Sailone - Microtransat 2026 Questions

[Sophie Brookes]

Hi everyone,

I'm part of Sailone, a 3-person student team from Portugal hoping to compete in MicroTransat 2026. Our vessel is a 2.1m autonomous sailboat currently in the build phase, with sea trials planned from July onwards off Setúbal.

We're running a Pixhawk with ArduPilot firmware, an ESP32 for motor PID and wind vane, and a Raspberry Pi Zero 2W for data logging and satellite comms via RockBLOCK Iridium. We're also integrating oceanographic sensors in collaboration with Instituto Superior Técnico.

We'd love to hear from anyone who's been through this before, particularly around:
- ArduPilot tuning for sail and rudder control
- Surviving real sea conditions with autonomous systems
- Anything you wish you'd known before your first offshore trial

We also have three specific challenges we're working through right now and would really appreciate any input:

1. Keel placement — We're still finalising ballast and keel position. How did you approach the trade-off between righting moment and drag? Any rules of thumb for a hull this size?

2. Rudder shaft watertightness & seaweed — We want to keep the rudder shaft completely watertight while also avoiding fouling from seaweed entanglement. What sealing method worked for you, and did you use any geometry tricks (angled leading edge, weed deflectors) to deal with debris?

3. Solar panel configuration — We're trying to optimise panel placement for a vessel that will heel and change heading constantly. Fixed flat mount, angled, or a mix? Did you find one layout significantly outperformed others in practice?

Happy to share more details about the build. Our project page is sailone.org if you'd like to take a look.

Thanks in advance - any advice is genuinely appreciated.

Sophie
Sailone Team

[Georg Niggli]

Hello! I'm Georg from ETH Zürich currently founding our universities Microtransat Team.

I don't have any experinece with offshore trails as I did not do any. 

For point three I'm currently designing and simulating MPPTs optimized for a quick change of solar performance. (with a tuned d term so they react fast) as most of the affordable off the shelf components are not quick enough. The Power point will always considerably drag. I think that the panel configuration is thus not so critical but what matters is that the serial strings that you have are not to long. As partial shadow will be an issue with the sail. I'm thus desining an MPPT in boost configuartion instead of buck.

I can post more as soon as I'm further with the design. 

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Von: microt...@googlegroups.com <microt...@googlegroups.com> im Auftrag von Sophie Brookes <sophieb...@gmail.com>
Gesendet: Wednesday, June 10, 2026 5:00:24 PM
An: microt...@googlegroups.com <microt...@googlegroups.com>
Betreff: [microtransat] Sailone - Microtransat 2026 Questions

 

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[Robin Lovelock on robin@gpss.co.uk]

Hi Sophie & Georg. Welcome to Microtransat.

You may get some useful information on Snoopy's pages, including what to do (like test on a lake first) and not to do (forget to get enough spares of products used :-)

My "Snoopy" page is on http://www.gpss.co.uk/autop.htm - linked to many others.

Try not to fall off your chairs laughing or going to sleep ;-)

Take Care - and don't get caught ;-)

Robin Lovelock in Sunninghill - and Snoopy :-)

http://www.gpss.co.uk & http://www.nhscare.info & http://www.gpshobby.info 

To view this discussion, visit https://groups.google.com/d/msgid/microtransat/AM9PR09MB4866E3F5986B586E12EE1D20A61A2%40AM9PR09MB4866.eurprd09.prod.outlook.com.

[Philip Smith]

I've sent off 2 boats into the Atlantic, and retrieved one of them (the other was found by lighthouse keepers in France).

