Mast position for a junk rig converting from Bermudan

I've seen a wooden yacht in fair condition bermudan rigged but I wish to change to a Junk rig.

What is the optimum position or is it dependent on boat type?

She is long keeled with a centreboard, canoe sterned and has a 3' bowsprit so the mast is a little forward anyway but not I think as far forward as is usually preferred for junk rigs.

Mike Slater


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Response
by: Mike Slater

Thanks Mike, that is very helpful. It sounds as though you are the owner of Mignonne as you have probably encountered this situation previously.

Regards

Mike

Junk Rig Mast
by: Mike

Positioning a junk sail is about getting the sail’s CE (Centre of Effort) positioned in front of the hull’s CLR (Centre of Lateral Resistance).

Too far aft and it will develop too much weather helm too far forward, lee helm.

The CLR will be fixed by the shape of the hull.

The CE will depend on the size and shape of the sail plan.

The sail plan can vary enormously, depending on the aspect ration, number of sails etc.

And of course it will depend on the mast position.

With a conversion, it is probably best to start of by looking at where the mast can be positioned, then design the sail plan to suit.

With a conventional single junk mast his will be forward of the original Bermudan mast position.

The unstayed mast is going to have to be keel stepped, so you need to look see if there are suitable floor timbers across which to fit a ‘keel step’.

Then have a look at the deck beams to see if there is a suitable position to place the ‘mast partners’ above the ‘keel step’ position.

Once you have established where you can put the mast then you can design the sail plan to suit.

However, this is not an exact science, the CE of a sail will alter as the wind strength alters and as you trim or reef the sail.

The CLR of the hull will alter somewhat as the boat heels and the underwater shape alters.

Having said all that it is rare for a junk rig to suffer from much lee helm, weather helm is much more common, so the further forward the CE the better.

I hope this is some help.

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