Why a Cat Ketch?

Posted by Graham Byrnes on Jan 1st 2015

You may have noticed that B&B Yacht Designs has several models that are cat-ketch rigged. For example the Core Sound 15 pictured below sailing at our annual messabout.

Perhaps you are not familiar with this rig, and think that it looks “old-timey.”

And, perhaps you think that this rig is not as “efficient” as a “modern” sloop rig.

First let us dispel some common myths about the cat ketch rig.

The rig type is, indeed, one that has been around for many years, and one which was greatly favored by the watermen of the East Coast before the age of power. The rig fell out of favor not because it was inefficient, but because working sailboats became obsolete, and the recreational sailboats which have been built since, are influenced not by the need for efficiency and speed, but by an artificial rating rule. Such rules, made to “equalize” boats on a race course, often penalized the very things which made a boat fast. So designers’ of “modern” boats designed boats that could get the greatest benefit from the lowest rating – and not necessarily the best and fastest boat they could have designed. When ratings were not an issue, the cat ketch has been a rig favored for it’s gentle ways. Several designers in recent decades have utilized this rig to great advantage on some contemporary, even avant-garde designs. In head to head competition, cat ketches have performed well. Our boats have an admirable racing record, although they were never designed as racers.

What are the unique advantages of the cat ketch rig and why have we chosen it for some of our designs?

Before going on, let us say: We are not missionaries for this rig. It is not a trademark of our designs in that it in no way represents the rig on the majority of our plans. It is however, a rig, which we have found to be extremely suitable for certain types of boats. So, it fits with our philosophy of making each design work as well as it can for it’s type, while retaining a cost effective approach without compromising quality or performance.

The well-designed cat ketch rig is a simple, inexpensive and balanced rig.

The sail plan spreads the sails along the length of the boat on two masts. The low center of effort afforded by the fore and aft, rather than upward, spread of sail, produces less heeling force.

Free standing masts require no rigging; making them quick to rig and unrig, easy to reef and inexpensive. They also offer an innate degree of safety: the masts bend during gusts, flattening the sail and de-powering the rig.

Each spar is lighter, smaller and easier to handle. This is really important with beach boats, day boats and other dry-sailed craft. It only takes a few minutes to rig. In our designs, up to about 20′, stepping the masts can be accomplished by one person. Being able to get in and out of the water quickly and easily makes sailing so much more accessible. If you have to contemplate an hour of preparation just to go sailing; it isn’t likely that you will go sailing for an hour! In today’s busy world you may have only a few days when you are free to take the whole day for sailing. On the other hand, we all have the odd hour or two of free time, and when the boat can be launched and retrieved in minutes, you can spend that hour sailing. Our larger or cabin boats utilize hinging masts in tabernacles that can also be setup quickly with one person

Docile. That is probably the best word for the behavior of this rig. Your days of yelling, “prepare to tack”, “tacking” – “let it go”, and “pull it in” are over. When you want to tack, you simply put the helm over and off you go on your new course. The sails will tack themselves. This may be a little un-nerving at first. If you have been sailing only sloops or ketches with headsails up until now, you will feel like you ought to be doing something. We’ve noticed however, that it takes the average sailor only about 3 tacks to get used to this laid back approach. By the 5th tack they are enamored and begin to aimlessly tack back and forth with a great big grin on their faces. The crew is equally happy, because they haven’t moved a muscle or been yelled at during the whole procedure. As delirious as the tack may make the laid back crew, they will really get excited by the jibe. Jibing has traditionally been a recipe for disaster, with such fanciful names as the Chinese jibe, invented to describe just one of the multiple possibilities for complications. In the cat ketch rig, jibing requires exactly the same degree of panic as the tack we just discussed…you just put the helm over, pull in some excess sheet if you wish and let her slide out the other side.

Upwind. The cat ketch rig is handy and comfortably close-winded. Provided you have a good hull under you (never blame a good rig for a poor hull design), she will go to weather nicely.

Reaching & Running: Since the sprit bisects the sail load, the area above and below the sprit are balanced. So when the sheets are eased, the sails go out and stay out with none of the collapsing and filling that is the bane of the normal jib behind main. Nor is there the twisting off of the typical mainsail, when the boom lifts and causes a “death roll” in strong winds. Somewhere between a very broad reach and a run, the main sail will begin to shake and lose power. This is not a problem, just turn off the wind a bit further, jibe the main across and return to your desired course.

As you have already learned, jibing, the bane of most downwind sail-handlers is a snap. With a cat ketch rig you can also sail directly down wind, wing and wing. The boat feels stable and whisks along nicely. If the wind gets up and things get hairy, on an unstayed rig (which includes most smaller cat ketches) you can just let those sails go forward of the beam. This will immediately stabilize the boat. Also, the sails when they are allowed to go forward (about 20° ), will keep the boat tracking downwind, so it makes a very easy time of what would be the most delicate conditions for a sloop or cat rigged boat.

