Wm Watt wrote:
Cutting a piece out of the middle of the hull should be no great
challenge. Just be careful to choose the locations of the joined halves
that they match exaclty.

How many boats have you seen that have the exact same hull profile
forward and aft of the centerline? Not many are designed that way.

Then sand off the inner surface around the cut
and apply a couple of layers of fibreglass soaked in resin through the
cockpit. Boat builders call it a "butt" join. I've used it in plywood
boats. While the boat is in pieces it should be easy to prepare the
inside, move the foot braces, etc.

That wouldn't be anywhere near strong enough. To do it right, you need
the inner glass, but you also need to feather the joint back a couple of
inches on the outside, lay in new glass to build the joint up to the
original thickness, then apply new gelcoat.

The challenge would come in enlarging the cockpit. I don't see how you
can cut a piece out of the middle of a kayak without effecting the
cockpit, and they tend to have moulded coamings to keep out the water
and to allow a spray skirt to be tied on. Before cutting I'd want to
figure out what to do about the cockpit.

The only feasible thing to do would be to remove the coaming first, then
enlarge the cockpit opening to the proper size after the boat is
shortened. If the cockpit is recessed or the shape of the deck changes
significantly, it will take a LOT of work to reinstall the coaming.

The bottom line is that this project simply isn't practical.

This idea of cutting a Kayak to size seems a bit dumb. Why don't you
just build a bigger storage space? Or if you want to work on a kayak
buy a stitch and glue kit for a smaller Yak. But if you insist on
cutting the kayak. Perhaps put in a 2 sturdy bulkheads about a 1 mm (or
less) apart and cut between them creating two water tight sections that
you can reconnect by butting the bulkheads together and bolting them
firmly in place. You might even want to have 3 reattach-able sections
stern cockpit and bow.

Thanks everyone for your ideas!

I'll let you know what happens!

Regards,

Nick

Brian Nystrom wrote:

How many boats have you seen that have the exact same hull profile
forward and aft of the centerline? Not many are designed that way.

"Exact same profile" not required, just at a single point. How many do
you want? These are 20 year old craft. The model names have been posted
so you are welcome to look them up and let us know. Not many are
designed symetrical fore-and-aft today but at one time all canoes and
kayaks were symetrical. The many ways designers use to keep selling
more boats is a topic for another discussion.

Say they are not symetrical. Then the front section can be inserted
into the rear section and locating the cutting lines is not as
critical. Asymetrical would be easier.


That wouldn't be anywhere near strong enough. To do it right, you need
the inner glass, but you also need to feather the joint back a couple of
inches on the outside, lay in new glass to build the joint up to the
original thickness, then apply new gelcoat.

It may or may not be strong enough in a patch or a scarphed panel but
this is a tube. Any tension on one side is compensated by equal tension
on the other. Just sand off the inside surface, position the two
halves, cellotape around the outside to keep the resin from oozing out,
and glasstape the inside. No need to do any fancy finish work to the
outside. One does need, however to cut the hull carefully so the two
pieces fit.
People have reported using single sided taped butt joins on plywood
boats to avoid the problem of finishing the outside surface. Apparently
it does actually work there.



The bottom line is that this project simply isn't practical.

Where does practicallity enter into the hobby of paddling or
boatbuilding?
Giving up a day's pay to drive 200 miles to paddle down a river is
practical?
My own boatbulding is motivated as much by curiosity as practicality.
Can it be done?
Some don't like to spend money but time is no problem.

Wm Watt wrote:

at one time all canoes and kayaks were symetrical.

Care to back that up with something resembling a fact.

It may or may not be strong enough in a patch or a scarphed panel but
this is a tube. Any tension on one side is compensated by equal tension
on the other.

You really don't understand what a hull does in the real world. Tension has to
be balanced by compression. Local loads have to be accommodated, not just
overall bending moments.

Mike

wrote:
Dear All,

I have recently acquired 2 fibreglass kayaks.

Given our lack of storage space, I am considering shortening them.

Has anyone done this before?

I have done some research into glass fibre moulding, and if I was to do
it, was planning on making a male mould that I would leave wedged into
the cut ends and lay the fibre over it. My brother has some experience
of glass fibre moulding and is prepared to advise too.

One is 3900 long, the other 4200 long. The width is around 600mm.

I have calculated the volume of the shorter one as being around 360
litres.

Surely I can afford to lose some volume given that some modern kayaks
are as little as 180 litres and I'm not that heavy?

I read a little somewhere about people shortening plastic kayaks, so I
would have thought this would be more straightforward?

I know it could be quite time consuming and messy but it seems a shame
not to make use of kayaks that would otherwise have been destined for
landfill!

I have had some advice from another couple of forums advising that the
paddling efficiency could be reduced, this is not too much of a problem
as I will only be covering short distances on a placid local river.

