Mast aft wing sail catamaran

Something a little different. I've recently made a couple of mast aft wing sails, one for a small trimaran and another for an RG65. Having made these it occurred to me that this type of sail might be particularly suited to a catamaran. To test this idea I've put a fairly rough boat together (the hulls are the floats of a Volans trimaran):







The mast aft sail is clearly not new and has been used on rc boats previously. One advantage of this type of sail is that it should reduce pitch poling as the sail produces an upward rather than downward force. This was the main attraction for trying it out on a catamaran. There is also an advantage of using a solid sail. A problem for soft mast aft sails is that it is difficult to stop the boom from lifting and spoiling the shape of the sail, fortunately this isn't a problem for a solid wing. The other new feature of this set up is the use of two lightweight masts and consequently only one stay. This type of sail puts a lot of tension on the mast and hull, using two masts on a catamaran this force is spread over a larger part of the boat. An added benefit of the design is that it is easily dismantled.

Here is a short video of my first attempt:


The boat needs quite a bit of work. It suffers from excessive lee helm, it doesn't yet sail very close to the wind and the rudder setup isn't ideal, however, it looks promising. In fairly strong winds it didn't pitch pole. With these hulls I've tested more conventional wing sails and had significant problems with pitch poling.

The boat is currently dismantled and undergoing modifications. Any suggestions would be appreciated.

I have made a couple of changes to the boat: the sail moved aft; adopted a single central rudder configuration. Conditions weren't great today with very strong gusty wind, but I sailed the boat anyway. Some footage below, not great, but it us interesting to see the behaviour of the boat in these conditions:



I'm happier with this setup, but now need some more moderate conditions.

Self adjusting camber and retractable dagger boards

Self adjusting camber and retractable dagger boards

I've made a couple of modifications to this boat. The camber now self-adjusts to give flat camber up wind and full camber down wind. I've also made the dagger boards retractable in preparation for adding foils. The footage below shows the approach that I am trailing:


Also, some footage of on-water testing:

I've made a test foil from polycarbonate (easy and quick to shape and bend) and installed in on the rotating foil system. Below is a short video which shows the new foil and the self-adjusting camber on the wing:

This thread became a bit distracted from the original goal and I found myself trying to optimise both a new foiling idea and a novel wing design. I decided to step back and focus on the wing. I've modified the boat and installed a simple central rudder and keel, and modified the wing somewhat. I'm happy with how the boat sails, but unfortunately it doesn't appear to be any more stable than a conventional wing.

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I think that what this boat really has going for it is that it is really simple and cheap to make.

Good job Jim, I was getting worried that you fell off the Planet because it had been so long since you posted, looks like your goal was accomplished.
Now work on those foils! LOL

Thanks Jim. I intend to come back to the foils soon, but I have quite a bit to learn first. What are your thoughts on the rotating foil system shown in the vid below? The idea is that the axis of rotation of the foils is inclined so that when vertical the foils are parallel to the boat and act like conventional dagger boards, but when rotated they become angled like typical foils. It seems to have potential to me, but I don't really know how effective the thick profile boards will be in the "non foiling" position?.
Jim.

In "Sail Racer" thread I posted the Airfoils Tools web site with my decisions and the 68 degree water Reynolds numbers for the NACRA 0010 T foil I am going to start with. The mold for the 0008 dagger or fin is done and test pull completed. Length of the
Foil must be what you are using to get the right Reynolds data, then you can use the Air Tools site to look at various foils and lift- drag ratios.

The T shape foil give me the dagger or fin and the lifting surface at the same time and I can vary how much fin depth I use by varying the spring pressure on the Bradfield system either manually or with a small servo to add or subtract spring pressure on both sides at the same time.

Hope this helps!

What translator are you using? my Bing Trans leaves a lot to be desired for German!!

Thanks for the tips, I needed some pointers on how to get started.

As for the translator, for the German I'm using Google Translator, which appears to be a bit deficient with regards to sailing terminology. American to Australian I'm coping ok, I just have to do a lot of conversions for the weird units you people use.

I know the feeling on the conversions!! LOL

Ok, I might be starting to get carried away:

Lot of flapping going on even in the stronger wind, too many elements?