The letter is clear. He needed the sailors to get the provisions to shore. If all he needed were the Powhatan's guns, he would've simply said he needed the Powhatan, not "300 sailors". What's the use of sending the Powhatan if you're not going to send sailors to man the guns? Your theory is not logical.
Had they done it, odds are the public would not have stomped thier feet and screamed, "It's ours, ours ours ours, and we want it back." The events surrounding Sumter appear very carefully crafted. It darned near takes a program to keep track of who's shafting who.
What's so complex about it? We wanted to send provisions to shore, Lincoln knew that as soon as he tried the Confederates would attack so he sent them to Florida instead. Better to do it that way than to lose both.
My theory? This whole thing started because you claimed the "guns" were for the "men."
The "guns" were for the gunboats. The "men" were for the "guns," not the other way around as you claimed. Neither the "men" nor the "guns" were at Sumter. It does seem that we can drop this, as you now appear to understand. I'm glad that we were able to enlighten you in this matter.
What's so complex about it? We wanted to send provisions to shore, Lincoln knew that as soon as he tried the Confederates would attack so he sent them to Florida instead. Better to do it that way than to lose both.
Then why send the other ships, knowing that they could do nothing? nolu chan has provided evidence that the men were not lacking in supplies, and even refused the idea of a resupply from anyone but the merchants of Charleston. Once again, it appears to be your theory which doesn't pass the sniff test.