I understand that bouyancy and waterline depth will be affected too.

Any thoughts/advice gratefully received!

Regards,

Nick

I may have missed it, but by how much are you needing to shorten these
boats?

From what you have written, you are looking to end up with something to
go swamping in, and they don't need to be particularly pretty. Also
does not sound like you are doing any wild water, just need something
highly manueverable to negotiate the backwater?

You might just clip the ends back to the desired length, and then glass
over the opening to be water proof. That way, the load handling central
structure will not be compromised, as well as the rocker that is needed
to turn easily. Also you will not have to mess with the combing if you
plan to use a spray skirt.

The sharp pointy ends are not needed really as demostrated in the newer
generation of playboats and creekers. You are not looking to achive
great speed characteristics, and depending on how good you are at the
glass work, will tell how the finished product will be.

You could always mount some sort of maiden form on the bow to scare off
the swamp gods, or maybe attract a mermaid! HYY

On 15 Aug 2006 02:50:18 -0700, in rec.boats.paddle
wrote:

I am considering shortening them.

Has anyone done this before?

I had one on a trailer and backed it into a trellis, once.

That probably doesn't count, though.

Jones

wrote:
This idea of cutting a Kayak to size seems a bit dumb. Why don't you
just build a bigger storage space? Or if you want to work on a kayak
buy a stitch and glue kit for a smaller Yak. But if you insist on
cutting the kayak. Perhaps put in a 2 sturdy bulkheads about a 1 mm (or
less) apart and cut between them creating two water tight sections that
you can reconnect by butting the bulkheads together and bolting them
firmly in place. You might even want to have 3 reattach-able sections
stern cockpit and bow.

Converting these to multi-piece kayaks is the only sensible solution
other than getting rid of them and buying appropriate boats.

Wm Watt wrote:
Brian Nystrom wrote:


How many boats have you seen that have the exact same hull profile
forward and aft of the centerline? Not many are designed that way.


"Exact same profile" not required, just at a single point. How many do
you want? These are 20 year old craft. The model names have been posted
so you are welcome to look them up and let us know. Not many are
designed symetrical fore-and-aft today but at one time all canoes and
kayaks were symetrical. The many ways designers use to keep selling
more boats is a topic for another discussion.

What some people have done as far as design is irrelevent. More than
likely, these boats are not symmetrical.

Say they are not symetrical. Then the front section can be inserted
into the rear section and locating the cutting lines is not as
critical. Asymetrical would be easier.

Are you kidding me? It's also quite likely that the ends are different
enough that one will not fit into the other. For that to work, the fore
and aft decks would have to be the same height, which is not common at all.

That wouldn't be anywhere near strong enough. To do it right, you need
the inner glass, but you also need to feather the joint back a couple of
inches on the outside, lay in new glass to build the joint up to the
original thickness, then apply new gelcoat.


It may or may not be strong enough in a patch or a scarphed panel but
this is a tube. Any tension on one side is compensated by equal tension
on the other. Just sand off the inside surface, position the two
halves, cellotape around the outside to keep the resin from oozing out,
and glasstape the inside. No need to do any fancy finish work to the
outside. One does need, however to cut the hull carefully so the two
pieces fit.
People have reported using single sided taped butt joins on plywood
boats to avoid the problem of finishing the outside surface. Apparently
it does actually work there.

It only works because the boats are fully glassed inside and out after
the panels are stitched. Perhaps some designs substitute fillets and
tape on the seams for inside glass, but either way, the boat is
substantially reinforced. I've never heard of a kayak kit or plan set
that uses/recommends but joints without exterior glass and some interior
reinforcement.

The bottom line is that this project simply isn't practical.

Where does practicallity enter into the hobby of paddling or
boatbuilding?

There's got to be a line somewhere. Perhaps others think this is a good
idea, but I don't.

Giving up a day's pay to drive 200 miles to paddle down a river is
practical?

I wouldn't do it.

My own boatbulding is motivated as much by curiosity as practicality.
Can it be done?

Maybe you should offer to shorten these boats for the OP, just to see if
it can be done.

Some don't like to spend money but time is no problem.

Knock yourself out, then!

Michael Daly wrote:
Wm Watt wrote:

at one time all canoes and kayaks were symetrical.

Care to back that up with something resembling a fact.

Moreover, at one time all river kayaks were not only symetrical but
were a standard 13 feet long. It wasn't until computer programs became
available that all the different shapes appeared.


It may or may not be strong enough in a patch or a scarphed panel but
this is a tube. Any tension on one side is compensated by equal tension
on the other.

You really don't understand what a hull does in the real world. Tension has to
be balanced by compression. Local loads have to be accommodated, not just
overall bending moments.

Any tension on one side is compensated by compression on the other.


Mike