A Photo & Discussion Forum for Wharram Design Enthusiasts
I'm wondering if anyone has had any experience with using vortex generators on a Wharram. I've been reading the early editions of Seapeople http://pca-seapeople.net/SeaPeople-009.pdf and the occasional reports I've read speak of significant improvements in tacking angle, speed and ease of tacking. JW has a basic design in the above magazine. I'm a bit skeptical, if the performance improvements are so good why don't we see alot more of this type of appendage, hence the question. Everything is fine in theory but I'm really interested in the practical application.
There are "vortex generators" fitted to the bottom of the tangaroa I have .. unfortunately i'm not in a position to give a before and after opinion on their efficiency however the "science behind the is the endplate effect similar to the wing tip winglets on modern airliners to reduce the size of the tip vortex on a foil and hence reduce the drag rather than increase lift. I suspect that the effect on a wharram hull is to place the vortex drag generated by the hull which is in effect a very long and shallow wingtip to a single point at the end of the flat plate rather then spread right along the after part of the hull as a large and turbulent eddy .. less drag more speed .. more speed more efficiency of the hull as a foil .. the more efficient the foil the lessening of the angular difference between the sails and foil therefore the closer we get to the number 42 (hitchhikers guide to the galaxy)
perhaps I should have looked at the attatchment first .. it would have saved a lot of typing ... what he said!
Bernd Kohler's article makes very interesting reading, but (as a Pahi owner) I was a bit puzzled by the statement that these wings wouldn't work on these hulls? The slight curve in the hull is at or above the waterline, so surely the effect would be the same as for a simple V-shaped hull? I have removed the dagger boards anyway on my Pahi 42, and still have reasonable windward ability, but I am interested to try out these antivortex plates. Hanneke told me that the dagger boards are meant for balancing the rig rather than for windward ability.
Presumably the forces on these plates are quite high, so what type of construction is recommended? Anyone tried plates like in Bernd's article? (Triangular/Delta shaped wings)
Hi gentlemen, many thanks for the comments.
Andy I also found Kohler's article interesting but not necessarily useful for Wharram owners hence the reference to the article in Seapeople #9 (link in the 1st post). On page 18 is an acticle and drawings from James that might be appropriate for your Pahi hull shape. There is also an interesting article by Tim Whelan on pages 16 & 17 who fitted them to a Narai Mk IV. See attachment.
I own a Tiki 30 which I sail in Singapore. I'm one of those who gets great pleasure from sailing a boat well to windward, downwind without spinnaker's or broad reaching is realtively boring and the Tiki 30 does sail very well to weather. If, however, I could improve tacking response and reduce leeway, as Tim's article suggests, then I'd be even happier. The area we sail has minimal wave action, wind waves only, but does have significant tidal flow. I'm planning on the next 6 months establishing some base line measurements in different wind speeds, with sea & tide as similar as possible, then fit the vortex generators and repeat the exercise. We seldom get breeze above 15 knonts so I won't get any information of the effect in higher wind speeds.
I'm planning a larger Wharrm retirement live aboard and am using the 30 as an experimental platform prior to building the bigger boat. Hope I'm not infringing copyright?
Hi - yes, the comments from JW really sum it up - test it out and compare before and after! I don't think I have time this spring to fit these plates before we lift into the water, but maybe this is a project for next winter.... From the diagram above I'd go for option B, seems the best for retro-fitting. Apart from the actual forces on the plate when sailing I realised that one also has to be careful about lifting straps - they are going to put a huge strain on the plates, or else I make them short enough so the straps go around the hull just outside the plates.
As we are mainly sailing here in Finland in the archipeligo, tacking and pointing ability is vital, so any improvement is worth the trouble. I'll certainly be looking into this further!