One Design Rudders? “One design” boats are manufactured to be as near as possible identical, and conform to standard measurements and weights. This makes them all “within class”rules. Although the Catapult was built as a one design boat, certain alteration have been accepted by the Catapult Association to keep the boat up to date and to allow replacement parts that are now less obtainable. The changes made over the years have been accepted with an eye to retaining the original concept and performance, so that any original boats are not too compromised. The main changes accepted by the Catapult Association (which has to consider fair and equal racing) have been to the mast type and rig design. So for the cruising owner any rig is fine and still reasonably competitive. The newer aluminium mast, and the round head sail from Hyde, are the current most common options. Sails are readily available but masts less so. For those wanting to know more about the history and development of the Catapult there's a write up on its history under “Sailing the Catapult Catamaran” on the Web Site Home Page entitled “The Boat”.

The Rudder Issue It was discover, by member George Evans, that there were some anomalies regarding Catapult rudder arm lengths. Some, boats constructed around 2007, may have been fitted with shorter tiller arms. These being about 100mm shorter. This 'short-tillerarm' anomaly was discussed at the 2014 Annual General Meeting (AGM). It was discussed whether boats with longer arms, could be cut down to the shorter length and still be within class rules. It was agreed that they could be, and this was ratified at the 2015 AGM. Should you plan to alter anything else, it's advisable to have a chat with John Peperell (Technical Measurement Officer) for advice first. This will avoid you doing anything that could make your boat “out-of-class”.

To cut or not to cut?

You know that’s the question...

At first sight the variation in tiller length may seem to be of little use. But, having shorter tiller arms takes the tiller connecting bar further aft. This creates a larger gap between the rear beam and the connecting bar, which in turn provides extra space for you to sit on the rear cross beam without fouling the rudder connecting bar. In very windy conditions this could make the difference between you staying upright or sticking the bows in and 'pitch-polling'. If you're not likely to go out racing in a near gale, don’t even bother with this mod. (Return to Catapult Home Page) (Return to Repairs and Mods Page)

The down side of shorter tiller arms is that the reduced leverage slightly increases the pressure felt through the rudder when sailing. If you notice this, or have to pull hard on the rudder to keep sailing straight, then move the mast rake slightly forward on the adjuster above the bridle wire. Moving the pin down one hole will shorten the fore-stay and tilt the mast forward slightly.

Which end to Cut? I decided to shorten mine at the forward (connector bar) end. The connector bar pins and internal spacer tubes in my tiller arms were corrosion free and unscrewed with no problem. Try removing the pins before deciding where to cut, to see if your luck's in. If the pins come free can be tapped through the spacer tubes, you can saw off at that end, but don't leave the overall length of the tiller arm less than 410mm. Note- Your tiller arms could have been shortened previously by someone, so check the information below in red italics before you start cutting. Compare both rudder lengths first, in case they differ. If they do, then obviously measure the length you are going to leave on, rather than what you are going to cut off.

A non-shortened tiller arm is 510mm long. A shortened tiller arm is 410mm long.

Cutting off at the aft (rudder stock) end. If you find that your connector bar pins or the internal spacer tubes are seized, you may prefer to leave that end alone and cut the tiller arms at the rudder stock ends. This would mean drilling out 6 rivets, cutting the tiller to length, re-fitting, re-drilling and replacing the six rivets in each arm. This is a lot of rivets to drill out and replace. If stainless steel rivets have been used they may be difficult to drill out. If so, you may need to grind the rivet heads off. But be aware that however careful you are, grinding is almost guaranteed to mark the rudder arms. Whichever end of the tiller arms you decide to cut, I would suggest assembling the basic boat frame when doing the work, as this will help with alignment and testing afterwards. If you find any problems with cutting at the aft end, I would appreciate the feedback – [email protected]

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Cutting off at the forward (pin) end. There isn't too much to go wrong with cutting at the forward end, but before removing each connector bar pin make a note of how many tiny spacer washers are fitted on each side of each one. These washers control the alignment of the rudder blades relative to each other, so they need to be fitted back onto the same sides and in the same positioned that they were removed from. Tip; Take photos first. Make sure that you drill the new pin fixing hole the same diameter as the old one and perfectly square. Mark where to cut and where to drill. Drill the new hole before cutting the tiller down. You can then copy the existing hole orientation and use the old hole (with a drill bit in it) as a visual guide if using a hand drill. I nearly drilled mine 90° out. This was because the pins are vertical and therefore it seems natural to drill a vertical hole. But there’s a 90° bend in the pins - yes! A drill press with a vice is best for this, alternatively use a helper to stop the rudder twisting and to visually check your drill angle against the drill bit in the old hole. Final warning! This work is so simple to do, that there’s a good chance you could mess it up by not concentrating. i.e. by drilling through the wrong face of the tiller arm, or not checking the overall length before cutting, etc. One last thing to get right is the correct angle of the connector bar pins before you finally tighten them.. (See photo below). This must be done on the boat. Don’t line them up at right angles to the tiller arm or your rudders won’t turn. Line them up at 90° to the HULL beam’s top surface.

Newly shortened tiller arm. Line the pin up at 90° TO THE HULL BEAM’S top surface.

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Rudder Alignment Take the opportunity, while the boat frame is set up, to check the rudder blades for alignment. The aim is to obtain equal measurement between the tiller bar ends and the base of the rudder blades in the raised position. (photos below) Remove any play between the rudder blades and the rudder stock before making any alignment measurements.

The above “linked” photos show a tape measure held between the port tiller arm and the starboard tiller arm giving a measurement of just over 75.5”or 1920mm (i.e. from left edge of the port tiller arm to left edge of the starboard tiller arm). Having measured as shown above, move the tape measure to the very end of the lifted rudder blades. This measurement should be identical to the first one. If not, you need to move washers from one side of the tiller arm pin to the other. Adjust until the forward tiller arm measurement is equal to the aft rudder tip measurement (not necessarily 1920mm.) The actual distance may vary slightly between boats I made the mistake of putting some copper grease on the pins when assembling them to prevent future corrosion. This allowed one of them to come loose while sailing. Retightening worked ok, but I had to tighten them harder than I would have liked. On reflection, assembling them dry might have been better. Update;- My connector bar pins came loose again while racing at YDSC, 2016. This was despite me having since washed the parts with acetate and re tightened them. Go figure! Syd - Catapult 506 First published August 2014 Amended December 2016 (Return to Catapult Home Page) (Return to Repairs and Mods Page)