You tease... why post the link to the brainteaser when the answer hasn't even been posted yet??
1 - the straight line boat: if a log floats at the same speed as the tide (5km/h), it will take 2 hours to travel 10km. I learnt that in high school
physics. However, a boat will have windage due to its sail luffing (even if it is pointing into [apparent] wind), so it will be a little slower than the log.
2 - The tacking boat (me). If tacking at rightangles (45 deg to the wind) we can use pythagorus theory (c2 = a2 + b2
)to calculate distance travelled. Therefore, if the hypotenuse is 10km, my tacks would be the total of 8km and 6km (14km).
If you are correct, and the windspeed generated by apparent wind
is 2.7knots, on top of the 5km/h generated by tide, then my speed would be more. If on my dart 18, I would prob be doing about 2 knots (4.5ish km/h?) through the water
, giving me a total speed of 9.5 km/h. So I would take just over 1 hour.
Therefore, I win.