An outfitter's whole day runs on one estimate: when the shuttle meets the group at the take-out. That estimate is distance over speed — and the speed is what the paddler adds to what the river is already giving them.
A 6.5-mile run with a 1.2 mph current and casual 2.5 mph paddling is 1.8 hours on the water.
The example
Three runs on the same river, differing in length and in how hard the group is expected to paddle.
| A | B | C | D | E | |
|---|---|---|---|---|---|
| 1 | Run | River miles | Paddle mph | Current mph | Hours |
| 2 | Short float | 6.5 | 2.5 | 1.2 | 1.8 |
| 3 | Full day | 11 | 2.5 | 0.8 | 3.3 |
| 4 | High water | 4 | 2 | 2 | 1.0 |
The formula
Speeds add, then distance divides:
How it works
Where each number comes from:
B2is river miles between put-in and take-out, measured along the channel — not the driving distance, which is usually much shorter.C2is paddling speed. A casual family in a tandem canoe is 2 to 2.5 mph; an experienced paddler in a sea kayak is 3 to 3.5.D2is the current, which changes with the gauge reading. Keep a small table of current by river stage and look it up rather than typing a favourite number.ROUND(...,1)to a tenth of an hour, which is six minutes — about as precise as this estimate deserves.
Add a stop allowance before you commit to a shuttle time. Groups swim, eat lunch, and pull over; an hour of stops on a three-hour float is normal, not exceptional.
Try it: interactive demo
Enter the river miles, the group's paddling speed, and the current.
Variations
Add a stop allowance
Padding the float for lunch and swim stops before you set the shuttle.
Latest safe launch time
Subtract the float from your last shuttle run to get a cut-off for the counter.
Pitfalls & errors
Current is not constant along a run. Slow pools between rapids drag the average down, so use a whole-run average measured against actual float times, not the speed of the fastest riffle.
Track actual put-in and take-out times for a season and back-solve the combined speed. Real groups are almost always slower than the arithmetic suggests.
Never subtract the current for an upstream leg without checking it is even possible. If the current exceeds paddling speed the denominator goes negative and the formula returns a nonsense negative time.
Practice workbook
Frequently asked questions
Where do I get the current speed?
How do I handle groups that stop constantly?
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