: I've always wanted an underdeck storage area for a
: pump and water bottles

You may only expect to need a pump if you have had a wet exit, and to use
a handpump, your spraydeck has to be open, so somewhere accessible from
the cockpit is the ideal place for it. But think: you might want your pump
if someone else has had a wet exit, in which case, opening your deck may
be a risk - do you want two of you with cockpits full of water ?

My choice is usually to keep the pump behind the cheek plate on the right
hand side of the cockpit easily accessible if the deck is off, but without
opening anything nominally watertight.

; would be nice to keep topside uncluttered. I'm
: considering possibly a half-cylinder or cone shape (open at both ends)
: made of strip, for whatever weight penalty may be involved.

A kneetube provides an excellent place to brace your knees, which is great
if your thigh braces are perhaps not up to much. But - once again considering
rescues - one way of getting back into your boat is to enter the cockpit
feet first from the aft deck, face downwards so you can keep low and stable.
Once far enough in, you flip over and sit down. This is very much more
difficult with a knee tube as there isn't room for your legs to cross over !
If you have a big keyhole cockpit, you may be able to enter by sitting astride
the boat, sitting into the cockpit and pulling your feet in last, which is
not impeded by the knee tube. So whether a knee tube is for you depends a lot
on the size of your cockpit, whether you hope to be able to self-rescue or
will always paddle in a group, and whether you will paddle in the rough.

Personally, I like a tiny ocean cockpit, but I tend to paddle in a group
so it's unlikely I will need to self-rescue, and my favoured technique
for self-rescue is re-entry and roll, so I am happy to have a kneetube.

: Are there any established designs for knee tubes that I should look at?
: Problems to avoid? Reasons to reconsider the entire idea? Thanks

I made three small forms to fit on a little baby strong back (a 1.2x0.8" bit
of timber) so that I could strip-build knee tubes as required. The size of
the tube was chosen to allow for a 10-cm diameter Kajak-sport hatch on the
cockpit end. It's useful for snacks and bits and pieces I will need whilst
at rest on calm water - not for things I'd want in a hurry or when it is
rough.

The link is to my printable plans for three forms for my knee tube. The
file isn't big (42k) but the graphic is 4640x2360 and is designed to print
on A3 paper at 300 dpi... so you may prefer not to try to open it in your
browser :-) The blue outline is the form nearest the cockpit, and the red
one for the one nearest the forward bulkhead. You adjust the length to fit
the distance from your cockpit rim to that bulkhead (or a bit longer, and
cut to fit if, like me, you have a non-flat bulkhead).

Bill Hamm: Not sure I'd want any emergency gear under the deck, when you
: may need it you'd have to pop the skirt

I have one of those spraydecks with a bale hole in the front, which is
big enough to get my hand and arm inside without taking off the deck.
As the bale hole is at the front of the deck, it would be adequate to
reach into at least the near end of a knee tube for something you could
find by feel ... probably easier than groping around in a bag on the aft
deck in rough conditions, anyway ! I've certainly used it to get a camera
from inside the cockpit and put it back again...

A knee tube is certainly a useful place to keep stuff you want on the water,
like suncream, snacks and drinks. Whether you want to use it for emergency
kit is a separate decision. I would probably be happy keeping flares in there,
since the manufacturers don't certify them to keep working if they have been
exposed to lots of sea water by being kept on the deck...

Andy