Fly or Ferry to Yakushima?

Hello,

I plan to be in Yakushima from May 12-14th. I will be taking the Shinkansen from Osaka to Kagoshima, then take the ferry to Yakushima. Then I also plan to take the ferry back to Kagoshima at 1pm on the 14th to make my flight that leaves at 8:30pm from Kagoshima airport back to the US.

I have read that the ferries are sometimes cancelled due to weather (rough seas) If so, I could miss my flight back to the US which would be pretty awful for me financially. I would also hate to lose time on Yakushima if there is a delay getting there.

Should I spend the extra $100 or so and fly from Kaoshima to Yakushima to be safe? Are the ferries cancelled frequently in May?

Also, is there any way to reserve ferry tickets in advance? I know the website is in Japanese only. I'm concerned I may get there and there could be none left...

Any information you can provide would be greatly appreciated! Thank you kindly in advance.

Sea conditons will not be bad most days.

Reservation(予約：個人) by call fastest.
http://www.tykousoku.jp/etc/office.html
http://ferryyakusima2.com/timetable.html

​I was in a similar situation last Oct , was initially going by ferry to the island, but decided to fly when I found out that 60 days advance purchase airfare was only a wee bit extra compared to high speed ferry .
It was a good decision, not only I could spend more time in the island, but avoiding ferry cancellation due to approaching typhoon was my lucky break.

Heather,

May is not the typhoo season and is perhaps the best season in the entire year to visit Yakushima. Ferry cancellations are few and far between during this month.
yesyakushima.com offer a free ferry reservation service so check the website for further details.

Thank you all for the good advice! I really appreciate it!