diff --git a/rowers/models.py b/rowers/models.py
index fa0c839d..15046a7a 100644
--- a/rowers/models.py
+++ b/rowers/models.py
@@ -173,13 +173,14 @@ class Rower(models.Model):
 
     # Power Zone Data
     ftp = models.IntegerField(default=226,verbose_name="Functional Threshold Power")
+    otwslack = models.IntegerField(default=15,verbose_name="OTW Power slack")
 
     pw_ut2 = models.IntegerField(default=124,verbose_name="UT2 Power")
     pw_ut1 = models.IntegerField(default=171,verbose_name="UT1 Power")
     pw_at = models.IntegerField(default=203,verbose_name="AT Power")
     pw_tr = models.IntegerField(default=237,verbose_name="TR Power")
     pw_an = models.IntegerField(default=273,verbose_name="AN Power")
-
+    
     powerzones = PowerZonesField(default=['Rest',
                                           'Pwr UT2',
                                           'Pwr UT1',
@@ -576,7 +577,7 @@ class AdvancedWorkoutForm(ModelForm):
 class RowerPowerForm(ModelForm):
     class Meta:
 	model = Rower
-	fields = ['ftp']
+	fields = ['ftp','otwslack']
 
 # Form to set rower's Power zones, including test routines
 # to enable consistency
diff --git a/rowers/templates/rower_form.html b/rowers/templates/rower_form.html
index c495cb23..9fc7b380 100644
--- a/rowers/templates/rower_form.html
+++ b/rowers/templates/rower_form.html
@@ -7,6 +7,7 @@
   <div class="grid_6 alpha">
     <p>
       <h2>Heart Rate Zones</h2>
+      <p>Set your heart rate zones with this form.</p>
       {% if form.errors %}
     <p style="color: red;">
       Please correct the error{{ form.errors|pluralize }} below.
@@ -27,6 +28,8 @@
   <div class="grid_6 omega">
     <p>
       <h2>Power Zones</h2>
+    <p>The power zones are defined relative to power as measured by the
+      indoor rower.</p>
       <form enctype="multipart/form-data" action="" method="post">
         {% if powerzonesform.errors %}
         <p style="color: red;">
@@ -127,10 +130,15 @@
   </div>
   <div class="grid_6 omega">
     <p>
-      <h2>Functional Threshold Power</h2>
+      <h2>Functional Threshold Power and OTW Slack</h2>
     <p>Use this form to quickly change your zones based on the power of a
       recent
-      full out 60 minutes effort. It will update all zones defined above.</p>
+      full out 60 minutes effort on the ergometer.
+      It will update all zones defined above.</p>
+    <p>The OTW Power Slack is the percentage drop of your On-the-water
+      rowing power
+      vs the erg power. Typical values are around 15%. This will lower
+      the power zones for your OTW workouts.</p> 
     <form enctype="multipart/form-data" action="" method="post">
       <table>
 	{{ powerform.as_table }}
diff --git a/rowers/views.py b/rowers/views.py
index 1b421e1f..2bead2fc 100644
--- a/rowers/views.py
+++ b/rowers/views.py
@@ -4394,7 +4394,11 @@ def cumstats(request,theuser=0,
 def workout_stats_view(request,id=0,message="",successmessage=""):
 
     r = Rower.objects.get(user=request.user)
-    
+    try:
+        w = Workout.objects.get(id=id)
+    except Workout.DoesNotExist:
+        raise Http404("Workout doesn't exist")
+
     workstrokesonly = True
     if request.method == 'POST' and 'workstrokesonly' in request.POST:
         workstrokesonly = request.POST['workstrokesonly']
@@ -4462,9 +4466,13 @@ def workout_stats_view(request,id=0,message="",successmessage=""):
     pwr4 = datadf['power']**(4)
     normp = (pwr4.mean())**(0.25)
     if not np.isnan(normp):
-        intensityfactor = datadf['power'].mean()/float(r.ftp)
-        intensityfactor = normp/float(r.ftp)
-        tss = 100.*((duration*normp*intensityfactor)/(3600.*r.ftp))
+        ftp = float(r.ftp)
+        if w.workouttype == 'water':
+            ftp = ftp*(100.-r.otwslack)/100.
+            
+        intensityfactor = datadf['power'].mean()/float(ftp)
+        intensityfactor = normp/float(ftp)
+        tss = 100.*((duration*normp*intensityfactor)/(3600.*ftp))
 
         if not np.isnan(tss):
             otherstats['tss'] = {
@@ -5298,7 +5306,11 @@ def workout_add_otw_powerplot_view(request,id):
                                   r.pw_at,
                                   r.pw_tr,r.pw_an])/r.ftp
 
