I don't know if anybody has already fixed the stock g_u_boat, but out of the box, it's really too easy to kill.
I glanced over it, looking also via the model viewer, and found a slight problem. The stock xdp doesn't have all the gun stations. In the model, there are three, and the visual looks along the lines of a type IX.
So anyway, I've fixed mine. Increased the damage points to where I think it's more accurate. Also added...and corrected...all three gun stations. The type IX usually were equipped with a 105mm Deckgun (used for finishing off ships if they didn't sink fast enough) that's on the fore deck.
On the tower is a 20mm, and the aft deck sports a 37mm Flak gun.
All works great...and yeah, they take more potshots at ya, and takes a bit more to sink it.
If there's any interest...I'll put it up.
INTEREST, INTEREST, and lots of INTEREST, Well done that man.