From D.D.S.C. Newsletter

Tony Loveday describes for us an easy method to weigh a boat and to find its centre of gravity (the position of) using a set of kitchen or bathroom scales.

You will need: 1. A piece of even ground (not necessarily level) 2. A set of bathroom or kitchen scales 3. A tape measure. 4. A plumb bob 5. Checks for the wheels 6. A calculator or a good brain.

General: 1. Chock both sides of the wheel to keep the trailer in position 2. All measurements should be made along the ground 3. The reference point on the boat may be any fixed point. 4. The accuracy of this method is dependant on the accuracy of the scale readings and the distance measurements. As a check, repeat the process several times and average the results

To weigh the boat: 1. Measure the distance B, from P (the point of contact of the towbar on the scale) to the centre of contact of the wheel on the ground. 2. Measure the distance Dl from point P to the reference point (transferred to the ground with the plumb bob) 3. Read the scale - S1 4. Move the boat a couple of feet along the trailer (in either direction) - be careful not to move the trailer. 5. Measure the distance D2 from point P to the reference point again. 6. Read the scale again - S2 7. The weight of the boat Wb is given by - Wb = B(S2 - S1) (D1 - D2)

To find the position of the centre of gravity: 1. Find the weight of the boat as above 2. Take the boat off the trailer - be careful not to move the trailer 3. Read the scale - S3 4. The distance of the centre of gravity of the boat from the reference point is given by – Xb = B - D1 + B(S3 – S1) Wb Note: if X is positive the c. of g. is aft of the reference point, and if negative, it is forward of the reference point. Darling Downs Sailing Club, Toowoomba, Queensland