"Ocean Swells" as originally published in "Crochet: The Complete Guide" by Jane Davis was flawed and incomplete (it was missing row 11 entirely and contained other errors); along with correcting all of that, this version is designed to use two different colored yarns simultaneously, bringing them up the side. The brought up yarn, along with first/last stitch and slip stitch, will be worked over when making the border.

I did 5 pattern repeats for a 50"x62" (ish) result and used approximately 550g of Knitpicks Worsted Weight Brava in Dove Heather for Color A and 480g Knitpicks Worsted Weight Brava in Asphalt Heather for Color B, about 2,245 yards of yarn in total. I used a L hook for the foundation and J hook for the main project.
This pattern uses American terms (ch= chain, st= stitch, sc= single crochet, slst= slip stitch, hdc= half double crochet, dc= double crochet, tr= triple crochet, sk= skip stitch, etc). Gauge does not matter, just be careful not to do too tight a stitch or there will be a noticeable ripple to the blanket.
Note: if desired a ch3 can replace the stacked sc at the start of the rows. See additional notes for tips (and pictures) on how to easily tell that the pattern is being done properly.
Foundation: with color A chain a multiple of 28 sts plus 6, turn. (either chain very loosely or use a hook 1 or 2 sizes larger than for the rest of the blanket)
Row 1: sc in 2nd ch from hook, slst, 5sc, hdc, dc, tr, dc, hdc, *9 sc, hdc, dc, tr, dc, hdc; rep from * across, ending with 5 sc instead of 9 sc, sltst, sc.
Row 2: Ch 1, turn, sc, slst, 3 sc, *ch 1, sk 2, dc, (ch 1, dc) 4 times, ch 1, sk 2, 5 sc; rep from * across, ending with 3 sc instead of 5 sc, sltst, sc.
Row 3: Ch1, turn, stacked sc, slst,*(2 dc in next ch sp) twice, 3 dc in next ch sp, dc in dc, 3 dc in next ch sp, (2 dc in next ch sp) twice, sk 2 sc, sc in next sc, sk 2 sc; rep from * across, sc, sltst, dc change to color B when completing last st.
Row 4: Ch 1, turn, sc, slst, sc across until 2 st remain, slst, sc.
Row 5: Ch1, turn, stacked sc , slst, ch 4, dc in 1st st, hdc in next st, sk 1, sc in next 9 sts, *sk 1, hdc, dc, tr, dc, hdc, sk 1, sc in next 9 sc; rep from * across, sk 1, hdc, dc, tr, slst, dc, change to color A when completing last st.
Row 6: Ch1, turn, stacked sc, slst, ch 4, dc in dc, ch 1, dc in hdc, *ch 1, sk 2, sc in next 5 sc, ch 1, sk 2, (dc, ch 1) 5 times, sk 2, sc in next 5 sc; rep from * across, sk 2, ch 1, dc in hdc, ch 1, dc in dc, ch 1, dc in 4th ch of ch, sltst, dc.
Row 7: Ch1, turn, stacked sc, slst, Ch 3, (2 dc in next ch sp) 3 times, sk 2, sc, *sk 2, (2 dc in next ch sp) twice, 3 dc in next ch sp, dc in next dc, 3 dc in next ch sp, (2 dc in next ch sp) twice, sk 2, sc; rep from * across, sk 2, (2 dc in next ch sp) twice, 3 dc in ch sp at end of row, dc in 3rd ch of ch, sltst, dc, change to color B when completing last st.
Row 8: Ch 1, turn, sc, slst,
sk 1, sc in each st across, ending with sc in ch sp near end of row, sltst, sc.
Row 9: Ch 1, turn, sc, slst, sc in next 4 sc, *sk 1, hdc, dc, tr, dc, hdc, sk 1, sc in next 9 sc; rep from * across, ending with 4 sc instead of 9 sc, sltst, sc, change to color A when completing last st.
Row 10: Ch 1, turn, sc, slst,
ch1, sc in next 2 sc, *ch 1, sk 2, (dc, ch 1) 5 times, sk 2, sc in next 5 sc; rep from * across, ending with 2 sc instead of next 5 sc, sltst, sc.
Row 11: Ch1, turn, stacked sc, slst,*(2 dc in next ch sp) twice, 3 dc in next ch sp, dc in dc, 3 dc in next ch sp, (2 dc in next ch sp) twice, sk 2 sc, sc in next sc, sk 2 sc; rep from * across, sc in the ch1 sp, sltst, dc, change to color B when completing last st.
Repeat rows 4-11 to continue pattern
When blanket is desired length, finish off color A, do not finish off color B as it will be used for the border.
Border- note: For a nice, even finish the border is stitched over the first sc/stacked sc and last sc/dc of each row. Insert hook in the space above the sltst (after the sc/stacked sc/dc and before the first st of the row's pattern).
Round One:
left side: With color B ch1 at the top of its last row, 1dc in each of color B's rows (2dc total per color B section), 2 dc in each of color A's rows (4dc total per color A section), repeat to last color A section (at the bottom of blanket) 2 dc in each of last 2 rows and (2dc, c1, 2dc) in corner.
bottom: 1dc along bottom until last st, (2dc, ch1, 2dc) in corner.
right side: 2 dc in each of color A's rows (4dc total per color A section), 1dc in each of color B's rows (2dc total per color B section), repeating until last of color A's sections. Work 2dc in first row then work (2dc, ch1, 1dc) into the stacked sc to make the corner.
top: dc, *2dc, 2 hdc, 3 sc (in set of 3 dcs), slst (in single dc in dc), 3sc, 2 hdc, 2dc, 1tr, (in sc) repeat from * until last swell ending with 3 dc instead of 2, tr in slst, (dc, ch1, 2dc) in last stitch to make the corner
finish left side: 1dc in last row of color 1, slst to first border dc
Round Two:
left side: ch1, sc in each dc, (sc, ch1, sc) in ch1 space of corner
bottom: sc in each dc, (sc, ch1, sc) in ch1 space of corner
right side: sc in each dc, (2sc, ch2, dc) in ch1 space of corner
top: dc in each st, (dc, ch1, 2sc) in ch1 space of corner.
finish left side: sc and slst to the first sc of the row and finish off.
Additional notes with (not the best, sorry) pictures:
When switching yarns make sure to not pull too tightly, it should match the length of the rows and have a little give. It should look, give or take, like this:

Quick ways to make sure the pattern is working out properly:
Rows 4 and 8: the 5th sc of 9 sc repeat should be in the center of the swell (in the previous row's dc in the dc in between the 3dc in chain spaces).

Rows 6 and 10: the 3rd sc of the 5 sc repeat should also be in the center of the swell

Rows 7 and 11: the single sc will be directly above the swell as well

also in Rows 6 and 10: the placement of the first dc of the (dc, ch1) repeat will be in the previous row's hdc which is the stitch above the second to last dc of the ending (2 dc in ch sp) part of the swell
(the underlined sk1 in row 8 and ch1 in row 10 are to emphasize the subtle differences between the pattern in those rows and those of rows 4 and 6 as I noticed I had a tendency to forget about them)And I just noticed the blanket was placed on the couch bottom to top so was photographed upside down and it's too dark to take another photo now. Whoops, sorry!
If you have any questions feel free to ask here or on discord.