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#2895467 - 01/08/19 11:11 AM Re: The Roberts Twonzer [Re: GWS]
patrolman Offline
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Registered: 07/28/05
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Question about the canard- isn't it supposed to prevent the main fin from cavitating? Wouldn't most of the cavitation happen at the tip? So shouldn't the canard be deeper?

Just thinking out loud....

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#2895780 - 01/08/19 08:30 PM Re: The Roberts Twonzer [Re: patrolman]
ghostshaper Offline
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Registered: 01/22/05
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Originally Posted By: patrolman
Question about the canard- isn't it supposed to prevent the main fin from cavitating? Wouldn't most of the cavitation happen at the tip? So shouldn't the canard be deeper?

Just thinking out loud....


I was surprised at how big the canards are on Robert's twonzer. From my own testing, I noticed that even w/ bigger canards, they still slide if placed w/ too much overlap. I really wanted to chat w/ him about his placement, but I was at the shop in the a.m. and they had no idea what time he was getting in.

From what I think I understand, the canard redirects flow onto the main fin, which increases pressure and keeps it from cavitating at a higher angle of attack at low speeds.

I gotta try to hunt down Wil and have a chat w/ him about the function of the canards. He mentioned to me that spreading the cluster will increase hold and draw out turns in bigger waves, which I knew from riding quads. When I met him in person, we talked more about bottom contours.
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Organized competition is entirely peripheral to surfing qua surfing. People surf for love. - William Finnegan

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#2896363 - 01/10/19 11:27 AM Re: The Roberts Twonzer [Re: ghostshaper]
patrolman Offline
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Registered: 07/28/05
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Originally Posted By: ghostshaper
Originally Posted By: patrolman
Question about the canard- isn't it supposed to prevent the main fin from cavitating? Wouldn't most of the cavitation happen at the tip? So shouldn't the canard be deeper?

Just thinking out loud....


I was surprised at how big the canards are on Robert's twonzer. From my own testing, I noticed that even w/ bigger canards, they still slide if placed w/ too much overlap. I really wanted to chat w/ him about his placement, but I was at the shop in the a.m. and they had no idea what time he was getting in.

From what I think I understand, the canard redirects flow onto the main fin, which increases pressure and keeps it from cavitating at a higher angle of attack at low speeds.

I gotta try to hunt down Wil and have a chat w/ him about the function of the canards. He mentioned to me that spreading the cluster will increase hold and draw out turns in bigger waves, which I knew from riding quads. When I met him in person, we talked more about bottom contours.


I have a mid length twinzer and this past weekend was out in solid overhead surf. The board is normally (small waves) pretty loose for its size. In the solid surf, going MUCH faster it no longer felt loose at all. Maybe the canard action is only kicking in at this higher speed?

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#2896673 - 01/10/19 10:49 PM Re: The Roberts Twonzer [Re: patrolman]
ghostshaper Offline
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Registered: 01/22/05
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Originally Posted By: patrolman
Originally Posted By: ghostshaper
Originally Posted By: patrolman
Question about the canard- isn't it supposed to prevent the main fin from cavitating? Wouldn't most of the cavitation happen at the tip? So shouldn't the canard be deeper?

Just thinking out loud....


I was surprised at how big the canards are on Robert's twonzer. From my own testing, I noticed that even w/ bigger canards, they still slide if placed w/ too much overlap. I really wanted to chat w/ him about his placement, but I was at the shop in the a.m. and they had no idea what time he was getting in.

From what I think I understand, the canard redirects flow onto the main fin, which increases pressure and keeps it from cavitating at a higher angle of attack at low speeds.

I gotta try to hunt down Wil and have a chat w/ him about the function of the canards. He mentioned to me that spreading the cluster will increase hold and draw out turns in bigger waves, which I knew from riding quads. When I met him in person, we talked more about bottom contours.


I have a mid length twinzer and this past weekend was out in solid overhead surf. The board is normally (small waves) pretty loose for its size. In the solid surf, going MUCH faster it no longer felt loose at all. Maybe the canard action is only kicking in at this higher speed?


