Modified Level Flotation

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Angela Copeland
5 years ago
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1 Modified Level Flotation Applies to: Mono-hull Boats (not catamarans, trimarans, or pontoon boats): Mono-hull means that if you can draw a continuous line around the hull at the waterline when the boat is at rest it s a mono-hull. If it makes two or more footprints in the water it s a multi-hull. I am repeating this definition because a lot of small pedal boats and small fishing boats are not mono-hulls until you put the passengers in them. With this load they are monohulls and must meet this standard. Less than 2 Horsepower (1.49 kw), gas or electric outboard motor, or: Manually propelled. (Oars, sculls, paddles or pedals, etc.) This category includes most dinghies and rowboats, and some small john boats. Requirements: The boat has to float when swamped that is, full of water in an upright level attitude. See the diagrams in each test for specific requirements. To test the boat for modified level flotation, you need to know the following: The maximum weight capacity (the safe load) your boat will carry. This is taken from the capacity label or from your capacity calculations. How much weight in people it will carry. This is also taken from the capacity label or from your capacity calculations. If you want to use 2 horsepower (1.49 kw) or less, you need the engine weight: = 25 lb. (11.34 kg) Then measure the following reference areas on your boat: Cockpit area. 40% reference area. Passenger area 70% reference areas. Two foot reference areas fore and aft. These are the same as the reference areas for basic flotation and level flotation. There are three tests to do. TEST 1. The first test is the level flotation test after an 18 hour soak. 1. Put your boat in the water. 2. Put half the persons weight in the boat assuming the maximum persons weight is less than 550 pounds. If over 550 pounds (249.5 kg), add (1/8) times persons weight minus 550) in the 40% reference area. The Center of Gravity of all the weights needs to be in the 40% reference area. That doesn t mean all the weights have to be in the 40% area, just the Center of Gravity of all the weights. 3. Pull the plug! 4. Let the boat fill up with water. Leave it that way for 18 hours. 5. When done it should float like this:

2 One end out of the water. The other end 6 (15.24 cm) inches or less under water (or out of the water too) measured at the inner side of the 2 foot reference (61 cm) area, at the centerline of the boat. No more than a 10-degree heel angle. (You can buy a device at a hardware store that measures this). Fig 6 TEST 2. The second test is the stability test. You need to do this one twice, once on each side of the boat. 1. Place half the weight for persons on one side of the boat. The center of gravity of these weights has to be in the 70% reference area on that side of the boat. You have a lot of lee way here. You can move the weights from front to back, or back to front to get the boat to pass as long as the Center of Gravity is in the 70% area, and 30% of the total passenger weight is in the 70% area. 2. Take the other half of the passenger weight out of the boat. 3. If this is a 2 HP 1.49 kw)or less boat, leave the 25 lbs (11.33 kg) where it is. WARNING! Make sure you have some ropes or straps attached to the boat to keep it from rolling over. If you don t have enough flotation to keep it upright, that s what it will do. Then the weights will fall out and go to the bottom of the pool or lake.

3 Fig 7 One end out of the water. The other end 12 inches (30.48 cm) or less under water (or out of the water too) measured at the 2 foot (61 cm ) reference area. No more than a 30 degree heel angle. Experience has shown that if it goes 30 degrees it will probably roll all the way over. Repeat this test on the other side, too!

4 TEST 3. The final test is without the passenger weights. Fig 8 1. Take all of the passenger weight out of the boat. 2. Let the boat settle One end out of the water. The other end 6 inches (15.24 cm) or less under water (or out of the water too) measured at the inner side of the 2 foot (61 cm) reference area, at the centerline of the boat. No more than a 10 degree heel angle. Some procedures to be used during testing: Permanently Installed Fuel Tank 20 Gals (75.7 L) or Less. Place weight of fuel on deck over CG of Fuel Tanks. Greater Than 20 Gal. (75.7 L) : Initially same as above. If boat fails fill tank to ¾ level with water. If still fails fill tank full with water. Time Allowed to Stabilize between Tests: 15 minutes.

5 Hull-to-Deck Joint: Seal hull-to-deck joint with tape on all boats prior to test. Location Of Outboard Motor Weight 3 inches aft of transom. (+/- 1 inch) (7.62 cm) 3 inches above transom. (+/- 1 inch) (7.62 cm) Flooded Bait Wells during Flotation Tests Remove riser from drain hole and let bait well flood /drain naturally. Trolling Motor Weight for Flotation Test If equipped with or wired for a trolling motor, the trolling motor and battery are to be considered gear weight. Kicker Motors If the boat is equipped with a pad or wiring for a kicker motor then flotation must be provide for the submerged weight of motor and controls. If the manufacture of the boat does not specify the horsepower for the kicker motor, then the horsepower will be assumed to be 10% of the main motor s horsepower. Weights will be from Table 4. How do I know it works? Test it! The best way to find out if your boat passes is to test it. You can do the test yourself, or have a laboratory do it, or if you are newly in business as a boat builder the Coast Guard will do it for you. Call the Coast Guard at

Flotation Introduction

Flotation Introduction Why are small boats required to have flotation, and why are there different requirements? Back in the 1950's and 60's the old Boating Industry Association (now NMMA) and the Yacht