Sand Friendly Auxiliary Wheels Many Catapult owners will agree that the standard 10 inch launching wheels are fine on smooth hard surfaces, but fall short of being ideal on shingle, or soft sand.

Fig.1: Auxiliary axle and wheels. Despite the Catapult's light weight, the small wheels can bog down in soft sand or shingle, sometimes requiring two people to make any progress. A slight improvement over the original 10” solid wheels is to replace them with 10”wheels with inflatable tyres (the outside pair in Figs. 1&2). Inflatable tyres definitely make the ride softer and kinder to the boat frame, but won’t help much with pulling the boat across shingle or soft sand beaches. I’ve tried using my own Dart 18 Euro-Trax axle with balloon tyres. But getting these under the Catapult proved impossible single handed, because the cups don't slide on the Catapult’s Hyperlon hulls, and the boat needs lifting very high to get them under. The heavy weight and storage room required for balloon tyres are other problems, not to mention the cost at £175 per wheel. WOW! What I wanted was something cheap and compact, yet light and easy to transport. (Return to Catapult Home Page) (Return to Repairs and Mods Page)

The solution I came up with, was these auxiliary wheels (Figs. 1&2) that simply clip into a hole on the inside of your own wheel frames. They eliminate the need to carry hull cups, or heavy wheels, and they support the boat perfectly. After weighing up the pros and cons, I decided on standard 16” wheels with inflatable tyres. These are used on most dinghy launching trolleys. These don’t take up too much car storage room and are lightweight.

Fig.2: The new wheels hold the original wheels just clear of the ground. My own axle was knocked up with what I had in the garage. For this article I’m assuming that you’ll use a single length of 25mm outside diameter thick walled alloy tube. Towing Note:- A tow rope tied around this axle removes all the downward pull on the bow that you get when being towed by the mast foot. The axle alone, (minus wheels) is worth using if you are towed regularly. The new 16”wheels work together with your 10” ones on soft sand. And the bracing effect prevents the dagger board arms from being stressed inwards by the boat’s own weight.

Auxiliary wheels travel inside the red bag.

The axle simply clips into position and dismantles in seconds, with no tools required. The wheels go into my red bag (left) and the axle travels with the boat on the roof rack. The red

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bag stops the tyres marking the hulls.

Materials and Tools Two 16” wheels with 1” (25mm) spindle holes. Obtainable via eBay at sensible prices. Around £20 a pair delivered. 1.5mts of 25mm outside diameter thick walled Aluminium tube. Thick wall alloy pipe is usually available on eBay. At the time of writing £20 for a 1.5m length delivered. Thin wall tube is lighter and cheaper, but use the thicker wall if towed *. Four 25mm ID plastic washers. I couldn't locate any suitable ones ready made. You may have to make these out of some thick plastic sheet. Use a 1” and 2” hole saw. (A vehicle number plate or a thin plastic chopping board etc. could be used) If you find a source of suitable washers, an email would be appreciated. [email protected] Four or more stainless steel Axle Retaining Pins, approx 3mm x 72mm: Known as “R pins”. (eBay again – 5 pins for £3.10 free delivery) Two 50mm long off-cuts from ~32mm plastic waste pipe. Security spacers.

*Optionally, Some

26mm (minimum) Inside diameter alloy tube to slide on between

the wheels. To reinforce the thin walled axle if towed by a tractor. Tools – A 25mm and a 50mm metal cutting hole saw, Hacksaw, Drill and drill bits, etc.

Fabrication Start by fitting your standard wheels into the assembled bare boat frame. Support the hull beam to keep one wheel off the ground, then spread the wheels apart to lightly take up any slack in the wheel frame channels, but no more. Measure the narrowest point between the inboard faces of the wheel frames. Add 30mm to allow 15mm of axle insertion at each end. My wheels frames were 1300mm apart, so a 1330mm length axle was required. There will be variations between boats, due to frame condition etc., so take your own boat's measurement before cutting. (Return to Catapult Home Page) (Return to Repairs and Mods Page)

The Axle Hole Drilling Guide (below) assumes a single piece of 25mm O.D. alloy tube.

