In every culture there are myths and urban legends that grow up and get passed on mostly by word of mouth. How they get started is hard to tell. Boating is no exception. There are many of these myths that surround the boating life. I do not mean the superstitions, such as don’t whistle on a boat, or don’t launch a boat on a Friday. This is about technical myths.

All of the following are statements I have heard people say, or I have seen in print. It always amazes me how seemingly competent people can continue to pass these on. I have even heard marine professionals say these things.  It also amazes me that boat owners don’t take the time to check the Internet or read books to find out the facts. 

Belief: Styrofoam flotation is banned by the Coast Guard.

Not True:  Styrofoam may be used as flotation.

33 CFR Subpart F - 183.101 -183.335 Flotation

§183.112   Flotation material and air chambers.
(a) Flotation materials must meet the requirements in §183.114 as listed in Table 183.114 when used in the: (1) Engine room bilge, (2) engine room, or (3) bilge, unless located in a sealed compartment.

Any means can be used to achieve the flotation requirements such as foam, air chambers, balsa, and other materials.  The Coast Guard requirement says that if you use flotation materials and if the flotational material is exposed to gasoline, oils or other chemicals that would degrade it, it must be resistant to these substances.  The most common flotation material is foam.  Some are resistant to degradation.  Polyurethane foam is.  Styrofoam is not.  However, you can use Styrofoam anywhere it isn’t exposed to these substances, or anywhere if the foam is encased. Foam isn’t even required. It just happens to be the easiest and most convenient solution.   See the next myth.

Belief:  "I am planning on using Coast Guard Approved Flotation Foam" 

Not True: 33 CFR Subpart F - 183.101 -183.335 Flotation See 183.114.  There is no such thing. The USCG does not approve flotation foam. Approval applies to certain items you must carry on board a boat. This includes things such as Fire Extinguishers, Personal Flotation Devices, and visual distress signals. Also some courses and schools for professional mariners are Coast Guard Approved. Flotation foam is not. Any one telling you they are selling Coast Guard approved flotation foam is violating the law and lying to you. If they say it meets the requirement of 33 CFR 183.114 then that means they, the foam manufacturer,  have tested it for resistance to gasoline, oils, bilge cleaners, etc. and it can be used in the bilge or areas where it is exposed to these things. But that is not Coast Guard Approval. Approval means that the Coast Guard has not only looked at the item and inspected it, but also tested it to see that it meets all of the regulations that apply. The Coast Guard does not do that for foam.

Coast Guard Certification and Approval:

US Coast Guard Approval:

Belief: The Coast Guard requires Battery Boxes (or ABYC does)

Not true  Here is the USCG regulation. 33 CFR 183.420

Sec. 183.420 Batteries.

"(a) Each installed battery must not move more than one inch in any direction when a pulling force of 90 pounds or twice the battery weight, whichever is less, is applied through the center of gravity of the battery as follows:

(1) Vertically for a duration of one minute.
   (2) Horizontally and parallel to the boat's center line for a duration of one minute fore and one minute aft.
  (3) Horizontally and perpendicular to the boat's center line for a duration of one minute to starboard and one minute to port.

(b) Each battery must be installed so that metallic objects cannot come in contact with the ungrounded battery terminals.

(c) Each metallic fuel line and fuel system component within 12 inches and above the horizontal plane of the battery top surface as installed must be shielded with dielectric material.

(d) Each battery must not be directly above or below a fuel tank, fuel filter, or fitting in a fuel line.

(e) A vent system or other means must be provided to permit the discharge from the boat of hydrogen gas released by the battery.

(g) Each battery terminal connector must not depend on spring tension for its mechanical connection to the terminal."

Notice, it does not say how the battery should be constrained or how to prevent inadvertent contact by shielding it.  A common method is to put the battery in a ventilated box.  However, the Coast Guard does not require a box.  The battery may be held with a strap or clamps and it can be shielded with boots on the terminals.  It can also be in a tray that keeps it from moving and will hold any spillage.

Here is the NFPA wording for batteries. It does not say they have to be in a battery box. It allows for other means of compliance.

