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Captain Ron Rico said, “If it’s gonna happen, it’s gonna happen out there.” Truer words have never been spoken about boating. Is your boat ready for ‘out there’?

The maximum safe distance you can take your boat offshore depends on the experience of the captain, the seaworthiness of your boat, your boat’s fuel range, the weather, and your willingness to take risks. A small inflatable boat can travel out 1 to 2 miles, a 20-foot center console can handle 5 to 10 miles offshore, and a cruiser can travel hundreds of miles. These numbers are just ranges, and the maximum safe distance you can go depends on the weather, your boat, and how good a captain you are.

Seaworthiness is a very general term used to describe how capable a vessel is and how much it can safely take. Unfortunately, there’s no tidy definition for what makes a seaworthy vessel. Beyond the type of vessel, knowing how far offshore you can safely go with a small boat is based on the overall experience and judgement of the captain.

Let’s look at an example – a captain named “Skipper”. Skipper has owned his open deck pontoon boat for several years. One year, he trailers it from his home lake to the Florida Keys. The boat is fun and manages the protected waters on Florida Bay easily. Then, Skipper decides to take the boat into the Atlantic to visit a reef. Seven miles offshore, a deepwater 5-foot swell begins to make the pontoon boat feel a bit small.

On the way home, an afternoon thunderstorm kicks up a rough chop and adds 30-knot winds to the mix. Now it’s too rough to keep the boat on plane, and it’s wallowing in the troughs of the waves. There’s green water on the deck, and it’s at high risk of capsizing. All the rolling has stirred up some sediment in the fuel tank, and the single-engine now sputters and dies. Is the vessel still seaworthy?

Table Of Contents

Safely Taking a Small Boat Offshore

Sure, a pontoon boat offshore in a Florida thunderstorm is an extreme example. But the same story can be told with pretty much any type of boat. Every design has a limit.

1. Experience of Captain/Owner

small boat on the ocean

There’s a saying, “You start life with a full bag of luck, and an empty bag of experience. Your goal is to fill up the bag of experience before your bag of luck runs out.” Many skippers get lucky, and hopefully, that’s what happens to the pontoon boat. But with careful risk management, even a new skipper could’ve kept a little more luck in his bag and saved it for another day.

The number one factor affecting the seaworthiness of all vessels is the skipper at the helm. No matter what the mode of transportation, 90 percent or more of all accidents are caused by human error.

What could Skipper have done differently? He should have checked the weather and known about the offshore swell and the possibility of thunderstorms. The fuel system may have worked fine on the lake, but once offshore years of neglect resulted in a bad situation. If his boat wasn’t ready for the conditions offshore, he could’ve rented a center console for the day on the reef.


2. Types of Boat

pontoon boat offshore

While the pontoon boat is wallowing in the waves, a 20-foot center console pulls alongside and helps out with a tow. The center console also has a rough, slow ride, but it’s dry and comfortable. Then, a 50-foot offshore fishing boat happily blasts past them doing 20 knots. Boat design and size are important factors offshore when the weather turns crappy.

The bigger boat has a bigger safety cushion. It takes more to push it to its limits. Some boats are unsafe in some conditions, and some are just uncomfortable. It’s up to the skipper to know what he or she, their crew, and their vessel can take. If it’s going to be unsafe, don’t go. If it’s going to be safe but still be uncomfortable, you probably shouldn’t go.


3. Fuel Range of Boat

The simple fact of the matter is you can’t take your boat any farther than your fuel will take you. And, if you want to return safely, you can only go half that distance.

Knowing the fuel range of any boat is tricky because it’s different every time you go out. You have to factor in the sea conditions, current, winds, and your speed. Don’t forget your boat’s bottom and running gear condition – algae and tiny barnacles can reduce your fuel efficiency by 30 to 40%.

Ask an experienced captain and they will tell you that the fuel gauge on most boats are notoriously inaccurate. Fuel tanks aren’t symmetrical and the typical gauge assumes the fuel level is linear. This means that your estimated fuel usage can be off, especially as you get to the bottom of the tank. If your boat is running at an angle, the fuel shifts toward the rear of the tank, which results in the gauge reading more fuel than you actually have. 

I know many boaters who rely on the manufacturer’s range, some how believing that it can’t be wrong if it was published in a sales brochure. In my experience, this number is always high because it’s based on ideal conditions. I’ve never encountered ideal conditions, even on a good day!

4. Boat Design and Engines

Boats with a higher freeboard can fare better in high seas. They keep more water off of the deck and therefore are more stable. Cutaway transoms reduce the boat’s overall freeboard, so full transom designs are favored. If a boat does have a cut-out transom, make sure it has a generous, self-draining well to go with it.

