Hi Guas 38,
I think, I missed something. Why are the white vektors coming from the foils so different in size?
Thank you all for the great ideas!
The dimensions of the testing pool are not all known. It is known the width is 12 m, the depth is 0.7 m (the maximum for the design is 0.5 m however).
The keel design was very interesting. We do have some concerns:
- There seems to be a larger net-force downward, causing a larger displacement. Is this correct and how much net advantage would you gain with this design?
- This seems difficult to construct. How would you advice us in this area?
- As we are most likely going for 2 masts with a high sail area, how would this keel perform as it would be necessary to place it deeper into the water?
We are still mostly focused on a monohull and are designing a hull at this moment.
Since keels are typically symmetrical foils the do not generate any lift when the boat is going straight ahead. Lift is generated as the angle of attack increases due to leeway. The more leeway, the greater the lift, until the foil stalls. The picture is assuming leeway, I am guessing the same amount for both keel configurations. I understand how they can draw a more favorable lift for their keel, but I am not sure why it would be larger. I know that the more perpendicular the foil is to the flow (leeway would put the flow parallel to the surface) the larger effective flow over the foil, but the cartoon does not always seem to follow.
This is the shape of the hull I am suggesting.
Now about the keel
I was imaging it as an aluminum that is carved and layered with 3 or 4 layers of carbon and then give it the desirable shape.
Just a draft of the keel and with 18degrees hilling.
Wolfgang,
I think that the rules are set so as to give monohulls a chance. The boat must fit in the 1x1 m box, but the top of the mast can only be a maximum of 1m above the water. Consequently there is little advantage for a multi to use the diagonal across the box, however there is a significant advantage for a monohull to do this (so much for encouraging boat evolution).
Jim
Hi Jim,
I could be wrong, but I understood a 100x30x60 box plus one (or several) 1 m rig.
Was it first a downwind and then an upwind leg?
There is two parts of the race. For the first run its a 140 deg wind speedrun. Then for the second run there is a loop around a buoy, starting downwind with the finish at the same line. So thats about 10m down and 10m upwind. The boxrule is as you say it is :).
For now we’re concidering a closed wing sail-design (https://www.google.nl/search?q=apex+wing&oq=apex+wing&aqs=chrome..69i57j0l5.6189j0j7&sourceid=chrome&espv=210&es_sm=122&ie=UTF-8#es_sm=122&espv=210&q=closed%20wing), with the hull still under some dicussion what would work best and is buildable with the materials and skills we have to work with (see the begin of the post for more info). Also there will be a folding mechanism to give the sail better downwind properties. Imagine the ring hinging open and folding to a big closed sail for downwind.
Thanks again for all the ideas guys! This is and excellent source of info for us!
keep the posts coming!
cheers from NL
Exactly! Although we need a way to get around the fact we can’t build a suitable catamaran. Also we would concider using two, or maybe even three slightly narrower oval ones. And don’t forget we will integrate a hinge to make a suitable downwind mainsail.
Thanks Wolfgang, in that case, I agree with you, I don’t see why it doesn’t suit a multi-hull? There are plenty of examples of rc multi-hulls that have shallow keels - yours looks great Wolfgang, but this is my favourite:
[QUOTE=Mij;69502]Thanks Wolfgang, in that case, I agree with you, I don’t see why it doesn’t suit a multi-hull?
Sweet article! Maybe if we get the sail right we won’t need a hinge. We recon getting it right the first time might pose a problem. A barn door might not be very classy, never the less it’s going to get us downwind at a reasonable speeds. Lets say, before we get the calculations done we can make the choice ;).
About the multi-hull, we’ve seen it being tried previous years, never really with a lot of success. A 30cm width is not going to give us enough stability if we want to compete with mono-hulls that are up to the max-specs. This model in the video looks a lot wider, and so those the one with this sail-plan we are trying out, we think there is more stability and speed (from the higher waterline-length) to be made from a mono-hull with a functional keel. The rules don’t allow the yacht to be placed sideways in the box, we’ve been over that with the judges.
