Marine Refrigeration Compressor Certification: What Gets Checked at Survey

Most certification checklists you find for marine refrigeration are written for yachts. They talk about ABYC wiring, 12 or 24 V DC battery banks, and appliance safety marks. If you are fitting out a fishing vessel with a three-phase semi-hermetic compressor, that checklist does not describe the equipment you are buying, the authority that inspects it, or the document that gets it through a survey.

This is the checklist for the other case: a compressor that has to hold a fish hold or a provision room, on a vessel that is classed, and on a route where you cannot call a technician.

Key takeaway

· A class society type approval is the document that matters on a classed fishing vessel. ABYC and household appliance standards belong to a different class of equipment.

· Type approval approves a model, on a named refrigerant, at a stated design pressure — not a "marine-grade" claim and not a whole system.

· Seven fields on the certificate decide whether your survey passes. A missing or mismatched field fails it, regardless of how good the machine is.

· The certificate says nothing about whether your duty point sits inside the compressor's operating envelope. That is a separate question, and it is the one most often got wrong.

· It also says nothing about motion. Rough-weather operation is solved by oil management and mounting, not by a certificate.

· On a vessel away from home port, the parts that stop the voyage are the valve plate, gaskets, oil pump and service valves. Those are the ones worth carrying.

1. The checklist you find online is written for yachts

Search for marine refrigeration certification and you will land on the same advice: check for ABYC compliance, look for a UL marine mark, confirm the unit switches between 12 and 24 V DC, check the amp-hour draw over 24 hours.

That advice is coherent — for a different product. ABYC is the American Boat and Yacht Council, and its standards are written for recreational craft. EN 60335-2-24 is the household refrigerating appliance standard. UL listings are electrical-safety listings. So is a CE mark. None of them is a classification society's type approval, and none of them is issued against a rule set for a fishing vessel.

The equipment is different in kind, not just in size:

The failure mode is not that the yacht advice is wrong. It is that a buyer follows it, buys an appliance-grade unit, and then discovers at survey that nobody ever asked the classification society anything.

2. What a fishing vessel is actually inspected against

A classed vessel is built and maintained against a rule set. For a fishing vessel under China Classification Society rules, the relevant documents are the Rules for Construction of Ocean-Going Steel Fishing Vessels and the Technical Rules for Statutory Inspection of Ocean-Going Fishing Vessels. Machinery installed in the refrigerating plant is assessed against the chapter those rules devote to it.

Two consequences follow, and both surprise first-time buyers.

First, the rules are about the vessel, not a supplier's parts list. The surveyor is not comparing your compressor to a marketing sheet. He is checking that the installed machinery is of a type the society has approved, that it is applied within the limits of that approval, and that the installation supports it.

Second, the approval is a document with a number. It names a manufacturer, a product type, a list of approved models, a refrigerant, a design pressure, the vessel types it is intended for, and a validity window. If any of those does not match what is on your vessel, the approval does not apply to your installation — even though the machine is physically identical to one that is approved.

A classed installation is judged as a system: the machine, the sea-water side, the gauges and the space around it. The compressor being approved is the start of the conversation, not the end of it.

That is why the practical question is never "is this compressor marine grade". It is "which model, on which refrigerant, is on the certificate, and does my duty point sit inside it".

3. Type approval approves a model, not a badge

A type approval is issued against a product type and a model list. The society reviews the design, the pressure containment, the electrical arrangement and the manufacturing control behind it, then approves those specific models. Change the refrigerant, change the design pressure, or move to a frame that is not on the list, and you are outside the approval.

This is the single most useful thing to understand before you compare quotes, because it changes what you ask for:

· Ask for the certificate number and the issuing branch, not a logo.

· Ask which models are on it, and whether your model code appears.

· Ask which refrigerant the approval was granted on.

· Ask the design pressure the approval covers.

· Ask the validity date and whether it is still in force.

· Ask what the approval excludes.

A supplier who cannot answer these six questions has not read their own certificate. A supplier who answers them without hesitation has, and that tells you something about how the rest of the order will go.

