We started playing 50 Fathoms in the end of 2016. We usually build our world ourselves and tinker with the mechanics (in the sense that we take the core rules and companions and add new edges or setting rules as needed), so we did with 50 Fathoms, too. Now, with the Adventure Edition, I went over it and tried to streamline it a bit more so it fits to SWADE. 50 Fathoms feels a bit dated now and doesn't seem to fit into the design philosophy of SWADE anymore.
Here are my impressions and suggestions about the game mechanics. I hope you find them useful for your own game or even for an update of 50 Fathoms.
Keep in mind these are just my impressions and considerations. They're subjective and not meant to be valid for every game. Maybe they're not even universally valid for ours
Also, please feel free to comment on them!
Unnecessary rolls
Rolling for travel time just eats up time without adding anything to our game, because a few days more or less usually don't change anything. If it matters, playing scenes or even Savage Tales to determine if the crew is delayed or gets by faster seems much more interesting than rolling on Boating every day. Now that SWADE has guideline travel times for sailing ships, we just use these.
The same can be said about determining the costs of Carousing. Even if you track money (we do), the money spent for carousing isn't worth randomly determining in my opinion. A guideline (in the case of 50F, 5-30 pieces of eight per evening) is completely sufficient.
Rolling to get drunk wasn't only never relevant, it's also a bit confusing in connection with spending more money to get rid of more Fatigue. So you spend more money to party harder but actually don't get drunk but order a band and dress up all fancy?
Related to this, Squanderous seems rather irrelevant. Doubling the price of carousing (which never mattered much to us) with a Hindrance that is as "heavy" as Poverty – which would fit the description as well and might have a noticeable to huge impact – seems unbalanced and superfluous. Frugal looks similar. (We had PCs with both of these)
Naval Combat
Covered by the Core Rules now, so that's how we run it. Using the rules for linked weapons was actually suggested by DoctorBoson before already, that cut down the number of dice for one broadside considerably.
With Deluxe, we got rid of rolling the lower of Shooting/Boating for shooting cannons very quickly. Together with a -2 (Unstable Platform), it's hard enough for the NPCs to hit at all to the point where shooting cannons was so boring that everyone just went for boarding immediately. For the PCs who want to get actually proficient at the cannons, raising two skills in addition to getting an Edge (Steady Hands) seems overkill.
Storms
I found these very harsh (basically it feels like "go Ace&Mage or go bust") and had the impression that they had a bit too many random elements (card draw and two dice rolls vs. one skill roll). After making sure they're actually as harsh as I read it and using them a few times in our game, I just replaced them with Dramatic Tasks. Maybe an updated version will fit with the new Dramatic Tasks?
Enabling Edges
Some of the Edges allow you to take specific actions so Skill get useful at all. I was told that this was a holdover from older design philosophies of Savage Worlds; in any case, buying a Knowledge skill to get an Edge to be allowed to use your Repair skill to repair guns (Gunsmith) or your ship (Ship's Carpenter) didn't sound appealing, so we got rid of that. McGyver and Mr. Fix it cover the uses of these Edges or the character specialization rather well.
Combat Edges
Dirty Fighter: Outdated because of the new tests, replaced with SWADE's Feint.
Improved Dirty Fighter: Really overpowered* in my opinion. I actually tried this in a bunch of games because it was in the german Core Rules, the only way to not make it overpowered is being stingy with Bennies, and who would want that?
Leadership Edges
Board 'Em: Doesn't seem to fit in with SWADE's take on flat bonuses, but since nobody ever took it, we didn't look into it much. Looks like a Support roll with Persuasion or something similar by the commander would cover that already.
Master & Commander: Not in active play atm, but since it's similar to what Ace did before, maybe just grant the crew a free reroll instead of the +2.
Professional Edges
Boarder: I'd swap the +2 for a free reroll to align with SWADE's other bonuses.
Rope Monkey: Rather complicated and needed a roll every time – two PCs took it so far, was used maybe once in total. Changed to granting the effects of Acrobat and Combat Acrobat when moving in the rigging (and also granting it for climbing in that case).
Scout: Why not just Danger Sense?
At least with SWADE (and the streamlined rules for surprise), having both Edges in the game would be pretty strong. Of course, you might just throw out Danger Sense and keep Scout.
Social Edges
Reputation: Gone with Charisma, I guess
Weird Edges
I'm not entirely sure what to do with the bonuses. Giving out free rerolls would probably yield silly results in combination, especially with Ace. The card drawing should still be fine even if you replace the storm mechanics with SWADE's Dramatic Tasks, though.
Ships
Need to be converted to SWADE stats. I took a few guesses and stats for our game. If anyone is interested, I could post them here later.
Gear
Cannons seem to have an abundance of detail. Not only can you fire different sizes, but you also have to track all these cannonballs and chain shots and whatnot, you also have to keep track of the gunpowder (convert casks into cargo space, calculate powder needed for your cannon size...). For understanding how to track cannon ammunition, I have to read p.28, p.30, p. 31 and p. 43.That's a bit much, don't you think?
Reloading times for cannons are in SWADE now, so we either use these or ignore them completely when Chase rounds are much longer than the usual six seconds because of the slower movement of sailing ships.
Careening
That seemed to be a bit too detailed for an FFF game (or any RPG in my opinion). Does anyone use these a lot?
Crew Upkeep
I found it a bit fiddly to calculate and subtract rations for each man and day in comparison to the simpler mechanics of the Science Fiction Compendium, so I'd rather track it just by day and adapt it to the crew size, if needed (E.g. if the crew size is suddenly halved after a particularly nasty fight).
Powers
Magic probably needs a revision as well, but since no PC ever wanted to play a mage, we didn't put time into that.
*Enemies have these, too, so it's not unbalanced in favour of PCs. Still no fun for us.
Here are my impressions and suggestions about the game mechanics. I hope you find them useful for your own game or even for an update of 50 Fathoms.
Keep in mind these are just my impressions and considerations. They're subjective and not meant to be valid for every game. Maybe they're not even universally valid for ours

