diff --git a/client/src/App.tsx b/client/src/App.tsx
index a984777..098c544 100644
--- a/client/src/App.tsx
+++ b/client/src/App.tsx
@@ -13,6 +13,7 @@ import SettingsForm from './components/SettingsForm.tsx'
 import InvitationAcceptance from './components/InvitationAcceptance.tsx'
 import AppTourOverlay from './components/AppTourOverlay.tsx'
 import { AppTourProvider, useAppTour, type AppTab } from './context/AppTourContext.tsx'
+import { UnsavedChangesProvider, useUnsavedChangesContext } from './context/UnsavedChangesContext.tsx'
 import { getActiveMasterKey, logoutUser, checkServerSession } from './services/auth.js'
 import { PlausibleEvents, trackPlausibleEvent } from './services/analytics.js'
 import {
@@ -48,6 +49,7 @@ const PENDING_PUSH_LOGBOOK_KEY = 'pending_push_logbook_id'
 
 function App() {
   const { t, i18n } = useTranslation()
+  const { confirmLeave } = useUnsavedChangesContext()
   const { registerNavigation, requestStartAfterLogin, isActive, currentStepId } = useAppTour()
   const [isAuthenticated, setIsAuthenticated] = useState(false)
   const [activeLogbookId, setActiveLogbookId] = useState<string | null>(null)
@@ -347,7 +349,14 @@ function App() {
     consumePendingPushLogbook()
   }
 
-  const handleLogout = () => {
+  const handleTabChange = async (tab: AppTab) => {
+    if (tab === activeTab) return
+    if (!(await confirmLeave())) return
+    setActiveTab(tab)
+  }
+
+  const handleLogout = async () => {
+    if (!(await confirmLeave())) return
     void logoutUser()
     setIsAuthenticated(false)
     setActiveLogbookId(null)
@@ -358,7 +367,8 @@ function App() {
     localStorage.removeItem('active_logbook_title')
   }
 
-  const handleBackToDashboard = () => {
+  const handleBackToDashboard = async () => {
+    if (!(await confirmLeave())) return
     setActiveLogbookId(null)
     setActiveLogbookTitle(null)
     setTourSelectedEntryId(null)
@@ -505,7 +515,7 @@ function App() {
         <aside className="app-sidebar">
           <button
             className={`sidebar-btn ${activeTab === 'logs' ? 'active' : ''}`}
-            onClick={() => setActiveTab('logs')}
+            onClick={() => void handleTabChange('logs')}
             data-tour="nav-logs"
           >
             <FileText size={18} />
@@ -514,7 +524,7 @@ function App() {
           
           <button
             className={`sidebar-btn ${activeTab === 'vessel' ? 'active' : ''}`}
-            onClick={() => setActiveTab('vessel')}
+            onClick={() => void handleTabChange('vessel')}
             data-tour="nav-vessel"
           >
             <Ship size={18} />
@@ -523,7 +533,7 @@ function App() {
 
           <button
             className={`sidebar-btn ${activeTab === 'crew' ? 'active' : ''}`}
-            onClick={() => setActiveTab('crew')}
+            onClick={() => void handleTabChange('crew')}
             data-tour="nav-crew"
           >
             <Users size={18} />
@@ -542,7 +552,7 @@ function App() {
 
           <button
             className={`sidebar-btn ${activeTab === 'stats' ? 'active' : ''}`}
-            onClick={() => setActiveTab('stats')}
+            onClick={() => void handleTabChange('stats')}
             data-tour="nav-stats"
           >
             <BarChart2 size={18} />
@@ -551,7 +561,7 @@ function App() {
 
