Epsilon Volantis A

A wing sail catamaran from the floats of a Volans Trimaran

I’m re-starting this thread under a new name (previously Volans tri to cat conversion). This thread will focus on the catamaran alone, and I have started another thread entitled Epsilon Volantis B for the RG65.

The story so far: I have been trying to use the floats from a Volans Trimaran to make a catamaran.

To begin with the boat was a little narrow:


Since increasing the beam testing conditions have not been ideal, either too much wind or too little:


The latest modification has involved shifting the mast aft in an effort to reduce a tendency to pitchpole:

I intend to post more videos of testing, and if I can make the thing sail reasonably well, some details of the build.

Shifting the mast and fins aft turned out to be a fairly major operation. In the process I also improved the dual rudder setup and added a stiffer carbon rod to the centre support. Some images below of the boat, once again ready for testing:

Conditions were ideal for testing the modifications today. I only managed to get a little footage. Camera ran out of batteries, and controlling the boat and the camera was a challenge:


Sailing the boat was like how I imagine trying to break in a young horse might be … lots of power and potential but a bit difficult to harness. It definitely needs some tweaking, but I think that there is a good chance that it will make a decent boat.

Great progress ! well done !!!

I’m struggling a little finding a setup of the sails and fins that produces good performance and reasonable stability. The latest setup is better, but still needs some refinement. A couple of clips below (sorry for the poor video quality):


Even the big boys (MOD-70’s) have a little trouble


The initial capsize looks pretty dramatic, but the real danger appears to be when the mast gives way, as the boats hit the water pretty hard. I’m quite happy to stand on the shore and go for the occasional … ok, regular … paddle when my boats capsize.

Recently I’ve been using this boat with a Mast Aft Wing Sail, and the boat has evolved somewhat on that thread. To summarise, I’ve added a rotating retractable foil system, the retractable aspect of which seems to work nicely, whereas the actual foiling is likely to be a long-term project). With the Mast Aft Wing Sail work on hold for the moment (while I work out how to strengthen the rig). I’ve gone back to a more conventional wing sail and installed a wing I have been using on a trimaran.

As you will see from the footage below, I am struggling somewhat. To begin with I haven’t yet found the optimal position of the retractable foils and the sails. I think that the foils are currently too far forward. The steering is also a bit difficult, which might have be due to a bit too much flex in the carbon rudder post I have been using, but probably wasn’t helped by having different shaped boards on each side. The tension in the jib is also not ideal. I’ve switched to a swing wing setup but I haven’t yet found a good solution to having a jib with this configuration.

Please forgive the quality of the footage, much of it was shot from a kayak with a camera in one hand while controlling 4 servos with the other.


All in all, the boat still needs a lot of work, and that is before I can really start trying to make it foil.

You are making great progress!!
Can you convert those foils to T foils, that way they would provide lift in the front?
Just like you did to the rudders, but put about 2.5 degrees up in them.

Thanks Jim, I will give that a try. I’d like to make an acute L-foil work, but T-foils might be an easier starting point.

Jim - keep in mind you need vertical surfaces to prevent leeway and provide lateral resistance. At the same time, you will have to race in light winds as well as foiling conditions (unless you are making a “one trick pony”). I’m can’t recall “what” Jim’s [Mij’s] ultimate “mission” was, but if it is racing, not just reaching back and forth - foils need to work up-wind, off-wind and be able to be raised in winds that are light, or water that has weeds. At the same time, some form of leeway reduction is needed.

The benefit of more underwater surfaces to promote foiling, has the downside of too much surface drag in light winds.

If the current AC Cup been held on Lake Michigan or Lake Huron, I would offer that the technology for foils would have been less of a factor, given unpredictable Midwest and Great Lakes winds. Then again, if the venue were such to provide a big time lag between races so boats could change out their foils, maybe it would be fun… like having race cars pit for different tires in the event of rain.

