Thanks for your input, all very scientific. Having the mast tested
using weights has some logic to it.

The boat is a proa, a multihull. The side says (there is only 1) is 4m
from the mast. Mast is 6m high. Righting moment could be rather high
as I was hoping for 50kg of water ballast in teh outrigger at 4m to
windward. 50L water ballast tank need not be full I guess.

The mast comes from a professional mast/spar maker.

The boat is a proa. Main hull is 23 long, 2 ft wide, boat weigh
unladen is less than 200kg. Not intending to break speed records.

I was hoping to do a comparison with a boat like a Hobie 14 cat. I
wonder what their mast dimsnsions woudl be, cannot recall the mast
section details of the windrush 12 cat that I used to sail, for some
reason never got around to measuring it. Feel that a hobie 14 - 12 has
simialr sail area/righting moment, is stayed out wide as per proa. So
what is good for that would be good for me.

N. Peter Evans

Nicholas says:

Thanks for your input, all very scientific.

;-)

The boat is a proa, a multihull. The side says (there is only 1) is 4m
from the mast. Mast is 6m high. Righting moment could be rather high
as I was hoping for 50kg of water ballast in teh outrigger at 4m to
windward. 50L water ballast tank need not be full I guess.

The mast comes from a professional mast/spar maker.

The boat is a proa. Main hull is 23 long, 2 ft wide, boat weigh
unladen is less than 200kg. Not intending to break speed records.

I was hoping to do a comparison with a boat like a Hobie 14 cat. I
wonder what their mast dimsnsions woudl be, cannot recall the mast
section details of the windrush 12 cat that I used to sail, for some
reason never got around to measuring it. Feel that a hobie 14 - 12 has
simialr sail area/righting moment, is stayed out wide as per proa. So
what is good for that would be good for me.


If you can weigh the boat, each hull singly, that would help. Yopu don't have
to take it apart, just slide a scale under each hull in turn and record the
weights (yes, it can really be that simple.)
From that, and with the 50 litres of WB, a rough RM can be obtained.

Let us know...

Steve

On 22 Oct 2004 20:52:21 GMT, Stephen Baker wrote:

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

It actually depends on the size of the rig and the momentum. The rig can be
undersized!!! ...and then it's the momentum that doesn't matter!

Since you don't know his boat, you can't say for shure ..and that's why I
didn't.


Morgan O.

Morgan O says:

It actually depends on the size of the rig and the momentum. The rig can be
undersized!!! ...and then it's the momentum that doesn't matter!

Morgan, for someone who professes to know little about the subject, I can only
say that you are accurate - you know little.

Since you don't know his boat, you can't say for shure ..and that's why I
didn't.

When you have designed boats that have raced around the world, and come home
with their rigs intact, then come back and tell me I'm wrong. Until then,
either buy the book I recommended to you, and read up on the subject, or be
quiet and stop giving out potentially dangerous information with no knowledge
of the subject.

Steve
Stephen C. Baker - Yacht Designer
http://members.aol.com/SailDesign/pr...cbweb/home.htm

On 23 Oct 2004 16:01:42 GMT, Stephen Baker wrote:

you know little.

I don't like people to give faulty advice anyhow. I just liked to give a
hint to PeterM.A about that.

...but I will not fall to your standards of attacking...

....explained this way...

If you have a rig in solid concrete, which would matter the most to the rig?
A) wind speed?
B) the momentum of the solid concrete?

take care... hope you understand something new now!



Morgan O.

On 23 Oct 2004 12:26:51 GMT, Stephen Baker wrote:

Nicholas says:

Thanks for your input, all very scientific.

;-)

The boat is a proa, a multihull. The side says (there is only 1) is 4m
from the mast. Mast is 6m high. Righting moment could be rather high
as I was hoping for 50kg of water ballast in teh outrigger at 4m to
windward. 50L water ballast tank need not be full I guess.

The mast comes from a professional mast/spar maker.

The boat is a proa. Main hull is 23 long, 2 ft wide, boat weigh
unladen is less than 200kg. Not intending to break speed records.

I was hoping to do a comparison with a boat like a Hobie 14 cat. I
wonder what their mast dimsnsions woudl be, cannot recall the mast
section details of the windrush 12 cat that I used to sail, for some
reason never got around to measuring it. Feel that a hobie 14 - 12 has
simialr sail area/righting moment, is stayed out wide as per proa. So
what is good for that would be good for me.


