It needs to be longer. The place to write with 18 words is a place like Twitter.
"Hubs" are more than just small bits and bites of random thought or activity. The hubs are article length. Several hundred words are good.
Somewhere in my search for hub length I saw 1500 words was a good target. Considering a typed page, double spaced, has about 300 words- you can see how much that is. I have also read that if your Hubs are really long (something I didn't realize until recently) that you should break them up into separate hubs (ie: part 1, part 2, etc). So, there is a little conflict of advice-- but probably a page or two would be a good hub.
I hope that helps a little! Good luck with your writing.