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@
> -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@yahoogrou
> Pomper <gardner@...
>>
>> 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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