When building a DIY floating dock, one of the most important steps is selecting the right dock floats. Buoyancy charts are invaluable tools that help ensure your dock remains safe and functional. Here’s a step-by-step guide to understanding and using a buoyancy chart effectively.
Step 1: Understand Your Total Dock Weight
Before referencing a buoyancy chart, calculate the total weight of your dock structure. This includes:
- Lumber weight: The wood used for the frame and decking.
- Hardware weight: Screws, bolts, brackets, and other structural components.
- Lumber: 822 lbs
- Hardware: 180 lbs
- Total Dock Weight = 822 lbs + 180 lbs = 902 lbs
Step 2: Determine Load Per Float
Once you know the total dock weight, divide it by the number of floats you plan to use. This calculation will tell you how much weight each float must support.Example Calculation:
- Total Dock Weight: 902 lbs
- Number of Floats: 5
- Load Per Float = 902 lbs ÷ 5 = 180 lbs per float
Step 3: Read the Buoyancy Chart
Now that you know the load per float, use a buoyancy chart to determine the appropriate float dimensions and depth. Buoyancy charts typically indicate how much weight a float can support while maintaining specific levels of freeboard (in our case, we are using float freeboard, or the amount of space between the waterline and the top of the float).
Key Terms on a Buoyancy Chart:
- Freeboard: The visible portion of the float above the waterline when unloaded.
- Max Buoyancy: The weight at which the float is fully submerged and level with the waterline.
Example Chart Reading:
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For a 3’ x 4’ float:
- At 150 lbs, the freeboard is 8”
- At 270 lbs, the freeboard is 6”
- With a load of 180 lbs, the freeboard will be approximately 7”
Important Note: Always Verify Against Live Load
After selecting floats based on the dock’s structural weight, always verify that the setup can handle your dock’s live load (the additional weight of people, furniture, and accessories).
For example:
- Dock Weight: 902 lbs
- Live Load: 1,580 lbs (6 people at 180 lbs each + 500 lbs of gear)
- Total Weight = 902 lbs + 1,580 lbs = 2,482 lbs
Distribute the total weight across your floats:
- Total Weight: 2,482 lbs
- Number of Floats: 5
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Load Per Float = 2,482 lbs ÷ 5 = 496 lbs per float
Refer to the buoyancy chart again. For a 3’ x 4’ x 12” float:
- At 496 lbs, the freeboard is approximately 2”.
This configuration ensures the dock remains functional and safe even under maximum load.
Final Thoughts
Buoyancy charts are essential for planning a stable and reliable dock. By understanding your dock’s total weight, calculating load per float, and referencing the chart to find the right float depth, you’ll ensure your dock has the proper freeboard for both unloaded and loaded conditions. Repeat this process for each section of your dock to achieve a safe and balanced design.
Happy dock building!