Works for the protection of yacht harbours have to be designed in the same way as those for commercial and fishing ports. However, there are aspects of the design which, though of secondary importance in such harbours, are of primary concern in the case of yacht harbours. for example the consideration which should be given for yachts entering a harbour under sail.
This report considers the features peculiar to yacht harbours, discusses the experience gained in attempting to solve the problems posed by them and makes recommendations for the design of such harbours. It is firstly necessary to identify these features in order to obtain an overall view and then each one is considered separately.
Depth in the entrance
It is well known that yachts do not exceed 4.5m in draught. In order therefore to reduce the cost of the work as much as possible breakwaters and entrances are usually sited where the depth at low water is not more than 4 to 5 m.
This leads to three considerations of great importance:
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The danger that the port entrance may often be on or closer to the shore than the wave-breaking contour which means that sometimes entry will be impossible.
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If the port is located on a sandy or muddy coast, or where there is much seaweed, sand bars may form at the entrance or within the harbour.
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Because of the limited depth, the maximum possible wave will have broken before it reaches the harbour. The cross section of the breakwater can therefore be considerably less massive than in the case of a deep water port.
Shelter within the harbour
A degree of wave motion is tolerated within a commercial port depending upon the size of the ships, type of traffic and frequency with which it is assumed to occur. In a yacht harbour there must be calm at all times and especially when there is a swell outside. Reflection from quay walls must also be avoided because crews frequently sleep on board and yachts have a frequency of rolling which quickly attunes itself to the wave motion in a harbour.
Height of the breakwater crest above quay level
The aesthetics of the works is of great importance in yacht harbours. One difficulty is that the quay level is low: somewhere of the order of 0.8 to 1.2m. With a quay cross section designed on orthodox lines, this makes the height of the breakwater crest above quay level about 6 to 8 m. This would be visually unacceptable from within a yacht harbour, so that care is needed in studying the section in order to reduce the height of the breakwater or in some way camouflage it.
Entering and leaving harbour under sail
Large yachts and motor boats use their engines when entering and leaving port. Smaller yachts, however, either do not possess or do not wish to use their auxiliary and prefer to enter under sail.
The harbour entrance should therefore be made so as to allow yachts to navigate under sail in differing sea and wind conditions. It must allow for the tacking of close-hauled yachts in congested conditions.
Littoral drift
The influence which a port located on a sandy coast may have on the stability of neighbouring beaches is not considered in this study. It is, however, closely related to the danger of shoaling in harbour entrances and so it is included among the aspects to be considered.
Inter-relationship of factors
So far we have identified the most important factors concerning yacht harbours. They are closely linked and must be studied together.
For example, a large entrance width is good from the point of view of avoiding traffic congestion and ensuring ease of navigation under sail but bad for providing good wave protection. Another example is that a low breakwater may not give sufficient shelter from winds.
