On 24 Oct 2004 14:52:10 GMT, (William R.
Watt) vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email


William R. Watt ) writes:

... what you usually see for boats is a graph
of righting moment against angle of heel. at some point there is a
maxiumum righting moment.


I think it should be clarified that the graph you see in the texts is an
abstraction and is not what happens on the water.

I think one I saw was real case.

On the water there are
more forces involved, especially on a mulithull. Take the extreme case of
a raft. One side is being raised through air while the other side is being
immersed in water. It's easy to push air aside but not water. As the raft
rotates there is a lot of turbulant drag around the side being pushed
through the water. There is a righting moment, but its not quite what is
calculated in the texts.

A cat is actually harder to tip than a barge, because weight, and more
importantly, buoyancy are at the extremes. With a barge, the water is
still pushing up under the middle of the vessel when it is quite
heeled. In fact it almost becomes a triangle as it tips.
************************************************** ***
Have you noticed that people always run from what
they _need_ toward what they want?????

On Sun, 24 Oct 2004 20:20:53 +0700, Egis/CORE
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

The day I give an RM30 about a catamaran is the day I get
worried....G

To stay in the real world, if you approach a mast manufacturer with
the intent of designing a mast you will be asked for the righting
moment, usually RM30, i.e., Righting Moment at 30 degrees. If you
approach a marine engineer/boat designer for information regarding the
strength of a mast you will be asked for the RM30.

************************************************** ***
Have you noticed that people always run from what
they _need_ toward what they want?????

Contact Rob Denney directly.
Unlike any contributor to this thread thus far, he knows about proas.

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

On Mon, 25 Oct 2004 02:44:31 GMT, Jim Conlin
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

Contact Rob Denney directly.
Unlike any contributor to this thread thus far, he knows about proas.
You are of course includeing yourself?

************************************************** ***
Have you noticed that people always run from what
they _need_ toward what they want?????

On Mon, 25 Oct 2004 01:55:38 GMT, Brian Whatcott
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

I have never seen so many different way of saying,
"Ooh, mast section selection is awfully difficult and mathematical,
and far too difficult for a regular person to consider...."


Noooo...."Based on the very limited information given, and an admitted
lack of knowledge about proas, which are completely different from any
other craft in build stability, and sailing methods, I will not form
an opinion about the corretc mast"

The guy is basing it on a 14" cat. Not a proa. He is also looking a
cruising, unlike a 14' cat. 14' cats are rarely sailed in 45 knot
winds, on a cruiser you may have no choice.


I hope you will realise sooner or later, that the basis of many mast
selections is in fact "cut and try" and "It worked on that and the
other so it should be OK on this..."

As you say "Cut and try". But don't ask me to say you are right based
on bugger all.

************************************************** ***
Have you noticed that people always run from what
they _need_ toward what they want?????

On Mon, 25 Oct 2004 02:44:31 GMT, Jim Conlin
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

Contact Rob Denney directly.
Unlike any contributor to this thread thus far, he knows about proas.


Which is what some of us were honest enough to say. No need for the
dig, thanks.
************************************************** ***
Have you noticed that people always run from what
they _need_ toward what they want?????

On Mon, 25 Oct 2004 12:54:59 +0800, Old Nick
wrote:
...."Based on the very limited information given, and an admitted
lack of knowledge about proas, which are completely different from any
other craft in build stability, and sailing methods, I will not form
an opinion about the corretc mast"

When asked for help, no matter how partial or sketchy the background
offered, if you cannot form an opinion, wouldn't it be better to
forebear from posting on the topic?

Brian W

Mt last post in this thread I think.

The outrigger is 15ft long, weighs 25kg unladen, but has 50kg of water
ballast. The outrigger is 4m from the main hull and always to the lee
hull. Yes crew can go out on the tramp towards the outrigger for more
righting moment, but unlikley in very strong winds due to safety.

The mainsail is 85sq feet. I have a jib, which is smaller, approx 60
sqr feet, but am thinking of cutting it up to make even smaller jibs
at far ends to balance the rig.

My feeling is that the windrush 12 cat I sailed had a rig that was
strong enough in huge blows and went like the wind. So if I new what
that was feel that similar would be fine. Rob Denney uses unstayed
carbon masts. My question has been posted on a site that he looks at
regularly but he has not posted. Dont want to annoy him again with
another email.

What I will do is look at rigs of small cats (closest to my 170kg
proa), and see what mast sections they are using. 14ft and 12 ft cats
seem the best comparisons for they go out in huge blows without undue
drama.

N. Peter Evans

peterMelbourneAustralia ) writes:

.... The outrigger is 4m from the main hull and always to the lee
hull. Yes crew can go out on the tramp towards the outrigger for more
righting moment, but unlikley in very strong winds due to safety.

traditionally crew hike to windward.
not a slave to tradition myself.

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