NFPA 302 says:  in 302-7.3

“A vent system or other means shall be provided to allow the discharge from the boat of hydrogen gas released by the battery. Battery boxes with a cover that forms a pocket over the battery shall be vented.” 

“Batteries shall be secured to provide immobilization to the extent practicable.” 

“Batteries shall be located in a liquid tight tray or battery box of adequate capacity to retain normal spillage or boilover of electrolytes. The tray shall be constructed of or lined with materials resistant to deterioration by the electrolytes.” 

“A non conductive, perforated cover or other means shall be provided to prevent accidental shorting of the ungrounded battery terminals and cell conductors.”

ABYC says similar things.  Standards for batteries are found in ABYC E-10.  Nowhere does it say they must be in a battery box, and it provides alternative means to comply.  Obviously the easiest way of meeting these requirements is a battery box, but it is not required and it is not a regulation.

Belief: If I change to a bigger Group Size battery I can increase my battery capacity:

This is one I have encountered in not only the boating community but in the RV world as well and anywhere automotive type batteries are used.  I have seen it in boating magazines, and web sites.  I have seen "experts" tell people that all they need is a larger group size. This one is usually related only to deep cycle or combo starting/deep cycle house batteries.  Combo batteries are usually marketed as RV/Marine batteries.  Usually the person wants to add equipment and needs more capacity or simply wants to make their batteries last longer. 

Not true.  The Battery Council International defines Group size as solely the physical dimensions of the battery. 

The BCI (Battery Council International)definition of Group Number is:

"BCI GROUP NUMBER- The BCI Group Number defines a battery by describing the following characteristics:
A.) Its maximum dimensions (L x W x H)
B.) Voltage (6 volt or 12 volt)
C.) Post configuration
D.) The type of terminal used (top, side, flag, etc.)
It should be noted that the BCI  Group Number does not designate a battery's capacity, it merely defines the above listed physical characteristics."

To increase battery capacity you need a battery with a higher CCA or MCA, or Amp Hour rating. Or you need to connect several batteries of the same capacity in parallel.  You can also increase capacity by going to true deep cycle batteries, such as golf cart batteries (normally 6 volt) or D8 batteries.  True deep cycle batteries have more and thicker plates in them than combo batteries and tend to release energy slower and longer than combo style batteries.

Belief: Do it yourself AC wiring:  "It is now illegal to use ROMEX or solid core electrical wire in boats – Many older boats are grandfathered provided it was wired that way at the factory.  If you wired it in the last 10 years it must be done with stranded copper wire only.  NFPA 302 – ABYC – CFR 33"

Not True:   I took this quote off a boating web site. This is really misleading. It is not illegal to wire your boat yourself. The Coast Guard requirement for stranded wire applies to boat manufacturers not owners. 33 CFR 183.425 says “a) Each conductor must be insulated, stranded copper.”  But, that regulation does not apply to boat owners.  Both ABYC and NFPA require stranded copper wire but they are voluntary standards.  You will not pass a survey if you have Romex (house wire), solid core wire, aluminum wire or automotive wire, but it is not illegal for the owner to use it. But, it is not good practice.

Boat owners should use marine wire, usually labeled UL 1426 Boat Cable. Stranded copper marine wire is required on new boats because it is safer and will last a lot longer. Marine wire is more flexible and less prone to breaking and corrosion than solid core wire or auto wire. The insulation is more resistant to oils and cleaners and other chemicals found on boats than on non-marine wire.

Belief: ABYC requires Tinned wire.

Not True. ABYC E-11 Electrical Systems E-11.14.2.4 says: "Conductors and flexible cords shall be stranded copper according to TABLE XI."

Tinned wire is recommended and can be used but it is not required by ABYC.

Belief: ABYC does not allow soldered connections:

Not true.  ABYC allows soldered connections but they cannot be the sole means of support for the wire.

"E-11.14.5.7 Solder shall not be the sole means of support of mechanical connection in any circuit. If soldered, the connection shall be so located or supported as to minimize flexing of the conductor where the solder changes the flexible conductor into a solid conductor"

Belief:  "Anything electrical within 7" of a battery will become corroded in a average boat."

Not True.  Where this came from, I don't know but I got the quote off a boating forum.

What they were referring to was the requirement for fuses or circuit breakers to be within seven inches of the source of power. Why this would cause corrosion is beyond me.

