Power on the hard - HELP - 50 amp

Good morning. Hope everyone had a terrific Thanksgiving.

I am new to a 50 amp system, always having a 30 amp connection to the boat's power system. Simply plugged it in and it worked.

I have tried the following and am unable to get power to the boat. I want to charge the batteries fully and disconnect. I would like to have power to do work on the boat over the winter. ANY help is appreciated.

I tried a connector that goes from the 50 amp plug to just a regular 110 plug - I don't get any power. I tried two different locations at the marina that have power. The stantion and a regular receptacle.

I tried going from the 50 that then split it to (2) 30's Hubbell YQ 230 - see picture. Still no power. I tried splitting it up and went to different locations in the yard with (2) 50' extension cords. I tried plugging them both in to one outlet. Still not goo.

Anyone with a 50 amp boat? How do you get power to it over the winter?

Do you have a copy of the wiring schematic (back of owners manual)? I looked online but things are not matching up like I would expect. There is an option for a single 50amp boat plug, but its 220v/50hz (US should be 220/60). The boat is a 1999 340 Sundancer correct?

Do you know of you have an isolation transformer on board? We have seen that before, and it would would most likely require a true 220v feed to the boat.

Can you snap a pic of the electrical connector on the boat itself (50a socket), one of the AC panel, and each end of the cord you used during the season?

Is there 30 amp receptical at the marinia? If so all you need is a 50 to 30 amp adaptor . I bought mine at west marine 2 years ago and works great to charge batteries and gives me power when I need to do work on the hars

I bought this a few months ago and it's been working fine to keep the battery charger going (and then I use the outlets as needed (i.e. for a vacuum or buffer)).

https://www.amazon.com/gp/product/B00VRY919Y/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1

50 amp for a 340DA?? I don't recall any every built. Euro models were 220VAC 50hz but still not configured for 50 amp loads.
So let's assume that someone modified the boat for a 50 amp service and it was done correctly with the correct circuit protection. Let's also assume your boat's equipment all operates on 120VAC like all other US spec 340DA. All US 50 amp services consist of four conductors of which all four are used if there is NO isolation transformer installed. If an Isolation transformer is used then three of the four are used.
Without Isolation transformer - two 120VAC legs out of phase (one red and one black), one common (white), and one ground (green).
With Isolation transformer - two 120VAC legs out of phase (one red and one black), and one ground (green).
If your boat has an isolation transformer you must provide it the two 120VAC legs (which together make 240VAC) that are out of phase. Providing two extension cords from the same source circuit will not provide the system the out of phase voltage that it needs to operate the transformer. The transformer then generates 220VAC and has a tap in the windings to make two 120VAC circuits. So as you can see, if with an isolation transformer, the supply power is not correctly out of phase it simply will not operate.
If your boat is using the 50 amp power without an isolation transformer then the white wire is required for both of the 120VAC legs as that is the return. Your arrangement as explained should work; however, be cautious that those tiny extension cords must be protected with probably no more than 15 amp circuit breakers. Regardless, this should be good for battery charging and plug-in tools.

Sounds like someone might have done a modification to your boat.
Just to be safe and eliminate any confusion:
Post pictures of the receptacle on your boat and your 110 panel in the cabin for positive identification.
Chances are good, even if there was a modification, that someone here will recognize what you have and point you in the right direction before you go and buy stuff you may not need.

Fire Marshall’s don’t allow unattended winter stored boats in boatyards to remain plugged in around here so the setup can’t be permanent.
Plus there are limited outlets where I store so courtesy prevails.
Check with your boatyard operator before leaving your unattended boat plugged in.
To get from the two 30 Amp receptacles on my boat to a single 15 amp outlet at the boatyard for the winter I use:
A Y adapter with two female 30’s to a single male 30.
A pigtail adapter with a female 30 on one end and a 15 male on the other.
A 12/3 heavy duty extension cord.
The adapters and connections are all in the trunk, under the shrinkwrap.
The extension cord snakes out from under the shrinkwrap.
I keep the extension cord rolled up and bungeed to one of the boat stands under the boat.
When I need electric I unroll the cord and plug it in to the boatyards outlet, then roll it up again before I leave.

My 2000 340 had two 30 amp connections NOT a 50 amp connector. BUT my dock had 50 amp power. I used a Marinco 50 amp male to two 30 amp female Y splitter. As others have asked, please take pictures of your power receptacles on the boat. I also have never seen a 50 amp 340.

What is the stantion or source? 30 amp or 50 amp?

Here is your YQ230 splitter. You must have two sources of power or it will not work. They must be on separate phases.

There should be light on your adapter. If the light is not ON then adapter doesnt sense two separated phases. If the light is on then you should have correct output. Make sure that switches on electrical panel are in correct positions. Shore power not generator, main switch on etc. Some boats have main breaker before electrical panel.