diff --git a/lib/www/client/source/src/components/decoder/saillines-string-decoder.vue b/lib/www/client/source/src/components/decoder/saillines-string-decoder.vue
index 49e1e85..b4cdf21 100644
--- a/lib/www/client/source/src/components/decoder/saillines-string-decoder.vue
+++ b/lib/www/client/source/src/components/decoder/saillines-string-decoder.vue
@@ -143,7 +143,7 @@ export default {
 
   props: {
     text: String,
-    fields: Object,
+    //fields: Object,
     //delimiter: String,
     headerRow: { type: [ Boolean, Number ], default: false},
     numberedLines: [ Boolean, Number ],
@@ -215,12 +215,18 @@ export default {
       // Properties of the sailline object
       const keys = [ "incr", "ntba", "remarks", "source_line", "meta.colour" ];
 
+      function to_bool (v, missing=false) {
+        return (v === undefined || v === null)
+          ? missing // Missing value meaning
+          : /^t(rue)|^[1-9-]+$/i.test(String(v).trim())
+      }
+
       // To transform the input text into the required format for each field
       const transformer = (key) => {
         const transformers = {
-          incr: (v) => Boolean(Number(v)),
-          ntba: (v) => Boolean(Number(v)),
-          remarks: String,
+          incr: (v) => to_bool(v, true),
+          ntba: (v) => to_bool(v, false),
+          remarks: (v) => (v === undefined || v === null) ? "" : String,
           source_line: Number,
         };
         return transformers[key] ?? String;
diff --git a/lib/www/client/source/src/components/project-settings/preplots-preplot.vue b/lib/www/client/source/src/components/project-settings/preplots-preplot.vue
new file mode 100644
index 0000000..f36fed3
--- /dev/null
+++ b/lib/www/client/source/src/components/project-settings/preplots-preplot.vue
@@ -0,0 +1,520 @@
+<template>
+  <v-card flat>
+    <v-card-text>
+      <v-form>
+        <v-text-field
+          label="Path"
+          v-model="value.path"
+        >
+          <dougal-file-browser-dialog
+            slot="append"
+            v-model="value.path"
+            :root="rootPath"
+          ></dougal-file-browser-dialog>
+        </v-text-field>
+
+        <v-select
+          label="Preplot class"
+          :items="fileClasses"
+          v-model="fileClass"
+        ></v-select>
+
+        <v-select
+          label="File format"
+          :items="preplotFileTypes"
+          v-model="fileType"
+        ></v-select>
+
+        <v-text-field v-if="value.class == 'S'"
+          class="mb-3"
+          label="Sailline offset"
+          prefix="±"
+          type="number"
+          hint="The value to add/substract to source lines to get to the corresponding sailline"
+          v-model.number="value.saillineOffset"
+        >
+        </v-text-field>
+
+        <v-expansion-panels v-if="isFixedWidthFormat"
+          :value="head.length ? 0 : null"
+        >
+          <v-expansion-panel>
+            <v-expansion-panel-header>Column settings</v-expansion-panel-header>
+            <v-expansion-panel-content>
+              <div class="mb-3" style="max-width:fit-content;">
+                <v-select v-if="head"
+                  label="Sample text size"
+                  hint="Choose how much of the file to display"
+                  :items="sampleSizeItems"
+                  v-model="sampleSize"
+                ></v-select>
+              </div>
+
+              <v-text-field
+                label="Skip lines"
+                hint="This lets you to skip file headers if present"
+                type="number"
+                min="0"
+                v-model.number="firstRow"
+              ></v-text-field>
+
+              <dougal-fixed-string-decoder
+                :text="rows"
+                :fields="fields"
+                :multiline="true"
+                :numbered-lines="firstRow"
+                max-height="300px"
+                :editable-field-list="false"
+              ></dougal-fixed-string-decoder>
+            </v-expansion-panel-content>
+          </v-expansion-panel>
+        </v-expansion-panels>
+
+        <v-expansion-panels v-else-if="isDelimitedFormat"
+          :value="head.length ? 0 : null"
+        >
+          <v-expansion-panel>
+            <v-expansion-panel-header>Column settings</v-expansion-panel-header>
+            <v-expansion-panel-content>
+
+              <v-container>
+                <v-row>
+                  <v-col cols="6">
+                    <div class="mb-3" style="max-width:fit-content;">
+                      <v-select v-if="head"
+                        label="Sample text size"
+                        hint="Choose how much of the file to display"
+                        :items="sampleSizeItems"
+                        v-model="sampleSize"
+                      ></v-select>
+                    </div>
+                  </v-col>
+                </v-row>
+                <v-row>
+                  <v-col cols="12">
+
+                    <dougal-delimited-string-decoder
+                      title="Fields"
+                      :text="rows"
+                      :fields.sync="fields"
+                      :header-row.sync="headerRow"
+                      :numbered-lines.sync="firstRow"
+                      :editable-field-list="false"
+                      :delimiter.sync="delimiter"
+                    ></dougal-delimited-string-decoder>
+
+                  </v-col>
