Annular wing surfboard fin story part 2:

continued from part

Yesterday we asked how one should compare the lift and drag characteristics of annular wings and flat plane wings, mentioned that they are typically compared only according to their planshape area, and suggested that this can lead to some misleading conclusions.

It's like this: when measuring the planshape area of an annular wing one is not measuring the true size of the wing. . .. . unlike a flat plane wing, where the planshape area captures accurately the size of the wing.

For example a rectangular flat plane wing with a span of ten inches and a chord length of 4 inches has a total area of 40 square inches, whereas a circular annuular wing with the same span and chord length has a total wing area of 128 square inches and a half pipe annular wing of the same diameter has an area of 64 square inches.

This becomes interesting when we see that the official word on annular wings is that they produce less induced drag, but more skin friction drag. Then the conclusion is drawn that because skin friction drag increases with speed while induced drag reduces with speed that therefore the annular wing is only suitable for low speeds.

That is the erroneous conclusion. . . .. . . it is erroneous because they compare wings of two different sizes. . . . and bigger wings have exactly the same properties which they describe: Less induced drag at low speeds and higher skin friction drag at high speeds.

Now a bigger wing also produces more lift, so if my contention is correct then we should expect that the annular wing being compared should also produce more lift than the flat plane wing, simply because it is bigger than the flat plane wing which it is being compared with.

Is this the case? Does an annular wing of a given span and chord lengthproduce more lift than its flat plane equivalent ? Yes it does, but this fact has been carefully hidden in the literature on the subject.

Ok, so how is it that this has happened ? What has been done is that during comparisons the angle of attack of the annular wing is lowerd until it produces the same amount of lift as the flat plane wing. At the same angle of attack as the flat plane wing,the annular wing would produce more lift, so they simply lower the angle of attack in order to hide this. Since annular wings operate at lower angles of attack than flat plane wings anyway, this trickery is effectively hidden .

There are several consequences of this lowering of the angle of attack of the annular wing during comparison:

1) The fact that the annular wing is simply bigger, is hidden.

2) The induced drag of the annular wing is lowered, this would be the case with a larger flat plane wing also ( when the angle of attack is lowered so is the induced drag and the lift.


So in order to make comparison with a flat plane wing in this case we need to choose an annular wing with a smaller diameter and the same surface area. Doing so will mean that the annular wing has the same skin friction drag at high speeds as the flat plane wing, and thus will have no disadvantage at higher speeds.

One might argue that in terms of lift the annular wing is effectively only as big as its planshape area, so therefore it is correct that it is compared on that basis. That is not correct however, as the evidence shows that the annular wing produces more lift than its planshape area suggests. . . .. . the total wing area contributes to lift because the wing is an enclosed tube.




A related subject which we will deal with tomorrow is that of fin size generally ( not specifically annular wing size, but all fins ) :

At a first glance it might appear that small fins are better for high speed and large fins are better at low speed, due to the fact that large fins produce more skin friction drag and that this increases with speed, whereas at low speed they have less induced drag . .. . . and since induced drag diminishes as speed increases the induced drag advantage is lost at high speed .

The answer is ' Yes for aircraft but not necessarily in the case of surfboards'. . . . . . . .. ..

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Surfboard fin guide part 3: The fin/surfboard junction

Every piece of research we have seen on this subject has come to the same conclusion: The fastest fin/ surfboard junction is a half round fillet at the base of the fin with a diameter of between 2mm and 5mm, not bigger, and not smaller.

Here are some fins with base fillets of 2 to 3 mm:





That's how we do it. . . the right way !

Why? Because when one strives to do the best job possible, every detail counts.

Today not one even one board in 20 million has the fin/surfboard junction done this way, they are almost all either fin boxed fins which have no fillet plus drag inducing gaps, holes and screws interfering with the water flow, or 'glass on' fins which have monstrous 'slow down' fillets many times bigger than the optimum . The manufacturers of these boards don't have the 'right stuff' . . . instead of making the improvement they would rather indulge in addle brained apologetics, in the hope that customers will swallow the hype and just keep on buying the sub optimal product. . . and of course they nearly all do.

This should sound familiar, as it's the same tactic used to sell the fins with flat spots and bumps in the base: " Shutp and eat your potatoes johhny if it's good enough for kelly Slater it's good enough for you " . . .. . and maybe it is but it isn't good enough for us !

