Subject: [harryproa] Re: Harryproa skin thickness?.
From: "Robert" <cateran1949@yahoo.co.uk>
Date: 2/5/2009, 7:27 AM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

-Fair enough. Probably wouldn't hurt to have a small rubbing strake
for cosmetic protection. I can't see that the ww hull would need any
more than 450g +/-45 degree glass or less in basalt, especially with
all the shelving and other furniture reinforcement.

. How much saving in kg per m2 is there for basalt replacement of 600
glass

I also was thinking about the reinforcement around the hatches. If
there were strips of tow wrapping around from the masts through to the
rudders and other beam, and the lines did not have to go around any
holes in the skin from hatches, then the reinforcing around the
hatches would be reasonably minimal. If the lines of tow had to go
around the hatches, then the reinforcing would have to be a lot more
substantial
Went over calculations of a flat bottom with about 10mm radius bilges
going to an outward taper for ww hull and having a 12:1 l/b ratio for
cruising load. There is not that much difference from the width at the
waterline for the parabolic section when unweighted to half the weight
for quite a wide range of tapers. In fact even going to a deep V only
reduce it by a third. A simple rectangular section with rounded bilges
comes a pretty good compromise of waterline width and surface area. A
very shallow V might make it a little stiffer and less slapping if it
ever flew a hull and came down again in a hurry
Robert

-- In harryproa@yahoogroups.com.au, Rob Denney <harryproa@...> wrote:
>
> G'day,
>
> It is not that long (25% of the boat length), and apparently does not
> need any more than it has. On Solitarry, there is a couple of 100mm
> wide 450 gsm uni glass layers along the gunwhales and keel but this is
> considerably narrower than Vis.
>
> regards,
> Rob
>
> On Thu, Feb 5, 2009 at 6:51 PM, Robert <cateran1949@...> wrote:
> > I was wondering about the side loads and compression loads on the long
> > lee bow and whether some extra is needed for these.
> >
> > --- In harryproa@yahoogroups.com.au, Rob Denney <harryproa@> wrote:
> >>
> >> G'day,
> >>
> >> I have not read Gerr's book, but he is highly recommended. According
> >> to our engineer he is way off. One layer of 600 inside and out,
> >> doubled up on the inside between the beams is his recommendation. For
> >> wider boats (1.6m vs 1m of Vis) with schooner rigs rather than one
> >> mast in the middle, the second layer can be eliminated.
> >>
> >> This is a good indication of the reduced loads on boats with
> > unstayed masts.
> >>
> >> I think Gerr is over simplified as there are too many variables and
> >> other ways of increasing strength/stiffness than just the skin
> >> laminate.
> >>
> >> regards,
> >>
> >> Rob
> >>
> >> On Wed, Feb 4, 2009 at 1:35 PM, Robert <cateran1949@> wrote:
> >> > -This seems too much glass. Maybe that on the bottom, but the rest
> >> > about half that except maybe between the beams on the lw hull. The
> >> > rest of the boat has very little in the way of sailing loads.
> >> > I was looking at 600g glass for the skins of a 50'/32'Harry but was
> >> > considering an extra layer on the bottom for abrasion resistance. I
> >> > was also looking at either 10 or 12mm core, eeven considering
double
> >> > layers of 6mm for tight bends, but Rob reckons I can probably
get away
> >> > with not needing to do this-- In harryproa@yahoogroups.com.au,
Gardner
> >> > Pomper <gardner@> wrote:
> >> >>
> >> >> Hi,
> >> >> I finally got hold of a copy of Dave Gerr's "Elements of Boat
> > Strength",
> >> >> which looks to have lots of good information, but it states
that is
> >> > really
> >> >> is not for multihull design, so I am not sure what to use and
what to
> >> >> ignore. From the various equations he lists, adjusted as best
I can
> >> > for a
> >> >> proa design, it seems that a 50' proa hull for something like
> > Visionarry
> >> >> should be built with 3 layers of 600gsm fiberglass cloth on the
> >> > outside and
> >> >> 2 layers on the inside, with a 14mm core. Is that similar to the
> > actual
> >> >> construction? If not, please correct me. If you could explain the
> >> >> differences, because of the proa design or my limited
undertanding,
> >> > I would
> >> >> be grateful.
> >> >>
> >> >> Thanks,
> >> >>
> >> >> - Gardner
> >> >> York, PA
> >> >>
> >> >
> >> >
> >>
> >
> >
>

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