Monday, May 29, 2017

Increasing Sail Area

One of the subjects I deal with frequently in email correspondence is the question of increasing sail-area of that shown on plans. The answer, of course, is that sail-area can be increased as much as you like, but is it advisable?

Here is part of the text of a recent email exchange on this subject which may be of interest:-

I have plans for the First Mate , bought a couple of years back before we bought and started to renovate our workers cottage here in Germany. I am nearing completion of the of the major work on the house and will have time to build the boat for myself and the rapidly growing 2 kids we now have.
We live in a land locked position with several large lakes to sail (10 suare km not to Somerset standards). However the winds are usually very light as a general rule. We can drive to the Netherlands and sail the inland waterways  again this involves making a weekend of the journey. ( 6 hour turnaround). 
The other use will be some trips down several of the main rivers that flow into the north sea. The planned trips back to Denmark and Sweden.
I have looked at and bought several sets of plans but have always come back to the Phoenix III/ First Mate as it will do everything without a fuss. 
Sorry about the long winded explanation.... Could I squeeze  up to 10 square feet more in a lug design? I'm looking for a rig that we can drop very quickly when we sail in the river and for when the kids get older, for them to sail on there own.

The author of this message is a knowledgeable and sensible fellow who was asking about a quite modest increase in sail-area (about 15%), but there are more things to consider than just the increase in area. Below is my reply:-

I can definitely draw you a larger Balance Lug rig, to any increment within reason. The issues are that as the rig area increases, the yard and boom lengths increase as well, and therefore they increase in cross-sectional area and weight, meaning that storage issues become more of a problem and the boat has more weight that needs to be driven by the sails - and so on in a cascading (well, slightly rippling..) manner. In addition, space under the boom becomes an issue, and you need to look at increasing the length and diameter of the mast.

What I put your way for consideration is the standard Balance Lug rig, with the standard spars, but with the heel of the boom pulled aft (I can show you the details of the rigging) almost to the mast, turning the Balance Lug into a Standing Lug. The aft end of the boom cocks up high, helping with room underneath for the helmsperson, and a nice consequence is that as the longer aft part of the boom swings out when eased, it is higher above the water. This helps to prevent the boom end dragging in the water, and sailing the boat over no matter how much the sheet is eased.

Not only does the boom move aft and up, but the centre-of-area also moves aft relative to the centre-of-lateral resistance. This allows one to set a jib to bring the centres back to the correct location, and provides much more boost and windward performance than a larger lug would have done. This is all achieved with virtually zero increase in rig weight and length of spars, as the jib is set flying i.e. not hanked onto a fore-stay. A jib set this way can be flashed out and in an a matter of seconds, and does not require silly roller furlers and such like. You still have the original Balance Lug available in an instant, simply by loosening the boom parrel. If required, you then move to reefing the Balance Lug normally, and there are few rigs better adapted to reefing than a Balance Lug - the Chinese Lug (or Junk) rig being a notable exception.

Let me know your thoughts - I'm happy to draw the bigger lug if that is your preference. I've attached a PDF to show you the idea.