{"id":990243,"date":"2026-08-09T07:30:13","date_gmt":"2026-08-09T07:30:13","guid":{"rendered":"https:\/\/vesselflag.com\/ais-class-b-vs-class-a\/"},"modified":"2026-08-09T07:30:15","modified_gmt":"2026-08-09T07:30:15","slug":"ais-class-b-vs-class-a","status":"publish","type":"post","link":"https:\/\/vesselflag.com\/es\/ais-class-b-vs-class-a\/","title":{"rendered":"AIS Class B vs Class A: Which Do You Need?"},"content":{"rendered":"<div class=\"vgblk-rw-wrapper limit-wrapper\">\n<p>Most commercial vessels subject to USCG carriage rules need Class A. Most recreational boats and smaller workboats that qualify under the CFR exemptions can legally use Class B.<\/p>\n<ul>\n<li><strong>SOLAS\/USCG-mandated commercial vessels, towing vessels \u226526 ft with more than 600 hp, vessels certificated for more than 150 passengers, and dredging vessels affecting navigation:<\/strong> Class A required.<\/li>\n<li><strong>Recreational yachts, smaller fishing vessels, and some passenger vessels not operating in VTS\/VMRS zones:<\/strong> Class B is acceptable, subject to CFR conditions.<\/li>\n<li><strong>All AIS transponders used to meet mandatory carriage rules in U.S. waters must carry a USCG type-approval number<\/strong> (series 165.155 for Class A, 165.156 for Class B). Confirm your vessel\u2019s category and operating area against <a href=\"https:\/\/navcen.uscg.gov\/ais-requirements\" rel=\"nofollow noopener noreferrer\" target=\"_blank\">33 CFR carriage requirements<\/a> before purchasing.<\/li>\n<\/ul>\n<p><strong>Pro Tip:<\/strong> <em>If you operate commercially in mixed traffic near a port or VTS zone, default to Class A even when the regulations technically allow Class B. The reporting rate and transmit power difference are not trivial in congested channels.<\/em><\/p>\n<hr>\n<h2 id=\"key-takeaways\">Principales conclusiones<\/h2>\n<p>Class A is the mandatory choice for most commercial vessels under U.S. rules, while Class B is permissible for recreational craft and select smaller commercial vessels that meet all CFR substitution conditions simultaneously.<\/p>\n<table>\n<thead>\n<tr>\n<th>Punto<\/th>\n<th>Detalles<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Regulatory trigger<\/td>\n<td>Self-propelled commercial vessels \u226565 ft, towing vessels \u226526 ft\/600+ hp, and vessels certificated for 150+ passengers must carry Class A.<\/td>\n<\/tr>\n<tr>\n<td>Power and reporting<\/td>\n<td>Class A transmits at ~12.5 W with updates every 2\u201310 seconds underway; Class B\/SO at ~5 W and Class B\/CS at ~2 W, both less frequently.<\/td>\n<\/tr>\n<tr>\n<td>Class B subtypes<\/td>\n<td>Class B\/SO uses SOTDMA (better in busy traffic); Class B\/CS uses CS-TDMA (opportunistic, lower cost, adequate for light nearshore use).<\/td>\n<\/tr>\n<tr>\n<td>Approval check<\/td>\n<td>Confirm the USCG type-approval number on the unit label: 165.155.xxx for Class A, 165.156.xxx for Class B, before purchase or inspection.<\/td>\n<\/tr>\n<tr>\n<td>Vesselflag support<\/td>\n<td>Vesselflag provides MMSI setup, type-approval verification, and flag registration packages that cover AIS carriage documentation.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<hr>\n<h2 id=\"table-of-contents\">\u00cdndice<\/h2>\n<ul>\n<li><a href=\"#how-do-class-a-and-class-b-ais-actually-compare\">How do Class A and Class B AIS actually compare?<\/a><\/li>\n<li><a href=\"#what-does-class-a-actually-do-on-the-water\">What does Class A actually do on the water?<\/a><\/li>\n<li><a href=\"#what-does-class-b-do-and-which-subtype-should-you-choose\">What does Class B do, and which subtype should you choose?<\/a><\/li>\n<li><a href=\"#who-must-carry-class-a-under-us-rules-and-when-can-class-b-substitute\">Who must carry Class A under U.S. rules, and when can Class B substitute?<\/a><\/li>\n<li><a href=\"#how-do-range-traffic-priority-and-satellite-detection-differ-in-practice\">How do range, traffic priority, and satellite detection differ in practice?