Best sailing speed

[Sea Shadow]

The HDPE custom ones come as a pair or you can get the original style (the centre item) xsinlgly. As far as I can see on my boat both rudder are identical.

[kurz]

The HDPE custom ones come as a pair or you can get the original style (the centre item) xsinlgly. As far as I can see on my boat both rudder are identical.

If both are same how can they work as foils?

[Neo]

Try this link. Should get you there.
http://shop.bwyachts.com/category-s/316.htm

Thanks, I see it now

If both are same how can they work as foils?

Very good question Kurz
Although it does say "Airfoil" ... which is kinda odd as it's sitting in water (Hydrofoil).

[Sea Shadow]

Vertically in the water the rudders would have an identical profile to have a neutral position straight ahead (i presume). When you turn you create a high pressure zone at the forward face of the rudder and a low pressure at the rearward facing (just like the sail). This would push the rear of the boat around, the other foil (keel) resists this turning motion (centre of effort??) and shortens it so you turn tighter. PS. This is only my layman's understanding on how the "foils" work.

[Neo]

Vertically in the water the rudder would have an identical profile to have a neutral position straight ahead (i presume). When you turn you create a high pressure zone at the forward face of the rudder and a low pressure at the rearward facing (just like the sail). This would push the rear of the boat around, the other foil (keel) resists this turning motion and shortens it so you turn tighter. PS. This is only my layman's understanding on how the "foils" work.

Yes, but as Kurt asked, that would require different profile shapes on each side of the rudder (just like a sail) ... Might be worth rechecking the profiles of the two sides of the rudders.

[Sea Shadow]

When travelling straight ahead, you would not want a high/low pressure zone on the rudders, just at the keel is symetrical in the front on view. You would only want high/low pressure to turn, this is achieve by angling the rudders (foils) - I assume the same concept occurs with aeroplanes and their tail rudder (including twin tail aeroplanes).

[Sea Shadow]

PS: I think what you would find is that the HDPE rudders are a more refined head on profile yet are identical for each side (ie. you don't have a starboard rudder and a port rudder). I do stand to be corrected by someone who has the HDPE rudders.

If you did have a different profile on each side of the rudder, then when you turn to the non-optimal face it would less effective. If each rudder had an optimal face for a particular turn then it would not work for the other direction. If you had the rudders with their more effective profile on opposite side, then one rudder would fight against the other when turning. (My brain is starting to hurt . Add to this heeling one you may only be using one rudder ....

Looking at my factory original, I can see no difference of the profile on either side of each rudder and the ruddder appear identical to each other ie, no port or starboard difference in the rudders.

[Neo]

From what I've read now it seems that the HDPE material is more flexible (and does deflect under way) but harder to break, but I'm have no understanding of how this "Airfiol" principal is supposed to be physically working on a rudder? ... especially as there's no difference between port and starboard rudder profiles

On the 26M the rudder brackets are already too thin/weak for the job. They often break using the standard fibreglass rudders which in my experience are pretty tough, for a hollow rudder ... and I'm not sure I would want rudders tough enough to rip out the rudder brackets after running aground.

Just FYI I found this old thread too ... http://www.macgregorsailors.com/forum/v ... hp?t=20170

[pitchpolehobie]

Anything like these airfoil rudders for the 26X?

[kurz]

Maybe BWY Should tell more about the function of this rudders and what is about the air foil skills...

[Sea Shadow]

Maybe BWY Should tell more about the function of this rudders and what is about the air foil skills...

I think you can ignore the "air" part of foil (suggest that it is a typographical mistake).

The rudders, keel and sail are foils (the sail being an airfoil). The sails can/do change shape (profile) depending on which way the wind blows, and create a low/high pressure zone that propels the boat.

The rudders and keels are vertical foils that give you directional stability and would not work as well if they had a different profile on the port and starboard of each side of the foil. Horizontal "hydro" foils provide lift and are profile to work in on direction ie. up. Submarines have hydrofoils to make them go up and down, but I doubt that their profile is different between the upper and lower face (in the horizontal position.

Looking at the description that BWY has for the HDPE rudders, other than "air" in the word "airfoil" it describes the refinements in the profile and effectiveness of them.

[kurz]

Sorry. I don't see the sence of talking of a foil it is on both same the same shape (like dagger board).

There is no lift.

[Neo]

Sorry. I don't see the sence of talking of a foil it is on both same the same shape (like dagger board).
There is no lift.

I second that motion

[kurz]

I asked Todd from BWY, here gis answer:

All rudders, centerboards, and keels have an “airfoil” design (unless they are simply a flat board, which is unusual), in truth the term airfoil is used because it is the generic term used when most of these shapes were developed, “foil” is a better term because our foils do not actually operate in air. In reality air and water behave very similarly other than the MUCH higher viscosity of water. The performance of the rudder or centerboard is in large part a function of the exact shape of the foil, all are trying to provide lift, either to help the boat sail upwind or to help the rudder turn with more authority, but the shape of the foil determines the amount of lift it creates relative to the drag it produces. Changing the foil shape by a small amount can create significant performance improvement.

Todd

well, that's his answer. Very nice to hear from BWY.
But in fact it makes no sense for me. Airfoil or in our sense hydrofoil are wings that have different shapes on both sides. If they are same like daggerboard the do not produce lift. So as long as both rudders are same - it makes no sense to talk about foils - thats my opinion.

[Sea Shadow]

I asked Todd from BWY, here gis answer:

All rudders, centerboards, and keels have an “airfoil” design (unless they are simply a flat board, which is unusual), in truth the term airfoil is used because it is the generic term used when most of these shapes were developed, “foil” is a better term because our foils do not actually operate in air. In reality air and water behave very similarly other than the MUCH higher viscosity of water. The performance of the rudder or centerboard is in large part a function of the exact shape of the foil, all are trying to provide lift, either to help the boat sail upwind or to help the rudder turn with more authority, but the shape of the foil determines the amount of lift it creates relative to the drag it produces. Changing the foil shape by a small amount can create significant performance improvement.

Todd

well, that's his answer. Very nice to hear from BWY.
But in fact it makes no sense for me. Airfoil or in our sense hydrofoil are wings that have different shapes on both sides. If they are same like daggerboard the do not produce lift. So as long as both rudders are same - it makes no sense to talk about foils - thats my opinion.

Given that the keel and rudders are vertical they would not ever produce "lift". The are designed to produce directional stability. If you made one side different to the other ir would not work. If in fact you biased both the keel the rudders to produded a high pressure on the port side then you would have the boat have a bias to go to the starboard side (or vice versa with the high pressure zone on the starboard side). This would then mean you would steer back to the port cancelling out any effect of having the high pressure zone on the port side. Essentially to work effeciently the keel and the rudders have to the symetrical in shape from a head-on view. Mind you the shape (identical on both side) can be altered to be more efficient and I suppose that is what they have done with the HDPE rudders.