Subject: Reducing beam afloat
From: Mike Crawford
Date: 5/14/2008, 9:58 AM

  Rafael Francke at Cat2fold has a very interesting design for a folding catamaran that can reduce its beam while on the water. 

  He created it along with Kurt Hughes in order to be able to enjoy the large deck space and stability of a catamaran while having the trailerability of a trimaran.  He also wanted to be able to use a standard non-telescopic trailer, as well as be able to reduce beam on the water in order to fit into marina berths.  In addition, he as a fold-down hard deck to span between the beams.

  You can see from the video how the scissors-action akas allow the boat to fold and unfold while stable, while also keeping each hull vertical (no stained/blistered topsides like with the Farrier method).

  While the boat is now up for sale, they did build it and sail it for two years.  It is a very smart design that allows one or two people to set the boat up and launch it without a travelift or crane.

  If I were to build a cat or proa that reduces beam on the water, I would use these scissors-action carbon fiber x-beams. 

  Telescopic akas could also work, but I'd worry about being able to keep the joints tight over time, and also about being able to keep enough bury to ensure a very stable beam.  Catamarans with stayed rigs have a slightly easier time with keeping telescopic beams tight because the compression load from the mast, combined with the side loads from the shrouds, keeps everything tied together.  A boat with an unstayed mast wouldn't have that effect.

  The scissors akas, though, extend across the entire beam when sailing, and would be rock solid when locked.  There would be no issue in terms of tightness, and given the full-beam length of each section, no worries about the buried telescopic joint being strong enough.

  This is also one of the few designs I could see working to reduce beam while afloat.  The video shows one person doing it with a winch, and I've seen another video of one person launching the entire finished boat.  Telescopic akas could also work, but you'd have to collapse each one at the same rate, otherwise you could get a jam.  The scissors akas would be much more tolerant to small differences in alignment between the hulls, and would also probably be less affected by friction.

  This design would obviously make it tough to have a full-beam solid walkway.  That would either have to be removable, foldable like the Francke design, or left out entirely.

  It wouldn't be a classic trailering solution, either.  Regardless of how the boat changes beam, I'm not sure there's a way to get a proa with double beds and a cockpit down to 8.5' for trailering without a permit.  The only way to do that would be to slide the leeward hull underneath the cockpit.  I suppose it could be possible to design a folding system to do this, but I'd worry about that making the boat too tall on the trailer, and I'm also not a fan of putting topsides in the water.

  By putting the wheel in the cockpit, though, or using tillers, you could have a system that gets the beam down to 12'.  That's narrow enough for a marina berth.  12' is also the maximum trailering width in the United States for getting a wide load permit that doesn't require escort vehicles with signs to lead or follow the main vehicle.

  There are problems with the design.  It could add 50 to 100 kg to the boat weight, it would add expense, and there wouldn't be room for the wheels and walkway in the existing location.  But if you want to fold on the water while keeping both hulls level, Francke's design is a workable solution.

       - Mike

Arto Hakkarainen wrote:
But that is the difference. In our boat I am the
galley slave. I don't mind working in the galley
regardless of location. And the layout I'm thinking
icludes galley located next to steps to cockpit and
saloon in the hull right next to galley by the second
double bed. I should draw it to make it easier to

Actually if you have looked at Grainger's Alfresco
catamarans you get the idea of the saloon in hull I
have in mind. Alternatively I'm thinking of
Shuttleworth like flared hull with enough beam to have
settees opposite each other with table between. And
combining the two would make it actually quite roomy
but would require part of the second double bed to be
used as settee (removable or folding backrest to make
it double berth again). Folding table (or table rising
to roof) would make access to second berth and head

But the marina issue seems to be different where you
sail. I have no problem finding permanent dock.
Marinas during our short cruising period are sometimes
very crowded. Getting place in marina sometimes takes
slow approach to carefully place the bow between two
boats and then pushing the boat between the other
boats with full throttle to slide between the two
boats in already full dock. Been there, done that...

Actually one morning when a boat tried to exit the
dock whole line of boats moved in same rhytm when they
tried to leave. Boats where so tightly packed that
they couldn't get out before half a dozen others
helped push next boats little further with feet. Now
figuring how to get a harryproa with over 8 m beam to
that marina... You get the picture.


--- jjtctaylor <> wrote:

> Arto,
> One point the boss made clear, she wants to be up,
> not down. Part of
> the sail appeal is social, so wants galley in the
> middle, and up not
> down in the hull. Need to see out forward (or back)
> to minimize
> seasick if must work at sea. Also MUST have galley
> near cockpit for
> activities and refreshment.
> I am able to find transient end dock space at many
> locations. Just
> not berthing slips. Makes it easier to park anyway.
> Permananent
> berthing slips for CATS are really hard to find. I
> have to wait 2
> years for new marina near Oriental, NC.
> JT
> --- In, Arto
> Hakkarainen <ahakkara@...>
> wrote:
> >
> > --- Robert <cateran1949@...> wrote:
> >
> > > About amount of flare: I would consider how
> much
> > > small tris like a
> > > kendrick have as a maximum. My idea is to have a
> > > eonough flare so that
> > > an 80cm wide hull at wterline can have enough
> room
> > > downstairs for a
> > > small saloon, ie about 1.4-1.5 m over all,
> giving
> > > about 330-35cm flare
> > > each side. I would have them just high enough
> for a
> > > comfortable
> > > backside to fit, and this would mean that chop
> would
> > > meet them. I t
> > > may be that this could help in resistance, as
> they
> > > my get a bit of
> > > lift off the chop if the flare is close to
> > > horizontal. decent bunks
> > > could be set above on the inward side, and still
> be
> > > less than 3m for
> > > wide towing. I'd like to flare slightly the
> inside
> > > of the lw hull to
> > > about1.2- 1.3m for a 'cosy' double. this would
> also
> > > increase the bury
> > > fo rthe crossbeams I'd also like to consider
> > > allowing the crossbeams
> > > to slide into the cabin, allowing the hulls to
> sit
> > > together, reducing
> > > overall width to less than 4.5m, more acceptable
> for
> > > marinas,
> > > hard-stand, narrow waterways and short term road
> > > transport.
> > > Robert-
> > >
> > This reflects also my thinking. Simple facts of
> life:
> > wife likes marina conveniences, marinas are full,
> with
> > wife onboard I have more chances to go sailing ->
> must
> > be able to find marina berth, which is easier with
> > less beam. Way to reduce beam for marinas would be
> > very welcome feature.
> >
> > Arto
> >

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