Belief:  If your boat has corrosion on the sterndrive or other underwater metal fittings you can stop it by cutting the green wire.

Not True.  The green wire, the third wire in AC electrical system, is there to protect you against shock.  Cutting it will not stop corrosion on your boat.

The explanation is much too long to go into here. See Corrosion On Boats.  But cutting the green wire in the AC system will cause a serious hazard of shock to people on the boat.  Corrosion is caused by other factors, such as DC current leaking into the water. 

Belief: Recreational Boats must be Coast Guard Approved (or certified).

Not True: The Coast Guard does not certify or approve recreational boats.  The terms US Coast Guard Certified and US Coast Guard Approved have specific meanings defined by law.  Recreational boats are certified, but it is the builder or manufacturer who must certify that their boats meet the requirements of the Federal Regulations. See Certified for more information.

Belief: Foaming in tanks. Encasing a tank in foam is a good way to protect it and support it.

Not A good Practice: I believe that foaming in a tank is a death sentence for a metal tank.  I could go on at length about this (and on occasions I have) but the surest way to trap moisture against a tank and cause it to corrode is to encase the tank in foam.  This is why the USCG made the installation of fuel tanks encased in foam so difficult. Sec. 183.516 Cellular plastic used to encase fuel tanks. Put simply, the bond between the tank and the foam breaks and moisture collects between the foam and the tank.  It has no way out and does not evaporate.  The tank corrodes.

ABYC Standard H-24 Gasoline Fuel Systems says the same thing as the USCG regulation. However, there are boat builders who believe that foaming in tanks is the way to do it. This is a controversial subject and there has been a lot of debate about it over the years.

Belief: All fuel system hose must be double clamped:  Not True: 33 CFR Subpart J Gasoline Fuel Systems

Sec. 183.558 Hoses and connections. 

(b) Each hose used—

(1) For a vent line or fill line must be: ..........

(c) Each hose must be secured by:

(3) A hose clamp.

The USCG requires double clamping, and so does ABYC, on fuel fill and fuel lines but the USCG is silent on how many clamps on a vent line. ABYC specifically says single clamped.

ABYC H-24 Gasoline Fuel Systems 24.12.9;

Hose connections used in the fuel tank vent system or the fuel distribution and return line system shall have at least one corrosion resistant metallic clamp with a minimum nominal band width as indicated in H-24 TABLE III."

So vent lines may be single clamped.  But I recommend you double clamp if possible for an extra measure of safety. Unfortunately some of the vent fittings on the market are not long enough for double clamping, so when you buy your fittings look for ones that are long enough.

Belief: "Loop's in fuel lines are a Coast Guard/ABYC violation.  Fuel must flow downhill to the tank without any traps as it can be a fire hazard if the boat burns."

Not True: This is a direct quote from a boating forum. The writer was speaking about the fuel tank vent line. Loops are not prohibited by the USCG or ABYC. The vent line needs a means of preventing water from entering the system, per ABYC.

"H-24.14.6
The tank vent system shall prevent the intake of water when tested to section H-24.18 Installation tests"A loop is one means of doing this.

The USCG fuel regulations doesn't even mention this. See 33 CR 183.501

Belief: Your powerboat must have an Anti-Siphon valve:

Not True.  33 CFR 183.568 The US Coast Guard requires an anti-siphon valve on inboard powered boats with permanently installed fuel systems, if the fuel tank is higher than the fuel inlet on the engine.  That means if the fuel line runs down hill from the tank to the engine, you need an anti-siphon valve.  If it runs uphill, that is the fuel inlet on the engine is higher than the tank, then you don’t need one.  These little valves cause a lot of problems and are always getting clogged by junk in the fuel.  If you don’t need it, get rid of it.  They are not required on outboard boats. ABYC standards do require them on outboards with permanently installed fuel systems, but only if the fuel system can siphon itself, which is the same as the USCG requirement for inboards.