<\/a><\/li>\n<li><a href=\"#what-does-installation-actually-involve-and-what-does-it-cost\">What does installation actually involve, and what does it cost?<\/a><\/li>\n<li><a href=\"#how-do-you-decide-which-class-is-right-for-your-vessel\">How do you decide which class is right for your vessel?<\/a><\/li>\n<li><a href=\"#how-do-you-verify-uscg-type-approval-and-register-your-mmsi\">How do you verify USCG type-approval and register your MMSI?<\/a><\/li>\n<li><a href=\"#vesselflags-take-when-class-a-is-the-right-call-even-when-class-b-is-legal\">Vesselflag\u2019s take: when Class A is the right call even when Class B is legal<\/a><\/li>\n<li><a href=\"#vesselflag-handles-mmsi-setup-registration-and-ais-compliance-paperwork\">Vesselflag handles MMSI setup, registration, and AIS compliance paperwork<\/a><\/li>\n<li><a href=\"#sources\">Sources<\/a><\/li>\n<li><a href=\"#faq\">PREGUNTAS FRECUENTES<\/a><\/li>\n<\/ul>\n<h2 id=\"how-do-class-a-and-class-b-ais-actually-compare\">How do Class A and Class B AIS actually compare?<\/h2>\n<p>The table below draws from the NAVCEN PDF comparison and NAVCEN\u2019s AIS types reference.<\/p>\n<table>\n<thead>\n<tr>\n<th>Dimension<\/th>\n<th>Class A<\/th>\n<th>Class B\/SO<\/th>\n<th>Class B\/CS<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td><strong>Transmit power<\/strong><\/td>\n<td>~12.5 W<\/td>\n<td>~5 W<\/td>\n<td>~2 W<\/td>\n<\/tr>\n<tr>\n<td><strong>Estimated practical range<\/strong><\/td>\n<td>Up to ~20 nm (typical)<\/td>\n<td>Up to ~10 nm (typical)<\/td>\n<td>Up to ~5\u20138 nm (typical)<\/td>\n<\/tr>\n<tr>\n<td><strong>Reporting rate (underway)<\/strong><\/td>\n<td>Every 2\u201310 seconds<\/td>\n<td>Less frequent<\/td>\n<td>Less frequent<\/td>\n<\/tr>\n<tr>\n<td><strong>Reporting rate (at anchor)<\/strong><\/td>\n<td>Every 3 minutes<\/td>\n<td>Every 3 minutes<\/td>\n<td>Every 3 minutes<\/td>\n<\/tr>\n<tr>\n<td><strong>Dynamic messages<\/strong><\/td>\n<td>Messages 1, 2, 3<\/td>\n<td>Message 18<\/td>\n<td>Message 18<\/td>\n<\/tr>\n<tr>\n<td><strong>Static\/voyage data<\/strong><\/td>\n<td>Message 5 (every 6 min)<\/td>\n<td>Messages 19\/24 (every 6 min, no voyage info)<\/td>\n<td>Messages 19\/24 (no voyage info)<\/td>\n<\/tr>\n<tr>\n<td><strong>Safety\/application messages<\/strong><\/td>\n<td>Transmit and receive (Msgs 6, 8, 25, 26)<\/td>\n<td>Receive only<\/td>\n<td>Receive only<\/td>\n<\/tr>\n<tr>\n<td><strong>Channel access<\/strong><\/td>\n<td>SOTDMA<\/td>\n<td>SOTDMA<\/td>\n<td>CS-TDMA<\/td>\n<\/tr>\n<tr>\n<td><strong>Regulatory carriage eligibility<\/strong><\/td>\n<td>All mandatory categories<\/td>\n<td>Select categories with CFR conditions<\/td>\n<td>Select categories with CFR conditions<\/td>\n<\/tr>\n<tr>\n<td><strong>Hardware cost (approx.)<\/strong><\/td>\n<td>$1,500\u2013$3,500+<\/td>\n<td>$400\u2013$900<\/td>\n<td>$200\u2013$600<\/td>\n<\/tr>\n<tr>\n<td><strong>Installation complexity<\/strong><\/td>\n<td>Higher (dedicated display, wiring)<\/td>\n<td>Moderado<\/td>\n<td>Moderado<\/td>\n<\/tr>\n<tr>\n<td><strong>Satellite AIS detection<\/strong><\/td>\n<td>Strong (frequent Messages 1\/2\/3)<\/td>\n<td>Moderate (Message 18)<\/td>\n<td>Lower<\/td>\n<\/tr>\n<tr>\n<td><strong>Chartplotter\/display integration<\/strong><\/td>\n<td>Full NMEA\/IEC 61162<\/td>\n<td>Full NMEA\/IEC 61162<\/td>\n<td>Full NMEA\/IEC 61162<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><img decoding=\"async\" src=\"https:\/\/vesselflag.com\/wp-content\/uploads\/2026\/08\/1786260278859_Diagram-comparing-AIS-Class-A-and-Class-B-features.jpeg\" alt=\"Diagram comparing AIS Class A and Class B features\"><\/p>\n<p>The single biggest operational difference is the combination of channel access and reporting rate. SOTDMA (used by Class A and Class B\/SO) reserves time slots in advance, so transmissions get through even in a crowded VHF environment. CS-TDMA (used by Class B\/CS) waits for a gap and transmits opportunistically. In a busy harbor with dozens of vessels, a Class B\/CS unit can miss its transmission window entirely, leaving a gap in your track on other vessels\u2019 displays.