A boat with a 10.2-foot beam does not go in a 10-foot slip, and the harbormaster does not build 12.2-foot slips. Slips come in standard widths — usually every 2 feet — so the assignment question is: beam, plus room for fenders on both sides, rounded up to the next width on the dock. CEILING does the rounding-to-a-multiple part in one function.
A 10.2-foot beam plus 2 feet of fender room is 12.2 feet, which rounds up to a 14-foot slip when slips come in 2-foot steps.
The example
Three boats on the waitlist and the slip each one has to be assigned to. Clearance is a policy number, not a physics number, so it stays editable.
| A | B | C | D | E | |
|---|---|---|---|---|---|
| 1 | Boat | Beam (ft) | Clearance | Increment | Slip width |
| 2 | Sea Ray 240 | 8.5 | 2 | 2 | 12 |
| 3 | Grady-White 306 | 10.2 | 2 | 2 | 14 |
| 4 | Catalina 36 | 12 | 2 | 2 | 14 |
The formula
One function does the whole job:
How it works
CEILING is ROUNDUP for multiples. Here is what happens inside it:
B2+C2is the width the boat actually needs: the beam plus a total clearance allowance. Two feet total (one each side) is a common marina minimum; sailboats with fixed fenders often want more.D2is the slip increment. If your dock has 10, 12, 14 and 16-foot slips, the increment is 2. If it has 10, 13 and 16, it is 3.CEILING(12.2, 2)returns 14, the smallest multiple of 2 that is at least 12.2. A 12-foot beam plus 2 is exactly 14, and CEILING leaves an exact multiple alone.- Compare the result against your inventory column. A 14 means a 14-foot slip or larger; it never means a 12 no matter how the skipper argues.
If your slips are not evenly spaced — 10, 12, 15, 20 — CEILING will not help. Use an approximate-match lookup against a sorted list of widths instead (see the variation).
Try it: interactive demo
Enter the beam, the clearance allowance, and the slip increment on your dock.
Variations
Uneven slip sizes
List your slip widths in a sorted column and use XLOOKUP in next-larger mode to find the first one that fits.
Length, too
Do the same for overall length against finger-pier length. A boat needs both to pass, so wrap them in AND when checking a specific slip.
Pitfalls & errors
Beam on the spec sheet is the hull. Rub rails, permanently mounted fenders and outboard cowlings can add a foot. Measure the widest point that will sit at dock level, not the number in the brochure.
In Excel 2010 and later CEILING.MATH does the same thing and handles negatives more sensibly. Plain CEILING is kept here because it works in every version, including the marina office's old one.
Do not use ROUND or MROUND. Both round to the nearest multiple, so a 12.9-foot need becomes a 12-foot slip and the boat wedges in on the first windy night.
Practice workbook
Frequently asked questions
What clearance should I use?
Why does a 12-foot beam get a 14-foot slip and not a 12?
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