           <button
             className={`sidebar-btn ${activeTab === 'settings' ? 'active' : ''}`}
-            onClick={() => setActiveTab('settings')}
+            onClick={() => void handleTabChange('settings')}
           >
             <Settings size={18} />
             {t('nav.settings')}
@@ -604,12 +614,14 @@ function App() {
 export default function AppWrapper() {
   return (
     <DialogProvider>
-      <AppTourProvider>
-        <PwaUpdatePrompt />
-        <App />
-        <AppTourOverlay />
-      </AppTourProvider>
-      <AppFooter />
+      <UnsavedChangesProvider>
+        <AppTourProvider>
+          <PwaUpdatePrompt />
+          <App />
+          <AppTourOverlay />
+        </AppTourProvider>
+        <AppFooter />
+      </UnsavedChangesProvider>
     </DialogProvider>
   )
 }
diff --git a/client/src/components/LogEntryEditor.tsx b/client/src/components/LogEntryEditor.tsx
index 32b7444..b5b0dd3 100644
--- a/client/src/components/LogEntryEditor.tsx
+++ b/client/src/components/LogEntryEditor.tsx
@@ -20,7 +20,7 @@ import {
   hasAnySignature
 } from '../utils/signatures.js'
 import type { SignatureValue } from '../types/signatures.js'
-import { buildLogEntryPayload, sortLogEventsByTime, type LogEventPayload } from '../utils/logEntryPayload.js'
+import { buildLogEntryPayload, sortLogEventsByTime, normalizeLogEvent, logEventsEqual, type LogEventPayload } from '../utils/logEntryPayload.js'
 import { hashEntryForSigning } from '../utils/entryCanonicalHash.js'
 import { signLogEntry } from '../services/entrySigning.js'
 import { getLogbookAccess } from '../services/logbookAccess.js'
@@ -35,6 +35,7 @@ import {
   type SavedTrack
 } from '../services/trackUpload.js'
 import { computeTrackStats, formatTrackStats } from '../utils/trackStats.js'
+import { useRegisterUnsavedChanges } from '../context/UnsavedChangesContext.tsx'
 
 function emptyTankLevels() {
   return { morning: 0, refilled: 0, evening: 0, consumption: 0 }
@@ -248,7 +249,60 @@ export default function LogEntryEditor({
     })
   }, [buildPayloadForSigning, signSkipper, signCrew])
 
-  const isDirty = savedFingerprint !== null && currentFingerprint !== savedFingerprint
+  const buildEventFromForm = (): LogEvent =>
+    normalizeLogEvent({
+      time: evTime,
+      mgk: evMgk,
+      rwk: evRwk,
+      windPressure: evWindPressure,
+      windDirection: evWindDirection,
+      windStrength: evWindStrength,
+      seaState: evSeaState,
+      weatherIcon: evWeatherIcon,
+      current: evCurrent,
+      heel: evHeel,
+      sailsOrMotor: evSailsOrMotor,
+      logReading: evLogReading,
+      distance: evDistance,
+      gpsLat: evGpsLat,
+      gpsLng: evGpsLng,
+      remarks: evRemarks
+    })
+
+  const applyEventFormToEvents = (eventData: LogEvent): LogEvent[] => {
+    if (editingEventIndex !== null) {
+      return sortLogEventsByTime(events.map((ev, idx) => (idx === editingEventIndex ? eventData : ev)))
+    }
+    return sortLogEventsByTime([...events, eventData])
+  }
+
+  const hasPendingEventForm = useMemo(() => {
+    if (!evTime.trim()) return false
+    const draft = buildEventFromForm()
+    if (editingEventIndex !== null) {
+      const original = events[editingEventIndex]
+      return original ? !logEventsEqual(draft, original) : false
+    }
+    return true
+  }, [
+    evTime, evMgk, evRwk, evWindPressure, evWindDirection, evWindStrength, evSeaState,
+    evWeatherIcon, evCurrent, evHeel, evSailsOrMotor, evLogReading, evDistance,
+    evGpsLat, evGpsLng, evRemarks, editingEventIndex, events
+  ])
+
+  const isDirty = savedFingerprint !== null && (
+    currentFingerprint !== savedFingerprint || hasPendingEventForm
+  )
+
+  const { confirmLeave } = useRegisterUnsavedChanges(
+    `log-entry-${entryId}`,
+    !readOnly && !loading && isDirty
+  )
+
+  const handleBack = async () => {
+    if (!(await confirmLeave())) return
+    onBack()
+  }
 
   const persistEntryToDb = useCallback(async (eventsOverride?: LogEvent[]) => {
     if (readOnly) return
@@ -483,7 +537,7 @@ export default function LogEntryEditor({
           setSignSkipper(normalizeSignature(preloadedEntry.signSkipper) || '')
           setSignCrew(normalizeSignature(preloadedEntry.signCrew) || '')
           loadTrackStatsFromEntry(preloadedEntry)
-          setEvents(sortLogEventsByTime(preloadedEntry.events || []))
+          setEvents(sortLogEventsByTime((preloadedEntry.events || []).map(normalizeLogEvent)))
           setSavedFingerprint(fingerprintFromStoredEntry(preloadedEntry))
           return
         }
@@ -516,7 +570,7 @@ export default function LogEntryEditor({
             setSignSkipper(normalizeSignature(decrypted.signSkipper) || '')
             setSignCrew(normalizeSignature(decrypted.signCrew) || '')
             loadTrackStatsFromEntry(decrypted)
-            setEvents(sortLogEventsByTime(decrypted.events || []))
+            setEvents(sortLogEventsByTime((decrypted.events || []).map(normalizeLogEvent)))
             setSavedFingerprint(fingerprintFromStoredEntry(decrypted))
           }
         }
@@ -783,25 +837,6 @@ export default function LogEntryEditor({
     return currentItems.includes(item.toLowerCase())
   }
 
-  const buildEventFromForm = (): LogEvent => ({
-    time: evTime,
-    mgk: evMgk.trim(),
-    rwk: evRwk.trim(),
-    windPressure: evWindPressure.trim(),
-    windDirection: evWindDirection.trim(),
-    windStrength: evWindStrength.trim(),
-    seaState: evSeaState.trim(),
-    weatherIcon: evWeatherIcon.trim(),
-    current: evCurrent.trim(),
-    heel: evHeel.trim(),
-    sailsOrMotor: evSailsOrMotor.trim(),
-    logReading: evLogReading.trim(),
-    distance: evDistance.trim(),
-    gpsLat: evGpsLat.trim(),
-    gpsLng: evGpsLng.trim(),
-    remarks: evRemarks.trim()
-  })
-
   const clearEventForm = () => {
     setEvTime('')
     setEvMgk('')
@@ -824,22 +859,23 @@ export default function LogEntryEditor({
   }
 
   const fillEventForm = (ev: LogEvent) => {
-    setEvTime(ev.time)
-    setEvMgk(ev.mgk)
-    setEvRwk(ev.rwk)
-    setEvWindPressure(ev.windPressure)
-    setEvWindDirection(ev.windDirection)
-    setEvWindStrength(ev.windStrength)
-    setEvSeaState(ev.seaState)
-    setEvWeatherIcon(ev.weatherIcon)
-    setEvCurrent(ev.current)
-    setEvHeel(ev.heel)
-    setEvSailsOrMotor(ev.sailsOrMotor)
-    setEvLogReading(ev.logReading)
-    setEvDistance(ev.distance)
-    setEvGpsLat(ev.gpsLat)
-    setEvGpsLng(ev.gpsLng)
-    setEvRemarks(ev.remarks)
+    const normalized = normalizeLogEvent(ev)
+    setEvTime(normalized.time)
+    setEvMgk(normalized.mgk)
+    setEvRwk(normalized.rwk)
+    setEvWindPressure(normalized.windPressure)
+    setEvWindDirection(normalized.windDirection)
+    setEvWindStrength(normalized.windStrength)
+    setEvSeaState(normalized.seaState)
+    setEvWeatherIcon(normalized.weatherIcon)
+    setEvCurrent(normalized.current)
+    setEvHeel(normalized.heel)
+    setEvSailsOrMotor(normalized.sailsOrMotor)
+    setEvLogReading(normalized.logReading)
+    setEvDistance(normalized.distance)
+    setEvGpsLat(normalized.gpsLat)
+    setEvGpsLng(normalized.gpsLng)
+    setEvRemarks(normalized.remarks)
     setEvLocationName('')
   }
 
@@ -866,27 +902,25 @@ export default function LogEntryEditor({
     if (readOnly || !evTime) return
 
     const eventData = buildEventFromForm()
-    let nextEvents: LogEvent[]
+    const isEdit = editingEventIndex !== null
+    const hadSkipperSignature = isEdit && !!signSkipper
 
-    if (editingEventIndex !== null) {
-      const hadSkipperSignature = !!signSkipper
+    if (hadSkipperSignature) {
       markSkipperSignatureClearedForEventChange()
-      nextEvents = sortLogEventsByTime(events.map((ev, idx) => (idx === editingEventIndex ? eventData : ev)))
+    }
+
+    const nextEvents = applyEventFormToEvents(eventData)
+
+    try {
+      await persistEntryToDb(nextEvents)
+      setEvents(nextEvents)
+      clearEventForm()
       if (hadSkipperSignature) {
         void showAlertRef.current(
           t('logs.sign_cleared_skipper_re_sign'),
           t('logs.sign_cleared_skipper_re_sign_title')
         )
       }
-    } else {
-      nextEvents = sortLogEventsByTime([...events, eventData])
-    }
-
-    setEvents(nextEvents)
-    clearEventForm()
-
-    try {
-      await persistEntryToDb(nextEvents)
     } catch (err: any) {
       console.error('Failed to auto-save event:', err)
       setError(err.message || 'Failed to save event.')
@@ -935,13 +969,28 @@ export default function LogEntryEditor({
 