Axle Hole Drilling Guide (not to scale)

Cut the axle tube to the length calculated and grind off any sharp edges. Drill small holes, about 4mm diam in the positions shown. Drill these all in the same plane. The “wheel width” (on guide above), may vary between wheel manufacturers, so the position of the innermost holes will depend on the thickness of your own wheels plus any washers. More on washers later. Cut a couple of 50mm long plastic wheel spacers from some domestic waist pipe or similar. These fit over the axle at the “50mm” dimension marks. Stops tyres rubbing, and prevents the axle coming out, or locking up, if an “R” clip gets lost. Using a 25mm (1”) hole saw, drill through one side plate of each wheel frame. Drill as low as possible to the bottom of the flat area (photo below). Drill a test hole in some scrap first. My 25mm (1”) hole saw made a 32mm (1 1/4”) diameter hole. My finished hole size of 32mm was OK, but don't go any bigger than this. Protect, or remove your 10” wheels while drilling the holes.

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Note the position of the small 'anti rotation' bolt. This is best placed forward of the large axle hole. (Inside edge of Starboard wheel shown)

Drill a small hole just forward of this to take a short (anti rotation) bolt. This bolt prevents the new axle spinning around in the locating hole. The 'R' pin will but against it if any rotation starts. This position also keeps the bolt out of the way while sliding the axle down into the locating hole. Fit and tighten a short nut and bolt in the hole. Use thread lock or a nylock nut. Cut off any projecting thread that might catch on the trampoline as it passes through. Before fitting the wheels to the axle you'll need four large washers: If you can't buy any suitable ones, you'll have to make them. (See materials and tools list).

Making washers. Clamp your chosen washer material and some scrap wood in a vice with the washer material facing you. Drill the 2 inch diameter hole first (but don't drill right through the plastic). Then drill the 1 inch hole (drill right through). Finish drilling the 2 inch hole.

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Assembling the Axle You obviously know how to assemble the axle, but don't forget to add the two outer safety spacers. I originally planned to fit extra security pins to prevent the axle jumping out of the holes in the wheel frames. But after some brutal towing tests over the RYYC dinghies cobbled slipway (now concreted over) they failed to spring out. It may seem counter intuitive, but the boats own weight actually grips the axle tighter. Note: When fitting the outside 'R' pins to the axle, check that the 'straight' part of each clips faces the anti-rotation bolts. Sketch on next page makes this clear.

Fitting the Axle to the boat. Fit your Catapult wheels as usual, but check the new axle locating holes are inboard with the small anti-rotation bolt forward of the axle holes. Tip; Mark the wheel frames PORT and STARB'D with coloured tape, then you only need to check that the axle holes are inboard when using the Axle. Roll the assembled axle under the back of the boat behind your boat wheels. While in this kneeling position, raise one side of the boat with your shoulder and plug the axle into the axle hole. Check that the straight part of the 'R' clip faces forward. Lift the other side in the same way while pushing the wheel frame outboard to allow the other end of the axle to be snapped in. This end’s 'R' clip should be facing forward if you checked this earlier. After a few practice fittings, you'll develop your own technique.

(Update Below)

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Position the straight leg of the 'R' clips as shown left , so that it won't release if the axle rotates. Latest Update – I have since fitted wooden plugs into the axle ends. These were just tapped inside after being dipping in glue. Then the surplus wood was cut off to leave about 3mm projecting. Then re-drill the 'R' pin holes. (photos below) Chamfering the wooden plug ends with a file, or grinder, helps with locating the axle and eliminates metal to metal contact. The plugs also protect the axle ends from distorting if dropped. Distortion will stop the wheels sliding on and off easily.

That's it, now enjoy your Catapulling... If you have any problems or comments please let me know – [email protected] Syd Gage Catapult 506

First published Sept2014 Last update December 2016 (Return to Catapult Home Page) (Return to Repairs and Mods Page)