mast strenght question
 

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 21 Oct 2004 17:01:27 -0700,
(peterMelbourneAustralia) wrote:
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?

========================================

You really need to consult with an experienced spar maker. One of my
old sailboats was once dismasted and I was surprised to learn that the
key engineering variable is not sail area or wind speed; instead it is
righting moment.

Correct. Whatever the rig, if you have it mounted on a barge, or the land,
you have a big problem. If. however, it's on a boat that will turn over. the
force needed to turn it over is a strong as the rig needs to be. Find a
sparmaker or an engineer.

"Wayne.B" wrote:

On 21 Oct 2004 17:01:27 -0700,
(peterMelbourneAustralia) wrote:
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?

========================================

You really need to consult with an experienced spar maker. One of my
old sailboats was once dismasted and I was surprised to learn that the
key engineering variable is not sail area or wind speed; instead it is
righting moment.

On Fri, 22 Oct 2004 04:46:23 GMT, Jim Conlin wrote:

Correct. Whatever the rig, if you have it mounted on a barge, or the land,
you have a big problem.
"Wayne.B" wrote:

On 21 Oct 2004 17:01:27 -0700,
(peterMelbourneAustralia) wrote:
========================================

You really need to consult with an experienced spar maker.

You could look up on boats with the aproximately the same righting momentum,
and add some mariginals.

For stable boats the wind is crucial since it adds as v^2. So you must put
in "your maximum weather" and this part you usually don't know for other
boat modells... and your rig maker will probably ask...??? ...yes! you!

WANTED! Straight, approximative momentum formula suitable for 1 hull dinghy
(no transformation C's added).

I found a momentum formula more suited for cat's (I think):
http://www.bijlard.demon.nl/page20.html
(part of the stability number)


Morgan O.

The distance btween the mast and the base of the shrouds has a big effect on
the stresses of the spar......Narrow beam boats put huge compression loads
on the mast spar... wider beam less compression..
Just another factor you should maybe consider...

"peterMelbourneAustralia" wrote in
message om...
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

Morgan O says:

For stable boats the wind is crucial since it adds as v^2.

For any boat, the stability (righting moment) is the only thing you need. Wind
is actually immaterial except for the small forces added by side-loading of the
spar by the main.

Steve

The load on the mast is Righting Moment (1 degree)/ Chainplate base *45

The mast strength is a function og EI l^2

Do you have the moments of inertia?
length?

"peterMelbourneAustralia" wrote in
message om...
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 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

Brian says:

snip Mr. Wizard experiment

Does the mast retain a set after this load? It's not strong enough!


Correction, Brian - it WASN'T strong enough ;-)

Steve

I knew you'd just love this one!

:-)

B

On 23 Oct 2004 01:19:18 GMT, ospam (Stephen Baker)
wrote:

Brian says:

snip Mr. Wizard experiment

Does the mast retain a set after this load? It's not strong enough!


Correction, Brian - it WASN'T strong enough ;-)

Steve