Tomatoes Are Slow to Ripen with Some Having Black Bottoms
I planted tomatoes this year. The plants seem to have done well but they seem to be taking a long time to ripen. When they start to turn red, every tomato so far has been rotted from the bottom.
Cool summer temperatures can really slow down fruit production and ripening on tomatoes. Like other fruits and vegetables, tomatoes ripen based on accumulated temperatures not just the number of days.
Patience is your answer at this point. Next season consider covering new plantings with floating row covers such as ReeMay or Harvest Guard at planting and until the temperatures warm. These materials let air, light and water through trapping the heat near the plants. I have had good luck speeding up fruit production by giving the plants a bit of added insulation early in the season.
As for the rotted bottoms, your tomatoes are suffering from blossom end rot. This is caused by a lack of calcium not a disease or insect. Don't get out the fertilizer as most soils have plenty. Root damage from shallow cultivation or late staking, fluctuating soil moisture, or cool soil temperatures can prevent the plant from absorbing the calcium it needs.
Correct these factors as needed to reduce future problems. The plant will adjust and the remaining fruit will be fine. Have your soil tested if you feel a calcium deficiency is the problem. In the meantime, cut off the rotted portion and enjoy eating the good part. The next set of fruit is usually fine and soon you will be overrun with tasty red tomatoes.