<\/p>\n<hr>\n<h2 id=\"what-does-class-a-actually-do-on-the-water\">What does Class A actually do on the water?<\/h2>\n<p>Class A is defined under IEC 61993-2 and is the standard required by IMO for vessels subject to SOLAS carriage rules. Its core technical behavior comes down to three things: SOTDMA channel access, roughly 12.5 W transmit power, and a reporting rate that updates other vessels every 2\u201310 seconds while underway.<\/p>\n<p>Those reporting rates come from Messages 1, 2, and 3, which carry dynamic position data including course, speed, heading, and navigational status. Message 5 broadcasts static and voyage-related information (vessel name, call sign, destination, ETA, draft) every six minutes. Together, these give other vessels and shore-based traffic management systems a near-continuous, high-fidelity picture of your movements.<\/p>\n<p>Class A also transmits safety-related text messages and application-specific messages (Messages 6, 8, 25, and 26). That matters in practice: a Class A unit can broadcast a safety text to nearby vessels or participate in port authority messaging systems. Class B cannot transmit those messages at all, only receive them.<\/p>\n<p>SOTDMA slot reservation is what makes Class A reliable in congested VHF conditions. The unit announces its next transmission slot in advance, so other stations know not to transmit at the same time. The result is consistent, predictable reception even when dozens of vessels share the same channel.<\/p>\n<p>For USCG compliance purposes, Class A units carry an approval number in the <strong>165.155.xxx<\/strong> series. That number on the unit label is what a Coast Guard inspector checks, not the brand name or the display.<\/p>\n<hr>\n<h2 id=\"what-does-class-b-do-and-which-subtype-should-you-choose\">What does Class B do, and which subtype should you choose?<\/h2>\n<p>Class B is defined under IEC 62287-1 and IEC 62287-2 and is explicitly described by NAVCEN as interoperable equipment that does not meet all IMO performance standards. That distinction matters for both safety and regulatory eligibility.<\/p>\n<p>Class B uses Message 18 for dynamic position reports and Messages 19\/24 for static data. Critically, it does not transmit voyage-related information (no destination, no ETA, no draft), and it cannot transmit safety or application-specific messages. It can receive them, but other vessels relying on your AIS data get a thinner picture.<\/p>\n<p><strong>The two subtypes behave very differently:<\/strong><\/p>\n<ul>\n<li><strong>Class B\/SO (SOTDMA):<\/strong> Uses the same slot-reservation scheme as Class A. Transmits at roughly 5 W. Better track continuity in busy channels. Recommended for recreational vessels operating near commercial traffic, busy anchorages, or offshore shipping lanes.<\/li>\n<li><strong>Class B\/CS (CS-TDMA):<\/strong> Transmits at roughly 2 W using opportunistic channel access. Lower cost. Adequate for low-density, nearshore use where traffic is light and the VHF AIS channel is not congested.<\/li>\n<\/ul>\n<p>Class B units carry USCG approval numbers in the <strong>165.156.xxx<\/strong> series.<\/p>\n<p><strong>Pro Tip:<\/strong> <em>In areas with heavy commercial traffic, like the approaches to major U.S. ports or the ICW near Miami or Houston, a Class B\/SO is worth the price premium over a Class B\/CS. The slot-reservation behavior alone reduces the chance of your position report being lost in traffic.<\/em><\/p>\n<p><img decoding=\"async\" src=\"https:\/\/vesselflag.com\/wp-content\/uploads\/2026\/08\/1786260247808_Technician-wiring-AIS-antenna-cable-on-boat-deck.jpeg\" alt=\"Technician wiring AIS antenna cable on boat deck\"><\/p>\n<hr>\n<h2 id=\"who-must-carry-class-a-under-us-rules-and-when-can-class-b-substitute\">Who must carry Class A under U.S. rules, and when can Class B substitute?