To answer you specific questions:

I've no experience of ardu-pilot. But tuning the rudder control is a nightmare, and I still haven't got it working as well as I'd like. There are too many variables for any sensibly simple control system. Wind direction and strength, waves, (which not only bash the boat off-course but can also upset the compass reading), trying to use as little battery as possible, heel, to name the ones I've thought of. But overall as long as its going in more or less the right direction its probably good enough. Perhaps an AI tuning system would be the answer, but that's beyond my skill level. (Or interest) 

I don't know first hand about surviving real sea conditions: I just build it robust and keep my fingers crossed. One thing though is to avoid fighting the ocean: you probably won't win. Instead, allow the rudder and sail to be moved by waves before anything gets damaged or broken. Eg a torque-limiting clutch on the rudder, and some sort of spring release for the sail sheet. At some sea-state the boat will be knocked down, so just allow that and get back up again for the next wave. One thing that confuses lots of people though is how to cope with big waves. I don't think these are really a problem as they rarely break out in the open sea (waves break at beaches because the water gets shallower) so a large wave is like walking over a big hill. you are going to twist your ankle on a small rock, not because you are on a big hill. Small waves of the size of the boat will cause it to veer off course, or my boat gets hit on the side of the hull which knocks it around. At some point the sea will be too rough for any progress, just live with it. 

Make sure your boat is self-righting!!!

My boat has been returned by helpful fishermen several times. Sometimes after it was disabled, but irritatingly sometimes within 24hrs of launch when it was going OK. So put signs on it telling helpful people what to do. 

If you can, do a test with your finished boat submerged in a tank of salt-water. You'll need a decent size tank for your boat, and lots of salt, but it might show up corrosion and leak problems whilst you still have time to fix them. Probably for over a week. 

1) you need to do trials to see what size sail, and keel you need. Make sure the wind is a realistic strength for the Atlantic conditions. I found that the best sail was much smaller than I originally expected. Keel drag isn't going to add much to the hull itself if it is a reasonably streamlined shape, so put enough keel on to keep the boat upright enough in what you estimate is the strongest wind that you need to cope with. I've decided there is no point rigging for more than force 5 as the sea will be too rough to make any progress anyway. My boat probably goes best in Force 4 (but only tested on a pond, so not much in the way of waves). You need more keel to make progress into wind as the sail will be in tight, than you do across the wind, so into wind sailing probably determines the keel size. I've recently increased the keel to get better into-wind performance as across-wind is good enough. (Ie the boat more or less reaches the maximum hull speed.) I'm not sure the answer on this, but make sure the centre of pressure of the sail is correct relative to the centre of lateral resistance. If the sail is too far back the boat will just weathervane into wind and be a pain to steer. Too far forward and you'll struggle going into wind. Do some early trials on mast placement before you get too much else fixed. And if you then alter the sail, the mast may need to be moved.

2) I've used 2 different methods for rudder control waterproofness. First was to put the servo in a waterproof box inside the hull with a sealed shaft coming out, then a push-rod to the rudder lever. This worked well I think, and it puts the seal in a protected space. Second method was to use a magnetic coupling between the waterproof servo box and the rudder shaft. This is more likely to be waterproof as the wall of the box isn't compromised at all, with magnets inside driven by the servo and outside on the rudder shaft. It is a bit sloppy though, but has the advantage of not allowing too much wave force on the rudder to drive back to the servo. I changed design because the second boat has a sloping rudder shaft that putting a crank onto looked very ugly and couldn't be hidden in the hull. So make sure whatever design you use that waves on the rudder can't back-drive and damage the servo. People have used various types of torque-limiting clutch, or spring loaded drive rod. Also, put some sort of a skeg in front of the rudder, so that any obstructions don't hit the front of the rudder and bend the shaft. Best if you can to support the rudder shaft at the bottom rather than cantilevered (although my first boat didn't have this). NOTE that I don't waterproof the entire hull, I use waterproof boxes and custom waterproofing for the bits with anything electrical in eg PV.

3) Very difficult to do any analysis on solar panel positions I would think. I've just put them flat recessed on the deck. Too many variables with sun angle, boat heel, shadow from the sails (as mentioned above) etc. Make sure they are waterproofed as sea water plus electricity is a very good corrosion enhancer.  Get as many on as you can. Regarding electronics to optimise the power point etc, I tried out some and although they do improve power in certain conditions, they can also make it worse. So in full sun there is an improvement, but in low light the chip wastes more current than it gains. Since in full sun I think I've got enough power anyway I removed the chips to optimise low-light conditions. I have just chosen PV cells to have a volts or two more than my battery to allow for volt drop through the regulator. (This also gets the PV to run near is best power point.) Volt regulator is set to 8.3V for a 2cell Li battery so no complicated charging. Just rely on the limited current from the PV to avoid charging too fast. This is at least simple even if not perhaps the ultimate optimum, but I didn't want to spend too much time on a PV charging circuit.

