Size and estimated wight of the Coat-of-Arms of the Vasa

Alexander,
Ha! This proved to be a puzzler, since no one seems to have recorded this dimension in our find records, and Hans Soop does not publish any thicknesses in his study of the sculptures. I cannot get to that part of the transom to measure at the moment, but can estimate that the maximum haeght above the background is at the shoulders and hips of the two supporting lions, which are about 250 mm high. The curtains and shield are less, around 120-200 mm. I will try to get a more definitive measurement with the total station once it comes back from its annual service.

We do not have a total weight, since it is not easy to decide what to include. The massive corner posts of the transom are sculpted but they are also essential structural timbers. In any case, the total weight of sculptures is probably not a significant contributor to instability, but it is something we could test.

We do not yet have an accurate stability model of the ship, since the key component, the location of the centre of gravity of the hull structure, has never been calculated. We have completed the documentation necessary to do this, but it would take some time to enter the data into the appropriate software. We have identified the following factors affecting stability:

1. Location of centre of gravity of empty hull, which we expect is far too high and the main culprit in the lack of stability - the upper works are simply too heavily built for the total displacement.
2. Location of centre of buoyancy in the loaded hull and its behaviour under heeling, which we can calculate easily, since it depends solely on the shape of the submerged volume of the hull. Analysis of this shows a behaviour typical of ships of this period, in that there is not very much lateral movement of the CB during heeling, and thus hulls of this type have very little form stability.
3. Amount and location of ballast (known).
4. Amount and location of other weights, the largest of which are the ship's guns, which represent about 5% of total displacement. This is on the low side for a sailing warship with broadside guns and thus not a fundamental problem for stability, but the headroom in the decks means that the upper gundeck and upper deck guns are higher above the water than they need to be, and thus contribute something to the high overall centre of gravity.
5. Location of the load waterline, which is known from testimony at the inquest in September 1628. Lieutenant Petter Gierdsson testified that the ship drew 14 feet forward and 16 feet aft, which we can plot easily, since the carved draft marks are still readily visible at both ends. This draft gives a total displacement of just over 1200 tonnes. At this draft, the maximum breadth is at the waterline, which is the maximum practical draft for ships with tumblehome. Ballasting the ship more can decrease stability, since the immersed and emersed wedges of water at heel are small, and thus the CB moves very little.
6. Lateral forces acting on the hull, in this case wind in the sails. We know which four sails were in use, both from Gierdsson's testimony and which four are missing from the sailroom (fore course and topsail, main topsail, mizzen), and we can estimate their sizes with reasonable confidence. Wind speed is unknown, as is the efficiency of the sails based on weave, cut and trim, so we can only estimate the heeling force, but testimony at the inquest was that there was almost no wind when the ship set off, not enough to pull the course sheets through the blocks. The local geography funnels the wind from the heights on the south side of the harbour down onto the water at a single point, which is where Vasa sank. Wind speed here can be several times what is experienced at the town centre, as modern sailors can attest.
7. Free moving weights. Admiral Erik Jönsson ran below to make sure that the guns were secured when the ship started to heel, and testified that none were loose. In 1961, when the ship was raised, the carriages still stood at their ports, so loose guns were not a problem. Loose water coming in through the lower gunports was, as it piled up on the port side of the lower gundeck with no way to escape, thus pressing the side farther down and destroying what little initial stability/righting moment the ship had. At some point (we do know when) the ballast shifted, almost all of it into the port bilge, which created a condition in which the ship was much more stable, but at a list of over 20 degrees!

Fred