We have people sending High Altitude Balloons around the world trying to use LoRaWAN and making progress on each launch, so I guess one question is how many boats do you want to send out before you get the comms working reliably.
If you look at the maps of the gateways (home page of TTN plus http://ttnmapper.org) you’ll see that there is a lot of blue and only a few dots in some places.
Yes, I guess you are right - lots and lots of blue!
I’m slowly coming to the realisation that this projected is either going to turn in to a fun thought experiment or become significantly more expensive that I first anticipated! 
Thanks for your input - back to the drawing board for me!
The advantage of satellite systems is that they work.
Most of the 868\915 modules will actually work on either frequency, but at reduced efficiency and range.
I would expect that you will only get contacts when within 2km to 5km of the coast, and only when there is a Gateway in that area. In a lot of places in the World there wont be a gateway in range.
Yes, the satellite would be best for a constant regular update.
I’m just trying to weigh up the risk of sending something out with only Lora in the hope that it might come into contact with a gateway at some point and be in range long enough to upload the historic cached data. I’m not really bothered about getting regular updates, I’d just like to see where it has been and maybe some other interesting info, but it’s pointless sending it out if I’m not going to get any updates at all. Writing the data locally while out of range then uploading when in range would be fine. I also have to consider that I don’t really want the boat to get too close to the shore in case it runs aground.
Having said all this, I haven’t a clue how I will even code the navigation system as the project is still in the very early information gathering stages!
Thanks again for your thoughts, it is really useful to get an expert opinion. 
And that concept is not a good fit for TTN, there are significant limits, both fair use and legal, to the amount of data you can ‘upload’.
Gotcha! I guess that Lora is out for this project and I’ll need to start saving for a satellite module!!
I would not dismiss it entirely.
But what you really need to do is organise your own a range test, to see how far reception really does go out to sea.
Cool, I’ll keep that in mind. I’ll be sure to report back if I get any further with this. I’m really excited about Lora and what it can do.
Thanks again. This is one of the few forums I’ve hit where there has been a super fast, friendly and helpful response. Keep up the good work! 
There is a formula about Line of sight calculation and if you add “1m” into it the reachable LOS is 3,6km. Not too much. Thats why ssailboats have the VHF antenna at the top of the mast ;-). So only baloon coverage or very close to land will help you transmitting your data unfortunately.
The situation is better than 1m. There maybe gateways on tall buildings near the coast, line of sight from the sea surface to a 100M tall building is ~36km. For example if one got within (say) 20km of New York I suspect there might be a reasonable chance of making a connection. You could plan your route to pass near big cities and/or known gateways on mountains etc.
If there is even a small swell near the craft then even that 1m may get lost! Plan on average height as 0m to allow for fact some time will be spent in troughs between wave peaks 
Then retry the formulae…(Obviously in heavy swell if craft at wave peak then you ‘may’ get suprisingly good range - but dont plan on it! 
)
Won’t the onboard accelerometer mean the uplink will occur at the bottom of the trough.
This is all rather academic as coverage along the coast for most of the world is non-existent and duty-cycle / FUP isn’t going to allow much in the way of catch up on data.
Would be better to put in an HF transmitter on morse …
Detect the moment of near weightlessness/highest -ve G force and Tx immediately?! 
…but agree with rest of your comments and others - not a great use for LoRaWAN/TTN unless using satellite! 
Hi folks,
Thanks so much for all your thoughts and feedback, it’s great to see that my question has sparked an interesting conversation and I appreciate all the responses.
They have given me a lot to think about. Maybe satellite comms with Lora backup.
I do like the idea of tracking the position on the wave and transmitting at the maximum height! I have yet to figure out the navigation system, how to track waypoints and avoid landfall, so this will add to my code requirements. 
If you want a small vessel to roam the seven seas I’d image it carrying an AIS transceiver to stay clear of big vessels. Such an AIS transceiver would also broadcast your boats position to surrounding vessels, but this signal is also picked up by satellites and the position can be watched for free on many vessel trackers. See Automatic Identification System on Wikipedia (no link as my user is to new)
I have googled around a bit and found this
Adding a LoRaWAN module would be a great thing to map out gateway on the coasts.
Hi Dekarl,
That’s a great idea which I didn’t know about, thanks!
I was aware of the AIS transceivers, but I wasn’t going to bother installing one in my boat since it will be under the minimum size requirement to necessitate one. I wasn’t aware that I would be able to do free satellite tracking if I did install one! I definitely need to do more reading into this hardware and how it would connect into the other devices in my boat.
I really appreciate you taking the time to have a Google about it for me and for providing the links. They were very interesting and have giving me lots of information about tracking my boat.
I still think it would be a good idea to install a Lora module due to it’s low cost and low power requirements and it would be a backup for gathering data from my boat and as you say I could plot costal gateways.
Thanks again for your thoughts and ideas!
Dochas.
No one said that. Re-read the post, it was “the position can be watched for free on many vessel trackers”, you should find out if getting the signal through the receiver network is free before you embark on any great voyages.
Ah yes, I guess I was a little over excited at the thought!! 
You are right, after some research it seems that the AIS trackers I have looked at charge to update their position via satellite. Sill might be worth considering though.
Thanks!
I believe that the satellite reception of AIS was effectively a hack (not the original intention, but satellites can hear it so it grew from localised to global). Which is pretty cool. There are net-tracking AIS receivers that would seem to be appropriate (cheap, waterpoof) for your purposes (random example, not an endorsement) – hopefully strong enough for the satellites to detect.
In an attempt to stay on topic for TTN: A LoRAWAN device would/should use a GPS location to switch bands, although I don’t know if there’s a dataset for that. There are not (m?)any stacks that can do simultaneous bands (without recompiling), but I’ve been working on it in the background and while it crashes for OTAA (some state somewhere…it’s hard) it’s working for ABP reliably. Can share, I need to get it into a state I can submit a github pull request but fixing OTAA seemed important
While I’m here, check out the r/autonomousboats subreddit. I’ve been collecting interesting stuff there on this topic, please add whatever you find.
Good luck!
Hello!
Thanks for all that really useful information, I really appreciate you taking the time to post. I shall investigate the links you have posted, particularly the Reddit forum as there seems to be a lot of useful information there. I’ll be certain to contribute any useful info on my travels!
I hadn’t even considered the need for switching bands for the location - in my ignorance I just assumed it would do as you said and broadcast and receive on both at the same time. I appreciate the heads up. I’ll add that to my list of issues!
Thanks again for your time.
Dochas.