Unnecessary rolls
Rolling for travel time just eats up time without adding anything to our game, because a few days more or less usually don't change anything. If it matters, playing scenes or even Savage Tales to determine if the crew is delayed or gets by faster seems much more interesting than rolling on Boating every day. Now that SWADE has guideline travel times for sailing ships, we just use these.
The same can be said about determining the costs of Carousing. Even if you track money (we do), the money spent for carousing isn't worth randomly determining in my opinion. A guideline (in the case of 50F, 5-30 pieces of eight per evening) is completely sufficient.
Rolling to get drunk wasn't only never relevant, it's also a bit confusing in connection with spending more money to get rid of more Fatigue. So you spend more money to party harder but actually don't get drunk but order a band and dress up all fancy?

Related to this, Squanderous seems rather irrelevant. Doubling the price of carousing (which never mattered much to us) with a Hindrance that is as "heavy" as Poverty – which would fit the description as well and might have a noticeable to huge impact – seems unbalanced and superfluous. Frugal looks similar. (We had PCs with both of these)
Naval Combat
Covered by the Core Rules now, so that's how we run it. Using the rules for linked weapons was actually suggested by DoctorBoson before already, that cut down the number of dice for one broadside considerably.
With Deluxe, we got rid of rolling the lower of Shooting/Boating for shooting cannons very quickly. Together with a -2 (Unstable Platform), it's hard enough for the NPCs to hit at all to the point where shooting cannons was so boring that everyone just went for boarding immediately. For the PCs who want to get actually proficient at the cannons, raising two skills in addition to getting an Edge (Steady Hands) seems overkill.
Storms
I found these very harsh (basically it feels like "go Ace&Mage or go bust") and had the impression that they had a bit too many random elements (card draw and two dice rolls vs. one skill roll). After making sure they're actually as harsh as I read it and using them a few times in our game, I just replaced them with Dramatic Tasks. Maybe an updated version will fit with the new Dramatic Tasks?
Enabling Edges
Some of the Edges allow you to take specific actions so Skill get useful at all. I was told that this was a holdover from older design philosophies of Savage Worlds; in any case, buying a Knowledge skill to get an Edge to be allowed to use your Repair skill to repair guns (Gunsmith) or your ship (Ship's Carpenter) didn't sound appealing, so we got rid of that. McGyver and Mr. Fix it cover the uses of these Edges or the character specialization rather well.
Combat Edges
Dirty Fighter: Outdated because of the new tests, replaced with SWADE's Feint.
Improved Dirty Fighter: Really overpowered* in my opinion. I actually tried this in a bunch of games because it was in the german Core Rules, the only way to not make it overpowered is being stingy with Bennies, and who would want that?
Leadership Edges
Board 'Em: Doesn't seem to fit in with SWADE's take on flat bonuses, but since nobody ever took it, we didn't look into it much. Looks like a Support roll with Persuasion or something similar by the commander would cover that already.
Master & Commander: Not in active play atm, but since it's similar to what Ace did before, maybe just grant the crew a free reroll instead of the +2.
Professional Edges
Boarder: I'd swap the +2 for a free reroll to align with SWADE's other bonuses.
Rope Monkey: Rather complicated and needed a roll every time – two PCs took it so far, was used maybe once in total. Changed to granting the effects of Acrobat and Combat Acrobat when moving in the rigging (and also granting it for climbing in that case).
Scout: Why not just Danger Sense?

Social Edges
Reputation: Gone with Charisma, I guess

Weird Edges
I'm not entirely sure what to do with the bonuses. Giving out free rerolls would probably yield silly results in combination, especially with Ace. The card drawing should still be fine even if you replace the storm mechanics with SWADE's Dramatic Tasks, though.
Ships
Need to be converted to SWADE stats. I took a few guesses and stats for our game. If anyone is interested, I could post them here later.
Gear
Cannons seem to have an abundance of detail. Not only can you fire different sizes, but you also have to track all these cannonballs and chain shots and whatnot, you also have to keep track of the gunpowder (convert casks into cargo space, calculate powder needed for your cannon size...). For understanding how to track cannon ammunition, I have to read p.28, p.30, p. 31 and p. 43.That's a bit much, don't you think?
Reloading times for cannons are in SWADE now, so we either use these or ignore them completely when Chase rounds are much longer than the usual six seconds because of the slower movement of sailing ships.
Careening
That seemed to be a bit too detailed for an FFF game (or any RPG in my opinion). Does anyone use these a lot?
Crew Upkeep
I found it a bit fiddly to calculate and subtract rations for each man and day in comparison to the simpler mechanics of the Science Fiction Compendium, so I'd rather track it just by day and adapt it to the crew size, if needed (E.g. if the crew size is suddenly halved after a particularly nasty fight).
Powers
Magic probably needs a revision as well, but since no PC ever wanted to play a mage, we didn't put time into that.
*Enemies have these, too, so it's not unbalanced in favour of PCs. Still no fun for us.
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