   const handleSubmit = async (e: React.FormEvent) => {
     e.preventDefault()
-    if (readOnly || !isDirty) return
+    if (readOnly) return
+
+    let eventsToSave = events
+
+    if (hasPendingEventForm) {
+      const isEdit = editingEventIndex !== null
+      if (isEdit && signSkipper) {
+        markSkipperSignatureClearedForEventChange()
+      }
+      eventsToSave = applyEventFormToEvents(buildEventFromForm())
+      setEvents(eventsToSave)
+      clearEventForm()
+    } else if (!isDirty) {
+      return
+    }
+
     setSaving(true)
     setError(null)
     setSuccess(false)
 
     try {
-      await persistEntryToDb()
+      await persistEntryToDb(eventsToSave)
 
       setSuccess(true)
       trackPlausibleEvent(PlausibleEvents.TRAVEL_DAY_SAVED)
@@ -972,7 +1021,7 @@ export default function LogEntryEditor({
       <div className="form-card" style={{ paddingBottom: '20px' }}>
         <div className="section-title-bar">
           <div className="section-title-left">
-            <button className="btn-back" onClick={onBack} style={{ padding: '6px 12px' }}>
+            <button className="btn-back" onClick={() => void handleBack()} style={{ padding: '6px 12px' }}>
               <ChevronLeft size={16} />
               {t('logs.back_to_list')}
             </button>
diff --git a/client/src/context/UnsavedChangesContext.tsx b/client/src/context/UnsavedChangesContext.tsx
new file mode 100644
index 0000000..4ef3a26
--- /dev/null
+++ b/client/src/context/UnsavedChangesContext.tsx
@@ -0,0 +1,77 @@
+import {
+  createContext,
+  useContext,
+  useCallback,
+  useEffect,
+  useRef,
+  useMemo,
+  type ReactNode
+} from 'react'
+import { useTranslation } from 'react-i18next'
+import { useDialog } from '../components/ModalDialog.tsx'
+
+interface UnsavedChangesContextValue {
+  setDirty: (source: string, dirty: boolean) => void
+  confirmLeave: () => Promise<boolean>
+}
+
+const UnsavedChangesContext = createContext<UnsavedChangesContextValue | null>(null)
+
+export function UnsavedChangesProvider({ children }: { children: ReactNode }) {
+  const { t } = useTranslation()
+  const { showConfirm } = useDialog()
+  const dirtySources = useRef(new Set<string>())
+
+  const setDirty = useCallback((source: string, dirty: boolean) => {
+    if (dirty) dirtySources.current.add(source)
+    else dirtySources.current.delete(source)
+  }, [])
+
+  const confirmLeave = useCallback(async (): Promise<boolean> => {
+    if (dirtySources.current.size === 0) return true
+    return showConfirm(
+      t('common.unsaved_changes_message'),
+      t('common.unsaved_changes_title'),
+      t('common.unsaved_changes_leave'),
+      t('common.unsaved_changes_stay')
+    )
+  }, [showConfirm, t])
+
+  useEffect(() => {
+    const handler = (e: BeforeUnloadEvent) => {
+      if (dirtySources.current.size === 0) return
+      e.preventDefault()
+      e.returnValue = ''
+    }
+    window.addEventListener('beforeunload', handler)
+    return () => window.removeEventListener('beforeunload', handler)
+  }, [])
+
+  const value = useMemo(() => ({ setDirty, confirmLeave }), [setDirty, confirmLeave])
+
+  return (
+    <UnsavedChangesContext.Provider value={value}>
+      {children}
+    </UnsavedChangesContext.Provider>
+  )
+}
+
+export function useUnsavedChangesContext(): UnsavedChangesContextValue {
+  const ctx = useContext(UnsavedChangesContext)
+  if (!ctx) {
+    throw new Error('useUnsavedChangesContext must be used within UnsavedChangesProvider')
+  }
+  return ctx
+}
+
+/** Register a form/view as having unsaved changes (cleared automatically on unmount). */
+export function useRegisterUnsavedChanges(source: string, isDirty: boolean) {
+  const { setDirty, confirmLeave } = useUnsavedChangesContext()
+
+  useEffect(() => {
+    setDirty(source, isDirty)
+    return () => setDirty(source, false)
+  }, [source, isDirty, setDirty])
+
+  return { confirmLeave }
+}
diff --git a/client/src/i18n/locales/de.json b/client/src/i18n/locales/de.json
index fc7ffb9..4f2ff26 100644
--- a/client/src/i18n/locales/de.json
+++ b/client/src/i18n/locales/de.json
@@ -6,6 +6,12 @@
       "beta": "Beta",
       "beta_hint": "Beta-Version — Funktionen können sich noch ändern"
     },
+    "common": {
+      "unsaved_changes_title": "Ungespeicherte Änderungen",
+      "unsaved_changes_message": "Du hast ungespeicherte Änderungen. Möchtest du die Seite wirklich verlassen? Deine Änderungen gehen verloren.",
+      "unsaved_changes_leave": "Verlassen",
+      "unsaved_changes_stay": "Bleiben"
+    },
     "nav": {
       "dashboard": "Dashboard",
       "vessel": "Schiffsdaten",
diff --git a/client/src/i18n/locales/en.json b/client/src/i18n/locales/en.json
index 60ea864..4714942 100644
--- a/client/src/i18n/locales/en.json
+++ b/client/src/i18n/locales/en.json
@@ -6,6 +6,12 @@
       "beta": "Beta",
       "beta_hint": "Beta release — features may still change"
     },
+    "common": {
+      "unsaved_changes_title": "Unsaved changes",
+      "unsaved_changes_message": "You have unsaved changes. Leave this page anyway? Your changes will be lost.",
+      "unsaved_changes_leave": "Leave",
+      "unsaved_changes_stay": "Stay"
+    },
     "nav": {
       "dashboard": "Dashboard",
       "vessel": "Vessel Profile",
diff --git a/client/src/utils/logEntryPayload.ts b/client/src/utils/logEntryPayload.ts
index 7731ef5..c8e4498 100644
--- a/client/src/utils/logEntryPayload.ts
+++ b/client/src/utils/logEntryPayload.ts
@@ -17,8 +17,47 @@ export interface LogEventPayload {
   remarks: string
 }
 
