This last year I have been to the DT 6 times, we take friends and family
there when they sail with us. We have gone direct from Key west 3 of the 6 times and direct from Naples the other 3 times. All 6 tips we had a great time going in summer, winter, spring and fall. As for the best time to go. Well, it depends on your boat somewhat and what you are comfortable with. If you want to sail both 2 and from, then winter might be good, but the wind
can be to strong on some days and you will more than likely have to tack back from DT, as the winds like to be out of the east, Southeast or Northeast. We have motored back from DT to KW a couple of times because we had crew that had to catch a flight on a certain day.
When we go from KW, I like to leave around noon, then anchor
at the Marquesas
Key on the south east side. Even in windy conditions the water
is flat and nice, but you almost always have a current
with the tides. Just tuck in about 100yards off shore in 8-10 ft of water.
Then day 2 head
for DT, about 9-10am, get there 3PM or so, through anchor right in front of the fort, and enjoy the sunset with the light house as a back drop. Assume picture taking.
We ussally spend day 3 at the fort, going to the wind jammer wreck to snorkel and dive, then a trip to the light house, with more snorkeling. They have moring balls, for both the wreck and light house.
Day 4, we take off either for Key West, early or we will go back to Marquesas Key if we want a more relalxed trip. 6 miles directly West of Marquesas is a tug boat wreck in 15-20 ft of water with a mast
sticking out of the water which makes a great snorkel or dive which we try to hit at slack tide on the way back. The curent can be ripping during mid tide, don't attempt a dive when the curent is ripping. We can usally make it all the way back to KW from DT in a day without having to do any night sailing. Your boat might be different.
We have been there in all 4 seasons and have not had a problem, but we watched our weather
window and didn't go if we thought there would be a chance of high winds. In the spring, summer and fall you are more likely to find days with little or no winds, in the winter you may have a week of 20+ winds which would be uncomfortable in the stretch beween Marquesas and DT, about 40 miles. Of course during Huricaine season you are always at risk, and must respect it.