Hi Graeme,

I like the Pelorus design and was looking at one for sale in Dargaville. The only problem for me is that she is not trailerable.

With regard to your center of effort quandary. On Arcadian I reduced the lead from 17% to ten% when I converted to junk rig, later I had to make keel modifications to restore it to 17% to get the helm to balance. Whether this was due to original imbalance in the Bermudan rig or other factors I do not know, I just know that when she was in her final form her helm was balanced. I would suggest working to the 15% to 17% lead suggested by Arnie. I also like a little more balance area on the actual sail as this reduces stress on the halyard, yard hauling parrel and sheet. It also reduces the weather helm when broad reaching or running.

Regarding the helm imbalance, I had the same problem with Arcadian and when I closely examined the existing rudder I found that one half of the original rudder shell had been installed backwards so she was never going to steer well. I totally rebuilt the rudder to a balanced shape similar to a NACA section. This totally cured the steering problems, especially under power. Paul Thompson had similar problems with La Chica and he cured it by building a new rudder, he has posted how he did it and you can follow his reasoning and results on the website.

With regard to sail area, the more the better as far as I am concerned. With a junk rig reefing is so easy that you do not need to worry about carrying a large rig and if it is not there you can not use it. Wood end plugs work well with aluminium tubes, reducing chafe problems at the ends, so you can always lengthen a batten by this means to get the sail area you want.

All the best with the project, David.

My Pelorus motor sailer, recently acquired, is a little different from the stock fibreglass version, being built in timber (strip planked) and measuring up at about 7.7m OA, about 7.44m  LWL, draft about 1.0m and, according to the travel lift driver, 3 ton displacement. I measured up the sails and found she has only 27.11 sq m of sail area (286 sq ft) under main and No 1 genoa. I have never seen a drawing or sail plan for one of these, so I have tried to make my own using a side-on photograph and measuring key points from the stem. I have determined the CLR by balancing underwater profile on a knife edge (excluding the rudder), and found the CoE of the Bermudian rig by the usual geometric method. The lead seems to be about 11 % of LWL. I have not yet discovered her helm characteristics under sail, but have found already that she is directionally unstable under power. (There is scope to shift a little bit of the ballast forward, but in the mean time I am leaving that problem to my friend Ray, the autopilot, who seems to have no problem with it.)

My goal is to find a suitable junk rig for this vessel, with a good increase in sail area, within the following constraints: mast to be mounted in a tabernacle and no higher than the current mast, sail to be not too complicated to make, as this will be my first attempt. A low aspect-ratio Arne-type cambered panel sail, built using one of Arne’s methods seemed to me to be a good starting point.

To see roughly where the mast would be placed, I sketched Arne’s 1.80 master sail plan directly onto my drawing, placing Arne’s CoE about 5% of LWL aft of where I think the original CoE was located.

This gives a lead now of about 7%

The diagram and a couple of photos can be found in my profile, member’s album.

I made the following discoveries: With 10% of balance the mast lands almost directly abaft a bulkhead position, and close enough to the front of the cabin that the tabernacle can be sunk to deck level, and there is not too much interference with the current internal layout.

That ticks the first box.

The masthead height will not need to be much more than 8m above deck. That ticks another box.

The most amazing discovery is that with this high-peaked sail, which looks so lofty on the drawing, the sail area is potentially raised from 286 sq ft to 372 sq ft – a whopping 33% increase – but with a masthead height lower than on the original Bermudian rig. Never did I imagine such an increase – in fact to get back to the original area (or slightly less) – the “working sail area” - would require two panels to be reefed. I have drawn this on the diagram too.

This increase in sail area seems at first to be rather too much, but is it possible for a vessel to have too much sail, provided it can be quickly and easily reefed – and provided the mast (which can not be reefed) is well within the limits of what the vessel was designed for? Provided the rig can function reasonably efficiently with two reefs in, there seems to me no reason why this boat could not carry 372 sq ft in light weather (the equivalent of flying a spinnaker) and drop down to a working rig of two panels down when the wind freshens a bit. Is this argument flawed in any way? If not, then I would expect a conversion along these lines to result in quite an improvement in light conditions.

The mast position worries me a little – my drawing shows barely 10% of balance and the boat’s interior design does not allow it to be easily moved aft – in fact a few inches forward would be better.

The forward rake of the mast is only drawn as 2% so really the only tweaking possible here is forward rather than aft.

Ideally (to retain my nice roomy forward cabin and to make getting in and out of bed easier) the mast would be at least 10 - 20cm forward of where it is shown here. To maintain 10% balance of the rig, Arne’s CoE would then be aft of the boat's original CoE by only about 3%, which suggests the rig is now too far forward.  On the other hand if we just consider lead with the proposed junk rig, and forget all about the boat’s original CoE, by moving the mast forward the lead is now about 8.5%, still a long way from the ball park figure of 14% to 16% lead which Arne says (in a recent post to L C-G) he aims for in a long keeled boat, calculated without rudder. On that basis the mast should be moved forward or raked forward even further (which it probably could be.) Getting slightly confused now.

Perhaps this is all worrying too much over small amounts, considering the parameters we are dealing with are theoretical, approximate, and relate to the static situation only.  I guess all that is required at this stage is just a little room for adjustment should that prove necessary later, but I don’t really want to move the mast aft of where it is drawn here – and I would also prefer not to reduce the small forward rake. Other planforms could be considered of course – though I have begun to rather like this one.

Finally, I would scale this rig down very slightly to bring the batten length from 5.077m to 5m (I believe this is the length of suitable stock tubing in this country) – the lineal scale factor for this is only .984 and the sail area would be reduced to about 360 sq ft.

I would be grateful for any appraisal of this proposition, especially the pointing out of any errors.