Asymmetrical Heron

Everyone loves the idea of putting a bigger spinnaker on a smaller boat. Andrew Chapman attached an asymmetrical spinnaker on his old timber heron. After a few adjustments to the boat and spinnaker, the asymmetrical was fitted and they were ready to sail.  

The first thing that is needed is a bow sprit, or spinnaker pole to carry the spinnaker forward. In this trial a simple removable non-launching pole was used and the boat itself was not altered.  Removable additions included a saddle on the bow to tie down the pole, a pin hole through the bottom of the mast to fix the pole, a block on the top of the mast for the halyard, blocks to direct the tack line and halyard to the back of the centreboard case and cleats each side at the back of the centreboard case.

The length of the spinnaker pole was determined so the spinnaker would have a good minimum clearance from the jib.  The test was with an aluminium pole 2.03 metres long 40 mm diameter with a 1.5 mm wall thickness that extends 900 mm from the bow.        

Where the pole meets the mast the pole is shaped, with a hammer, so that it fits the curvature of the mast.  A pin is placed through the pole and mast to secure the pole.  The pole extends beyond the mast to enable it to contain the exit block for the tack line, which directs the tack line to a block at the bottom of the front bulkhead. The red rope behind the pole is the spinnaker halyard, which runs down to a block at the base of the front bulkhead.  The tack line and halyard blocks are side by side and they direct the ropes to each side of the centreboard case.  Cleats to secure the tack line and halyard are placed each side of the back of the centreboard case.

The pole is tied down at the bow using the forestay fixing point and a saddle. While the pole is offset at the mast the offset is less at the bow so the exit block for the tack line ends up on the centreline of the boat. The exit block at the front of the pole is set back about 80mm and rubber stoppers are fitted, for safety, to each end of the pole.

The black rope at the front is the tack line running back to the bagged spinnaker, the pink and mauve rope is the spinnaker sheet and the blue and white shock cord secures the spinnaker bag. 
 
Mark Rimington and Sam Haines UK Sailmakers in Sandringham were given the controlling dimensions to design and make the sail.  They are 2.0 metres along the foot 3.2 metres along the leech and the straight line length of 3.6 metres from the tack to the top of the halyard.  To fit this particular sail it is essential that when setting up the spinnaker pole the distance between the tack line exit block and the halyard block at the top of the mast is 3.6 metres.

The spinnaker was trialled over two days and increased the boats speed on broad reaches and down wind.  On a dead run the spinnaker can be held out on the opposite side of the main to get more power.

- Andrew Chapman/Heron Assn