How is you’re opinion and insight on surface treatments? I know they are not allowed in the competitions, but I’m pretty sure some wiz-kid has thought something up ;).
A couple of things:
[ul]
[li]My understanding is that there is limited benefit on using a wing on a monohull, as the maximum hull speed can be reached with a conventional sail. This has been discussed previously on this forum.[/li][li]In my experience you will struggle to make a wing sail sufficiently light for a monohull.[/li][li]I think that you are getting distracted by trying to use the whole box. I think that the 1988 AC when a 18.29m wing sail cat beat a 27 monohull by the largest margins on record perhaps demonstrates that there may be an advantage in simply making the biggest multi your box will allow.[/li][/ul]I should qualify my comments by saying that I think that I have found it quite difficult to make multis on a model scale perform to their potential. I’ve had particular trouble up wind, although my recent wing sail cats perform much better.
Perhaps a lifting foil on a light narrow cat, something like this?
Might need to employ my rotating foil concept to go upwind?
http://www.rc-network.de/forum/showthread.php/419289-Adjustable-foils
Why not just use an IOM. You should be able to put a shorter more efficient rig on one and still be within the rules. Another option would be a slightly enlarged 36R which uses a smaller box but has unlimited sail area.
As I understand this event, this wouldn’t be evolution.
I assume, even a thrown away code zero at the biginnig of the upwind leg wouldn’t be welcome.
I still try to figure out how a closed circular wing (oval or not) would react on a mono while heeling 
This is a great idea Jim, I think that I will try to make it.
Hi Guys!
We’ve been looking into the cat, the numbers are not looking very positive. It’s going to be to small to be sailing upwind well, the hulls are very probably going to interfere if we make the length as long as we would like. Also, the whole trick with a catamaran is the sailing on a single floater, but (for the guys that had some physics) the mass-inertia of such a small boat is tiny compared to it’s larger brother, this has as effect that ,for instance if you were sailing a fullsized cat you have 3 seconds to react on wind changing of steering, that would be a power 4 (as mass-moment is calculated in m^4) smaller, giving you about 1.2 seconds instead. That with some latency from the controller and lack of experience and feedback is not going be pretty. So, the choice for us is a mono-hull. We will be designing from the Delft yacht-hull database. That’s a database with about 100 hulls tested in a water tank on efficiency and other properties also under heel and drift. The hull we found looks quite similar to the IOM hull, only having a flatter bottom and being slightly more narrow at the back.
The closed loop wing is interesting. We’re going to do some testing in the wind tunnel down the road, but for now it look like a symmetrical foil is going to give the best results. We will probably see if making the sail wider at the bottom than at the top is going to give us a positive effect and save us top-weight. The pro’s of this sail is that it has an natural notion to turn to the wind. This means it will create a moment against the heeling moment. So less heel during a side wind, thats positive. But then again, there is very little fact known about this concept.
So, in two weeks we will be building the hull. Thats as soon as we are finished with calculations. Do you know a good example how to build one like these from balsa?
Greets!
A wind tunnel… now I am truly jealous.
Ok, I’ll stop trying to convert you. If you are going to build a wing I suggest that you look at the techniques used for model aircraft. I use Depron foam which is good in that it is easy and fast to work with, but doesn’t have as smooth a finish as I would like. I think the shrink wrap over balsa technique would give a better finish, but looks quite laborious. The most important things to concentrate on are to keep the wing light and to make sure that the mechanics work smoothly. For conventional wings I have one servo mounted in the base of the wing to control the flap, and I use a rotating mast arrangement. I haven’t had much success with using a jib with this type of sail. If I have the jib tensioned properly I have problems with the mast rotating nicely. I have had more success with mast aft rigs on monohulls. These are interesting sails, mine are very light and perform very nicely both into and with the wind. However, they are no good in very light winds and suffer from having a “naked mast” and quite a bit of rigging, all of which create drag.