Whitecap Industries 3/4 In. Barb 316 SS Thru-Hull 6541

Whitecap 6541 Thru-Hull Fitting | 3/4" Hose Barb | 316 Stainless Steel | 1-1/8" Hull Cut | Stainless Finish

The Whitecap #6541 is a 3/4" hose barb thru-hull fitting in 316 stainless steel with a natural stainless finish. Suits cockpit drains, livewell inlets/outlets, raw water intakes, and other above- or below-waterline through-hull penetrations on fiberglass, wood, and composite hulls up to 5/8" thick.

Product Details:

• Part Number: 6541 (Whitecap Industries)
• SKU: WC6541
• Manufacturer: Whitecap Industries
• Type: Thru-Hull Fitting — Hose Barb, Straight
• Material: 316 Stainless Steel
• Finish: Stainless (natural)
• Hose Barb Size: 3/4 in.
• Flange Diameter: 1-7/8 in.
• Thread Length: 1 in.
• Barb Length: 1 in.
• Overall Length: 2-1/2 in.
• Hull Cut (Hole Saw): 1-1/8 in.
• Maximum Hull Thickness: 5/8 in.
• Condition: New

Additional Information

316 Stainless Steel — Marine Grade Material:

The Whitecap 6541 is machined from 316 stainless steel — the correct alloy specification for marine thru-hull fittings. 316 stainless contains molybdenum, which significantly improves corrosion resistance in saltwater and chloride environments compared to 304 stainless. Thru-hull fittings are in continuous contact with seawater and bilge moisture; using a 316-grade fitting rather than 304 or a lower grade reduces the risk of crevice corrosion and pitting at the hull penetration over time. Confirm your existing or adjacent fittings and hull hardware are compatible metals to avoid galvanic corrosion between dissimilar metals.

Dimensional Reference — Installation Planning:

• Hose barb: 3/4 in. — fits 3/4 in. ID hose; confirm hose ID matches the barb before ordering
• Flange diameter: 1-7/8 in. — the exterior flange that bears against the outer hull surface; size the backing plate to extend beyond the flange perimeter
• Thread length: 1 in. — the threaded shank that passes through the hull and accepts the interior hull nut
• Barb length: 1 in. — the hose barb engagement length inside the boat
• Overall length: 2-1/2 in. — total fitting length from barb tip to flange face
• Hull cut: 1-1/8 in. — use a 1-1/8 in. hole saw to cut the hull penetration
• Max hull thickness: 5/8 in. — the threaded shank length limits installation to hulls 5/8 in. thick or less at the penetration point; measure hull thickness before ordering

Straight Thru-Hull Design:

The 6541 is a straight thru-hull fitting — the hose barb projects straight inboard from the hull, simplifying hose routing in applications where a 90-degree or angled fitting is not required. Straight fittings offer lower flow restriction than angled fittings and are the preferred choice where hose routing allows a direct run from the fitting to the connected component.

Below-Waterline vs. Above-Waterline Installation:

Thru-hull fittings installed below the waterline require a seacock or ball valve mounted directly to the fitting interior to allow the penetration to be shut off in the event of a hose failure or fitting leak. ABYC H-27 and NMMA standards require a seacock on all below-waterline penetrations except cockpit drains that self-drain above the waterline at rest and underway. For above-waterline installations (cockpit drains, livewell overflows), a seacock is not required but a proper sealant and backing plate installation is still mandatory. Confirm the installation location relative to the waterline before selecting fitting type and planning the installation.

Installation — Sealant and Backing Plate:

All thru-hull fittings require a marine-grade sealant and a backing plate on the interior hull surface:

• Sealant — apply a marine polysulfide or polyurethane sealant (such as 3M 5200, 4200, or Boatlife Life-Calk) to the flange face and shank before inserting through the hull; do not use silicone — silicone does not bond reliably to wet or contaminated surfaces and does not have adequate adhesion for structural hull penetrations
• Backing plate — install a backing plate (plywood, HDPE, G10 fiberglass, or aluminum) on the interior hull surface, bedded in sealant, to distribute the compressive load of the hull nut across the hull laminate and prevent the nut from crushing or cracking the hull skin; size the backing plate to extend beyond the 1-7/8 in. flange perimeter
• Hull nut — thread the hull nut onto the shank from the interior against the backing plate; tighten until the flange seats firmly against the hull exterior and sealant squeezes out around the flange perimeter; do not overtighten

Installation Notes:

• Measure hull thickness at the installation point before ordering — maximum 5/8 in.
• Use a 1-1/8 in. hole saw for the hull penetration
• Confirm hose ID is 3/4 in. to match the barb
• Apply marine polysulfide or polyurethane sealant to flange face — do not use silicone
• Install a backing plate on the interior hull surface under the hull nut
• Below-waterline installations require a seacock or ball valve — confirm ABYC H-27 requirements for your installation
• Inspect fitting and sealant annually for signs of weeping, corrosion, or sealant deterioration

Frequently Asked Questions

1. What size hole saw do I need?
1-1/8 in. hole saw for the hull penetration.

2. What hose size does this fitting accept?
3/4 in. ID hose. Confirm your hose's interior diameter is 3/4 in. before ordering.

3. Do I need a seacock with this fitting?
Yes, if installed below the waterline — ABYC H-27 requires a seacock on all below-waterline penetrations (with limited exceptions for self-draining cockpit drains). Above-waterline installations do not require a seacock but still require sealant and a backing plate.

4. What sealant should I use?
Marine polysulfide (Boatlife Life-Calk) or polyurethane (3M 4200 or 5200). Do not use silicone — it does not bond reliably in wet or below-waterline conditions and is not suitable for structural hull penetrations.

5. Why is 316 stainless better than 304 for marine thru-hulls?
316 stainless contains molybdenum, which improves resistance to crevice corrosion and pitting in saltwater and chloride environments. 304 stainless is susceptible to rust and pitting in prolonged saltwater contact — not suitable for a permanently submerged or bilge-area fitting.