Politics of the time
I love ships, and would love to see an earlier and more powerful American navy.
But I'm afraid that the discussion about material capabilities is not all that important, until the political dimention is resolved.
This was not a case of preparing for a war, then fighting it. In the early days of the revolution, it was merely an attempt to force Britian to change the way the colonies were governed, whereas building a fleet is clearly not intended for that, but to engage in open, offensive battle on the high seas. (Or at least, it would certainly seem that way to both the people paying for it, and the British.)
This fleet would haveno puropse for legitmate defence...the Royal Navy takes care of that, and quite well.
In short, IMVHO, laying down a war fleet is tantamount to a declaration of war...years before the fleet is usable, or the political will is there for such an extravagance.
In comparison, a militia IS a necessary part of the colonial scene, with a recognized role--and can also be assembled much faster.
If you want a significant force of revolutionary ships of the line, here's one way to go, perhaps.
1769: At a Royal Navy dockyard, a lieutenant inspecting a vessel laid up in ordinary stumbles, dropping his lantern. Within minutes, the ship is ablaze, and the fire spreads to other reserve ships. by the time the fires have burned themselves out, most of the reserve fleet is gone.
More ships are needed, badly, and Parliament chooses to build some in the new world simply because the timber is there, as are yards that can do the job.
As the 1770's march on, the Yankee build ships make progress--three in Portsmouth, 6 in Boston, and so forth down the coast. In fact, they make progress faster than the ones built in England. And the yards are making sure to build fast and well...if they prove that they are the place to build, more government contracts will be in the offing.
Now, you have ships available for an American revolutionary navy. Make sure the ordnance is over here when things explode, and you have something to play with. It's still an uphill fight to make it work, but there's some raw material to play with.