Tecnoseal 00550 Series NACA Profile Shaft Collar Anode

Tecnoseal 00550 Series NACA-profile shaft collar anodes are split sacrificial anodes for marine propeller shafts from 19mm to 35mm. This combined range contains nine shaft-bore sizes in zinc, aluminium and magnesium, giving 27 variants. Every model is 25mm wide, with a 55mm or 66mm outside diameter according to shaft size. Match the exact shaft diameter, available clearance and required alloy before ordering.

What Is This Shaft Anode Used For?

The two-piece collar clamps directly around an exposed propeller shaft. With clean, direct metal-to-metal contact, the anode becomes part of the vessel's cathodic-protection system and is consumed in preference to the shaft and other electrically connected underwater metal components.

The NACA profile gives the collar a streamlined external form, but it does not remove the need to confirm the exact internal bore, axial space and rotational clearance.

Key Features

• Brand: Tecnoseal
• Product category: NACA-profile marine shaft collar anode
• Series: 00550 to 00557, including alloy-specific suffixes
• Shaft-size range: 19mm to 35mm
• Available shaft sizes: Nine metric and imperial-equivalent sizes
• Available alloys: Zinc, aluminium and magnesium
• Number of variants: 27
• Axial width: 25mm across the range
• Outside diameter: 55mm or 66mm, depending on shaft size
• Mounting: Split collar secured mechanically around the shaft
• Application: Marine propeller shafts with a matching measured diameter
• Manufacture: Made in Italy by Tecnoseal

Compatible Shaft Sizes and Part Numbers

• 19mm / 3/4in: 00550 zinc, 00550AL aluminium or 00550MG magnesium
• 20mm: 00550/1 zinc, 00550-1AL aluminium or 00550/1MG magnesium
• 22mm / 7/8in: 00551 zinc, 00551AL aluminium or 00551MG magnesium
• 25mm: 00552 zinc, 00552AL aluminium or 00552MG magnesium
• 25.4mm / 1in: 00553 zinc, 00553AL aluminium or 00553MG magnesium
• 28.6mm / 1 1/8in: 00554 zinc, 00554AL aluminium or 00554MG magnesium
• 30mm: 00555 zinc, 00555AL aluminium or 00555MG magnesium
• 31.8mm / 1 1/4in: 00556 zinc, 00556AL aluminium or 00556MG magnesium
• 35mm / 1 3/8in: 00557 zinc, 00557AL aluminium or 00557MG magnesium

Part-number note: The 20mm aluminium model uses Tecnoseal code 00550-1AL. The corresponding zinc and magnesium models use 00550/1 and 00550/1MG.

How Do I Select the Correct Variant?

Measure the propeller shaft accurately and select an anode with the same internal diameter. Then confirm the available axial space, finished outside-diameter clearance and required alloy.

• Exact shaft diameter: Do not substitute a nearby size. A 25mm collar is not suitable for a 25.4mm / 1in shaft.
• Axial space: Allow at least the specified 25mm collar width, plus suitable installation and service clearance.
• Outside clearance: Models from 19mm to 25.4mm have a 55mm outside diameter. Models from 28.6mm to 35mm have a 66mm outside diameter.
• Rotational clearance: Confirm that the installed collar clears the stern tube, shaft bracket, hull and nearby fittings throughout shaft rotation.
• Alloy: Match the vessel manufacturer's cathodic-protection specification and operating water.

Which Anode Alloy Should I Choose?

• Zinc: A conventional selection for salt-water operation where zinc is specified.
• Aluminium: Generally selected for salt or brackish water and lower in mass than the equivalent zinc collar.
• Magnesium: Generally selected for fresh-water operation and normally unsuitable for prolonged salt-water use because it may be consumed too rapidly.

Use the alloy specified by the vessel, shafting or equipment manufacturer and keep the selection consistent with the existing cathodic-protection system. Water salinity, connected metals, shore-power arrangements and stray-current conditions can affect the correct choice.

Installation and Maintenance

Clean the shaft to bright, bare metal where the anode will sit. Position both halves squarely around the shaft and tighten the fasteners evenly in stages so the collar seats securely without rocking or leaving an uneven gap.

Do not apply paint, grease, sealant or insulating compound between the anode and shaft because direct electrical contact is required. After installation, rotate the shaft by hand where safe to confirm clearance around the complete collar.

Inspect the anode during scheduled servicing and after extended operation in a different water type. Replace it when substantially consumed, cracked, loose or no longer able to clamp securely. Investigate unusually rapid or uneven consumption rather than fitting a larger anode without identifying the cause.

Alloy Standards and Manufacture

Tecnoseal manufactures zinc, aluminium and magnesium sacrificial anodes at its foundry in Grosseto, Tuscany. Alloy composition is checked using scheduled spectrometric measurements against the applicable material specification:

• Zinc alloy: US Mil Spec A-18001K
• Aluminium alloy: US Mil Spec A24779 SH
• Magnesium alloy: US Mil Spec A21412 SH

Frequently Asked Questions

• What does NACA profile mean? It identifies the streamlined external form used by this Tecnoseal shaft-collar series. The exact shaft bore and outside clearance must still be checked.
• Can I fit a 25mm collar to a 25.4mm / 1in shaft? No. These are separate variants and the internal diameter must match the shaft.
• Is a 20mm version available? Yes. Select 00550/1 zinc, 00550-1AL aluminium or 00550/1MG magnesium.
• Are all variants the same outside diameter? No. The 19mm to 25.4mm models are 55mm outside diameter; the 28.6mm to 35mm models are 66mm.
• Are the fixing fasteners included? Do not assume hardware is included unless the selected product offer specifically states this. Use the correct serviceable fasteners for the model.
• Can different anode alloys be mixed on the same vessel? Do not change or mix alloys without checking the vessel or equipment manufacturer's cathodic-protection specification.
• Why do equivalent alloy variants have different weights? Zinc, aluminium and magnesium have different densities, although matching base-model variants share the same nominal geometry.
• Can the anode be painted? No. Keep the sacrificial surface and shaft-contact faces free from paint and insulating coatings.

Specifications