Taken to it’s extreme, you can make delicate and gentle downwind landings in any weather by just letting the sheets go and allowing your sails fly forward completely, at the same time lifting your centerboard and letting go of the rudder pennant to lift the rudder…you glide into your (shallow) landing under complete control. This is a far cry from the usual tension and chaos of a downwind landing on a blustery day.

The anatomy of the cat ketch rig:

There are two masts, one set close to the bow which is the mainsail and a mizzen which is usually near or just aft of the center of the boat. The mainsail is larger than the mizzen – although the sails are much more evenly divided size-wise than in a jib-headed ketch. (And to answer the question many ask: yes if the forward sail is smaller it is a cat schooner – not a cat ketch rig).

The sails may be of any shape – some have gaffs; others, like our designs are marconi and have sprits not booms.

We chose sprits rather than booms because they are quick to rig and cheap to build and easy to stow (smaller models use simple and available fir closet rod)…

The sprit is a diagonal spar which holds the sail between the clew and the mast – it serves the same purpose as a boom. We like it in small boats particularly – because it eliminates the boom moving across the cockpit of a small boat and eliminates the need for a boom vang. If you are in the way during the tack, the sail just slides over you harmlessly (the one exception: do not sit directly in front of the mizzen mast on the middle seat, or you could get hit with the main sheets or the clew end of the sprit).

The sprit is attached to the clew with the end poked through a loop of webbing or rope. The forward end fits into a rope which is lashed to the mast (a snotter). This controls the height of the sprit and the relative leech and foot tension. Because these are all “soft” fittings, they are easily adjustable. There is a line to a cleat so that you can adjust sail draft while underway.

Sprits may be either straight or curved. We have done some informal tests and have not found that the curved sprits are enormously superior, although some people prefer them.

We are asked if full wishbone booms are more efficient, and yes, they are – but the little bit of extra efficiency comes at the expense of simplicity and cost.

If you are a good wood worker and like laminating things, curved sprits and wishbones are a nice touch and they can be made quite pretty.

The sprits are placed on opposite sides of the sails; in other words if the mainsail has the sprit on the starboard, the mizzen will have it on the port. Although the sail flops over the sprit on one tack, it does not affect the efficiency as much as it might appear to.


Shortening sail can be accomplished in two ways. In smaller models, the simplest way is to first, remove the mizzen and place the main in the center (single) sail position (given on all our plans for this rig). If the wind continues to pipe up, change down to the smaller mizzen sail. The second way to reef – which may the most desirable on the larger models, and an option for the smaller models for those who may not be comfortable with the mast exchange, is to have normal reef points in the sail and add halyards.

The combination of the sprit rigged cat ketch and a centerboard board allows for a great deal of adjustment for balancing out the boat in any conditions. If there is some lee helm in light wind, the board can be lowered further, moving the center of lateral resistance (CLR) forward or you can adjust the sails without lowering the board – sheet in the mizzen or let out the main…or combine the three options. Weather helm? Reverse the procedure. Normally (as designed) the helm should be neutral at 8-14 knots, with an increasing weather helm as the wind increases. When the sail/board adjustments are not quite enough to neutralize the helm, you can reef. You will always be able to trim to balance the helm in any conditions, by these methods.

Some Tips for Sailing a Cat Ketch:

  1. Because the sprit bisects the angle of the sail, there is very little load on the sheets. A simple cleat is all you need.
  2. Our designs call for, and we strongly advocate the use of double ended sheets, so that no matter which side of the boat you are sitting on, you can adjust the sheet without leaving your position. (Remember this is laid-back sailing).
  3. In windy or gusty condition, you always have the end of your double ended sheet close at hand and if you get a strong gust and feel you have heeled to an uncomfortable angle, just let the mainsheet go to reduce wind pressure and heeling force. WARNING: Be sure that you release the mainsheet (the forward sail) first. If you let the mizzen go first, it moves the center of effort forward and the boat will bear away which will increase the pressure and heeling and could cause a capsize.
  4. When sailing in light air, if your sails get a vertical crease close to the mast, ease the luff tension.
  5. When the wind is heavier if you see horizontal crease near the mast, increase the luff tension.
  6. Use the snotter line to adjust the relative tension of the foot and leech, they should be evenly and equally curved. So if the leech is tight and the foot is full, lower the angle of the sprit and for a tight foot and loose leech raise the sprit angle.
  7. Grounded! The day will come when you will run her aground in a strong breeze and you’ll get the centerboard stuck so you can’t raise it. The boat will swing around to a somewhat beam-on position. Now in most boats you’d be in a nice pickle…but with the cat ketch, just let the main (foresail) go and the center of effort will go so far aft that she will spin around and tack – then you can re-sheet your forward sail and sail off.