Subject: Re: [harryproa] Re: Larger model hulls on (Aurora) vid
From: Rick Willoughby
Date: 8/19/2010, 2:38 AM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 

Todd

By feathering I am referring to a full size version where you want to release sail force by releasing the sheet or whatever is controlling the sail AoA.  The symmetrical sail does not feather when released or only over a very narrow range.  An interesting test would be to release your control rods to the mast and see where the sail rotates.

The middle mounted rudders do provide a load release mechanism that allows leeway when clear of the water.  I can see the benefit in that.

At speeds above a few knots on a full size craft ventilation will be performance limiting.  Hence I see merit in under the hull rudders.  They could be under the windward hull if you want some force release mechanism.  The instant that they ventilate will cause the boat to round up a little so some inbuilt protection. If the front one goes first then there will be an instant of lee helm before the aft one lets go.

Your cambered thin wing will have a working range of a few degrees when on the wind.  The lift drops to under half about 5 degrees either side of maximum lift.  The 10% series 07 foil will work over twice that range and if you went up to a 20% thick section it would have twice the lift and work over 25 degree range - so more progressive.  Having double the lift coefficient allows you to halve the sail area.  This means the maximum drag when the sail is perpendicular to the wind is halved so risk of capsize is reduced.   You can provide this same protection by putting more curve into your thin sail and reducing the area but it will still only have a narrow range of operation.

Rick 
On 19/08/2010, at 2:58 PM, tsstproa wrote:

 

Thanks Rick

What do you mean by feathering?

More range in what way pointing ability or same sail size for higher wind strengths or both ?

I'm sailing right in front of a shallow shelf so tring to keep boat close for through water hull shots. At 5:00 in Last part of video thinking of a way to show leeway if any. I'm not moving the steering boards just manipulating the sail only. Boat pretty much stays in same position as it see-saws back and forth actually gains ground in the puffs.

Also starting at 2:35 on the clip look as it heels and slides sideways don't no if thats a good thing or not, but better than digging and catching an edge. An argument for center hung boards vs leeward hung boards might correct of hinder the situation. I know the canted of hull helped the slide.

No, I'm using symmetrical.

When I put the camera down the performance goes up two hands vs one. Towards the end of the day I was tring everything to get it to ride on leeward hull alone in the 4.5 mph wind it wouldn't thats a good thing to me. I'm hoping in about 6 to 8 range it will still stay somewhat planted. In more wind canting the rig to windward or reducing sail size.

Todd

--- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@...> wrote:
>
> Todd
> Very nice work.
>
> It is so simple with the rigid bi-directional wing. The only problem
> is lack of feathering but that could be overcome.
>
> A thick sail section like I did for the rudder would have wider range
> of control. It might be a bit more progressive on the controls
>
> Are you using asymmetrical rudders?
>
> Rick
> On 19/08/2010, at 11:05 AM, tsstproa wrote:
>
> > CatPrao ProaCat AURORA 36'' x 1/2'' x 3'' with 12'' rocker. hulls
> > are canted 20degrees outward.
> >
> > http://www.youtube.com/watch?v=FCEvPdnhShk
> >
> > Todd
> >
> >
>
> Rick Willoughby
> rickwill@...
> 03 9796 2415
> 0419 104 821
>


Rick Willoughby
03 9796 2415
0419 104 821

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