When we neared the end of our floating deck construction, we faced a bit of a problem after laying the penultimate decking board. A small space remained that still had to be covered with decking -- yet a full decking board would be too much for the space (only so much "lip" can be allowed to hang over the edge, unsupported). So we had to rip or "rip saw" the final decking board, meaning we had to cut it lengthwise (as opposed to across).
The picture here shows how to rip a decking board, should you need to do so, yourself. First, to stabilize it, temporarily screw the decking board down to the overhang that you'll be trimming off shortly (see below); it doesn't matter if you damage this overhang, since you'll be removing it anyhow. Carefully measure where you'll need to be cutting the decking board, and mark accordingly (the chalk line may come in handy here). A metal guide (see picture) can be used to guide you as you make the cut with your circular saw.
If you wish to ensure that you will not have to bother rip sawing the final decking board to make it fit, try this tip:
At the very beginning of the project (even before you set the deck blocks down), after you have raked the ground on the site so as to make it approximately level, lay out all the decking boards you wish to use -- right there, on the ground. Abut them, side by side, just as they will appear when the floating deck is completed.
Now measure the width of this "faux deck." Once you have that measurement, you can "work backwards" to figure out what the exact dimensions of your frame should be, to incorporate precisely this number of decking boards (plus the 1-inch lip on both ends). That way, you obviate any need for rip sawing, which can be a somewhat intimidating operation for the beginner.
You may be wondering, "Well, why not just multiply the width of the decking by the number of boards used, instead of going through all that?" But you've hit precisely upon the problem: the decking is approximately, 5.5 inches wide, but only approximately. Each board is a fraction off, and those fractions add up quickly! So it really is easier to lay the boards out and just measure the whole thing, if you're intent on avoiding any rip sawing.
But back to our project.... After the last decking board was in place, we trimmed off the excess on the deck board ends on the side opposite the house. We wanted a 2-inch lip here, which was marked by snapping a chalk line; we ran the circular saw along this chalk line to complete our floating deck construction.
We built our floating deck in July. By October, the lumber had time to dry out some, and we then applied a coat of Thompson's Water Seal to conclude the project.