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Phil's Boat

The Boat

Progress so far

I bought the boat hull on eBay in June 2013. Since then I have been adding supports for decking, fixings for the battery box and mast, and filling as much as possible with two part waterproof foam. Iíve also rigged the sails my wife made for the boat (thanks due to Mandy here).

On Sunday 15th June 2014, the boat made its maiden voyage at the Cambridge Model Boat Club pond, on the outskirts of Cambridge. This was only a test of the sailing ability of the boat, as the control was using a standard radio control system, with me controlling the rudder from the bank. Overall this was reasonably successful, but it did highlight that the rudder is too small. Steering was not as responsive as needed, and it had difficulty tacking, and gybing. Sailing along on a reach was OK though.

23 June 2014
I have now enlarged the rudder, but not tried it out yet...

26 Jan 2016
As I haven't updated this for a long time, I have forgotten a fair amount of what I've been doing. So here is a somewhat incomplete history.

The larger rudder did help, but it was still difficult to gybe. Or tack, but that isn't surprising as the boat is so slow. The mainsail is on a fixed length sheet (rope), so the boom moves out to about 15 degrees from the boat centre line, then is held on the sheet. This position was chosen to give reasonable performance into wind. The boat would point pretty well (within 45degrees to wind) and sailing in light winds was OK.

However, due to the problem with gybing, and what I thought was too much heel most of the time I decided to use a smaller mainsail. This is the same height as the picture of the boat in the garden, but shorter along the boom. This did improve the ability to gybe without apparently sacrificing any speed.

(We're now probably up to january 2015)

About this time I became concerned about how low in the water the boat was floating. The boat hull is not waterproof, and it is filled with expanded polystyrene (EPS). The theory being that there is no way I could keep it dry for many months, so I may as well bow to the inevitable and instead ensure the boat floated even when wet. My first attempt (before the EPS) was the two part foam as mentioned in the Boat tab. I gave up with this as I couldn't reliably mix this to produce long life foam. Sometimes it worked fine (and I have some samples from september 2014 that are still exactly the same size as when poured), but other times is started collapsing within two weeks. Instead I cut a sheet of EPS into many pieces with a hot-wire, to fill the hull. Despite being as careful as I could be, there was still about a litre of water in the hull. This was contributing about a kilogram of weight (two pounds). I decided I wanted the boat to float higher, so I replaced all the EPS, being even more careful and sanding the cut pieces to fit better. This reduced the water somewhat, but only down to about 0.75kg, so probably  not worth the effort. I also replaced the battery for a smaller capacity one (1.2Ah). This all helped, but the boat is still really too heavy, and floats a bit low. This is also a problem because it doesn't need to heel much before the deck starts to get submerged, which decreases the righting moment, meaning it tips too easily. Without changing hull though, I can't see what to do, so I'll stick with it.

I was also progressing with the navigation system, to the point where I could try out sailing round a track on the pond. I wrote some program to self-generate a route, based on the point the boat was at when the software re-boots. Then I made the software reset if the boat was upside-down for 10 seconds, so simply by turning the boat upside-down on the bank, then pointing it at the lake whist it booted up, it generated its own GPS course to follow. This is only for testing. Trying it out by walking round the lawn, it seemed to work.

So off the the pond to try out its self-navigation. (Up to now, most sailing had been under radio control, or using the RC to generate a compass heading to see how well the boat could follow that, which it appeared to OK.)

Navigation round the course worked pretty well, and the boat did actually come back to the back! Success. I had to stop this sail when it got cloudy, and as the battery had gone flat, the boat was in danger of shutting down in the middle. Feeling pretty pleased that the boat had been autonomous, at least for a few hundred metres anyway, I went home.

