Suggest you read Ocean Passage Making and landfalls-Rod Heikell et al;World Cruising Routes-Jimmy Cornell.They can be had from Alibris second hand for not alot of money.
I have never crossed an Ocean by boat but I know when the Hurricane seasons are N and S hemisphere;not to be in the wrong places at the wrong times;I have run the Panama canal on Google earth numerous times;and already I am familiar with major harbour entrances having read World pilots freely downloaded from NGA web site not forgetting freebe charts of the Pacific and NZ from Land Information New Zealand
Even now I could find my way into Mangonui harbor and to Russell in the Bay of Islands having studied the charts and seen them from the land.
One other major issue in my opinion is knowing the boat.
When I bought my current boat with a coastal trip of 200 miles ahead of her I was bothered that I was low on fuel with no guages to check and no where to fill up.So when the water pump in the indirect cooling seized luckily in a canal the day after hammering my way to shelter in a force 7 I was completely suprised and of course had no tools on board despite being quite capable of stripping an engine.As for the fuel I had about 60 gallons!!
Despite a competent survey I later found the eye in the end of the main boom and several shackles almost worn away!Likewise some of the ropes had seen better days and when I got in the canal where I needed long warps found I had none and had to tie shorter ones together.
Sometimes it can take several years of sailing(or a stormy Ocean passage) for a serious fault to show!