In Farm Frenzy Viking Heroes, what's the point of putting the yak in the boat?

[ThrowMoney]

In Farm Frenzy Viking Heroes, once you've fully upgraded the boat, you can "put" a yak into it by clicking a circle on the sail. Once in, you can take it back out if you want. What's the point of doing that? I haven't seen any change in boat speed, boat capacity or sale prices.