You can see the American entry along the lines of cause and effect of European naval strategies. In the British strategy blockading German trade, the United States was dissatisfied with the loss of commerce. However, the British and French were able to replace the lost trade volume with quite a bit to spare. The only thing the Germans could do was to try to retaliate and reduce her enemies' trade accordingly, leading to the unrestricted submarine warfare that played a large role in drawing the US into war.

The question is what would have happened in the event that American neutrality was respected by the British. Germany, free to conduct trade, isn't nearly as threatened by growth in British and French imports at the expense of their own. The Germans have more imports and thus more war material, but so do the Western allies who haven't lost substantial cargoes in a desperate submarine campaign. In the end it would be a wash on the battlefield, except with the absence of American reinforcements.

However, under a logistical view of the German surrender, you assume it's the crippling lack of food and catastrophic shortage of petroleum which forced them to come to terms. You simply cannot bring the Germans to that level of subsistence if you allow them to trade with the United States, which was the world's bread basket and fueling station. So, in the end, that blockade appears to have been the most important naval decision of the war.

On another note, a strategic naval success for Germany can be seen in the cruisers Breslau and Goebben, which ultimately drew Turkey into the war on the side of the Central Powers, and effectively blocked the southern supply route to Russia. The Ottomans were coming off of embarrassing defeats by the likes of Italy and Greece, and were engaged in their own naval arms race with the Greeks. They had a couple dreadnoughts on order in England when WWI broke out, which were promptly seized and put into service for the Royal Navy.

Germany, sensing the dissatisfaction of the Turkish population, spread rumor that they would replace the lost ships with dreadnoughts of their own. They then instructed Goeben and Breslau to dock in Istanbul, with the crews ultimately donning Turkish naval uniforms. The ships, whether with the approval of the Turks or not, entered the Black Sea flying the Turkish ensign and raided Russian commerce. This led to a declaration of war by the Entente against the Ottomans, and effectively closed the Dardanelles for the war. The importance of this event can be seen in the later Gallipoli campaign in which the British felt it necessary to attempt to force the opening of the Straits, but to no avail. With two cruisers, the Germans were able to tie up a substantial bit of Allied power in the Middle East, and helped starve the Russians.

Whose?