1.
Build a vertical spring that is at least 100 studs long, and take note of its target length.
2.
Delete the tall block next to the spring and move the boat or block to be measured on the top end of the spring. To attach the boat to the top end of the spring, place a plastic block on top of the latter and scale it so that it connects to the build.
3.
Now unanchor the whole setup.
3.1. If the spring barely moves from its original height, try decreasing the stiffness and setting the damping to 1/10th of the latter. Do this as many times as it takes to move it somewhere decently below the very top.
3.2. If the spring compresses to the very bottom, try increasing the stiffness and setting the damping to 1/10th of the latter. Do this as many times as it takes to move it somewhere decently above the very bottom.
4.
Once the spring stops oscillating completely, anchor the whole setup again.
5.
Place a rope block next to the original spring and take note of its length.
6.
Now, put the values into the calculator and press calculate.
Use the resulting weight for other calculators.