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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