Aquasport Boats: Positive Floatation ?

[Boatdood]

To answer the original two questions:

Are all boats required to have positive flotation?
No
Will a '99 215 Explorer float if holed?
I don't know. I've never tested one.

Unfortunately without a good test none of us can be sure of the results. I've tested quite a few boats for flotation though from 13' to 26'; with a few surprises along the way. The 13' failed, and the 26 passed, by the way, but what does the test consist of and what is passing?

Positive flotation to me means simply that the boat will float when swamped. The attitude and level of float is what it is as long as the boat stays on top of the water. A good example of this would be back in '73 when a couple of buddies were offshore in their twin 196 Aquasports. One fellow had the misfortune of having his through hull drain going to the front storage box break off dumping water in the bilge. The boat didn't sink but it went down enough to be useless to him. Nothing was above the water but a few feet of the bow. He was hauled in the other boat and the boat was abandoned. The boat was retrieved by a freighter off the coast of Venezuela a good while later. Now that's positive flotation but it may as well have been no flotation for all the good it did. The boats back in those days had two foam logs comprising the stringers that went from front to rear of the boat under the floor. This set up didn't give near enough lift in the rear to hold the engine up and they'd go down by the stern. But even this level of flotation is not required for boats over 20'.

Legal requirements for flotation as well as any other boat building standards are provided by the USCG only. The other agencies such as the NMMA and ABYC have standards and recommendations but not the weight of law. The CG does have fairly stringent standards for boats under 20', but that is no guarantee that they are obeyed and the boats will actually float as prescribed. The standard is referred to as positive level and upright flotation. While much better than positive flotation this still allows portions of the boat to remain under water that will render them beyond salvage to the occupants. In other words the people can remain in the boat, quite wet, and wait for help, but it beats treading water. The 26' I tested a couple of years ago did much better. After it was swamped with all compartments filled with water the occupants could walk around the boat with nothing more than their feet wet. I was one of those occupants. The two of us actually got on one rear corner of the boat to test stability while swamped; still no one got wet. The very real twin Yamaha 150hp engines were cranked with the batteries that were still above water, and the water was planed out. Now that is a very secure feeling but the law doesn't guarantee a boat to provide this level of protection, not even a new boat.

A few years ago I was at a boat show in NJ and noticed a couple of CG auxilliary officers watching a video of a boat cut in half running on the water. They commented to each other and to me that they all are built that way. Really? I questioned. So I told them this story:

On my way to NJ I passed through numerous states. All of those states had various law enforcement agencies such as the Highway Patrol, local sheriff's offices, and city police. Many of these LEO's had speed detection devices at their disposal, but still in every state and every road I traveled people broke the speed limit. Of course they wondered what this had to do with flotation in boats, and I was getting there. The only regulatory agency in this country with law on their side charged with enforcing flotation standards in boats is the CG, and they have only one test facility manned by one guy. In other words one LE agency, and only one radar gun for the whole country and every boat builder in it building boats under 20'. And we're supposed to believe they all would pass a test because the law says so?

Enough of that. I noticed that several folks commented on flotation foam itself. Actually the law does not regulate the foam or even require it, so builders can use whatever works for them. I know some builders have used open cell foam in the past but it's rare even years ago. Closed cell foam comes in many varying qualities and even weights. Most builders use 2lb density for flotation purposes, but it comes in weights up to 7 lb or even more. Foam is comprised of many little bubbles much like balloons. We all know that if you fill a latex balloon with helium in the morning by that evening it will be sitting on the floor, but it you fill one of those shiny Mylar balloons with helium it will still be flying high days later. The helium molecules actually migrate, or permeate through the walls of the balloons and do so much quicker through the latex. The same thing can happen with closed cell foam and water. The walls may be closed but with time the water can end up inside the bubble rendering it worse than useless. Damage to the foam can speed this process as can low grade foam. The better builders go to the extreme measure of providing drainage channels in the body of the boat where the foam is contained so water can drain away instead of being trapped so it can migrate into those little bubbles dramatically increasing the useful life of the foam. This is why some boats get heavier as they age, and others seem to stay fit and trim much longer.

[RickK]

Great explanation BD  

[seabob4]

AAARRRGGGHHH!!!!!  I HATE flotation crap!  I mean, from an engineering standpoint.  Give me some wire!

Great post, Tom...  

[kraw2]

Yes they will float BUT they will easily capsize and turn over. At least 2 newer boats up here in the Panhandle of Florida have taken on water from the stern and filled to a point where the boats bow pointed up and overturned. But they did "float".

[Mcdiver]

When I saw this topic, the only thing I could think of is "yeah, i'm positive my boat floats".

[TheKid]

Trace, just don't hit anything an you'll be alright. Worst case is you hit a mola mola and need to change a prop offshore.

If you can do that, go for it. I do and I am sure my stringers are soggy.

And...I have hit a mola offshore. Not fun but was able to safely change my prop 25miles offshore.


Disclaimer....of course there is a lot more involved heading out past the horizon. What I mean is wondering if your boat will float if it is swamped should be lower on the list.

[c master]

You gents can hammer me here...I'm really just thinking with my keyboard...

In most of the photos I've ever seen of capsized outboard boats, they're upside down, with the bow sticking out, and the stern under water.  Matter of fact, wasn't there some pro football player who got caught in a storm out of St. Pete or someplace a few years ago?  They were clinging to that upside-down hull like grim death...no handles!  I think one of them drowned...but the boat didn't go down.  The problem for them was the cold water.  In fact I rarely hear about small boats just going to the bottom...people report seeing hulls floating around out in the Gulf pretty often, covered with bird sh*t and barnacles.  Could have gone adrift, come down a river, etc.  But they've obviously been floating for a long time.  

Anyway, I have foam under the gunwales of my old 170.  It might be open-cell, but I can guarantee it's dry (because it's "so dry that it's sort of crumbly"!).  Was it ever enough flotation to keep the boat from sinking?  I dunno, but I'm guessing it was intended to keep the boat upright when full of water.  ( From a displacement standpoint, once a small outboard boat fills with water, it wouldn't take that much flotation to keep it at the surface, or at least bow-up/stern-down).  Right?  

So beyond the gunwale foam, I don't really "get" the idea behind flotation in the stringers.  I mean, if the stringers were sealed, plus being under the relatively sealed self-bailing floor, was that really for flotation?  I would have guessed it was more for structural integrity of the "boxes"...minimizing the necessity of using heavier wood for the stringer walls.   If it was for flotation, why didn't AS fill the rest of the bilge areas with foam?  I don't think I have any other foam under my floor, except the stringers.   It's like the joke about the two blondes talking...one says, "Do you smoke after sex?"  And the other one says, "I don't know...I never looked!"