Understanding Water Draft & Air Draft for the Great Loop
When you’re cruising the Great Loop, understanding draft is essential for a smooth, safe, and enjoyable journey. Both water draft (the depth your boat sits in the water) and air draft (the height from the water to the highest point of your boat) will impact your route, navigation, and even your overall experience.
In this post, we’ll break down what these terms mean, why they matter, and share some essential tips on how to navigate low bridges and shallow waterways—an important part of your planning for the Great Loop.
What is a Water Draft?
Water draft (often called “draft”) refers to the distance from the waterline to the bottom of your boat’s hull, essentially how deep your boat sits in the water. This measurement is crucial when traveling through shallow areas, as it determines the minimum depth of water you need to pass through safely. If the water is too shallow and your boat’s draft is too deep, you risk running aground or damaging your boat.
Understanding your boat’s draft will help you plan your route and avoid areas where the depth could be problematic. Most Great Loopers will encounter some shallows, particularly in some regions of the Loop, so knowing your boat’s draft is the first step in avoiding potential mishaps.
What is Air Draft?
The air draft is the height of your boat above the waterline, from the water’s surface to the boat's highest point (usually the top of the mast or a raised bridge). This measurement is crucial when you need to pass under bridges, especially low bridges, which are a common obstacle on the Great Loop.
Navigating under low bridges is one of the most challenging parts of the Loop for many boaters. If your boat’s air draft exceeds the clearance listed for a bridge, you must plan your route accordingly. Sometimes, you may need to lower your mast or take an alternate route.
Why Does Draft Matter?
Both water draft and air draft are important for several reasons:
Safety: Understanding your boat’s draft helps you avoid running aground or hitting submerged objects, which can be dangerous and cause damage.
Route Planning: Certain areas of the Loop, like the Lake Okeechobee or parts of the Illinois Waterway, have known shallow sections. Knowing your draft helps determine if you can safely pass through or need to adjust your route.
Bridge Navigation: If you’re passing under bridges, knowing your air draft ensures that you won’t accidentally hit a bridge, which can cause serious damage to both your boat and the bridge structure.
How to Measure Water Draft & Air Draft
WATER DRAFT
To measure your boat’s water draft, check your boat’s specifications for the manufacturer’s recommended draft. If you’re unsure, you can measure it manually.
One way is to lower a weight tied to a line off the side of the boat to the lowest part of your boat and measure the length of the line to the waterline. Keep in mind that the boat’s load will impact how low it sits in the water.
AIR DRAFT
For air draft, simply measure the distance from the waterline to the highest point of your boat (mast, radar arch, etc.).
Remember that your air draft may change slightly depending on how heavily loaded your boat is or if you have items on top like antennas, flags, or windlasses. Always factor in some extra clearance to account for wave heights or wind conditions.
Tips for Handling Low Bridges & Shallow Waterways
Check Bridge Clearances: Before you depart for a bridge-heavy section of the Loop (like the canals, Illinois waterways, or the ICW), check the listed clearances for each bridge along your route. Some may be adjustable, but many are fixed, and you need to know if you’ll clear them.
Plan for Mast Lowering: If you have a tall mast, be prepared to lower it when navigating areas with low bridges. Many Loopers will either drop their masts or hire local professionals to assist. In some cases, there may be marinas or facilities with the necessary equipment for mast lowering.
Use Local Resources: Many boaters will share up-to-date bridge information and tips on local conditions. Boat forums, Facebook groups, and Great Loop-specific resources like ActiveCaptain provide valuable details on bridge heights and water depths.
SHALLOW WATERWAYS
Lake Okeechobee is notorious for having shallow areas, and the water level can fluctuate depending on the time of year. Check real-time water levels before crossing, and plan your route accordingly to avoid running aground.
When traveling through canals or sections south of Chicago, such as the Illinois Waterway, be mindful of dredging schedules and potential sediment buildup that could affect water depth. Many areas have marked depths, so pay attention to local markers and always leave some margin for safety.
Prepare for Tides & Weather: Water depth can vary due to tides, rainfall, or even boat wakes. Be mindful of weather patterns that affect water levels, particularly if traveling in more tidal regions.
Use Technology & Navigation Tools: Apps like Navionics, Waterway Guide, or ActiveCaptain are fantastic resources for real-time checking water depths and bridge clearances. These can give you peace of mind when navigating unfamiliar waters.
Water draft and air draft are crucial considerations for every Great Looper. By understanding your boat’s draft, measuring it accurately, and using the right tools, you’ll be better prepared to navigate low bridges and shallow waterways confidently.
With a bit of preparation, you can avoid surprises and enjoy the adventure of a lifetime as you cruise along America’s Great Loop!