Now, how much difference does all this make in terms of drag ?

The Annular wing fin story part 1 : Why does this alaia board have a tunnel ?

Because they feel good


It's the experience !



We have lots of technical mumbo jumbo on the subject of annular wings, including the reason why the hydrodynamic and aerodynamic establishment are sometimes unable to understand them properly: Just how does one compare a semi circular or circular wing with a flat one? Do we compare wings of the same planshape area? Or do we compare wings which produce the same amount of lift in a given situation? Perhaps we could compare wings which have the same surface area ? The establishment tends to do the first i.e they compare flat and annular wings of the same planshape area. . .. . that leads to some misleading conclusions which have kept annular wings in relative obscurity , as we shall see. . .

A metallica inspired poem from Surfer Dave

. The Thing That Should Not Be

Messenger of trim in sight
Dark paulownia filled outline

Hybrid children watch the sea
Pray for TomBloke, roaming free

Fearless Wretch
Insanity
He watches
Lurking on the high sea
Great Old One
Forbidden site
He searches
Hunted 13 footer is rising

Immortal
In madness You dwell

Crawling Chaos, undergunned
Cult has summoned, twisted crowd

Out from website once possessed
Banned for life, for rounded fins

Fearless Wretch
Insanity
He watches
Lurking out to sea
Timeless sleep
Has been upset
He awakens
Hunter of the Pipeline is rising

A message from M in Taranaki re. the Nugget

" where is the creator of such fine surf crafts?

id like to publicly thank the crazed hippy. after four or five months of ownin one of his masterpieces im more than stoked to say the man is a genius. still waitin for a sick day at the groyne to test its bazza ridin capabilities but otherwise she has defo proven her worth.

iv had nothin but stoke from otha naki surfers about it. most reckon it should be hung up on walls. then they see the oldskool styles i display on it and there like 'cool man i dig your groove'. actually a quote from one guy was 'everyone should have one' and i agree.

anyway

CHEERS ROY. KEEP THE STOKE. "

The flatboard method of surfboard construction

As can be seen by our construction pictures, Power surfboards use a flat board system of surfboard construction whereby flat panels are made and then bent and laminated together on a rocker jig, in order to get the desired bottom and deck curves. The system is excellent in every respect

We have been using the flat board method of surfboard construction since May 1995, and as far as we know we were the first to build surfboards using the method.

Since then, and in our opinion due to our promotion of the system on Swaylocks.com the method has been adopted by Sunova surfboards (post 2004) Firewire surfboards, and Mike Sabin surfboards.

Due to requests from a compsand.com member we have refrained from talking about how my flat board method has been used in compsand construction. . . . . apparently it is supposed to be a secret.

The reason why we are mentioning it now is that we have heard that a patent for a version of flatboard construction is in the pipeline, and want to stake our own claim to the genesis and ownership of the flatboard method which we use.

We realise that the flatboard method used by some compsand.com members, and by Sunova and Firewire differs from my own in that one of the flat boards is tapered prior to bending the boards on to a rocker table, and by the use of EPS and other foams instead of framed wooden panels. Nevertheless the system is based on exactly the same principles which we have been using and have publicising since 1995.

If in the future we decide to use EPS panels in our parallel profile surfboards, then we will do so, as we invented the system independently 14 years ago, and have the right to do it if we want to.

Some credit must go to Reuel B Parker of Parker Marine Enterprises, whose book ' The new cold molded boatbuilding' probably inspired my flatboard system even though we weren't conscious of the connection initially.

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Surfboard fin guide part two: TheEmpire fights back on the flat foils

The surf industry people at surfer magazine decided to ban 'Tom Bloke' from their surfboard design forum for mentioning that the vast majority of commercially available fins are incorrectly foiled as they have flat areas in the fin base, and that they are thus sub optimal equipment often nonetheless marketed as the best available.


In response to the truth about fin foils pointed out by 'Tom Bloke' on their forum we have a rather garbled and badly thought out answer to the flat fin problem posted by Shawd DeWitt from the Rainbow fin company. Here are the main points made by Mr DeWitt, in defence of the fact that all the Rainbow fin company fins have flat areas in the foil:

1) It is too expensive to foil a fin correctly:

" To make a perfect fin in it would more than double the foil and finish time and would add $15-$20 to the retail price of a tri set. "

2) Flat spots don't matter because the Earth looks flat when we are standing on it, and water doesn't care about flat spots:

"Water does not know or care about flat spots.
The earth is round but where we are it looks flat."

3) Fin makers make the best foils for all conditions, fin makers make fins with flat spots, therefore flat spots are ok.
"The foil that fin makers put on their fins is what works best in all conditions."


4) Shawd uses fins with flat spots himself, so it's the right thing to do
"Every fin that goes on my board comes directly off our shelf."

5) An attempt at the 'pro surfer use them so they must be ok ' argument. . . except that he seems to forget that he is talking about flat spots in fins

"If a fin foil being perfect was important then no pro surfers would use glass ons".

The rainbow fin company have made over one million fins, which, according to what Mr DeWitt is saying, all have incorrect foils with flat areas.

Here's a Rainbow fin with the typical inefficient flat area at the base, the good news is that Mr DeWitt claims that the error can be fixed for only $15 to $20 per set.. . . . if all the million Rainbow fins with flat zones are sent in for correction then that's $20,000,000 worth of fin work for the rainbow fin company. Do your bit to support the USA surf industry in these difficult times for them, by getting your fin foil corrected.

Perhaps they will even fix the flats in all the FCS fins !



As expected, all the 'arguments' in defence of poorly foiled fins with flat zones used by Mr DeWitt can be found in our list of bad arguments used by the surf industry in defence of flat fins over here . . . . .. . all except the 'Earth isn't flat, but appears to be from over here. so flat fins are ok' argument quoted above. . . .. that's a new one !


Quotes are from this surfermagazine thread entitled "Flat spots on fins"

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The final touches on the 12'9" Makaha model

Prout paipo board

Here's an interesting Prout bodyboard from the late 1950's or early 1960's

It's 4'1" long by 11" wide.

We have been thinking of making alaia boards with some nose rocker built in, so it was cool to see this old model, which is for sale at present on Trademe in New Zealand

Surfboard fin guide Part One: The flat spot

When buying or making a surfboard fin, most people just want something which works ok and looks the part. If however one wants a perfect or as near perfect a fin as possible, there is one bad foiling fault which should be avoided.

This foiling error is the Flat Spot. Here is an example of the flat spot on a fin:

As can be seen from the photo above, there is a large triangular area at the base of the fin which is flat. In this area the cross section of the fin will not follow a smooth underwater foil shape, but will instead have a flat sided shape with hard corners or bumps. Water flowing around this area of the fin will become turbulent, causing drag, slowing the board down and possibly even causing cavitation and 'spinning out' when the fin stalls due to the water flow separating from the fin

The fin above is from a major well respected Californian fin manufacturer. This might seem surprising, but the fact is that the vast majority of surfboard fins, including those from the world's 'best' fin makers, all have the hydrodynamically incorrect flat spot. It is almost impossible to find a correctly foiled fin, although they do exist.

The flat spot syndrome has become so entrenched that surfboard buyer's guides even show fin foil diagrams which supposedly show the buyer how a fin should look, but which are grossly incorrect. Here's one such example from a popular surfing website, diligently pointing newbie surfers in the wrong direction:
The truly ghastly foil shown above actually represents a rectangular foil section at the base of the fin. Rectangular fin sections are basically unfoiled pieces of fin panel, and are like towing a bucket in terms of drag.


Here's the same diagram, corrected somewhat in the fin base area by ourselves:


Here's another example of a poorly foiled fin from a supposedly leading USA fin retailer, the contour lines in the glass panel reveal quite clearly that a nearly flat spot extends half way up the fin:



And here's another example from one of the ( currently) most revered surfboard manufacturers of the moment. This fin is very nicely foiled, except in the base area, where the contour lines reveal a bad flat area with associated lumps and corners. . . this time the error has been kept to the base of the fin and hasn't gone halfway up the fin as it usually does. It seems likely that the fin maker is aware of the problem and has tried to avoid it to some extent:


So, why do fin manufacturers make these inferior fins?

There are several answers:

1) Because that's the way they have always done it, and if the fins sell, then the manufacturer has accomplished his goal.

2) They don't know any better, and don't want to improve.

3) Because in the case of fins with tabs for fin boxes ( which make up most of the fin market these days) it is tedious and difficult to foil the fin correctly when near the fin tabs. . . . so they simply don't bother, knowing that the marketing will sell the fin rather than the quality of the foil section.

4) There is a race to the bottom in terms of low price and cheapness of manufacture, and the market won't support ( they assume) the cost of a well foiled fin, which can take 3 or 4 times as long to make, at least. It is more effective to market the fin as the best and then fail to deliver. .. most people won't know the difference

5) The Gumby with a rotary disc grinder factor. Most fin foilers use a rotary grinder or disc sander, and armed with these tools they make a few passes alomng the leading and trailing edges of the fins, this makes a parallel band and inevitably leaves an unfoiled piece at the widening base of the fin. . . . the rotary sander doesn't reach the middle of the fin, and so instead of using another tool to finish the job properly the fin is left unfinished. . . if the job takes longer than 20 minutes it's a no go.


Here are badly foiled quad fins from a foiler with over 40 years experience, it wouldn't pass in the Americas Cup, so why does it in the surf industry ?

It is often assumed that those who have been doing it the longest have learnt the most and that therefore they do the best job. In fact, repeating the same mistake for decades does not improve anything.



To be continued. . . . ..

The 'lightbulb' 5-11 tunnel finned hollow wooden surfboard

Finished !

It's fast, handles well, and the fin holds in nicely.

Replacement fin for the FP 13 in Hawaii

The new Black Patu fin was picked up by NZ Post Express courier at 1:06 PM today, a fateful moment in the history of surfing.


We celebrated by going surfing at Clyde St, the second session on the new 12-9 Makaha. The Makaha and I rode about ten waves all the way to the beach, I noticed when paddling out after each ride that I couldn't remember the ride right after it happened. . . . this is a definite sign that it was going well, as it is evidence that the instinctive Lizard mind is ruling. We like that, but it doesn't make technical report fodder.

New fin for the Future Primitive board in Hawaii

Here's the new fin, ready after 3 days and nights of intense work. This one is definitely not going to snap, it's very strongly built.

The parcel with the new fin is on its way via Express courier, eta 2 to 4 days. . . we hope it's two days as there's a big swell due soon

Garrett McNamara rides the 13 foot 'Future Primitive' surfboard at Pipeline

Yesterday Garrett rode the big board at Pipeline in 4 to 5 foot ( Hawaiian ) waves, and got tubed on two waves, one on a left and one right hander at backdoor. He is very positive about the boards capabilities, and is now looking forward to riding 2nd and 3rd reef pipeline on her . Thanks Garrett !




Photo seandavey.com






Unfortunately the board lost the fin, which had been cracked at the base for several months, and repaired. We have been working full time to make a new fin ( with more robust glassing ) it is nearly ready and will be sent on the express courier two days from now. Bill Ward from Haleiwa has generously offered to arrange for the new fin to be installed, thanks Bill.

Here's the new fin under construction today, it's identical to the original fin except that we are using stronger cloth and have improved the wood layup.

12-9 Makaha ride report

We were expecting the cyclone swell to have come in, but were too early so the waves at Clyde st were marginal. . . . . waist high and weak to the point that the few surfers out were not really getting any rides at all. In spite of this, armed with the new 12-9 I was able to catch at least 20 waves, most of which gave a long ride to the beach. The board catches waves like a dream and is utra smooth to ride, I caught every wave I paddled for except one.





The swell should be a lot bigger on Monday so we look forward to riding the board in some more powerful waves.

First surf on the new 12'9" Makaha

. . . . will happen tomorrow, there's a cyclone swell starting to show on the East Coast so we'll head over to Mount Maunganui for a dawn session

Hopefully we'll get over 40mph on a head high wave, or at least 30 anyway. The gps units and cameras are ready to go, the bottom of the board has been sanded fore and aft with 600 grit and polished with coconut oil, and the board is waxed up with two bars of Northern Light organic boardwax.

Deck and bottom panels for the new Future Primitive 12 footer

We decided to build another Future Primitive 13 footer, and after having built the first frame panel I kept thinking that it looked like a rather small board, almost like a shortboard.

Anyway it turned out that I had pulled out the template for the original 12 foot version from 1997.

It's all good though as the 12 footer is such a great board, and is way 'looser' than the 13.

Here's some edge gluing of planks action, with plank edges untouched since they left the mill rough sawn 5 years ago :

". . 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

Tunnel fin with FCS fin box tabs

Paulownia, epoxy resin, and stainless steel: