30A to 50A changeover

It sounds like you're bigger than their average boat. Yes they can do it for one or two slips or yes you can use a twin 30A female to 50A male Y adapter, but you need to check if they have a 2nd 30A outlet on the pedistal for you to use. The adapter is a bit expensive (almost $500), but every 50A boat should have one on board. Eventually they'll visit a marina with only 30A available.
Check to see if your boat is 250v (most likely) or 125v (older Carvers come to mind) before you get the adapter or ask the marina to change over.

Yes the marina can go to a larger gauge wire normally required to increase amperage to 50amp. Also a new pedestal would be required unless they retrofited the exisiting one. Yes you can purchase a couple of different power cords that will work. Your suggestion would work but depending on how the boat is wired might not provide power to what you want. The better suggestion is from NYCAP and go with a double 30a to a 50a especially if you have access to one pedestal that has two 30 amp receptacles on it.

The marina may be able and willing to put 50amp service if you have an annual contract. The easiawst way is to use a smart Y

as others mentionned it will hook up to TWO 120/30 but they MUST be on opposing phases or the circuitry in the Y will not let any power thru.

FALSE, You cannot use a Y adapter and only plug it into 1 30 amp connection. A 50 amp connection is 240 volts, and a 30amp connection is 120volts. So plugging a Y into only 1 30amp connection will only give you power on probably half of your electrical panel (120volt stuff) and nothing 240 volts can work. You need 2-30amp connections to get 1- 50amp connection to work. Maybe you can run a 30 amp cord from another pedestal to where your's is located and plug the Y into the 2-30amp connections. With a Y, you can still pull 50 amps of electricity.

You may be able to find a step-up transformer to take your single 30amp, and convert it to 240 volts, but you will have limited usage and maybe only 25 amps of power.

It sounds like you've outgrown your marina. What any marina would be doing with a 60x20 slip with one 30 amp outlet boggles the mind unless it's a work or transient slip. You can get a 30 to 50 adapter, but that's something you only do for an overnight, in a pinch. You'll kill every 120v or 240v user on your boat.
With only a single 30 amp outlet at each slip I suspect that their main panel is maxed. Can't seeing such a marina swallowing the expense to upgrade for one boat. Sounds like you've got some sweet talking and/or more likely looking to do.

Ok, the 2nd 30amp outlet has to be run from a different wire(s) and breaker then the 30amp that is on your pedestal. For example if they have an extra 30amp outlet in the slip next to you that is being un-used, they could in fact use that wiring. What the poster is trying to say, they cannot take one heavy gauge hot wire with a 60amp breaker and wire two 30amp outlets from them and you could then get 220 volts/50amps from it.

But yes if they could wire a second outlet, you can use a Y. You can also take a 30amp shorepower cord, and hook it to another pedestal down the dock and hook that to one side of your Y and the other side to your pedestal and achieve 220volts 50 amps.

As for the Searay, it depends on the size and model. Most of the smaller searay's are 120volt 30amp shorecords. I've even run 55' and 56' sedan bridges that were wired for either a 240volt 50 amp cord, but were also wired for a 30amp 120 volt cord (but you could only run 120 volt items from it such as battery charger, refrigerator, water pump, but not items such as a/c's or hot water....W/D.

You have to be sure that each 30 breaker in the main panel are on opposite sides of each other, otherwise you will only get 120 V...not 240..would be surprised if all pedastel breakers are on same side of the main panel.

Check the boat in person and see if it has a 30amp plug on the port side of the cockpit next to the other one. If it is not there, it may have one in the garage under those opening hatches on the transom. I am pretty sure the sedan bridges from that era all had 120v 30amp outlets and the breaker panel should also indicate a 120volt 30amp breaker and be set up for it. Keep in mind, you will only be able to operate light items and will have to run the generator for anything wired for 240 volts such as a/c's, water heater, washer dryer, stove.......etc.

Just pulled up the specs on that boat and it seems to show (2) x 50 amps. Only time I remember seeing that they were 50/125 which means your situation may be more complicated than you think. When I've run into that in the past both 50's were needed, one for the a/c and the other for everything else. I'd recommend calling the broker Monday to get the facts and then speak with your dockmaster to get his suggestions. Good luck.

It s hard to give you precise advice since we re not sure of what the boat has

looking at that picture the cable looks small to be 120/240-50, it looks like. 120-50. This would explain why there seem to be 2 inlets on the pic and 2!listed in the listing

if so, you can plug either one to a 50 to 30 amp adapter. This will give you up to 30 amp service limited and protected by the 30 amp breaker onthe dock

if you don't gave any 220v appliances (stove compressor or dryer) you van plug the second one into an another outlet without worry about opposing phase

I do suspect tha 15 years ago sea Ray was still using "small boat" stuff and 120/50 was still popular

now if this is a 120/240-50 cord you need a smart y which will only activate with both legs hooked up and on opposing phase.

I use smart Ys once in a while on the 70 I run when stopping at marinas that don't have two 120/240-50 outlets. It works fine although we can't run everything obviously

IMO you can't go further without knowing what is on the boat now.

My setup has a single 50 and a single 30. I can use the 30 in a pinch but you have to watch the draw. Block heaters and AC together are a no-no with just 30 amps.

My previous summer slip had only 30 and it is managable if you are just using AC for dehumidification at the dock.

I have never ever seen searay use 120 volt 50amp shorecords. Remember Searay's are built on the east coast, and the 120volt 50amp is a west coast thing. I have run a 100 different Searays and most of them will have 1 120volt 30amp shorepower cord, even if the boat was wired for a 240volt 50amp cord. I'm willing to bet money that that spare cord is a 120volt 30amp connection.

I think you should talk to the marina manager before you do much else.
Besides the fact that we really don’t know what you have for power cords on the boat, you also don’t know what might be available from the marina.

Even though there is only one 30 amp outlet at the pedestal, the cable FEEDING the pedestal may have enough conductors to make an additional 30 amp 125 volt outlet a pretty easy fix.
I know that every outlet in our little marina was wired this way and that was done 30 years ago.
Any electrician that has a little knowledge of boats would most likely take this into consideration.
As Pascal pointed out, the outlets must be opposing phases to work without a hazard.
Further, if you are a good customer, ie; buy stuff from the marina, spend money at the marina, they are more likely to install a bigger cable & outlet for you.
Our marina has done installed 60’s for folks pretty much on demand, especially if the customer is going to stay and pays their bills on time…….
They may ask you for help on the cost, although our marina does not, they consider it an overall upgrade.
They also have the capacity to add more load, which is also a factor the marina manager would prolly know.

Get the real specs on the boat cords.
Talk to the marina people.
That’s where to start.