-        
+
+        ftp = r.ftp
+        if w.workouttype == 'water':
+            ftp = ftp*(100.-r.otwslack)/100.
+
 	hrpwrdata = {
 	    'hrmax':r.max,
 	    'hrut2':r.ut2,
@@ -5306,7 +5318,7 @@ def workout_add_otw_powerplot_view(request,id):
 	    'hrat':r.at,
 	    'hrtr':r.tr,
 	    'hran':r.an,
-	    'ftp':r.ftp,
+	    'ftp':ftp,
             'powerperc':serialize_list(powerperc),
             'powerzones':serialize_list(r.powerzones),
 	    }
@@ -5356,6 +5368,9 @@ def workout_add_piechart_view(request,id):
                                   r.pw_at,
                                   r.pw_tr,r.pw_an])/r.ftp
 
+        ftp = float(r.ftp)
+        if w.workouttype == 'water':
+            ftp = ftp*(100.-r.otwslack)/100.
         
 	hrpwrdata = {
 	    'hrmax':r.max,
@@ -5364,7 +5379,7 @@ def workout_add_piechart_view(request,id):
 	    'hrat':r.at,
 	    'hrtr':r.tr,
 	    'hran':r.an,
-	    'ftp':r.ftp,
+	    'ftp':ftp,
             'powerperc':serialize_list(powerperc),
             'powerzones':serialize_list(r.powerzones),
 	    }
@@ -5414,6 +5429,9 @@ def workout_add_power_piechart_view(request,id):
                                   r.pw_at,
                                   r.pw_tr,r.pw_an])/r.ftp
 
+        ftp = float(r.ftp)
+        if w.workouttype == 'water':
+            ftp = ftp*(100.-r.otwslack)/100.
         
 	hrpwrdata = {
 	    'hrmax':r.max,
@@ -5422,7 +5440,7 @@ def workout_add_power_piechart_view(request,id):
 	    'hrat':r.at,
 	    'hrtr':r.tr,
 	    'hran':r.an,
-	    'ftp':r.ftp,
+	    'ftp':ftp,
             'powerperc':serialize_list(powerperc),
             'powerzones':serialize_list(r.powerzones),
 	    }
@@ -5469,6 +5487,9 @@ def workout_add_timeplot_view(request,id):
                                   r.pw_at,
                                   r.pw_tr,r.pw_an])/r.ftp
 
+        ftp = float(r.ftp)
+        if w.workouttype == 'water':
+            ftp = ftp*(100.-r.otwslack)/100.
         
 	hrpwrdata = {
 	    'hrmax':r.max,
@@ -5477,7 +5498,7 @@ def workout_add_timeplot_view(request,id):
 	    'hrat':r.at,
 	    'hrtr':r.tr,
 	    'hran':r.an,
-	    'ftp':r.ftp,
+	    'ftp':ftp,
             'powerperc':serialize_list(powerperc),
             'powerzones':serialize_list(r.powerzones),
 	    }
@@ -5526,6 +5547,9 @@ def workout_add_distanceplot_view(request,id):
                                   r.pw_at,
                                   r.pw_tr,r.pw_an])/r.ftp
 
+        ftp = float(r.ftp)
+        if w.workouttype == 'water':
+            ftp = ftp*(100.-r.otwslack)/100.
         
 	hrpwrdata = {
 	    'hrmax':r.max,
@@ -5534,7 +5558,7 @@ def workout_add_distanceplot_view(request,id):
 	    'hrat':r.at,
 	    'hrtr':r.tr,
 	    'hran':r.an,
-	    'ftp':r.ftp,
+	    'ftp':ftp,
             'powerperc':serialize_list(powerperc),
             'powerzones':serialize_list(r.powerzones),
 	    }
@@ -5581,6 +5605,9 @@ def workout_add_distanceplot2_view(request,id):
                                   r.pw_at,
                                   r.pw_tr,r.pw_an])/r.ftp
 
+        ftp = float(r.ftp)
+        if w.workouttype == 'water':
+            ftp = ftp*(100.-r.otwslack)/100.
         
 	hrpwrdata = {
 	    'hrmax':r.max,
@@ -5589,7 +5616,7 @@ def workout_add_distanceplot2_view(request,id):
 	    'hrat':r.at,
 	    'hrtr':r.tr,
 	    'hran':r.an,
-	    'ftp':r.ftp,
+	    'ftp':ftp,
             'powerperc':serialize_list(powerperc),
             'powerzones':serialize_list(r.powerzones),
 	    }
@@ -5638,6 +5665,9 @@ def workout_add_timeplot2_view(request,id):
                                   r.pw_at,
                                   r.pw_tr,r.pw_an])/r.ftp
 
+        ftp = float(r.ftp)
+        if w.workouttype == 'water':
+            ftp = ftp*(100.-r.otwslack)/100.
         
 	hrpwrdata = {
 	    'hrmax':r.max,
@@ -5646,7 +5676,7 @@ def workout_add_timeplot2_view(request,id):
 	    'hrat':r.at,
 	    'hrtr':r.tr,
 	    'hran':r.an,
-	    'ftp':r.ftp,
+	    'ftp':ftp,
             'powerperc':serialize_list(powerperc),
             'powerzones':serialize_list(r.powerzones),
 	    }
@@ -6387,6 +6417,10 @@ def workout_upload_view(request,
                                           r.pw_at,
                                           r.pw_tr,r.pw_an])/r.ftp
 
