You'll need a PCC for countries where you've lived for 6 months or more non-stop.
Were this a international tourism cruise sort of thing? Where you dock in each country for a few weeks/days? If so listing them under the travel history should not trigger a PCC request.
If you worked on-board a ship then I'm not sure what's the best course of action then. This time, in my opinion, should count within whatever your country of residence was at that time, because this travelling is simply part of your work. I think any stamps that go into your passport/ travel document should be included in your travel history, nothing more.
I'd call to inquire or at least hear other opinions.
Who needs a police certificate?
In general, you and all the people in your family who are 18 or older need to get a police certificate. You must get one from each country or territory where you have lived for six or more months in a row since the age of 18. (For example, if you lived in a country for eight months but left on a two-week vacation, that counts as living there for eight months.)
For the country you currently live in, the police certificate must be issued no more than six months before you apply.
For countries where you have lived for six months or more, the police certificate must be issued after the last time you lived in that country.
If your certificate is in a language other than English or French, send it when you apply, along with the original copy of a translation done by a certified translator.
http://www.cic.gc.ca/english/information/security/police-cert/intro.asp
