This build has changed somewhat from my original plans, and the technique is evolving as I go along. The main change is that I’m building in such a way that I can fairly easily change the bow shape down the track if necessary. I like to idea of the snubbed nose bow, but I’m a little uncertain how it will perform at this scale. I’ve basically cut the bow off and sealed it and I will shape a bow out of foam, still snubbed nosed to begin with. This will be attached to the hull, covered with resin and silica and sanded to shape. This approach will be a little heavier, but the foam bow should be easy to replace. I will use the same technique for the floats. Hull currently 135 g.
I’ve also decided to build a bit longer than 65 cm. The hull will probably be a bit longer and the rudder will protrude behind the stern. Over all I anticipate that it will be a little over 70 cm.
There “IS” an RG-65 Multihull class trying to form during past year or two. Building to overall 65 cm would allow another boat, plus make resale (if so desired) a bit higher. Going off on your own dimension leaves very little to compare to - both speed and setup. Just a personal point of view.
Point taken Dick. With this boat I will have some flexibility with the length. In particular if I move the rudder within the length of the hull, and use the original bow length the boat will be within 65 cm.
The reason that I’m not too concerned about the length at the moment is that building these boats is very much a learning experience for me. The original design is really just a starting point and will be modified constantly as I learn more and try to optimise the performance (consequently resale is very unlikely). At present I really don’t think that my designs are worth replicating. If, in a few years time, I think that they are I will be more careful to stick within the class rules. As for comparison, unfortunately I’m not aware of anyone else sailing 65M multis in my part of the world.
For this boat, for the first iteration I want it to be as simple as possible, with the expectation that it will become more complex. I’m trying to make as few perforations in the hull as possible (by the time I’m finished with a boat there isn’t much of the original material left, my current boat looks like a colander), hence the rudder attached to the stern. I’m still not sure if I will need a single rudder in the main hull or rudders on the floats. As for the length of the bow, I’ve set this up to be easily changed and anticipate that there will be several variations along the way. At the moment the shape that I’m considering looks better a little longer than the original plan.
With hull and floats almost complete I’m starting to work on a wing. I’m going to try more conventional wing sail design, with a shape similar to those used on the AC45 and AC72 cats. To begin with I will use the depron foam technique I’ve used previously, with a few modifications. The major change is that I’m going to build the wing in 4 separate but connectable sections. With this arrangement it will be possible to remove the top section, or sections, in strong wind conditions.
The photo below shows the approach that I am using for the front element. The core is 9 mm foam and the shell 2 mm. Squares holes are cut into the foam core to reduce weight.
The bottom section is attached to the mast and other sections can slide onto and off the mast (and may need to be pinned in place). I’m still working out how the sections will be attached to one another, and whether to control the flaps individually or together.
Almost finished. Hull and internals now assembled. The hulls need some final attention and probably should be painted, but I’m too impatient to see how it sails.
Current weight - 730 g with everything apart from the wing, a little heavier than I had anticipated, but it is also slightly bigger than the original plan.
Now with a wing sail. A 4-panel wing constructed from 9 mm and 2 mm Depron foam. Upper 2 panels can be removed in strong winds. Weight with servo - 150 g.
Round about 1.24 she really is showing an incredible turn of speed - congratulations!
One thought that occurred to me while watching, with a wing you don’t get the same visual feedback of stalling - you can’t see back-winding etc. A couple of ways of overcoming this could be the fitting of a wind indicator at the masthead combined with the fitting of leach tell-tales.
Other than that, it’s a fascinating development project - keep up the good work!!
Overall the boat performed quite well, but seems to be a bit susceptible to pitch poling. It went over a couple of times (off camera), generally when hit by a gust whilst going down wind. The main hull only flew once (again off-camera), and it looked a bit unstable. I wonder if these problems might be reduced with a rudder T-foil?
In terms of tacking, it seems to be ok in light winds, but no good in stronger winds.
One other major issue, looking at the footage I found that I had the flaps incorrectly set quite a bit of the time. It would be good to have some sort of indicator to show which way the flaps are set.
Hi Jim …great progress compared to what you started out with, congratulations !
The first minute of the vid looks really good and considering only had main (no jib) looks like that wind speed was near the limit for the high AR main.
In gusts it definitely looks over powered, t-rudder should help prevent pitch-poling but could not help thinking maybe little more ballast (centre hull) in higher wind speeds may make it more little stable or if you want wider wind range lower the C.E with shorter aspect ratio and then you may be able to introduce a self tacking jib which will give you more power & speed in lighter winds and then just run main in higher winds :rolleyes:
Thanks Alan. A lower AR wing sounds worth trying. I haven’t found a good way to introduce a jib with the swing wing arrangement. Attaching it to the mast produces too much friction for the rotation of the main, and I didn’t have much success with a jib as part of the swing rig arrangement. I actually quite like the simplicity of the single wing. It is a very clean arrangement, quick to set up and little to go wrong. My plan with this boat is to keep it simple and only have the wing, but to design some flexibility into the wing by having the option to add height, or change the size of the flaps.
Nice work; will be intrigued to see how it goes. As you say, it has become more complex… I would not be surprised if the America’s Cup boys are watching with anticipation ready for their next big idea…
Thanks for the plot. It does feel like I have lost some lift at low angles of incidence.
Some footage of the boat with the new wing and a T-foil rudder - wind was stronger in the middle of the pond so some of the footage is a bit hard to make out. Seems to tack reasonably well, and goes fast downwind. Still need stronger wind to see if it will fly the main hull.
Ok, I might leave this story here for the moment. For my sailing to improve I need to spend some time practicing without a video camera :D. I might call back in if I ever get it foiling :rolleyes:.
Overall, I’m happy with the boat. It might not do everything I initially hoped, but it is a big improvement on my previous effort. Thanks to those who provided advice and support along the way.
Isn’t that what the design / R&D process is all about? OK, so it didn’t quite foil, although I’m convinced you’ll get there - your development of the hulls & wing has been a lesson we can all learn from and for that I applaud your efforts. I for one have never had much interest in multi-hulls but having followed your ideas and advancements you’ve certainly got my interest which itself is quite a feat!!
I sincerely hope that at some point in the future you’ll return to this thread with footage of her foiling - perhaps it’ll take a re-alignment of weight distribution, a refinement of wing design/control or just practice! Whatever it takes I look forward to reading of your advancements.