Thanks to some less than accurate assistance from Metservice, Scream encountered all sorts of annoyances rounding Cape Colville. Cape Colville poses a challenge that many cruising sailors will find novel.
The tide runs at a couple knots between Cape Colville and Great Barrier Island. As every sailor from Alaska to Seattle knows well, this causes problems that do not occur elsewhere. When the tide is opposed, the current is sufficiently strong to slow movement considerably, keeping the boat in the straight. The more interesting condition occurs when the current is favourable, but the wind is contrary. In these conditions the current shortens the apparent wavelength of the wave and swell. The seas become steeper, and usually somewhat higher. This situation is called a tide rip.
The gist of the matter is that rounding Cape Colville is not practical with an opposing wind. Either the current is eating up what distance that could have been made good to windward, or the tide rip is dissipating most of your forward motion into water on deck.
This is especially difficult at Cape Colville as most vessels want to travel north east from the Hauraki Gulf to the Cape and then south east, or north west from the other direction and then south west. Easterlies and westerlies are both uncommon in New Zealand waters. For the westward passage, the usual counter clockwise (backing) shift works, but is essentially motoring in calm conditions as the SE to NE shift is almost always very light. For the eastward passage, the backing wind changes make conditions less favourable, so planning for a wind change mid-route is out. And, as the westerlies tend to be strong, travelling north east on the first leg with the north westerly will be uncomfortable. So you either run before the south wester, which is typically gale force, then hug the coast once east of Cape Colville, or you also motor in the calm.
Best of luck, either way.