Polycore has got a good reputation as being pretty consistent in
quality. Not all chines manufacturers are dodgy. It is possibly to
fill the cores with a low density fireproof foam, but it will cost
more and weigh more. The convection cells can occur, but the size of
the cells would make it a much better insulator than say double glazed
windows. I would expect for a 20mm core with a skin on either side, an
R value of at least 1.2. Not brilliant but better than a non cored skin,
RObert--- In harryproa@yahoogrou
>
> Two+ things that make me worry about Polycore:
>
> 0) It's not Nidacore. Yet.
>
> 1) Given the location of manufacture, unless extremely strict
external supervision, front-
> to-back is in place, it's doubtful it'll live up to its spec sheet,
as it's likely anything that
> melts will be added to the mix as long as it can't be readily
detected. Not prejudiced - just
> an interested observer of the scene. Sample testing would be an
excellent idea.
>
> 2) Although polypropylene honeycomb is a fantastic material,
especially in regards to
> impact absorption, it is not a good insulator unless the cells are
foam-filled.
> Unobstructed convection within the cells doesn't yield a good R
value. Perhaps there's an
> extremely low-density foam that can provide the thermal barrier?
>
> Mike
>
> --- In harryproa@yahoogrou
> >
> > Those beer guts are moveable ballast!
> > It is possible to have a Harry with a thinner skin , but it means
> > extra stringers and ring frames. I don't really see a polycore
> > outerskin as overkill as it gives some stiffness to help give a smooth
> > finish, and it reduces the framing required. It also provides
> > insulation against noise and temperature. I can see distinct advantage
> > going for the thicker core for these attributes alone. I don't have a
> > fear of timber. I have a 25 yo small cat which has no problems with
> > rot. I would prefer spruce as a frame rather than aluminium for skin
> > on frame
> > Robert
> > --- In harryproa@yahoogrou
> > wrote:
> > >
> > > Hi Robert
> > > It will be interesting to see the numbers that Col comes up
with for
> > > the weight of the structure using the internal frame, as from
what i
> > > hear the numbers should be pretty keen. There is a company on the
> > > coast using the method, Southern clipper yauchts i think and their
> > > quite happy with it ,although they use a polycore skin which seems
> > > overkill. The owner reports substantial time savings with the
method.
> > > At the end of the day everything is a compromise , the truth is
> > > though that half the time people go to extrodinary lengths to
reduce
> > > weight in the structure and then add it all back and then some
> > > with "stuff". I recently heard that some card was heard to
comment at
> > > the finish of the Brisbane to Gladstone race that one of the multi
> > > million dollar boats would have gotten a better weight saving by as
> > > king all the crew to lose at least 15 to 20 kg than tipping it all
> > > into carbon. This was said after seeing all the beerguts lined up
> > > along the rail of said boat at the finish.
> > >
> > > What it comes down to is comprimise and or price , if we take
safety
> > > as a non negotiable but look at price, how much are we willing
to pay
> > > $30,000 for 300kg weight saving ? $20,000 >, $10,000?.
> > > I can get a 300kg weight saving for 5-6 thousand by buying a water
> > > maker and having smaller tanks.
> > >
> > > Dont get me wrong ive got a 22' foam composite hovercraft under my
> > > belt and a near patalogical fear of wood in boats, but i dont
want to
> > > be guilty of dismissing things without checking them out fully ,
plus
> > > its kinda fun playing devils advocate. Im already about to go ahead
> > > with a boat design that hasnt event been built before so thats
> > > probably enough ground breaking for one project, but as i said the
> > > mental excersize is good fun.
> > >
> > > Keep the comments coming.
> > >
> > > Cheers Tim --- In harryproa@yahoogrou
> > > <cateran1949@
> > > >
> > > > -If you separate the structural from the waterproofing, you add
> > > > weight. A thickness of pure grp that is thick enough to prevent
> > > > oil-canning as you describe, would be at least as heavy as a foam
> > > > sandwich. You still have the internal skin as well. The foam
core is
> > > > only. about 1/3 to 1/4 the weight of the sandwich If you were
happy
> > > > with the stringers showing through, then it does seem feasible.
> > > > ALuminium does have corrosion problems in marine use. A lot of
work
> > > is
> > > > put into insulating fittings from masts to avoid this. There
is also
> > > > the effect of stress concentrations of screws and rivets. GLuing
> > > works
> > > > so much better for distributing loads. I think if I were to
use skin
> > > > on frame, I would go with a few layers of some of the skins
used in
> > > > such structures , some of them are basically shrink wrap.
pOssibly a
> > > > fibre reinforced polyprop skin might be the way to go. Portabotes
> > > seem
> > > > pretty tough just with polyprop. I am not sure how it compares
with
> > > > grp, in price.
> > > > There is some argument for the puncture proofing, but I am not so
> > > > sure about it. Is there any difference between putting a knife
into
> > > a
> > > > sheet held tight on a drum or sitting on a piece of foam. I
haven't
> > > > done the experiment, but am not sure which way it would go.
> > > > Vacuum bagging is used to get a high glass resin ratio. It is not
> > > > possible with hand layup.
> > > >
> > > > stiff panels made with Polyprop can take an enormous bang without
> > > > delaminating as the material absorbs the shock, and bounces
back, I
> > > am
> > > > not confident this would happen over an aluminium frame. My
> > > suspicions
> > > > is the the polycored material would come out better. CHeck out the
> > > > information about impact resistance on the polycore website
and the
> > > > Nidaplast website.
> > > > Robert-- In harryproa@yahoogrou
> > > > <clairebarker5@
> > > > >
> > > > > ---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
<cateran1949@
> > > > > 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
> > > <harryproa@>
> > > > > > 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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