Getting a Certificate of Inspection on a RHIB

Who does what

• The owner is the applicant and the party the Certificate of Inspection is issued to. The owner files the application for inspection, is responsible for the vessel meeting the regulations, presents the boat for the deadweight survey and the inspections, and receives the stability letter and the COI.
• The naval architect is not required by regulation but is usually recommended by the Marine Safety Center, and in practice does most of the work on the owner's behalf: builds the model, prepares the plans and the stability calculations, assembles the submission, sends it to MSC and answers MSC's questions. Most submissions arrive at MSC from a naval architect acting for an owner.
• The Marine Safety Center (MSC) in Washington is where the submission goes — the plans, the calculations, the survey results. MSC reviews it, corresponds until it is satisfied, approves it, and issues the stability letter. When MSC approves, it hands the approved package off to the OCMI and to the owner.
• The OCMI (Officer in Charge, Marine Inspection — your Coast Guard Sector) receives the application for inspection, provides the marine inspector who witnesses the deadweight survey, receives MSC's approval, conducts the initial inspection of the vessel against the approved plans, sets the route and persons permitted, and issues the Certificate of Inspection.

Decide the service: passengers, persons, route

A "small passenger vessel" under Subchapter T carries more than six passengers (with at least one for hire) and is under 100 gross tons. Once you cross six, the boat must be inspected and certificated, and the COI will state three numbers you need to settle at the start: the passengers permitted, the total persons permitted, and the route.

Passengers permitted

Subchapter T offers three ways to count passengers — length of rail, deck area and fixed seating — but on a RHIB only one of them applies in practice: fixed seating. Rail and deck-area counts are for larger decked vessels and are not used for inflatable-collar boats.

• Fixed seating: one passenger for each 18 inches of seat width, on seats secured to the deck, bulkhead or bulwark, built to avoid injury and trapping, with ready escape, aisles of at least 24 in (30 in if the aisle is longer than 15 ft) and at least 30 in from seat front to seat front where seats are in rows.
• Tube (collar) seating: sitting on the collar is accepted by some OCMIs and not by others — it depends on the Coast Guard Sector you are in. If you intend to count tube seating, settle it with your OCMI before the arrangement is drawn, because the seating drawing is what the passenger count, the stability load conditions and the COI all rest on.

Route

The OCMI records the route on the COI. RHIBs do not do oceans; the routes you will see are coastwise and limited coastwise (with geographic limits — distance offshore, named waters, seasons), and for some boats lakes, bays and sounds. For stability the Subchapter S weather criterion maps the route onto three exposure classes — exposed, partially protected and protected waters — which set the wind pressure in the wind-heel check. The exposure class you ask for is the single biggest lever on whether an inflatable-collar boat with a top will pass, and it is usually the first thing to decide.

Apply for inspection, then submit everything to MSC

The very first thing is the application. Coast Guard form CG-3752, Application for Inspection of U.S. Vessel, goes to the OCMI of the zone where the inspection will happen — and for a new build or a conversion it must be filed before construction or conversion starts. That application opens the case; the OCMI's acceptance of the construction, arrangement and equipment is the prerequisite for the first COI.

Then the plans and calculations go to the Marine Safety Center — not to the OCMI. Subchapter T allows the plan submission to be made to MSC, and for the stability package on a RHIB that is where it must go. MSC reviews, approves, and hands the approved package to the OCMI and to the owner. The OCMI inspects against what MSC approved.

Plans before construction

Outboard profile, inboard profile, and arrangement of decks, in duplicate.

Plans and calculations before the COI

As applicable to the vessel: midship section; survival craft embarkation stations; machinery installation (propulsion and control, steering, ventilation, exhaust); electrical installation (one-line, cable lists, panelboards, protection); fuel system; lifesaving, fire detection and extinguishing arrangements; and the stability plans and calculations.

The stability plans (Subchapter S)

For MSC's stability review: general arrangement with inboard and outboard profiles; lines; curves of form; a capacity plan with the centers of gravity of tanks and stowage; tank sounding tables with free-surface data; and draft mark locations with their vertical reference points. The same package must be in the inspector's hands at the deadweight survey.

Build or convert to the standards

Hull structure

A small passenger vessel must meet the structural design standard listed for its hull material:

A hull built to a different standard may be accepted on the basis of satisfactory service or under the alternate design provisions, at the OCMI's discretion.

