Stainless steel
- Highest strength for cleats and anchor points under heavy load
- Can still stain and pit in salt, and corrodes where it touches other metals
- Heavy, and hot to the touch in sun
Industry
Injection Molding for Marine
On a boat, metal corrodes, sun bleaches everything, and every part is shaken for hours at a time. Plastic does not rust, which is why so much deck hardware and electrical gear is molded.
Why plastic
Molded or stainless deck hardware
Stainless still wins in some places. Plastic wins in more than people expect.
Molded plastic
- No rust and no corrosion between different metals
- Light, and color is molded in, so there is nothing to chip
- Needs UV stabilized grades and careful design where loads are high
Around the boat
Marine parts and what they face
Deck, cockpit, and engine space are three different climates.
| Part | Main threat | Usual resin |
|---|---|---|
| Hatches, deck plates, and vents | Sun, foot traffic, and waves | ASA or UV stabilized polypropylene |
| Cleats, fairleads, and rod holders | Sudden rope loads and sun | Glass filled nylon, UV stabilized |
| Junction boxes and cable glands | Spray and condensation reaching electrical parts | Polycarbonate or nylon with a soft seal |
| Bilge and livewell pump parts | Salt water, debris, and running dry | Glass filled PPO or polypropylene |
| Fuel system fittings | Gasoline and ethanol blends | Nylon or acetal grades suited to fuel |
Electrical
Keeping water out of the box
Salt water in a junction box is a short circuit that shows up weeks later as corrosion.
- A continuous seal groove around the lid, or a soft seal overmolded onto it, is where sealing is won or lost
- A flat, stiff lid flange presses the seal evenly. A flange that bows between screws lets water in
- Cable entries through molded glands need the gland threads to hold their size so the seal compresses the same every time
- Metal screws in plastic bosses should be stainless, or brass inserts molded in, so nothing rusts at the joint
FAQ
Questions from marine product teams
Will white deck parts turn yellow?
Unprotected resins do. ASA and UV stabilized grades hold color much longer in sun. White is the hardest color to keep, so the grade matters most there.
Who handles marine standards and ratings?
Ratings belong to the finished product and are tested by the brand. The molder runs the resin grade and design that passed, unchanged from order to order.
Can boat builders order small runs?
Yes. There is no minimum order quantity, which suits boat builders whose yearly volumes are modest and spare parts customers who order one or two at a time.
Can one tool run several colors?
Yes. Color is set at the press, so the same hatch can ship in white, gray, and black for different boats.
Keep reading
Related guides
Sealed boxes and the resins that survive salt and sun.
ASA
Holds color in sun.
ASAGlass filled nylon
Cleats and loaded hardware.
Glass filled nylonEnclosures
Sealed boxes for electrical parts.
EnclosuresGrommets
Cable pass throughs.
GrommetsPump housings
Bilge and washdown pumps.
Pump housingsIndustrial and transportation
Duty cycles across the sector.
Industrial and transportationIndustries hub
Every sector page in one index.
Industries hubNext step
Tell us where on the boat it goes
Upload CAD with where the part sits, whether it sees salt spray or fuel, and the color. DFM checks seal flanges and loaded features. NetProto manufacturing is ISO 9001 certified.