Sailing at Safety Bay yesterday in about 18-20 knots.

6m sail,
107 Litre FSW board
28cm Weed fin
96kg

I was having trouble getting planing and when I was I could hardly go up wind at all.
(made much worse by the guy who could hardly kite going up staight up and down the middle of the pond)
I always seem to have problems at Saftey Bay pointing upwind unless it is really blowing.


Is my fin too small? I think the board came with a 31cm (non-weed fin) Is there a definitive conversion between weed and none weed fins?
Or am I just too fat and rubbish?
I have changed to a waist harness this year would this make much of a difference?

I thought maybe a weed fin is supposed to be longer due to the rake ie: a 31cm non weedy translates to about a 33-35cm weedy?

I dunno I don't use them but thought I heard that...?

At 96 kg maybe a bigger fin and a bigger sail would be an advantage.

Mark _australia said...

I thought maybe a weed fin is supposed to be longer due to the rake ie: a 31cm non weedy translates to about a 33-35cm weedy?

I dunno I don't use them but thought I heard that...?

They are longer but the measurement is the vertical height. Can't remember the proper term...

you need a longer weedie to achieve the same depth (from board to tip measured perpendicular to board)



That's what i thought

Cheers for all the replies..
I was sort of hoping for some advice that involved buying a slightly larger weedy (cheapish fix)

But in reality I knew the answers would be "bigger sail" or "lose some weight" . Just got to decide If its gonna be easier to part with some cash or some weight.

well there are weedys and weedys, some are crap some are OK. so it's hard to say.
Any flex in a weedy will seriously impair it's lift, whereas with a pointer, a bit of flex just changes the plane of lift a bit.
A lot of weedys are just pointers boxed at a greater angle, these are most likely to be the crap ones, to flexi and not enough thickness to chord ratio.

I think if you have a stiff pointer and a very stiff weedy of the same thickness to flow ratio. they'll have similar lift properties even though the weedy will have a bit more area.

pweedas said...

Geez, that's an awfully complicated reply.
>>>>>

As are weedys unfortunately.

Guess I could have just said, put the fin across your knee and if you can bend it more than a few mm throw it out, or give it a couple of layers of carbon.

leftfield said...

Just trying to Clear the weedy v non weedy stuff up.

My weedy is quoted as 28cm ( Which is its depth perpendicular to the board)

And measures as about 40cm along the leading edge.

So what does this equate to in non weedy terms??

I have a 28 cm weedy (flying objects) and I use it with the same set up (85L board & 5.8 sail) where I would use a 32 cm pointer (vector) if there was no weed. Having said that, that board and sail worked very well with a 24 weedy on the day in question.

pweedas said...

Geez, that's an awfully complicated reply.
Just tell him he's fat. It's a much simpler answer.

(sorry. This is an awfully nice shiraz. IT seems to be improving as I get furhter down )

I'm sorry. How rude of me!
There must have been something in that bottle that I was allergic to. After a while it made my balance go off and my eyes went funny. I've no idea why that would be.

Weedies. Yes I have one and I use it nearly all the time. As mentioned, the size is measured as the vertical distance from the base of the board so a 32cm weedy will have a much bigger area than a 32cm pointer so you would think it would go better upwind,.. but,..
Be aware that a weedy will change the dynamic balance of the board and you will find you need to sail with more weight on the back foot to go upwind or even hold the same track tacking in and out.
This is because the effective centre of lift / thrust / whatever of the fin is considerably more rearward of that of a pointer so it's a bit like moving your footstraps forwards.
I ended up cutting about 3 inches off the top rear of my weedy which mostly restored the original balnce points and still left it with more area than the original pointer. It now goes better upwind, gybes better and grinds over sandbanks better.

So to maintain similiar performance, across and upwind from a pointer to a weedy what lengths should I be looking at to replace a 38cm and 42cm pointer ?

col5555 said...

So to maintain similiar performance, across and upwind from a pointer to a weedy what lengths should I be looking at to replace a 38cm and 42cm pointer ?

It's hard to say really because it depends on the fin. They all have different profiles. Some are pretty sleek while others are almost paddles.

I'm not an expert so in my case I just got one with the same vertical depth (32cm) and cut it back a bit. I used it for some time before I cut it in case it turned out to be fine the way it was, but in the end I decided it needed a few thou off the top.

I notice in the link Decrepit posted above, the fin design is better than mine because they have moved the fin forwards on the mounting to counteract the rearwards movement of the centre of pressure when you angle the fin back. So everything I say here would not apply as much to those fins or any fin with a similar mounting position relative to the fin box.

I've posted a photo of my fin below and you can see that the fin is all rearwards of the original mounting point resulting in movement of the COP about 3 inches rearwards. That's a lot for a fin so I was pretty sure a bit of hacking wouldn't hurt things.



I left the cut edge fairly square and didn't round it off at all except to smooth it a bit. The cut is angled down slightly to keep positive water pressure on the edge. I think this might help prevent cavitation but it's just my guess.



I was surprised that cutting it back seemed to make so small a difference to the spin out on the board. I figured it was because the larger fin had more rearward component and thus needed more force on the back foot, so the two cancelled out.
It doesn't seem to spin out more with the top 3 inches (about 70mm) off it. So my 32cm weedy is now a 25cm weedy and it works real good.

It's a bit daunting to take a hacksaw to your nice new weed fin because if you cut off too much I think it would be hard to stick the bits back on again.
Although I'm tempted to cut off another 20mm.

I should also add that I'm a long way off being on the top pro windsurf team so all I was looking for was something that shed the weed fast, sailed well balanced and didn't spin out. It sort of does all that now.

I probably should add, I'm 85kg dry weight, 90kg wet, and it's on a 111 litre board, and usually a 5.2m to 6.5m sail on that fin but it's a little over finned on the 5.2

pweedas said...

pweedas said...

Geez, that's an awfully complicated reply.
Just tell him he's fat. It's a much simpler answer.

(sorry. This is an awfully nice shiraz. IT seems to be improving as I get furhter down )

I'm sorry. How rude of me!
There must have been something in that bottle that I was allergic to. After a while it made my balance go off and my eyes went funny. I've no idea why that would be.

Weedies. Yes I have one and I use it nearly all the time. As mentioned, the size is measured as the vertical distance from the base of the board so a 32cm weedy will have a much bigger area than a 32cm pointer so you would think it would go better upwind,.. but,..
Be aware that a weedy will change the dynamic balance of the board and you will find you need to sail with more weight on the back foot to go upwind or even hold the same track tacking in and out.
This is because the effective centre of lift / thrust / whatever of the fin is considerably more rearward of that of a pointer so it's a bit like moving your footstraps forwards.
I ended up cutting about 3 inches off the top rear of my weedy which mostly restored the original balnce points and still left it with more area than the original pointer. It now goes better upwind, gybes better and grinds over sandbanks better.

I should do that to all my fins..actually I already do by beachstarting on weedy rocky thingies & hitting bottom and ruining the tips..