<\/h2>\n<p>Under USCG and 33 CFR guidance, the following vessel categories are generally required to carry Class A AIS:<\/p>\n<ul>\n<li>Self-propelled commercial vessels 65 feet or more in length<\/li>\n<li>Towing vessels 26 feet or more in length with more than 600 horsepower<\/li>\n<li>Vessels certificated to carry more than 150 passengers<\/li>\n<li>Dredging or other vessels engaged in operations that affect navigation<\/li>\n<li>Vessels operating on the Western Rivers (as defined in 33 CFR) above the Huey P. Long Bridge<\/li>\n<\/ul>\n<p>Class B substitution is allowed for a select segment of mandatory users, but only when specific CFR conditions are all met. Those conditions typically include:<\/p>\n<ul>\n<li>Not operating in a VTS or VMRS zone<\/li>\n<li>Not exceeding speed thresholds specified in the applicable CFR section<\/li>\n<li>Not exceeding applicable passenger count limits<\/li>\n<li>Using a USCG type-approved Class B device (165.156.xxx)<\/li>\n<\/ul>\n<blockquote>\n<p><strong>Regulatory reminder from NAVCEN:<\/strong> A select segment of mandatory AIS users may meet carriage requirements by using a Coast Guard type-approved Class B device in lieu of Class A, but only subject to specific conditions in the Code of Federal Regulations. Operating in a VTS or VMRS zone, exceeding speed limits, or carrying more passengers than the CFR threshold allows will void the Class B substitution. Always confirm your vessel\u2019s operating profile against the current CFR text before relying on a Class B unit for mandatory carriage compliance.<\/p>\n<\/blockquote>\n<p>Voluntary users (recreational boaters not subject to mandatory carriage) can use either class, but any device used in U.S. waters must be FCC certified. For <a href=\"https:\/\/vesselflag.com\/es\/what-is-commercial-vessel-certification\/\" target=\"_blank\" rel=\"noopener\">commercial vessel certification<\/a> requirements that intersect with AIS carriage, the vessel category and operating area are the two variables that determine everything.<\/p>\n<hr>\n<h2 id=\"how-do-range-traffic-priority-and-satellite-detection-differ-in-practice\">How do range, traffic priority, and satellite detection differ in practice?<\/h2>\n<p>The technical specs translate into real safety consequences on the water.<\/p>\n<p><strong>Class A advantages:<\/strong><\/p>\n<ul>\n<li>Higher transmit power (~12.5 W) means other vessels detect you at greater range, giving them more time to plot your course and take avoiding action.<\/li>\n<li>Faster reporting (every 2\u201310 seconds underway) produces a smooth, continuous track on other vessels\u2019 displays. A vessel doing 20 knots updates its position every few seconds, which is the difference between a clean track and a series of disconnected dots.<\/li>\n<li>SOTDMA slot reservation means your position reports get through even when the VHF AIS channel is heavily loaded with traffic.<\/li>\n<li>Messages 1\/2\/3 are the message types most reliably captured by satellite AIS receivers, giving you better coverage in offshore areas where terrestrial receivers are absent.<\/li>\n<\/ul>\n<p><strong>Class B limitations that matter:<\/strong><\/p>\n<ul>\n<li>Lower transmit power reduces detection range, particularly in conditions where VHF propagation is already marginal (rain, terrain, antenna height).<\/li>\n<li>Message 18 is less frequently transmitted and carries less data. Vessels relying on AIS for collision avoidance get a less complete picture of your movements.<\/li>\n<li>CS-TDMA access means a Class B\/CS unit may fail to transmit at all during peak channel loading, creating gaps in your track precisely when traffic is heaviest.