Belief: The Coast Guard (or ABYC) bans Stainless Steel tanks:

Not true: The only tank material that is banned is ternplate, a tin-lead metal that is very prone to corrosion.  Stainless tanks are permitted.  However, they are very prone to a condition called crevice corrosion, so ABYC recommends they be 20 gallons or less with domed ends.  This minimizes the welds where they are most subject to corrosion. They should be mounted where they will be dry and can be inspected on all sides.  Only 316L or 317L stainless should be used.  As with all the above, tank regulations are manufacturer requirements.

Belief:  "Look at ABYC H-24 Gasoline Fuel Systems. Gasoline fuel tanks may not be installed in engine compartments."

Not True: ABYC does not prohibit fuel tanks from being installed in engine compartments.  This is why ignition protection, ventilation, and fuel systems regulations exist.  Fuel tanks are frequently located close or in the same compartment as the engine.

Belief: It is illegal to exceed the horsepower rating on my boat.

Maybe; Why maybe?  This is a gray area. The Federal regulation requires boat manufacturers to post a label with the recommended maximum safe horsepower for outboard powered boats.  It only applies to mono-hull boats under 20 feet in length.  Horsepower is determined using a formula contained in the regulation.  Under Federal law a boat owner can put any size engine they want on their boat.  However, the catch is, some states have passed laws making it a violation to exceed the values on the capacity label.  Insurance companies also may cancel your insurance if they discover the boat has an engine that exceeds the horsepower rating.  If you have an accident and an investigation shows it was related to overpowering then the owner could be held liable in a law suit by the injured parties.

The Following Item Has Been Revised

Circumstance: I was cited by the police for not having a capacity label on my boat: AMENDED 01/10/2011 

This could be a requirement:  Previously I had said this is not a requirement. However a law enforcement officer who is very knowledgeable about boating law questioned this.  In his state the law makes this both a manufacturer and owner/operator requirement. So I queried the US Coast Guard to get a clarification. This is the response;

“Several states have passed laws requiring operators to have a capacity plate on their recreational boats.  To date, Pennsylvania is the only State that I am aware of that actually has a website for operators to get a capacity label.  I get many phone calls from boaters in States with such laws that have no idea where or how to get a label.  We do have preemption authority but we don't normally use it on operator requirements such as a capacity label, or speed limits, or proximity to other vessels, or wearing life jackets from November to March, etc.  The Alabama kill switch was an attempt at a manufacturer requirement that we preempted.  You need to change your web-site to make it clear that a capacity label is a manufacturer requirement except in States that have made it an operator requirement.”   

The label is a manufacturer requirement. But the boat owner can be held responsible for the label in some states.  Only Pennsylvania has a system in place to issue the label to boats that don’t have one.  If your boat is missing the label you should try to get a new one from the boat manufacturer.  If the manufacturer is no longer in business, or the boat is so old the manufacturer no longer stocks the labels, you can have one made.  But first you need to know what the values were that were on the label.

The US Coast Guard does not keep records on the capacities and does not supply these labels to manufacturers. The manufacturers make them or have them made by an outside source. So if you need one you will not be able to get it from the Coast Guard. However, they may be able to help you with the correct format for the label if you are having one made. See the page on Labels.

Belief:  I have both a capacity label and a label showing the number of seats. If the seating label has more seats than people on the capacity label, then I can use the seating label as the capacity.

Not True:  The seating label is placed on the boat voluntarily by boat manufacturers to show you where it is safe to sit.  This grew out of boat manufacturers trying to find a way to show boat operators and passengers where it is safe to sit to prevent injuries and deaths.  Even though it is common sense that it is unsafe to sit on a gunwale, or transom, or the bow, and especially on pedestal seats when the boat is underway, some people just don't get the word. Boat operators often fail to follow safe operating basics, such as sitting in designated seats when the craft is on plane, maintaining a balanced load or giving themselves an unobstructed view from the helm.  Many boats have casting platforms, storage lockers and other surfaces which are inappropriate for seating when a boat is on plane.  So the American Boat and Yacht Council and the National Marine Manufacturers Association developed a label showing where it is safe to sit. It is simply an information label.