Fire-retardant resins (FRP hulls)

If the hull, decks or superstructure are FRP, the resin must be fire retardant: accepted by the Commandant as meeting MIL-R-21607E(SH), or shown by an independent laboratory to have an ASTM E-84 flame-spread index of not more than 100 when tested in laminate form (reinforcement of any form, minimum 40 % resin by weight, with the laminate schedule and resin designation in the report). A vessel built with general-purpose resin instead is limited in how it may be used and must carry an approved smoke-detection system in accommodation and service spaces.

The collar

The inflatable collar is treated as reserve buoyancy that can be lost one chamber at a time. MSC's technical note for rigid-hull inflatables sets the compartmentation expectation — the collar is divided into chambers so that no single puncture removes more than a limited share of the collar's buoyant volume (on the order of 15 %), which for a boat over about 30 ft means six or more chambers — and defines the deflated-chamber stability cases the vessel must pass (Step 6). Manufacturer's tube drawings showing the baffle positions and chamber volumes are part of the submission.

Everything else the inspector looks at

Seating (177.820), deck rails and guards (177.900–177.960), means of escape, ventilation of machinery and fuel-tank spaces, fuel systems and tanks, electrical, lifesaving, fire protection, and — specific to open boats — drainage of cockpits and well decks. These are inspected against the regulations, not calculated here, but several of them (a seat moved, a tank relocated, foam added) change the weights that go into the stability model.

Choose the stability route: simplified stability test, or stability calculations

Subchapter T gives a small passenger vessel two ways to show intact stability. They are different in kind, not degree:

• The simplified stability test (SST) — 178.310(c), 178.320, 178.330. A physical proof test in front of a Coast Guard marine inspector: the full passenger weight is put aboard to simulate the least stable condition, the boat is heeled by shifting weight, and the freeboard and heel must stay inside fixed limits. No calculations, no lines plan, no MSC review of hydrostatics. Open only to monohulls of not more than 65 ft, with not more than 12 passengers on international voyages, one deck above the bulkhead deck, no tumblehome over 2 % of beam, and whose stability has not been questioned by the OCMI. A vessel that passes it is outside Subchapter S altogether.
• Stability calculations — 178.310(a). Starting from the hydrostatics of the hull (the curves of form computed from its lines) and a measured lightship, the vessel is shown by calculation to meet Subchapter S (46 CFR Parts 170 and 171: the weather criterion, the righting-arm criteria and passenger heel) in every condition of loading and operation. The calculations and the plans behind them are submitted to and approved by the Marine Safety Center, which issues the stability letter.

The model, the lightship and the load conditions

The hull and collar model

The calculation needs the underwater and above-water shape of the boat: the rigid hull, the inflated collar, the deck, the console, the top and anything else that catches wind or enters the water as the boat heels. From the model come the curves of form — displacement, centre of buoyancy, metacentric height and the righting arm at each heel angle — for every draft and trim the boat can take. That is the hydrostatic table every page on this site is reading from.

The lightship

The weight and centre of gravity of the empty, complete boat. It is estimated from the model and the build, then measured by the deadweight survey (Step 7). MSC will not accept a lightship that rests on an estimate alone.

Load conditions

Subchapter S requires compliance "in each condition of loading and operation". MSC's plan review guide for small passenger vessels spells out what that means for a passenger boat, and adds a condition specific to RHIs:

Passenger distribution "shall reflect the arrangements of the vessel": people are placed where the seating drawing puts them, not spread evenly as an abstraction. Each person is 185 lb.

The criteria the boat must meet

Weather criterion (wind heel) — 46 CFR 170.170

The boat must have enough metacentric height to resist a steady beam wind on its projected lateral area:

GM ≥ P · A · H ÷ (W · tan T)

• P — wind pressure, set by the route: 0.0025 (protected), 0.0033 (partially protected) or 0.005 (exposed) long tons/ft², each plus (L/14200)².
• A — projected lateral area above the waterline, in ft², including the hardtop and everything under it; H — height of the centre of that area above half-draft, in ft.
• W — displacement in long tons; T — the limiting heel angle, the lesser of 14° or the angle at which a set fraction of the least freeboard is immersed, as MSC applies it to RHIs.

MSC's RHI technical note gives two ways to apply it: the general form above with trim held fixed, and an alternative in which the equilibrium heel under the wind heeling moment, read from the actual righting-arm curve, must be less than T.

Righting-arm criteria — 46 CFR 170.173

For vessels of unusual proportion or form — which an inflatable-collar boat is — the righting-arm curve itself must meet minimum area, range and GZ requirements in each load condition.