<\/li>\n<li>Satellite AIS aggregators capture Message 18, but with less frequency and reliability than Messages 1\/2\/3, which affects your visibility in long-range tracking systems used by fleet managers and maritime authorities.<\/li>\n<\/ul>\n<p>Consider a night approach to a busy anchorage. A Class A vessel approaching at 12 knots updates its position every few seconds. A Class B\/CS vessel at the same speed might update every 30 seconds or more, and in a congested channel, some of those updates may not transmit at all. The watch officer on an anchored ship sees a vessel that appears to jump position rather than track smoothly. That is not a theoretical concern.<\/p>\n<hr>\n<h2 id=\"what-does-installation-actually-involve-and-what-does-it-cost\">What does installation actually involve, and what does it cost?<\/h2>\n<p>The most important installation decisions come before you buy the unit: antenna placement, GNSS source, power and grounding, and feedline quality determine whether your AIS performs to spec or underperforms regardless of which class you choose.<\/p>\n<p><strong>Installation checklist:<\/strong><\/p>\n<ol>\n<li><strong>VHF antenna:<\/strong> Mount as high as practical with a clear 360-degree view. AIS shares the VHF marine band (161.975 MHz and 162.025 MHz). A dedicated AIS antenna is preferable; a splitter is acceptable for Class B but adds insertion loss.<\/li>\n<li><strong>Coax and feedline:<\/strong> Use low-loss coax (RG-8X minimum; LMR-400 for longer runs). Every 3 dB of feedline loss halves your effective transmit power.<\/li>\n<li><strong>GNSS\/EPFS source:<\/strong> Class A requires an external GNSS input per IEC 61993-2. Many Class B units have an internal GPS, but an external source improves accuracy and redundancy.<\/li>\n<li><strong>Power and grounding:<\/strong> Connect to a dedicated, fused DC circuit. Poor grounding causes noise that degrades both transmit and receive performance.<\/li>\n<li><strong>NMEA\/IEC 61162 integration:<\/strong> Connect to your chartplotter via NMEA 0183 or NMEA 2000 so AIS targets appear on your navigation display. Confirm the chartplotter supports AIS overlay before purchasing.<\/li>\n<li><strong>Separation from other transmitters:<\/strong> Keep the AIS antenna at least 3 feet from your primary VHF antenna and further from radar to avoid desensitization.<\/li>\n<\/ol>\n<p><strong>Approximate cost ranges (hardware only):<\/strong><\/p>\n<ul>\n<li>Class A hardware: roughly $1,500\u2013$3,500 or more, depending on display and integration features.<\/li>\n<li>Class B\/SO hardware: roughly $400\u2013$900.<\/li>\n<li>Class B\/CS hardware: roughly $200\u2013$600.<\/li>\n<li>Professional installation labor: typically $300\u2013$800 for a straightforward installation, more for complex wiring or antenna work on larger vessels. These are approximate figures; get quotes from a certified marine electronics installer.<\/li>\n<\/ul>\n<p>Class A installations often require a dedicated display or MFD integration. Class B units typically connect to an existing chartplotter, which keeps total system cost lower.<\/p>\n<hr>\n<h2 id=\"how-do-you-decide-which-class-is-right-for-your-vessel\">How do you decide which class is right for your vessel?<\/h2>\n<p>Start with the regulation, not the budget.<\/p>\n<ol>\n<li><strong>Is your vessel subject to mandatory AIS carriage under 33 CFR?<\/strong> If yes, identify your vessel category (self-propelled \u226565 ft commercial, towing \u226526 ft\/600+ hp, passenger &gt;150, dredging, Western Rivers). If any category applies, Class A is your baseline requirement.<\/li>\n<li><strong>Does your vessel qualify for the Class B substitution?<\/strong> Check all three conditions: operating area (no VTS\/VMRS), speed profile, and passenger count. All must be met simultaneously. If any condition fails, Class A is required.<\/li>\n<li><strong>Are you a voluntary user (recreational or not subject to mandatory carriage)?<\/strong> You can choose either class. Move to the operational questions below.