A free spitfire cutaway surfboard fin template

Here's a free spitfire fin template suitable for mid sized longboards from 9 to 11 feet long, it can be scaled up and down for shorter and longer boards.

Olo of the Sun 19 foot surfboard , Spitfire cutaway fin, adding tubercules

Tubercules being added to the Olo of the Sun's spitfire cutaway fin:

Tuberculed cutaway spitfire fin, simplicity vs complexity and the myth of Occam's razor.

Here's the tuberculed cutaway spitfire fin resin coat with the second resin coat.

Recently a critic of the tuberculed fin ( Our friend Mr Black from the 'Surf a Pig blog http://surfapig.blogspot.com/2010/07/tubercules-and-other-gimmicks.html  ) complained that it is overly complex and that simpler solutions are better, in an attempt to apply Occam's razor to fin design.



It was suggested that this ( very nice ) fin is simpler:

The concept of simplicity is however problematic as it's impossible to determine what is simplest. Such judgements are arbitrary. There's no evidence to support the idea that simplicity is more efficient, and in fact simplicity is a very complex and problematic concept to use as it is impossible to know what it means in practice.



From Wikipedia:



"  When scientists use the idea of parsimony, it only has meaning in a very specific context of inquiry. A number of background assumptions are required for parsimony to connect with plausibility in a particular research problem. The reasonableness of parsimony in one research context may have nothing to do with its reasonableness in another. It is a mistake to think that there is a single global principle that spans diverse subject matter.[10]

 As a methodological principle, the demand for simplicity suggested by Occam’s razor cannot be generally sustained. Occam’s razor cannot help toward a rational decision between competing explanations of the same empirical facts. One problem in formulating an explicit general principle is that complexity and simplicity are perspective notions whose meaning depends on the context of application and the user’s prior understanding. In the absence of an objective criterion for simplicity and complexity, Occam’s razor itself does not support an objective epistemology.[9]

The problem of deciding between competing explanations for empirical facts cannot be solved by formal tools. Simplicity principles can be useful heuristics in formulating hypotheses, but they do not make a contribution to the selection of theories. A theory that is compatible with one person’s world view will be considered simple, clear, logical, and evident, whereas what is contrary to that world view will quickly be rejected as an overly complex explanation with senseless additional hypotheses. Occam’s razor, in this way, becomes a “mirror of prejudice.”[9]

 

It has been suggested that Occam’s razor is a widely accepted example of extraevidential consideration, even though it is entirely a metaphysical assumption. There is little empirical evidence that the world is actually simple or that simple accounts are more likely than complex ones to be true.[21]"





http://en.wikipedia.org/wiki/Occam%27s_razor

Cutaway spitfire fin for the Future Primitive 12 foot pintail

Some preliminary foiling, the fin is 12 inches deep by 3/4" thick, 6 layers of paulownia

". . a board is born from the flames. "

A new 7'9" Island Rocket built by Rosan to olosurfer plans in Okinawa.In the designer's opinion the Power Surfboard parallel profile constant rail section system is the Haiku of surfboard design.Once initiation is achieved one realises that the strict rules of the parallel profile system are actually liberating

Hollow wooden Nugget single with spitfire fin ready to go SOLD

Black graphite Power Surfboard spitfire fins have been called 'Patu' fins because they resemble the Maori war club of that name. This one is laminated paulownia glassed with thick blue Swanndri wool and epoxy resin. The Swanndri wool is equivalent in thickness to about 4 or 5 layers of 6 ounce fibreglass cloth.Here's the wee beastie all polished up with beeswax polish and ready to enter the water:The 4mm diameter fillet at the base of the fin can be seen here. The most hydrodynamically efficient fillet for a surfboard fin is between 2mm and 5mm in diameter, this can only be acheived if the fin is set into the board rather than glassed on.The small cutaway at the fin base improves the holding tenacity of the spitfire fin.Theplanform of the spitfire fins is the most efficient flat plane fin shape in existenceThe 'Spitfire' fin is based on the wing of the Spitfire WW2 fighter plane. We were the first to apply these fins to surfboards in 1995, and advertised them as Spitfire fins. Now there is another company ( Revolution surf) doing Spitfire fins, but we were the first by 11 years.The story with the Spitfire fin is that it has the lowest induced drag of any fin or wing planform, essentially this means that it has less tip vorteces and a better lift/drag ratio than other shapes. It is the fastest most efficient flat plane non twisting wing planform possible.It is interesting to note the turning characteristics of the spitfire compared with its rival the Messerschmitt 109. The ME109 with its narrower linearly tapered wing had a tighter turning radius than the spitfire, but the spitfire had a higher turn rate. In other words the spitfire could maintain such a high speed during the turn that it would complete a 360 degree turn before the ME 109 even though it travelled through a larger turning radius. The closest surfboard fin to the ME109 fin is probably the wavegrinder.Another characteristic of this fin other than low drag and its ability to maintain high speed through turns is its benign stall characteristics . When the Spitfire fin starts to stall it does so first near the base of the fin, this makes the onset of the stall predictable and the stall easier to avoid. In comparison the linearly tapering wing like the ME109 or the wavegrinder will give less warning of the impending stall and will basically spin out suddenly and without warning. The spitfire fin does have a higher stall speed though.The characteristics of elliptical planform fins were predicted by the classical lifting-line theory developedby Ludwig Prandtl and published in 1918."The first closed-form solution to be obtained from lifting-line theory showed that in-duced drag could be minimized by using anuntwisted wing of elliptic planform.The classical lifting-line theory developedby Ludwig Prandtl and published in 1918 wasthe first analytical method to satisfactorily pre-dict the performance of a lifting wing. Moreover,until the development of the digital computerin the early 1960s, it was the only analyticaltool available for wing design. Early compar-isons between results predicted from lifting-linetheory and experimental data showed remark-able agreement. Even with modern computa-tional fluid dynamics (CFD) , it is difficult to im-prove on the induced drag predictions derivedfrom lifting-line theory."http://209.85.173.104/search?q=cache:feNokN7nsukJ:www.aiaa.org/aerospace/images/articleimages/pdf/phillipsjanuary05.pdf+spitfire+wing+drag+theory&hl=en&ct=clnk&cd=1&gl=nzBottom line is that they are a very fast fin, with a high speed turning capability and a high turn rate.Goretex vent:

Spitfire-Tunnel fin for the 12-9 Makaha

The fins are shown here with the main Spitfire cutaway fin sitting in its slot and the tunnel fin placed in position, it will actually be a bout 3/8ths of an inch lower once set in to the board.There are 73 pieces of paulownia in the tunnel fin, which is a two layer lamination with a wool/polyester blend cloth in between the laminations. The fin is glassed on the outside with bamboo cloth and the inside is resin coated.Six laminations of paulownia are used in the main spitfire fin, with 36 pieces in total. This cutaway fin has developed from the original spitfire fin to the point where it is hardly recognisable as a spitfire fin, but we still use the name as it is an upright planform fin using ellipitical leading and trailing edges.