coast of
polyurethane. It weights only 15 lbs or so. We have never failed a
frame. I think skin-on-frame is the most optimum way to build a sea
kayak ever devised, and the oldest methods appear to be still the best,
especially when using modern materials. As far as lumber goes I have
used Doug fir, western hemlock and red cedar. I like cedar the best,
light and easy to work, and rot resistant. But you can use what ever
you have available, as long as it is reasonably light and relatively
free of knots and other defects. Anything and everything has been used
in a kayak frame, even bamboo.
>>From the middle of nowhere in southwest Georgia,
>
>
It would be nice if you can connect up with some local builders and see
what they have built. Is there anyone on this list in SW Georgia? Or
better get together with them at a builder's gathering and try out their
kayaks to get a better feel for how changes in the design will affect
how it feels in the water. There are several gatherings a year around
the Puget Sound area of builders, there may be some clubs where there
are builders that would be happy to share their expirance with you. Ask
at the nearest kayak shop, or check out the qayaqUSA site as well.
Good luck, keep us posted on you progress. Go get a few books, and get
started.
Peter
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