Passenger heel — 46 CFR 171.050

With all passengers crowded to one side, the heel must not immerse the deck edge (or exceed the stated limit) — a check on freeboard as much as on GM. MTN 01-08 §5.7 gives the general and alternative applications for RHIs in the same pattern as the weather criterion.

Collar puncture — MTN 01-08 §5.4.2

Each collar chamber is deflated in turn, in each load condition, and the damaged boat must still show:

The aft chambers usually govern: they carry the engines' weight and sit where the passengers are heaviest.

The deadweight survey

The stability-calculation route needs a measured lightship. Part 170 requires it to be established by the ASTM F1321 procedure, incorporated by reference, in the presence of a Coast Guard marine inspector. For a RHIB — where the vertical centre of gravity is established conservatively from the model and the weight list, and the weight and fore-and-aft centre are what need confirming — MSC accepts the deadweight survey: F1321's lightweight survey, freeboards read port and starboard, without the inclining. The survey procedure is written in advance and sent to MSC with the submission; the inspector initials the field readings.

Preparations

• The vessel as complete as practicable; dunnage, tools and anything not part of the boat removed; everything that is part of the boat (life floats, fire extinguishers, anchor) aboard or its weight and position recorded.
• Tanks empty and dry, or at a known level whose weight and centre can be computed; the test procedure says which.
• Fixed ballast installed before the survey. Ballast is part of the lightship; MSC expects weight added or removed after the survey to total less than about 2 % of the lightship, or the survey is repeated.
• Calm water, adequate depth, mooring lines slack so they do not load the boat.
• A written survey procedure submitted to MSC in advance: the vessel, the date and place, the weights to be aboard, the tank condition, where the freeboards will be read and from what reference.

The readings

Freeboard is read from a reference mark of known height above baseline down to the water, port and starboard, at enough stations along the length to fix the waterline — three is the F1321 minimum; five (bow, quarters, midship, stern) is normal practice and over-determines trim so that errors show. The reference heights come from the drawings or model, not from the boat. Seawater density is measured. From the fitted waterline the model gives displacement and longitudinal centre of buoyancy; subtracting the known weights aboard gives the lightship weight and LCG.

MSC review and the stability letter

The package goes to the Marine Safety Center: the stability plans, the lightship from the witnessed survey, the load conditions, the calculations against every criterion, the collar drawings and deflated-chamber cases, the downflooding points, the fixed ballast and foam flotation, and the allowable passengers and crew by deck. MSC reviews it, asks questions (expect correspondence), and when satisfied approves the package and issues the stability letter, which states the conditions under which the vessel complies — route, persons, loading restrictions, fixed ballast, anything else it depends on. MSC sends the approval and the letter to the OCMI and to the owner; from that point the OCMI inspects against the approved plans.

The letter is posted under glass at the operating station. Its conditions become conditions of the COI.

Initial inspection and the Certificate of Inspection

With MSC's approval and the stability letter received by the OCMI and the owner, and construction complete, the OCMI's marine inspector conducts the initial inspection for certification: structure and arrangement against the approved plans, machinery, electrical, fuel, lifesaving, fire protection, and the condition and workmanship of the whole. The OCMI then sets the route and the persons permitted and issues the Certificate of Inspection — valid for five years for a domestic small passenger vessel, with an annual inspection within three months either side of each anniversary.

Living with the COI: changes, drydock, renewal

• Alterations. Repairs or alterations that affect safety — explicitly including "alterations affecting stability" — may not be made without the OCMI's approval; drawings or specifications of the proposed change go in first. A top, a longer bracket, heavier engines, a relocated tank or bench, added ballast: each one means an updated stability submission to MSC before the work.
• Amended COI. A change in persons, route, dimensions, equipment or owner is recorded by an amended certificate, with the same expiry.
• Drydock and internal structural examinations. For a boat in salt water the regulation requires them at least twice in every five years, no more than three years apart; in practice a RHIB is on a two-year drydock and internal structural exam cycle. Expect the inspector to ask for the fuel tank to be removed so the tank, its foundation and the hull beneath it can be examined — plan the tank installation so that is possible without cutting the boat apart.
• Annual inspection every year, within three months either side of the COI anniversary: the same scope as the inspection for certification in less detail, and it includes an in-water portion — the inspector sees the boat afloat, running gear and systems operating, not just tied to the dock. The inspector endorses the COI when it passes.
• Renewal by a new inspection for certification every five years.

Rule → model: where each requirement goes