Calculators
Quick answer
16 calculators for fishing electronics and boat rigging. Every one shows its formula on the page, labels each figure as a published engineering figure, a rule of thumb or something that only exists on your own boat, and returns "not published" rather than an estimate where no published figure exists.
Three rules apply to all of them, and they are the reason this site exists. The working is visible, so you can check it against your own manual rather than trusting a black box. Every number declares its basis, because an ABYC drop limit and the two pounds of thrust per hundred pounds convention look identical in a results table and are not remotely equivalent. And where nobody publishes a figure, the answer says so: we do not print an ampacity by wire gauge, and we do not print a knot strength percentage, because in both cases a single number would be wrong in a direction that matters.
Trolling motor sizing
- Trolling Motor Thrust Calculator How much thrust your loaded boat actually needs, at two pounds per hundred for sheltered water and five per hundred for wind and current, and which stocked motor and system voltage that lands on.
- Trolling Motor Shaft Length Calculator Measure from the bow mounting surface to the waterline, add the allowance for how rough your water gets, and get the stocked shaft length that keeps the prop buried.
Batteries and charging
- Trolling Motor Run Time Calculator Real run time from your own amp hours and draw, with the Peukert effect and the depth of discharge guideline both applied, because a 100 Ah lead acid battery does not run a 50 amp motor for two hours.
- Battery Capacity Calculator The rated capacity you need to hold a given draw for a given number of hours, worked backwards through the same Peukert and depth of discharge arithmetic.
- Lithium vs Lead Acid Usable Capacity Calculator What the same nameplate amp hours actually deliver in each chemistry at your own draw. This is the number that decides whether lithium is worth three times the money.
- Onboard Charger Sizing Calculator Charger amps per bank for your bank size and chemistry, and how long it takes to put back what a day on the water used.
Wiring and protection
- Marine Wire Gauge and Voltage Drop Calculator The smallest AWG that holds the ABYC three percent drop over your own run length and current, with the drop each gauge would actually produce alongside it.
- Fuse and Breaker Sizing Calculator The standard fuse or breaker size for a continuous load, the manufacturer figure where one exists, and where ABYC says the device has to physically sit.
Sonar and displays
- Sonar Cone Coverage Calculator The diameter and area your transducer actually covers at a given depth. In ten feet of water a 20 degree cone sees a circle about three and a half feet across.
- Chartplotter Screen Size Calculator Width and height of any stated screen diagonal, so you can check a unit against the console space you actually have before it arrives.
- Transducer Mount Selector Which mounting style suits your hull, your speed and what you need the transducer to read, and which ones are ruled out before you start.
On the water
- Kayak Weight Capacity Calculator What is genuinely left after the paddler, the gear, the battery and the motor, against the manufacturer rated capacity rather than a Coast Guard plate, because kayaks do not carry one.
- Anchor Rode and Scope Calculator How much rode you need at your depth, counting bow height and the tide still to come in, which is the part people leave out and then drag at three in the morning.
- Downrigger True Depth Calculator The counter measures cable, not depth. Enter the blowback angle off the rigger and get the depth the ball is genuinely at.
Boat systems
- Livewell Pump Sizing Calculator Well volume from your own measurements, and the pump flow rate that turns the water over often enough to keep fish alive without running them through a washing machine.
- Fuel Burn and Range Calculator Burn rate and range from your own horsepower and speed, with the old one third out, one third back, one third in the tank rule applied to the answer.
Researched, not professional advice. These calculators work arithmetic on the numbers you give them. The capacity plate on your boat, the manual for your own motor, battery and charger, and ABYC E-11 for anything electrical are what actually govern. Marine electrical work is not house wiring, a lithium battery needs a charger with a lithium profile, and in early season the hazard is cold water immersion rather than depth.