We've accepted asymmetric fins, so moving on to the whole board is a logical step. The physics of sailing on one tack is so asymmetrical it's highly unlikely a symmetric hull is the best way to do it.

This suggestion is working on the principal of moving the lifting vectors closer to the one line. It uses Oldie's idea of offsetting the mast base so the sail could be more effectively raked overhead for vertical lift. It's starting to morph a little towards a kite board as far as lift vectors are concerned, but it's still a windsurfer, any of us could hop on and sail away.

The fin could be fixed at ~75 degrees or back-foot-adjustable on the fly. It could be spring loaded and use a handbrake type ratchet mechanism. You could crank it on to lighten the hull load in flat water or ideal conditions, or kick the ratchet and ease back foot pressure to bring it more upright if the tail got too lively in rough conditions. The hull is stepped port to starboard to reduce planing area at speed, but still keep the planing length long for control.

Like a kite it probably sails best windward rail down. We currently try and trim a bit on the leeward rail for max speed. Maybe that's a fin angle thing rather than a hull thing?

The sail would be a bit in your face but with the fin kicked to 90 deg it should work on the other tack.

Ian, you obviously have too much time on your hands!

Great thinking though!

You could always have twin mast tracks, then you could use the board for both tacks, depending on venue/conditions.
Just a matter of deciding how offset to put them.
Same with the fins, two boxes, but do you angle them in or out?
The only thing symmetric then would be the hull.

I don't understand why people who make asymmetric fins don't yaw them in the box so that the board is going straight when the fin has a bit of angle of attack?

Means the rails are doing what they're designed to do instead of crabbing along sideways.

i like reading these ideas it's all good stuff. and completely over my head with the physics discussed here.

but i would have thought designers should be looking to the fin and sail instead of the board.

a speed sailor flat out doesn't really have any board in the water.

the 2 big areas of drag are the sail and the fin and probably more the fin than the sail.

Select to expand quote

nebbian said...

I don't understand why people who make asymmetric fins don't yaw them in the box so that the board is going straight when the fin has a bit of angle of attack?

Means the rails are doing what they're designed to do instead of crabbing along sideways.

Actually it is the other way around. A board with a symmetrical fin 'crabs' more. The assy fin works at a lower angle of attack.

Select to expand quote

sailquik said...

Actually it is the other way around. A board with a symmetrical fin 'crabs' more. The assy fin works at a lower angle of attack.

Yes I realise that, but if you build a symmetrical fin then there's no point yawing it in the box, is there!

It seems no-one has tried to make the board go dead straight relative to the water, they make it dead straight relative to the chord of the fin. So if you've got a degree or two of fin AoA then so does your board. Seems a bit silly to me.

Sort of like when designing model planes, and you realise that you need to angle the fuselage at 0 degrees to the airflow, not the wing chord.

Select to expand quote

nebbian said...

I don't understand why people who make asymmetric fins don't yaw them in the box so that the board is going straight when the fin has a bit of angle of attack?

Means the rails are doing what they're designed to do instead of crabbing along sideways.

I thought they DID do that. Its just common sense.

Select to expand quote

Ian K said...

We've accepted asymmetric fins, so moving on to the whole board is a logical step. The physics of sailing on one tack is so asymmetrical it's highly unlikely a symmetric hull is the best way to do it.

This suggestion is working on the principal of moving the lifting vectors closer to the one line. It uses Oldie's idea of offsetting the mast base so the sail could be more effectively raked overhead for vertical lift. It's starting to morph a little towards a kite board as far as lift vectors are concerned, but it's still a windsurfer, any of us could hop on and sail away.

The fin could be fixed at ~75 degrees or back-foot-adjustable on the fly. It could be spring loaded and use a handbrake type ratchet mechanism. You could crank it on to lighten the hull load in flat water or ideal conditions, or kick the ratchet and ease back foot pressure to bring it more upright if the tail got too lively in rough conditions. The hull is stepped port to starboard to reduce planing area at speed, but still keep the planing length long for control.

Like a kite it probably sails best windward rail down. We currently try and trim a bit on the leeward rail for max speed. Maybe that's a fin angle thing rather than a hull thing?

The sail would be a bit in your face but with the fin kicked to 90 deg it should work on the other tack.

Thanx for this Ian, It would be great to have a pool of funds where we could trial these ideas out,........... build, test/trial, fine tune etc........

Select to expand quote

Ian K said...

We've accepted asymmetric fins, so moving on to the whole board is a logical step. The physics of sailing on one tack is so asymmetrical it's highly unlikely a symmetric hull is the best way to do it.

This suggestion is working on the principal of moving the lifting vectors closer to the one line. It uses Oldie's idea of offsetting the mast base so the sail could be more effectively raked overhead for vertical lift. It's starting to morph a little towards a kite board as far as lift vectors are concerned, but it's still a windsurfer, any of us could hop on and sail away.

The fin could be fixed at ~75 degrees or back-foot-adjustable on the fly. It could be spring loaded and use a handbrake type ratchet mechanism. You could crank it on to lighten the hull load in flat water or ideal conditions, or kick the ratchet and ease back foot pressure to bring it more upright if the tail got too lively in rough conditions. The hull is stepped port to starboard to reduce planing area at speed, but still keep the planing length long for control.

Like a kite it probably sails best windward rail down. We currently try and trim a bit on the leeward rail for max speed. Maybe that's a fin angle thing rather than a hull thing?

The sail would be a bit in your face but with the fin kicked to 90 deg it should work on the other tack.

I can tell that set-up would be fast by the way you've got your toes curled up

Decrep, you could put a heap of threaded inserts in the board in various spots instead of mast tracks, to work out the best spot on the proto.

I sketched up a sililar thing a couple of years back, it was a formula board with twin fins set at 45 degrees and the board was sliced either side of the mast track right down the centre.
Both sides were tilted up at 22.5 degrees so to get going you have the whole board in the water and as you speed up you roll it over onto one side, giving you a speed board 50cm wide with an offset mast track.

Anyone got an old formula board they want to sacrifice?

Patent Pending #A256493257

How about making the mast track a piece of traveller track athwartships and the mast base on a traveller car so it drops to the lee side after changing tacks, similar in principle to a self tacking jib on a sailboat.

Maybe dangerous for freestyle trickery on the foredeck tho!

What about having a sort of turn table mast base. The base is circular and fixed centrally as usual but the uni connection is eccentric and can be rotated from one side to the other.

If the fin is going to rock from side to side it will do that automatically when loaded from the opposite side. You'd feel the tail of the board take a step sideways in mid gybe... kerlunk.