page 402, line 5 of of section 12.2: Amplitude of 1 m would be more correct than 3 m.

page 402, figure 12.1 (b): The ellipses are drawn incorrectly. The (vertical) minor axis should tend to zero for ellipses approaching the bottom. The diminishing of the (horizontal) major axis should be negligible.

page 402, line 6 above figure 12.1:

"5 The amplitude a of the surface is essentially independent of the"

could be replaced by

"5 The amplitude a of the surface is in practice somewhat dependent on the "

page 405: In order to correct eq. (12.5), replace a (two places) by - a

pages 412-413, comments to figure 12.8 and to items 5 and 6 on p. 413:

It is not clear from the figure how the time interval τ is defined. Six zero crossings, three upcrossings and three downcrossings, are seen on the figure. Further let us assume that ten wave crests (local maxima) are seen.

If there are n +1 zero-upcrossings, then τ (as used for definition of the mean zero crossing period T_z = τ/n ) should be the time from the first to the last zero-upcrossing. On the figure n + 1 = 3, hence n = 2, in contrast to last line of item 5 on p. 413. Note that in practice n ought to be a large integer, say one hundred or more.

If there are m +1 wave crests, then τ (as used for definition of the mean crest period T_c = τ/m ) should be the time from the first to the last wave crest. On the figure m + 1 = 10, hence m = 9, in contrast to second line of item 6 on p. 413. Note that m can be larger, but not smaller, than n.

page 417, second line after eq. (12.47): " 'energy period', is" should be replaced by

" 'energy period', which is typically 70 to 90 % of the peak period T_p , which is".

page 417-418: Eq. (12.48) could be replaced by "T_e/T_z is typically 1.1 to 1.3." [Observe that the last line of eq. (12.50) should, correspondingly, be applied with some caution.]

page 418: In eq. (12.49), T_z should be replaced (two places) by T_e

page 418, lines 18-19: Delete the sentence: "Contours of equal numbers of occurrences per year are also drawn."

page 418, second line of section 12.5: Delete "as it changes kinetic and potential energy". [Comment: In a propagating wave, the energy (half of which is kinetic energy) remains unchanged. Also, the kinetic energy of a water particle moving in a circular orbit remains constant.]

page 419, line 5 of second paragraph: "increase in height as they go up the" to be replaced by "increase in height (crests more elevated and troughs more lowered) as they go further into the tapered horizontal".

page 419, figure 12.13: This drawing does not give a correct impression of the Tapchan. It does not show the lowering of wave troughs as the wave moves further into the horizontal tapered cannel. The drawing gives the impression that there is an inclined ramp, which is not true.

page 421, line 6: Replace "air cavity's shape" by "water cavity's shape" or by "OWC structure's shape".

A final comment: The text would convey more optimism and fighting spirit if "difficult", on page 400, line 5 from bottom, were replaced by "a challenge", and if "fearsome", on page 401, line 11, were replaced by "challenging".

JF 2006-11-18
e-mail: johannes.falnes(a)ntnu.no