Where does this 'Saying' come from..?

[Virdi]

'Pushing the boat out'

i.e. When somebody spends a lot of money on something or doing something.... I'm sure u know what I mean

 

[Tom0]

http://www.phrases.org.uk/meanings/push-the-boat-out.html

This phrase originates with the literal meaning, i.e. pushing boats from wherever they are beached and into the water. People have for centuries built boats that were too large for an individual to move. Helping a seaman to push the boat out was an act of generosity - a similar to the modern-day act to helping to push a car that is broken down.
The phrase became used in UK nautical circles to mean 'buy a round of drinks' sometime during the 1930s. For example, in J. Curtis' You're in Racket, 1937:

"This bloke you're meeting up the Old Jacket and Vest to-night, let him push the boat out, the *******. Surely he can pester for a tightener if you're hungry."
​

By 1946, John Irving had listed the term as Royal Navy slang, with that meaning - in Royal navalese: a glossary:

"Push the boat out, to, a boatwork term used to imply paying for a 'round of drinks'."​

Hope that helps

 

[semi-pro waster]

I don't honestly know but I'd suspect as it is synonymous with "making a splash" or "making waves" that it may have evolved as another way of saying the same thing and implying largess. After all pushing the boat out will make a splash/waves.

But on reading the above perhaps not.

 

[Sinque]

Delete

I've just got out of bed and my mind isn't working yet, totally mis-read the title...