Half of my AC panel is out

One leg on your shorepower cord isn't getting voltage on one of the legs would be my thought. 2 of the legs are 120V, third is a neutral. 2 hot legs of 120v, make 240v.

If using a 120/240 Vac shore power service, one of the legs is open from a open breaker, or open in the wire lead.
You may have hidden service entrance breakers also; Usually hiding in or around the hull near your service entrances connects are mounted.
I recall on some boats this size, there is a parallel breaker on the panel to join both sides to single 120Vac lead.

On that boat, Luhrs uses a 240v-50 amp cord, and simply splits the leg to 120v on one side of the panel (left), and 120v on the other side (right) of the panel, they don't use both legs together or 240v systems at all on that size boat.

If a single 120Vac lead was used.
If a 120/240V cord is used, then no parallel breaker.

Just the three pole connected together breaker as seen at the very top of the photo.

Get a multi-meter. Unplug the cord on the boat side. You should get 220-240V between the 2 L shaped circuits, and 120v between each L circuit and the flat blade circuit. If it's the cord and the cord is the age of the boat, just buy a new cord, they have a lifespan.

Replace the cord once you re sure it is the problem or at the very least the connector causing the issue. This this must be arcing inside and about to cause a fire.
Also if any evidence of arcing can be seen on the terminals of the inlet on the boat, replace the inlet. Number one cause of boat fires

Hot legs, split legs, poles ....ugh !
What was the O.P topic again ?!

Yup get a new cord as suggested .

Before spending the money on a new cord try a different pedestal. Power cords are pretty resilient. Where you plug into gets pretty abused. Would hate you to spend several hundred dollars only to find that the receptacle was bad. How many people have you seen plug in and not give their plug the clockwise turn that locks it. Then the plug wobbles back and forth in the receptacle with every gust of wind loosening the receptacle.

Question
If a boat has a 50 amp power cord but 110v appliances, can I plug that 50 amp cord into a single 30 amp shore power with an adaptor?

In an emergency, maybe.
Depends on a few other questions first;
Do you have 50A service 240 or 120Vac service entrance?
Any 240 equipment like A/Cs, water heater?
Why do you ask?

Do we need to open a new thread on this topic?

I have only one 30 amp shore power available at the dock and would like to buy a boat with 50 amp power cord.
Looking at Tiara 4400 Sovran 2005- I think it has all 120 v appliances

It is OK if I can not run everything at once

Man, That's a lot of stuff on that panel.
I can not imagine a later model boat with the old 120v-50A service.
I can not imagine that much A/C equipment running on a single 120V-50A line.
I'm sure it would have 120/240v-50A service.
Somewhere out of the picture must be A-B Buss switches and volt meters.

So, make a pigtail joining the red and black wires together, supplied by a single 30A service.
Still, In an emergency, maybe.

Myself, Less one hell of an emergency, I would not even try.

Is this a private dock with only one 30A service?

I can't see any problem in that.
It's dead obvious that you'll never be able to draw more than 30A, which depending on your needs of running concurrently several AC equipment might be a problem or not.
But the worst that can happen is that the shore power breaker will trip off whenever you should draw more than 30A.

Just check with the marina that there is a 30A breaker inside the pedestal, which should be normal practice, but you never know.
Missing that, you would risk to overheat and short circuit the dock wiring...

I'm guessing you have never witnessed 30A connects frying and the dock breaker not tripping or tripping after the damage has been done..

You can run some 120V stuff as long as you monitor load. However, you will only have power on one side of your panel or the other, not the entire panel.......so you may have power to battery chargers, but no air conditioning or vice versa.