4. Our certificate, field by field

This is not a claim we make loosely. Blait is certified by an international classification society, and the document is CCS type approval ZG24PTB00058_01, issued by China Classification Society Zhejiang Branch on 29 October 2024 and valid to 28 October 2029. Page 1 carries the manufacturer, the approval basis, the intended vessel types and the validity; the additional pages carry the approved model list with displacement, nominal capacity, rated power and the approved condition for each model.

Page one of the certificate: manufacturer, approval standards, intended vessel types and the validity date. The approved models are on the additional pages.

Our marine four-cylinder range is the range this approval covers, and it sits inside the wider T-Series semi-hermetic range. Read the certificate the way a surveyor will — seven fields, in this order:

Two details on that page are worth pointing out because buyers skip them.

"Notations: Nil." Some certificates carry additional notations — restrictions, conditions, or a reduced scope attached to the approval. Ours carries none. That is a cleaner position than a certificate with conditions buried in a notation, and it is the field to check on any certificate you are handed, from any supplier.

Rated speed. The approved condition on each model is stated at 1450 r/min, which is a 50 Hz machine. If your plant runs 60 Hz, the duty point moves — capacity rises and so does the current — and the approval was not written at that point. This is exactly the sort of gap that a "marine-grade" badge hides and a certificate exposes. Ask before you order, not after.

5. The three mismatches that still fail a survey

An approved model can still fail, because approval attaches to the model and the survey attaches to the installation. In practice it goes wrong in three ways.

The refrigerant does not match. The approval is for R507. A build charged with R404A or R22 is a different build, and on a classed vessel you need the approval that matches the gas actually in the system. We build all three, but they are not interchangeable on a certificate — the paperwork follows the refrigerant, and the oil follows the refrigerant with it. Ester oil for the HFC refrigerants, mineral or alkylbenzene for R22.

The design pressure does not match. An approval at 3.2 MPa covers a system designed around that. If the plant is designed higher, or if the condensing side is running near the limit because the sea-water side is fouled, the margin the approval assumed is gone. The certificate did not create that margin; your condenser maintenance does.

The duty point is outside the envelope. This is the most common one, and the certificate cannot catch it, because the certificate is not a performance document.

6. The certificate does not tell you whether your duty point fits

An approval says the model is acceptable for the service. It does not say the model will do your job. That is a separate question with a separate answer: the operating envelope for the refrigerant, and the capacity at your evaporating and condensing temperatures.

The envelope for the four-cylinder range on R404A and R507A: evaporating temperature across the bottom, condensing temperature up the side, and the region that needs additional cooling marked. A duty point outside the envelope is a different machine, not a different setting.

Three things follow from that figure, and they matter more on a vessel than on land:

· The condensing temperature is set by the sea-water side. A fouled condenser or a warm coastal water temperature moves you up the vertical axis, and capacity falls as it does. On a tropical route the same machine delivers less than it did in the yard.

· The low-temperature corner needs additional cooling. Roughly, once you are deep into frozen-hold duty with a high condensing temperature, liquid injection control is required, not optional. A machine supplied without it will run, and will not last.

· Two-stage becomes the honest answer below a certain point. When the ratio between condensing and evaporating pressure gets large, single-stage discharge temperature goes past what the oil tolerates. That is a frame change, not a setting change — our two-stage range exists for exactly that duty, and it is a different approval conversation. Below the point where two-stage stops being enough, the honest answer is a different refrigerant altogether: our carbon dioxide series runs down to −50 °C.

So the sequence is: confirm the model is approved, confirm the refrigerant matches, then confirm the duty point sits inside the envelope with the condensing temperature your route will actually give you. Only the first of those three is on the certificate.

7. Motion: what a certificate does not cover

Yacht advice often claims a compressor must be "certified for 30 degrees of pitch and roll". Treat that claim carefully. A classification society type approval is a containment and design approval; it is not a tilt rating, and a supplier who tells you their certificate covers a roll angle is describing something the document does not say.

