One of the popular modifications seen on Gem 550s in Canberra is the addition of a spinnaker sock.  There are many reasons to consider introducing this modification to your Gem.

Advantages

Ease of use – this would be the primary reason most skippers decide to incorporate this modification.  If you have a trainee crew it is far easier to teach them the steps to raising and lowering the spinnaker via the sock.  It has fewer steps in the process compared to the traditional method.

Safety – often cited by those skippers with inexperienced crew.  “If something goes awry, dump the halyard and pull this!”

Operational – less chance of foul up (note less, it is not foolproof!)

Disadvantages

More wear on the spinnaker – friction from sock.

Appearance – lets face it, they are not the most attractive item on the boat!

Spinnaker Ring

If you decide to have a spinnaker sock your first issue is - where are you going to fit the spinnaker ring.  The majority of Gems have pulpits, so the usual method is to modify this. 

There are two schools of thought on this – aesthetic vs functional. 

Aesthetic - If you would like to incorporate your spinnaker ring in the pulpit with the minimum of visual disruption, consider the design shown in the upper two photos.  A bar is welded about 14 cm from the leading edge of the pulpit.  If you decide on this design ensure the new bar will not interfere with your forestay.

Functional – This design has practical advantages over the "aesthetic" model.  The ring is tilted upwards which gives the spinnaker easier (less drag) access and egress.  This in turn results in less pressure for the crew to deal with when operating the sock. 

Spinnaker Retrieval Loop

The next modification is also easily accomplished and requires a bit of industrial strength sewing.  In the middle of the spinnaker have your sailmaker sew in a loop.  It is essential that the sailmaker places this loop on a reinforced patch to distribute the load during retrieval.  Otherwise, on your first retrieval in strong winds you are likely to pull the middle out of your spinnaker!

Retrieval Line

You will need about 10 metres of retrieval line.  There is a balance here also.  If the line is too heavy it will pull the spinnaker down in light winds.  If it is too small in diameter it is hard on the crews hands when retrieving.  Make sure you have a suitable place to secure the end of your retrieval line on the boat.  You will not be the first boat to have lost their retrieval line up the sock!

Spinnaker Sock

Any sailmaker or person with access to an industrial strength sewing maching will be able to produce a sock for you.  I do not think there is any great science in coming up with the specifications for your sock.  The only issue that could trip you up is the width of the sock.  If the sock is too narrow this will result in excessive drag.  This results in increased resistance, which, of course, means more strength is required to operate the sock, which in turn increases the chance of something breaking.  Note that the sock is tapered.

The popular material for producing the socks is shadecloth.  For non-oz readers, it looks like waterproof hession.  It is made of a form of “plastic” and is used here for putting over pergola’s and outdoor entertaining areas.  Anything that is light and weatherproof will probably do the job for you.

Fitting

Lash the spinnaker sock mouth to the ring.  You will need a loop at the tail end of your sock so it can be secured to the boat at the rear of the cabin.  Also have a loop sewn into your sock about half-way along its length to provide support.  Otherwise when the sock gets wet it can drag itself overboard.

With a bit of common sense it is not difficult to incorporate a spinnaker sock on your Gem that will give you years of trouble free use.