+                ftp = float(r.ftp)
+                if w.workouttype == 'water':
+                    ftp = ftp*(100.-r.otwslack)/100.
+
 	        hrpwrdata = {
 	            'hrmax':r.max,
 	            'hrut2':r.ut2,
@@ -6394,7 +6428,7 @@ def workout_upload_view(request,
 	            'hrat':r.at,
 	            'hrtr':r.tr,
 	            'hran':r.an,
-	            'ftp':r.ftp,
+	            'ftp':ftp,
                     'powerperc':serialize_list(powerperc),
                     'powerzones':serialize_list(r.powerzones),
 	        }
@@ -6631,6 +6665,10 @@ def team_workout_upload_view(request,message="",
                                           r.pw_at,
                                           r.pw_tr,r.pw_an])/r.ftp
 
+                ftp = float(r.ftp)
+                if w.workouttype == 'water':
+                    ftp = ftp*(100.-r.otwslack)/100.
+
 	        hrpwrdata = {
 	            'hrmax':r.max,
 	            'hrut2':r.ut2,
@@ -6638,7 +6676,7 @@ def team_workout_upload_view(request,message="",
 	            'hrat':r.at,
 	            'hrtr':r.tr,
 	            'hran':r.an,
-	            'ftp':r.ftp,
+	            'ftp':ftp,
                     'powerperc':serialize_list(powerperc),
                     'powerzones':serialize_list(r.powerzones),
 	        }
@@ -6840,9 +6878,13 @@ def workout_summary_restore_view(request,id,message="",successmessage=""):
                               r.pw_at,
                               r.pw_tr,r.pw_an])/r.ftp
 
+    ftp = float(r.ftp)
+    if row.workouttype == 'water':
+        ftp = ftp*(100.-r.otwslack)/100.
+        
     rr = rrower(hrmax=r.max,hrut2=r.ut2,
 		hrut1=r.ut1,hrat=r.at,
-		hrtr=r.tr,hran=r.an,ftp=r.ftp,
+		hrtr=r.tr,hran=r.an,ftp=ftp,
                 powerperc=powerperc,powerzones=r.powerzones)
     rowdata = rdata(f1,rower=rr)
     if rowdata == 0:
@@ -6951,9 +6993,13 @@ def workout_summary_edit_view(request,id,message="",successmessage=""
                               r.pw_at,
                               r.pw_tr,r.pw_an])/r.ftp
 
+    ftp = float(r.ftp)
+    if row.workouttype == 'water':
+        ftp = ftp*(100.-r.otwslack)/100.
+        
     rr = rrower(hrmax=r.max,hrut2=r.ut2,
 		hrut1=r.ut1,hrat=r.at,
-		hrtr=r.tr,hran=r.an,ftp=r.ftp,
+		hrtr=r.tr,hran=r.an,ftp=ftp,
                 powerperc=powerperc,powerzones=r.powerzones)
     rowdata = rdata(f1,rower=rr)
     if rowdata == 0:
@@ -7272,6 +7318,7 @@ def rower_edit_view(request,message=""):
 	if powerform.is_valid():
 	    cd = powerform.cleaned_data
 	    ftp = cd['ftp']
+            otwslack = cd['otwslack']
 	    try:
 		r = Rower.objects.get(user=request.user)
                 powerfrac = 100*np.array([r.pw_ut2,
@@ -7279,6 +7326,7 @@ def rower_edit_view(request,message=""):
                                           r.pw_at,
                                           r.pw_tr,r.pw_an])/r.ftp
 		r.ftp = max(min(ftp,650),50)
+                r.otwslack = max(min(otwslack,50),0)
                 ut2,ut1,at,tr,an = (r.ftp*powerfrac/100.).astype(int)
                 r.pw_ut2 = ut2
                 r.pw_ut1 = ut1
@@ -7286,7 +7334,7 @@ def rower_edit_view(request,message=""):
                 r.pw_tr = tr
                 r.pw_an = an
 		r.save()
-		message = "Functional Threshold Value Changed"
+		message = "FTP and/or OTW slack values changed."
                 messages.info(request,message)
 		url = reverse(rower_edit_view)
 		response = HttpResponseRedirect(url)
@@ -7635,9 +7683,13 @@ def strokedatajson(request,id):
                                   r.pw_at,
                                   r.pw_tr,r.pw_an])/r.ftp
 
+        ftp = float(r.ftp)
+        if row.workouttype == 'water':
+            ftp = ftp*(100.-r.otwslack)/100.
+            
         rr = rrower(hrmax=r.max,hrut2=r.ut2,
 		    hrut1=r.ut1,hrat=r.at,
-		    hrtr=r.tr,hran=r.an,ftp=r.ftp,
+		    hrtr=r.tr,hran=r.an,ftp=ftp,
                     powerperc=powerperc,powerzones=r.powerzones)
         rowdata = rdata(row.csvfilename,rower=rr).df