does anybody have a link to a good site that explains what kind of fin does what......
Ive just made a new allglass/carbon fin for my bginners board and the main criteria was simplicity and wont get destroyed when grounding and short enough that the rig wont tangle with it, but Im fascinated to know if all the wierd and wonderful shapes Ive seen are just this years "thing " or if there are certain things to look for in a fin

this is as far as Ive got

Select to expand quote

landyacht said...

does anybody have a link to a good site that explains what kind of fin does what......
Ive just made a new allglass/carbon fin for my bginners board and the main criteria was simplicity and wont get destroyed when grounding and short enough that the rig wont tangle with it, but Im fascinated to know if all the wierd and wonderful shapes Ive seen are just this years "thing " or if there are certain things to look for in a fin

this is as far as Ive got

looks great landyacht, pleased to see your useing a wheel "consolidator"

There are lots of things to look for, however at the beginner standard you simply won't notice the difference.

It's only when you start using a GPS and really start cranking that you find how changing your fin really affects things.

Select to expand quote

Flipper11 said...

i thought you stopped trolling

there just my smileys stop picking on me

Select to expand quote

nebbian said...

There are lots of things to look for, however at the beginner standard you simply won't notice the difference.

It's only when you start using a GPS and really start cranking that you find how changing your fin really affects things.

expand on the above statement. this essay is worth 20marks in your final score

A thicker foil is easier to use and will spin out less, a thinner foil has a higher top speed.

A more upright fin will point higher but be harder to turn and a swept back fin will turn easier.

Theoretically the most efficent shape is the elipse like maui ultra fins, but I'm wondering why dolphins have a typical surf style/shape?

Flex in the find, particulary at the tip make it more foregiving/easier and a stiff fin gives better performance.

Select to expand quote

Little Jon said...

A thicker foil is easier to use and will spin out less, a thinner foil has a higher top speed.

A more upright fin will point higher but be harder to turn and a swept back fin will turn easier.

Theoretically the most efficent shape is the elipse like maui ultra fins, but I'm wondering why dolphins have a typical surf style/shape?

Flex in the find, particulary at the tip make it more foregiving/easier and a stiff fin gives better performance.

Nice summary. Thanks Little Jon.

Flex in the find, particulary at the tip make it more foregiving/easier
I have a JP 33 Weed with a flex tip, and am curious about "forgiving/easier".
What does it mean?
I bought it to match my 6m sail. It holds 6m, but slides on 8.

Should the last 3-4cm of flex tip be counted in the overall length when matching the sail (given it is soft).

Select to expand quote

Little Jon said...

A thicker foil is easier to use and will spin out less, a thinner foil has a higher top speed.

A more upright fin will point higher but be harder to turn and a swept back fin will turn easier.

Theoretically the most efficent shape is the elipse like maui ultra fins, but I'm wondering why dolphins have a typical surf style/shape?

Flex in the find, particulary at the tip make it more foregiving/easier and a stiff fin gives better performance.

thanks for that great dummies intro
I do believe I will shortly be travelling faster and straighter into the wall of the dam than I was previously

Select to expand quote

Little Jon said...

... but I'm wondering why dolphins have a typical surf style/shape?

I was wondering that too, and then I thought "Maybe it's because they don't cruise around upside down with a windsurfing rig stuck in their guts"

Maybe that's it...I dunno.

In answer to the original question, and put very simply;

Long, straight fins ("pointers") are for slalom / speed type boards. The length of fin you need is determined primarily by the tail width of the board (at the point where the fin is). So a wide formula type board has a very long fin, and a speed board has a small one.

The raked back straight ones are "weedies". They serve much the same purpose but they shed weed and generally don't perform as well as pointers.

The curved ones are wave fins -they're good for turning.

If you are a beginner or intermediate, don't worry about flex - it's a high-performance thing and you won't notice it.

RE: The length of fin you need is determined primarily by the tail width of the board

I thought it was the sail size, and the board buoyancy?
At least that's what the "fin size calculator" takes into the account

Select to expand quote

Obelix said...

RE: The length of fin you need is determined primarily by the tail width of the board

I thought it was the sail size, and the board buoyancy?
At least that's what the "fin size calculator" takes into the account

Sail size is factor, but far less significant than tail-width.

Consider that you could use the same board and fin with several different sized sails, but you would almost never use the same fin with different sizes of board.

Select to expand quote

AUS1111 said...

Consider that you could use the same board and fin with several different sized sails, but you would almost never use the same fin with different sizes of board.

Hmmm I do

What can I say, it's my favourite fin

Ado, There's a certain Lockwood 23cm 35deg fin, that I'm finding very versatile, goes in my 43cm speed board and my 59cm slalom.
Found it also works really well in 2cm of water and waist deep mud the other day. (much better than it does trying to chop thru rocks at hardies)

speaking of 2cm of water, on our salt lake , when its wet we have these big spots with Very shallow water, but with consistent depth and smooth hard salt underneath. Has anybody built a windsurfing skimboard or even experimented with anything similar. 30knts of wind will only produce a wave 5cm high. even deep water for us is only 20cm

Lateral resistance is the issue...

About the only way you can have fun on that sort of surface is with a kite [}:)]

I modified an ancient board to a twin fin, but it had too many problems to work well.
Thinking about crashing in ankle deep water at 30 + knots, kind of took the imperative out of developing it further. It's still sitting in the shed waiting for me to get stupid enough to get it working properly.

Select to expand quote

decrepit said...

