Subject: [harryproa] Re: Shunting improved by moving CLR or CofE?
From: "RobinW" <luca.antara@gmail.com>
Date: 10/18/2009, 11:56 AM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 

Hi Robert,

To distinguish some more....
I am Robin (or Robinho when I am in Portugal or Brasil). I've been reading the forum for a while now and while Rob knows a lot about the physical sailing you seem to have a handle on the 'physics' of sailing.
I've been reading it for a while because I'm building a Harryproa in Portugal and the lee hull is almost complete, so it's too late to change the size....
I started to join the discussion after Rudolf's problems with the changing of the position of his rudders, but I have been concerned for a while about how and where the rudders should be fitted and have to make a decision in the near future. Rob's latest rudder design with them swinging on the beams to kick up seems the best solution so far. He has a sheer pin set up so that when it breaks, the lines from the quadrant come loose, so I am fascinated by your reference to pulling a string. Can you explain in more detail?

Cheers,
Robinho (I'm offshore Rio, Brasil at the moment.)

--- In harryproa@yahoogroups.com.au, "cateran1949" <cateran1949@...> wrote:
>
> Hi Luc,
> To distinguish between us , I am Robert and Rob Denney is Rob
> Rob knows a lot more about sailing than me.
>
> Getting up to 20m would be very nice but it may be worth checking that your really need that size as legal obligations start to proliferate as you go bigger.
>
> A single lightly loaded sheet is definitely something nice to have but reducing the height of a mast is also if you have to go under bridges.
>
> The boats shunt pretty well as they are when the rudders ares sorted in position, size and fairing and I don't think that the addition of a leeboard is as much hassle as a second mast so I don't think this should be too much of an issue.
>
> Steering with the sails can be done but you still need some lw resistance aft as the bows still offer so much more than the stern once the load is on them , but you merely need less. Rob used to sail with the first EL in light conditions when sitting close to the lee hull with just the sails while sailing in shallow water, but once you have a cruising boat with the other great hull in the water, the luffing torque increases and you need something further aft in the water to compensate, but it doesn't have to be full depth.
> Hopefully, with the design of the rudders rotating round a mini beam, all that will be required to reset the rudders is pulling on a string.
>
> Hope you can get your boat together. It has been a long time before the start on mine and for a while I thought I might have to abandon ship,
> regards,
> Robert
>
> --- In harryproa@yahoogroups.com.au, "RobinW" <luca.antara@> wrote:
> >
> > Hi Rob,
> >
> > Yes, I can see that it might be a little easier with just one sheet instead of two for a small Harry but for a 15 m (or 20 m as mine is), I figure the one extra step to get going in the right direction would be easier than struggling with the shunt; one could leave the new aft sail flapping about before doing the 3rd step sheeting it in. Hopefully, it should be possible to do fairly easily single handed with practice, and though I do not plan to single handed, I have to bear in mind that there might be occasions when crew (or myself) is incapacitated.
> >
> > I'm glad you agree with my thoughts about reducing the load on the rudder; it is nice to get feedback from someone who knows a lot more about sailing. Would you agree then that it should be possible to sail without the rudders being used for steering? I'm thinking here of a situation where both rudders are lowered and you run over a submerged container, log, coral reef or something at high speed, losing both rudders temporarily until the sheer pins can be replaced?
> > Oh bollocks. Actually, the truth is that I think it would just be great fun to sometimes steer with only the sails :-))
> >
> > --- In harryproa@yahoogroups.com.au, "cateran1949" <cateran1949@> wrote:
> > >
> > > Hi Luca,
> > > Three of the Elementarrys have started out with twin masts and two have changed to single masts. This is mainly because of he hassle of having to deal with two sheets and two rudders single handed. The system works well enough with the single rig most of the time which is why Rob was so so disappointed by the problems of Blind Date. Rare Bird's set up works well provided there is enough draught to have the rear rudder fully down for its own balance.
> > >
> > > I am going with twin masts on my Harry, partly for being able to sail in skinny water using the sails to reduce the load on the rear rudder and partly to have slightly smaller mains. I will make sure the lw hull is built so I can convert to a ballestrom rig if the twin rigs prove more trouble than they are worth
> > >
> > >
> > > --- In harryproa@yahoogroups.com.au, Luca Antara <luca.antara@> wrote:
> > > >
> > > > The BD sailing discussion has been about a Harryproa already built and
> > > > therefore has obviously emphasized the more feasible alterations that can be
> > > > done to an existing proa by looking at moving the CLR rather than the
> > > > CofE.Rudolf
> > > > has just pointed out that BD had a tendency to luff up anyway after a shunt
> > > > unless she was already pointing downwind somewhat, which leads me to think
> > > > that the Cof E is too far back and results in larger loads than necessary on
> > > > the rudders.
> > > > For a boat that is still at the design stage (at least for the masts, sails
> > > > and rudders) I can see three possible CofE solutions that could change the
> > > > dynamics of shunting. The first is the obvious one of having a larger jib
> > > > and smaller main, but this would not work with a Ballestron rig if the Cof E
> > > > became forward of the mast, and anyway, Rob has indicated that the jib is
> > > > already quite difficult to raise. The second is to have a wing mast which
> > > > should bring the CofE of the main forward (same possible problem as solution
> > > > 1 with the Ballestron rig).
> > > > The 3rd is to have 2 masts. I have never shunted a proa but from my
> > > > windsurfer experience moving the mast (and therefore CofE) fore and aft, it
> > > > should go like this.
> > > >
> > > > 1. While heading upwind a little, let go the fore sail sheet and there
> > > > will be a tendency to luff up more as the CofE has temporarily moved way
> > > > aft.
> > > > 2. Let go the aft sail sheet and sheet it in immediately as the fore
> > > > sheet in the new direction, which gives a temporary CofE way forward.
> > > > 3. Sheet in the new aft sail once up and running.
> > > >
> > > > Other benefits of 2 masts could be the ability to move the CofE at will by
> > > > sheeting in or out the aft sail and thereby reducing the load on the
> > > > rudders. In theory one might be able to take the steering load completely
> > > > off the rudders and steer on a reach with just with the sails, as with my
> > > > windsurfer which obviously has no rudder steering.
> > > > Does anyone (Rob,Doug?) have a proa with 2 masts that can verify or disprove
> > > > this?
> > > >
> > > > Also from my windsurfer experience, I had theorized that the CLR could be
> > > > moved aft by raising the fore rudder but this does not seem to work for
> > > > BD.....
> > > >
> > > > Cheers,
> > > > Robinho (mech.eng. windsurfer).
> > > >
> > >
> >
>

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