+                </v-row>
+
+              </v-container>
+            </v-expansion-panel-content>
+          </v-expansion-panel>
+        </v-expansion-panels>
+        <v-expansion-panels v-else-if="fileClass == 'saillines'"
+          :value="head.length ? 0 : null"
+        >
+          <v-expansion-panel>
+            <v-expansion-panel-header>Column settings</v-expansion-panel-header>
+            <v-expansion-panel-content>
+
+              <v-container>
+                <v-row>
+                  <v-col cols="6">
+                    <div class="mb-3" style="max-width:fit-content;">
+                      <v-select v-if="head"
+                        label="Sample text size"
+                        hint="Choose how much of the file to display"
+                        :items="sampleSizeItems"
+                        v-model="sampleSize"
+                      ></v-select>
+                    </div>
+                  </v-col>
+                </v-row>
+                <v-row>
+                  <v-col cols="12">
+
+                    <dougal-saillines-string-decoder
+                      subtitle="Sailline data"
+                      :text="head"
+                    ></dougal-saillines-string-decoder>
+
+                  </v-col>
+                </v-row>
+
+              </v-container>
+            </v-expansion-panel-content>
+          </v-expansion-panel>
+        </v-expansion-panels>
+      </v-form>
+    </v-card-text>
+  </v-card>
+</template>
+
+<script>
+import DougalFileBrowserDialog from '@/components/file-browser/file-browser-dialog'
+import DougalFixedStringDecoder from '@/components/decoder/fixed-string-decoder'
+import DougalDelimitedStringDecoder from '@/components/decoder/delimited-string-decoder';
+import DougalSaillinesStringDecoder from '@/components/decoder/saillines-string-decoder';
+
+import { mapActions, mapGetters } from 'vuex'
+
+export default {
+  name: "DougalProjectSettingsPreplotsPreplot",
+
+  components: {
+    DougalFileBrowserDialog,
+    DougalFixedStringDecoder,
+    DougalDelimitedStringDecoder,
+    DougalSaillinesStringDecoder
+  },
+
+  props: {
+    value: Object,
+    rootPath: String
+  },
+
+  data () {
+    return {
+      fileClasses: [
+        { text: "Source points", value: "S" },
+        { text: "Vessel points", value: "V" },
+        { text: "Sail lines", value: "saillines" }
+      ],
+
+      preplotFileTypeList: {
+        "S": [
+          { header: "Fixed width" },
+          { text: "SPS v1", value: "sps1", fixedWidth: true },
+          { text: "SPS v2.1", value: "sps2.1", fixedWidth: true },
+          { text: "P1/90", value: "p190", fixedWidth: true },
+          { text: "Other fixed width", value: "fixed-width", fixedWidth: true },
+          { header: "Delimited values" },
+          { text: "P1/11", value: "p111", delimited: true },
+          { text: "CSV", value: "csv", delimited: true },
+        ],
+        "V": [
+          { header: "Fixed width" },
+          { text: "SPS v1", value: "sps1", fixedWidth: true },
+          { text: "SPS v2.1", value: "sps2.1", fixedWidth: true },
+          { text: "P1/90", value: "p190", fixedWidth: true },
+          { text: "Other fixed width", value: "fixed-width", fixedWidth: true },
+          { header: "Delimited values" },
+          { text: "P1/11", value: "p111", delimited: true },
+          { text: "CSV", value: "csv", delimited: true },
+        ],
+        "saillines": [
+          { text: "Sail lines CSV", value: "x-sl+csv" }
+        ]
+      },
+
+      head: "",
+      sampleSize: 8192, //1024;
+      sampleSizeItems: [
+        { text: "512 bytes", value: 512 },
+        { text: "1 kiB", value: 1024 },
+        { text: "2 kiB", value: 1024*2 },
+        { text: "4 kiB", value: 1024*4 },
+        { text: "8 kiB", value: 1024*8 },
+        { text: "16 kiB", value: 1024*16 },
+        { text: "32 kiB", value: 1024*32 },
+      ],
+    };
+  },
+
+  computed: {
+
+    preplotFileTypes () {
+      return this.preplotFileTypeList[this.fileClass] ?? [];
+    },
+
+    isFixedWidthFormat () {
+      return this.preplotFileTypes.find(i => i.value == this.fileType)?.fixedWidth;
+    },
+
+    isDelimitedFormat () {
+      return this.preplotFileTypes.find(i => i.value == this.fileType)?.delimited;
+    },
+
+    rows () {
+      if (this.head) {
+        if (this.firstRow) {
+          return this.head.split("\n").slice(this.firstRow).join("\n");
+        }
+        return this.head;
+      }
+      return "";
+    },
+
+    fields: {
+      get () {
+        return (this.value?.fields && Object.keys(this.value.fields).length)
+          ? this.value.fields
+          : {
+            line_name: {
+              type: "int"
+            },
+            point_number: {
+              type: "int"
+            },
+            easting: {
+              type: "float"
+            },
+            northing: {
+              type: "float"
+            }
+          };
+      },
+
+      set (v) {
+        // console.log("set fields", v);
+        this.$emit("input", {
+          ...this.value,
+          fields: {...v}
+        });
+      }
+    },
+
+    fileClass: {
+      get () {
+        return this.value?.class;
+      },
+
+      set (v) {
+        this.$emit("input", {
+          ...this.value,
+          class: v
+        });
+      }
+    },
+
+    fileType: {
+      get () {
+        return this.value?.type;
