A friend and I were just speaking of such things last night - though not in relation to boating. He has one of the(Below) mentioned devices - which works fine - with no Ethernet connection to an internet source - though that can be done, as well, if you have "Cable or DSL". He used his to "take advantage of Wi-Fi that may be available", until he signed-up for service - which he did - eventually...(Get me?), though should work fine for what you are speaking of, as well. In other words, you may not always/ever use the standard router-to-modem functions it can provide, but, for the price/size/potential of the repeater section, the normal, Ethernet functions take-up little extra space - just looks like/is, also, a normal router, if/when you can "plug-in".
So, add to your List of Wi-Fi "boosters" to check-out -
Hawking Technology HAW2R1
There are several other models - some made to be "completely" outside mounted(12v? Don't know..? HAW2R1 is a "wall wart" unit, so maybe, it, too, could be used with DC..?)...
It's not a booster, perse - though it is... It does the booster-thing a somewhat different way - which should eliminate the possible difficulties of "standard" boosters, which try to amplify the channel you are trying to use(Sometimes with unsatisfactory results.)... This model is a rather standard router, with dual-diversity antennas(Long used for wireless microphones, etc. Wi-Fi calls it "MIMO"), to "choose" the best signal getting to wherever your device is, in relation TO the router. So it has two antennas to distribute Wi-Fi to your devices - a feature seen on many routers, today. However, this unit has a third antenna AND a separate transmitter and receiver, acting as the "repeater", that, rather elegantly, "creates a whole separate network"(Read-up on it.). The "R1" model has a "high-gain/directional" antenna(Others available - whips, outdoor, etc.), FOR the "separate" network it establishes for itself(Changes nothing on how you use your devices to "do" Wi-fi.). Though much of the high-gain is likely provided by simply putting the antenna outside or up higher, or in a "better spot", using a coax cable from the unit, rather than the usual antenna stuck on the back of the router under a table, it should be "better" all the way around.
The "extra hardware" on the hawking device is remindful of the old "Wi-Fi PCI cards", used before Wi-Fi was put into most devices, to get Wi-Fi from "some other wireless modem" - maybe even in your neighbors house..?
All that said, you may appreciate having a "real computer" available to set it up, on the web(Often easier and more comprehensive - more settings - though you can set it up simply, from it's own CD, as my friend did - he had no computer, only phones, at the time.) - just like any router.
A very non-precise explanation of what it does would be that the unit gets it's Wi-Fi, from the marina's router(Say, "Channel 6" - whatever?), in the low router band(2.4Mhz.), then, converts and distributes it to your devices on "some other" Wi-Fi channel, automatically(Same band. Say, using Channel 11, instead.), so you have a "clean" Wi-Fi channel of "your own" to use, while it "hides" Channel 6, from your devices "available Wi-Fi" view - you, just "logging-in" as normal, first, to the marina Wi-Fi, then, your devices to YOUR Wi-Fi. So, yes, a bit more "fooling around". Though, again, should work better - potential for hundreds of feet better! And be simple enough. Matter of fact, you could "allow distribution" to other friendly boats, nearby, by shouting over your log-in info, to aid in their suffering, as well - though it also offers all the usual security features.
Worth a look. "Search" Hawking Technology - their devices available lots of places. Basically, a "300N" router, with "repeater. May do the trick. Price - quite reasonable. "True Outdoor" models not quite so "quite", though still reasonable.
By the way - When you run into poor Wi-Fi at a marina(Camp Ground, etc.), you might suggest that the owner investigate one of these widgets for their use? To any visitor with the password(Or if left "open"), it may improve Wi-Fi for the whole place - over just opening-up his "normal" router for customer use, again, at a reasonable cost.
The addition of one or more of these widgets around a large space could be just the ticket.
On the other hand(As inferred, above.), IF you have a modern Wi-Fi router, with "removable/changeable" antenna ports(SMA-type jacks?), ANY "gain/directional" antenna(Cheap to pricey!) to replace what's there now, or, even putting a coax cable on the router, then running the cable to a window and attaching the router's own little "rubber ducky" antenna to the end of the cable, may provide a considerable boost in signal with no further effort, at all.
...73's back at ya