Recreational boat manufacturers are required to put a capacity label on mono-hull boats under 20 feet in length. The number of persons on the capacity label is the number you should use. You will see a similar label on many other types of boats, including canoes, kayaks, pontoon boats and inflatables.  The manufacturers voluntarily (in the USA) put these on other boats because it is good business and safety sense to do so. In Canada and Europe the label is required on all recreational boats (with a few exceptions).In the USA the label is a manufacturer requirement. The boat owner does not have any responsibility under Federal law for this label, not even for complying with the values on the label. (they do in Canada)  However, most states have passed laws making it illegal in the particular state to exceed the capacities on the label. So if you live in one of those states you can be cited by state or local law enforcement for exceeding the capacity on the label. Also your insurance company may take a dim view of exceeding the capacities.  So, use the Capacity Label as a guide to how many passengers you can carry, and the seat label as a guide to where they can safely sit.

Belief:  I have an old boat with no capacity label, but I found a formula in a boating book that says if I multiply length (L) times the width of the boat (B for Beam) and divide by 15 that will tell me how many people I can carry. 

Maybe:  This formula, L X B/15, has been around a long, long, time.  I have traced it as far back as the 1940’s.  In the boating world, that is ancient. It has shown up in a lot of well respected boating publications, books, and even in the US Coast Guard Boatbuilders Handbook. It is not the formula that boat manufacturers and builders are required to use to determine persons capacity for recreational boats, or for commercial passenger carrying boats. The formula is a rule of thumb. It is only meant to be used as a rough estimate. It is in the handbook only as a way to estimate the number of passengers.  It is also only intended for use with small mono-hull boats, usually outboard powered but it has been used for small inboards.  It should never be used for boats more than 25 or 26 feet in length.  It is simply not applicable to larger boats. It also does not apply to canoes, kayaks, multihulls, inflatables, or pontoon boats.

Belief:  The US Coast Guard uses 160 pounds per person to rate the capacity of recreational boats and/or commercial boats.  I hear this one everywhere. It was recently stated in a BOATUS article. 

Not True: Here is an e-mail I sent to BoatUS concerning this.

"The Coast Guard does not and has never used 160 pounds per person for capacity ratings on recreational boats.  This is a common boating myth and where it got started is beyond me.   But since I spent 25 years working in the Coast Guard Office of Boating Safety I think I can explain how capacity is determined.

It starts with displacement weight. Displacement weight is the amount of weight a boat would displace if you weighed the hull down to the point where water would start to come in. Essentially that is the weight it would take to sink the boat.  That amount is divided by five for outboard boats, and by seven for inboards. The result is the Maximum Weight Capacity.  That is the amount of weight you can safely put in the boat including motor gear, batteries, controls and people.  To find the persons capacity you then subtract the outboard motor weight, batteries, full fuel tank.  But a manufacturer must use the outboard weights in the Coast Guard's Table, or the ABYC table for outboard weights. The result is persons weight in pounds. To find the number of persons those pounds represent, the Coast Guard uses a formula: persons weight plus 32 divided by 141.  The result is rounded to the nearest person. 

Also the boat manufacturer does not have to use this maximum number. They cannot exceed the numbers for maximum weight capacity, maximum persons capacity and persons but they can use a smaller number, and many manufacturers do downrate.  The amount of flotation that goes into the boat is based on; the hull weight, the persons weight and the outboard motor weight.

For inboards a similar exercise is used to determine  maximum weight capacity, maximum persons capacity and persons. But the engine is not treated separately. It is considered part of hull weight.

Perhaps the confusion comes from commercial vessels.  On the commercial side of the Coast Guard they use a persons weight to determine how much weight to use when performing stability tests. Here s a quote from a paper on this on my web site entitled How Much Of A Load Is Too Much?:

On a commercial vessel, the number of passengers is estimated based on the lesser of the following criteria:

1.  Length of rail: one passenger for each 30 inches of rail at the sides and stern., or,

2.  The deck area; one passenger per 10 square feet of deck area, excluding spaces listed in 46 CFR 176.113, which include, among other areas, concession stands, toilets, lifesaving gear storage spaces, required aisle area,  or

3. The fixed seating areas, or fixed seating; one passenger for each 18 inches of fixed seating width.

The stability of the vessel is then determined using the number of passengers allowed based on the initial determination. An SST (simplified stability test) is conducted, based on the Coast Guard criteria of 140 pounds per person.  If the boat does not pass the stability test then the number of passengers is based on the weight of passengers that would pass the test at 140 lbs per passenger. The Ethan Allen investigation has determined that this weight is too low, and should be at least 174 pounds.  The Coast Guard has raised it to 184"

See HOTTOPICS; How Much Of A Load Is too Much?

