I stumbled across a very good Fort Forrest desciption in the Official Records of the Navy. Acting Volunteer Lieutenant Behm, commanding the Southfield, described it in a report written on 11 Feb 1862:
“The fort was made by hauling two canal boats along the shore and then filling up with sod, or rather both mud and sod, interlined with and braced on the outside with timber. The whole battery had seven 32-pounders, all stolen from the United States. One of the canal boats was fired and the magazine was blown up. The other is the C.A. Nichols , of Norfolk, VA.,and when we have all we want out of her I shall have her set on fire also, and then there will be nothing to build on again.”
He further states: “The fort is about 220 feet long, and, as I said before, was mounted by 7 guns.”
Putting all of the pieces together, a steam dredge was used to dig a channel for the barges to get them near the shoreline at Redstone Point between 25 September 1861 and 4 October 1861. The floating battery Superior with 4 guns mounted arrived at Roanoke Island on 7 September 1861. The floating battery Nichols arrived on 5 October 1861. The two floating batteries were pulled into the channel, wooden braces were added around the inside and out, and mud and sod was placed around the outside to provide more protection.
I love it when a story comes together!