The largest whaling fleet in the mid 17th century was Dutch. The Dutch pioneered the whaling grounds around Spitsbergen, mostly hunting the Bowhead Whale.

The Dutch whaling fleet consisted of 70 ships in 1654 and 148 ships in 1670.

http://en.wikipedia.org/wiki/Whaling_in_the_Netherlands

Most of these ships seem to have been three masted. See these paintings:

http://en.wikipedia.org/wiki/File:Abraham_Storck_-_Walvisvangst.jpg

http://en.wikipedia.org/wiki/File:18th_century_arctic_whaling.jpg

Judging by the paintings, the ships look to have been circa 100-130 feet long on deck.