Excellent find! Once I have worked out what I need I might use this approach, although I will probably just cover the foam with carbon. If you are going to the effort of making molds for the foils this is going to be quite some boat.
A larger wing and strong winds showed up the weaknesses in the current rig. For this sail I tried to keep it as light as possible and didn’t reinforce the foam with a carbon rod. Combined with masts which appeared to be too flexible, the sail tended to bow in gusts and hence made the boat more susceptible to pitch poling. The whole rig also collapsed a couple of times:
I will rebuild the rig with stronger masts and a reinforced sail before testing again. In an effort to recover something from the session I tried some tow tests of the foil. I was trying to use a kayak, so i couldn’t maintain the necessary speed for long, but the tests did demonstrated that the rudder and rudder attachment were not strong enough. The following footage shows a short acceleration without the rudder, if you squint, it is almost possible to believe that there is a little lift of the hull with the foil attached and immersed (hull closest to the camera):
Surprisingly the one aspect of the boat to behave today was the retractable foil system.
The main reason for the molds is I can vary the thickness of the foil when I layup new foils. It is only a simple step once you have the plug smooth, parting board, surface coat and 5 layers of 10 oz glass at 90-45-90-45-90.
Sounds like a good approach. I can see that I have a lot to learn about foils. It is a whole new (and addictive) ball game. I’ve shifted this foiling part of the discussion to another thread “Epsilon Volantis A”.
Ok, so I’m a little obsessed with this mast aft wing sail. In particular I’m keen to see how well it can perform against conventional sails on a monohull. To do this properly I decided that I need to test it on a commercial boat that I can find other people racing (this fortunately aligned with my plans to purchase a more conventional boat so that I can learn to sail these things properly). So, I’ve purchased a new and popular boat (I won’t name it, but I can’t really hide what it is), and I’ve started to try to develop a mast aft wing for it.
I’m trying to keep the wing as light as possible, so it is made from 3 mm and 2 mm Depron, strengthened by a single 2 mm o.d. carbon tube. The boat with the first iteration of the sail is shown below:
On the water it it works ok, but I still have some work getting the mast support system right. Something I’m a bit confused by is the extent of weather helm I’m getting. To make the boat jibe I had to move the sail much further forward than my rough calculations had predicted and cut some material off the flaps.
I intend to put some time into optimising this wing/rig before testing it against conventional sails. Any assistance or suggestions would be appreciated.
Some footage of the first test below:
I’ve been reading up on the causes of weather helm and I think I might have identified my problem. It could be caused by the imbalance created by having a large area of sail on the leeward side of the boat when the sail is sheeted out. If this is correct I should be able to reduce the problem by moving the pivot point of the wing towards the stern.
Hi Jim,
the RC-Laser should have the same ‘problem’.
And yes, move the pivot point more aft and use the rig more like a swing rig.
(My first thought was:
to much heeling and therefore the centre of effort leeward outside the hull, seen from above, kind of leeward outboarder, time to change to a lower rig)
Thanks Wolfgang. I have moved the pivot point aft and made the front element a bit thinner with a more rounded front edge (also strengthened the rigging).
Testing in light winds it performed much better. No problems jibing and generally much easier to control. However, tacking took a bit of practice, it was very important to sheet right in before turning through the wind, otherwise it would stall and turn back to the original tack (not obvious from the clip below, only became apparent when the wind picked up, by which time I had run out of batteries for my camera). Much more difficult than before, perhaps I have moved the pivot point too far? One other potential issue, I don’t think that the boat sailed as close to the wind as it did before.
I’m not yet convinced the sail is going to perform well in stronger winds. When testing the previous version It appeared to me that the weather helm got worse as the wind got stronger. Is this to be expected? I wondered if it might have something to do with the non-triangular shape of the sail causing the centre of effort to move aft as the difference in wind velocity moving up the sail increased as the wind velocity increased? Might this be why the laser has a triangular sail (thanks for the reminder, I had forgotten about this boat)?
I will test in stronger winds before trying your suggestion regarding reducing the height of the sail. The mast is already shorter than the conventional version of this boat, but I guess with the extra weight of the wing it makes sense to reduce the height.
Hi Jim,
thanks for sharing your impressions!
As you know, the RG65 is known as a class that is sometimes critical thru a tack because of the low boat weight.
Was the heeling angle too much? Was the centre of effort outside the hull?
There should be two major aspects about weather helm (if that’s nonsens, please someone correct me, I’m still learning):
a) the balance between the centre of effort (sail area) and the centre of the lateral area below the waterline.
b) the heeling angle.
You got a balance boat only with a certain heeling angle, above that angle you got weather helm, below that you got leeward helm.
that’s why they use different sets of rigs with well balanced boats according to the windspeed; when they got too much (heeling), they change to the smaller rig.
I would try a sail with less cord, like a sailplane-wing.
The centre of effort should be closer to the centreline of the hull while a reach or a running (when the wing is let out).
I think, the ‘mast aft wing sail’ should perform best on a stable platform like a multihull.
Momentarily I’m stuck with soft sails, but perhaps next winter I’ll try a D-rig with your depron wings.
Tuppes, think twice!
The advantage of the ‘mast aft wing sail’ is the inclined axis of rotation.
When the wing is sheeted out you should get some upward directed force to ease the bow (of your multihull) while a reach or a running.
Reducing the angle of the inclined axis of rotation would reduce the desired effect.
Thanks again Wolfgang. You made me realise that I have been thinking of this wing the wrong way. It is the profile of the wing when the boat is healing that is important. Hence the profiles that are used for stable multis are not ideal. To get a sail with good lift when the boat is healing will, as you suggest, require a wing with less chord. I guess that I also need to reconsider the shape of the front element so that the cross section at the healing angle is the correct profile.
Jim.
I’ve returned to the RG65 and modified the wing. It is now more like the first wing I tested with a thick chord and relatively short. The flaps hinge points are now inside the front element and the flaps are made of a thinner foam (2 mm). The boat seems to sail much better:
Did it point higher, what were the wind speeds?
The wind was supposed to be ca. 10 knots, but I think it was generally a little less. It did appear to point higher. The previous configuration had the pivot point for the front element back from the leading edge. For this latest wing this pivot was at the leading edge. In the previous position tacking became difficult as the wind became stronger because the portion of the sail, if not sheeted in tight, could catch the wind and create a force acting against the tack. So although moving the pivot point aft brought the centre of effort of the sail closer to the centre line of the boat, the boat is actually easier to sail with the pivot point at the leading edge.
I’ve also tried this sail in stronger winds, ca. 15 knots and still behaves quite nicely:
Next I’m going to test an idea a friend suggested and try two narrow wings.