<\/li>\n<li><strong>What traffic density do you operate in?<\/strong> Busy commercial ports, VTS zones, offshore shipping lanes: choose Class A or Class B\/SO. Light nearshore recreational use: Class B\/CS is adequate.<\/li>\n<li><strong>Do you need to transmit safety or application-specific messages?<\/strong> If yes, only Class A can do that.<\/li>\n<li><strong>What is your integration setup?<\/strong> Confirm your chartplotter supports AIS overlay. Check whether you need a dedicated display (more common with Class A).<\/li>\n<\/ol>\n<p><strong>Questions to ask any vendor before purchasing:<\/strong><\/p>\n<ul>\n<li>What is the USCG type-approval number (165.155.xxx or 165.156.xxx)?<\/li>\n<li>Is the unit IEC 61993-2 (Class A) or IEC 62287-1\/2 (Class B) certified?<\/li>\n<li>Is it SOTDMA or CS-TDMA? (For Class B, this is the most important subtype question.)<\/li>\n<li>Is a display included, or does it require an external chartplotter?<\/li>\n<li>What is the firmware update policy?<\/li>\n<\/ul>\n<p><strong>Decision output:<\/strong><\/p>\n<ul>\n<li><strong>Choose Class A<\/strong> if mandatory carriage applies, if you operate in VTS\/VMRS zones, or if you need safety message transmission.<\/li>\n<li><strong>Choose Class B\/SO<\/strong> if you are a voluntary user in moderate-to-heavy traffic and want better slot-reservation behavior.<\/li>\n<li><strong>Choose Class B\/CS<\/strong> if you are a recreational boater in low-density, nearshore waters and budget is a primary constraint.<\/li>\n<\/ul>\n<hr>\n<h2 id=\"how-do-you-verify-uscg-type-approval-and-register-your-mmsi\">How do you verify USCG type-approval and register your MMSI?<\/h2>\n<p>Verification is a two-step check: confirm the USCG approval number on the physical unit, then confirm MMSI licensing and encoding.<\/p>\n<ol>\n<li><strong>Check the unit label physically.<\/strong> The USCG type-approval number must appear on the unit itself, not just in the manual. Class A units show 165.155.xxx; Class B units show 165.156.xxx. Photograph the label and keep it with your vessel\u2019s documentation.<\/li>\n<li><strong>Verify on CGMIX\/CG EQList.<\/strong> The Coast Guard Maritime Information Exchange maintains a list of type-approved equipment. Cross-reference your unit\u2019s approval number against the current list to confirm it is still valid.<\/li>\n<li><strong>Use NAVCEN\u2019s VIVS service.<\/strong> The NAVCEN FAQ documents the Vessel Information Verification Service (VIVS), which lets you confirm that your vessel\u2019s MMSI is broadcasting correctly and that the data matches your registration records.<\/li>\n<li><strong>Obtain or confirm your MMSI.<\/strong> U.S.-flagged vessels requiring mandatory AIS carriage must obtain an MMSI through the FCC (via a ship station license). Recreational boaters can obtain an MMSI through authorized agents. The MMSI must be programmed into the AIS unit before operation. Full guidance on MMSI registration requirements covers the FCC process and what documentation you need.<\/li>\n<li><strong>FCC certification for voluntary users.<\/strong> Any AIS device used in U.S. waters must be FCC certified, regardless of whether carriage is mandatory. Confirm the FCC ID on the unit or the FCC database before purchase.<\/li>\n<\/ol>\n<p><strong>Documentation to keep aboard:<\/strong><\/p>\n<ul>\n<li>Copy of USCG type-approval certificate or label photo<\/li>\n<li>FCC ship station license (mandatory users) or MMSI assignment letter<\/li>\n<li>Vessel registration or documentation papers<\/li>\n<li>AIS installation record (installer name, date, antenna configuration)<\/li>\n<\/ul>\n<p>Vesselflag\u2019s MMSI and AIS compliance guidance covers the specific steps for yacht owners navigating both FCC and flag-state requirements simultaneously.