Nick....
If Ray is suggesting chain as a weight, remember when the presumed weight of anchor and chain is deployed to the bottom, the combined weight negative to the flotation of the vessel......chain out = displacement reduced = free board increased
.....if the vessel were tethered to a wharf [in a perfect world] the weight of chain is shared equally between the vessel & the wharf
1. Sharing equally means the vessels 1/2 alters it's displacement
2. The other 1/2 is neutral to the mass of the earth as the total mass was always there in the first place
I understand tethering usually refers to horses.,.....but am sure you get my drift
Derek