Re: Skuldelev 2

On Thu, 20 Apr 2006 18:33:32 +0100, "Vaughan Sanders"
<vjs@xxxxxxxxxxxxxxxxxxxxx> wrote:


"Eric Stevens" <eric.stevens@xxxxxxxxx> wrote in message
news:4g9d421743hsav1jm2h4fajs6tlg7f57n1@xxxxxxxxxx
On Wed, 19 Apr 2006 17:33:44 +0100, "Vaughan Sanders"
<vjs@xxxxxxxxxxxxxxxxxxxxx> wrote:

snip


According to all the calculations, Skuldelev 2 will come about under sail
in
lighter winds than Eagle, certainly she is more vulnerable to capsize in
stronger winds than Eagle if the sail is mishandled.

But I have never been any claiming any problems under light winds. I
have _always_referred to the difficulties experienced under not-light
winds.

If she will come about in light winds she will certainly come about in
strong winds.


I doubt that there is anyway Skuldelev 2's sail could put enough pressure
on
the mast to carry it away when tacking, you will note that the Skuldelev 2
has the same mast stays bow and stern.
Explain why you think the sail could put more pressure on the mast when
she
is head to wind (effectively sailing backwards) than when she is sailing
downwind?

You are twisting my words. It is the later large square-riggers which
could get into trouble when caught aback in strong winds.

The forestays on a square rigger are connected to the bowsprit or the
forward mast, the backstays are connected diagonally to the rails (sides)
there are also shrouds that give lateral resistance.


Note the sheeting lines, the sail would not set, most of the wind would
just
spill. A mast that can't withstand a tack wouldn't last seconds running
off
the wind, what do you think happens when you smash into the back of a
wave?
The hull tries to stop and the mast and sails want to keep going, the
forces
are huge compared to those in a tack

Hmm. You seem to think that the intertia forces of the mast and rig
are greater than the wind forces. Not so.

Depends what you mean by wind forces, I've explained "apparent wind" to you
before, that's the inertia the sail knows

You should realise that you are talking to an engineer. 'inertia' is
not a force.

So when I catch a rail on my board at high speed and it catapults me right
over the top of the sail it has nothing to do with inertia :-))
I've run aground at high speed a few times, me and the sail always keep
going and landing some distance in front of the board, usually the mast foot
breaks

So you have a sail board and a book about a US Coastguard square
rigged training vessel. I guess that makes you an expert :-)



Can you give an example of a mast on any sort of rig being carried away
when
tacking ? - you seem to think a sail will only back when presented square
on
to the wind?

This all arose from a discussion of wearing ship vs tacking ship. My
point is that it is not possible to tack a square rigger without
having the sail square onto the wind at some stage - unless of course
you drop or furl the sail during the manouver

You can spill wind from a sail by releasing the sheeting line, again it is a
wing and can also be "stalled".

Skuldev2 is square rigged.

By backing the sail it will not come square to the wind until you are
falling off on to the opposite tack, that's when the "let go (sheeting
lines) and haul" order is given

Skuldev2 is square rigged.


In fact it backs while sheeted in hard on a tack, the sail will
automatically back if there is enough speed to bring her head to wind, if
not you can use the sheeting lines and yard to make it back.
Think of the driving force as a V, when the sail backs the driving force
is
still forward but on the opposite side of the V, it would only be
backwards
if you present the sail square to the wind.




We've been through all this before. No matter how you argue, it is not
possible to swing a square sail from one side to another during a tack
without momentarily presenting the full face of the wrong side of the
sail to the wind.

We need to use both sides of the sail if she won't turn under her own
momentum.

You now seem to be agreeing with me, even if for the wrong reasons.

If she has turned through the eye of the wind under her own momentum the
sail will only back momentarily as you haul before stalling.

That's an advance. You at least agree that the sail will back as the
vessel swings through the eye of the wind. The duration of
'momentarily' depends on how fast you can swing the yard around the
mast.

They were using the sheeting lines to haul the sail on the Skuldelev 2, both
*** and brace would have to be released, so the sail couldn't set when
hauled square to the wind.

It would still wrap around the mast.



Of course, but a sail doesn't work unless it is set, you just release the
sheeting lines and it will flap like a flag

All of which is hard on both the gear and the crew. I'm not saying it
wasn't done in light winds because I expect it would be, but in
heavier going it was not practical and this is why they preferred to
wear ship if they had to go onto another tack. Of course in really bad
weather they couldn't really carry out that manouveer either. Then
they had to tack by heaving to, lowering the yard and swinking it onto
the other tack and then trying to hoist the sail while the ship lay on
the new course. Not an easy manouver at all in gale conditions.

You have lost me here Eric, how do you tack by heaving too? - how does she
come onto the opposite tack if she is stopped? - she will just swing back
broadside to the wind and probably be capsized in a blow.

As I said, very difficult and dangerous. That's why they preferred to
run in heavy weather, even if it took them in completely the wrong
direction. But if, for example, they were embayed ... they had no
option but to try to sail out.


But we want to "back" the sail if she won't come about under her own
speed,
so we want to present the opposite side of the sail to the wind, but at no
time will it be necessary to for the sail to set square on to the wind,
that's what the sheeting lines are for.
Even if she turned through the wind under her own speed, "backing" the
sail
would.assist with hauling the yard on to the opposite tack, handled
properly
the wind will do most of the work.

Not on a balanced square sail.

You have lost me again, do you mean balanced with the sheeting lines?
You just use the sheeting lines to transfer the balance from one side to the
other.

Equal areas on each side of the mast.



All kinds of peculiar tricks have been used with different variants of
square rigs to deal with this problem, not the least of which was
momentarily dropping the yard and furling the sail before swing the
yard 90 degrees or more about the mast.

Eric Stevens

Explain why you need to drop the yard to "feather" (douse) a sail?
The Eagle has 10 fore and main sails, do you really think all these yards
could be dropped and the sails furled while she keeps turning :-))

Surely you are not trying to compare the advanced sail handling system
of Eagle with Skuldev2?

She is rigged the same as the wind-jammers of old,...

With respect - nonsense.

... the wind acts on her
sails exactly the same as Skuldelev 2.


Eagle can only point 75 degrees to the wind compared to a possible 60
degrees of Skuldelev 2 (Knarrs can point this high)
To bring Eagle about you need to fall off a few degrees to pick up speed,
judgement is needed here, speed over shortest turning distance. Only 10 to
15 degrees of helm is needed to turn her through the wind as like all
sailing ships close hauled she has a weather helm, "a tendency to want to
turn into the wind".
Full rudder acts as a brake particularly in light wind.

(A simplified version of Eagle tacking)
On the command "helm alee" rudder is applied while simultaneously hauling
the stern spanker boom amidships, the mainsail quickly starts to luff and
is
doused, then as the foresail luffs it is backed and the mainsail hauled on
to the opposite tack while still blocked by the foresail. At this point
she
is approx head to wind, as the backed foresail pulls her around the
mainsail
is set on the opposite tack along with the spanker, then as she falls off
the order is given to let go and haul the foresail, at this point because
the foresail is backed the wind will assist with the haul if the timing is
correct.

Jamie





Eric Stevens


Now if you won't to talk about something difficult in a blow, reefing
Skuldelev 2's sail the way it was done in the video would be impossible
without clews and sheeting lines at reefing points on the sail I would
think.
Multi sail square-riggers were reefed from the yards, not all at the same
time.

Jamie





Eric Stevens

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