+      },
+
+      set (v) {
+        this.$emit("input", {
+          ...this.value,
+          type: v
+        });
+      }
+    },
+
+    firstRow: {
+      get () {
+        return this.value?.firstRow ?? 0;
+      },
+
+      set (v) {
+        this.$emit("input", {
+          ...this.value,
+          firstRow: v
+        });
+      }
+    },
+
+    headerRow: {
+      get () {
+        return this.value?.headerRow ?? false;
+      },
+
+      set (v) {
+        this.$emit("input", {
+          ...this.value,
+          headerRow: v
+        });
+      }
+    },
+
+    delimiter: {
+      get () {
+        return this.value?.delimiter;
+      },
+
+      set (v) {
+        this.$emit("input", {
+          ...this.value,
+          delimiter: v
+        });
+      }
+    }
+
+  },
+
+  watch: {
+
+    async "value.path" (cur, prev) {
+      if (cur != prev) {
+        this.head = await this.getHead();
+      }
+    },
+
+    async sampleSize (cur, prev) {
+      if (cur && cur != prev) {
+        this.head = await this.getHead();
+      }
+    },
+
+    fileClass (cur, prev) {
+      if (cur != prev && cur == "saillines") {
+        this.fileType = "x-sl+csv"
+      }
+    },
+
+    fileType (cur, prev) {
+      switch (cur) {
+        case prev:
+          return;
+        case "sps1":
+          this.fields = {
+            line_name: {
+              offset: 1,
+              length: 16,
+              type: "int"
+            },
+            point_number: {
+              offset: 17,
+              length: 8,
+              type: "int"
+            },
+            easting: {
+              offset: 46,
+              length: 9,
+              type: "float"
+            },
+            northing: {
+              offset: 55,
+              length: 10,
+              type: "float"
+            }
+          };
+          break;
+        case "sps2.1":
+          this.fields = {
+            line_name: {
+              offset: 1,
+              length: 7,
+              type: "int" // SPS v2.1 has this as float but Dougal doesn't support that
+            },
+            point_number: {
+              offset: 11,
+              length: 7,
+              type: "int" // Ditto
+            },
+            easting: {
+              offset: 46,
+              length: 9,
+              type: "float"
+            },
+            northing: {
+              offset: 55,
+              length: 10,
+              type: "float"
+            }
+          };
+          break;
+        case "p190":
+          this.fields = {
+            line_name: {
+              offset: 1,
+              length: 12,
+              type: "int"
+            },
+            point_number: {
+              offset: 19,
+              length: 6,
+              type: "int"
+            },
+            easting: {
+              offset: 46,
+              length: 9,
+              type: "float"
+            },
+            northing: {
+              offset: 55,
+              length: 9,
+              type: "float"
+            }
+          };
+          break;
+        case "fixed-width":
+          this.fields = {
+            line_name: {
+              offset: 1,
+              length: 4,
+              type: "int"
+            },
+            point_number: {
+              offset: 11,
+              length: 4,
+              type: "int"
+            },
+            easting: {
+              offset: 44,
+              length: 8,
+              type: "float"
+            },
+            northing: {
+              offset: 53,
+              length: 9,
+              type: "float"
+            }
+          };
+        case "csv":
+          this.fields = {
+            line_name: {
+              column: 0,
+              type: "int"
+            },
+            point_number: {
+              column: 1,
+              type: "int"
+            },
+            easting: {
+              column: 2,
+              type: "float"
+            },
+            northing: {
+              column: 3,
+              type: "float"
+            }
+          };
+          break
+        case "x-sl+csv":
+          this.fields = null;
+          break;
+      }
+    }
+
+  },
+
+  methods: {
+
+    async getHead () {
+      console.log("getHead", this.value?.path);
+      if (this.value?.path) {
+        const url = `/files/${this.value.path}`;
+        const init = {
+          text: true,
+          headers: {
+            "Range": `bytes=0-${this.sampleSize}`
+          }
+        };
+        const head = await this.api([url, init]);
+        return head?.substring(0, head.lastIndexOf("\n")) || "";
+      }
+      return "";
+    },
+
+    ...mapActions(["api"])
+  },
+
+  created () {
+    this.$nextTick(async () => {
+      this.head = await this.getHead();
+    });
+  }
+
+}
+
+</script>
diff --git a/lib/www/client/source/src/components/project-settings/preplots.vue b/lib/www/client/source/src/components/project-settings/preplots.vue
index a8ad9a1..3893c37 100644
--- a/lib/www/client/source/src/components/project-settings/preplots.vue
+++ b/lib/www/client/source/src/components/project-settings/preplots.vue
@@ -3,51 +3,43 @@
     <v-card-title>Preplots</v-card-title>
     <v-card-subtitle>Preplot files location and format.</v-card-subtitle>
     <v-card-text>
-      <v-tabs v-model="tab">
-        <v-tab v-for="item in preplots">{{tabNameFor(item)}}</v-tab>
-      </v-tabs>
 
