Lenticular sails

[sirfbus1964]

Hi guys,

 I take it by the lack of response to my last post you lot also think I'm a crank.

I've been researching building my own boat and noticed what problems everyone has with sails,

or was it because I'm new to this and posted the discussion in news and not here.

As a mechanic I know that simple solutions often work the best, as Bertrand has shown Lenticular shaped sails is the way forward, if  Ship Theory is to be believed then the Vikings could hold the answer, rafting their boats made them more stable at sea, easiest way ship the oars lash them down and together across two boats,you know yourselves a flexible catamaran puts less strain on the hulls,

back to sails, an unstayed  mast in the middle of each hull acts like a biplane or being a kite boarder myself acts like stacking foils.

Bertrand's problem is swapping that shape from one side to the other.

My solution is simple,as I sat by the river looking at the old church I noticed  a sign saying how Turner had painted that same bridge, and realised that art too has advanced down the years, It was the simple drawings of Viking ships that didn't explain why they could sail rings round everybody the answer was they did something we've forgotten, they worked with nature not against it.

Back to Junk rigs at the front we now add a luff flap what if early drawings of these were wrong,

Tai chi tell us the answer; balance.

A double lug rig,same sail either side of the mast, using the wind to flatten one side you then have a perfect Lenticular sail, personally I like the Vikings dimensions of a fully balanced sail 3 times longer than the height looks a lot like a power kite as opposed to the Junks 2/3 the height to length.

Please don't think I'm just a crank I know another Yorkshire man sailors thought that about but eventually captain Cook proved them wrong

[kim whitmyre]

I doubt anyone is harboring thoughts of you being a crank :-) Most problems with sails can be traced to inadequate awareness of how to shape them according to conditions. Which is what you just said...;-)

[sirfbus1964]

also if sails ain' just kites then why's this work;http://outrigmedia.com/outrig/uncategorized/2011/10/19/diamond-rig-...

[Bertrand FERCOT]

Hello Sirfbus1964

I've looked with attention the video "diamond sail rig" . It seems to be a very interesting idea. The big problem on a real boat is to have a safe and reliable system able to turn the mast under great sail forces and without leaks from the deck. Other difficulty is the reliability of the double rolling sail system. And at the opposite of the rectangular Vicking sails the center of sail effort of a such rig is very high.

The problem with this kind of rig with the mast in the centre of the sail is you can't tack facing the wind : you have to turn 270° by downwind (instead 90°) and it could be dangerous in crowded area or near rocks........

 

As a drawing is the best international language, please can you make a drawing of your double lug rig and how you generate a good lenticular shape even in light winds.

 

Bertrand

 

 

 

[sirfbus1964]

dear Bertrand,

please forgive my poor drawing i'm not used to a computer so learning as i go,

the attached drawing is a view from above,i.e. plan

[Bertrand FERCOT]

Thanks Sirfbus1964 for your drawing.

OK, now I understand, the profile is not generated by the battens but by a belly in each sail and with a such rig you can tack facing the wind. Do you wish to test it on a little boat or a tender?

Perhaps on my next tender (I've to built) I'll test a such double sails with a low rectangular shape as the Viking sail you've put a link but with double wishbones to generate the curve instead a belly in the sails .

Now my masts are built ( http://maheyo.free.fr/spip.php?rubrique6 ), it's time to finalise the design of my  double wishbones to built them.

Their profiles will have a deep lenticular shape to be able to generate a  powerful sail force without angle of attack......

 

Bertrand

 

 

[sirfbus1964]

finally I knew you of all people would get what i was on about,the only reason the battens bend is so they meet at either end of the sail. It is the cut of the sail that forms your lenticular shape,the tapes either side of the mast restrict the sails so that only one side can move 10%,pulling the other side flat against the mast, giving one curved and one flat side.as the boat tacks the wind flattens the other side and the low pressure pulls the belly to the other side of the mast. 

I knew you were onto the right idea,as my power kite has a flat front and a bowed back,people think they fly because they are airfoil shaped, but the only time they have the airfoil in the wind is when they are "parked" directly overhead the power comes from them deflecting the wind, which they also use to keep their shape,i.e. 

[kim whitmyre]

Here ya go:

 

P28foiler

[sirfbus1964]

not much about the sail plus there ain't much space aboard for cruising 

[Mawibo]

It's hard to think of a new revolutionary rig, one can think everything has been done especially with millions of bucks.

Kitesurfer, paragliders could bring something new but my favorite innovation regarding simplicity, balance and ease of reefing has to go to Garry Hoyt's new rig. It is AMAZING and makes a lot of sense.

You can watch a well detailed video here:

http://www.garryhoyt.com/id32.html

Here are a few tips...

The gaff stays up.

Nothing is really new but rearranged.

The sails is kept away from the mast.

I wonder how it would work on a multihull but still I find this inspiring.

Tell what you think.

 

 

[kim whitmyre]

Here's the page on the sail: "Thick Sail"

It's a "lenticular sail." You made no mention of hull(s). It's very interesting: the "battens" stack as the sail is lowered  for reefing. It's very much like Bertrand's tiki 30 sails; he has a picture looking up one of the sails that looks very similar.

 

Mawibo, that does look interesting. . .I have a friend who wants a single mast on his boat in progress. I'll see if he knows about the Hoyt rig.

 

[sirfbus1964]

the Hoyt sail is an amazing update of a junk rig even though Garry denies this, the Thick sail is a foil like Bertrand's but with hitec  battens the lenticular sail is D shaped, most other sails concentrate on the curved side, the only way I can see it working is if you sail like a Proa and shunt instead  of tacking i.e. 

[Alfred Archibald Linthorne]

I believe I read somewhere that James Wharram did not think Junkrig Sails are of much use on his desines because of flutter or flapping of the sails causing wear . Since then I have read in an article in the Junkrig assoc about scalloping the edges of the sail to prevent flutter also sewing 3 ply nylon on the edge also reduces this problem any thoughts ? I welcome your input.