Who remembers their Trigonometry ? (related to OffCourse Calibration)

[swbca]

The factory instructions for calibrating the width settings of the OffCourse system use field measurements including a skier observing the results of a series of gun angle adjustments until the angle appears to shoot the marker the correct distance from the boat. They provide a method for the skier to ski a path 37.5 feet from the boat centerline to make this observation.

 

To confirm those results, I want to start with one single field measurement and then use "Trig" to set the downward angle of the two paint-ball markers.

 

I have measured the vertical peak of the OffCourse gun trajectories at 4'11" above the lake surface with the boat traveling at 32mph.

 

Its a compound Trig problem because the Guns are angled down (calibrated by the user) to set the course width and are also aimed forward 30 degrees, requiring a longer flatter trajectory to hit the 37.5 foot course width.

 

Known Values

1. The trajectory of the left and right barrel intersect in the middle of my boat at 4'11" above the lake surface at 32mph.

2. The guns have a fixed angle to shoot 30 degrees forward of a straight sideways shot - - lengthening the shot's distance to reach the 37.5' course width.

 

Calculated Value

Disregarding normal projectile drop, what angle from horizontal should the guns be set to hit 37.5 from the boat centerline ? Rounded to the nearest .1 degree.

 

I believe you start by calculating the distance of the shot with the guns angled forward 30 degrees. Then calculate the guns vertical angle to hit the water at that distance.

 

Using Trig calculators on the web I couldn't figure out those 2 simple problems.

 

Reward for best correct answer(s) 5 "likes" on your 5 most recent posts :).

 

The guns aim forward 30 degrees and should aim down (derived)

[UWSkier]

Man, you could complicate a two person parade... Just go skiing! Lol It'll never be a perfect representation of the real course due to any number of variables, but it is an excellent "close enough" training tool. I've set mine once and using weight bags and a bullet level, haven't had to set it again in 9 months.

 

How do you compensate between empty and full fuel tank and its effect on the running attitude?

[swbca]

@UWSkier

There are a lot obsessions possible in slalom skiing or any other competitive sport. The more the merrier. I've learned from experience that Sail Boat Racing, Car Racing and Competitive Skiing success depends on perfecting everything you can with your equipment and your skills, then sailing, driving or skiing as much as you can. Both my drivers are out of town.

 

Your question about fuel level applies to any method of maintaining your calibrating OffCourse. I always have less than 10 gallons in the tank and then don't worry about it. Knowing the OffCourse gun angles makes it easy to adjust for the 60lb difference in my driver's weights without stumbling over additional weights that aren't permanently stowed somewhere.

[lundberg]

 

first triangle to get the horizontal distance. cos(30 degrees) = 37.5/x x = 43.3 feet

second triangle to get downward angle. tan(a) = 43.3/4.92 a = 83.52 degrees (angle from vertical)

 

angle from horizontal = 90 - 83.5 = 6.5 degrees

[swbca]

@lundberg Thanks a lot; my method using the manufacturer's instructions are a little narrower than that, measured at 7.0 degrees. I am learning that real-time variables, like wind and skier pull tend to swamp the decimal points. Every .5 degree swing changes the marker width by about 2.5 feet.

[Drago]

The boat is blue

[swbca]

@Drago save your trolling for twitter

[swbca]

@Gloersen "Obtuse" is that the Trig answer you are refraining from offering to answer my original question ? Asking a high school math question on this forum seems to really get people bent out of shape ? Go for it see what kind of insults you can come with.

[Drago]

@swbca I used to ski with Schnitz. He logo'ed his ski with mirror lettering. I asked him not to put that on mine, and, "Doesn't that distract you when you're skiing?!". His reply was , The boat is blue. Meaning he is concentrating on his skiing and not allowing anything to distract him, including me and my questions.

 

Oh, and: Lighten up