Subject: Re: [harryproa] HP balance
From: "Rick Willoughby rickwill@bigpond.net.au [harryproa]" <harryproa@yahoogroups.com.au>
Date: 3/26/2019, 1:54 AM
To: "harryproa@yahoogroups.com.au" <harryproa@yahoogroups.com.au>
Reply-to:
harryproa@yahoogroups.com.au

 

The HP has thrust and drag misaligned when sailing in light wind and that misalignment produces weather helm.  However the big rudders just outboard of the beams can be used to balance the boat effectively by raising the leading rudder with the trailing rudder remaining immersed (or just letting the leading rudder free but that produces extra drag).  That shifts the CLR aft and the helm required to track straight can offset leeway.


When first testing the swinging dagger board on the 18m proa, the locking pin worked its way out unknown to us and the board swung enough until the pull down rope was taught to shift its centre of resistance about 1m aft of the middle.  It made a difference to the balance of the boat and we were not only sailing faster than an adjacent 50ft mono but also higher.  When we shunted to the new tack we could not point at all with the board hanging forward of its locked position.  It took three attempted shunts before we realised the locking pin had come out and the board was now forward of where it should be so increasing the weather helm. 

Rick

On 26 Mar 2019, at 1:38 pm, ryanonthebeach@gmail.com [harryproa] <harryproa@yahoogroups.com.au> wrote:

Let me know if I have got this right: (Assuming a schooner rig, two mains no foresail)


As the HP is symmetrical there is a challenge of compensating for a moving CE (Center of Effort). i.e. when shunting the CE which is aft of the center flips over to the other side. If the dagger boards are both equally down the CLR will be in the center. This may leave a larger gap between the CE and CLR, which would result in weather helm and push the nose into the wind… which is why after a shunt you would sheet the fore main sail in first, wait to pick up enough speed for the rudders to bite, then sheet the aft main in and counter a bit with the rudders. It seems constantly fighting the weather helm with the rudders would compromise performance a little though. 

Alternatively, you can move the CE aft, the dagger boards could be individually adjusted. I.e. after a shunt the fore dagger lifted and the aft lowed some moving the CLR back to just ahead of the CE and thereby balance the boat.  

Questions:

=>Moving the CE: Seems like quite a bit of effort to raise and lower the dagger boards on each shunt. Has anyone figured a system with lines running back to the helm station to make this easier to balance the boat? Most cats worth their salt have boards and a system for this.

=>Is a more central CLR possible? This seems like a much bigger challenge to solve. Did see a video of one large proa with a movable mast base, really doesn’t seem like a practical idea given mast loads etc. 


=>If the most practical approach is moving the CE back with the boards, closer to the CLR for balance, are there disadvantages to having both CLR and CE far back, a longer nose…?


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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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