Fishing electronics and boat rigging
Work the numbers before you rig the boat
Quick answer
16 calculators and 262 computed reference pages for trolling motor thrust, battery run time, marine wire gauge, sonar coverage, kayak capacity and anchor scope. Every figure is labelled as a published engineering figure, a rule of thumb, or something that only exists on your own boat, because on this subject those three are not the same thing.
Start with a number you do not have yet
- 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.
- 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.
Two complete build ladders, because there are two boats
A powerboat rig is limited by console space and budget, and it carries its batteries permanently. A kayak rig is limited by weight against a manufacturer capacity figure, every time, and unlike a powerboat under twenty feet a kayak carries no federal capacity plate at all. Pushing both through one ladder would give bad advice to both, so there are two.
Powerboat rigs
Kayak fishing rigs
Look up a computed answer
- Trolling Motor Thrust at Every Boat Weight How much thrust a loaded boat needs at each condition, and the system voltage and battery count that thrust decision actually commits you to. 20 pages
- Trolling Motor Run Time at Every Capacity and Draw Real run time with the Peukert effect and the depth of discharge guideline both applied, in flooded, AGM, gel and LiFePO4. 42 pages
- Battery Capacity Needed at Every Draw and Duration The rated capacity that holds a given draw for a given number of hours, in each chemistry. 20 pages
- Marine Wire Gauge at Every Current and Run Length The smallest conductor that holds the ABYC three percent voltage drop limit, at 12, 24 and 36 volts, with the drop every candidate gauge would produce. 30 pages
- Onboard Charger Sizing at Every Bank Size Charger output per bank by capacity and chemistry, and how long a real recharge takes. 15 pages
- Sonar Cone Coverage at Every Depth The diameter and area a transducer cone actually covers, which is far less than most people expect. 39 pages
- Fish Finder and Chartplotter Screen Dimensions Width and height of every stated diagonal, so a unit can be checked against real console space. 16 pages
- Kayak Usable Load at Every Rated Capacity What is genuinely left after the paddler, at the seventy percent convention, and why a kayak rating is a manufacturer figure rather than a federal one. 40 pages
- Anchor Rode Length at Every Depth and Scope Rode needed counting bow height and tide, which is the part people leave out and then drag at night. 40 pages
Three kinds of number, labelled separately
The AWG circular mil table, the marine voltage drop formula and its copper constant, the ABYC E-11 three and ten percent drop limits, the rule putting overcurrent protection within seven inches of the battery, the trigonometry of a sonar cone and of downrigger blowback, Peukert equation, and a manufacturer own published maximum current draw. These do not move because somebody disagrees with them.
Two pounds of thrust per hundred pounds of loaded boat. Fifty percent depth of discharge on lead acid. Seven to one anchor scope. A quarter to a third of line rating as strike drag. Seventy percent of a stated kayak capacity as usable load. All taught everywhere, all useful, and none of them published by anybody.
The capacity plate. Your own motor published draw. Your own transducer cone angle. Your own battery rating and your own measured cable run. Nothing on this site supplies one of these, and nothing on this site can override one.
There is a fourth category we handle by refusing to fill it in. Where no published figure exists, we say so. We publish no ampacity indexed by wire gauge, because ABYC E-11 ampacity depends on insulation temperature rating, engine space location and conductor bundling, and one number by gauge alone would be wrong in the direction that overheats a cable. We publish no knot strength percentage, because published tests of the same knot disagree with each other by wide margins. A blank that says "not published" is a better answer than a number nobody can stand behind.
What is on the site
| Section | Pages | What it is |
|---|---|---|
| Calculators | 16 | Every one shows its formula and labels the basis of every figure it prints. |
| Computed reference | 262 | Nine clusters generated from the same formulas the calculators use. |
| Spec sheets | 86 | Every figure each manufacturer publishes, with nothing estimated. |
| Guides, roundups and charts | 153 | Researched from published specifications and owner-review consensus. |
| Complete rigs | 6 | Two ladders of three tiers, every item priced and linked. |
| Verified products | 278 | Every ASIN resolved live and every returned title read against the product claimed. |
The safety part, which is not the fine print
Marine electrical work is not house wiring. A boat is damp, moving, vibrating and ungrounded. A connection that would be fine inside a wall corrodes from the inside here and heats up, which is why marine cable is tinned and finely stranded and why overcurrent protection goes within seven inches of the battery positive terminal. Everything between the battery post and that device is unprotected, and a battery can deliver enough current into a chafed cable to set fire to a boat nobody can walk away from.
A lithium battery needs a charger with a lithium profile. A lead acid profile either never reaches the bulk voltage the pack needs or holds it at a float voltage it should not sit at, and neither failure announces itself until the damage is done.
Never load a boat past its capacity plate, and note what that rule actually covers: monohull powerboats under twenty feet propelled by machinery. Canoes and kayaks are not covered, so a kayak stated capacity is the manufacturer own figure with no standard behind it, and nothing but your own judgement is checking it.
Wear the life jacket. And in early season, understand what the hazard actually is: not the depth of the water, the temperature of it. Cold water immersion takes your breath first and your hands second, long before it reaches your core, and a life jacket you are sitting on does nothing at all.
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