+const LOG_EVENT_FIELDS: (keyof LogEventPayload)[] = [
+  'time', 'mgk', 'rwk', 'windPressure', 'windDirection', 'windStrength', 'seaState',
+  'weatherIcon', 'current', 'heel', 'sailsOrMotor', 'logReading', 'distance',
+  'gpsLat', 'gpsLng', 'remarks'
+]
+
+/** Normalize partial/legacy events so all fields are strings (safe for form + save). */
+export function normalizeLogEvent(event: Partial<LogEventPayload> | Record<string, unknown>): LogEventPayload {
+  const e = event as Record<string, unknown>
+  const timeRaw = String(e.time ?? '').trim()
+  const normalized: LogEventPayload = {
+    time: timeRaw.length >= 5 ? timeRaw.slice(0, 5) : timeRaw,
+    mgk: '',
+    rwk: '',
+    windPressure: '',
+    windDirection: '',
+    windStrength: '',
+    seaState: '',
+    weatherIcon: '',
+    current: '',
+    heel: '',
+    sailsOrMotor: '',
+    logReading: '',
+    distance: '',
+    gpsLat: '',
+    gpsLng: '',
+    remarks: ''
+  }
+  for (const key of LOG_EVENT_FIELDS) {
+    if (key === 'time') continue
+    normalized[key] = String(e[key] ?? '').trim()
+  }
+  return normalized
+}
+
+export function logEventsEqual(a: LogEventPayload, b: LogEventPayload): boolean {
+  return LOG_EVENT_FIELDS.every((key) => a[key] === b[key])
+}
+
 /** Chronological order: earliest time first (HH:MM). */
-export function sortLogEventsByTime<T extends Pick<LogEventPayload, 'time'>>(events: T[]): T[] {
+export function sortLogEventsByTime<T extends LogEventPayload>(events: T[]): T[] {
   return [...events].sort((a, b) => (a.time || '').localeCompare(b.time || ''))
 }
 
@@ -43,7 +82,7 @@ export function buildLogEntryPayload(input: LogEntryPayloadInput): Record<string
     destination: input.destination.trim(),
     freshwater: { ...input.freshwater },
     fuel: { ...input.fuel },
-    events: sortLogEventsByTime(input.events.map((e) => ({ ...e })))
+    events: sortLogEventsByTime(input.events.map((e) => normalizeLogEvent(e)))
   }
 
   if (input.trackDistanceNm !== undefined) payload.trackDistanceNm = input.trackDistanceNm