Subject: Re: baidarka Date: Tue, 21 Nov 2000 17:58:26 -0800
From: Douglas Ingram (redcanoe@pangea.ca)
Date: Wed Dec 06 2000 - 10:51:37 EST
James,
You are quite welcome. Its not always that I am able to offer something of
relevant value to this list, not being a kayaker and all, but I am glad to
do so when able.
Deadrise affects that portion of the bottom from the keel to the chine.
That point is fairly obvious on some boats, such as a Greeland kayak, but
less so on "slack bilged" craft. One will have to make some decision where
the bottom is no longer the bottom and is no the side.
Tumblehome is not the great bugaboo that some make it out to be, and neither
is flare the great panacea. Each must be used in balance given the design
criteria. Same thing as primary and secondary stability, they must be in
balance to give the paddler a continuous and predictable sense of the boats
stability curve. There have been boats that I have paddled where the
balance has not been kept. The max width was near the waterline, and then
there was a very tight curve into tumblehome to keep the gunnels narrow for
easy paddling. The combined effect resulted in a very hard chine and no
reserve bouyancy. Any heeling over was like trying to balance on the edge
of a cube. It was a teetertotter, one wiff the wrong way and BOOM, over she
goes! Many new canoe designs are incorporating soft bilges for easy
predictable heeling, max width well above the waterline for effective flare,
and the a tight turn, or shoulder, about 3-4" below the gunnel, producing
enough tumblehome where it is actually needed, for easy paddling.
What tumblehome does do is this:
-continuous curvature of the ribs provides a structure of greater stiffness
for its dimension.
-reduces the width that the paddler must reach over in order to acheive a
good stroke without banging their hands
-makes a boat look sleeker due to narrower gunnel width
-actually increases the depth of the boat while it is heeled over.
That being said, one can actually have the effect of flare and tumblehome in
the same boat, as long as the max. width is above the waterline.
It has been my observation that most kayaks have a narrow enough width that
tumblehome is not always necessary for issues of reach and hand banging and
that many kayaks have their gunnels low enough that the tumblehome is built
into the deck rather than the hull.
Douglas
> Thankyou for clarifying, Douglas! Does that mean that deadrise would only
> be appropriate when speaking of the angle to the first stringer? How
would
> you express deadrise on a round bottom sailboat? Just curious...
>
> You are absolutely right, expanding the gunwales on Raven would and did
> increase rocker. This, of course, was not a problem on Raven (nor would
it
> be on most baidarkas) as the final straw that led to this surgery was when
I
> got locked into a trough during a spring squall in Canada and could not
turn
> her downwind to save me. Literally. I also think the additional rocker has
> added greatly to her stability, helping accomplish the other goal of this
> rebuild. Heron was planned with this flare in her, so the rocker there
was
> not affected.
>
> Another aside: I have never understood any purpose to tumblehome. Prijon
> built that into some of their sea hulls, and I always found it a curious
> design choice. The net effect would be an increase in primary stability
but
> with a marked decrease in secondary, as the additional heel would not act
to
> shift the center of bouyancy farther outboard, as happens with flare. The
> result, and I have seen this with my own two eyes on a waterlogged
> girlfriend, is to make the Prijon hull into one of the wettest surprises
in
> the business... ahh, this boat is sooo stable... ooops... glug glug.
>
> ----- Original Message -----
> From: "Douglas Ingram" <redcanoe@pangea.ca>
> To: <baidarka@lists.intelenet.net>
> Sent: Tuesday, December 05, 2000 7:17 AM
> Subject: Re: baidarka Date: Tue, 21 Nov 2000 17:58:26 -0800
>
>
> > A few observations, if I may.
> >
> > Deadrise is the angle that the bottom of the boat establishes using the
> keel
> > or centerline as the point of the angle, and a horizontal line, called
the
> > baseline. For example, a perfectly flat bottom boat has zero deadrise.
> >
> > Flare is one term ( tumblehome and plumb being the others) used to
> describe
> > the angle that the sides make relative to a verticle line parallel to
the
> > centerline.
> >
> > It has been my observation, when working on canoes when the thwarts are
> > removed, that the sides want to spread outwards, therby increasing
flare,
> > and having comparatively little effect upon dearise.
