From: Guillemot@aol.com
Date: Thu, 9 Mar 1995 21:44:25 -0500
Message-Id: <950309214424_44831799@aol.com>
To: baidarka@imagelan.com
Subject: Re: Bifid bows (fwd)
] From: kork@imagelan.com (Kirk Olsen)
] > From: mark_stirling@mindlink.bc.ca (Mark Stirling)
] >
] > I find it interesting that George Dyson notes the "twig" across
the
] > bow to be baleen - a strong elastic material. This would in fact
strengthen
] > the bow piece cantilever style from wave pressure on top when plunging
into
] > waves.
Following the civil engineering principle, "You can't push a rope", I think
baleen would not provide much structural support to the cantilever. Granted
the baleen is rather stiff, structurally it is probably more like a rope than
a rod. The structure of the bow is plenty strong as it is and doesn't really
need extra support.
] > It is important to consider bow design with the conditions that
] > determine it. I have paddled a wood boat of narrow design on the west
coast
] > for a number of years and this boat has a low volume bow.
]
] I think the shape of the bow is critical with regard to what will happen
] when you paddle into a wave. A thin verticle bow will slice into the
] wave. A triangular cross-section will try and pop back to the surface.
] I think the bow on the Necky kayaks is an extreme example of the
] triangular bow design. The bifid bow is an interesting mix of designs.
] The lower jaw looks like it will slice into the wave and the upper
] jaw will try to lift up out of the wave. (now if I could just finish
] my bifid bowed kayak I could verify this)
There are several factors that will help the buried bow lift out of a wave. A
triangular cross section provides buoyancy which in turn provides lift. Now
the water has to go somewhere. A flat deck is not good at shedding water.
Many of the bifid bow kayaks have flat-to-shallow-V decks. Alternately look
at the kayak Dick Bunyan is making in Zimmerly. The sheer is at about 1/2 the
height of the deck, producing a steeply sloped deck. I suspect the high
volume and water shedding deck of this boat would let it handle steep seas
very well. I suspect (from the comfort of my chair) that this form would
handle steep waves better than the typical bifid bow.
] > With a following
] > sea I have had kelp get caught on deck and had to back out. A bifid bow
] > would be no more likely to catch than a solid one if bow volume is low.
] I think cross-sectional design of the bow could make a big difference here.
] Even with comparable bow volumes. I have a marathon flatwater racing
] canoe with a 16 inch verticle stem that slices right through waves. I
] think the addition of some hull flare would make a monumental difference
] in how that boat paddles in waves, as it is a wave of the same size as
] the bow will usually come into the boat.
Another means of keeping the bow out of the water is "dynamic" lift. Take as
an example the wings on the bow of some surf skis. The faster the boat is
moving the more lift is provided. The wing is a radical example. Less
radically, this lift may be provided with a hollow bow section and an upward
sweeping sheer. The angle of the sheer must stay above the oncoming water to
maintain the effect. Imagine the effect if the water starts pushing on the
top of the wave ski wing! A sudden nose dive followed by a power-perl. Again,
the deck shape will affect the downward force the water is able to bring to
bear in a perling situation. I also think rocker helps wave handling
characteristics.
Flipping through Zimmerly. If I were to chose a bow form to try in surf, I
would pick the King Island kayak in figure 73 (fig. 181 in Chappelle). I
think the high upward sweep and steep deck would provide a relatively dry
ride. The short 14'8" length may also be an advantage. (not the aesthetically
best looking kayak but....)
Nick Schade