Date: Sat, 19 Apr 1997 23:55:03 -0700
From: LEW PLUMMER <jayhawk@sos.net>
To: baidarka@lists.intelenet.net
Subject: Re: bow piece
John Winters wrote:
>
> Lew wrote;
> > It is very likely that the original goal was to create a long, deep and
> > fine, therefore, quiet bow entry. Fine entries mean low flotation at
> > the bow end. The flexible baidarka requires lift at the bow to help
> > shape itself to wave forms, to maintain its water line and hydrodynamics
> > in rough water. The upper bow provides a wide horizontal, high volume
> > section above the thin entry. The extra upper bow flotation works in
> > conjunction with the location of the keel flex joint and the combined
> > boat structure hysteresis. All of this requires a concave shaped bow.
> > We see this in some molded boats today, it makes a dryer boat.
>
> A long quit entry is more simply made and the bifid bow is a
> counterintuitive way to achieve it. More importantly, the upswept bifid bow
> is only different from any other bow above the wateline. As for maintaining
> a drier boat, it is a mistake to equate the flared bows of high speed ships
> etc. with the requirements of kayaks. Dry decks are not essential to kayaks
> (no one walking around up forward) and they can better be achieved in small
> lightweight craft using straighter flare or even convex surfaces.
>
> I think to establish that there was a hydrodynamic reason for the
> configuration we would have to show that the configuration was indeed
> better (I know of no studies that do this and my own certainly don't
> support it). I there is no plausible hydrodynamic purpose we have to assume
> that they native builders were misguided which seems unlikely given the
> amount of effort put into these configurations.
>
> > Skin boats don't generally lend themselves to concave shapes. Today's
> > sealants and woven skin materials can be pulled into concave shapes by
> > sewing across the boat and pulling both sides together. This may pull
> > at the weave but can still be reliably sealed. Nylon materials and
> > urethane sealants are very stable over time and many conditions
>
> > Leather, on the other hand, cannot be pulled in, in the same manner as
> > modern materials, and reliably sealed for any length of time. The
> > properties of leather can vastly change with time and conditions.
> > Leather is not as stable as modern materials. This is especially true
> > with split grained leathers that may have been used to make the boats as
> > light weight as 18th century Europeans described.
>
> I did not experience this problem and could produce the concave shape even
> using poly film by using and outside stringer.
>
> > To accomplish what is effectively a concave shape in leather and
> > maintain a reliable seal the Aleut stabilized the seam along the edge of
> > the wooden bifurcated bow structure. This places a sealable seam in
> > contact with structural support. There are other ways to accomplish the
> > concave shape in leather but they don't look nearly as cool and most add
> > weight.
>
> I think the "cool" look may have more in it than one might suspect.
>
> Cheers
> John Winters
> Redwing Designs
> Specialists in Human Powered Watercraft
> http://www.onlink.net/~jwinters
John,
Baidarka, as we know them, have few real advantages over modern kayaks
in flat water. One of the missing ingredients, the ingredient that
could make the baidarka plane, is probably paddling knowledge and power
of the Aleut. Planing a kayak requires a narrow margin of conditions
and one of those would be flat water. Flat water is something the
Aleutian Islands don't have a lot of. The next best thing to flat water
is a boat design that can adapt to moderate wave conditions and still
plane (early written comment substantiates this). One of the reasons
for the location of flotation at the ends and the flexibility may aid in
the transition to a plane. George Dyson wrote a paper of a modern
interpretation of the Baidarka substantiated by historical written
comment. If you don't have a copy call George at 360-734-9226.
The Baidarkas I referred to are early straight lower section designs,
not the surface piercing or up curved bow. When the Russan / Europien
influx stabilized Aleutian societies ( stability by death ) it seems
that work boats were more prevalent and the bifurcated up turned bow was
most likely a decoration.
I have built both bow types. The first is an upturned 1860s bow design
that has no advantage at all except maybe breaking up waves during a
traverse. My second boat is a 18" beam, semi deep "V" with an early
19th century straight bifed bow. Number two handles beautifully in the
rough water. It pierces the wave tops very much as Bill Low indicates
his boats do. On the other hand the 1860's model isn't nearly as
friendly in on coming waves.
I have experimented with tanned goat and split cow hide, they do open up
at the seams when pulled. I haven't tried to seal them with pitch/shell
... sealant used by the Aleut. If you have I would be interested in the
results. Also how different are sea mammal skins from goat or cow?
Salt water also effects the leather. The early Irish oak bark tanned
leather for there boats. When compared with many other tanning methods,
both modern and ancient, the oak bark leather failed fatigue test until
it was combined with salt water. The oak bark tanned leather in salt
water out distanced all others on a shoe sole roller test fixture. How
did the Aleut tan boat leather? Did they? I understand that the life
of a Baidarka was short, one season for the skin and two or three for
the frame.
My vote at this time is that the bow of the 18th century baidarka had an
important hydrodynamic purpose that worked in concert with a flexible
frame, a truncated stern, a "V" bottom, ballast stones, sea creature
skins and many years development of operator skill and strength.
I am in the process of designing an adjustable experimental craft that
may help in answering some of these questions. I will be using a
powered draw line for the missing paddler.
Through no fault of your own, some of my comments in the previous note
were taken out of context I can only blame my lazy writing style. I
didn't mean that kayak decks should be dry but some modern designs seem
to try. I would include outside stringers as one of the other methods.
I think it's great to have these discussions don't stop.
Early Europeans wrote of speeds in relative flat water at ten knots or
more. I would really like to know what Cook saw and wrote about all
those years ago. I am referring to his comment about a 12 foot baidarka
traveling at 7 knots. Was it surfing, planing or making one hell of a
bow wave.
Regards, Lew