can't deduct our mortgages either.
There are hundreds of references to this issue on line, you can start with this one
First of all, this doesn't affect me at all as I'm in the US. But since this is the Internet and it is a rule that I argue about stuff I neither know or care about this quote from the link you sent me is of interest.
"The general limitations on business expenses are set out in section 18. Paragraph 18(1)(a) provides that no outlay or expense is deductible in computing the income of a taxpayer from a business unless it was made or incurred for the purpose of gaining or producing income."
Deducting a runabout to get to work would not be deductible in the US either. It would be treated as personal travel from home to work. If however you bought a boat for the purpose of teaching sailing and you used it a couple weekends for a personal trip I doubt the whole boat would be considered personal use.
And as I said before you could have a valid business reason for that trip even without students. You could be checking out a new anchorage, testing a new anchor or any of a hundred "reasons" to make your teaching trips better.
And even if the two trips were deemed personal there would reasonably be some way to not deduct just that portion.
Even the US president can take personal trips in Air Force One if he pays standard commercial fair.
Also since you are in Canada, there is a good chance you never got to use the boat for personal use.
Short Season joke here. (:-
Just read Uricanejack's post so ignore the above. Apparently, your tax code is wicked strict. Have to pay for health care somehow.