Mast Trim on a Swan 44 MK II

Mounting of the Mast

1. The Mast is set with the strap just below the Babystay

2. Upper shrouds, forestay and backstay are tightened to take out the slack.

3. The rear mast wedge is inserted in the mast collar.

4. The genoasheet is used to pull the mast to the stern using the large genoa winches. A lot of force is required.

5. The two foreward wedges are inserted.

6. The genoasheet is released.

7. The wedges are fixed using a large hose clamp just above the mast collar.

8. The rubber mast collar cover is mounted using another large hose clamp

Vertical alignement of the Mast

1. A steel tape measure is hoisted to the masttop with the main halyard

2. The distance from the mast top to the chainplates is measured on both sides

2. The upper shrouds are adjusted until the distances ob both sides are equal. This ensures a vertical alignement of the mast.

Tensioning the upper shrouds

1. A 2 m long folding meter stick is fixed at the top end to one shroud so that there is an approximate gap of 5 mm between the free lower end and the top end of the turnbuckle. The gap is measured exactly using a sliding caliper and the value is noted.

2. The turnbuckle on one side is tightened until the gap of 5 mm reaches a value of 5 + 1,5 mm.

3. The turnbuckle on the other side is subsequently tightened until the gap reaches a value of 5 + 3 mm.

The upper shrouds are of Nitronic 50 coil -17 rod. 8,4 mm, min.
breaking load 7940 kg
stretch 0,00105 mm/mm/1000kg
1% of tbe breaking load ->  stretch of 0,00008337 mm/mm/79,4 kg = 0,08337 mm/m = 0,16674 mm/2m
3 mm stretch/2 m equals a pretension of 18% of the breaking load.

Discussion: Rod rig is commonly believed to be stiffer than standard 1×19 stainless steel rigging. This is a myth. 8,4 mm  -17 rod has a stretch of 0,00105 mm/mm/1000kg and a minimum working load of 7940 kg. 1×19 stainless steel wire comes in 10 mm diameter with a working load of 7250 kg and a stretch of 0,001157 mm/mm/1000kg and in 11 mm diameter with a working load of 8770 kg and a stretch of 0,000936 mm/mm/1000kg. To achieve the same breaking load as 8,4 mm rod you have to use 11 mm 1×19 stainless steel wire which results in a lower stretch and an even stiffer rigg. The common mistake is to compare rod rigging to stainless steel rigging with the same diameter. See:

4. The same procedure was repeated for the lower shrouds (D1), except the tension was reduced to 1,2 mm/2m