> >
> > The increase in flare effected upon an already built structure is
> coincident
> > with an increase in curvature of the gunnels, that is, they are less
> > straight. Now, as the gunnel is a fixed length, this increase in
> curvature
> > has the interesting effect of reducing the distance between the stems.
> > While the difference will not dramatically affect the boats length, it
is
> > enough to significantly affect the amount of rocker. As the stems are
> > pulled closer together, they are pulled up. If you need help to
visualize
> > this, use a letter envelope to simulate the boat.
> >
> > Douglas Ingram
> >
> > ----- Original Message -----
> > From: James Mitchell <mariner@seanet.com>
> > To: <baidarka@lists.intelenet.net>
> > Sent: Monday, December 04, 2000 4:21 PM
> > Subject: Re: baidarka Date: Tue, 21 Nov 2000 17:58:26 -0800
> >
> >
> >
> >
> >
-
This archive was generated by hypermail 2b27
: Mon Jan 01 2001 - 01:00:02 EST
> >
> > > If I understand your terms correctly, I am talking about the angle of
> the
> > > deadrise. You are correct about the "V" being decreased at the keel.
> > > Because of the way I did this, the effect is proportionally larger as
> you
> > > approach the gunwale; therefore there is very little impact on
> waterline;
> > > and even less impact on the angles at the keel. I haven't had a chance
> to
> > > paddle in wind yet, and such would be a very subjective test anyway;
> > > however, Heron and Orca have much the same flare/keel arrangement and
> > track
> > > very well.
> > >
> > > I would guess that the tightness of the skin has more to do with
> tracking
> > > than the changes I made. Because of some unfortunate temperature and
> > > humidity changes, Raven's skin came out looser than I wanted (hurray
for
> > > working outside). But one benefit of a loose skin is better tracking,
> > > because the keel and the stringers become more exposed as the skin
wraps
> > > around them.
> > >
> > > Incidentally, Raven, Orca, and Chinook are all for sale if anyone is
> > > interested.
> > >
> > > ----- Original Message -----
> > > From: "Native Ways" <nativeways@hotmail.com>
> > > To: <baidarka@lists.intelenet.net>
> > > Sent: Monday, December 04, 2000 1:54 PM
> > > Subject: Re: baidarka Date: Tue, 21 Nov 2000 17:58:26 -0800
> > >
> > >
> > > > James,
> > > > When you peak of "flare" are you talking about the beam, or the dead
> > rise
> > > > from the keel to the chine, making it more of a V hull? It sounds
like
> > you
> > > > increased the beam on Raven at mid-ships but left the old ribs as-is
> > which
> > > > would, I think, flatten the bottom a little, effectively making less
> > "V",
> > > > and a shallower cock-pit area. No? How is tracking with a beam wind
> > > compared
> > > > to before?
> > > > Greg
> > > >
> > > >
> > > > >From: "James Mitchell" <mariner@seanet.com>
> > > > >Reply-To: baidarka@lists.intelenet.net
> > > > >To: <baidarka@lists.intelenet.net>
> > > > >Subject: Re: baidarka Date: Tue, 21 Nov 2000 17:58:26 -0800
> > > > >Date: Sat, 2 Dec 2000 18:32:55 -0800
> > > > >MIME-Version: 1.0
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> > (PST)
> > > > >From owner-baidarka@ns1.intelenet.net Sat Dec 02 18:47:18 2000
> > > > >Message-ID: <006e01c05cd1$58265000$c79c2640@hjdm2528>
> > > > >References: <OE69qJfhUbfh9aKOMpZ00002180@hotmail.com>
> > > > >X-Mailer: Microsoft Outlook Express 5.50.4133.2400
> > > > >Sender: owner-baidarka@lists.intelenet.net
> > > > >Precedence: list
> > > > >
> > > > >Yeah, I think flare has a lot more to do with the stability than
does
> > > width
> > > > >per se. Since our discussion, I completed and tested Raven. I can
now
> > > hang
> > > > >her on her gunwale and spin her; previously, I couldn't take my
eyes
> > off
> > > > >the
> > > > >water. This is the second hull I have done this too, the first
being
> > > Orca,
> > > > >with same result. And Heron, which was designed from the beginning
> with
> > > the
> > > > >additional secondary flare, I have actually dosed off while sitting
> in
> > > the
> > > > >reeds at Spencer Island in the late afternoon summer sun. I think
> you
> > > > >could
> > > > >fish all day in that boat.
