Journal of Archaeology in the Low Countries 4-1 (October 2012)Joep Verweij; Wouter Waldus; André van Holk: Continuity and change in Dutch shipbuilding in the Early Modern period. The case of VAL7 and the watership in general.

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5 Indications of change

Basic design considerations in wooden shipbuilding relate to intended use of space or function, structural strength and stability for safe sailing in the context of its area of operations, and manoeuvrability for specific purposes like for example trawling. These considerations must be sufficiently accommodated in the resulting hull form and construction. Additionally, there may be other design factors like the cost of maintenance, intended operational life, crew accommodation requirements, type of working equipment and rigging needed. Finally, the cost of construction with associated labour and logistics must be taken into account. Up to the eighteenth century geometric design methods were not used in Holland (Hoving 2006). The shipwright used rules of proportion from experience in which all ship elements were interrelated. Therefore inferences made from the analysis of hull form and ship construction should tell us something about the mindset of the shipwright as it relates to ship design. Data from archives, paintings and models help to interpret design changes. The wreck data reveal that two design changes occurred in the sixteenth century.

The first design change involved an increase in linear dimensions of more than 20 per cent, which translated into more inboard working space and more fish well volume. Table 5 gives the numbers showing an increase of length (length of hull minus length of fish well) and an increase in width and height. This first design change also involved a change from a lap-strake shell to a flush planked shell (table 4) with an average increase in planking thickness of more than 30 per cent (table 5). The frame density increased, the average distance between frames being 25 per cent less (table 5).

Table 5 Changes in volume and strengthening (see ^{[note 5]}).

Designation	Length of hull (m)	Length of fish well (m)	Max. width of fish well at 1st bulkhead (m)	Deck height above keel base (m)	Fish well volume (m3)	Average shell planking thickness (cm)	Average distance between frames (cm)	Construction year estimate
ZN44	10,3	3,62	4,4		10,1	3	45	15d 16a
NP33	10,92	3,62	4,6		11,1		47	16a
ZM22	10,03	3,61	4,3		9,9	3,5	45	16b
ZN42-1	10,95	3,7	4,6	2	11,7	3	45	16b
ZN74-1	10,67	3,64	4,2	1,85	10,5	4	46	16b
ZN74-2	10,84	3,62	4,24	1,8	9,7	4	46	16b
NP40	9,8	3,65	4,3		10,1		44	16b
Mid value	10,4±0,6	3,65±0,05	4,4±0,2	1,9±0,1	10,7±1	3,5±0,5	45,5±1,5

OW10	12,53	3,86	4,95	2,25	13,2	5	37	16b
OG33/34	13,56	3,58	5,55		13,3	5	37	16d
VAL7	13,8	3,82				4	30	16d
OU86		3,66	4,96			4,5	30	17a
NR13	12,36	3,42	5,17		11,7	4,5	35	17a
NE160						6	38	17c
Mid value	13.1±0,7	3,64±0,22	5,25±0,3	-	12,5±0,8	5±1	34±4

The geometric data indicate that working space and storage volume increased commensurate with additional strengthening measures to the ship construction. The function of compass timbers (table 4) in this context was to strengthen the chine of flush hull ships. From the tables 3 and 5 it can be concluded that the fist design change occurred within one or two generations of waterships in the second quarter of the sixteenth century. The data from tables 1, 2 and 4 do not indicate otherwise, but the dating bracket is very large in some cases. OW 10 is interpreted to be a watership in transition, as not all constructional change had been adopted yet.

Table 6 Changes in relation to manoeuvrability (see ^{[note 5]} ).

