Eaux mon creech! Mar a thuirt Sinatra, "Where will I begin?"...
This could take a while...
Tha mi air bàta-survey his an ceann tri seachdainean
Now, faced with that, I thought, "What's this 'his an ceann' business?" So I l00ked at the English: all I can assume is a mispront where you've put "his" - not sure what for though. Anyway, if I wanted to put something like "I'm on a survey ship for the next 3 weeks" into Gaelic, I think "fhad" might feature somewhere ("fad" would do) - something like "Bidh mi air bàta-surbhaidh fhad 3 seachdainean" - or possibly "fhad na h-ath trì seachdainean" if it's not obvious you're starting now.
Bidh mi ga' feuchainn a sgrìobh innteart leabhar-clàraidh gach latha.
The big puzzle here is "innteart": what is it? Anyway, so you'll be trying to keep a diary of events. One thing you should mind is that, when you look up a verb in a Gaelic dictionary, that's exactly what you get - a VERB - which is not often the same as the associated noun-thingies. In English, these "noun-thingies" are things like (let's take the verb "write") writing (present participle), written (past participle) and write (as in such constructs as "I can write" or "I am trying to write"). The point is, just because you find "sgrìobh" in the dictionary doesn't mean you can use "sgrìobh" for all those noun-thingies - it is actually a proper verb: it does NOT mean "to write", it is not an "infinitive", technically, it is the "dependent present", something you'd get after, e.g. "nach" or "gun": "you say [that] you'll write" => "tha thu ag ràdh gun sgrìobh thu". If you want more af a noun-type "write", as in "i'll try to write", the form you need is "sgrìobhadh".
The usual term for a "log-book" (assuming you don't mean a set of trigonometrical tables etc.) is "leabhar-aithris". However, "leabhar-clàraidh" is understandable. Now, you have a couple of things wrong at the start of the sentence - you're trying to write it, but you've got something more like you're trying it (ga feuchainn): you actually need "a' feuchainn" here. Also, the usual way of saying you're trying to do something is to use "feuch ri", so "Bidh mi a' feuchainn ri..."
And then we're usually going to get the infamous "Gaelic inversion": literally, "I'll be trying a diary to write", as it were - so
"Bidh mi a' feuchainn ri leabhar-aithris a sgrìobhadh". Note where there ARE, and ARE NOT, apostrophes in that.
You're in Kodiak - fine. Just mind that it's always "fhathast".
I'm not too comfortable with "ullachadh", but I suppose it'll do. Can't think of a better way of saying "getting ready" at the moment. "In the evening" is obviously "san fheasgair". No doubt you'll be busy.
I lurv the construction "co-bàta" - never heard of it, but it's easily understandable. If I'd coined it, I'd probably be tempted to put "co-bhàta", but still.
Now, what you don't say is stuff like "Bha latha math". Logically, it might look OK - but it actually mean "A good day was" - and I suspect you don't usually say that in English: it begs the question "Was what?" So, what you'd usually do in Gaelic is to say "Bha latha math ann" - literally, "A good day was in it", which is the equivalent to "It was a good day" in English. Being a mite pedantic, you could say "Bha e na latha math" (It was in its good day), but "Bha latha math ann" is what people actually say and is simpler.
As for missing your ZZZs and being hyped up on coffee, it might be better to say something like "Chaill mi mo chadal agus cha robh ach cofaidh annam airson cumail nam dhùisg" or some such.
Tha thu toilichte, indeed! It's usually put "'S toil leam a bhith air bàrr nan tonn a-rithist"
Have fun - and don't forget that all the big brown bears, narwhals and other creatures you might come across are fluent Gaelic speakers and really appreciate it if you try to speak Gaelic with them.