Deep Vee hull design

Another design feature is hull shape. Deep vees are usually favored offshore for their soft rides, but modified vee designs with between 17 and 21 degrees of deadrise offer a great ride and more stability on small boats.

Staying afloat is an important part of boat design. Cockpits should be self-draining with big scuppers. Boats should be built with as much foam flotation as possible.

When it comes to engines, a decision about reliability must be made. Many single-engine vessels operate safely offshore, but the comfort that comes by having a completely separate backup system is a very worthwhile investment. Another option is to add a small kicker motor that can get you home in a pinch.


How to Calculate the Range of Your Boat

If you want to know exactly how far your boat can be taken offshore, I recommend calculating the fuel consumption under real world conditions. This isn’t difficult to do, but you have to do it correctly in order to get an accurate result. 

I prefer to use run time at a given speed to determine my boat’s range. Why? Because I usually run at the same speed when I’m heading offshore, and it’s easier to measure time than distance when you’re on the ocean. Continue reading to see how I calculate a boat’s range.

Calculation Method

Here is a step-by-step method to calculate your boat’s range.

  1. Clean the hull. You need to remove all algae, barnacle, and other accumulation from the bottom of your boat. Clean your running gear too.
  2. Inspect your prop. Check your propeller for dents and other damage. Repair or replace it as needed.
  3. Fill your tank. Add fuel to your tank and fill it completely. 
  4. Record engine hours and trip meter. You need to keep accurate readings for all available information. Some boats have trip meters that provide mileage. Record this along with the hour readings.
  5. Time your trip. Use a stop watch (an actual stop watch or your smart phone) to record the exact time you’re out on the water. Travel from the marina fuel dock (or your launch site) to a landmark like a bridge or buoy and then return to the fuel dock. This test run should be at least 2 hours to give you an accurate measurement.
  6. Refuel your boat. This last step is important to getting an accurate reading. Fill your tank up to the exact level it was when you started. Don’t rely on your fuel gauge – it’s not accurate!
  7. Do the Math. With your trip data, use the method below to calculate your boat’s range.

Determining a Safe Distance Offshore You Can Travel

On my test trip, I burned 30 gallons of fuel running from the fuel dock to a marker buoy and back again. The round trip distance is 40 nautical miles. The entire trip took 2 hours at an average speed of 20 knots. 

Let’s do the math – 30 gallons divided by 2 hours is 15 gallons per hour. My boat burns 15 gallons per hour at 20 knots. 

What about miles per gallon? 40 nautical miles divided by 30 gallons is 1.3 miles per gallon.

Now you know how far your boat can travel on a full tank of fuel. Write down these numbers and refer to them when you’re planning a trip or you’re out on the water. I always assume these numbers are “ball park” estimates and not absolute constants.

Remember. Things change, and you don’t want to end up drifting miles offshore.


Planning a Trip for Maximum Offshore Distance

Here’s a simple method I use to determine how long a full tank of fuel will last.

Whenever I’m planning an offshore trip, I build in a factor of safety. There’s nothing worse – or more dangerous – than running out of fuel when you’re far offshore. 

  • Take 5% off the top. It’s almost impossible to fill your fuel tank to the top. I’ve tried and I always end up making a mess. For a 100 gallon tank, assume you’re starting out with 95 gallons.
  • Include a 10% reserve. Don’t assume that you can bring your boat back on fumes. Give yourself enough reserve fuel to deal with the unexpected – winds, currents, getting lost…
  • 40/20/40 Rule. Assume you’ll use 40% of your fuel getting out, 20% at your destination, and 40% to get home.

I find that the 40/20/40 rule works reliably well in almost every situation. It takes about the same amount of fuel to get out as it does to get back. I also find that I like to troll around and explore the area when I arrive at my destination. For me, most of the time (and fuel) is spent travelling to and from my favorite fishing spots, which is why 40% out and 40% back works best. You may find that your trips have a different breakdown. Use whatever works for you.


Safety Considerations

When considering the safety of the passengers and crew, start at the worst-case scenarios.

The first dangerous situation on a boat is fire. (Read our article on fire extinguishers) Nothing burns faster than fiberglass filled with tanks of combustible substances. Wiring and electrical connections are the primary concern, but gasoline or LPG vapors are possible sources too. Fire extinguishers are a must-have, and they must be easily accessible. A life raft is a good idea if you’re headed offshore.

Secondly, the next most dangerous situation is flooding and sinking. A seaworthy vessel doesn’t let water in. You can include in this the risk of capsizing in rough conditions. Bilge pumps can help stem the flow, but they are far undersized and incapable of keeping the ocean out if the hull is compromised.

