It’s important to know your boat well, and there are some things you need to know early. Such things include engine specifications, dimensions, and the boat’s draft. But what is the draft of a boat and why is it important?
The boat’s draft is the space between the waterline and the boat’s lowest point. In this article, we’ll take a look at the boat draft meaning and other important information.
Keep reading to learn more.
Table of Contents
The draft of the boat or boat draught is the measurement of the straight vertical distance between the waterline of the boat and the lowest point of the boat, though the boat draft definition may vary somewhat between people.
This lowest point is usually a part of the keel or the skeg of an outboard or external engine. But what does draft mean on a boat?
Knowing the draft of a boat is extremely important because this distance determines how shallow the water you can sail with that boat is. This means that a boat with a draft of 6 feet cannot boat through waters that are just 5 feet deep.
However, the base figure of a boat’s draft is not the actual clearance from the water bed; it’s a good idea to allow a bit more distance to ensure that the boat is clear of any obstacles.
Even if there is enough clearance, we can’t be sure that the boat won’t get caught up with anything else on the ground. Rocks or seaweed could still spell trouble for us and our boat.
Boat Draft Specifics
There are a few other important things to know about boat draft. The first is the draft of boats using outboards. It would be normal to see two draft figures for such boat types: drive up and drive down; they may also be called draft up and draft down.
Draft up on a boat is the boat’s draft when the outboard is raised, allowing the boat to traverse more shallow waters.
Draft down or drive down represents the draft for when the engine is deployed and thus reaches deeper into the water.
There are also average boat draft figures for different boat types. While we cannot assume that these apply to all boats, it’s a good way to see which boat types are more capable of sailing in shallow waters.
- Sailboat – 4 to 7 feet
- Daysailer – 3 to 5 feet
- Catamaran – 2 to 4 feet
- Dinghy – less than 1 foot
- Motor yacht – 1 to 4 feet
Looking at the list above, we can see that sailboats are expected to reach further into the water. This is due to the fin on the sailboat’s keel. In contrast, a dinghy that does not use a motor is capable of traversing more shallow waters.
Measuring Boat Draft
When purchasing a boat, the boat draft is among the expected figures included in its specifications. However, this figure uses the boat’s dry weight and would not properly represent the boat’s state while on the water.
There is also the possibility that the draft figure is not indicated, and this is when it is important to know how to measure draft on a boat.
Before measuring the draft, you need to establish the waterline first. It helps to load up the boat in the way that you do for most outings. Fill up the fuel tank and load up your supplies, then mark the waterline with tape or anything you’d like to use.
You should still be mindful of the maximum draft for a boat that may be indicated in the manual, which is the operational limit of the boat.
Measure the straight vertical distance between the waterline and the lowest point of your boat. Take note of this figure as it will be the base draft of your boat.
You can make use of an online boat draft calculator if you have access to one. If not, we can still calculate manually.
- Measure the length and width of your boat’s deck. Calculate the boat deck’s area by multiplying the figures of length and width, with the width being the measurement of the beam on a boat.
1. Boat area calculation
25 ft x 6 ft = 150 ft
- Have the measurement of your base draft on hand. We’ll use a measurement of 5 ft for this practice calculation.
- Initial draft measurement = 5 ft
- You need to determine the unit weight of water you’ll be boating in. That’s 64 pounds per cubic foot for saltwater and 62.4 for freshwater. Let’s use salt water for this exercise.
- Determine the weight of each passenger or cargo. That weight is then divided by the unit weight of the water. Let’s assume we have two passengers, one weighing 180 lbs and the other at 200; note the result for each.
2. Passenger weight calculation
180 / 64 = 2.81
200 / 64 = 3.13
- Add the resulting figures in the passenger calculations; if you have more passengers, just repeat the step as many times as needed. Add the figures together. For this instance, we have a total of 5.94.
- This figure will then be divided by the boat deck’s area that we calculated earlier (150 ft). The result should then be added to the initial draft measurement.
3. Resulting draft
5.94 / 150 = 0.04 ft
5 ft + 0.04 ft = 5.04 ft
The resulting figure is the total draft of the boat when it is loaded with your usual gear and fuel along with two passengers aboard. Remember to calculate both passengers and any cargo for an accurate figure.
Now, this is a bit of a long calculation process. You can also just load everything up on the boat then jump into the water and measure it there. This works as long as you don’t mind going for a bit of a swim.
Frequently Asked Questions
1. Does boat draft include prop when measuring?
Yes, it does. For motorboats that use an outboard engine, the skeg will be the lowest part of the boat and the prop will be near it.
2. Which motorized boats have the lowest draft?
Motorized boats that use an inboard motor or jet propulsion are known to have the lowest draft.
3. What is the draft marker?
Some boats have markings on the hull indicating how deep the hull should be underwater. These are the draft markers.
Now you know what the boat’s draft is. You’ve also learned that the boat’s draft is essentially its minimum water depth for operation. Calculating the boat’s draft can be complicated, but it is still worth knowing how to do.
Should you encounter someone asking what is the draft of a boat, please share what you’ve learned with them as well. If you have any comments or suggestions, feel free to drop them below.
Remember to boat safely.
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