diff --git a/src/lib/services/yachts.service.ts b/src/lib/services/yachts.service.ts
index af2c603..864083e 100644
--- a/src/lib/services/yachts.service.ts
+++ b/src/lib/services/yachts.service.ts
@@ -5,9 +5,10 @@ import { companies } from '@/lib/db/schema/companies';
 import { createAuditLog } from '@/lib/audit';
 import { NotFoundError, ValidationError } from '@/lib/errors';
 import { emitToRoom } from '@/lib/socket/server';
+import { diffEntity } from '@/lib/entity-diff';
 import { withTransaction } from '@/lib/db/utils';
 import type { z } from 'zod';
-import type { createYachtSchema } from '@/lib/validators/yachts';
+import type { createYachtSchema, UpdateYachtInput } from '@/lib/validators/yachts';
 
 type CreateYachtInput = z.input<typeof createYachtSchema>;
 
@@ -98,3 +99,88 @@ export async function getYachtById(id: string, portId: string) {
   if (!yacht) throw new NotFoundError('Yacht');
   return yacht;
 }
+
+export async function updateYacht(
+  id: string,
+  portId: string,
+  data: UpdateYachtInput,
+  meta: AuditMeta,
+) {
+  // Defense-in-depth: owner changes must go through /transfer, not PATCH.
+  const dataRecord = data as Record<string, unknown>;
+  if (
+    Object.prototype.hasOwnProperty.call(dataRecord, 'currentOwnerType') ||
+    Object.prototype.hasOwnProperty.call(dataRecord, 'currentOwnerId')
+  ) {
+    throw new ValidationError('use /transfer to change ownership');
+  }
+
+  const existing = await db.query.yachts.findFirst({
+    where: eq(yachts.id, id),
+  });
+
+  if (!existing || existing.portId !== portId) {
+    throw new NotFoundError('Yacht');
+  }
+
+  const { diff } = diffEntity(
+    existing as unknown as Record<string, unknown>,
+    data as Record<string, unknown>,
+  );
+
+  const [updated] = await db
+    .update(yachts)
+    .set({ ...data, updatedAt: new Date() })
+    .where(and(eq(yachts.id, id), eq(yachts.portId, portId)))
+    .returning();
+
+  void createAuditLog({
+    userId: meta.userId,
+    portId,
+    action: 'update',
+    entityType: 'yacht',
+    entityId: id,
+    oldValue: diff as Record<string, unknown>,
+    newValue: data as Record<string, unknown>,
+    ipAddress: meta.ipAddress,
+    userAgent: meta.userAgent,
+  });
+
+  emitToRoom(`port:${portId}`, 'yacht:updated', {
+    yachtId: id,
+    changedFields: Object.keys(diff),
+  });
+
+  return updated!;
+}
+
+export async function archiveYacht(id: string, portId: string, meta: AuditMeta) {
+  const existing = await db.query.yachts.findFirst({
+    where: eq(yachts.id, id),
+  });
+
+  if (!existing || existing.portId !== portId) {
+    throw new NotFoundError('Yacht');
+  }
+
+  // NOTE: bypassing the shared `softDelete(...)` util: it sets the raw
+  // column key `archived_at`, which Drizzle does not recognise (the JS
+  // key is `archivedAt`) and therefore emits an empty SET clause. Until
+  // the utility is fixed, do the update inline.
+  await db
+    .update(yachts)
+    .set({ archivedAt: new Date() })
+    .where(and(eq(yachts.id, id), eq(yachts.portId, portId)));
+
+  void createAuditLog({
+    userId: meta.userId,
+    portId,
+    action: 'archive',
+    entityType: 'yacht',
+    entityId: id,
+    ipAddress: meta.ipAddress,
+    userAgent: meta.userAgent,
+  });
+
+  emitToRoom(`port:${portId}`, 'yacht:archived', { yachtId: id });
+}
diff --git a/src/lib/socket/events.ts b/src/lib/socket/events.ts
index f6f8968..d43e748 100644
--- a/src/lib/socket/events.ts
+++ b/src/lib/socket/events.ts
@@ -79,6 +79,8 @@ export interface ServerToClientEvents {
 
   // Yacht events
   'yacht:created': (payload: { yachtId: string }) => void;
+  'yacht:updated': (payload: { yachtId: string; changedFields: string[] }) => void;
+  'yacht:archived': (payload: { yachtId: string }) => void;
 
