What's Wrong With This Picture: 170 MONTAUK Antenna

VHF Marine Band radios, protocol, radio communication theory, practical advice; AIS; DSC; MMSI; EPIRB.
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What's Wrong With This Picture: 170 MONTAUK Antenna

Postby jimh » Sat Aug 20, 2022 11:08 am

Boston Whaler offers 170 MONTAUK customers the option of having a VHF Marine Band radio and antenna pre-installed. From their website I found several images showing the antenna location. Figure 1 below demonstrates the position very clearly. A short, three-foot antenna is mounted to the Starboard side of the helm console, and the antenna appears to have an insulating radome covering the radiating element.

Fig. 1. VHF antenna location on 170 MONTAUK as installed at the factory. Note the absence of any rigging for a Bimini top on this boat. The presence of a trolling motor and fishing rods suggests this boat was intended for angling.
170MONTAUK_RadioAntennaLocation.jpg (105.75 KiB) Viewed 3088 times

For me there are several problems with the antenna location as illustrated above. My concerns are in two realms: the antenna location as it relates to the operation of the radio, and the antenna location as it relates to the operation of the boat.

With regard to the radio operation aspect of the antenna location, I see these problems:
  • the vertical separation between the antenna and the transmitter is nil; most manufacturers want three-feet of separation, and the vertical separation is the most important.
  • the radiating portion of the antenna is very close to the helmsman; at 25-Watt power level the helmsman's eyes are looking right at the radiation source
  • the metal frame of the windshield railing is very close to the antenna radiating element, and that is a fundamental no-no.

With regard to the boat operation aspect, I see these problems:
  • the boat as shown has no weather canvas, that is, no Bimini top, and the antenna as mounted appears to interfere with a Bimini top, which is probably why none was installed on the boat in shown in Figure 1;
  • the antenna cannot be folded down to horizontal, as it would create an obstruction to movement in the boat, nor can the antenna be folded 180-degree as there is insufficient clearance, and thus whenever the boat is in operation the antenna must be moved into its operating position;
  • the antenna presents a potential hand held or grab rail for anyone to inadvertently grab onto, and the radiating element most likely lacks sufficient strength and could be broken off by someone grabbing for it in rough seas.

These problems are not unique to the 170 MONTAUK boat, but I believe that the Unibond hull construction contributes to the console-mounted antenna base as being perhaps the most practical method of installation, although not the most practical method for overall best radio performance and best operation of the boat.

If there won't be an overhead obstruction at the center console, a much improved mounting for the antenna is to employ a four-foot extension mast, and mount a lightweight antenna (such as a GAM SS-2) atop the mast. The use of the extension mast delivers significant improvements:
  • vertically raising the antenna creates the necessary vertical separation between antenna and transmitter
  • raising the antenna improves the range of the radio system
  • raising the antenna gets the operator and crew farther away from the antenna and its radio radiation.
The added four-foot mast does not affect the antenna in the non-operating position in any way different than the short antenna shown above; the antenna must be tilted 90-degrees for stowing when not in use, just as before, and there is no effect on vertical height when stowed. With regard to being used inadvertently as a grab rail, a strong extension mast on a strong mount will have better endurance than the plastic antenna mount and small diameter radiator shown in Figure 1.

In general, to have the antenna base attached to the center console seems to rule out having a Bimini top. I suspect that for most boaters, having a Bimini top is a higher priority than having the radio antenna attached at the console. If not at the console, then where can the antenna be located?

To answer that question we must know if the boat is going to be extensively used for angling. Anglers generally want no obstructions near the boat transom that could interfere with their angling rods and lines. This requirement tends to rule out mounting a radio antenna near the transom.

The Unibond hull construction tends to limit the paths that any electrical cable can take on a 170 MONTAUK, with the concealed rigging tunnel under the deck from console to transom being about the only easy way for cable to be run. This influence tends to put the radio antenna aft of the console and toward the transom.

By using a strong ratchet mount as the antenna base, a radio antenna can be mounted in the stern of the boat and then be tilted down and out of the way while angling. This seems to me to be the best solution all-round. I envision the antenna installation being done as follows:
  • install a strong ratchet mount base to the inwale of the Starboard cockpit near the transoms, in the area seen in Figure 2 below;
  • choose an extension mast length and antenna length so the antenna can be folded down and forward and lie below the gunwale top; and
  • route the transmission line to the console via the rigging tunnel, the exact manner to be determined on location or as suggested below.
Fig. 2. View of cockpit inwale of 170 MONTAUK as potential antenna base mounting location.
170MONTAUK_Inwale.jpg (108.52 KiB) Viewed 3088 times

Based on what can be seen in Figure 2, the antenna base would be mounted slightly forward of the aft-most vertical rail of the side rails. The transmission line could be routed into the compartment below the stern quarter seat, and from there should have access to the rigging tunnel. I would expect that the typically transmission line length provided with the antenna would be 15-feet, and that length should be sufficient to allow reaching to the radio at the console via the rigging tunnel. Because the mount cannot be through-bolted, the location should try to take advantage of any embedded reinforcement material below the laminate in this general area. If there are not embedded reinforcements, the load of the base should be spread using a base plate that enlarges the area of contact between the ratchet-mount and the laminate surface. Again, this may have to be resolved on location.

Because the boat is powered by a spark ignition engine, there will be some radio noise generated from the engine. Modern engines tend to have reasonably good suppression of ignition generated radio noise because they rely on internal computers to control the engine. Noise interference from the engine spark ignition would also interfere with the computer operation, so modern engines are better suppressed for noise radiation than old outboard engines. But the best approach to reducing engine generated radio noise will again be vertical separation between the antenna and the engine, so the extension is further important to best radio operation.

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Re: What's Wrong With This Picture: 170 MONTAUK Antenna

Postby Jefecinco » Sun Aug 21, 2022 12:16 pm

On our previously owned 190 Montauk the VHF antenna mount was in about the same location [as shown above in Figure 1]. However, our antenna was mounted to the top of a Shakespeare extension mast. The antenna was a Digital 3-foot stainless steel model. Performance was exceptional. We did not have a Bimini top on the boat as it was used primarily for angling. When towing the boat the mast folded down to rest on the top of the RPS back cushion. The metal antenna could be removed by a push-and-twist for storage. The folded position also allowed for easy installation of the boat cover without interference.

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Re: What's Wrong With This Picture: 170 MONTAUK Antenna

Postby jimh » Mon Aug 22, 2022 7:47 am

Jefecinco wrote:On our previously owned 190 Montauk the VHF antenna mount was in about the same location [as shown above in Figure 1]...[atop an] extension mast....We did not have a Bimini top on the boat as it was used primarily for angling.
As mentioned in the initial article, mounting the antenna base to the console and using an extension mast to raise the antenna is a good solution as long as the boat will never have any sort of overhead canvas top.