Boat Building Forum

Find advice on all aspects of building your own kayak, canoe or any lightweight boats

stability-good designs
By:Randy Knauff
Date: 10/14/2001, 12:51 am
In Response To: Re: Chesapeake hull shape (Dean Trexel)

: I haven't done a CLC boat but have done a Pygmy. The hull panels in the
: middle should only be about 5 degrees or so from horizontal. The flatter
: the kayak is amidships, the more 'initial stability' the kayak has. There
: are 2 kinds of stabliltiy, initial and final stability. A kayak with low
: initial stability would feel 'tippy' or 'squirrly' as you sit upright in
: it and swivel your hips. It doesn't feel like it takes much of a shift to
: get the boat to start leaning. If the boat had a deeper V hull, the boat
: would feel very tippy. Your kayak has a fairly flat bottom to make it less
: tippy. Final stability, while irrelevant to your question at hand, is
: represented by the amount the boat can be leaned before it tips over. It's
: tough to describe without diagrams, so I'd recommend getting Nick Schade's
: book for reference. But basically, a true V-hull would have low inital
: stability but high final stability, meaning it would feel tippy at first
: but you could lean it quite a bit before tipping over, and a true
: flat-bottomed boat would have high initial stability (like a flat-bottomed
: fishing boat or Grumman canoe) but couldn't be leaned as far before
: tipping over.

Actually, if you look at Nick's book on page 8, it shows that the flat bottom boat has better secondary stability than any other shape other than widely flared hull. It can be leaned further over and still have righting moment because the CB stays outside the CG longer.

The width of the water line plays an important part, the wider it is the more aggressively you have to lean it in sideways waves for secondary stability. The narrower, the easier to lean into the waves, but also easier to tip over if you misjudge or don't brace well.

In real paddling life secondary stability is relative to the loading of the kayak, the size/height/weight proportion of the paddler and leaning/bracing skill of the paddler.

Your kayak was designed as a compromise between the two
: designs -- sharply Vee'd in the bow and stern for efficiency and almost
: flat amidships for more stability. You will find that even the most
: expert-level Greenland-style kayaks have almost flat bottoms -- they're
: just made much narrower.

: Changing a stitch-n-glue design is difficult. The panels will really only go
: together one way as they are cut, so the only way to modify the design is
: to make the panels a different shape. Go at your kayak with that Skil-saw
: at your own risk! :)

Good point, the design of most of these boats is well worked out and measurements changed other than distance between stations may be asking for trouble and mismatched pieces.

Randy

Messages In This Thread

Chesapeake hull shape
Jed -- 10/13/2001, 11:43 pm
Re: Chesapeake hull shape *Pic*
Chip Sandresky -- 10/15/2001, 1:29 pm
Re: Chesapeake hull shape tweaks
Pete Croft -- 10/15/2001, 10:09 pm
Beam reduction???
Randy Knauff -- 10/16/2001, 4:07 pm
Re: Beam reduction???
Pete Croft -- 10/16/2001, 4:56 pm
Re: Chesapeake hull shape tweaks
LeeG -- 10/16/2001, 12:34 am
Re: the ultimate yakin' vehicle *Pic*
Dean Trexel -- 10/16/2001, 1:34 am
Totoro! *Pic*
Ross Leidy -- 10/16/2001, 11:34 am
Re: EEEKK!!
LeeG -- 10/16/2001, 9:36 am
Re: VW gets a nose job
Dean Trexel -- 10/16/2001, 1:06 pm
A woodstrip Westfalia conversion, maybe? *NM*
Shawn Baker -- 10/16/2001, 10:44 am
Re: Chesapeake hull shape
Val Wann -- 10/14/2001, 7:10 pm
Re: Chesapeake hull shape
steve hartmann -- 10/14/2001, 9:48 pm
Re: Chesapeake hull shape
Mike Scarborough -- 10/14/2001, 12:08 pm
Re: Chesapeake hull shape
Dean Trexel -- 10/14/2001, 12:05 am
stability-good designs
Randy Knauff -- 10/14/2001, 12:51 am
Re: flat bottom hull
Bob Marshall -- 10/14/2001, 8:55 am