2023.02.07 - Gone Cold Again

The last few days have been a little cold. Sub-zero temperatures overnight and never getting higher than around 7 Celsius during the day. As a result I've not done much to Naiad as epoxy work is next up other than to contact the moorings manager to see if there is another mooring that is full tide so that Naiad doesn't sit on the mud anymore. She is going to check and get back to me.

Instead I've been preparing a few other things in preparation for Naiad being the right way up again. Specifically, the AIS transmitter I bought back in October. This is a specially designed unit for small watercraft that do not have a chartplotter with an AIS transponder and was designed by a very clever chappie over in the States. There is a distributor in Spain meaning that buying one from this side of the pond doesn't incur horrendous shipping charges. The web page for the AIS can be found here: Open Marine.

The unit comes as a kit and is simple to put together following the very clear instructions and I had quickly assembled it back in October a week or two after it had arrived. Around that time I also bought a marine VHF handheld radio, an Icom IC-M94DE which has an integrated AIS receiver. With these two pieces of equipment Naiad has the capability to send and receive AIS information.

So what is AIS and why would a boat as small as Naiad benefit from one?

AIS stands for Automatic Identification System and many of the details can be found on this Wikipedia page. Suffice it to say that it is a system that broadcasts information about the vessel to the area around the vessel. Heavy commercial shipping is required to have class A AIS transponders fitted whereas lighter commercial shipping can use class B units. Pleasure craft do not have to use AIS at all but for those that do there are a number of other classes of AIS depending on what is required.

So why am I fitting Naiad with an AIS transmitter?

The problem with Naiad from the point of view of a large commercial vessel is that Naiad is small. So small, in fact, that she is virtually invisible to the naked eye from the bridge of a ship and also gets lost in the wave clutter on a ship's radar. This is true for most pleasure boats under about 50 ft in length. With an AIS transmitter fitted it doesn't matter how small Naiad is, she will show up in a ship's navigation system and not only that, brief details are also shown. More importantly, her exact location, course and speed will be known to any ship fitted with an AIS capable chartplotter and that is all of the big ones. Quite a lot of fishing boat also have AIS fitted for the very same reason. With one fitted they stand less chance of being hit by another ship when tending their tackle, for example.

So, I have the AIS transmitter, I have provisioned it, that is connected it to a computer and entered Naiad's details and I have checked it and the VHF by setting up the AIS in the workshop and going for a walk with the VHF handheld. Sure enough, I could see the AIS on the handheld and could query the AIS to find out Naiad's details.


Now I have to find somewhere to mount it. 

On top of the mast is the obvious place but if I do that. I'll not be able to fly a burgee up there. The next obvious place is on the afterdeck. Here the problem is firstly that the boom overhangs the stern so every time the boat tacked the boom would hit the antenna and possibly (probably) break it and secondly the range from the AIS so low down is very small. Probably less than 4 nautical miles.

After some thought I have decided that it will be installed on the side of the mast just above the shrouds. That should mean that the antenna doesn't protrude above the mast truck or not enough to get caught up in the burgee. It is also clear of all the lines so it will not get caught up in those and it it high enough to have a decent transmission range. At a height of 6m above sea level the range is around 6 nautical miles which is good enough for the places I'm going to be sailing.

Next I'll have to get a mount to screw onto the mast upon which the AIS will itself be mounted and a long exterior waterproof ethernet cable since this is how the AIS unit is connected to the power and control box which will be mounted in the cabin. That in turn also means that I have to buy a deck gland through which the cable will pass. The gland has to clamp tightly around a 6mm diameter cable but also allow an ethernet plug to be put through it as well. The plug needs a 20mm hole through which to pass.

The antenna mount was fairly easy to find albeit quite expensive. That should arrive in the next week or so.

I went down to the Yacht Club on Saturday last for the AGM and I was able to visit the local, very well stocked, chandlery. Needless to say they had a number of different deck glands and I found one that will suit.

The last part I had to buy was the waterproof cable. Armed with a tape I went down to the Hay Barn in which the mast is suspended from the beams and measured the length of the mast from the shroud partners to the foot. Then into the workshop to measure from the chainplates to the aft end of the cabin. Rounding up that came to a minimum of 6m meaning that I have a 10m exterior grade shielded cat 7 ethernet cable arriving tomorrow.

All the parts for the AIS are now either in my possession or on order and once they arrive I'll be able to make a nice wooden mounting block for the side of the mast upon which to mount the stainless steel antenna mount and install it. The fitting of the system together will have to wait until Naiad is almost ready to be launched as I'll need the mast up once the AIS is mounted in order to fasten the cable to the shrouds and run the cable through the deck and connect it up. Then I'll go for a walk again with the VHF and check that it is all still working.

Not much physical work done these last few days but a lot of money spent.

Time for a cup of tea.