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On 21 Oct 2004 17:01:27 -0700,
(peterMelbourneAustralia) wrote:
I am almost finished designing a 23ft proa and am aware of a new
aluminium section for sale; I would like to know if it will be strong
enough for a mast.
The proa has a mainsail around 100sqr feet (a little less). At either
end are small furling jibs for balance (30 sqr ft). The mast is round
section, 6m high, 82mm in diameter and 2.6mm thick. It is made of the
proper high grade aluminium from a professional mastmaker. It does not
have a track, the mainsail being attached to the mast via lashings.
There are 3 stays at the top, one forward, one aft and one to
windward, 90 deg to other 2. Three stays is all a proa needs!!!!
From my days sailing windrush catamarans, I am a littel worried that
the 82mm diameter might not be enough. I know circular section is not
high performance but that is not of concern. I am keen on this section
because it is new, made of high grade metal, from a professional and
failry cheap, $250 Australian.
I intend to go cruising, thus needs to be able of withstanding strong
winds. Have every intention of reefing when gets blowy. 23ft proa
weighs 200kg unladen.
Will/should 82mm diameter be sufficent?
N. Peter Evans
A 3.5 in diam round section with 0.1 inch walls sounds reasonable.
You might like to proof test the mast in your application.
Take 4.5 lb /sq ft as the wind load at 60 mph.
130 sq feet would load the structure with about 600 lbs if caught
broadside in a 60 mph gust,.
Support the mast at the foot and at the level of the stays, then
dispose the weight of 600 lbs of kids - perhaps eight or ten of 'em?
Have them sit along the mast in a representative way.
.. Does the mast retain a set after this load? It's not strong enough!
Brian Whatcott Altus OK
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