|Subject: [harryproa] Re: Reducing beam afloat|
|From: Mike Crawford |
|Date: 5/15/2008, 1:46 PM|
This discussion has helped clarify two things for me:
a) I still prefer the scissors system for a variety of reasons, including the ability to radically reduce a boat's beam..
b) Point A above may be moot.
Rob has sold me on the idea of 360 degree beam-mounted rudders that kick up in both directions, and I don't see that working with a scissors setup. Doh! Robert also makes a good point about using a series of blocks to collapse the system.
It might also be possible to rig an expansion/contracti
The beams would probably have to be rinsed and dried before collapsing in order to keep out the salt and sand, but that's not too tough. The rudder mounts would have to on the outside of the the ww /external beam section, but that should also be easy to take care of.
The real question is how wide and narrow can the boat be with telescopic beams. (the following dimensions are rough estimates)
Let's take a Harry and expand the top of the ww hull a bit in order to provide enough room in the cockpit for a wheel. A 9' ww hull comprised of a 6' cockpit and 3' lower section, next to a 3' lw hull, would yield a 12' beam when fully collapsed. The external beam section would then be attached to the ww hull, because it connects to the overhanging bunk/cockpit section, and the internal beam section would be attached to the lw hull.
Fully collapsed there would be 6' of beam between the hulls. If you want 3' of overlap between the beam sections, that only provides for 3' of expansion, yielding a total beam of 15'. That's a bit narrow.
You might be able to get get another 3' of expansion by allowing the internal sections to extend into the ww hull when the boat is collapsed. It would be a bit inconvenient when trying to access the head while at a marina, but it could work. That would yield a total beam of 18', which is starting to approach the stock beam of 22'.
Moving to a 14' beam when collapsed would yield an expanded beam of a full 22' (beams penetrate ww hull when collapsed), or 19' (beams never enter ww hull). 14' might be the beam of a 40'-50' monohull, and is not hard to find at most marinas. It's also somewhat easy to transport a 14' wide boat by trailer, though since this would require an escort vehicle, it would be best done only once or twice a year.
A 22' Harry could have a single 3' x 10' removable walkway between the hulls, and that would probably be light enough to manhandle into and out of position when collapsing (provided it's not done every day). As Arto said, though, simpler is often better. As long as the cockpit is big enough, there's nothing wrong with all trampoline/netting between the hulls.
A Visionarry would probably require a collapsed beam of 16' to get an expanded beam of 26' if the beams extend into the ww hull when collapsed, or 18' to get to an expanded beam of 27' if the beams do not extend into the ww hull when collapsed. A 16' to 18' beam is still probably within reason for many marinas. It's definitely a lot better than 27'.
Is 3' of overlap enough? Probably. That's the current bury of the beams into the lw hull, so it should work. I just wouldn't know how to do the analysis on the overlapping joint -- it has been too many years since I did torsion calculations, and I also don't know how square carbon beams would respond. That might be best left to a computer running a finite element analysis program.
I still think that the scissors beams are the best option if you want the ability to take a Visionarry-sized boat down to a 12' to 14' beam when collapsed. But that would require either a lot of hassle with beam-mounted rudders, or more likely, hull-mounted rudders.
On the other hand, if you want to expand and collapse on a regular basis, and want beam-mounted rudders, telescopic is the way to go.
Since transportation over roads is part of my long-term plan, I could use either system on a Harry, but would have to go with a scissors setup on anything with a larger beam.
Peter Southwood wrote:
Hinges are a pretty high stress concentration. I have my doubts that
it is lighter than a sliding system. The sliding system has really no
extra weight other than a bit of bearing surface. Maybe a few
kilograms at the most. Rob and Mark had no problems with Elementarry'
sliding system with slightly thicker beam at full out and full in
allowing easy movement at other points. I would have thought this was
easier to handle the racking loads as the highest stress is at the
beam/lw join where the scissor folding system has a hinge and the
sliding system is no different from the usual system. Controlling the
sliding in and out could be done with two simple winches and about six
small snatch blocks or a continuous line system.
-- In harryproa@yahoogrou
> Hi Robert,
> Hinges for swinging are easier to get to work smoothly while still
keeping stresses and play small than sliding beams, unless you have
developed an improved sliding system that hs no play, can take racking
loads, slides easily without jamming on both beams, and prevents one
beam sliding in or out more than the other, which could lock
everything up, and still has fewer moving parts and critical failure
points than swing hinges, and locks easily and reliably when deployed
for sailing. Also should weigh less.
> ----- Original Message -----
> From: Robert
> To: harryproa@yahoogrou
> Sent: Thursday, May 15, 2008 9:50 AM
> Subject: [harryproa] Re: Reducing beam afloat
> -A simple sliding in telescoping beams is pretty simple.There is
> plenty of bury available. three metre wide ww hull and only narrowing
> by less than two metres, leaves a metre to play with. There is a bit
> of fiddling to anchor the the ends but not insurmountable. The
> advantage, is there are no fancy hinges , just simple beams and
> sockets I don't see too many problems with sealing the crossbeams, as
> the sockets could be separated from the inside volume, or just wrap a
> boot around the point of insertion. I looked at folding systems and I
> worked out how a folding system to trailing is possible. Just a bit of
> drama in removing the mast, but not insurmountable. I felt that if I
> had to trailer, then I can simply take the beams out, but I could see
> situations where I would like to quickly narrow and still be able to
> gently sail.
> -- In harryproa@yahoogrou
> > G'day,
> > Cat to fold is an interesting solution. To get 3560 degrees on the
> > mount the rudders on the beams, although this may mess up the
> > Could also put the rudders in the hulls in daggerboard cases, if you
> > wanted to scissor it.
> > regards,
> > Rob
> > >
> > >
> > > I am aware of cat2fold desing and actually thought it
> > > would be the best solution for a folding big proa.
> > > Trailering is not an issue for me. Accessing marinas
> > > is. The scissor-like mechanism of cat2fold design
> > > would probably offer most reliable and solid solution
> > > to folding while afloat. To get reasonable beam while
> > > folded steering wheels should be in the cockpit
> > > (tillers would be better but I haven't been able to
> > > figure out how to get 360 degrees rotation functional
> > > with tillers). Rigid walkway and optional dingy ramp
> > > would be hard to fit to folding option though. They
> > > would be very nice but I haven't been able to figure
> > > out those details yet. One monohull design had
> > > removable walkway part of cockpit bottom that doubled
> > > as gangplank. Perhaps removable/folding walkway and
> > > dinghy ramp that can be lowered while folded. Two
> > > gangplanks that can be attached between hulls as
> > > walkway? Or perhaps just live without the added
> > > complexity..
> > > again.
> > >
> > > Arto
> > >
> > >
> > >
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