Select the right fasteners for your boat building project.
"My Boat Plans" is a collection of over 500 boat plans, from simple dinghies to larger cruisers. It includes step-by-step guides, video tutorials, and more.
Download NowFasteners are the joints that hold a boat together, and they fail quietly when they are the wrong size, the wrong metal or set too far apart. A sound fastening plan picks the right type and gauge for the load, spaces them so the material is held without splitting, and gives every screw or bolt enough engagement to do its job.
The choices are interlinked. The application and material thickness set the fastener type and length, the expected load and the metal's strength set the size, and the spacing governs how many you need and where a backing plate becomes essential.
Enter the materials, thicknesses, load type and expected load, choose the fastener metal, and the calculator recommends a size, spacing and minimum length so you can turn a joint into a bill of hardware you can trust.
Screw length ≥ 1.5 × material thickness; Bolt length ≥ thickness + 0.5; Count ≈ run ÷ spacing| Metal | Strength (psi) | Best Use |
|---|---|---|
| 316 Stainless | 85,000 | Deck hardware, through-bolts |
| Silicon Bronze | 40,000 | Planking, below-water joints |
| Galvanised Steel | 60,000 | Hidden framing, freshwater |
| Marine Aluminium | 35,000 | Light, non-structural trim |
Fastener metal selection by marine environment.
Formula verified against standard naval-architecture references · Updated October 2026
Size follows the load and the material. Light planking and panels take small screws at a few inches' spacing, hardware such as cleats and winches needs through-bolts with backing plates sized to the fitting's load, and structural joints take larger bolts set closer. This calculator recommends a gauge and spacing from your application, thickness, load and metal, giving you a defensible starting point rather than a guess from the bin.
Spacing trades holding power against labour and splitting risk. Planking commonly runs at four to eight inches on centre, hardware at a few inches, and structural bolting at engineering-driven intervals. Tighter is stiffer and stronger but slower and harder on the material near edges. The tool suggests a spacing for your application; adjust toward tighter where the load is high or the panel must lie dead flat.
Silicon bronze is the traditional fastener for planking because it is strong, works well in wet timber, and can be driven so its head swells and seals. 316 stainless is stronger and is the choice for hardware and through-bolts, but in salt water it can set up galvanic corrosion against other metals. Many builders use bronze in the hull and stainless for deck gear, isolating wherever dissimilar metals meet.
Whenever a fastener carries a real pull-out load on a thin deck or bulkhead: cleats, chainplates, stanchions, winches and anything a line or person bears on. A backing plate spreads the load over a large area so the fitting cannot tear through the laminate. Use thick, stiff plates bedded properly, and treat small screws in bare fiberglass or ply under load as a guaranteed future failure.
Divide the length or perimeter of the joint by the chosen spacing to get the count, and check that the total shear capacity of the fasteners comfortably exceeds the expected load with a safety factor. Long runs need many fasteners, and hardware with a pull load needs enough bolts that no single one carries too much. The calculator reports the count so your hardware order matches the plan.
Individually no, across a whole boat sometimes yes. A few hundred bronze screws are light, but large aluminium or steel fasteners, backing plates and through-bolted keels add up, and on a weight-sensitive build they belong in the mass budget. It is a small effect compared to a mis-sized engine or tank, but tallying hardware weight keeps the estimate honest.