---Im an absolute amature at this, so love the feedback, obviously
most of you have far more experience and knowledge on the subject .
It seems to me when you seperate the functions of structural support
and waterproofing (a simplification) a number of things may be
possible
1. Skin can be thinner, within reason it still has to be able to
take the inevitable rough and tumble but other than this and the need
for it to be thick or stiff enough not to "oil can" between the spans
of the inner frame ,you dont require the skin to perform any other
function.
2. As the skin is thinnerbut has the same or slightly greater glass
resin content as "normal" it should stand point loadin as well if not
better than a composite panel as its harder to push through one thick
layer than two thin skins seperated by a layer of foam/poly.
3. In the case of a collision on a light stiff composite panel two
things happen , if the hits big enough and the panel deflects enough
stiff as it is the panel will catastrophically delaminate, tear the
skin through point loading and you no longer have an "I" beam
composite panel. In a framed structure the skin can deflect and
absorb energy signifigantly more before failure , when it does you
have a hole in the skin, bad enough but you havent compromised the
structural strength. Stress it some more and the frame deflects
bends, maybe to the point of a permanent buckling but no catastrophic
failure.
4. Thin skins eg all glass, bend easier so can be formed to tigher
more complex shapes, plus would be easy to lay up on a table with no
need for vac bagging and would be fair.
5. With corrosion i think its a case of possibly seeing more problems
than actually may exist. If were glassing the frames to the skins
(not everywher remember) then were not screwing ,if we use all glass
we dont have rot,(and or we use the pre treated plys available), lets
remember theres an awful lot of ally in the marine industry for good
reason, a bit of caution and common sense and you should be okay.
6. It would appear( i repeat appear )to present the possability of a
quick cheap build ,no expensive composites (possibly not even any
ply) the possability of using resins not epoxies a reasonably fair
surface off the table. the ability to do a huge amount of the
glassing in one hit on the table not turning and doing the other side
as in an all glass skin you finish the skin in one go.
Your Thoughts?
Cheers Tim
In harryproa@yahoogrou
wrote:
>
> 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
wrote:
> > >
> > > 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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