A class Worlds: mainsail designs

WOW ! take a look at all that RADICAL A-cat development. A boomless mainsail with only 6 battens !

Who else would have thought of that !

Wouter

Why don't you borrow an A Cat and go and sail it at a regatta, you will almost certainly end up with a bunch of people who enjoy the same sport you do, get to sail a fabulous boat and hopefully go home realising that it does not really matter which cat class you sail in, its all good fun and its your choice. I am guessing you built your own F16 so that you could

improve

a few things on it. All new cars still have 4 wheels and an engine, but they are getting better. Be nice!

Gotta admire Ben for doing something radical and for Randy to think above the top of the mast.

I'm not sure the boomless part is a step forward, downwind you need to ease the outhaul and sheet the main, so I dont know how well a boomless main would work downwind. I would be interesting to hear from someone sailing if Randy is fast downwind or not.

Bill

Interesting.

Randy started that idea years ago with P19MX mainsail..

He used a thick wooden batten to get the sail to stand up over the mast....

Affectionately named...

da woody

... It seemed to go OK, very senstive to main sheet tension but the class died shortly afterwards.

Daniel,

The point here is not about the A-cat or the class directly, but about how some people write up trivial or even old modifications as radical developments.

Lets face it, developping a full foiling moth was radical, developping a sold wingsail rig in the C-class was radical, but removing a single batten from the bottom of the sail and removing the boom is not radical by any stretch of the imagination. It is already a stretch to call it development as many other designs have already gone down that route before.

Sorry, just the way I see it.

Wouter

You are correct, the main is not radical and Richard Roake came back and corrected that point one 2 or 3 of these threads a few weeks ago, so drop it, it is already dead and beaten over the head a long time ago. As to the wing, for what it is, it does fall under the radical design aspect of this conversation. It is a take off of what the C-Class has featured for years, but it also is a wing designed for how an A handles and sails. The simple fact that you have enough drive to do this and take it to the worlds as your first major regatta is a big and some would say radical step.

When I first mentioned Randy's new main, I said it was different, not radical, think it was Tom Siders who hung that label on it.
When Randy first mentioned it to me I ran a couple of aero run's in the computer on it. The main benefit that I could see was not so much that you got more power from the sail, but that you should a fairly good chance of reducing the overall drag by a good margin and that would help your point. In addition, you'd probably be able to get the top to fall off easier in the puffs. In addition to the tip, he added a small sweeper to the base to starighten the flow there and I believe that this was a useful addition, again, not for power but to reduce drag.
Couple of computer comparison pics attached.
RG

the other pic

I did and I am windswept who just posted the comment above your 2 stating that.

Sorry Tom, you posted while I was posting mine and I didn't see it, didn't mean to beat you up.
Cheers
RG

Appreciate you giving us the inside scoop RG.

HI RG,

Please could you explain what is a

Sweeper

I guess it is a kind of winglet which aims to reduce induced drag at the footsail level?

Thanks in advance

EK

Hey, is that an XFLR5 run I see there? Thank you for sharing what most sailmakers would lock down at the bottom of their treasure chest.

I can see that the sail have a bit better L/D ratio in theory. Was the theorethical L/D delta between the sails proportionally the same over the windspeed range? You dont think using XFLR5s 2.5D algorithm can be a problem for the results.
Interesting that you choose to use 0deg twist <img src=

alt=

/>

Erwan, the sweeper is just the flat part at the bottom/tack of the main, just straightens the stream lines (blue) and reduces the turbulence.
Rolf, yes its XFLR, and yes the 2.5D algorithm is a problem, but the example was just to see the differences due to geometry.....in the full up CFD run I did the differences are markedly smaller but still there. The L/D delta varied markedly over the wind range, just showed the 20 knot case as it high lighted the differences best.
Cheers
RG

Could you explain the loss of drag by using this shape. Is it from the tip vortex or is it coming from somewhere else. Just curious.

BTW, windsurfers have been using this top batten config for quite a few years now...

A-Cat Sail Innovation:
In 1988, Greg Goodall and his brother designed a sail with a wishbone/boom system which was quite similar to Randy design at the bottom.
The boom was half a wishbone from the mast until mi-chord of the sail and then a basic alloy tube was soldered just like an half boom
As a result the fore part of the footsail sweep the trampoline and you have a vertical

step

in the footsail
and then the remaining horizontal part on the sailchord.

Boomless

is a consequence of this design, the alternative is the Greg Goodal wishbone/boom.

I would like to mention than 20 years ago the BIM A cat were also boomless, the consequence was a

give-up

in windward angle as a consequence of a

fat

sail section at the foot level, (More induced drag I guess)

Also more embarrassing, when you released the mainsheet in the gusts, the sail started being

fatter

, therefore more powerfull before to open at the top.

In addition, the downhawl tension was much less useful without boom ie: sails twist more easily under downhawl when the footsail was tighten flat with a boom.

Hope it could feed your thinkings

Cheers

Erwan

Regarding the tip vortex: Is there anything in the A cat rules that would prohibit a winglet to address that tip vortex? The A rules are open enough to allow hard sails, and winglets are a proven win on airfoils...

The winglet could be hard (like a wing sail) or soft (like a kite) or pressure-inflated (like a baloon) or wind inflated (like a parasail). If wind-inflated, it might be possible to design one that blows full on the windward side and flattens itself to leeward.

If the winglets were hard (e.g.: Carbon) and pivotted around a batten, and settled to a '^' position at rest by gravity, then the wind underway would lift the windward winglet into position and press the leeward against the sail. It would even work in light air if the rotational axis was near the center of gravity of the part that rotates. If fitted to a hard sail, the leeward foil might fit in a rebate on the leeward side for cleaner airflow.

*That* would be radical. Not sure it's legal or worth the weight aloft, though.

Another possibility is a simple end plate atop the mast or as the top part of the sail. End plates are another proven win for constrained airfoils. If you extend the '^' flopper concept to an end plate, the plate could have camber on each side to match the target sail camber, so that when it flopped from side to side the leeward plate would be flush with the sail cloth, and the windward side would have useful camber to help it do its job. Care would be required to pick the right angle of attack and profile for such a cambered end plate, but it could be used to form a featherweight simple auto-tacking winglet.

,
--Glenn

A friend (schooled in avionics) and a former crew mate ones asked me :

What is the difference between a winglet and a zero angle of attack wingtip

The question was retorical and I understood what he meant.

Basically wingtip can also be had by adding a zero angle of attack wingtip on top and in line of the active wing section. On cats we approximate this by letting the tops twist off.

This is also to most simple method of descreasing wing top vortex on A-cats as they don't have a mast length limit.

Wouter

I put a very light aluminum

L

on each side of the top of my Glaser sail on the Marstrom. Camber was no problem, as their sail is flat at the very head anyhow. Yarns tied at the back of the head seemed to be better behaved than without the little 2" end plate.
The end plate on the boom was not effective, as it was usually too far away from the sail.
Woody Cope said it was OK with him unless I started beating him regularly. Not likely.

1.

Small sweeper

-- isn't this usually the extra sail area below the mast? What is the meaning on a boomless boat?
2. I assume the benefit of a boomless rig is that you can close the gap between the main sail and the trampoline?