The beauty of the design Rob is working on for us is that the hulls
will need little or no lining, Col is going to get some figures to
gether re weight per square mtr for comparison, im not saying this
method is for me , more that when new things come along people can be
dismissive or suspiscious (me included) and that a open mind is one
that learns.
Its a funny thing in this world but very often things arent done a
certain way because thats the best way but because thats how
everybody else is doing it , im sure Rob is very familar with that
promoting a design that makes eminent sense but meets with huge
paranoia and resistance .
Im also sure thatRob is familar with people that say something wont
work and state a very plausable reason why but at the end of the day
his designs are out there sailing despite the reasonings to the
opposite.
When looking at something as different as this i think we need to
realise that not everything will be obvious at first look. Rob just
realized something quite significant recently re the load carrying of
Proas, now if it only just occured to he who has spent a significant
portion of the last ten years thinking "proa" then ill keep
investigating, for fun and edification .
Just to add a little to the pot, what if the skins were 3mm ply what
weight then .Remember the function of the skin is now only a
waterproof barrier. What if the skin was pure fibreglass, same or
better point loading no need for epoxy as with ply do it up on a
table to size . Col has had one example in the water for two decades
still going strong, although this had the frame welded which would
actually detract from its strength. the skins can actually be glassed
to the stringer frames so little or no screw fastening is possible.
Come on guys lets do a little brain storming !
What do you think would happen with this type of construction in a
collision versus a cored hull. Not a dinky weight dropped on a panel
that bounces, 3-4 tonn of boat doing 10knts doesent bounce when
striking a pointy bit of rock you get a long rip .
Cheers Tim
--- In harryproa@yahoogrou
wrote:
>
> Looked at he website, and the internal frames are covered with some
> kind of skin. Any skin has to add at least 1kg /m2.If you have to
have
> an inner skin, it may as well be part of the sandwich. You are also
> hiding the frames and can't check for corrosion easily. Stainless
> steel into alloy can cause corrosion. The stainless steel screws
into
> the ply , unless as Rob pointed out, you drill and presaturate the
> hole, are a means of getting rot. The chines still need to be
rounded,
> glassed and faired, though the glassing could be part of the final
> exterior glasing This seems a a fair amount of work and risk to me.
> --- In harryproa@yahoogrou
> >
> > Not sure how you do one and a half sheets of double bias. I am
> > assuming the extra sandwich thickness and glass are to eliminate
the
> > internal framing
> >
> > Looking at the weights
> > 20mm core 1.6kg/m2; glass 1.8kg/m2; resin-depending on type of
core,
> > effort in edge joining, holes, shaping cuts, scrim for polyprop
> > honeycomb` .9-1.5kg/m2. This gives a total of 4.3-4.9kg/m2
> > With internal frames, this could possibly reduce to 3.2kgm2. I was
> > wondering how the internal frames are covered-That could add
> > significantly more weight
> > Epoxy saturated 6mm marine ply is in the order of 4.5kg/m2. The
ply
> > still needs almost .5 kg abrasion and surface cracking protection
on
> > the outside, and still needs the inner frame.
> > Costs of the foam sandwich depends on type of core, type of
resin,
> > and very much source of materials: for 20mm core $35-70/m2; resin
> > $10-20/m2; glass $10-15/m2 I think you would find the costs of
going
> > with the ply would be similar or slightly more with the cost of
the
> > frame. I must admit the simple meccano approach to the frames
appeals,
> > but for the shape of a Harry, I don't see an advantage. Simply
make
> > some big flat sheets,with judicious leaving out of glass where you
> > want to bend, pull or push them into shape - possibly a little
extra
> > shaping on the ends- and the basic hulls are there, except for the
> > main bulkheads where the crossbeam loads are concentrated. I
reckon a
> > Visionarry hull up to topsides could be done with less than 4m2 of
> > external fairing and much of the internal work will be covered by
> > internal furniture. Anyway, thats what I am aiming at. I hate
adding
> > good materials, only to sand it off again. Don't know how much
fairing
> > is required on the aluminium frame set up
> > Robert
> >
> >
> >
> >
> > --- In harryproa@yahoogrou
wrote:
> > >
> > > G'day,
> > >
> > > Col is a very smart bloke, has been designing boats for yonks
and has
> > > always been full of ideas, most of them good.
Experimentation is a
> > > good thing and so is caution , so talk to Col and at least a
couple
> > > of people who have built with it. Maybe build his little canoe
as a
> > > test. Then do the numbers and decide which suits you best.
> > >
> > > I worry about corrosion of alloy and screw attachment of ply,
which
> > > often rots around fastenings unless they are individually over
> > > drilled, filled with glue and redrilled. I also think
> > > glass/ply/alloy will be heavier, maybe more expensive and
require
> > > more finishing. Could be wrong on all counts.
> > >
> > > If you talk to Col, say hi from me, tell him your boat will
almost
> > > certainly be 20mm foam or Polycore with one and a half layers
of 600
> > > double bias each side and some serious strength required
around the
> > > mast and the beams, but no other bulkheads. Surface area of
> > > Visionarry lee hull is 57 sq m. I will be very interested to
see
> > > what he suggests, and how it competes with the panel build
method.
> > > Also ask him about the large flat)ish) cabin roof and floor
areas
> > >
> > > regards,
> > >
> > > Rob
> > >
> > > On Wed, Apr 9, 2008 at 3:40 PM, Tim Barker <clairebarker5@
wrote:
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > Hi Rob/ all
> > > > Visited Col Clifford today , as much to see his radial
engine as
> > have a
> > > > yack about build methods, very interesting guy and very
cluey.
> > > >
> > > > What are your thoughts about the alloy internal frame
system , as a
> > > > person who has done quite a bit of metal fabrication it makes
> > sense to
> > > > me and offers some build speed advantages as far as i can
see .
> > Coupled
> > > > with the idea of glassed ply skins it should be very cost
effective
> > > > tough and simple to build.
> > > >
> > > > For those on the site who arent familiar the method involves
> standard
> > > > ally extrusions and cast ally fittings which allow the frame
to be
> > > > fabricated from ally without welding, it is then skinned in
ply or
> > > > composite however the skin basically only has to act as a
> waterproof
> > > > membrane not as a structural member and also to hold the
> structure in
> > > > tension, light strong simple . WWW.ccplans.
> > > >
> > > > What are the various opinions out there.I myself am very
> > suspiscious of
> > > > ply or timber however i know that this is a fairly basless
> predjudice
> > > > given modern methods and materials hence the ongoing
> investigation of
> > > > different methods and materials.
> > > >
> > > > Coupled with the relative costs of some of the composite
cores
> on the
> > > > market and the slowly dawning realization that using these
> composites
> > > > may result in a craft not much lighter (if at all) but
> substantially
> > > > more expensive than a craft using ply skins has certainly
eroded my
> > > > predjudices.
> > > >
> > > > Cheers Tim
> > > >
> > > >
> > > >
> > >
> >
>
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