<\/p>\n<hr>\n<h2 id=\"vesselflags-take-when-class-a-is-the-right-call-even-when-class-b-is-legal\">Vesselflag\u2019s take: when Class A is the right call even when Class B is legal<\/h2>\n<p>The regulatory question and the safety question are not always the same question. A vessel that legally qualifies for Class B substitution is not necessarily well-served by it.<\/p>\n<p>Commercially operated workboats in mixed traffic near major U.S. ports are the clearest edge case. The CFR conditions for Class B substitution may technically be met, but operating at lower transmit power with opportunistic channel access in a channel shared with container ships, tankers, and ferries is a risk that the regulation does not fully capture. Class A\u2019s SOTDMA slot reservation and higher power are not bureaucratic requirements in that environment. They are the reason other vessels see you.<\/p>\n<p>Large pleasure yachts that cruise internationally face a different version of the same issue. Many flag states and port authorities outside the U.S. expect Class A on vessels above a certain length, and a Class B unit that meets U.S. CFR conditions may not satisfy the requirements of a foreign port authority or a charter inspection. Fitting Class A from the start avoids that problem entirely.<\/p>\n<p>The practical caveat before any inspection: verify the type-approval label on the unit, not just the box or the manual. USCG inspectors check the label. Keep a photograph of it with your vessel\u2019s papers.<\/p>\n<hr>\n<h2 id=\"vesselflag-handles-mmsi-setup-registration-and-ais-compliance-paperwork\">Vesselflag handles MMSI setup, registration, and AIS compliance paperwork<\/h2>\n<p>Choosing the right AIS class is step one. Getting the documentation right for a USCG inspection or a flag-state registration is where most owners run into delays.<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/vesselflag.com\/wp-content\/uploads\/2026\/07\/1771260086041_vesselflag.jpg\" alt=\"Pabell\u00f3n del buque\"><\/p>\n<p>Vesselflag offers MMSI licensing support, USCG type-approval verification guidance, and <a href=\"https:\/\/vesselflag.com\/es\/registro-de-banderas\/\" target=\"_blank\" rel=\"noopener\">flag registration packages<\/a> that include documentation checks for AIS carriage compliance. Whether you need a straightforward MMSI assignment, help confirming your vessel\u2019s carriage category under 33 CFR, or a full <a href=\"https:\/\/vesselflag.com\/es\/register-commercial-vessel-step-by-step-guide-2026\/\" target=\"_blank\" rel=\"noopener\">commercial vessel registration<\/a> under an international flag that satisfies both U.S. and foreign port requirements, Vesselflag manages the paperwork from start to finish. The process is fixed-fee, transparent, and handled by specialists who work with maritime regulations daily. Start with a document review to confirm what your vessel needs before your next inspection.<\/p>\n<hr>\n<h2 id=\"sources\">Sources<\/h2>\n<p>These are the authoritative technical and regulatory references used throughout this guide.<\/p>\n<ul>\n<li>AIS Requirements | Navigation Center<\/li>\n<\/ul>\n<hr>\n<h2 id=\"faq\">PREGUNTAS FRECUENTES<\/h2>\n<h3 id=\"what-is-the-main-difference-between-ais-class-a-and-class-b\">What is the main difference between AIS Class A and Class B?<\/h3>\n<p>Class A transmits at higher power (~12.5 W) with position updates every 2\u201310 seconds using SOTDMA channel access and can send safety messages. Class B transmits at lower power (2\u20135 W depending on subtype), reports less frequently using Message 18, and can only receive, not transmit, safety and application-specific messages.<\/p>\n<h3 id=\"which-vessels-are-required-to-carry-class-a-ais-in-the-us\">Which vessels are required to carry Class A AIS in the U.S.?<\/h3>\n<p>Under 33 CFR and USCG guidance, self-propelled commercial vessels 65 feet or more, towing vessels 26 feet or more with over 600 horsepower, and vessels certificated for more than 150 passengers are among those required to carry Class A. A select group may substitute a USCG type-approved Class B device if all specific CFR conditions are met.