When faced with a catalogue of marine whip antennas all of differing heights, it's not always easy to choose which will give the best results..

Obviously if you want high performance you will want the longest antenna you can fit, especially if you are mainly operating on the lower HF frequencies where every metre counts. However, it the vessel is not long enough to support it at the speeds you travel in the sea conditions your vessel encounters regularly, antenna life may be significantly reduced.

The following chart is offered as a guide to selection. If you are in any doubt or have special conditions, please contact us.

It is important to ensure that minimum mount spacings in side mounting antennas are observed and in the case of type 18S/D the gate end top mount is fitted, otherwise the antenna may not have adequate support to survive wind conditions. In the case of high speed vessels, it is usually better to fit a slightly smaller antenna than normally indicated for displacement hull vessels unless the antenna is designed for the purpose.

Moonraker Marine Whips

When it comes to choosing antennas for GMDSS fit there are several factors that should be taken into account. Vessel (or platform) size, is important but what conditions the vessel is likely to encounter and where individual antennas can be mounted should also be taken into consideration, as deck space is often at a premium.

Antenna requirements relating to MF/HF/VHF communications state that separate receiving antennas are required for the MF or MF/HF DSC watchkeeping receiver, the VHF DSC watchkeeping receiver (if fitted) and the 2182 KHz watchkeeping receiver. In addition, a spare antenna should be provided for the MF or MF/HF transceiver. MF and/or MF/HF tranceiver antennas must be vertically polarised and a minimum of 8 metres in length. Moonraker has been supplying antennas for GMDSS fit for quite some years now and we are always happy to advise on individual solutions and to modify antenna designs to suit where system capability requires.

For a typical GMDSS solution (if there is one) we would normally recommend the following

• For the transmit antenna , our 10 metre 100 Series or 8 metre 80 Series antenna systems have been designed specifically for ocean going vessels of differing lengths. Both antenna systems are available side mounting (100W / 80W) or base mounting with with side feed (100B/S / 80B/S) or base feed (100B / 80B). A manual or screw operated tilting mount is available to suit types 100B/S and 80B/S. Both series are approved by the Australian Maritime Safety Authority for GMDSS fit.
  
• For the receiving antenna , we recommend our side mounting type 23H/S(wind survival to 240 km/h) or base mounting type 23B (wind survival to 250 km/h), should be used instead.
  
• For VHF we recommend our normal type MD HB dipole (2.2 dBi) or our high gain type MD G3 collinear antennas (5 dBi). The MD/G3 is only available side mounted, but the MD/HB may be side, base or swingdown mounted.
  
• For HF emergency back-up antenna we recommend our 5.5metre (18ft) type 18S/R system, where a duplicate of the main HF antenna is not carried. The 18S/R is easily assembled from two sections that store below deck then screwed into a permanent deck mount.