tag:blogger.com,1999:blog-4583713304018339582.post4939384454371658617..comments2023-10-12T17:00:57.752+13:00Comments on Harmen’s sailing blog.: Hull asymmetryHarmen Hielkemahttp://www.blogger.com/profile/17685933562845390237noreply@blogger.comBlogger8125tag:blogger.com,1999:blog-4583713304018339582.post-45804114119475418592010-06-23T04:35:01.751+12:002010-06-23T04:35:01.751+12:00Hi Guys:
very interesting post, indeed. I wonder h...Hi Guys:<br />very interesting post, indeed. I wonder how you would incorporate the dimple in a stripe planked canoe like Garys T2 and if the dimple would also be effective on the Amas leeside? <br />Any help?<br />Thank you very much for this highly interesting blog.<br /><br />Best<br /><br />Max<br /><br />max@der-reporter.deAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-4583713304018339582.post-6868611911261554732010-02-10T00:55:19.201+13:002010-02-10T00:55:19.201+13:00Hi Illwind
Sorry you didn't leave me an email ...Hi Illwind<br />Sorry you didn't leave me an email address or a name to reply to.<br />Your catboat would be fine with an asymmetric, pivoting lee board on each side if you want a shallow draft foil.<br />look at the traditional sail boats of the Netherlands for ideas. Lee boards will be relatively easy to build and retrofit.<br />I always admired your catboat designs they remain a favourite of mine.<br />Please don't give up too easily.<br /><br />Hope you read this message.<br /><br />Best<br /><br />HarmenHarmen Hielkemahttp://www.harmen.co.nznoreply@blogger.comtag:blogger.com,1999:blog-4583713304018339582.post-35965290583078084162010-02-08T07:43:24.823+13:002010-02-08T07:43:24.823+13:00We bought a fat catboat with no centerboard. The s...We bought a fat catboat with no centerboard. The seller assured us that a taught line from the bow to a stick held below the transom would provide ample lift.<br /><br />We were too gulible.<br /><br />Wish you would gove us more objective info.<br />Hopefully,illwindnoreply@blogger.comtag:blogger.com,1999:blog-4583713304018339582.post-50285458404276607022009-12-16T13:48:27.363+13:002009-12-16T13:48:27.363+13:00Very impressive discussion. What's the right ...Very impressive discussion. What's the right amount of dimple? Is there a guideline rule of thumb % based on the mid point lee hull offset or some other dimension? <br /><br />timpeever123@yahoo.comTim Peevernoreply@blogger.comtag:blogger.com,1999:blog-4583713304018339582.post-19398011615808578582009-05-07T08:13:00.000+12:002009-05-07T08:13:00.000+12:00Hello Harmen,
I've been looking at the Kiribati h...Hello Harmen,<br /><br />I've been looking at the Kiribati hull shape on the computer lately, for a new project. When you draw the shape without the dimple and look at the area curve (rather than the hull lines), you see a very quick turnover at the centerline from increasing area (front half) to decreasing area.<br /><br />This is a consequence of the "long V" profile of the Kiribati-style underbody.<br /><br />There is considerable drag involved in making such a quick transition, because you are forcing the water to reverse lateral and flow and then accelerate in the opposite direction. The sharper the change in direction of the area curve, the higher the acceleration.<br /><br />On the lee side (high pressure side) of the Kiribati-type underbody, the effect is to force water to flow downwards along the hull, then under the keel- exactly what you don't want.<br /><br />When you use the dimple, this effect is much smaller. The area curve transition is much flatter, so lateral acceleration of the water through the CL transition is greatly reduced, with a consequent reduction in drag, and the waterflow loses much of its vertical component. It stands to reason that better lift to windward would result from less water flow across the keel- which is why the dimple goes on the lee side.<br /><br />This is pretty much the same thing that the "coke-bottle" shape accomplishes for jet aircraft. The effect of the volume of the wings on airflow along the fuselage is to create a similar quick rise and turnover in the effective volume curve of the aircraft, creating a premature shock wave at transonic speeds.<br /><br />John DalzielAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-4583713304018339582.post-64751962519225867942009-04-28T10:54:00.000+12:002009-04-28T10:54:00.000+12:00Been reading up on rudders, and just saw the 'Schi...Been reading up on rudders, and just saw the 'Schilling rudder'. It has a hollow mid section and flared tip (in profile). Is this the same principle I wonder? And the 'Gurney flap'. Both are said to increase lift - thats sounds useful! <br />I also look at Garys latest blog post: Austonesian Sail Types and wonder if the various 'crab claw' sails get some Gurney effect from the spar at the trailing edge, especially say type c?DavePhttps://www.blogger.com/profile/04404681676111443388noreply@blogger.comtag:blogger.com,1999:blog-4583713304018339582.post-90784067158657461542009-04-27T13:53:00.000+12:002009-04-27T13:53:00.000+12:00Harmen, thanks for the lesson! I remember reading ...Harmen, thanks for the lesson! I remember reading a cryptic reference to the dimple in an old J.S. Taylor article, and was always curious about it. <br /><br />Cheers,<br /><br />MichaelProafilehttp://proafile.comnoreply@blogger.comtag:blogger.com,1999:blog-4583713304018339582.post-7058875745134048792009-04-26T02:16:00.000+12:002009-04-26T02:16:00.000+12:00Fascinating! I'm glad Gary ratted you out on t...Fascinating! I'm glad Gary ratted you out on this dimple ;-) I would not have noticed it on the photo, or if I had, I would have disbelieved my eyes and thought that the dimple was an optical illusion. Interesting that the little concepts I learned when I was a technical writer for Pratt & Whitney writing about turbines and rocket engines is often applicable to boats -- but of course, incompressible water is always "in shock". -- WadeWade Tarziahttp://wtarzia.comnoreply@blogger.com