A Photo & Discussion Forum for Wharram Design Enthusiasts
After more then ten years of sailing my Tiki 26 Freyia, I decided I needed to do something to get her a better speed when surfing or sailing downwind in stronger winds. The biggest problems we had was that over a certain speed like 10-12 knots, Freyia has the tendency to sink her sterns so deep that first the outboard leg and then the whole cockpit would "touch down" and so bringing the speed down to 6-8 knots. As a friend of mine had a bunch of helicopter wings and rotors laying around I persuaded him to give me some parts of an heli-heck rotor blade made out of solid carbon and glass fiber at the front and filled with closed cell foam in the middle part.
Last June I found time to add these wings to the stern of each hull, just in front of the rudder, and during my sailing trip, could experiment with the adjustments of angle and get some nice results.
After adding these winglets Freyia is now sitting much higher with her sterns when starting to surf down waves of 3 feet or higher. When getting over 25 knots of wind we seldom touch down anymore, but could have a couple of days when we would run at 9-11 nm in one hour. So these little foils bring the v-hull the much needed gliding surface aft. Each of the four foils is about 12 inches (25 cm) long and has a profile very similiar to a NACA 10 one. I calculated that each hull should get a lift of about 20-30 kg at about 10 knots when the attacking angle would be about 10°. I have made the angle of attack a bit adjustable, (but I need to go swimming for doing so) and found out that they must be nearly horizontal when the boat is not moving. The angle comes from the stern sinking deeper when speed gets up. Giving them bigger angles was not helping but adding more drag and slowing the boat. When running on the engine full throttle and horizontal adjustment I did not loose any measurable speed loss. Only when sailing at 2-3 Beaufort Freyia might have lost a 1/4 of knot, compared to no foils.
So over all I am very pleased with this addition, one additional bonus being to be able to climb aboard Freyia easily when boarding after a swim, instead of putting down the ladder.
I will add some pictures of my construction, please feel free to ask any questions..
Sorry a short correction: the profile is similiar to a NACA 0015, and not a 0010...
well this is just when really driving her hard and fully loaded for cruising, with stuff'n gear down there in the Greek waters, with two anchors, ropes and fenders and dinghy and dinghy's outboard and fridge and batteries and solar cells and food and water and gas and drifter and spannakers and decktent and Goped etc. etc...So probably around 1400 kg or so with two aboard. But with that much gear loaded I sail her unreefed up to 28 knots of apparent wind when going against and about 20 knots apparent when running with the wind. And specially when I am pushing her hard and having smaller waves she is prone to touch down with the deepest part of the cockpit, which is the front of the outboard-well. This happens latest at 16 knots, she simply puts the handbrake up :-)
I once did about 125 (Methoni to Preveza) miles on one day from 5'00 til 22'00 under full sail and a huge spinnaker, wet and fun and passing every monohull under 58 feet...But this was with nearly no waves just along a coast with the wind blowing with about 6-7 Beaufort from the land...
A very interesting experiment Matthias, thanks for sharing it with us.
Zest is a glass Tiki just like Freyia. I've not had the "touch down" problem (yet), but we've never been as heavily loaded and we've never hit 16kts... Our fastest has been 14, so I guess we've more fun to come! The sterns do sometimes squat a bit though and maybe we'll look at winglets later if it becomes a problem. You mentioned yours are 12" long, but did you mean the fore and aft dimension or across the boat? What is the other dimension? What material did you use for the strengthening plates you've fixed to the hulls/skegs? You were lucky to have a friend with helicopter rotors laying around - You don't often hear that!!
Do you find the winglets reduce the pitching motion in short steep waves? Sometimes my motor cavitates in that situation and I wonder if the winglets might steady the sterns enough to help.
The winglets are each pertruding 12" from the boat, with four of them the theoretical spanning is short of 1 Meter.
I have put a stainless plate 4mm thick bolted through the skeg and an hollow steel tube soldered on with a bolt screw going from endplate to endplate of the heli parts. I faired the skeg first with epoxi and reinforced with glass and then fitted the plates which I waxed and removed again after curing, I then bedded the plates in sikaflex and bolted on. I decided not to bolt the angled parts of the plates to the hulls, but think its important that thes angled corners applly pressure there for stability reasons. I did do no calculations for material thickness and probably ovebuild these stainless parts a bit, but better to strong then to weak...
The length in fore and aft is something like 12 -15 cm, I would need to measure a leftover somwhere in my workshop... By the way : I was a bit afraid at the beginning of testing if Freyia would now eventually bury her bows in case the sterns would lift to much, but seemingly the lifting effect is not to big. Freyia as usual was always keeping her nose high even when we hit a bigger wave when going faster then the wavepattern. Anyhow Freyia is sailing very wet at such high speeds, water flying from the bows, waves washing on the sides of the central cockpit through the open spaces under the seats, and also at the front of these sitting boards next to the mastbeam. I did build a sprayhood as well this year, and the sailing got much dryer, but not bonedry especially when sailing against the wind and waves keep on splashing against the side of the hulls, and the wind blowing this spray aft into the cockpit.
