Messing around with Boats

The design of the 20cm r/c yacht 'Catharine'

Now I had another project to occupy my mind, the boat. I had no idea if it was even possible, I had never seen a boat sail on so small a pond, only 2m by 3m, but it seemed it should be possible. I had a 2-channel radio set from another project, so I started sketching a boat around these parts, just using one channel to control the rudder. I could place the batteries at the bottom of a deep keel to give it stability, and get everything into a hull about 20cm long. The unstayed 'cat rig' of a Laser dinghy was simple to make and could tack without needing to manhandle the sails. I estimated the speed I would need to get 'steerage way' and figured it would cross the pond in as little as ten seconds.

Why go to the bother of designing my own boat, why not buy a kit? Two reasons: the least being that I suspected that I would not find a kit which could sail in a 2m wide pond with turbulent winds, and the main one being that I wanted to. Designing is what I enjoy doing, and there is little education in building to someone else's design.

Early plans To test the viability of my idea I tried it out on the computer with a sailing simulator. I set up a Laser sailing in a light wind, sheeted the sail to about 30 degrees, ordered the crewman to sit still and tacked and gybed up and down a lake on rudder only. No problem, it would happily sail on all points without touching the sail, and ten seconds was ample time to gain speed enough to tack, you could do it in three. Thus encouraged, I got on with planning and construction.

Looking around the workshop I collected a length of 20mm floorboard which I planed and routed to make a clamshell sandwich hull, and some odd modelmaking bits: a piece of 6mm aluminium tube for a mast and bits of brass sheet rod and tube to make a rudder, Another bit of floorboard hollowed out made a battery case and keel, filled with petroleum jelly to protect the batteries from inevitable leaks. The first attempt was poor, it was barely even buoyant. Not enough hull volume for the weight. So the woodwork went in the bin and I cut down weight where I could, changing the AA size batteries to AAA, making a smaller keel and a wider hull. This one actually made it onto the pond, bearing a sail cut from the polythene sheet of the pond liner, where she capsized at the merest breath of wind. When she did stay up, she ignored the rudder and stood resolutely head to wind. After 20 minutes she sank. The casually varnished timber had become waterlogged and warped, separating the halves of the clamshell. Attempting to dry her out in a warm air cupboard resulted in horrendous cracks and splitting and made the warping even worse. Sailing off the end of the world

A week later the wood had dried out and the cracks closed up, but by then I had moved on to hull Mk3, even broader in the beam, heavily varnished, a silicone and paper gasket between the halves, holes carefully chiselled rather than hacked out with a router. The mast was now as far forward as it would go and fitted with a small sail, like a yacht's storm trisail made delicately from cling film with button thread glued along the edges, tied on to wire loops on the boat. Tying on the tiny halyard, downhaul, clew, kicking strap, mainsheet, outhaul and boom lift made my fingers feel huge and clumsy and reminded me how age is degrading my near vision. The force from the sail took me by surprise, it had not occurred to me that while the water speed of the model scales down from the full-size original, it is still sailing in more or less the same wind, so the 'scale' windspeed is much higher, and sails need to be relatively smaller.

Fire down below!

Screwing on the keel / battery pack, now fitted with a connector plug to avoid resoldering the wires every time, there came disaster. As I tightened the last screw boiling petroleum jelly sprayed out of the plug hole. The connector had shorted the batteries and they were heating up fast. Despite unscrewing the keel as quickly as I could the batteries were destroyed, they were at about 120C and their plastic sleeves had melted. The 'Catharine'

Finally I had a watertight boat with adequate buoyancy, although still a drama queen when it came to heeling and capsizing every time a gust hit. To be any use for radio controlled sailing she really had to be self righting, which meant a big change. I made an extension piece to more than double the depth of the already large keel. Almost there, reasonably stable but not quite self righting. Kitchen sink tests showed I was only 15g short, so I took a short cut and glued 20g of lead to the keel, and up she came. Now I wish I'd kept the AA batteries, they would have been just right. Maybe next time. Not much like a Laser dinghy any more, the design constraints beginning to show. That is as it should be with an original design.

The 'Catharine'

A visitor pointed out that all boats must have a name, so she was duly labelled 'Catharine' after the lady who's idea started it all. This Catharine now sailed, just about. The mast had gone slightly too far forward and the rudder was dwarfed by the massive keel. The mast step was designed to be easily moved. The rudder got a major redesign, the simple brass original cut down to make a mounting plate for a huge semi-balanced affair cut from polystyrene sheet. Now we were really getting somewhere and she clumsily managed to sail to all four corners of the pond, hampered by an invasion of spirogyra algae which decided it rather liked the clear water. After a lot of messing about with rakes and things I found by far the easiest way to remove the weed was to dip in the transmitter antenna, whirl it around a couple of times and pull it out with a heavy 'catch' of algae on the end.

Reaching Sailing in a light breeze' Browsing around Usenet I read about a radio control event at a lake which boasted a waist-deep pit for photography. Hey, I can do that! All I have to do is stand below the dam and look over.

After a couple of weeks of practice and a little tweaking the Catharine will tack and gybe up and down the pond for hours on a nice day, only hitting the side when caught out by an exceptional gust or algae string at a critical moment. Wind is really the only complication, it gets a bit turbulent up here. The prevailing wind blows pretty much straight up and over the wier, which is about as helpful as I could hope for, and being 6m aloft, there is rather more wind than at street level. Even so the steep terrain throws a lot of vortices, and wind reversals are not uncommon. I had to learn some techniques to cope with this, for example the turbulence is often fairly predictably cyclical. One day I had periods of about 30 seconds flat calm, then a build up to a knock-down gust of about 5mph over about ten seconds, falling just as quickly back to calm. Beating was no problem, bad sailing just lead to a broach on the gust and on around onto the other tack as the wind fell. Turning downwind was nigh impossible, the tiny boat would quickly slow down and stop in the calm, water is thick on this scale. As the wind rose and she acquired steerage way I would steer off, only to catch the gust broadside and broach right back up again. The trick was to steer the wrong way, use the gust to tack, then carry on to lee as the wind fell, coming to rest if not actually facing downwind then at least broad enough to get onto a run before the next gust hit. When it did she waddled comically, gybing uncontrollably in the turbulence, but stayed upright and came down the pond fast.