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Antenna Allowances For The Modern Yacht – A Wicked Conundrum

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Growing up navigating by sextant and lead line taught us to appreciate modern electronics. We love radar, GPS, SONAR, and AIS. We are attached to free wifi, and data via cell service. What we don’t like is a hodge podge of antennae strewn here and there. So the farm – as in antenna farm – is on the design priority list during the concept phase, to make sure there is an orderly way to install them all.

There is the usual array of whips (2 VHF, AIS, Weather Fax, two wifi, and two cell). These are straightforward, but the lower radar provides an interesting challenge. If it directs its beam at the flat inner mast wall, that signal is going to reflect back, bounce all over the place, and create false echoes. Hence the stealth style angled plate. This is designed to reflect that energy outward and up, into an area where it won’t bounce back.

There has to be a system to get up here for maintenance and this is where the mast steps come into play.

In addition to these whips and radars, there needs to be space for GPS antennae, as well as perhaps a satellite compass and possibly Iridium or other sat com system. Most of these take a one-inch pipe thread. We’ll weld four of these stubs to the roof perimeter to facilitate their installation.


Posted by Steve Dashew  (February 18, 2012)




15 Responses to “Antenna Allowances For The Modern Yacht – A Wicked Conundrum”

  1. Alain M Says:
    Hi Steve, That’s mean two dead angle (or spot) on the lower radar… But if we take account of the motion from boat, what is the really result? It needs to be tested! Have you done some really life test in this way of do the deflecting? I remember one morning fog , so heavy that you cannot see one friend 2 meter away, with a radar who was working half way only due to a knock down few days before, very uncomfortable… Regards Alain

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    Steve Dashew Reply:

    Not tested but suggested by someone whose business it is to know about these things.

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  2. Kees Says:
    Hm, Not sure that placing a normal radar transmitter right next to VHF/GPS/WiFi/Cell antennas is such a great idea. Sure there is (some) protection built in to a proper receiver but running the radar will degrade signal reception and might even cause permanent damage. Why not replace the upper one with a FMCW radar (e.g. Navico Broadband)? This will reduce the load on those inputs by a few orders of magnitude. It will also give you a choice of radar picture depending on the needs of the moment (FMCW being better at close range and seeing hard targets in rain and pulse radar being better at long range + seeing rain.) Even better, place the antennas on top of both radars. BTW this interference issue also holds just for the antennas themselves. Even two VHF antennas next to each other is definitely not recommended by the manufacturers. So what you call ‘straightforward’ actually isn’t in my opinion. It may look nice but electronically speaking such a concentrated antenna farm is not ideal.

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    Steve Dashew Reply:

    The Simrad BB is a definite possibility. We’ve been told that the antennae placement should be fine by folks who are expert in this, which we are certainly not. Also, the whips are further away from each other than it may appear.

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    Kees Reply:

    Steve, I just thought of two alternatives for your radar deflectors. 1) Make the deflector out of an absorbing material (at X band) that is a ‘black hole’ to the radar beam. This would reduce ghosting even more. 2) Make the top half of the structure carrying the antennae out of fiberglass; or maybe just change the upward carrying columns to be out of alloy tubing on the corners with fiberglass panels in between to recreate the current square look and hide all the cabling.

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  3. David Sutton Says:
    Well said Steve. I have to say that this is another excellent example of how you design a WHOLE vessel and not just a collection of systems and structures. On so many vessels this is merely an afterthought, which is alarming as it can turn out to be a serious safety issue if your nav or coms don’t work properly. This is especially true when these systems are not integrated into the vessel from the factory and are added on later. Personally I have had wonderful support from Shakespeare when designing a system. If you get a hold of the right person they can give you excellent feedback on where the interference issues will arise. I suggest such measures to all who are looking at investing in modern communications and navigation systems. Looking forward to seeing some interior and engine room details soon. Cheers, David

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  4. David M. Says:
    Steve, With an increasing number of electrical systems being added to an aluminum boat what new safety feature are you adding to protect critical systems from lighting strikes? David M.

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    Steve Dashew Reply:

    To date we have had only one of our aluminum yachts hit by lightning (of which we are aware). So, we think the natural tendencies are probably favorable compared to plastic. That said, there are measures that can be taken between antennae and the devices to which they are attached, that we have installed at owner’s request.

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  5. John Ozechowski Says:
    Have you considered an optical sight? Something with both Low level TV and Infrared?

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    Steve Dashew Reply:

    Not so far, John: Until recently, did not see their value cost wise as the stabilized units we looked at were $60,000+. Understand that is c hanging. It is the t hermal imaging that is most interesting to us (ice!).

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    John Ozechowski Reply:

    If I should win the lottery or something and be able to afford one of these beautiful boats, I will want the optical sight on it. I work with these things and they have become the most useful tool we have. Besides ice they are also incredible good at picking up other floating objects (Except for a brief time at sunrise and sunset just about everything floating is a few tenths of a degree hotter or colder than the sea water. Floating objects show up very easily. Also with the image displayed on one of your screens you can keep a watch behind you (for example) without having to be constantly turning around. And it comes in handy for seeing things much closer up. The zoom on some units is pretty good. (Please note that I do not work for any IR company. I just like the tools)

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    Steve Dashew Reply:

    More detailed info would be welcome, including recommended models.

    Patrick S Lasswell Reply:

    When the Navy Reserve showed a certain federal law enforcement agency with maritime province their set of (older) toys in 2007, the most interest was generated by the optical systems we got from FLIR. As a matter of full disclosure, the nice people from FLIR live just down the road from me and I am inclined to say nice things about them. In my experience, they do as much as they can to ease my conscience in doing so by providing stellar quality equipment. Since the wars currently in play are being put on the back burner for reasons not germane to this discussion, the nice people at FLIR might be looking more seriously to their commercial applications. I cannot vouch for this system personally, but it seems pretty good for an inexpensive option: http://www.flir.com/cvs/americas/en/maritime/view/?id=54280 When I am spec-ing your yachts for military use, I have something a lot more like this in mind: http://gs.flir.com/surveillance-products/star-safire-hd/hd I expect the latter to cost at least an order of magnitude more than the former, and I’d want at least two of them outboard of the superstructure horns, and I’d prefer four to seriously counter swarm attacks.

    John Ozechowski Reply:

    The Star-Safire is the Cadillac of the FLIR systems line. The non-HD version cost about $275K in quantity and weighs about 110 lbs. (So I’d expct this one to come in at closer to $300K each) Video performance is unequalled though. Also can include laser range finder, autotracking, spotter scope (2 deg field of view, high magnification). Great sight but you pay for the performance.

  6. John Ozechowski Says:
    I’m most familiar with the FLIR systems units. The non-military one that looks like the best fit is the M-618CS. It is a 640×480 thermal/daylight gyro stabilzed unit. I found one price (shopepal.com) for $34K

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