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
> > > > 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
> > > > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Daily Digest | Switch format to Traditional
Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe