Fins also called skegs are the engine under water, boards are the engine on the water and the sail over the water. Fins are a key element in the entire equation that were ignored in the early days of the longboard. They used to have a U.S. box connection where the placement of the fin was slightly adjustable. Those connections are also called Chinook or A-box. Now most fins go into the tuttle or power box one way and one position.
There are giant formula fins like in this image. Rarely have I seen such flex or asymmetry on land...Other fin types are free-ride, slalom/free-race, weed, wave, bump n jump and freestyle. Perhaps I missed some ? What sets types apart ? The obvious factor is length and is often cited as the measuring stick. Fins or foils as I like to call em have MUCH more character than that !! There are factors such as width {top and base}, area, thickness, rake (angle of attack) and material (carbon, G10, etc) which affects flex and stiffness. Just recently discovered that Fanatic boards use GFK fins. What's that? Craig Gerntenbach of Fanatic informs me these are just "moulded polyester fins, with good twist characteristics". Length and shape together make up the type of fin more than anything quickly visible.
What are the fin "parts" really called ? check here: http://www.vmgblades.com/learn/fin-parts/
Oh yeah! They come in ALL shapes n sizes.
Here's a couple of pics showing the "rake" on the fins, straight up n down 53 cm race vs 47 cm weed vs 40 cm slalom:
What are the fin "parts" really called ? check here: http://www.vmgblades.com/learn/fin-parts/
Oh yeah! They come in ALL shapes n sizes.
The most bizarre is the hydrofoil.
See in this video, just how much fins actually "flex" while in the water:
Just as sails have ideal wind ranges, so do fins... In other words it is important to match board, sail and fin for the conditions and the type of sailing one is about to do. I call this aligning the engines :-)
Lately wave sailors have been using boards with two (2) and even four (4) fins. So, once again we are off to new horizons :-) Locally I have NOT seen any dual or quad fin setups and personally know just enuff about the single fin. Suggest you look elsewhere if u r lookin 4 info on dual or quad fins - sorry mate. However, here is an interesting discussion on quad setups by Keith Teboul: http://www.vimeo.com/17300703
Last year, 2010, the water was extraordinarily low here and as such, there were many board and fin repairs in the area. My fins took a beating and I like to try n fix my stuff myself. Fin repair happens in the off-season, but this was the first year where a light sanding was NOT enough. After searching the web and writing on a few forums, I tried and like Marine-Tex. Bit of a pain to apply and one must discover the trick of sanding it wet. This makes me wonder, will it be susceptible to damage when wet ? :-) time will tell...
Personally have a long 53 straight up race stiff fin for my 10-oh sail. The 47 weed fin does well for the 8.5 and gets used for the 10-oh as well. A 40 cm slalom fin is my ticket to fun with my 7-oh. Fin suppliers now have charts for sailors to choose fins. Nowadays board width is a factor in fin selection as well. My personal fin favorites are Select Fins - they are known to whistle at high speeds - just sand one side of the back edge of the fin. Custom Fins exist that are very specialized -- like the Black Projects Fins which has specs like 40, 45 or 50 knots !!!! Wolfgang Lessacher makes world renowned fins and will ship. Check www.designlessacher.com
In the past people changed sails to change things up. Now people are realizing the fin is just as important. Personally have one fin for each sail. Cannot be bothered having more than one weed fin, but this may become a factor when I get into the smaller sail sizes... Here's a picture from the WindSurf Magazine of July 2002 giving a fin overview. As you can see, there are lots of shapes and sizes, all with their special purpose and special function(s)... 
Believe the following chart was taken from the Select Hydrofoils website showing relationship between board width, fin sizes and sail sizes:
Surprisingly the 7 or 8 degree angle or rake on the race 53 and the slalom 40 do not seem that different !! The weed fin seems to have a rake of about 40 degrees. Some are advertised at 45 degrees for extreme weeds.
Just found an article in the July 2006 Windsurf Magazine with Gonzalo Costa Hoevel. He calls choosing fins a 3 step system. Step one is about board analysis. Ironically he says to put planing fins on the faster boards and faster fins on the early planing boards. He says the early planers have straighter outlines and need fast fins with some rake, small tip area and less flex or more stiff. The faster boards are "rounder" and he suggests power fins or early planers. These fins have less rake/angle (more straight up n down), more area in the tip and softer flex. The video of the fin above and the formula bent fin for me seem to exhibit a lot of flex. Step two for Gonzalo is assessing your goal and step three is knowing your fins. He says the softer fin gives more "kick" or "lift". Upright means planing AND upwind control - like a keel. The profile or thickness plays a factor as well. He states "A fin with a thicker foil gives you more power, upwind angle, but sacrifices top speed. A thinner foil gives you better top speed, butt in lighter winds you lose early planing and upwind angle. A fin that has the thickest point of its foil forward creates a smoother, more controlled riding sensation. Moving the foil back gives you more speed, but it's a more technical-riding fin - especially when going upwind." He also mentions that people overlook area of a fin and compares this to only analyzing sails based on luff length !! Here is a video that covers some areas regarding windsurf fin physics. They actually are saying that at over 40 knots pressures cause water to boil at room temperature !!
Fins are usually made with hi-tech components and are precise pieces of equipment. As such, they do NOT give them away. I have about one fin per sail and they are about $200 each. Some people also have overlap since they may require weed fin(s). Used fins are closer to $100 each and can easily be repaired with Marine-Tex. Just remember to sand wet. Here's a good link with everything you wanted to know about fins, butt were afraid 2 ask: http://www.carbonsugar.com/design/everything-you-should-know-about-fw-fins/
Wrote to Roger Jackson of Starboard about undersizing fins and this is what he said:
Hi Joe,
You are underfinned if when you reach top speed and "push" laterally across the top of the fin it lets go and spins out.
My personal "rule of thumb" for fin length is the fin has to be greater than 1/2 the board width or OFO width.
The wider the board and the greater the footstrap off set, the more the 1/2 board width applies.
On a Futura or other freeride board with inboard and outboard footstrap positions, you can generally run a smaller fin (perhaps < 1/2 the OFO width) with the footstraps in the closer to centered positions.
The smaller fin (or underfinned) also depends alot on sail size and overall board speed.
I have really tiny (<25 cm) speed fins that are great if you can head off wind and get them up to > 25 knots board speed.
At 30 knots + board speed they are solid as a rock, but if you have conditions where you can't get them up to speed, you can push them loose any time you like if your speed is < what it takes for these tiny fins to "hook up" and stay hooked up.
Hope this helps,
Roger
What are F4 fins? {note to self}
Just found an article in the July 2006 Windsurf Magazine with Gonzalo Costa Hoevel. He calls choosing fins a 3 step system. Step one is about board analysis. Ironically he says to put planing fins on the faster boards and faster fins on the early planing boards. He says the early planers have straighter outlines and need fast fins with some rake, small tip area and less flex or more stiff. The faster boards are "rounder" and he suggests power fins or early planers. These fins have less rake/angle (more straight up n down), more area in the tip and softer flex. The video of the fin above and the formula bent fin for me seem to exhibit a lot of flex. Step two for Gonzalo is assessing your goal and step three is knowing your fins. He says the softer fin gives more "kick" or "lift". Upright means planing AND upwind control - like a keel. The profile or thickness plays a factor as well. He states "A fin with a thicker foil gives you more power, upwind angle, but sacrifices top speed. A thinner foil gives you better top speed, butt in lighter winds you lose early planing and upwind angle. A fin that has the thickest point of its foil forward creates a smoother, more controlled riding sensation. Moving the foil back gives you more speed, but it's a more technical-riding fin - especially when going upwind." He also mentions that people overlook area of a fin and compares this to only analyzing sails based on luff length !! Here is a video that covers some areas regarding windsurf fin physics. They actually are saying that at over 40 knots pressures cause water to boil at room temperature !!
Fins are usually made with hi-tech components and are precise pieces of equipment. As such, they do NOT give them away. I have about one fin per sail and they are about $200 each. Some people also have overlap since they may require weed fin(s). Used fins are closer to $100 each and can easily be repaired with Marine-Tex. Just remember to sand wet. Here's a good link with everything you wanted to know about fins, butt were afraid 2 ask: http://www.carbonsugar.com/design/everything-you-should-know-about-fw-fins/
Wrote to Roger Jackson of Starboard about undersizing fins and this is what he said:
Hi Joe,
You are underfinned if when you reach top speed and "push" laterally across the top of the fin it lets go and spins out.
My personal "rule of thumb" for fin length is the fin has to be greater than 1/2 the board width or OFO width.
The wider the board and the greater the footstrap off set, the more the 1/2 board width applies.
On a Futura or other freeride board with inboard and outboard footstrap positions, you can generally run a smaller fin (perhaps < 1/2 the OFO width) with the footstraps in the closer to centered positions.
The smaller fin (or underfinned) also depends alot on sail size and overall board speed.
I have really tiny (<25 cm) speed fins that are great if you can head off wind and get them up to > 25 knots board speed.
At 30 knots + board speed they are solid as a rock, but if you have conditions where you can't get them up to speed, you can push them loose any time you like if your speed is < what it takes for these tiny fins to "hook up" and stay hooked up.
Hope this helps,
Roger
What are F4 fins? {note to self}