Designation	Ratio length outside hull to length inside hull	Keel depth under the hull (cm)	Stem angle from vertical (degrees)	Stern angle from vertical (degrees)	Ratio length aft to length forward of 1st bulkhead	Ratio mast distance from 1st bulkhead to ship length	Construction year estimate
ZN44	0,26	15			2,03	0,12	15d 16a
NP33	0,24	13	45	30	2,02	0,12	16a
ZM22	0,26	13	45	30	2,27	0,09	16b
ZN42-1	0,25	12	45	30	2,17	0,11	16b
ZN74-1	0,25	13	35	25	1,94	0,12	16b
ZN74-2	0,25	15		25	2,57	0,12	16b
NP40		13	35	35	2,44	0,1	16b
OW10		15	45	30	2,15	0,09	16b
Mid value	0,25±0,01	13,5±1,5	40±5	30±5	2,3±0,3	0,10±0,02

NP40	0,37						16b
OW10	0,3						16b
OG33/34		34	18	30	1,68	0,06	16d
VAL7	0,27	20	5	35	1,55	0,08	16d
OU86		34	25	25			17a
NR13	0,35	28	15		1,56	0,07	17a
NE160			20				17c
Mid value	0,32±0,5	31±3	15±10	30±5	1,62±0,07	0,07±0,01

The second design change occurred in the second half of the sixteenth century. Most likely this was a gradual process of change. Table 6 shows in the second column that NP40 in the first half of the sixteenth century already featured an increase of ship length outside the hull relative to the total keel length by at least 15 per cent. In the second half of the sixteenth century the change process continued. The second set of wrecks in table 6 feature an increase in the vertical thickness of the keel by 50 per cent and an increase of the steepness of the stem by 25 per cent. From the combination of increases it is inferred that the lateral surface area of the underwater hull was increased.

Observed changes in construction in the previous paragraph support this interpretation. The keel plank was gradually replaced by a keel beam, the stem was less curved in the vertical plane and positioned on top of a longer keel, large skegs and a cutwater were used to increase the lateral surface area, and the garboard strakes aft did not end up in a rabbet but extend alongside the sternpost (table 4).

Last but not least, there are indications that the ability to trim the ship was improved. Later designs had a shorter aft end relative to the overall ship length, while at the same time the fish well did not change its relative position (table 6). This means that the centre of gravity must have shifted forward. At the same time the mast position relative to ship length was shifted aftward (table 6). These shifts change the relative horizontal distance between centre of gravity of the hull and centre of wind pressure in the sails in a structural manner (fig. 10). In fact, that distance was decreased thus potentially reducing the leeward tendency of the ship under sail. The interpretation is that shipwrights made deliberate attempts to improve manoeuvrability by increasing the lateral surface area underwater and by improving the ability to trim the ship.

Figure 10 Lateral position of centre of gravity and centre of wind pressure from calculations made by Folkersma for the OW10 ( ).

More changes in the ship construction and space distribution are observed when shipwrecks are compared. But data is lacking too much to confidently label them as design changes. For example, the use of king planks in the deck construction may have been omitted (OW10 seems the have been the last one, however ZO69 had notches that instil doubt). Also data indicate that hanging knees have replaced the rider beams in the deck construction over time (OG33/34, NP4-1, ZO69, OC60, OT23, OU113, NQ65-1). An interpretation is that this would increase safety on deck as the workspace was more obstacle-free. There are indications that by the end of the sixteenth century the fish well volume decreased, possibly suggesting changing priorities in ship function (NR13, NE160). The increasing use of a covering board on top of the ship sides may have improved the water tightness of the hull (NC12, NQ65-1, OG33/34, ON10/11, OU86, ZG80). The manner in which strakes were scarf-joined show an increasing amount of variation over time (OW10, OG33/34, VAL7, NR13, NE160). Some wrecks show an additional use of rope-like fibres and tar in the seams of the strakes (VAL7, NE160), while earlier shipwrecks only showed the use of moss. This may be an indication of changing production and maintenance methods in shipyards. Economic pressures may have existed like an increasing scarcity of moss of the right specimen or some gain in costs as the application of rope fibres is less labour intensive.

Many constructional differences found in the watership wrecks as well as the additional data from archival records indicate that more design changes must have been made than only the two identified in the sixteenth century. The large degree of variability found in ship construction data may be a focus for future research, when archaeological data from other local ship types are studied.