I've never experienced this, so I can't explain it. Sounds counterintuitive, though. Most boards loosen up w/ speed.
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Organized competition is entirely peripheral to surfing qua surfing. People surf for love. - William Finnegan

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#2897543 - 01/13/19 01:35 PM Re: The Roberts Twonzer [Re: GWS]
twinzerfan Offline
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Registered: 10/26/06
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Loc: Santa Cruz/UK/Florida
I always thought of canard placement like the way sails work. The jib smooths the flow over the main sail making it more effective. If you open the slot that effectiveness changes, however as the wind increases, such as board speed, less slot is needed for same effect. But, it still has to be trimmed correctly or the sails will stall or deform (which shows the flow) and you slow down

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#2897550 - 01/13/19 01:51 PM Re: The Roberts Twonzer [Re: twinzerfan]
GWS Offline
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Originally Posted By: twinzerfan
I always thought of canard placement like the way sails work. The jib smooths the flow over the main sail making it more effective. If you open the slot that effectiveness changes, however as the wind increases, such as board speed, less slot is needed for same effect. But, it still has to be trimmed correctly or the sails will stall or deform (which shows the flow) and you slow down


Interesting. Although a genoa (previously called an overlapping jib) is a foresail that closes the gap between the main the foresail entirely, in fact overlapping. In some cases substantially. And its used in light air.



As a kid I used to crew on boats before roller reefing. I used to hate when they would put one of those things up in light air when I knew it was going to blow in an hour. Because I was the poor slob who had to go up there and drop the beast, wrestle it into a bag and raise the smaller jib sail.

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#2897551 - 01/13/19 01:51 PM Re: The Roberts Twonzer [Re: ghostshaper]
ghostshaper Offline
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+1
agree w/ the sail analogy

Originally Posted By: patrolman
Maybe the canard action is only kicking in at this higher speed?


canards are supposed to prevent stall at higher aoa at low speeds
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Organized competition is entirely peripheral to surfing qua surfing. People surf for love. - William Finnegan

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#2897554 - 01/13/19 02:08 PM Re: The Roberts Twonzer [Re: GWS]
SlicedFeet Offline
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I have 4 boards that are quads with added canards, 6fins.

They all perform the same. A 610, 78, and two 90 longboards. I feel the canards increase the speed of the board on roundhouses and bottom turns. Also they are steady as F in the pit, like being on a sidewalk.

For me, I tottaly get the canard. On birds of prey, the reason why they are so agile is that they use their canard to speed up their tight turns when hooking prey. If the canard slowed them down in a turn, theyd be extinct. smile

I have found that the 6 fin is its own beast, it doesnt work if you just add canards to a traditional quad set up.

Looks like Roberts has put lots of testing on his fin placement too for his Twonzer.

Board look cool.





Edited by SlicedFeet (01/13/19 02:09 PM)
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#2897583 - 01/13/19 03:00 PM Re: The Roberts Twonzer [Re: GWS]
twinzerfan Offline
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Registered: 10/26/06
Posts: 1414
Loc: Santa Cruz/UK/Florida
Well said GWS!

Im sure theres something to do with the area of the sail too, especially in light airs.

I laughed out loud at your story too cheers

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#2897587 - 01/13/19 03:08 PM Re: The Roberts Twonzer [Re: GWS]
twinzerfan Offline
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Registered: 10/26/06
Posts: 1414
Loc: Santa Cruz/UK/Florida

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#2897592 - 01/13/19 03:34 PM Re: The Roberts Twonzer [Re: GWS]
patrolman Offline
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Registered: 07/28/05
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I've spent a lot of time messing about in boats (not as much as tom@daum who should chime in). The sail doesn't need to overlap to affect the air flow on the main sail. In fact if you look at perfomance boats these days most no not have overlapping jibs.


The air/water cavitates on the outside edge (leeward in sail terms). The canard's inner edge which is working efficiently, even if it itself is cavitating, keeps the outside edge of the main fin from cavitating.

My question is about the depth. Most jibs will reach the mast head or 7/8th or 3/4s of the way up. The canard on boards is less than 50%. Also the main sail on a boat doesn't need the canard at the mast head because you can twist the sail, something you can't do on a surfboard fin.

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#2897708 - 01/13/19 10:42 PM Re: The Roberts Twonzer [Re: patrolman]
Spinafex Offline
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Registered: 09/10/12
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Originally Posted By: patrolman
I've spent a lot of time messing about in boats (not as much as tom@daum who should chime in). The sail doesn't need to overlap to affect the air flow on the main sail. In fact if you look at perfomance boats these days most no not have overlapping jibs.


The air/water cavitates on the outside edge (leeward in sail terms). The canard's inner edge which is working efficiently, even if it itself is cavitating, keeps the outside edge of the main fin from cavitating.

My question is about the depth. Most jibs will reach the mast head or 7/8th or 3/4s of the way up. The canard on boards is less than 50%. Also the main sail on a boat doesn't need the canard at the mast head because you can twist the sail, something you can't do on a surfboard fin.



Roberts twonser canards look to be about 3/4 of the rear fins. The rears are smaller than regular twins.
Does anyone have ride reports?

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