I modified an ancient board to a twin fin, but it had too many problems to work well.
Thinking about crashing in ankle deep water at 30 + knots, kind of took the imperative out of developing it further. It's still sitting in the shed waiting for me to get stupid enough to get it working properly.

thanks for the tip decrep, my tri fin conversion didn't work eitherthe 9"side fins were inserted from the tail and all they did was cause drag ,when i took them out i had 2 rooster tails so i filled them in with foam, now i'm wondering if tail cutouts can cause drag

I had this silly thought of maybe 2 strips of 10 or 20mm deep aluminium T section .
What kind of dimensions would you be considering for a board.
I had a thought of 2 little wheels overhanging the stern and a little one over the bow that would be out of the water when moving?

Select to expand quote

landyacht said...

I had this silly thought of maybe 2 strips of 10 or 20mm deep aluminium T section .
What kind of dimensions would you be considering for a board.

Yes I know that thought, it occurs to me every once in a while.

The trouble with a long narrow foil, is the ease of flow from high pressure to low pressure so they aren't very efficient. so you'd need more area than a conventional upright fin. unless they're running very close to the bottom, that will stop the flow.
You also get the benefit of ground effect, so you need less planing area for the same lift.

How flat is the lake bed???? is it possible to have the T section just clearing the bottom by 5mm or so?

Hmm not exactly a foil is it, might not do much good at all.
I don't have enough engineering skills to work that out, trial and error is my bag.

Of course this thing is not going to turn!

Select to expand quote

I had a thought of 2 little wheels overhanging the stern and a little one over the bow that would be out of the water when moving?

Nup, too much drag, don't see how you can have wheels touching the bottom when stationary, but out of the water when planing

Select to expand quote

landyacht said...

speaking of 2cm of water, on our salt lake , when its wet we have these big spots with Very shallow water, but with consistent depth and smooth hard salt underneath. Has anybody built a windsurfing skimboard or even experimented with anything similar. 30knts of wind will only produce a wave 5cm high. even deep water for us is only 20cm

kite heaven

The trouble with a long narrow foil, is the ease of flow from high pressure to low pressure so they aren't very efficient. so you'd need more area than a conventional upright fin. unless they're running very close to the bottom, that will stop the flow.
You also get the benefit of ground effect, so you need less planing area for the same lift.

How flat is the lake bed???? is it possible to have the T section just clearing the bottom by 5mm or so?





the surface is hard and smooth enough to rollersate on!!!
I had a thought in my sleep-what about 2 longish strips of ally angle along the sides of the board that would stop air escaping from the edges and improve the ground effect?
hmmmmmmm............







Hmm not exactly a foil is it, might not do much good at all.
I don't have enough engineering skills to work that out, trial and error is my bag.

Of course this thing is not going to turn!

Select to expand quote

landyacht said...




the surface is hard and smooth enough to rollersate on!!!
I had a thought in my sleep-what about 2 longish strips of ally angle along the sides of the board that would stop air escaping from the edges and improve the ground effect?
hmmmmmmm............

I'm sure you mean water not air, and yes, that was my thought to improve the ground effect.
if you could get it working, it could be really fast.
And if the ground effect works well, there wouldn't be much board in the water, once really under way, may be less than a square foot, so the strips wouldn't need to be that long, you just need enough lateral resistance.
Going sideways wouldn't be fun, those strips would dig in and trip the board up, resulting in a head first catapult in to that hard smooth surface in front of the board.
So another reason the strips need to be kept shortish, and a bevelled rail from as far back as possible. This will give some chance of controlling a sideways slide.

couple of thoughts in my sleep. any suggestions for the dimensions. long and skinny or short and fat?
suggestions of "your daft...mad...etc duly noted.
thoughts appreciated on the section. keep in mind you get to walk back if something breaks( on the board)

so Im not the only one with an active mind ,sitting watch the rain fill up my beloved salt lake AGAIN.
its so frustrating to arrive at our lake and see tiny little wavelets being whipped up on the wet side of the causeway, and being stuck with only a landyacht,sailing on a tiny evaporation pond

kind of like this. 6" water on mainlake ,pond dry, 30knts

The trouble with designing something different from scratch in your head, is getting stuff wrong.

Don't forget your going to have to get the thing moving, ( I guess that's why you were thinking of little wheels)

Unless what you've drawn, can slide on the bottom, you'll just stick to it as soon as you step on.

So I think it needs enough floatation to keep it off the bottom when starting.
Also I'd go for small low aspect ratio fins rather than the ally angle.
May be even 3 fins to get enough lift.
Foils will develop more lift, and resist sliding sideways better than flat plate.

What you've drawn is more of a kite board, and could work well in that mode, cause the kite can pull you off the bottom.

And I guess I should explain in more detail my reservations.

When you get catapulted hooked into a windsurfing rig, you don't just skate across the surface at the speed you where going.
The rig flings you in an arc at the end of the harness lines, accelerating you faster than you were going, then slamming you straight down into the water.
I've seen Benders GPS read 60kts after a bad catapult, (he was probably doing mid 30s before the catapult) and the way he was wobbling around afterwards, he probably had a mild concussion. That's into waist deep water, anything less is getting very dangerous.

I've seen someone break their neck when their fin hit the bottom.

He had to wear a halo brace for months, and was off the water for around a year I think.

The name you pencilled in "Spirit of stupidity" seems quite apt.


SERIOUSLY, DON'T DO IT!


Use a kite instead. It's far easier than learning to windsurf, and much safer on this sort of surface.

Select to expand quote

decrepit said...

When you get catapulted hooked into a windsurfing rig, you don't just skate across the surface at the speed you where going.
The rig flings you in an arc at the end of the harness lines, accelerating you faster than you were going, then slamming you straight down into the water.
I've seen Benders GPS read 60kts after a bad catapult, (he was probably doing mid 30s before the catapult) and the way he was wobbling around afterwards, he probably had a mild concussion. That's into waist deep water, anything less is getting very dangerous.

Trust me, listen to what decrep says. going 30+knts in 25mm of water soiunds like a good way to end up in a wheel chair to me