You are of course correct Dick, That is why my F48 will have quickly removable T foils in the hulls with blank inserts (2 bolts each) and a trunk for a dagger board in the central pod. That hopefully will me enough options to experiment with for now. LOL

Hello Dick,

I agree with your comments regarding the problems with foils up wind and in light winds, this is certainly a problem with my current setup. I have some ideas in this respect which I will come back to in a later post.

Regarding my goals, I’m basically trying to come up with a multihull which is attractive to a wide range of people. I have a few basic criteria:
[li]Size - I think that it needs to be smaller than 1 m. For most people the Mini40/Formula48 scale is a bit too big to transport easily.[/li][li]Stability - I’m a kayaker, so I don’t mind paddling after my boats to turn them back over (I’m probably the only rc sail boat enthusiast who get a good physical work out every time they sail:D), but this is a barrier for most people. In this regard the best option I have come across is the mast-aft wing sail. I haven’t got the rig right yet, but the performance to date suggests that it will produce a very stable boat;[/li][li]Cost - More than one hull is always going to be a barrier. With this boat by using the hulls of an existing boat which can be purchased as spare parts, this is not such an issue. I estimate that the boat currently costs less than USD 400 in total to build;[/li][li]Build difficulty - It is possible to build this boat in a day. It is mostly held together with cable ties, with only 4 joints that need to be glued;[/li][li]Performance - Of course, it needs to be fast and foiling would make it more attractive.[/li][/ul]On most of these criteria, I think that I am getting close. I’m not sure that the boat will be fast enough to foil, but there are still a few things to try.


As Dick noted above, it would be good to be able to switch between vertical surfaces and foils. Below is a new rotating foil configuration which I a considering which might achieve this:

The view is a cross section seen from in front of the boat. The angle of the pivot and the angle of the connection between angled sections of the boards would need to be carefully selected to obtain the desired angle of the foils. Any thoughts as to whether this arrangement can be made to work?

Hi Jim,

why not a combination of Position A and Position b.

With longer daggerboards (vertical section below the leeward hull in Position B) you should get the vertical surface needed.
And with the windward foil/daggerboard always rotated upwards this should help minimize the drag.

Hello Wolfgang,

Re-reading my last post, I don’t think that I explained the proposed setup very well. I’ve roughly put together what I’m considering using foam and tape. The footage below shows it in action:


Due to the angle of the axis of rotation of the foil, in Position A the near vertical board immersed in the water is parallel to the boat, while in Position B this part of the board is at an angle (set to be suitable for foiling), while the other section of the board (now the vertical section) is parallel to the direction of the boat.

Hopefully this is now clear.

Regarding your suggestion, I’m not sure that I understand correctly, do you mean that one foil be in Position A while the other is in Position B?


Hi Jim,
Yes, that was im my mind.

In Position A (should be a light wind mode for a close hauled?) I supposed, that both foils (used now as daggerboards) would still produce a force now directed sideways,
to the leeward at the leeward hull and to the windward at the windward hull.

Without heeling both forces should be equal, but when the boat starts heeling, the leeward force should win, sadly to the false direction.
(the leeward daggerboard is deeper in the water than the windward).

But seeing the vid, I’m not sure anymore. Perhaps you can prevent/eliminate those sideway forces by the angle of the axis of rotation.

Guy’s, there is a problem with outward facing foils, something about lift efficiency. On boatdesign.net I believe. I’ll post a link if I can find it again.

Thanks Jim, I’d be interested to see it if you can find it again. Here is another variation, based on the same angled pivot axis approach, that produces inward facing foils:

As Wolfgang suggested, this could also use combinations of Positions A and B.

I’ve built a trial version of the vertical daggerboard/inward facing angled foil system (shown in they previous post). The foils are a bit rough (ca. NACA0009 - hand shaped balsa covered by 2 sheets of carbon), but hopefully sufficient to test the idea. The footage below shows the system in action and some preliminary on-water tests. Unfortunately I got to water a bit late in the day, so I didn’t make much progress, but the signs are good.