We have finally reached the point where the boat can be weighed, so let’s begin.
Firstly the supporting blocks at the stern are moved a little so that they are clear of the hull.
The trailer is leveled using the jockey wheel to raise the tongue.
A suitably sized block of wood put under the hitch to serve as a reference.
The centre beam of the trailer is marked using a plumb bob and a pencil.
The weighing system is installed and the tongue lifted off the reference block.
And the result for the first measurement is 41.8 kg. The distance between the center of the wheels and the point at which the weight was taken was also measured at 3375 mm.
The blocks were put back under the stern and the boat lifted up using a trolley jack so that the trailer could be moved forward a little.
The distance wasn’t that far, just 145 mm but that should be sufficient.
Here is the second line on the trailer, 145 mm away from the first.
The boat was let back down onto the trailer and the tongue weight measured again. this time the weight is 21.9 kg.
The boat was then put back to her original position on the trailer and the tools and wot-not put away.
So, what is her weight? The calculation is 3375 / 145 * (41.8 – 21.9) = 463 kg.
I have to say that this is about 130 kg heavier than I expected since Naiad weighs 305 kg. Still, I’ll re-weigh Naiad the next time she is out for maintenance. Now, let’s talk errors. The scale is +/- 0.1 kg. The distance the trailer was moved has an error of +/- 1 mm and the length from the wheel centres to the lifting point is +/- 5 mm.
So, we have values of:
M1 = 41.7 – 41.9 kg, M2 = 21.8 – 22 kg, delta = 144 – 146 mm and L = 3370 – 3380 mm.
So the calculated weight minimum will be 3370 / 144 * (41.7 – 22) = 461 kg and the maximum will be 465 kg.
So we can say that according to the measurements made today that Shoal Waters weighs 463 +/- 2 kg. Close enough.
Time for a cup of tea.