Have you ever thought what would happen if your rudder fell off when you were out sailing. The calamity is perhaps only one down from losing a mast. What would you do? Could you still steer the boat? This question was posed to me recently when I, along with a number of others, were taking a U.S. Sailing Instructors course. As part of the class we each had to present a short lesson and mine was steering a boat without a rudder!
Though not easy, this is possible and learning how will help you understand better how your boat sails and how best to tune the rigging and set the sails. Imagine you are out sailing on starboard tack with the wind on your beam (Fig 1). Your sails are working to propel the boat forwards and to leeward but the hull section below the waterline (Fig 2) including the keel (or centerboard) is resisting the motion to leeward and so your boat moves mainly forwards. This underwater section that stops the boat moving sideways is important. If the sideways push from the sails is too far forward or too aft the boat will pivot rather than move sideways and the boats course will change. To compensate for this happening the rudder is normally used to keep the boat on course. But without a rudder, the only way to keep on course is to set the sails so that no pivoting occurs.
The underwater section of the hull pivots around an imaginary point called the center of lateral resistance (CLR). If a push is applied at this point the boat would move exactly sideways. On a sloop rigged vessel the mast is placed close to the center of lateral resistance (though in practice it is always forward of this point). Now it becomes clear that if sailing only with a jib (Fig 3), the force of the sail will cause the boat to pivot and the bow to move to leeward. In other words, a boat with just a jib and without a rudder will turn away from the wind. The opposite happens with the mainsail (Fig 4) and the boat heads towards the wind. When the sails are set perfectly the forces from the jib and mainsail will be equal and the boat will be balanced (Fig 5). This is the ideal, and those sailors who win races will achieve this set nearly all of the time.
Without the rudder it should now be clear that you can steer the boat by using the sails. If you sheet in on the jib and let the mainsail luff then the boat will turn away from the wind; if you do the opposite and let the jib luff and sheet in on the main it will head up into the wind. By slight adjustments of the sail trim you will be able to steer!
The sails are not the only thing that can affect the way the boat sails. The weight of the crew is an important factor as is obvious when you watch any racing sailboat beat to windward with the crew all leaning out on the high side.
If the crew weight is too far forward, the underwater shape of the boat will change as the bow goes down and the stern comes up (Fig 6) with the result that the center of lateral resistance will move forward. Now there will be more sail area aft of the CLR than forward of it and the boat will try and turn up in to the wind. The opposite happens when crew weight is too aft. Moving the crew weight forward or aft will help steer the boat.
When a sailboat heels over the effect is that it tries to turn up into the wind and to stop this happening a lot of weight is needed on the rudder. When the boat is upright, the combined force of the sails is directly above the center of forward resistance (CFR) of the hull (Fig 7). The sails push forward and the drag of the hull tries to prevent this. When the boat heels these forces are no longer above each other and the effect is to turn the boat into the wind (Fig 8). It is therefore desirable to keep the boat sailing as upright as possible to stop this happening and this explains why a racing crew is always on the windward side when beating. You can use this healing effect as another way to help steer a boat without a rudder.
And so when your rudder falls off you can steer your boat using the sails and the weight of the crew as follows:
To turn the boat into the wind you can:
- Sheet in mainsail and/or let out jib
- Move weight forward
- Heel boat to leeward
To turn boat away from wind you can:
- Let out mainsail and/or sheet in jib
- Move weight aft
- Heel boat to windward
Next time you are out sailing try tying your rudder amidships and using the sails and crew weight alone to steer the boat. This will certainly help you learn about how your boat handles and will help improve your sail trim. But one piece of advice. Don't try this when there are lots of other boats close by! The only time I have had to sail a boat without a rudder was back in England when I was dinghy sailing. A couple of miles from home our rudder broke off and we had to get back. We used sail trim and crew weight to steer but it was not easy. For a while we would do fine but suddenly we would find ourselves heading up, tacking and then gibing so that our course home took a rather circuitous route which included numerous pirouettes. From the air it must have looked like an extremely amateurish ballet under sail! But we did make it eventually.