Isla de Gran Canaria Travel Forum

Hi, everyone, I am coming to Las Palmas Dec. 20-25. I wonder if there is frequent boat lines between Las Palmas (or another point in Gran Canaria Island) to, say, S.C. de Tenerife? Are there other boat trip destination that is also worth a day trip? I understand that there are the "Armas" line, the "Transmediteranea", and the "Olsen Fred" company. But when I get one their websites, it seems they are saying no tickets are availalbe?? Also, although people say a trip between Las Palmas and SC de Tenerife taken only 45 minutes, for about 20 euros, on their websites it is said to take 1 or 2 hours, for 40-80 euros!! Why such difference? Is it because of the holiday season? Is it better to book those expensive tickets on line now, because they are hot and may run out, or there are actually plenty so I should buy them when in Las Palmas? Please advice, any information / suggestion appreciated!!