Re: Skuldelev 2

On Wed, 19 Apr 2006 17:33:44 +0100, "Vaughan Sanders"
<vjs@xxxxxxxxxxxxxxxxxxxxx> wrote:


"Eric Stevens" <eric.stevens@xxxxxxxxx> wrote in message
news:3ija42lmppun7omkmnkjl5268l6auodt2j@xxxxxxxxxx
On Tue, 18 Apr 2006 18:45:19 +0100, "Vaughan Sanders"
<vjs@xxxxxxxxxxxxxxxxxxxxx> wrote:


"Eric Stevens" <eric.stevens@xxxxxxxxx> wrote in message
news:rmc942tjalodcjk8fel37d658v7cccobmm@xxxxxxxxxx
On Mon, 17 Apr 2006 23:11:01 +0100, "Vaughan Sanders"
<vjs@xxxxxxxxxxxxxxxxxxxxx> wrote:


--- snip ---


Off course Hæsten could have just "feathered" the sail or "douse" as the
Mericians call it :-))
I'm just waiting for someone to tell me these ships can't "tack", I got
the
bible for Christmas :-))
It made my son laugh, he was on a square rigger off the Barrier Reef in
Oz
when they were forced to make an emergency tack when cut up by a racing
yacht, they just backed the sail and dragged her around :-))
Dad you know that why do you need a book :-))

Presumably at least a two-master where they hauled the sails on the
foremast aback. You can't really do that on a single mast rig. :-)



Eric Stevens


Why ?
Handling one sail is a lot easier than handling multiple sails

But you can't sail through a tack on a single masted square rigger by
hauling your single sail aback. As soon as you do that you lose
driving power and end up hove to. It's when you have two masts that
you can keep driving off the after masts while you swing your bows
around with the forward mast.

Much the same thing happens with a single-masted sloop or cutter which
is 'slow in stays'. You haul the jib 'aback' to help you sail through
the turn.

Ok, explain how the wind gets to the mainsail as she comes head to wind?
You only have the foresail that will work, both main and spanker are doused
(feathered) - blocked by the foresails.

I that you employ repeated shifts of subject as a debating technique
but even you will be hard put to find a sloop or cutter with the
mizzen mast necessary to carry a spanker.

To answer your question, the mainsail on a fore and aft rigged sloop
(I have to make that point clear in view of your introduction of a
spanker - I don't want to find that suddenly YOU are talking about
square sails) doesn't get any wind when the vessel is head to wind. If
the vessel does not carry sufficient way to enable her to turn onto
the other tack her bow has to be sailed around by the already backed
foresail.

A backed sail has the same driving power but in the opposite direction.btw,
that's why it is used to heave too, an emergency stop for man overboard for
example.
If you want to stop a vessel drifting to leeward while hove too you need to
keep setting and backing the sail, sailing backwards and forwards





Ok Eric, tell us how to tack the Eagle.
http://www.uscg.mil/hq/eagle/abouteagle/Small_Eagle.jpg.htm
"To manoeuvre EAGLE under sail, the crew must handle more than 22,000
square
feet of sail and five miles of rigging. Over 200 lines control the sails
and
yards, and every crew-member, cadet and officer candidate, must become
intimately familiar with the name, operation, and function of each line."

Eagle displaces 1,816 tons compared to the 25 tons of Skuldelev 2 and has
a
power to weight ratio of 13.41 compared to 14.1 of Skuldelev 2.
Skuldelev 2 has power to spare compared to Eagle, the 14.1 figure is for a
full crew of 70 warriors, who are approx a fifth the displacement of
Skuldelev 2.

Eagle has 22 sails, the foresail and mainsail are identical in size and
far
larger than the 1300 square feet of Skuldelev 2's sail, she has a draught
of
17 ft compared to the 3 ft of Skuldelev 2.

So, do you really think any meaningful comparison can be made of two
ships so different?

Yep, Skuldelev 2 has power to spare compared to Eagle, especially as she
comes head to wind when the Eagle's foresails alone have to haul her through
the eye of the wind.

How does Skuldev2 with her single square sail have ANY power when in
the eye of the wind? (Unless of course you want to sail her
backwards).


To answer your question, I would not try to tack her in any kind of
wind for fear of carrying a mast away. I would instead 'wear ship' by
turning down wind.

With you at the helm of Hæsten's longship, Alfred the Great would have died
of old age before Hæsten made it to Beenfleet :-))


You might find that in light winds the ability to
tack might be supported by the 1000hp cater[pillar diesel with which
the 'Eagle' is fitted. :-)

Hmm, perhaps you would like to compare a bank of 30 leeward oars driving 25
tons to a 1000hp driving 1,860 tons ?

25 tons + 30 rowers plus other crew plus ballast. I suspect you have
never tried using sweeps to move a large boat. I can assure you it is
not easy.

The Eagle is a sail training ship, I have the manual in front of me, nowhere
does it mention using the engine to cheat while tacking :-))

So that's why you introduced the Eagle out of the blue. You have a
book ...

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.

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.

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.

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

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.

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.

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.


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?

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

.

Relevant Pages

  • Re: Skuldelev 2
    ... I'm just waiting for someone to tell me these ships can't "tack", ... Handling one sail is a lot easier than handling multiple sails ... explain how the wind gets to the mainsail as she comes head to wind? ... tell us how to tack the Eagle. ...
    (soc.history.medieval)
  • Re: Skuldelev 2
    ... Skuldelev 2 will come about under sail ... is head to wind than when she is sailing ... The forestays on a square rigger are connected to the bowsprit or the ... A mast that can't withstand a tack wouldn't last seconds running ...
    (soc.history.medieval)
  • Re: Skuldelev 2
    ... Skuldelev 2 will come about under sail ... is head to wind than when she is sailing ... The forestays on a square rigger are connected to the bowsprit or the ...
    (soc.history.medieval)
  • Re: Skuldelev 2
    ... stronger winds than Eagle if the sail is mishandled. ... has the same mast stays bow and stern. ... is head to wind than when she is sailing ... The forestays on a square rigger are connected to the bowsprit or the ...
    (soc.history.medieval)
  • Re: Skuldelev 2
    ... I'm just waiting for someone to tell me these ships can't "tack", ... he was on a square rigger off the Barrier Reef in Oz ... You can't really do that on a single mast rig. ... Handling one sail is a lot easier than handling multiple sails ...
    (soc.history.medieval)