Muck bottoms can be a challenge. Installing a dock in muck traditionally means getting a long pole and augering it in until it hits something solid. This can work but it takes a considerable amount of effort and in some cases you will never find the bottom. It also requires you to purchase a much longer dock post than you would otherwise need installing the post in a different way.
A few inches of muck is not a problem for most standard size dock bottom plates so if this is what you are dealing with you need not be concerned. Most standard sized bottom plates are around 6”. If you have muck that is sinking in at 6”-14” or so before it gets solid, a larger plate is the simplest option.
Most manufactured large plates are around 12”. Many of these are stamped steel that attach to the bottom of your dock post by welding or a thumb screw if they are really cheap. These can work, but since they can bend, they are usually not as strong as competitive cast units of the same type. Castings that are designed correctly are very strong. Another advantage to two piece castings is that you can push the pole through them as far as you want. This will also give you additional stability with a soft bottom.
Large cast plates are the simplest option for a soft muck bottom, however if you are getting into a rough situation with more than 14” of muck you may have to use bottom boards. The way to do this is to use a small bottom plate clamped up the pole about 1.5’. Under that you place a treated plywood board that is at least 2’X2’ square. The board will need to have the pole pushed through it so a hole saw will be required if you are making these on your own. Depending on the situation these can be a relatively economical way to keep your poles from sinking in the muck. This is also a decent way to put a boat lift into a soft bottom situation. You can use as large of a board as needed. We suggest using at least ¾ inch for this purpose. Treated plywood will last for many years without rotting.
There are some permanent options such as Bigfoot for mounting bases in the muck but they are basically a topic on their own. We will try to cover that in more detail in the future.