There's a kayak tour headed to the fort every morning in the summer offered by Portland Paddle (which I operate). It's generally best to go there with a guide if you are kayaking. We offer rentals too, but we require certain skills of anyone paddling to the fort without a guide. Info here: https://portlandpaddle.net/tours#fortgorges Friends of Fort Gorges also can arrange tours by motorboat with advance notice.
Depending on the size of your group and what you were hoping to do. The easiest way to get out to the fort is Via watertaxi. Due to the drop off area, which is a seawall with no float, .most operators will only pick up and drop off 2-3hours before and after the high tide. It will cost about $90 for a 6Pax boat and COI (passanger vessels that can carry more than 6) can be hired to bring your group out there starting at $250 per hour.
Hey Fred this is actually a good question. Fort Gorges is a awesome place to go visit. But it is also the hardest. As Jonathan said you can go to a Kayak rental place. You can also get a water taxi to drop you off. I personally dont know the charge rates for them. Or you can get a private boat to go. But row ashore on a dingy or zodiac. But the dangers about that is you have to watch out for the current/ What type of tide there is. And also the weather! Hope this helps you out on your adventures!
There are some sea kayaking operations that take folks out there, not sure about motor
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