Re: [Paddlewise] Skeg Jammers etc

> You'd have to ask Paul.
Will do. FWIW, I can't imagine anyone seriously suggesting that only one
type of kayak can complete challenging trips, although you can read on kayak
manufacturer's websites that their kayak is pre-eminently suitable for
certain testing trips.

> Appeals to authority don't much impress me.
Disregard for knowledge and experience is the opposite evil.

> ... lots of kayak designers can't figure it ... One kayak
> company, who's new models are rudderless, trims them very stern down.
Which brand of kayaks are these? Good to see someone is bringing out
rudderless models.

Don't the centre of buoyancy and the centre of mass line up once the boat is
on the water?  If the CoM is not aligned vertically with the CoB, doesn't
the kayak hull shift in the water until it is? I understand the CoB to be
the point through which the forces counteracting sinking appear to act. If
the CoM is measured along the kayak when it is out of the water, the
difference when the boat is on the water is the mass of the kayaker sitting
in it which may alter both centres. If the kayaker's centre of mass is
determined to be somewhere in the gut behind the navel, then that point
should be aligned vertically over the kayak's centre of mass to have the
boat float in trim.
Picking the kayak up and balancing it determines the position of the centre
of mass of the kayak along its length. Then plonk the boat in the water, and
the centre of buoyancy is at that point. Tell me if I'm wrong.

> A Swede-form kayak is likely bow heavy when
> picked up at the longitudinal center of buoyancy (with a paddler in it)
and
> the opposite for fish-form.
Now I'm lost. If the centre of mass of the paddler and the kayak are aligned
vertically, and the boat is at rest on the water, then the centre of
buoyancy will align vertically through both those centres, won't it,
whatever the plan shape of the hull? Do you mean that because Swede form
kayaks likely have more storage room in the stern, and conversely Fish form
kayaks more storage room in the bow, that there is a probable difference in
the distribution of the load placed in each type? But that depends on how
you pack it, which is what we have been discussing. So there is no necessary
likelihood that a Swede form boat will be likely to be bow heavy when picked
up at the longitudinal centre of buoyancy, because that point, by
definition, is lined up with the centre of mass, with or without a paddler
in the boat.

> However, the easiest way I know of to determine the center of
> buoyancy of most existing kayaks is with a level.
Since the centre of buoyancy is at the centre of mass of the displaced
water, and both are aligned vertically when the kayak is at rest, why isn't
the centre of mass of the kayak on land a good approximation to the centre
of mass of the water is displaces when floating. Could you explain this use
of a level a bit further?

> I get excellent repeatability on retesting the same hull.
You are way ahead of me. Every time I turn the boat radically, it spins
through a different arc. The turning effect depends on a lot of things,
including how close to having a cold wet ear I want to be.

> Very little difference since my slight modification referred only to a
rare
> class of kayaks, those already balanced in a side wind...
That's something else to think about. What side wind? A kayak balanced in a
10 knot wind will not be a kayak balanced in a 20 knot wind, for the same
forward speed of the kayak. I suppose a kayak designer should try for
balance in the winds a boat is likely to be paddled in. That will mean that
higher winds will weathercock a boat designed to balance in lower winds. And
a boat designed to balance at 3.5 knots paddling speed in 15 knots beam
wind, will drop off downwind when stationary in the same wind. What
approximate beam winds should boats be designed to balance in?

>What could be simpler. Load all heavy dense
> items (and bags) in the stern and the light ones in the bow. It is an easy
> simple to follow rule and you only have to load the kayak once, no
lifting,
> balancing or logs necessary.
Next fully loaded trip I will try this, as far as possible. I will also pick
the boat up when it has been loaded and see how it behaves according to the
backbreaker test. We may be talking about achieving the same end. I have
never had to repack the boat numerous times to achieve fore-and-aft balance
on the pick up test. If any adjusting is done, it is just to move say a
water container or food bag from back to front or vice versa. Same thing as
your lateral adjustment with soft drink bottles. Things trim better with
Coke?

Cheers, PT
***************************************************************************
PaddleWise Paddling Mailing List - Any opinions or suggestions expressed
here are solely those of the writer(s). You must assume the entire
responsibility for reliance upon them. All postings copyright the author.
Submissions:     PaddleWise_at_PaddleWise.net
Subscriptions:   PaddleWise-request_at_PaddleWise.net
Website:         http://www.paddlewise.net/
***************************************************************************