sail aerodynamics

[CarlosK2]

Roger Taylor

An eccentric Briton? No, a realistic and rational man.

 

[brian eiland]

ATTN CARLOSK2:
Would you PLEASE take you ramblings over to your own subject thread !!

You are NOT contributing useful material to this one !!

 

[Eurosnob]

Benford design has this little gem of a sketch at the head of this page -> Benford Design Group https://www.benford.us/index.html?cruisingsail/

If I'm seeing this correctly, the main mast is a square rig with the following flying from it.

* A triangular 'square' sail
* A triangular top sail
* Two genoas

Now obviously anything you throw up a mast will work for some value of 'work' due to drag, but could this be made to work as anything other than a downwind windjammer?

Are you even ready to discuss the mizzen?

 

[gonzo]

For example

what to do in box "D-F10" besides requesting rescue? After the crew was ejected due to yacht bad behavior, the yacht turned (see the end of the video) and crossed the Atlantic alone, where it was found by some fishermen

It is unusual for the whole crew to be ejected. Wearing a harness would prevent that. If a boat gets home safe without the crew, there is probably no problem with the yacht. The bad behavior was from the crew.

 

[wet feet]

I think the answer to the question posed in post #978 is "scarcely".For any rig to go upwind it usually requires a tight luff to maintain an effective sail shape and I can't imagine that happening.I suspect that the design was aimed at those who like the idea of an "old time" aesthetic and who would have a substantial engine down below to allow them to get to places where their design selection can be admired by those with similar tastes.I would doubt that any actually got completed with such a rig and I don't suppose there would be a stampede of volunteers to ascend those ratlines when reefing is needed.It might make a nice picture on a daydreamer's wall.

 

[CarlosK2]

The funny thing about this thread is that it starts like this: - I don't want the typical, correct answer, but a different one

A simple exercise

With 10-12 knots of wind, position the sailboat at 30° AWA with only the mainsail

Sail like this for a while

Then hoist the StaySail... Woooow

A mysterious Force appears

It's low pressure, suction, on the leading edge of the StaySail

and the amount depends on the trailing edge of the MainSail

But

But this magic of 1 magnificent Wing built with 2 elements (StaySail + MainSail) refers to

(A) Upwind and
(B) a Wind range and an Angle of Attack

If the leading edge of the StaySail is so valuable ... then logically you'd want a huge headsail and a small mainsail acting as a 'flap'

Yes, if you want to win a summer regatta in the 1970s-1990s

But that way you have a terrible rig from a versatility standpoint

In other words: different winds and different angles.

The most logical thing in a rational world ... in a distant galaxy ... would be to see:

many tiny sailboats, some with fractional 3/4 rigs MainSail = 2 x StaySail, and others with Chinese rigs

and on the other hand, larger sailboats with two masts

To put things on top another things

In this world, which is precisely the planet of the apes, we have recently witnessed the pinnacle of this industry:

a gigantic motor vessel...

on top ... a 75-meter (!) high mast, and to add insult to injury, positioned at the bow (approximately 40% LWL) just like in 1860, and for even more fun, large sails furled at the bow.

the grandfather...
and his grandson

 

[CarlosK2]

1 Ton, 1917

Learning to fly in the U.S. Army https://www.gutenberg.org/cache/epub/72902/pg72902-images.html

my proposed Peace Treaty with the naval architects is as follows:

vessels from 30 tons to 1 million tons for you, and furthermore, although they can generate considerable lift and fly, we'll give you the small motorboats.

and the sailboats of 10 tons and below for aeronautical engineers and model aircraft enthusiasts.

 

[Jamie Kennedy 108]

You can sail up wind with just one sail, and the sail doesn’t even need to be curved. The keel or centerboard and rudder can also be flat plates. Not ideal but they still work.

To answer the OP, the sail doesn’t push the boat forward when going upwind. It pushes the boat mostly sideways, and a little bit forwards. The keel or centerboard and rudder and the hull are going a little bit sideways with leeway. So they push the boat mostly sideways to the windward side of the boat, and a little bit backwards.

These all cancel out plus a little bit left over to overcome the hydrodynamic resistance on the hull.

 

[Jamie Kennedy 108]

I think the roll of the slot is simply to maintain reasonably attached flow behind the main/jib combination when pushing total thrust towards the stall point when you are underpowered with sail area; and to simply let more flow through unopposed to decouple the two sails to focus on lift/drag efficiency when you are overpowered with sail area; all while maintaining optimal heel and windward helm; even while going through rough chop and dodging competition to get clear air off the start or rounding the leeward mark or trying to foot your way back to the next shift and keep the beer flowing to disgruntled crew members.

too simple;-)

this is why a sail a laser

 

[Jamie Kennedy 108]

“Don’t stand in the slot !!!”

If someone does have to stand up and go forward to go do something I’ve always favoured them standing just aft of the mast on the windward side, or if up on the bow behind the forestay on the windward side and down low. Never in the slot wind gods forbid.

Is there any validity to this?
Does it depend on conditions?

 

[gonzo]

If you have telltales on the shrouds, look at them on the slot. They are usually hanging down or moving around in turbulence. A foresail will deflect the air flow on the mainsail. However, the huge genoas are for beating rules because the overlap is not measured. The reason biplanes disappeared is because a single foil is more efficient.

 

[Doug Halsey]

Biplanes may have disappeared, but flaps & slats (on airplanes) haven't.

Single foils are more efficient when operating at low lift coefficients. Multiple foils aren't just more efficient, they are absolutely required when operating at very large lift coefficients

 

[Doug Halsey]

If you have telltales on the shrouds, look at them on the slot. They are usually hanging down or moving around in turbulence. A foresail will deflect the air flow on the mainsail. However, the huge genoas are for beating rules because the overlap is not measured. The reason biplanes disappeared is because a single foil is more efficient.

Telltales hanging down are not always a bad thing. Sure, they're indicative of flow separation and possibly more drag, but you have to consider what you need from your sails in each situation.

If you're beam reaching, you often need maximum lift, since at an apparent wind angle of ninety degrees, the lift component of the sail's force vector is in the thrust direction. Maximum lift is almost always associated with some degree of flow separation.

And if you're broad reaching, the drag component of the sail's force vector also contributes to the thrust.

Only when sailing to windward or close reaching should you attach much importance to them (pun intended) .

 

[gonzo]

Biplanes may have disappeared, but flaps & slats (on airplanes) haven't.

I agree with the similarities. However, the proportion of a genoa to a main is orders of magnitude larger than a flap or slat to a wing.