Sorry I can't comment on your design or function. I'm always leary about using other log ins to sign onto websites other than the one it is designated for. That goes doubly for Facebook and Google. But, that's just me.
As far as log books go I am planing on going the other way. I use a written log in a bound book as Capta describes where I keep my voyage log and any other notes pertaining to the boat. I plan on taking a photo of each page as it fills up (probably with my cell phone) and eventually upload it into a file in the cloud. Then I will have several backups of it and can access it whether I am on the boat or not. The one thing about a written log and notes on paper is it always works and will never get obsolete. Having back ups in the cloud (or on the phone) allows me access the data no matter where I am.
I came to this epiphany last week when I went to do a quick check on the boat and look at the sketch I made last season of dimensions for a new sail cover. The sketch I made was in the log book. I took a photo of the sketch and can now use it at home to fabricate the new sail.
This is a sensible approach.
We definitely want a record which won't disappear over time. Hand written is not bad for that but can get water damaged and does suffer from normal decay... but maybe not for the time span you have a boat.
When the ExCel spread sheet appeared it represented a sea change (pun intended) for me as a way to deposit, reference, access, manipulate all manner of information and data. It is incredibly powerful, flexible, adaptable. It has great graphic capabilities.. of course can be printed, or sent in an email, or posted to the www, transported on digital media (evolving technologies) Although I don't do it... you can insert/import photos. It's so flexible and powerful it seems it can almost do anything! Of course you can copy and paste and edit tabs or cells or even the entire workbook which is a very efficient way to work.
I set up an ExCel for each client/project I have with tabs for aspects of the project. I have annual tabs for which I use as templates for the next (new) year, editing out what no longer applies.
Writing is nice... when you can read it! But it's also not data. I prefer to enter information as text, numbers which is dynamic and not simply pixels such as a photo of a log book page. I also see immense limitations in template forms to fill in data. They are perhaps more organized... but inflexible.
I would be surprised to learn that sailors are not using excel for their "logs" as it seems a no brainer. It does require a decent size screen/interface to work with... so a smart phone is not optimal. But a tablet could work and definitely a laptop or a PC.... and those are seen more and more on boats.
Try it... you'll like it and never go back