> > > > >
> > > > >----- Original Message -----
> > > > >From: "Phil Sharp" <srelt@msn.com>
> > > > >To: "BaidarkaSubmission" <baidarka@lists.intelenet.net>
> > > > >Sent: Wednesday, November 29, 2000 5:22 PM
> > > > >Subject: Re: baidarka Date: Tue, 21 Nov 2000 17:58:26 -0800
> > > > >
> > > > >
> > > > > > Thanks for the idea James. I had not considered doing it that
> way.
> > I
> > > > >had
> > > > > > thought about increasing gunwale width, but then proportionately
> > > > >increasing
> > > > > > the stringer width as well, and maybe adding one more stringer
> each
> > > > >side
> > > > >to
> > > > > > support the added width. Your idea is intiguing, though. Now,
do
> > you
> > > > >do
> > > > >any
> > > > > > fishing from your kayak, and if not, do you think you could if
you
> > > > >wanted
> > > > >to?
> > > > > > Sorry it took me so long to get back to you; I have been out of
> > town.
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > Phil Sharp
> > > > > >
> > > > > >
> > > > > > SeaCaller
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > ----- Original Message -----
> > > > > >
> > > > > >
> > > > > > From: James Mitchell
> > > > > >
> > > > > >
> > > > > > Sent: Tuesday, November 21, 2000 9:39 PM
> > > > > >
> > > > > >
> > > > > > To: baidarka@lists.intelenet.net
> > > > > >
> > > > > >
> > > > > > Subject: Re: baidarka Date: Tue, 21 Nov 2000 17:58:26 -0800
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > Phil, I recently modified my first hull to increase its
stability.
> > > > > >
> > > > > >
> > > > > > Originally it was 17'-2" x 20.5", now it is 17'-1.5" by 22.25".
> All
> > > the
> > > > > >
> > > > > >
> > > > > > increase is at the gunwale. I replaced all the deck beams to
> > increase
> > > > >the
> > > > > >
> > > > > >
> > > > > > width, moving the old ones forward a station (and retrimming
> them).
> > > > >Most
> > > > > >
> > > > > >
> > > > > > had to be replaced.
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > The modification has worked very well. With no noticeable
impact
> on
> > > > >speed,
> > > > > >
> > > > > >
> > > > > > I have easily increased the effective stability nearly double to
> the
> > > > >point
> > > > > >
> > > > > >
> > > > > > where I can hang the hull on its gunwale clear above the cockpit
> > rim.
> > > > > >
> > > > > >
> > > > > > Prior, if I tried that, it would have capsized. What I have
> > confirmed
> > > > >here
> > > > > >
> > > > > >
> > > > > > is the impact of flare on the stability. I would encourage you
to
> > > build
> > > > >as
> > > > > >
> > > > > >
> > > > > > much flare into your hull as possible. That way the stability
will
> > be
> > > > >there
> > > > > >
> > > > > >
> > > > > > when needed, but won't slow you down when you don't.
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > ----- Original Message -----
> > > > > >
> > > > > >
> > > > > > From: "Phil Sharp" <srelt@msn.com>
> > > > > >
> > > > > >
> > > > > > To: "BaidarkaSubmission" <baidarka@lists.intelenet.net>
> > > > > >
> > > > > >
> > > > > > Sent: Wednesday, November 15, 2000 8:26 AM
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > > Do any of you fish regularly from your Baidarkas? If so, did
> you
> > > > >change
> > > > > >
> > > > > >
> > > > > > the
> > > > > >
> > > > > >
> > > > > > > dimensions to make it more stable? What are those
> > > dimensions--length,
> > > > > >
> > > > > >
> > > > > > width?
> > > > > >
> > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > > > Thanks.
> > > > > >
> > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > > > SeaCaller
> > > > > >
> > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > > >
> > > >
> >
>srelt@msn.com___________________________________________________________
> > > > > >
> > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > > >
> > > > > >
> > > > > >
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