sail aerodynamics

sail performance optimalisation by constant gap: "double"-masts.

This is not an answer on the theory and calculations of pressure.
I am looking for a solution to the imperfect forms and “unused” areas of a conventional main- and front sail combination, thus creating higher efficiency and power.
I hope I can ask you guys at this thread for advice if and why yes or why not the below idea (S3b) can work (or not).

As stated numerous times in this and other threads, a conventional main- and frontsail attached to one mast complement each other. The air bended from the flow at the main takes care of a higher angle of attack at the jib which provides the jib with more power and height, however the effect of the flow/pressure around the jib influences the air-angle of attack at the main slightly negatively.
Even the beautifull SRW sail has a front sail.
1. Is there any information on the optimum distance between front of jib and front of main/mast, to produce the optimum effect on the angle of attack?
Maybe there is something like the ideal ratio or relation between d and d1, or between bottom leech lengt and d1?
(see sketch 1)

Further: current sail shapes are still triangular, with a trend towards square heads on main.
These triangular forms, and the fact that the stays are connected to the top (or fractional) of the mast, conclude in wide sections at deck-level and a wide overlap, in medium width and overlap halfway the mastheight, and in small sections and no overlap at the top of the forestay. You can observe a changing ratio between x to x1, y to y1 and z to z1.
(see sketch part 2a and 2b)

2. Is this the best option regarding production of lift and power of the sails?

Taken the imperfections, could it aerodynamically be improved by:
a. taking a turnable wingmast with square head for main.
b. then adding a second identical wingmast on a turntable at an ideal distance from the first.
c. The turntabel is able to turn the masts at any deal position regarding the air-bending-effect, so they work well together.
d. When tacking, the turntable turns to the other bow, the lee-mast becomes the windward mast, the windward one becomes the leeward mast.
e. The booms will be operated with lines just as conventionally.
(see sketch part 3a and 3b)

With this configuration:
f. I will need a very reliable turntable as all sailing forces need to be absorbed or translated through this tot he hull.
g. I will be able to use square heads so I catch the higher windpower, and delete the non-effective bottom- and top-areas of conventional triangular rigs.
h. I will be able to control the distance between front- and mainsail to an optimum.
i. I will be able to control twist in both sails to an optimum with less control-lines and vangs.

Again, considering I will manage to manufacture a sturdy and functional turntable (or sliding-system), the question is if this is a configuration that helps increasing saillift and sailpower compared to conventional sails (even to SRW)?

Is there anyone who can help me with this, as I will be very happy to receive any feedback as I read stuff from sailors and scientists on this thread.
With positive feedback I will make a floating working prototype.

Regards, PEDEKO

 

In my opinion:
1) Even if it managed to produce some more lift than a conventional sail (and only in a narrow range of points of sailing), the weight penalization and the mechanical complexity would eat away any practical advantage.
2) The turntable would be an invitation for the corrosion, and the maintainance costs would be high (compared to clasic sails).
3) The downwind performance?
Cheers

 

Daiquiri,
thanks for your reply!
1. This configuration will not work in all points of sailing, especially on a reach and downwind.
What I am hoping and looking for, is that can someone, positively or negatively, state that eliminating the inefficient bottom- and toparea of jib and main (as conventional) by this configuration performs better.
2. I am aware that there are serious weight-, reliability- and complexity-issues to be expected.
Until now I did not look serious into that, but I will have to!
3. Downwind performance: maybe I achieve an "acceptable" when the turntable can rotate freely 360 degrees, but very likely I will need a spinnaker of some kind.

Again, thanks for your reply!
Regards, PEDEKO

 

Slot Configurations

Are you asking several different questions with this posting??,..
1) slot configuration question
2) twin wingmast question.
That is how I am interpreting your question.

Would my slot question I posted awhile back be of a similar nature to what you are asking?

This is the only answer I received to my question, and I am still trying to 'digest it'

 

Twin Wing Mast

Perhaps you should have a look here:
The new – “Kelsall Cat Rig”
The twin wing rig with a difference.
http://www.kelsall.com/TechnicalArticles/SummaryOfArticles.htm

 

Like this??

http://www.boatdesign.net/forums/sailboats/wing-drive-6698.html

 

I'm a bit confused; as you say in the quote above, a conventional rig where the apparent wind hits the jib first works very well, because of the upwash. However, in your rig won't the wind hit the two rigs at the same time, therefore preventing them from creating favourable upwash?

 

Semi-Rigid Wing (SRW) subject revisited

Since this Semi-Rigid-Wing (SRW) subject has been mentioned again recently, I spent a little time revisiting it this morning (my memory is just not what it use to be, so I have to spend time rereading things ).

So I looked back at that blog again to see if I could figure out exactly what this new technology was. This blog doesn't really define the SRW technology, but does discuss rigging the vessel for it,...and some interesting sheeting angles for the accompanying headsail.

 

I think what PEDEKO is referring to here is analogus to something I have often reposted:

 

Hi CT249,
Thanks for your reply!
The idea is that this turntable allows me to change the position of the two masts.
So I will be able to look for the best position to each other and find the optimum upwash.
Well, thats the idea anyway.
When there is even a small extra gain in having these two masts/sails interact compared to a single wing mast (Soft wing like SRW favorable because of reef ability) I will make a prototype.
Thanks again,
PEDEKO.

 

Hi philSweet,
yes something like that.
The idea is to have 2 soft windsails and it should be the preferable means of power so will be on say a trimaran to exploit the power.
In the case of fixed wings on a motorsailer, that use is a different one.
But yes, 2 interacting masts/sails.
Regards!
PEDEKO

 

Hi Brian,
thanks for your reply:
I wasn't aware of the Kelsall Twin Cat Rig, although I did see the french 24 hour record breaker cat some years ago, which has the same configuration.
The faster cats and tri's sail al lot of their watertime upwind, in which case the Kelsall config needs to have the masts OR far enough out of each other so the leeward leds catch wind, OR steer a little bit off (as advised by Kelsall).
There might be an advance in use with my idea to be able the change the position s of the masts during sailing.
But the thoughts about the much simpler stay's and other advances at the Kelsall cat rig is absolutely recognizable, so thanks for that!!
Regards,
PEDEKO

 

Ah, OK. Thanks

 

Hi Brian,
yes that's analoge to my posting.
There is one addition and that is that the distance between my idea's "front-sail" and "mainsail" (actually leeward- and windward mast) is constant from bottom to top (or adjustable) according to what is the best distance to have the optimum upwash effect.
I am aware that there is probable little to gain and that the practicality is conflicted by the complexity, costs etc... but when there is a gain, I will make it happen on a prototype.
Thanks!
PEDEKO

 

That is a very good idea. Try it.
The K8 minitransat is on the right way as well.
http://www.k8sports.com/the-boat.html