Ideas for craft that do not fit anywhere else (incl. DownWind Faster Than The Wind)
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Postby Fredthecharlie » Sun Sep 30, 2018 5:36 pm

A Norwegian team with a boat called SB Met have completed the course sailing from Newfoundland to Ireland, the result has still to be ratified and will probably be after its data recorder has been recovered when it sails itself back to its home port in Norway.
www.microtransat.org provides a photo and a link to the teams own web site sailbuoy.no

John Perry
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Re: Microtransat

Postby John Perry » Thu Oct 11, 2018 8:11 pm

Well done the Norwegians, is the AYRS team (Mike Howard et al) still interested in this challenge. Still possible to do it faster!

I took a look at the Norwegian teams website http://sailbuoy.no/. It would seem that they have a simple design, the rudder being the only actuated control surface. Hence less to go wrong and little power required to keep it sailing. Indeed, the sailing and navigation functions are achieved without the use of solar power - apparently the vessel can sail and navigate itself for 6 months on just the power from an internal battery. This makes it suitable for use in high latitudes where there is little or no solar power available. The vessel can be fitted with solar cells, as it was for the MicroTransit Challenge, but these are optional and are used to power a payload of instruments for collecting oceanic data. The main opjective of the team appears to be commercially sponsored oceanography, so presumably this Atlantic crossing was a publicity and marketting excercise rather than their primary goal.

The vessel has a single wingsail with symetrical camber and this is freely pivoted with no control over the angle of attack other than a bit of string that keeps it within a certain angle from the centreline of the vessel - from the pictures I would guess that this angle is something like 45 to 50 degrees each side of centre. Despite the simplicity of this 'sheeting' arrangement the craft can tack to windward, albeit rather slowly, as shown by a polar performance diagram on one of the webpages.

I thought another interesting aspect is the very high (by conventional standards) ratio of underwater lateral area to sail area. The vessel has a deep keel, obviously shaped to minimise the risk of entanglement with weed/debris and the lateral area of the keel appears to be about twoce the sail area. I imagine that this craft often has to operate with high ratios of wind speed to boat speed and that favours a large keel but a keel that is much larger than the rig does look a bit strange! The rig is also placed close to the bow so that its centre of effort is well forward of the keel centre of lateral resistance. I guess that means 'lee helm' but it may well also mean that the boat will stay on course with minimal helm movements.

I like that the Norwegians tested their model boat by ramming it with a ship! The ship's helmsperson needed several attempts to score a direct hit and the little sailing boat just bounced off without significant damage to either vessel.

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Re: Microtransat

Postby mikehoward » Mon Oct 22, 2018 4:37 pm

Yes, Well Done to the Norwegians! But before we go overboard let us look closely at what they achieved and how they achieved it.

SB MET was a commercially available piece of kit, professionally built and operated by a commercial company with years of remote operated marine vehicle offshore survey history. I viewed a similar craft operated by the National Oceanographic Centre here in Liverpool, maybe eighteen months ago. Their craft cost close to £200,000 and is powered by an underwater oscillating device which is wave powered. In early 2018 it undertook a voyage from the Antarctic Ice Shelf to the Falkland Islands, a distance of two thousand miles. SB MET is basically a very similar craft except it was sail powered.

However there are two very obvious differences between SB MET and LITE AYRS, the AYRS inspired MicroTransat Challenger.

SB MET was entered in the UNMANNED CLASS which means its operating software could be updated or altered remotely during its voyage. Redirection with the foresight of weather data can be a huge influence to this class of craft. SB MET had no directional control other than allowing the wind and current to propel it forward. Have a look at its average speed - little more than the speed of the Atlantic Drift.

LITE AYRS was designed to meet the criteria for AUTONOMOUS CLASS, meaning that once released, the craft had to navigate itself to the finish line by directional control along a predetermined set of waypoints. This Challenge is still open to allcomers!

It is still not to late for AYRS to fully back this exciting challenge with words, deeds and lots of money!

John Perry
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Re: Microtransat

Postby John Perry » Tue Nov 06, 2018 2:14 pm

The link below is one of several papers about ocean research work carried out using SB-MET.
The author does not go into detail about how SB-MET navigates itself, the main purpose of the paper being to discuss the capability of SB-Met to carry out wave height measurements. However, it is clear from this paper that the SB-MET has the ability to navigate itself to a specified waypoint, then, if required, hold station in proximity to that waypoint for a period of time, then, if required, move to another waypoint, and so on. So I don't think it is correct to say that SB-MET 'has no directional control other than allowing the wind and current to propel it forward'. For the trial covered by this paper the craft found its way across something like 100 miles of the north sea to reach two waypoints in turn, holding station for a week at each waypoint with a positional accuracy of +/- 2km.

From reading a bit about SB-MET I am pretty sure that the on-shore operators are able to modify any preset waypoints while the craft is underway at sea and so it is not autonomous in the sense that once released from the shore no one on the shore is able to influence its navigation. However, surely it would be a rather trivial matter to make the craft autonomous in that sense simply by disabling that part of its software that allows navigational data such as way points to be edited while the craft is at sea. I would have thought that this would make the craft suitable for the autonomous class of the MicroTransat challenge but I can imagine that the operators would see that as a reduction in its capablity, making it less useful for its commercial purpose.

I would agree that the SB-MET is quite a slow vessel, as one might expect given its small sail area and large wetted surface. I am sure that there is potential for faster trans-atlantic crossings by model yachts if anyone feels they would like to take up that challenge.

Incidentally, an AYRS member made a small wave powered craft based on the principle of the Liquid Robotics Wave Glider and he brought it along to one of the AYRS meetings at Thorpe several years ago, can anyone remember more details? I think the craft was radio controlled and met expectations for performance.

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