Lerlamadrid the ramp at the base of the Mount is concrete except for the last bit at a very low spring tide but even then it is hard sand so no problems. The only problem with this ramp is that there are not many parking spaces so if it is a really nice morning in a weekend you need to be there soon after daylight to get a parking spot or else you will have a long walk from further back along the street where you may find a parking spot and if you leave it until after say 8am you will not get a spot at all as all the parking will be taken up by people walking around the Mount or doing other things at the Mount.
I use this ramp a lot, nice and quick to get out of the harbor, can be a bit difficult retrieving the boat if there is a strong southwester or southerly blowing as it is a bit exposed to that wind direction, especially if you are by yourself.
Also if there is a decent swell running and you are wanting to fish up along Matakana Island or go out to Karewa Island be careful as there is a bar to the left of the main shipping channel where waves peak and break at times (it is a good kilometer or so out from the entrance where the bar is), so if there is a decent swell running head out the main shipping channel past A Beacon (big Pole about 1 km out from the entrance) and then head back around to Matakana or Karewa Islands.
If heading east towards Papamoa, Motiti etc nothing to worry about even if there is a bit of a swell running.