Research Note

A question had arisen as to how to compute the dimensions of the garboard timber. Many responses later the following was finally arrived at.
[ed.]

I have to retract my earlier suggestion that Goodwin was wrong in his formula for the garboard dimensions. Although I still question it, my reasons have changed. In proposing a different formula, I used a depth for the keel of 24" and a thickness of 8", which made the garboard 6" at the rabbet and 3" at the top. Unfortunately, my basic assumption was not correct.

Keel dimensions, taken from Deane, Falconer and others, indicate that the keel was basically square in cross section. Deane lists the depth x breadth dimensions for a first rate as 21" x 22", down to a sixth rate as 13.5 x 13. Although Deane is 100 years earlier than our period of interest, Joel points out that the Victory keel is square, and my examination of contemporary cross section drawings from the late 18th Century indicates similar square keel dimensions. The apparent additional depth for the keel is supplied by the addition of the false keel, which was six to eight inches deep.

So if the keel is square then the dimensions of the garboard are the same, whether you take the depth or breadth measurement from the keel. This still leaves us with a garboard that is half as thick as the keel at the bottom where it meets the rabbet. This seems like a great waste of wood, and, as pointed out already, makes for a rabbet that substantially cuts into the keel which must have weakened it considerably. Is this what was done? Well . . . maybe.

As for the waste of wood, this was not as great a concern in earlier days when England had lots of timber for ships. Later, as the supply of oak diminished, the garboard planks were made of elm. I suspect that this was because finding two long, straight oak timbers would have been very difficult. Even the keel had scarphs (scarfs?) every 20 feet or so. However, that many scarphs in the garboard would surely have let in too much water.

The depth of the rabbet was reduced by making the garboard a pentagon rather than a quadrangle in cross section. Goodwin has a good drawing of this on page 7 of Construction and Fitting. In that drawing, the garboard at the keel is quite thick at the rabbet, and the reduction in thickness is continued up through the second garboard plank to the bottom planks. He calls this 'old style', and contrasts it with a 'modified style' introduced by Seppings in 1815 which has a much thinner garboard.

However, even Goodwin's drawing does not match his formula. His listed dimensions for the keel are 21" x 21". Using his formula, the garboard should be 10.5" thick. (21 x 2/3 x 3/4). But careful measurement under magnification, taking the thickest part of the plank, measures out to only 9.75". Although this is certainly not conclusive, it is suggestive.

Examination of several contemporary cross section draughts do not show this thickening of the garboard. Most show it no thicker than the rest of the bottom planking. This is true even in drawings that are careful to show the relative thicknesses of the wales and the diminishing strakes. (See, e.g., page 73 of "The 50-Gun Ship" by Rif Winfield, and page 38 of "The Ship of the Line, Vol. II" by Lavery). Perhaps this is an oversight by the drafter, but it is, again, suggestive.

I attempted to directly measure the thickness of the garboard by measuring the drawn width of the rabbet on those contemporary draughts that show both top and bottom lines. Most of the reproduced drawings were so small that I could make no measurements with any adequate level of confidence in their accuracy. Those that were large enough seemed to indicate a garboard thickness of approximately 1/4 to 1/3 the drawn depth of the keel. So, for our ship with the 21" keel, this gives a garboard thickness of from 5" to 7" at the rabbet. If anyone has large sets of plans from NMM, this could be done with more accuracy.

It is unfortunate that Goodwin did not indicate the source or sources for his formula. I suspect that it is much older than the Napoleonic Era, and may go back to the Seventeenth Century, when wood was more plentiful and ships were overtimbered. A thicker, heavier garboard could have been thought to be like another wale, stiffening the hull and perhaps reduce hogging.

So those are my thoughts. They do not represent the opinions of the management of this station and, as Dennis Miller reminds us, I just might be wrong.
{Dan Pariser}

Underhill's Sketch No 42 [detail]

Underhill's Sketch No 43 [detail]

Very Good, and if you take a look at Sketch No 42 and 43 in Underhill's Plank-on-Frame Vol. 1, page 58 you can see this.

Sketch 42 being the more modern with iron knees and fittings, while sketch 43 is all timber and shows the garboard as a massive tapered (Lower to upper edge) timber and that the tapering across the width was carried on across the next two planks.
{Dave M.}

It is unfortunate that Goodwin did not indicate the source or sources for his formula. I suspect that it is much older than the Napoleonic Era, and may go back to the Seventeenth Century

The problem of timber supply was apparently not as great as writers would have us think (a topic which I shan't go into now) but any supply difficulties seem always to have been concerned more with compass timber than with long straight lengths. The floor timber so shaped would have been more difficult to acquire and more expensive than making the garboard thicker.

The elm used for the garboard was for greater rot resistance and the fact that elm is very tough wood. Its grain is knotted together and splits only with great difficulty, as any who have tried to turn a dead elm into firewood can attest. Elm was also available in long straight lengths, 50 or 60 feet, being an upright tree, where the preferred oak tended to provide, and indeed was more valuable as, curved or compass timber.

I think if you add in the thickness required to finish off the midsection shape to the need to be able to cut it out, in the rough, with a saw, you may be very close to the numbers Goodwin uses. Try taking a cross section of the 17th Century garboard and drawing lines connecting the corners and the timber gets pretty big.
{J B Sanborn}

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