The intake grate frame is the hull-mounted structural frame that carries the bar grate across the waterjet inlet duct, protecting the impeller from debris while feeding a clean, undisturbed flow to the pump. It sits in the flush inlet tunnel on the bottom of the hull, where it sees high velocity flow, cavitation, galvanic interaction with the hull and impact from floating debris. Buyers come to us because grates that flex fatigue at the bar junctions, because bar spacing that drifts from drawing changes the inlet flow, and because repair of a distorted frame during a short refit window is expensive. We cast the frame and bars as one piece and machine the mounting face flat.
Specifications
| Item | Specification |
|---|---|
| Casting process | Silica sol investment casting, one piece frame with integral cast bars |
| Material options | Duplex 2205, super duplex 2507, nickel aluminium bronze C95800, CF8M / 316L stainless |
| Dimensional tolerance (ISO 8062-3 CT grade) | CT7 to CT8 as cast; CT6 on hull mounting face and bolt hole pattern |
| Machining | CNC milling of hull mounting face, bolt hole drilling, counterbores and bar edge profiling |
| Surface finish (Ra) | Ra 3.2 um on flow surfaces, Ra 1.6 um on hull mounting face and sealing land |
| Corrosion / wear protection | Passivation, epoxy or antifouling coating, isolation bushings and sacrificial anodes for galvanic control |
| Weight range | 12 kg to 160 kg per grate frame |
| Typical lead time | 4 to 6 weeks including tooling, 3 weeks for repeat orders |
Scope and options
Key features
- Frame and bars cast integrally, removing the welded bar joints that crack under flow induced vibration.
- Bar spacing and bar leading edge radius held to drawing across the full inlet area for consistent flow.
- Hull mounting face machined flat within 0.10 mm over the full length to prevent distortion on bolting up.
- Duplex material provides high yield strength with resistance to chloride pitting and cavitation.
- Isolation provisions built in to control galvanic corrosion against aluminium hulls.
- Reverse engineered to fit the existing inlet tunnel opening when drawings are not available.
Applications
- Waterjet propulsion units on patrol craft and pilot boats
- Moreover, Fast crew transfer vessels and offshore wind service boats
- Workboats and harbour utility craft with jet drives
- Fast ferries and passenger catamarans
- Rescue craft and military light craft with jet propulsion
- Inlet tunnel refits and intake grate replacement during scheduled maintenance
Images
Quality & compliance
Grate frames ship with EN 10204 3.1 material certification and heat number traceability, along with mechanical test results for the supplied grade. Dye penetrant inspection of the bar to frame junctions is standard, with ultrasonic and radiographic examination available on request, and we provide a dimensional report covering bar spacing, mounting face flatness and bolt hole position. Ningbo Ruican supplies components to shipyards and marine OEMs; classification-society type approval of the finished part remains the customer’s responsibility, and we support that process with the material, NDT and dimensional documentation the surveyor requires.
FAQ
Why cast the frame and bars in one piece?
Moreover, welded bar joints are the usual failure point, cracking under flow induced vibration and debris impact. A one piece casting removes those joints entirely and gives a smooth fillet at each bar junction, which spreads the load into the frame and resists fatigue far better.
How do you handle galvanic corrosion on an aluminium hull?
We supply duplex or bronze frames with electrical isolation provisions, including isolation bushings in the bolt holes and a non-conductive gasket on the mounting land. Sacrificial anodes are added and bonded so the frame is protected rather than the hull.
Can you match an existing inlet tunnel opening?
Yes. Where the drawing is unavailable we take a template or 3D scan of the tunnel opening and machine the replacement frame to fit, including the existing bolt pattern. This avoids hull modification during a short refit window.
Does bar spacing affect waterjet performance?
It does. Spacing and bar leading edge radius both influence inlet flow quality and cavitation behaviour at the impeller. We hold both to drawing and inspect them across the full inlet area, reporting the measured values with the part.
What is the delivery time for a replacement grate during a refit?
From an approved drawing we typically deliver in three to six weeks depending on size and finish. Tell us the drydocking date at enquiry stage and we will build the schedule backwards from it and confirm a committed date.
Do you offer antifouling or cavitation resistant coatings?
Generally, we can apply epoxy antifouling coating or a cavitation resistant elastomeric coating to the inlet surfaces. Coating specification is agreed at quotation stage so that surface preparation and machining sequence are planned correctly.
CTA
Send your waterjet intake grate drawing, hull material and refit date for a quotation within 48 hours. Contact window: Wendy She — sales@cnsandcasting.com — WhatsApp +86-13777124360. Ningbo Ruican supplies one piece cast intake frames in duplex, super duplex and bronze, with isolation and coating options for aluminium and steel hulls.