Autumn 2015

So far most of my sailing had been in lightish winds. Force 3 or less. However, even in these light winds, I had noticed that gusts tended to knock the boat completely over, so the mast was virtually in the water. There are several issues at work here. One is that the boat is rather too heavy for its size, and so floats very low in the water. This means that well before 45degrees the deck is already starting to go underwater. This greatly reduces the righting moment, so the boat heels further. A second problem is the fixed sheets. When a gust hits, the sail is basically side on to the wind, so giving a very large heeling force.

I then checked the pilot charts I had previously found on the internet to see what wind strengths were likely in the atlantic. It seems that Force 4 is about average, so having a boat that only sails in up to Force 2 wasn't going to be much use! Something needed to be done.

What was needed was a self adjusting mainsheet.

At this time I finally managed to work out how to make a simple mechanism that would keep a rigid aerofoil at a constant angle into the wind, using a weather vane and a cam. (I'd been thinking about this for months.) I then discovered that Ivor Bittle had a very similar system which he had patented, and prototyped on a catamaran. At least he showed it worked. So I constructed my system and replaced the sail with it. It was useless. Basically it would barely sail on a reach, and couldn't make any upwind progress at all. The problem seemed to be that the system just swung back and forth around the mast so the wings rarely faced the right way. Rather disappointed, I abandoned this scheme.

Springs seemed to be a possible method of self-adjusting the sails. I found some suitable springs and stared putting them around the boom until it sort of worked. It was more complicated than expected because the boom pivoted a few cm away from the mast, and the outhaul caused forces in the opposite direction to what I wanted. So I had to negate this force with on e spring, then add the ones I wanted. It looked dreadful and I never sailed it.

The breakthrough was to buy a pLastic bearing large enough to go around the mast and fix the boom to this. Now both the sail and boom rotated around the mast, meaning outhall wasn't a problem. What looked like it should work, (and I proved this using Excel) was a spring from the end of the boom to a point slightly behind the mast. This gave pretty close to what I wanted, which was for the mainsail to let out when it was in a strong wind, but sheet in when in a light wind, or going more into wind. However, it meant the boom jammed when in a strong wind going downwind as the spring hit the mast. To overcome this I replace the fixed point behind the mast with a large bearing, so the bearing was eccentrically mounted around the mast. This gives the same effect as fixing the spring behind the mast, but allows 360 degree rotation. As long as there isn't a jib, so I removed this.

A trip to the pond with this single sail configuration showed the system worked pretty well. Some experimentation with the spring was required, and then it self adjusted pretty well, and coped much better with gusts. A trip to the pond in stronger winds (probably up to force 4) showed much better strong wind and gust behaviour. It was also much better downwind than the fixed sheet as the sail could open up, giving much better downwind speed. Close hauled was worse however, as there was virtually no force on the boom when close to the centre line. I thought this was a price worth paying. Another notable point from the pilot charts (which gives the percentage of the time for each direction of the wind and its average strength) is that the wind direction is actually very variable, and doesn't seem to blow from even the prevailing direction for much of the time. So close hauling isn't a total necessity. As long as you can avoid being blown downwind too much, you can make progress when the wind is favourable.

The first version of the eccentric bearing system used a stainless metal bearing. Looking up the metal actually used it became clear that the bearing was going to corrode in salt water. I have a 3D printer that has hardly been used, so decided to try and make a plastic bearing using this. I bought some 4mm diameter acetal balls, and printed innner and outer races. The cage wasn't so successful, and I had to modify a simple cylinder with a soldering iron. With a bit of fettling, and squeezing the outer race to a bit of an oval, I managed to assemble it. This produced a pretty decent bearing once the cage was pressed on. So I quickly bodged up a bit of brass to fix the spring to (the other end is attached to the end of the boom), and went back to the pond. Again, this worked pretty well, but it looked like more eccentricity was needed as the sail sheeted out too far, too easily.

I then 3D printed a larger bearing using 6mm diameter glass balls (sold for a BB gun), and fixed this up similarly.

