When is it safe to collect at the beach?

The tides are created by the gravitational forces of the Moon and the Sun. No two tides are same time day after day. On average there are two high tides a day and two low tides, but not always... sometimes there might be 3 of one and 1 of the other. Just depends of the timing. 

Tides do not create waves and the big waves you see in pictures are not a result of the tides themselves.

Swells are what creates the waves that we see crashing along the rocky shore making the big splashes that everyone loves to see. Swells are what unbroken waves are called. There's a lot of science behind understanding these but the easiest way to think of it is the bigger the swell and the longer the period, which is the distance between each swell, the bigger the wave will be and how much energy potential it has.

For example, if you have a swell forecast of 4' with an interval of 8 seconds the size of the wave will be significantly smaller than one thats 4' but has an interval of 12 seconds. In many ways the period is the more critical part of all of this. For instance if a swell is forecasted at 4' at 16 seconds and compare that to one thats 10' at 8 seconds which do you think would have more energy? It may seem counterintuitive but the 4' would have more energy behind it! 

Here's some science about it

 https://www.surfline.com/surf-news/forecasting-tutorial-wave-period-explained/96751#

Well the quick answer is yes! The prudent answer is sometimes..... 

You'd want to take the info from above and put them together to see if the conditions are safe along the beaches to do so. Its also important to remember that not all beaches are the same and not all beaches have the same slope, geography and bathymetry (the underwater geography).

The "King Tides" are in themselves not a very big danger unless you're on a beach that typically doesn't have much room to begin with. The danger comes from when there is the high tide combined with a significant swell event. But just like referenced above, even during non "King Tide" events if there is a large swell event there may not be much beach to enjoy even at LOW tide!

"Sneaker Waves" are a tricky thing to actually define and predict.....

On the surface they'd be simply waves that com up farther than most of the other waves that are happening at that particular time. Sometimes they surge 30' sometimes they can surge well past even the high tide line. Remember the whole thing above about "King Tides"? This is the portion where people get it wrong with the info. The dangerous bit of ANY high tide is the occurrence of these "Sneaker Waves". With some careful consideration there are tell tale signs of the though. They can AND do occur any time of the year if the beach conditions are right and the swell is right.

"Sneaker Waves" occur when multiple waves overlap and create a single wave which makes this new wave faster and more powerful than the ones by themselves. Typically they occur after a period of gentle waves that have been breaking and the water from those waves kind of recedes back out to sea. In doing so they create a fair bit of resistance for the waves behind them that are pushing shoreward. If after awhile a few of them have done this the waves that are on their way in are essentially stacking up and eventually overcome the resistance of the first waves receding direction and shoot towards shore! You can see these simply by watching near the water line and immediately out 50'-100'. Sneaker waves aren't breaking waves like you would see some surfers riding. It's typically a small wall of whitewater from 1' tall up to shoulder height. Even the velocity of a 1' wave can easily knock a full grown person down!

The most ideal conditions for "Sneaker Waves" is when you have multiple swells coming from both far away and nearby storms that are arriving along the coastline at the same time. Again, this is where checking the local swell forecast is handy!