Glad to hear you are going to take a stab at 20 Bridges!! It’s a fantastic swim.
Excellent question, as with most training decisions, do what works for you and what you’re comfortable with. NYOW requires that you submit an 1hr swim as part of the selection process. The 28.5mi swim usually takes 8-10hrs but know that this is a current assisted swim – you’re not expected to swim a mile in 15mins in still water. 😉
Here’s my general guideline:
1. Training for marathon swimming and marathon running is similar. You usually never do a full marathon during your training.
2. Salt water, current, and other environmental training are, in my opinion, more important than pure mileage.
3. Take a look at what other athletic activities you’re doing. Pairing your swimming with other activities will help you keep muscle strength, work on your cardio, and cut down on the need to do a bunch of garbage miles in the water (extra mileage and can actually cause shoulder injuries).
4. You can do races as part of your training plan but definitely not required. Some people do this with many marathon swims under their belt and others, it’s their first one. The key is finding the confidence in yourself to complete it!!
Hope this helps! Feel free to reach out with any other questions!