FleetOne antenna relocation & new composite antenna mount.

Composite antenna mount.  

The Cobham Sailor Fleet One Inmarsat system was an 'add on’ by the prior owner. The antenna was mounted atop a Scanstrut pole and its two struts (forming a tripod), all of which was wedged into the cluttered transom/cockpit area. One of the struts obstructed the port side cockpit locker lid, preventing it from opening fully. There were other additions, including solar panels, mounted in the shadow of the a wind generator, which reduced their output by 50%. As you can see in the photo,  Sakura was bristling with high-tech and no-tech clutter. (The photo reminds me a bit of the Apollo lunar lander model I had as a kid.)   In an effort to simplify things I have removed both the wind generator and the satellite antenna's scan strut pole, along with several other items,and am re-thinking the various parts and pieces and how the entire collection can be more coherently integrated.  When the boat is reassembled I will post before and after pics.  

As already stated, Sakura was equipped wth a Cobham sailor FleetOne satellite telephone and Redbox router.   I had been advised that this system was out of date and decided to replace it with the  cheaper, faster and more popular Starlink.  I have since reconsidered this and will retain the Inmarsat system, and use it for emergencies, weather, and minimal messaging.     

Revising the Antenna mount.

The FleetOne antenna is fairly compact and at 2.6kg is not terribly heavy.   After some thought, I decided to mount it on a platform bolted to the arch and extending forward far enough for the antenna to clear the solar panels. (The stern light is at the rear and must remain unobstructed)   While at the boat I templated the curve on the top of the arch so I could construct a fitted composite bracket at home.  

There were a few things to consider in designing the mount:

• it must be compact, lightweight, and adequately stiff and fatigue-resistant as the antenna is a mass perched at the end of a lever that subject to constant cycling..  
• The antenna mounting area is flat while the other end must conform to the curve of the arch, where it will be secured with the 4XM8 through-bolts that had previously secured the wind generator's mounting post.   
• The solar panels reside above where the bracket will mount, so the bracket must be low-profile enough fit beneath them.
• There should be access to the wiring opening on the top of the arch, which will be covered by the bracket, otherwise future access will be quite inconvenient.  This may not matter much in practice.   I will prepare by making a curved panel that can be secured as a cover.   
• The installation should be simple, require zero maintenance and not look like a DIY effort.  

With all that in mind, I decided to use two layers of  a honeycomb core material called Nidacore, sandwiched between mulitple layers of biaxial stitch-mat, laminated with epoxy resin.  (Nidacore is not ideal for this, but I had some on hand)  Construction is kinda' like one of those hazelnut wafer cookies that shouldn't be good, but is.   

After making a form from some scrap, the various alternating layers were progressively laminated.    The Nidacore layers were beveled at one end to conform to where they  landed against the transition to the curved section, and this bevelled area was bedded/bonded with very thick glass-filled epoxy putty for strength and to ensure no voids.   . (This is the where the stresses from the constant flexing will concentate).  The 'glass was tripled across that area as well, but otherwise runs end-to end for strength, including a lamination between  the two layers of Nidacore,  The exposed edges were filled with dense glass-filled epoxy putty which was smoothed and radiused, then glassed over twice by wrapping the edes of a final bottom layer of stitch mat up, and then this overlapped with the top layer down around the entire perimeter. .In the photos you can see some carbon fibre tape laid into both sides beneath those final layers of stitch mat.   No reason for this other than I had some on hand, as one does, but it likely adds to the stiffness.  (and will make the boat go faster)  Before the final laminations were done,  the antenna mounting  holes were laid out and bored oversized, then filled with putty and pilot drilled.  Finally, reinforcing discs were fastened where the mouting bolts bear.    It will require some trimming to fit and will therefore be painted on site.  I will use 3m 4200 to bed/adhere it to the arch for extra security and to prevent it from shifting/wandering.  

 

Dimensions of the antenna below.  One thing I should have provided for but did not, is the mounting footprint of the slightly wider Starlink antenna.   Making an adaptor is pretty straightforward, but less elegant..  

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