The next potential disaster waiting to happen is injury or sickness. When offshore, how quickly can help arrive, or how fast can you get back to shore? You’ve got to have a great first aid kit and know how to use it.

There are hundreds of other what-if scenarios you could run through. These are just some of the big ones.


Critical Equipment for the Offshore Vessel

As a starting point, you should look at what the Coast Guard requires for a vessel of your size. This should be considered the bare minimum and is a starting point for outfitting your boat properly. Here is a list of a few additional items you will want to consider.

  • Fire extinguishers and a fire suppression system
  • Bilge pumps of adequate capacity, because factory-installed systems are seldom enough
  • Extensive medical and first aid kits, plus first aid training for the skipper and crew
  • Type 1 offshore life vests for everyone on board
  • VHF radio, plus SSB radio or satellite phone if you’re out of VHF range
  • EPIRB (Emergency Position Indicating Radio Beacon, which uses its GPS and radio to signal for help when out of the range of all other forms of communications)
  • Flares and visual distress devices appropriate for offshore use
  • Liferaft and emergency supplies, including food and water (All liferafts should be kept where they can be deployed at a moment’s notice.)
  • Have an anchor with lots of rode on board in case your engine fails

Other Considerations for Taking Your Boat Offshore

  • Fuel Management

Use the thirds rule for fuel management, and always depart with full tanks. Use a third of your fuel to get there, a third of your fuel to get back, and always keep a third in reserve. Don’t just trust your gauge, always do your fuel calculations manually. Make sure your boat has good enough range to operate where you intend to take it.

  • Navigation

Know how to use your GPS and compass, and be able to use dead reckoning navigation when out of sight of landmarks. (Learn about boating navigation apps in this article.)

  • Fuel Systems and Contamination

Make sure you maintain your fuel system. Nothing stirs up sediment and water in a fuel tank like an offshore chop. Use a high-quality fuel-water separator with a sight bowl, and inspect it every day before you head out. Always carry spare filters onboard.

  • Weather

Check your weather from multiple sources. The National Weather Service publishes marine zone forecasts. They can be found online and on VHF weather channels. There are also many weather apps.

  • Float Plan and Getting Help

Boaters should file a float plan with a relative or friend. And all boaters should always have an active tow boat membership with BoatUS or Seatow, regardless of where they are boating.


What to Expect in a Small Boat

Taking any vessel offshore is all about the weather and your planning. Yes, your boat needs to be safe and well equipped. But exercising good judgment and picking good weather is just as important. Pay special attention to the wind speed, height of wind-driven waves, ocean swell, and tides and currents.

If you take your boat out on a calm day, it won’t be much different than boating on a large lake. The farther away from the land you get, the more prominent the wind-driven waves get. The more wind you add, the rougher your day. Offshore weather reports also include the wave period. This is the time, in seconds, that it takes to pass from one wave trough to the next. The shorter the period, the rougher and more uncomfortable the ride. If the waves are predicted to be four feet with a four-second period, the ride will be miserable in nearly any small boat. But if the waves are four feet with a ten-second period, it will be a lovely day on the ocean.

Ocean swell is usually not a problem, but for small boats, it can make it difficult to stay on plane and very uncomfortable. The biggest hazard with swells occurs over shallow water. If your inlet passes over a bar, dangerous breaking waves can develop.

Always consider how wind and current will combine. This is especially important when navigating inlets or other tight spots where the current speeds up. If the wind and current are in opposite directions, the waves will pile up with a very short period. The result can be dangerously steep waves that can easily swamp a small boat. It is always best to pass through inlets at slack current, or at least wait until the current and wind are aligned. Inlets are especially challenging since there is limited room to maneuver, and the real conditions inside the inlet are hard to see as you approach it.


Conclusion

This is far from a comprehensive article on taking a vessel offshore. If you’re new to boating or considering some ocean wandering for the first time, a safe boating course is a wise investment. These courses cover weather, navigation, maintenance and troubleshooting, and many other topics of importance.

Taking your small boat offshore is a great way to explore new territory, and smaller boats save you money in many ways. You can explore shallow waters that the big boys can’t, and you can take your boat with you nearly anywhere. But careful weather planning is important, as is having the where-with-all to say “no” when the weather stinks. Still, a well-equipped small boat is perfectly capable of offshore exploring.

 

John Allen

With more than a decade of experience cruising the lakes in my Crestliner Grand Cayman pontoon boat and my Boston Whaler, I now want to share everything I've learned with my community here at Boating Hub.

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