204:
33:
173:
A modern refinement of the half-tide dock uses a "gate-flap", which replaces a fixed sill with a hinged flap that opens as the tide rises, and closes as the tide ebbs. When open, the gate-flap rests horizontally at the seabed level. Operation is usually hydraulic, with automatic control; and warning
145:
The sill of a half tide dock must be set sufficiently far below the daily high tide mark to allow ships to pass over it. Obviously this was easier to achieve with small ships of shallow draught, or in areas with a large tidal range. Inside the dock, the depth of water beneath the sill's level depends
174:
lights or alarms will indicate when the gate-flap is about to be lowered or raised. The advantage over the older fixed sill is that, when the gate-flap is down, there is greater draught available to boats as there is no sill providing an obstacle.
141:
prevents the level dropping below a certain point, meaning that the ships in the dock remain afloat, although they still rise and fall with the tides above this. Half tide docks are particularly useful in areas with a large tidal range.
153:
being calculated for heights above it (i.e. clear draught in and out of the dock). This importance has often continued for many years after the original sill had been replaced, as at
203:
149:
The importance of the sill, and the tide's height above it, is reflected by these dock sills becoming an important local datum level and for
116:
50:
97:
54:
69:
265:
76:
270:
220:
83:
243:"A Study of Changes in High Water Levels and Tides at Liverpool during the Last Two Hundred and Thirty Years"
43:
65:
146:
only on the depth to which the dock was excavated, although this obviously increases construction costs.
186:
190:
223:, a dock where pumps, or incoming river flow, are used to maintain the docks at a high level.
90:
134:
158:
259:
194:
32:
150:
17:
154:
242:
162:
137:. Typically the dock is entered at high tide. As the tide ebbs a sill or
209:
Peel inner harbour at high water (the gate-flap is at the extreme left).
182:
178:
248:. Proudman Oceanographic Laboratory. pp. 3, 77. Report Number 56.
138:
26:
161:, or where the dock had disappeared entirely, such as
57:. Unsourced material may be challenged and removed.
8:
117:Learn how and when to remove this message
233:
199:
177:Such gate-flap systems are in place in
7:
55:adding citations to reliable sources
25:
202:
31:
42:needs additional citations for
1:
241:Woodworth, Philip L. (1999).
169:A "gate-flap" half-tide dock
287:
193:(the latter two in the
133:is a partially tidal
266:Coastal construction
51:improve this article
127:
126:
119:
101:
16:(Redirected from
278:
271:Docks (maritime)
250:
249:
247:
238:
206:
122:
115:
111:
108:
102:
100:
66:"Half tide dock"
59:
35:
27:
21:
286:
285:
281:
280:
279:
277:
276:
275:
256:
255:
254:
253:
245:
240:
239:
235:
230:
217:
210:
207:
171:
123:
112:
106:
103:
60:
58:
48:
36:
23:
22:
15:
12:
11:
5:
284:
282:
274:
273:
268:
258:
257:
252:
251:
232:
231:
229:
226:
225:
224:
216:
213:
212:
211:
208:
201:
170:
167:
165:in Liverpool.
159:Severn Estuary
131:half tide dock
125:
124:
107:September 2014
39:
37:
30:
24:
18:Half Tide Dock
14:
13:
10:
9:
6:
4:
3:
2:
283:
272:
269:
267:
264:
263:
261:
244:
237:
234:
227:
222:
221:Floating dock
219:
218:
214:
205:
200:
198:
196:
192:
188:
184:
180:
175:
168:
166:
164:
163:Old Dock Sill
160:
156:
152:
147:
143:
140:
136:
132:
121:
118:
110:
99:
96:
92:
89:
85:
82:
78:
75:
71:
68: –
67:
63:
62:Find sources:
56:
52:
46:
45:
40:This article
38:
34:
29:
28:
19:
236:
176:
172:
148:
144:
130:
128:
113:
104:
94:
87:
80:
73:
61:
49:Please help
44:verification
41:
195:Isle of Man
151:tide tables
260:Categories
228:References
77:newspapers
155:Sharpness
215:See also
187:Douglas
183:Padstow
179:Swansea
157:on the
91:scholar
189:, and
93:
86:
79:
72:
64:
246:(PDF)
98:JSTOR
84:books
191:Peel
139:weir
135:dock
70:news
197:).
53:by
262::
185:,
181:,
129:A
120:)
114:(
109:)
105:(
95:·
88:·
81:·
74:·
47:.
20:)
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.