On paper CBTF seems to be a great way to go, some success in full scale races seem to support the paper. The main issue seems to be the problems with moving a big hunk of lead. What would be the effect of the twin linked foils on a multihull? Will the twin linked foils solve the multihull Achilles’
heel, agility?
Kristopher
I think twin foils with both turning opposite directions for steering and collectively upwind would be great.In monohull applications the twin foils work well BECAUSE of the canting keel which allows the boat to be sailed at shallower angles of heel than it otherwise would be with a fixed keel.In models around one meter LOA the problem with CBTF is wetted surface because the design “tricks”(thick high aspect foils) can’t be used effectively at that length. But on a multihull with it’s natural stability the twin foils would work very well, I think.
The problem is that in winds of 5-6mph and over foils would add a lot more to the boat. Now if you had the foils turn(vertical fins + foils) as well without adding significant weight the boat MIGHT be able to tack while up on the foils–a huge bonus but difficult to work out in practice.
The concept is definitely worth looking at closely. For a non foil multihull I’d say the chances are 99% for a drastic improvement in tacking speed.The downside would be the possible need to retract the forward foil downwind to reduce wetted surface.
Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing
I think if one built rotating slots similar to dagger board trucks you would be able to retract the foils while sailing. Would require some engineering trickery, but might be worth it.
Kristopher
Dick-
You pretty much have to exclude foilers when it comes to talking multihulls, they are really too different. I have seen the video that Doug sells, which includes a couple of his foiler designs. It really is amazing for someone that has not seen one of these boats. For those that have not seen the video, tacking looks like changing direction in a car. Its really that fast. Hopefully I can get my hands on one of these videos and transfer some of it to the internet.
My interest in the twin foils is more concerned with non-foil boats. Of course if you can get a boat up on three foils and twist the foils to windward…
As far as headsails go, I will try to get some pics up this week on the website. I have played around with a strange boom-thing for a while that works with big headsails and spinnakers. It does not require an extra channel.
I think before we can really say we are sucessful with spinnakers we have to be able to add on to a little boat like a Victoria. Many of the systems I have seen are too complicated. Micro servos have become so cheap, but seem to rarely be applied in sailing; I certainly think they should be.
Kristopher
I’m not sure what spinnaker systems you’ve seen but the one on the Spinnaker 50 is extraordinarily reliable and relatively simple; I see no reason given the right winch why you couldn’t put it on anything.Cost in weight and space are the key determining factors. Another is: do you adversely affect the upwind SA of the boat you’re considering adding a system to?
If the choice on a multihull has to come down to foils or spinnaker because of weight and other considerations I would vote foils without a doubt for reasons mentioned above.
Putting a spin system on a Formula 48 would be a piece of cake though if you used a normally sheeted asymetric you would be adding a pound and a half–not to mention that they are illegal…
Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing
Double post? What double post…
Dick, I’m not quite sure what you’re thinking without seeing a sketch but here are some ideas to ponder. John Beavis in New Zealand has designed an asymetrical system for his F100 that uses a tube for the boom on a swing rig. The spinnaker is pulled into the boom and the asymetrical sheeted to the boom.
Hasn’t been sailed sailed yet but will be an interesting experiment.
As far as I’m concerned the most important consideration on an rc spinnaker is: does it lift the hull down wind? If it does not it probably isn’t a good system. We’re all familiar with the behaviour of 50’s,IOM’s and other one meter and smaller boats downwind: some of them dive pretty easily. If you consider that a spinnaker will roughly double sail area or at a minimum increase it by 50% then the spinnaker system MUST lift downwind or else it will exaccerbate the diving problem.
I’ve found through MUCH experimentation that there is an optimum angle that the spinnaker should be set: as much as you can get!
On the 53" Melges model the boat had an asymetrical and a 12" pole that we lengthened a little; you can see pictures of Aussie 18’s with their raked back spinnaker luff.
On America One and the Spinnaker 50 the angle is such that those symetrical spinnaker systems actually lift the bow when hit by a gust-you can see it happen. That is the critical effect because then you have defeated the natural tendency of a small hull to pitchpole; you can then carry the spinnaker in winds you couldn’t carry the main and jib alone! In adding any kind of sail like a spinnaker you had better pay attention to this “lift” phenomenon or your boat will pitch pole even quicker…
Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing
So Doug, do you think it is possible to make a sucessful spinnaker on a small (under 30") boat? What do you think the limitations will be? I see the biggest problem as being the actual sail itself, they are a real pain to make.
Kristopher
Kris, I think you’re exactly right: the sail will be the biggest limitation-my sailmaker(Scott Morgan) has made more spinnakers for models than anyone I know of and that small a sail would be somewhat difficult. But the biggest problem with the sail is the material available. Airx is the lightest at .4 oz per sq. yd -only available in white but as the sail gets smaller the material should ideally get lighter.
After a lot of experimentation I settled on a 2.5 " hole/trough as working the best with half ounce nylon -our standard material. But even with that the hardest thing for the winch to do is pull it down. Setting in any wind strength is a piece of cake compared to the force required to pull it down.
So maybe half ounce airex will work-otherwise finding a material will be difficult.
The second problem depends on the material used for the sail and that is the winch: its got to pull it down fast and the set up must include a way to induce and remove slack from the downhaul-the critical function of the winch. Pulling the sail up doesn’t matter if it has a big pucker in it due to the downhaul being tight. The drums I get from Guyatt are all made with three winding paths one of which is used for the slack inducement/ removal.
For trim if you uses a symetric any small servo with 180 degrees of travel will work. An asymetric sheeted to a “jib boom” with the jib boom sheet connected to the main winch on a una rigged boat is the simplest system I’ve heard of so far- but it still requires slack inducement/removal in the downhaul…
Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing