Yakolew-- the effects disappear when the province changes culture (this can take a short or long time, I'm uncertain of the factors involved. I've seen it happen in a few years before, but I haven't done it often enough to give a proper guess)
Tapewormlondon-- Not really. If you use the Colonial Map Mode (cloud icon above the mini-map) you can see trade winds, which reduce attrition if you work with them and increase attrition if you work against them. Being coastal reduces attrition compared to being 'out at sea'. Gaining military access from Castille or Morocco would be a major benefit to discover south America, you can land your ships in Canary Islands or nearby and go from there. Remember, "Months at Sea" increases attrition penalties, so even at 100% you want to depart from somewhere closer to your destination to reduce the total attrition you'll suffer. Historically there was a 'triangle' of trade, due to the trade winds, which go from Spain/North Africa, to Brazil/Carribbean, to New England/Halifax, back to Europe-- the game rewards using this type of route. Shooting straight across the Atlantic from England to Northeast USA/Canada is a high-attrition route, though if you get access or a colony at Greenland you can avoid the nasty wind by using a northern route.