Because of the nature
of the rig a junk sail works best on an
And with most junk rig conversions the mast will need to be positioned
of the bermudan mast position.
So, before you start to design the sail you need to check your boat for
suitable position mast, then design the sail plan to suit.
Positioning a junk sail is about getting the sail’s CE (Centre of
positioned in front of the hull’s CLR (Centre of Lateral
Too far aft and it will develop too much weather helm too far forward,
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,
sails etc, and of course it will depend on the mast position.
Having said all that, it is rare for a junk rig to suffer from much lee
weather helm is much more common, so the further forward the CE the
However, this is not
exact science, the CE of a sail will alter as the wind strength alters
you trim or reef the sail.
The CLR of the hull will alter somewhat as the boat heels and the
It is because of the desirability of having an unstayed mast
that the junk
rig conversion of catamarans can be problematic, though some have
this by having a twin rig with a mast in each hull.
And shrouds can be used though this will greatly reduce the versatility
Tabernacles have been used on some smaller boat junk rig conversions
still need as much bury between the pivot and heel as for fixed masts,
calls for an intrusive ‘slot’ extending below decks.
The CE can be moved forward by raking the mast forward.
Forward rake is seen on many Chinese
vessels but with a single masted junk rig conversion there is a danger
this may cause too much downwards press on bow.
For a single masted rig the recommended rake is 'plum'.
The first consideration
for a junk rig conversion is having sufficient ‘bury’ to support
An unstayed mast is only attached to the boat at the mast step and at
partners, the distance between these is known as the ‘bury’.
As a rough guide this should not be less than 1/10th of mast height
deck or the length of boat.
The next consideration is how the loads on the mast will be transferred
spread to and from these two positions.
Even though loads on a junk mast are less than with a bermudan rig they
still be considerable.
So, the mast partners and the mast step need to be strong, affixed to
beams, bulkheads or floors and able to spread the loads without causing
strain on the hull shape.
First check that there are suitable floor timbers across which to fit a
This should span and be fixed to at least two floors, preferably more.
The mast step should be strong enough to take loading in any direction,
particularly sideways, towards aft and vertically down.
have a look at the
deck beams to see if there is a suitable position to place the ‘mast
partners’ directly above the ‘keel step’ position.
The partners support the mast at deck level and spread loads across the
They should be supported between two main deck beams and two carlines
reinforced with tie bars and logging knees.
Once you have established where you can put the mast then you can
sail plan to suit your junk rig conversion.
Give a man a fish and
feed him for a day.
Give him a fishing lesson and he'll sit in a boat drinking beer every
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However, I need to point out that I am an amateur wooden
boat enthusiast simply writing in order to try to help other amateur
wooden boat enthusiasts and while I take every care to ensure that the
information in DIY Wood Boat.com is correct, anyone acting on the
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