Christmas 2015

A few days after Christmas a severe southerly storm blew up, so I took the boat off to Grafham Water, about 20miles from Cambridge. The sail was making a din flapping severely even in the car park. It was about force 6 or 7. Much stronger than I had been out in before. Fortunately the car park was on the downwind shore, so i figured the boat would get blown back if it didn't work, or broke. The waves breaking on the shore meant my wellies weren't high enough to launch off the beach without getting filled up, so I walked a bit around to a sort of breakwater where I could throw the boat in to deep enough water. After this unceromonious launch, I scrambled back up to get the transmitter. The boat was spending most of its time with the mast horizontal, but was making a little progress across the wind. (For a reservoir, there was a decent swell, about one foot in the deep water which then broke in the shallows.) Then I found that the rudder had minimal to no effect. Whatever I did the boat slowly carried on across the wind. This was a problem as its direction would have sent it off across the lake, to the other side about a mile away. This would have taken a couple of hours, and probably ended up on an inaccessible part of the bank. So I was very relieved when I managed to get it to gybe and head back. It got washed up on the beach, close enough to shore for a rescue without filling my wellies.

To make the most of this trip I adjusted the spring and had another go, with pretty much the same result, only just managing to gybe and get the boat back to shore. It looked again as if the rudder was too small (or ineffectual for some other reason), or the sail was too big. Thinking I was pushing my luck already, and not wanting to have to retrieve the boat from the other side of the reservoir I went home.

January 2016

After the problems at Grafham, I thought that perhaps an aerofoil instead of a sail would be better. It should have a better lift to drag ratio (I thought), so wouldn't heel as much in a strong wind, and get more speed. These two things should both help steering.

I made an aerofoil based on NACA 0021, (which has a thickness 21% of its length) from a sheet of plastic bent round some formers. Mounted vertically on the mast, with a plastic bearing at the top and bottom allowed it to pivot around the mast. This looked just like an aerofoil should and I thought it should work pretty well. (The aerofoil is upright like an aeroplane's rudder, not like the wings.) Using the same spring and eccentric bearing system that had worked well on the sail, I set off to the pond.

Note that I had to change ponds after Christmas as the first one I used had been taken over by a fishing club, who put a big fence all round. I remembered a farmer had a small reservoir nearby, and went and asked if I could use it. He was very obliging and allowed me to sail there. The reservoir is actually much better than the larger pond as it is raised up above the surrounding fields, and only has trees along one edge. This gives a much better wind, with much less turbulence.

The new aerofoil sail didn't seem to be terribly efficient. Despite being in a strong wind (at least force 4) the boat wasn't exactly zipping along. And it was heeling at least as much as the sail. The heeling causes a couple of problems, first the boat heads up into wind, making gybing very difficult, or often impossible until a lull. Second, the boom and end of the 'foil drag in the water, meaning that the 'foil catches the wind side-on, making it heel more. (This effect will be familiar to anyone who has tried to learn to sail a Laser in a reasonable wind. Or is it just me?)

Back at home I raised the 'foil up the mast, and shortened the boom, to give more clearance when the boat heeled a bit.

At the pond the next day, I threw the boat in from the shallow water, and was somewhat surprised and alarmed when the boat just capsized and lay there. Fortunately the wind blew it back to shore, I lowered the 'foil and had another go, but basically unless the boom was right down by the deck, it capsized. This explained some of the heeling problem, as the 'foil is too heavy.

February 2016

I bought some lighter plastic and lightened the internal ribs, managing to make an aerofoil that was half the weight of the first one. My wife also made a smaller sail: shorter in height, and boom length, as the mid size sail was too prone to being blown over in stronger winds (ie anything above about force 3). So I now had two options: a lightweight 'foil, and a storm sail.

Another trip in about force 4 (on a freezing day) showed that the sail performed better than the 'foil in every respect. With the sail, the boat went faster, could gybe and tack at least as well, and the sail is much lighter than the 'foil. So I'll probably abandon the 'foil and stick with the sail.