What actually happens to a semi-hermetic compressor at sea is an oil problem, and it is solved mechanically:

· Oil leaves the crankcase and has to come back. Long suction runs, traps and low gas velocity let oil sit in the line instead of returning. On a vessel the run from the hold to the machine room is often long and not vertical.

· The level in the crankcase is the thing to watch. A machine that has been running at an angle with a starving oil pump shows it at the sight glass before it shows it anywhere else.

· Mounting and pipe support do the rest. Rigid pipe clamped to a flexing hull transmits movement into the compressor flange. Vibration isolators under the feet and proper support on the suction line are not accessories.

If you want a defensible answer on motion, ask for the installation requirements rather than a certificate: mounting, pipe support, oil management, and whether an oil level switch or oil differential switch is fitted. Those are the items that decide whether the machine survives a bad passage, and they are all inspectable.

8. Spares that decide whether the vessel sails

A vessel in remote water does not fail because the compressor was unapproved. It fails because one small part was not on board.

The parts that stop a voyage on a semi-hermetic are predictable, and they are the same parts on every frame:

Hold duty: the machine holds temperature against a door that opens, product that comes in warm, and an evaporator that ices. The spares list on a vessel is written for this room, not for a parts list.

This is why we keep the spare parts range as a standing line rather than a special order, and why the valve plate is treated as a wear item with a part number, not as evidence that the compressor has failed.

9. Before it ships

The certificate proves the design. It does not prove the individual machine. What we do to each unit before it leaves is the part a buyer can actually verify:

· Bench run. Every machine is run before packing, so oil pressure, noise, vibration and valve action have been demonstrated on that serial number.

· Leak test with the valves fitted. The shell is tested with the service valves and rotalock joints installed, because those joints are where a leak appears in year three.

· Oil charged to the refrigerant. The grade is fixed by the gas, not by preference, and the machine ships with the grade the approval implies.

· Nameplate and serial number. Model code and serial are the two things we need to tell you which frame you have and which parts fit it.

· The certificate, on request. If your surveyor wants the document for the model you ordered, ask for it with the order — it is quicker than asking after the vessel is in the water.

Frequently Asked Questions

Is a class society certificate legally required for a fishing vessel compressor? It depends on the vessel and the flag. For a classed vessel, the surveyor works to the society's rules, and equipment without a type approval is difficult to accept. For an unclassed vessel the requirement may not be legal at all — but the same document is what an insurer, a yard or a buyer will ask for, so the practical answer barely changes.

Does our CCS certificate cover the whole refrigeration system? No. It covers the compressor. Evaporators, condensers and control boxes supplied by others sit outside the approval. That boundary is stated on the certificate, and it is worth reading before you assume the whole plant is covered.

Can I run R404A or R22 if the certificate names R507? Not on the strength of that certificate. The approval attaches to the refrigerant, and the oil follows the refrigerant. We build the range for R507, R404A and R22, but the paperwork has to match the gas in your system, so tell us the refrigerant before we quote.

What if my vessel is classed by a different society? Then you need that society's approval, not ours. We will tell you what we hold rather than imply coverage we do not have. Where a society accepts a manufacturer's test and design records, the conversation starts from the same file.

Does the certificate cover rough weather or a roll angle? No, and no type approval does. Motion is handled by oil management, mounting and pipe support. Ask about the installation requirements and about whether an oil level or oil differential switch is fitted — those are the real answers.

Can you supply the certificate for the serial number I received? We can supply the certificate for the model, and the nameplate and serial number tie the machine to its build record. Send both and we will confirm which frame you have and which approval applies.

Send us the model and the serial number

If you already have a Blait machine, the model code and serial number off the nameplate tell us which frame you have, which refrigerant it was built for, and which approval applies. If you are specifying a new installation, send the hold volume, the evaporating and condensing temperatures you expect, the refrigerant and the supply voltage — and we will tell you whether the duty sits inside the envelope before you commit to a frame.

For a vessel under classification, tell us the society and the route. Contact our engineering team with those four numbers and you will get an answer about the certificate, not a brochure.

Related reading: how to choose between a screw and a piston compressor, how to check a refrigeration compressor step by step, and what is inside a semi-hermetic compressor.