If you can weigh the boat, each hull singly, that would help. Yopu don't have
to take it apart, just slide a scale under each hull in turn and record the
weights (yes, it can really be that simple.)
From that, and with the 50 litres of WB, a rough RM can be obtained.

Let us know...

Steve

Perhaps he could take a little help of old Archimedes! (do some maths on
displaced hull volume) ;o)


Morgan O.
Wondering if the man go'na bite this time too?

Morgan says:

If you have a rig in solid concrete, which would matter the most to the rig?
A) wind speed?
B) the momentum of the solid concrete?


If you had a boat with infinite righting moment, it would be dry land, not a
boat. Not an apple, just another orange...

..but I will not fall to your standards of attacking...

not attacking, Morgan, just quoting you at the beginning of this series of
threads.

Steve "plonk!"

On Sat, 23 Oct 2004 16:58:02 GMT, Morgan Ohlson
wrote:

On 23 Oct 2004 16:01:42 GMT, Stephen Baker wrote:

you know little.

I don't like people to give faulty advice anyhow. I just liked to give a
hint to PeterM.A about that.

..but I will not fall to your standards of attacking...

...explained this way...

If you have a rig in solid concrete, which would matter the most to the rig?
A) wind speed?
B) the momentum of the solid concrete?

take care... hope you understand something new now!



Morgan O.

You are absolutely right. If the rig were mounted in concrete the
important force would result from wind velocity and sail area.

However -- we are discussing a rig installed on a BOAT and the
important force is righting moment.

i.e., in the case you are discussing the mast is fixed and therefore
the effective area of the sail is constant. In the case of a spar
mounted on a movable base, i.e., a boat, the spar moves and therefore
the effective area of the sail changes with changes in wind velocity,
thus the important figure is the force opposing the spar movement, the
righting moment.

Most people who have any knowledge of boats understand this fact
instinctively.




Cheers,

Bruce
(k4556atinetdotcodotth)

On 23 Oct 2004 01:19:18 GMT, ospam (Stephen Baker)
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

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 ;-)


Actually I have to disagree. It is even _more_ not strong enough now!
G
************************************************** ***
Have you noticed that people always run from what
they _need_ toward what they want?????

On 23 Oct 2004 12:26:51 GMT, ospam (Stephen Baker)
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

I reckon the guy who said to talk to a spar maker had the right idea.

At least check out a google of

"righting moment" multihull

If you can weigh the boat, each hull singly, that would help. Yopu don't have
to take it apart, just slide a scale under each hull in turn and record the
weights (yes, it can really be that simple.)
From that, and with the 50 litres of WB, a rough RM can be obtained.

This is a really light boat, IIRC.....here we go..... "23ft proa
weighs 200kg unladen."

Sounds scary actually, as a cruiser.

This means that weighing the boat and using that as a righting moment
would be questionable, as the weight of crew and gear would
_significantly_ alter the system. You need to weigh in "cruising
trim".

And how far apart are the hulls, etc?

Also some proas' righting moments when the ama is to the lee will be
the floatation capability of the ama.

What you need to do is place the boat in the water and do some real
righting force tests, under loaded conditions IMO. This was not
uncommon practice as I remember it.

Also wrt multihulls. They release pressure on the mast much more by
acceleration than by heel. Their righting moment should never be
_needed_ ....joking G.

Seriously:
- they load a mast very high in a puff, because they are not
supposed to heel more than a very small amount. IIRC (and it's been a
while) and extra 20% (?) or more needs to be added to the mast/stay
strain for a multi over a mono.
- when sailing at speed on a brorad reach, and _being kept flat_ as
multihulls largely should, their high speed generates significant
apparent wind. This has to be accounted for.
- multis can actually suddenly _increase_ their righting moment as
the weather hull lifts from the water, or as the lee ama of a tri /
proa touches the water.

Also, on a multi, especially a lightweight one, the mast and stays
hold the boat together. So there are many other strains on the rigging
as the boat gets twisted about by wind and waves.

I mucked about designing, building and repairing cats. I have owned
and sailed several, including a Crowther 23' International. It weighed
maybe 450Kg unladen, and had a _heap_ more mainsail than that being
suggested. But it had a huge mast. 150mm * 100mm * 4mm, maybe. I can't
find the specs any more.
************************************************** ***
Have you noticed that people always run from what
they _need_ toward what they want?????