-      <v-tabs-items v-model="tab">
-        <v-tab-item v-for="item in preplots">
-          <v-card flat>
-            <v-card-text>
-              <v-form>
-                <v-text-field
-                  label="Path"
-                  v-model="item.path"
-                >
-                  <dougal-file-browser-dialog
-                    slot="append"
-                    v-model="item.path"
-                    :root="value.rootPath"
-                    :mimetypes="[ 'text/plain', '*.sps' ]"
-                  ></dougal-file-browser-dialog>
-                </v-text-field>
+      <v-expansion-panels v-model="panel">
+        <v-expansion-panel v-for="(preplot, idx) in preplots_" :key="idx">
+          <v-expansion-panel-header>
+            {{ titleFor(preplot) }}
+          </v-expansion-panel-header>
+          <v-expansion-panel-content>
+            <dougal-project-settings-preplots-preplot
+              v-model="preplots_[idx]"
+              :root-path="rootPath"
+            ></dougal-project-settings-preplots-preplot>
 
-                <v-text-field v-if="item.class == 'S'"
-                  class="mb-3"
-                  label="Sailline offset"
-                  prefix="±"
-                  type="number"
-                  hint="The value to add/substract to source lines to get to the corresponding sailline"
-                  v-model.number="item.saillineOffset"
-                >
-                </v-text-field>
+            <v-btn
+              outlined
+              color="red"
+              title="Delete this preplot definition"
+              @click.stop="deletePreplot(preplot)"
+            >
+              <v-icon left>mdi-delete-outline</v-icon>
+              Delete
+            </v-btn>
+
+
+          </v-expansion-panel-content>
+        </v-expansion-panel>
+      </v-expansion-panels>
+
+      <v-btn
+        class="mt-5"
+        color="primary"
+        :disabled="!lastPreplotIsValid"
+        @click="newPreplot"
+      >
+        <v-icon left>mdi-file-document-plus-outline</v-icon>
+        New preplot
+      </v-btn>
 
-                <v-expansion-panels :value="head.length ? 0 : null">
-                <v-expansion-panel>
-                  <v-expansion-panel-header>Column settings</v-expansion-panel-header>
-                  <v-expansion-panel-content>
-                    <dougal-fixed-width-format v-model="item.format" :sample="head">
-                    </dougal-fixed-width-format>
-                  </v-expansion-panel-content>
-                </v-expansion-panel>
-                </v-expansion-panels>
-              </v-form>
-            </v-card-text>
-          </v-card>
-        </v-tab-item>
-      </v-tabs-items>
     </v-card-text>
     <v-card-actions>
       <v-btn
@@ -77,45 +69,42 @@
 </style>
 
