If you enable vanish on a tugboat it doesn't work. 

can you explain in detail by what "it doesnt work" means?

Do you fail to run the vanish command?

Do you go into vanish but players can still see you ?

The tug boat fails to move ?

It says Vanish is enabled, but you are still seen by players.

It has been 4 weeks, any thoughts on this?

Fixed in 1.8.8