Thanks for your interest
Thanks Matthias, that's a lot of useful information. I agree it's better to over-engineer in this area, as I've always thought the skegs look like one of the more vulnerable parts of these boats.
I get the same problem of water coming up around the seats when sailing fast in rough seas. I'm rebuilding mine to include some locker space under, and at the same time I'm going to try to reduce the amount of water that can come through. I've not yet fully decided on the design for that, but it will include an extra strip of wood on the cabin sides above the boards to hold them down better, maybe with soft neoprene in the back of the slot. I'll improve the fit to the mast beam, and probably have separate little boxes there to contain the halliards when the sails are up.
Hi Matthias, many thanks for the interesting information in this thread.
I owned a Tiki 26 10 years ago and remember a few times being spooked by the way she was squatting down .I even went looking for water in the aft bilges even though it didnt make sense.I also experienced quite serious hobbyhorsing in seas that I didnt think were rough enough to produce the effect I was experiencing.I thought about ways to reduce this and like you, considered a horizontal hull surface at the rear of the boat.However due to work commitments at the time I sold the boat.
I now have another tiki 26 project on the go and a little while ago went over this problem in my head.However I had finished the major work on the lower hulls & didnt want to give myself even more work.I was also worried about the extra surface area drag if I added some sort of fin. So it is really good to know that the winglets are not slowing you significantly .I think I will do something about this problem, but maybe not before I launch .
I am also considering a sprayhood. I have had different ideas & at the moment I am wondering about a hood at the rear of the cockpit.But I have to build a cockpit first! I would love to see pictures of the sprayhood you made if you have any.
I need t search my picturestorage for the sprayhood pictures.. I have basically one that starts at the mastbeam and covers the whole cockpit from side to side, there are two stainless rods that are folding down to the upperside of this beam and the roof of the hulls, just next to the cockpit. In the middle where the mast is I put a zipper, and the rwo stainless tubes have a removable middle part a bit longer then the mast diameter so I can put the sprayhood flat on the beam and leaving the mast clean. There is an also an opening in the sprayhood for the mast which can be closed nearly tight when the sprayhood is up. So quite a complicated setup but for a couple of reasons:
1. I wanted the sprayhood to start with the front of the mastbeam, so all water flying from there would be stopped
2. I have all anchoring gear and ropes for mooring etc in a box filling the front of the cockpit, as high as the benches on the side, so I needed to leave that accessible, and I must be able to bring the anchors to the front beam.
3. I changed the cockpit even more having a second bench going from side to side, where I store the drifter, spinnakers and which is the second base of point 4.
4, When anchoring, we put a simple igloo-styled tent in the cockpit, with very comfortable mattrasses :-) ,for doing so, the cover of the front anchoring storage has a doubled and hinged top which folds to the middle box and forms a platform on which we can put the tent.
5. In case of high wind, storm conditions I wanted to be able to get no additional windage, so folding down was imminent.
6. The sprayhood had to be big enough that the one on watch while sailing at night could laydown covered from wind and wetness,
There where other facts to be consideres like: the foresails sheets must run free of the sprayhood, and there must be enough room for the mainsail.
The result is quite pleasing for us. It did take about a week to fabricate this thing on place in greece with a lot of trying, measuring, restitching etc. I used a simple sewing machine and a much to small camping table for sewing, which made it even more of a p.i.a. :-)
So in my last years summersailing blog at www.mutius.weebly.com at the earlier posts there are two or three pictures showing the results...
Sorry for being so long
I have long storage pockets under the sidebenches, about as deep as the cockpit hangs, made out of trampolin material, thats where we store everything that can get wet, is wet (snorkeling gear, hooks and paddles for the dinghy etc ) plus the water jerrycans and the fuel supply for the outboard engine. Its nice, to never put such wet stuff in one of the hulls :-)
Sometimes waves slam in the front of these storages, with water coming out under the benches/boards and flooding the space under the sprayhood...
This one is shorter :-)
about hobbyhorsing, I think it is helping quite a bit, but it is not eliminating the problem. On the other side I think that under severe hobbyhorsing conditions, like when going under engine against waves of 75-150 cm, the winglets might add some stronger drag, simply because they are moving more up and down through the water then observing a longitudinal flow direction.
Best wishes, Matthias
Thanks Matthias, that's interesting. I hadn't thought of making the storage pockets out of trampoline material but it makes a lot of sense. It would certainly keep the weight down.
Thanks for an interesting topic. I am curious if you considered fitting the winglets onto the rudders themselves - there is quite a discussion at Sailing Anarchy at the moment on doing this on beachcats. Also, when you experimented with less of an angle of attack, was there still a benefit in pitch control (hobby-horsing)?
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