<\/p>\n<h3 id=\"what-channels-does-ais-use-and-does-the-class-affect-that\">What channels does AIS use, and does the class affect that?<\/h3>\n<p>AIS operates on allocated VHF marine band frequencies. The class affects how a unit accesses those channels: Class A and Class B\/SO use SOTDMA (reserved slots), while Class B\/CS uses CS-TDMA (opportunistic access), which is less reliable in congested traffic.<\/p>\n<h3 id=\"what-is-class-b-ais-and-when-is-it-enough\">What is Class B AIS, and when is it enough?<\/h3>\n<p>Class B AIS is defined under IEC 62287-1\/2 as interoperable equipment that does not meet all IMO performance standards. It is adequate for recreational vessels and smaller commercial craft operating outside VTS\/VMRS zones, at permitted speeds, and within the CFR substitution conditions. For busy commercial waterways or mandatory carriage without a qualifying exemption, Class A is required.<\/p>\n<h3 id=\"how-do-you-verify-that-an-ais-unit-is-uscg-type-approved\">How do you verify that an AIS unit is USCG type-approved?<\/h3>\n<p>Check the physical label on the unit for a USCG approval number in the 165.155.xxx (Class A) or 165.156.xxx (Class B) series, then cross-reference it against the Coast Guard Maritime Information Exchange (CGMIX) equipment list. The NAVCEN FAQ also documents the VIVS service for confirming that your MMSI is broadcasting correctly.<\/p>\n<h2 id=\"recommended\">Recomendado<\/h2>\n<ul>\n<li><a href=\"https:\/\/vesselflag.com\/es\/ais-for-vessels-explained-what-every-mariner-must-know\/\" target=\"_blank\" rel=\"noopener\">AIS for Vessels Explained: What Every Mariner Must Know<\/a><\/li>\n<li><a href=\"https:\/\/vesselflag.com\/es\/ais-for-boats-what-every-owner-must-know-in-2026\/\" target=\"_blank\" rel=\"noopener\">AIS for Boats: What Every Owner Must Know in 2026<\/a><\/li>\n<li><a href=\"https:\/\/vesselflag.com\/es\/what-is-ais-licensing\/\" target=\"_blank\" rel=\"noopener\">AIS Licensing for Vessel Owners: MMSI and FCC Rules<\/a><\/li>\n<li><a href=\"https:\/\/vesselflag.com\/es\/mmsi-ais-compliance-essentials-yacht-owners\/\" target=\"_blank\" rel=\"noopener\">MMSI and AIS compliance essentials for yacht owners<\/a><\/li>\n<\/ul>\n<\/div>\n<p><!-- .vgblk-rw-wrapper --><\/p>","protected":false},"excerpt":{"rendered":"<p>Discover whether your vessel needs AIS Class A or Class B for compliance. Learn key differences and make the right choice today!<\/p>","protected":false},"author":3,"featured_media":990247,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[174],"tags":[],"class_list":["post-990243","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog"],"_links":{"self":[{"href":"https:\/\/vesselflag.com\/es\/wp-json\/wp\/v2\/posts\/990243","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/vesselflag.com\/es\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/vesselflag.com\/es\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/vesselflag.com\/es\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/vesselflag.com\/es\/wp-json\/wp\/v2\/comments?post=990243"}],"version-history":[{"count":1,"href":"https:\/\/vesselflag.com\/es\/wp-json\/wp\/v2\/posts\/990243\/revisions"}],"predecessor-version":[{"id":990246,"href":"https:\/\/vesselflag.com\/es\/wp-json\/wp\/v2\/posts\/990243\/revisions\/990246"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/vesselflag.com\/es\/wp-json\/wp\/v2\/media\/990247"}],"wp:attachment":[{"href":"https:\/\/vesselflag.com\/es\/wp-json\/wp\/v2\/media?parent=990243"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/vesselflag.com\/es\/wp-json\/wp\/v2\/categories?post=990243"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/vesselflag.com\/es\/wp-json\/wp\/v2\/tags?post=990243"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}