Subject: baidarka bow/prow design of a kayak
From: Peter A. Chopelas (pac@premier1.net)
Date: Wed Feb 14 2001 - 20:25:39 EST
Hi folks,
I have been pulling together ideas to build another skin on frame kayak but
there seems to no clear consensus on how the prow should be shaped since
both native designs and popular production models have all kinds of
variations.
By prow I am referring to the shape and angle of the part of the kayak bow
that makes first contact and splits the water as the hull moves forward. I
understand that you want to separate the water with the least amount of
resistance or displacement, so sharp is usually better but this is traded
off against volume and buoyancy. To compensate you can I suppose have the
bow fairly wide at the gunwales to prevent the bow from diving when in the
trough of waves and a secondary benefit would be to keep splash and spray
defected away from the foredeck and cock pit. Though of course there is a
limit you would want to this width at the gunwale level since it would
splash and slow you down real fast when penetrating waves and real rough
water.
The steepness of the line of the prow varies quite dramatically and I do
not understand why there is such variation because I do not see the
advantages with the very steeply sloping prows. They make nice and sexy
looking kayaks with real pointy bows that look like they are ready to slice
through anything the ocean can give. But all I can see this does is
shorten water line length since a very narrow prow would do the same thing
without losing water line length. Do these steeply sloping prows help cut
chop or deflect splash and spray, or help keep the bow from diving in heavy
seas by moving the buoyancy forward when it dives?
It seems to me that keeping the gunwales fairly wide at the bow would
accomplish the same thing without loosing length (or bow storage volume
either). Many baidarka enthusiasts seem to think that the ugly (IMHO)
bifed bow is best suited for rough seas. It has a fairly fine prow and a
wide upper piece to keep it from diving. The slot in the bow is there
either by tradition or that you can not make hollow shapes in skin on frame
construction, depending on who you ask. If this bow is so superior why
does not more commercial manufactures simulate it? In fact the Aleut
baidarka seems to have a number of design feature that make it well suit to
long distance travel in harsh climates, both the bow and stern shape allow
maximum waterline length and directional stability and minimum exposure to
winds. But this design is rather unique to all native skin boats, so why
is it not more widely used?
Even more curious is that the manufacturers of most factory hard shell
kayaks, where of course you would not need the slot to create a hollow
shape in the bow, appears copy the Greenland style bow, often with the
steeply raked prow. And even the slick (but otherwise useless IMHO)
sharply pointed sterns are often copied as well. Are they doing this only
for marketing purposes (looks fast, so it must paddle fast)? Or this there
something else I am missing about the sharp Greenland style bows and
sterns?
I know in the racing kayaks the prow is nearly vertical to get the longest
WLL from the limited overall length limitations . In a recreational kayak
this would not likely be well suited to rough water because of the bow
would want to dive into the waves. Even so I would think the best WLL
would still come from a near vertical bow (and stern) and resisting dive
could be accomplished with good design above the normal water line.
I have also observed many hard shell manufactures that not only make
steeply raked prows, but also very fine narrow bows as well. This would
seem to slice nicely through waves, but would allow a lot of waves and
splash to strike the paddler and cock pit and cause the bow (and stern) to
dive in heavy seas. I can not think of an advantage to such a shape but
many manufactures do it anyway. Is this again done out of ignorance or for
marketing or is there some other advantage to such a bow I do not know
about.
I am just guessing but in traditional Greenland style kayaks with the sharp
bow and the steep prow would certainly be easier to make than a baidarka
bow, and might have advantages in water choked with ice, or for landing on
ice flows. I can imagine that rapidly sliding up on to an ice flow with a
wounded animal in tow that the sharp Greenland bow would definitely have an
advantage. Not something recreational paddlers would be concerned with.
Another advantage is with a shorter water line length it would certainly
turn easier, but at the cost of directional stability (tracking) and WLL.
But is seems they could have simply made a shorter kayak if that was what
they wanted. Because they certainly could have used less steep prows and I
do not know why else they would choose such a bow shape.
My overall question is how does bow shape affect the performance of the
kayak, what advantages are there to the steeply raked Greenland style prow
if any? Do I understand their function properly? The narrow steep prows
sure look neat, but I can not think of any advantages.
What are the consideration I should take in making a bow for a general
recreational kayak. I am thinking that I will make a fairly vertical prow
(like at 45 to 60 degrees, to keep the water line length), in a low profile
bow prow (to keep the windage low), with gunwales held as wide as practical
at the top to prevent diving and keep as much volume as possible, yet not
too wide or it will not penetrate waves well. I do not particularly care
for the look of the bifed and it looks like too much work to build for
questionable benefits (though I may build one this way eventually). I also
think the traditional baidarka stern has many advantages and do not find
the looks so objectionable, though I will likely try to improve it some too
by running the gunwales all the way to the back.
Thanks, your thoughts would be much appreciated.
Peter
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