However, I was inaccurate.  The figure 140 pounds per person was used for boats with a combination of adults and children,  but if all the passengers were adults, then 160 pounds was used.  But still, that is for commercial boats, not recreational.  For recreational boats the number 141 is not a weight. It is a constant that was found by analyzing capacities of recreational boats. 

Belief: Galvanic Corrosion Vs Electrolysis. 

Which is the correct term? I still hear a lot of professionals, let alone amateurs, referring to Galvanic Corrosion as Electrolysis.  The differences are complex although they are similar processes.  But the correct term is galvanic corrosion.  See Corrosion on Boats

Belief:  You shouldn't use aluminum boats on salt water.

Not True:  Another complete myth.  Aluminum boats do just fine on salt water.  Builders who make aluminum boats should use marine grade aluminum in the 5000 or 6000 series, such as 5052 or 5083.  These alloys are made specifically to resist corrosion in the marine environment, especially salt water.  The aluminum can be left bare, because it has a natural oxide coating, or it can be painted.  But painting aluminum involves a process you must follow for the paint to adhere correctly, and endure.  Also the boat should be protected from corrosion by anodes (some call them zincs although they are many different alloys) and by correctly installing the electrical system to prevent stray currents on the hull or in the water.  If the boat has an Alternating Current (AC) system on board it should have a galvanic isolator or an isolation transformer to protect it from stray current corrosion as well.  But if properly built and well maintained an aluminum boat will last as long as any other material.   For more info on aluminum see My Hottopics on Aluminum

Belief: Cored Composites are stronger than solid laminates.

Not True:  See Passagemaker Magazine Myth Buster That Infused Hulls Are Stronger .   Many thanks to Phil Friedman for this one.

Belief: " I was told that butt connectors to hook up a bilge pump are the only way the Coast Guard is happy." (found on a boating forum 06/27/2020

Not True:  This is another good example of someone being told something by someone who doesn't know what they are talking about.  The Coast Guard does regulate some wiring on boats but not the type of connections used to hook up the bilge pump. See 33CFR 183.401

Belief: If your boat does not have a rudder, it does not have to registered. (10/19/2022)
Here's a quote from the forum where a person asks: "It is my understanding that the single component, of a vessel, that determines whether or not it is required to be registered, is the "rudder." In other words, a vessel "with" a rudder is "required" to be registered, while a vessel without a rudder is "not" required to be registered. "

Not true: Boat registration requirements have nothing to do with whether or not you boat has a rudder. If this were true then in the USA alone, hundreds of thousands of outboard boats would not have to be registered.

Actually registration of small craft in the US is a Federal requirement that States register certain types of boats. All this can be found in Title 33 Of the Code of Federal regulations specifically parts 173 and 174. I won't get into the weeds on this but what has happened since that regulation was enacted is that each state has decide that they each have different requirements above and beyond the Federal, which started long ago with boats having mechanical propulsion of 10 HP or more, but now applies to any boat with any means of mechanical propulsion.

33 CFR 173.11 Applicability says in part;
"This subpart applies to each vessel equipped with propulsion machinery of any type used on waters subject to the jurisdiction of the United States and on the high seas beyond the territorial seas for vessels owned in the United States except (and there is a laundry list of boats that don't have to register, mostly publicly owned boats, but nothing about rudders.)

But I'll cut this short by stating that having a rudder has absolutely nothing to do with it.

And the rest of the story: Perhaps this person is confusing registration, which is required by Federal Regulation and administered by the States and territories, with documentation, which is done by the Coast Guard. Documentation can be done for boats measuring by volume more than 5 net ton's. That 5 net tons relates more to the boats cargo volume than to the actual volume of the entire boat. I won't get into the nitty gritty of documenting a boat, but in the rule regarding measurement they take a measurement from the "rudder post". However, if the boat does not have a "rudder post" there is an alternate measurement rule. So documentation does not exempt or exclude boats not having a rudder.

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