Calculating Courses for Motorboat Travel with Constant Current

[jiboom]

a motorboat moving at 8km/h relative to the water travels from A to a point B 10km whose bearing from A is 150. it then travels to C,10km from B and due west of B. if there is a current of constant speed 4km/h from north to south,find the 2 courses to be set.


having a bit of trouble with the book answers here.

for first course i have set the relative velocity of boat to water at 150 to the north,
then velocity of Boat is 8 and v water is 4 pointing down.

in my velocity triangle i have v water going up at end of v rel which is at 150 to the vertical,then v b completes triangle.

now in this triangle i work out the angle to be 14.5,15.5,150. so my bearing will be

180-14.5=165.5 but the book answer is 135.5.

but to get this i need an angle of 44.5 in the velocity triangle,but one of those angles is 150...

so either I am doing it wrong or book is lying...





for the second course the book answer is 060 but how can this be?


C is due west of B so how can they set a course of 060?the current is only from north to souht,not east to west. i get the 60 in my velocity diagram but then need to add 180 to get bearing of 240.

 

[jiboom]

any ideas?

 

[jiboom]

cheeky bump/

having a lot of trouble with rel motion agaisnt a current. got all other questions in the exercise but these allude me. my methods must be ok if I am getting the non current questions right so only need a nudge in right direction.