   // Document events
   'document:created': (payload: { documentId: string; type?: string; interestId?: string }) => void;
diff --git a/tests/unit/services/yachts.test.ts b/tests/unit/services/yachts.test.ts
index a53098b..3e8ba4f 100644
--- a/tests/unit/services/yachts.test.ts
+++ b/tests/unit/services/yachts.test.ts
@@ -1,8 +1,8 @@
 import { describe, it, expect } from 'vitest';
-import { createYacht } from '@/lib/services/yachts.service';
-import { makeClient, makePort, makeAuditMeta } from '../../helpers/factories';
+import { createYacht, updateYacht, archiveYacht } from '@/lib/services/yachts.service';
+import { makeClient, makePort, makeYacht, makeAuditMeta } from '../../helpers/factories';
 import { db } from '@/lib/db';
-import { yachtOwnershipHistory } from '@/lib/db/schema';
+import { yachts, yachtOwnershipHistory } from '@/lib/db/schema';
 import { eq } from 'drizzle-orm';
 
 describe('yachts.service — createYacht', () => {
@@ -65,3 +65,98 @@ describe('yachts.service — createYacht', () => {
     ).rejects.toThrow(/owner not found/i);
   });
 });
+
+describe('yachts.service — updateYacht', () => {
+  it('updates name and notes', async () => {
+    const port = await makePort();
+    const client = await makeClient({ portId: port.id });
+    const yacht = await makeYacht({
+      portId: port.id,
+      ownerType: 'client',
+      ownerId: client.id,
+      overrides: { name: 'Original Name' },
+    });
+
+    const updated = await updateYacht(
+      yacht.id,
+      port.id,
+      { name: 'New Name', notes: 'Updated notes' },
+      makeAuditMeta(),
+    );
+
+    expect(updated.name).toBe('New Name');
+    expect(updated.notes).toBe('Updated notes');
+
+    const [row] = await db.select().from(yachts).where(eq(yachts.id, yacht.id));
+    expect(row!.name).toBe('New Name');
+    expect(row!.notes).toBe('Updated notes');
+  });
+
+  it('rejects when id does not exist or is cross-tenant', async () => {
+    const portA = await makePort();
+    const portB = await makePort();
+    const clientInB = await makeClient({ portId: portB.id });
+    const yachtInB = await makeYacht({
+      portId: portB.id,
+      ownerType: 'client',
+      ownerId: clientInB.id,
+    });
+
+    await expect(
+      updateYacht(yachtInB.id, portA.id, { name: 'Hijack' }, makeAuditMeta()),
+    ).rejects.toThrow(/yacht/i);
+
+    await expect(
+      updateYacht('nonexistent-id', portA.id, { name: 'Phantom' }, makeAuditMeta()),
+    ).rejects.toThrow(/yacht/i);
+  });
+
+  it('rejects attempt to change currentOwnerId via update', async () => {
+    const port = await makePort();
+    const client = await makeClient({ portId: port.id });
+    const yacht = await makeYacht({
+      portId: port.id,
+      ownerType: 'client',
+      ownerId: client.id,
+    });
+
+    await expect(
+      updateYacht(
+        yacht.id,
+        port.id,
+        { currentOwnerId: 'some-other-id' } as unknown as { name: string },
+        makeAuditMeta(),
+      ),
+    ).rejects.toThrow(/transfer to change ownership/i);
+  });
+});
+
+describe('yachts.service — archiveYacht', () => {
+  it('sets archivedAt to a non-null timestamp', async () => {
+    const port = await makePort();
+    const client = await makeClient({ portId: port.id });
+    const yacht = await makeYacht({
+      portId: port.id,
+      ownerType: 'client',
+      ownerId: client.id,
+    });
+
+    await archiveYacht(yacht.id, port.id, makeAuditMeta());
+
+    const [row] = await db.select().from(yachts).where(eq(yachts.id, yacht.id));
+    expect(row!.archivedAt).not.toBeNull();
+  });
+
+  it('throws NotFound for cross-tenant or missing yacht', async () => {
+    const portA = await makePort();
+    const portB = await makePort();
+    const clientInB = await makeClient({ portId: portB.id });
+    const yachtInB = await makeYacht({
+      portId: portB.id,
+      ownerType: 'client',
+      ownerId: clientInB.id,
+    });
+
+    await expect(archiveYacht(yachtInB.id, portA.id, makeAuditMeta())).rejects.toThrow(/yacht/i);
+  });
+});