Yes, and that was almost certainly what caused the second explosion.
No German U-boat attacks on merchant shipping means that the United States does not enter the war. Period. Unlike FDR and WWII, Wilson actually was trying to keep America out of the war, and without a casus bellum, there would be no American entry.
Indeed, until the U-boat attacks on civilian ships began, there was a good deal of sympathy for Germany in the United States, and the loudest outcries in the American papers were against Britain on account of the strict blockade against Germany. We would never see America join the Central Powers, of course, but with this POD (which isn't that far-fetched), we would certainly never see America in the ranks of the Allied powers.
Of course, this does not mean that the Allies wouldn't go on to win the war against Germany anyway, but it does mean that the victory would take place later and would cost much more in blood.
On the other hand, we might see a peace agreement from mutual exhaustion in late 1917, as Germany had won the war against Russia and the Allies didn't have the promise of American intervention to maintain their hopes of eventual victory.