Jib Turning Block Calculator

This page relies on this math, a little trig, and a lot of programming.
by Allen Edwards
2/16/2008

Use at your own risk. It has been debugges but may stil have errors. The bright side is that it doesn't matter that much as you can adjust it when fitting it by putting the lines on and alighning it for a good lead angle. As of this date, I have checked all the sections with a variety of test cases.
Allen

Use this table to enter the locations of the three components of the jib sheet system. The X axis is aligned with the axis of the turning block in that the long axis of the physical block will end up pointing down the X axis. What I did was make measurements on deck, then rotate those measurements to align the block the way I wanted. There is a section at the bottom to make the rotation calculations. To get the sheet angle where you want it, you can play with the spacing from winch to turning block and the block height. Be sure to check the pad heights so they are not too low, or even under the deck, and not too high so you can't get bolts long enough.

	X	Y	Z
Winch
Car
Turning Block

Input the diameter of the Shieve:

The equation of the plane is: 0 * X + 0 * Y + 0 * Z + 0 = 0

Sheet angle winch to turning block is: 0 degrees (Line on block is at 0, 0, 0)
Sheet angle car to turning block is: 0 degrees (Line on block is at 0, 0, 0)

Solve for a point on the plane:

X	Y	Z
		0

Find lead in angle between a point on the plane and another point:

X	Y	Z
		0

Angle between points is -0 degrees
Angle between poins on plane at these x,y locations is -0 degrees
Difference is 0 degrees

Some hard coded analysis here (Papoose only):
Angle to car1 (22, 11) = 6.95, -6.95
Angle to car2 (35, 11.5) = 4.66, -4.66
Angle to car3 (75, 11.5) = 2.26, -2.26
Angle to winch2 (39, -1.72) = 10.88, -10.88
Angle to winch3 (39, -5.28) = 10.79, -10.79

Use this to calculate pad edge lengths where lengths are normal to foot block and pad is aligned with X and Y axis
Enter the edge X and Y locations in the 4 edge entry areas. These numbers are relative to the center of the turning block, not absolute locations.
Enter plane to pad offset in center

0		0

0		0

washer wedge is at 0 degrees and tangent is 0

Enter a position on the face of the pad to get the thickness of the pad normal to the pad top.
Use this to calculate the length of a bolt, for example.
Note: X* and Y* are measured on the sloping surface of the pad, not the deck.

X*	Y*	Z*
		0

height of pad at that point is 0

Enter a second position on the face of the pad to get the thickness of the pad normal to the pad top.
These numbers are relative to the center of the turning block, not absolute locations. Use this to calculate the length of a bolt, for example.
Note: X* and Y* are measured on the sloping surface of the pad, not the deck.

X*	Y*	Z*
		0

height of pad at that point is 0

Rotate a coordinate system to align at another angle:

angle
X		0
Y		0

L-36.com is owned and maintained by me, Allen Edwards, owner of Papoose hull #5 built in 1956. I also own Allen Edwards Photography. Please visit at Palo Alto Photo . com

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