Good luck

Phil Smith

www.philsboat.info 

[Philip Smith]

Sophie,

I thought of some other things to suggest which aren't in your questions, but may be helpful.

I'm assuming you have Radio Control (RC) on your boat for initial testing. (If not, you need it.) Put the aerial well above the deck level. What I've found useful is to be able to change program parameters using the RC when at the pond doing trials, and also to be able to switch immediately between human control and autonomous control. This is easier than altering the program and downloading it, and means you don't need other break any waterproofing to perform changes. I've got two methods: One is to be able to have a limited number of options available whilst the boat is sailing using switches on the RC transmitter. The main 3 choices are: manual control; autonomous control to keep to fixed heading; autonomous control to follow pre-programmed course. Within the autonomous options, I can switch between a limited number of different PID algorithms for example. The more channels you have on your RC the more complicated you can go. I only have 3 channels so one is for rudder (the sail control is passive), the others can be used for autonomous/manual or algorithm options. This is enough for most visits to the pond. The other type of changes are ones made at the bank where I have a menu system to be able to alter individual parameters, eg proportional rudder gain. I've only recently introduced this and it helps a lot with tuning. (I have a LCD visible in the waterproof electronics box so I can see what parameter I'm changing. Normally the display shows things like wind direction, rudder position, battery volts etc.)

Second thing is to have an EEPROM collecting data during trials. I log things like lattitude, longitude, heading (where the boat is pointing) bearing (where is should be pointing) rudder angle, boat heel, detected wind direction, and various others. You can decide what is important. I then download these bace at home and import into excel so I can see what actually happened, and hopefully figure out why. You need an EEPROM anyway to record the course during the race, but during trials you can set logging to a much higher frequency (every second is what I use), rather than every 1/4 hour during the race.

Third thing you can do, since you are using Iridium, is to be able to send messages to the boat. If you use this during the race you will need to enter in the "unmanned" category. You could use this to control the boat during the race, albeit at a low frequency. However, it also gives you the option of disaster recovery: this is how I retrieved my boat when I realised it wasn't making any progress. I sent direction override commands to bring it home. 

I've just had a quick look at your website. I suggest you make sure there isn't anywhere on the keel where seaweed can catch. I guess the design is more of a sketch at the moment, but try to blend the keel bob into the rest of the keel on the leading edge so it is a continuous slope. Same point about the rudder: add a skeg in front of the rudder to direct seaweed away from the rudder. Hull shape looks good, as long as it isn't stable upside-down. I've also looked a bit at your dashboard etc. Looks very helpful, and probably means the EEPROM is not needed for logging during trials. However, RC switching during testing would still be useful as is easier than trying to do anything with a laptop beside a pond (or the sea, or on a boat) to change options whist sailing. It is bound to be raining!

Good luck with the aerofoil sail. I tried this after a suggestion from a sailing friend. It was useless! And heavy. Although some Americas Cup boats used a rigid aerofoil sail, they were actually two parts so could make a non-symmetrical shape. A Symmetrical aerofoil isn't a very good sail unless it is at the exact correct angle to the wind, (and even then isn't much better than a flat sheet)  and mine never achieved this. A fabric sail has the advantage that the wind blows it into a non-symmetrical shape which is much better, and seems much more forgiving of sub-optimum angle of attack. The latest version of Americas Cup boats have gone back to a fabric sail, athough it is double-skinned to give thickness to the aerofoil and blends better into the mast. A rigid sail should be more robust though, and you'll discover how it sails during trials. It is perhaps just me that couldn't get it to work as other people have. 

Phil