Sandy Boat plans

Spritsail with Jib Set Flying

When I posted about the Sailing Pilot Boat-inspired design that I have started for Geoff Leedham, I was reminded about how much I like the Spritsail rig with a jib set flying.

Bertil Anderssons drawing of Lotsbat Skum

Back in about 1998, I think, I was working over what I thought would be the optimum-sized boat for solo and two-up beach-cruising ( see post here). The whole process became an obsession, and one of the things that I worked over in minute detail was the choice of rig. Over many decades I had sailed my existing boat with a range of different rigs, and had gathered a worthwhile amount of general daysailing and cruising experience using un-conventional rigs.



After much head-scratching, I settled on the spritsail with a flying jib (i.e. a headsail not hanked onto a stay), having been influenced by the writing of a number of people, of whom Phil Bolger was the most influential.

Why the spritsail? Here are my reasons: -

• I wanted the shortest practical spars, and in particular, I want to be able to store the spars inside the boat. Several reputable authorities had written that the spritsail sets the maximum sail area on the minimum length mast;
• A jib or staysail would be nice when sailing to windward - particularly a flying jib on an un-stayed mast;
• The rigging needed to be very simple, and preferably easy to make and repair by hand using wood and line;
• It was important to me that the centre-of-areas in the sail-plan be as low as possible to reduce the heeling moment;
• The possibility of using the mainsail as a boomless sail as well as being usable with aboom was desirable. In really tough conditions, a boomless sail is a safety feature, as there is no boom to trip during a knockdown - you can alway ease a boomless sail but not so a boomed one;
• A spritsail can be brailed if properly set-up.

The above list made lots of sense to me, but the overwhelming advantage seemed to be that the spritsail is one of the very few rigs which can carry a jib without any shrouds or back-stays. Any headsail needs plenty of tension in the luff or else it will sag off to leeward, drastically damaging windward performance. Usually the rig with a headsail of any sort needs shrouds with plenty of drift, and/or backstays in order to keep the luff taught.  A friend of mine who sails a Bolger Folding Schooner finds that it is necessary to drop his jib when going to windward, because the boat goes faster without it! This is because there are no stays and the jib sags badly when on the wind.

In the case of the spritsail, the sprit is placed under considerable compression by the snotter at the lower end (the heel end of the sprit). This compression is required to hold the head of the mainsail up and out and to keep the head of the mainsail taut.

Here you can see how the sprit pushes the head of the mainsail upwards and outwards

The above photo illustrates how the sprit tensions the head of the mainsail. The tension in the head of the sail is transmitted to the masthead, where it pulls aft strongly (somewhat like stays) and that, in turn, puts tension in the luff of the jib. A wonderful side effect is that as the wind gets stronger, the tension in the head of the sail gets greater, with the result that the tension in the luff of the jib increases just when it is needed - all in a rig which can be made by hand from a few bits of wood and some line!

Phoenix III getting to windward in fresh conditions with the jib standing very well, despite the lack of stays. In most other free-standing rigs the luff of the jib would be sagging badly.

Here is the same boat in even windier conditions, with a reef in the mainsail. Despite the reefed main and the blustery wind, the jib is standing very well once again. Note how the sprit snotter has been stretched by the stong wind and consequent high tension on the snotter - the crease from throat to clew highlights the problem - but the jib is fine.

In the photo above, the winds are lighter, but the boat is being sailed without the jib. Despite the lighter winds, the head of the mast is bending aft because there is no jib providing support. The mast bend has reduced head tension in the mainsail, allowing the unwanted throat to clew crease to form. Phoenix III was designed to balance well with or without the jib. Note how the tiller is pretty much centred, indicating that there is very little weatherhelm despite having only the mainsail set.

No rig is perfect, but the sprit rig offers simplicity, drive, low centre-of-area, short spars, and the ability to set a jib effectively without any stays. Perhaps the Scandinavians, Melanesians, Chinese, Dorymen, and Thames Bargemen, to name just a few, were several steps ahead of us...