Fin cavitation?sail size?

> 10 years ago
Reply
Register to post, see what you've read, and subscribe to topics.
busterwa
busterwa
3782 posts
3782 posts
19 Mar 2010 9:03pm
Just a quick question..
When conditions dictate and i am running larger sails it seems when i push the boom to a downward acute angle for maximum power over jump and bump swell(keeping sail square to board.) i seem start sliding out.I can shake it off by changing direction and pumpin the deck.
I was just wondering is this a fin size problem or is board problem.
it happens on my wave board aswell. dosent seem to happen on my big tugboat 130 litre though fin size is same on freeride and tugboat board width is different?
sailpilot
sailpilot
QLD
787 posts
QLD, 787 posts
19 Mar 2010 11:15pm
Fin size? type? sail size? wind strength?
Gestalt
Gestalt
QLD
14968 posts
QLD, 14968 posts
19 Mar 2010 11:17pm
busterwa said...

Just a quick question..
when i push the boom to a downward acute angle for maximum power


i can't visualise what you mean here.?
Mucksy
Mucksy
QLD
217 posts
QLD, 217 posts
19 Mar 2010 11:32pm
Gestalt said...

busterwa said...

Just a quick question..
when i push the boom to a downward acute angle for maximum power


i can't visualise what you mean here.?



Gestalt, I think he is referring to closing the foot of the sail down onto the back of the board.

Busterwa, its probably because you are applying too much back foot pressure. try driving more through the front foot. do an experiment next time your sailing - when fully powered up, can you take your back foot out of the foot strap? if not then you are applying too much back foot pressure.

Give it a go then get back to us. :)
nebbian
nebbian
WA
6277 posts
WA, 6277 posts
19 Mar 2010 9:48pm
Did you try moving your harness lines back on the bigger sail?
Gestalt
Gestalt
QLD
14968 posts
QLD, 14968 posts
20 Mar 2010 12:24am
that makes sense mucksy.

another thing is to not bag out your bigger sail just because the wind is light.

tension for the apparent winds.
petermac33
petermac33
WA
6415 posts
WA, 6415 posts
20 Mar 2010 5:24pm
mucksy........do an experiment next time your sailing - when fully powered up, can you take your back foot out of the foot strap? if not then you are applying too much back foot pressure.


i must be doing something wrong then, i sail with maximum back foot pressure on all points of sailing.

i dig back foot toes in [lifting heal] to lift up windward rail. this helps to stop board spinning out.

a wider tail board, you need a little bigger fin.

use half a metre smaller size sail [rigged fuller] should solve the problem.


pepe47
pepe47
WA
1382 posts
WA, 1382 posts
21 Mar 2010 8:35pm
After reading a very good thread from Roo, I adjusted my rear footstraps to their forward position and have not managed to cavitate since.
Following the guidelines of a previous sail to fin ratio thread/guide I've noticed that I'm actually keeping up with people instead of being left behind.
Roar
Roar
NSW
471 posts
NSW, 471 posts
22 Mar 2010 8:15am
bottom line is in lighter winds you need to use a bigger fin to stop spin outs.

in stronger winds as you go faster the fin generates a lot more lift countering the back foott presure so you can drop down a few sizes . In light winds there simply isnt enuf speed for the fin to generate that same amount of force.

Think of it as a wing on a plane - it requires a certain amount of speed before there is sufficient lift to take off. A glider with huge wing span requires very low velocity in comparision to a jet fighter which requires a lot of velocity for the small wings to take effect.

Please Register, or first...
Topics Subscribe Reply