The US Coast Guard and associated marine manufacturing standards have guidelines for flotation in smaller boats, typically 20 feet and less. This ensures that the boat is able to remain floating during an “unplanned” event.   Larger boats have been excluded from these guidelines for some reason, probably having to do with their practicality of having reserve buoyancy.  My Formula 330 had some foam flotation chambers built into the hull structure that offer some buoyancy in case the boat were to become flooded with water.  However, since it is a larger boat and not subject to any testing nor certification requirements, it is not certain that there is enough flotation.  I checked with the manufacturer, they verified my assumptions, and indicated that the boat may substantially submerge, but probably would not sink.

Since the boat is a family oriented boat, I decided to add some flotation to improve its ability to remain floating if it were ever to become flooded.  I had done this on my sailboat years ago, which had no built-in flotation at all.  My previous powerboat - a Formula 242SS - had ‘positive flotation’, so it was not an issue.

In order to evaluate the feasibility of adding flotation to my Formula 330 SS, I did some calculations to see how much flotation might be needed and if it would fit in the available space within the boat’s structure.

Calculations:

I used the densities of the various types of material as well as the boat’s specified weight and the approximated weight of the components to calculate the volume of water that these items would displace if submerged in water.  I did not count the displacement of the fuel tank; that will be included in the flotation number, because in a ‘floating’ situation, the volume stays constant while the weight of its contents is variable.

The calculations are outlined below:

Material

Fiberglass

Wood

Stainless Steel

Aluminum

Engines (Steel/Iron))

Fuel (Maximum)

Total Displacement (submerged) >>>>>

Approx. Weight (lbs.)

6,000

300

400

200

2,000

960

÷

÷

÷

÷

÷

÷

Density

95 lbs/Cu FT   =

30 lbs/Cu Ft  =

490 lbs/Cu Ft   =

168 lbs/Cu Ft  =

490 lbs/Cu Ft   =

N/A

Cubic Feet (Submerged)

63 Cu Ft

10 Cu Ft

0.8 Cu Ft

1.2 Cu Ft

4 Cu Ft

Included in Flotation #’s

79  Cu Ft

The specified ‘dry’ weight of the boat is 8,900 lbs . . . add the fuel and it is 9,860 lbs.  . . . add some reserve for people and gear  . . . call it 11,000 lbs.  So, the needed displacement of materials for the various weights are as follows:

Loaded Boat: 11,000 lbs / 62.4 lbs/Cu Ft = 176 Cu Ft

Fueled Boat: 9,860 lbs / 62.4 lbs/Cu Ft = 158 Cu Ft

Bare Boat: 8,900 lbs /62.4 lbs/Cu Ft = 142 Cu Ft

I did some measuring and came up with an estimate of 67 cubic feet of flotation (foam + fuel tank volume) that was in the boat.  Add the 79 Cu Ft of material displacement to the foam displacement and it results in approximately 146 Cu Ft.  So the bare boat is probably able to float . . . (146 Cu Ft vs. 142 Cu Ft).  So, I would need to add some additional flotation to accommodate the more typical loading conditions.

My plan was to add more than just merely what would be necessary, in order to cover any inaccuracies in the estimations and to make the boat float higher in the water if it became swamped.  Based on the amount of open space that was underneath the cockpit sole and elsewhere, I estimated that I could probably put about 20-25 cubic feet of foam throughout the boat.  This would give 1,500 - 1,800 lbs. of extra buoyancy and put the total displacement near the upper end figure of 176 cubic feet.

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