 <script>
-import DougalFileBrowserDialog from '@/components/file-browser/file-browser-dialog';
-import DougalFixedWidthFormat from './fixed-width-format';
-import { mapActions, mapGetters } from 'vuex';
+import DougalProjectSettingsPreplotsPreplot from '@/components/project-settings/preplots-preplot';
 
 export default {
   name: "DougalProjectSettingsPreplots",
 
   components: {
-    DougalFileBrowserDialog,
-    DougalFixedWidthFormat
+    DougalProjectSettingsPreplotsPreplot,
   },
 
-  props: [ "value" ],
+  props: [ "rootPath", "preplots" ],
 
   data () {
     return {
-      tab: null,
-      preplots: [],
-      head: ""
+      preplots_: [],
+      panel: null
     }
   },
 
   computed: {
 
-    currentItem () {
-      if (this.tab !== null) {
-        return this.preplots[this.tab];
-      }
+    lastPreplotIsValid () {
+      return this.preplots_.length == 0 || this.validPreplot(this.preplots_[this.preplots_.length-1]);
     },
 
     isValid () {
-      return this.preplots && this.preplots.every( item => item.format != null );
+      return this.preplots_.every(preplot => this.validPreplot(preplot));
     }
 
   },
 
   watch: {
-    value (newValue) {
-      this.reset();
+
+    preplots () {
+      if (this.preplots.some( (i, idx) => i != this.preplots_[idx] )) {
+        this.preplots_ = structuredClone(this.preplots);
+      }
     },
 
     currentItem: {
@@ -130,47 +119,84 @@ export default {
 
   methods: {
 
-    tabNameFor (item) {
-      switch (item.class) {
-        case "S":
-          return "Source";
-        case "V":
-          return "Vessel";
-        default:
-          return item.class || "?";
+    titleFor (preplot) {
+      let str = "";
+
+      if (preplot?.path) {
+        str += preplot.path;
+      } else {
+        const idx = this.preplots_.findIndex(i => i == preplot);
+        if (idx != -1) {
+          str += `Preplot ${idx}`;
+        } else {
+          str += "Preplot <no path>";
+        }
+      }
+
+      if (preplot?.class || preplot?.type) {
+        str += " (" + [preplot.class, preplot.type].join("; ") + ")";
+      }
+
+      return str;
+    },
+
+    validPreplot (preplot) {
+
+      const predefined_formats = [ "sps1", "sps2.1", "p190", "p111", "x-sl+csv" ]
+
+      const common = (preplot?.path &&
+        preplot?.type &&
+        preplot?.class &&
+        preplot?.fields);
+
+      if (common) {
+        if (predefined_formats.includes(preplot.class)) {
+          // Predefined formats do not require a field definition
+          return true;
+        } else {
+          return !!(preplot?.fields?.line_name &&
+            preplot?.fields?.point_number &&
+            preplot?.fields?.easting &&
+            preplot?.fields?.northing);
+        }
+      }
+      return false;
+    },
+
+    deletePreplot (preplot) {
+      const idx = this.preplots_.find(i => i == preplot);
+      if (idx != -1) {
+        this.preplots_.splice(idx, 1);
       }
     },
 
-    async getHead () {
-      if (this.currentItem) {
-        const url = `/files/${this.currentItem.path}`;
-        const init = {
-          text: true,
-          headers: {
-            "Range": "bytes=0-1024"
-          }
+    newPreplot () {
+      if (this.lastPreplotIsValid) {
+        const preplot = {
+          path: "",
+          type: "",
+          format: "",
+          fields: {},
         };
-        this.head = await this.api([url, init]);
-        this.head = this.head?.substring(0, this.head.lastIndexOf("\n")) || "";
+        this.preplots_.push(preplot);
+        this.panel = this.preplots_.length - 1;
       }
     },
 
+
     reset () {
-      if (!this.value) {
-        return;
-      }
-      this.preplots = JSON.parse(JSON.stringify(this.value.preplots));
+      this.preplots_ = this.preplots;
     },
 
     save () {
-      this.$emit('input', {preplots: [...this.preplots]});
+      this.$emit('input', {
+        preplots: this.preplots_
+      });
     },
 
     back () {
       this.$emit('close');
-    },
-
-    ...mapActions(["api"])
+    }
 
   },