Subject: Re: [harryproa] steering with delta COE-CLR
From: Rick Willoughby
Date: 6/7/2011, 8:46 PM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 

Ben 

It will produce a lot of turning moment.  These are the biggest forces on the boat so separating them small amounts creates huge moments.  It works well with windsurfers but takes practice.

One of the potential issues is instability.  If the mast is moved forward to bear away the angle of attack increases and it will drive more unless it is near stall. It could be like balancing a marble on a ball - that is my experience with windsurfers as I was often wet.  There is never equilibrium.  Then there is the situation of a seaway where the CoE and CoP will be shifting about both longitudinally and laterally creating different moments.  This is the main requirement for rudders so the boat can hold a course as not all things can be accommodated by the main elements.

I tried steering with two wings on a model boat years ago without any success but that is less positive than shifting a sail relative to a board. 

You may also need means to steer when the sail is down.

Connecting the sail and board on a common beam that could be tilted fore and aft would probably be the simplest to engineer. 

Rick
On 08/06/2011, at 1:27 AM, bjarthur123 wrote:

 

rick,

there's an interesting brainstorming session going on over at the yahoo proa group concerning all possible ways to steer a proa. not sure if you're following it, but wanted to get your thoughts on one idea in particular: changing the relative COE and CLR to induce a yaw torque.

for now let's not consider the practicalities of how exactly to move sails and/or foils fore to aft. rather, i'm more curious about the possible theoretical advantages.

the benefit, i think, over changing the AOA of a foil or sail, is that lift is not decreased nor is drag increased. seems faster then. but how does the maximum possible turning force compare to that of conventional rudders?

consider your proa, the one with a solid wing sail slightly longer ww hull. if one were to get rid of the two rudders and mount the non-rotating leeboard under one of the bows and the sail on the other bow, how much torque would there be compared to what your planned rudders could put out?

just curious how much of a difference in the fore-aft position of the COE and CLR would be needed to achieve the same steerage.

practically, i'm thinking of a fixed mast and a leeboard mounted on rails on the lee side of the lw hull, but wondering how much it would have to be moved fore-to-aft, and whether the length of the boat is enough.

thanks,

ben


Rick Willoughby
03 9796 2415
0419 104 821

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