🤿 Water Sports Tools

What swell height, period and wind actually mean — including why the same height at a longer period is a completely different day.

The International Scale of River Difficulty explained by what each grade means for a swimmer — and why the same number differs between rivers.

CO2 and O2 tables built from your personal best, with a timer — dry training only, and the reasons that restriction is not negotiable.

Log dives with depth, time, gas and buddy, with totals, a depth profile and the milestones operators ask about — stored in your browser.

Convert between true and apparent wind in either direction, with a vector diagram — and see why the wind forward of the beam is never what you feel.

An interactive points-of-sail diagram, plus who gives way to whom under the collision regulations and the caveats that matter.

Hull speed from waterline length, plus the sail-area and displacement ratios that describe how a boat will actually behave.

How much rode to pay out, including bow height and tide — the two things people leave out and then wonder why they dragged.

The volume your board should be, from weight and ability — and why riding too little volume is the commonest mistake in surfing.

What to wear at any water temperature, adjusted for session length and how much you feel the cold — plus why fit matters more than thickness.

Board volume, length, width and paddle length for your weight and what you actually want to do on the water.

Which kayak type suits you, and whether your load is genuinely within capacity — not merely still afloat, which is a different question.

Maximum operating depth, best mix and equivalent air depth — the three nitrox numbers, with a depth diagram.

Work out your breathing rate from a real dive, then plan gas time at any depth on any cylinder — with the reserve rules that make the plan usable.

A starting weight to get in the water with, the in-water check that actually settles it, and how long before you can fly.

Maximum persons from length and beam, plus a load check against the plate — people, gear and motor — with what the plate does and does not cover.

Theoretical speed from RPM, pitch and gear ratio, your actual slip against GPS speed, and what an unusual figure is telling you.

Tide height at any hour by the rule of twelfths, with the water actually under your keel once draft and a safety margin come off.

How far you can see from a given eye height, and at what distance a lighthouse or headland comes into view — with the refraction correction.

Course to steer against a current, dead reckoning, set and drift from a fix, and true to compass — the four sums of coastal piloting.

Type a charted light like Fl(3)WR 15s 21m 18M and get it back in plain English, with the flash pattern drawn out.

Gallons an hour from engine power, miles per gallon at any throttle setting, and how far you can go while still keeping a third in reserve.

What your pump really moves once you account for lift and hose, how long the battery runs it, and how badly a hole out-floods it.

Line diameter and length for your boat, how many fenders and what size, and the anchor scope measured from where it is actually measured.

The federal equipment your boat must carry at its length, as a checklist — plus a float plan you can copy and leave with someone ashore.