Gerr, Strip Planking

[Tony Fish]

Does anyone have experience using the Dave Gerr's 'Elements of Boat Strength' scantling number method for calculating strip-plank thickness? (Chapter 11) There seems to be a mistake in the calculation example given for 'Logger Bobber' in formula 11-3, determining the strip-plank thickness for an exterior only sheathed hull.

The equation given is 16.51 x Sn^0.3, the example, 16.51 X 2.97^0.3, which, if I'm not going crazy =22.89ish, whereas the example gives an answer of 24.7. This may seem to be a trivial difference for such a method of scantling determination if it is going to be rounded up anyway to say 25mm, but....

In formula 11-7 a strip-plank thickness is given for use with internal and external sheathing, given as 15.24 x Sn^0.34. The example answer I agree with. The problem is I would expect the thickness required to reduce if internal sheathing is added, which in his example, it does by 3mm if the answers are correct, but I don't believe the first one is.

The two equations given, 11-3 and 11-6 give a very small difference. Am I doing something wrong or is there a miss-print in the book? Which equation should I trust?

Also on page 157 (top right) it says, 'With internal frames, bulkheads and backbone structure, no internal hull sheathing is required or recommended Does anyone know a reason why it is not recommended?

While I'm at it, The ABS Guide for Off-shore yachts gives a formula for the required thickness of carvel planking.(7.5.1) It seems to give a small very small thickness, or alternatively a large frame spacing, (going by my very limited knowledge of wooden boat construction). Any comments/suggestions?

[Tony Fish]

If anyone was interested, it turns out it was a typo in the book. I managed to contact Dave Gerr and he confirmed this. The equation should be 16.51 x Sn^0.37