Posted on 01 July 2012
Written by Eric Sorensen
Sooner or later your boat-handling skills will be put to the test. Is your boat up to the task, and will you be on your game?
If you use your boat often enough and have the normal boater’s sense of adventure, it’s pretty likely that you’ll eventually find yourself in big seas. One minute you’re heading another five miles offshore to follow the fish reports. A few fish later and, the next thing you know, you look up from the fishbox to see that the wind has piped up and the 3- to 4-foot seas have turned into 5 to 6 feet — and growing.
It can — and inevitably will — happen to people who often use their boat in the ocean. Sometimes worse than 15- to 18-footers offshore are 6-footers in a wide, shallow body of water such as Pamlico Sound that can quickly go from flat calm to short, steep and breaking waves every couple of boat lengths. It’s like hitting a brick wall every 20 seconds. Either way, your boat and your skills will be put to the test.
The question is how to prepare for trial by wind and wave: Make sure you are in a seaworthy boat, and by seaworthy I mean stubbornly resisting Mother Nature’s best efforts to capsize or sink it. The key to achieving this is very simple: 1) keep the boat adequately stable, and 2) keep the ocean out of the boat. Every other objective is background clutter.
A little preparation can go a long way toward keeping yourself upright and floating in quickly deteriorating conditions. The first has to do with the boat. Let’s look at some key stability points.
Stability is largely a function of weight distribution, hull shape, sail area and free surface effect. Center of gravity follows a weight addition, so as you add weight in the bilge, CG shifts down and the boat becomes more stable. That’s why a builder puts the engines, batteries, fuel and water tanks, and other heavy objects as low as possible. If you add batteries or any other heavy weight to the boat, or a large amount of medium-density objects such as extra anchor lines and canned foods, put them as low in the hull as is feasible.
An outboard boat is going be slightly less stable than an inboard simply because the engines are mounted up on the transom rather than down in the bilge. On the other hand, outboard boats tend to be more maneuverable and faster, which makes them more agile when it comes to avoiding breaking waves.
When you add a tuna tower and side curtains up high on an express boat or higher still on the flybridge of a convertible, you lose some righting energy, with a very strong beam wind causing a heeling moment and diminishing reserve stability. The cleaner the boat is high up — the less windage it has — the more stable it will be dynamically. So in very high seas and strong winds you should consider removing the side curtains.
One thing I’d be careful about when modifying a boat is replacing the old 2,800-pound diesel with a shiny new 1,200-pound engine — and adding a big hardtop and hard enclosure where there used to be a canvas Bimini top and plastic side curtains. Adding weight up high and subtracting it down low decreases stability.
The most statically stable condition will be when your fuel and water tanks are full and no one is up on the bridge or tower. That’s because full tanks are heavier, driving CG down and stability up, and because full tanks have little, if any, free surface effect. Free surface, created by the energy of liquid sloshing back and forth from side to side (whether from fuel in the tank or water in the bilge), detracts from stability as a function of the square of the beam of the water surface. That’s why fuel tanks should be baffled to minimize sloshing and bilges should be kept dry.
When it comes to stability, don’t be fooled into thinking that because you have the beamiest hard-chine 40-footer in the marina it is more seaworthy. A 42-by-13-footer will be a much better boat all-around than one measuring 37 feet by 14 feet, 9 inches. The overly wide boat can be too stable, following the wave gradient too closely (metacentric height is too high on such a boat), and therefore more prone to capsizing in heavy weather. Short, wide boats are less comfortable (they pound and snap-roll), less efficient (they tend to run bow high, which adds form drag), and are less seaworthy than boats with moderate beam.
We know that weight distribution and hull form determine static stability and that kinetic energy from wind, wave and vessel momentum (and the vessel’s distribution of weight, or gyradius) determine dynamic stability. A poor hull form also can affect dynamic stability in very meaningful ways. For example, a boat with a large, tall superstructure that extends almost to the bow will be more prone to broaching when running down-sea. That’s simply because of the inertia, particularly the gyradius or flywheel effect of the weight up high and well forward that accentuate pitch and roll; the problem is that pitch and especially roll, combined with yaw, are what create that most dangerous condition, a broach, when running in a following sea.
Beyond hull form and CG, the ability to control yaw is to a large degree dependent on your steering gear, whether in the form of outboards or rudders. A boat with a lot of resistance forward, from a deep bow with a lot of profile (underwater area), combined with CG forward in the hull, a large and forward deckhouse, along with flat hull sections aft and too-small rudders, is going to be a broaching machine.
A boat that is nicely balanced CG-wise will still get into trouble down-sea if the hull entry is too fine, in some cases burying the bow deeply before developing enough buoyancy and dynamic lift to quickly come back up. A boat with a full keel running down-sea can be thrown into a broach if it is traveling at less than wave speed, so the keel can make the boat less controllable in certain conditions. If it is extended too far aft, it will slow the boat’s turn rate and overall agility appreciably.
When it comes to avoiding sinking, a Boston Whaler is the extreme example of the unsinkable boat, with the hull not only using foam for positive buoyancy in a damaged condition but also using foam structurally. There is enough foam by volume in a Whaler to displace enough water to keep it afloat in any conceivable condition of damage. Even in a boat with some foam, but less than in a Whaler, the foam acts as a barrier, serving as a membrane to slow or prevent water flow into the breached hull.
The hull of a larger boat can be compartmented or divided into many small sections so that a single breach will flood only a small portion of the vessel, leaving enough stability and buoyancy to remain afloat and upright in moderate sea conditions. But providing enough compartmentation to keep a 40-footer afloat is impractical for most boats because the cabin would need an extra, fairly high and obstructive bulkhead (better in this case to make the cabin sole watertight), and the engine room and lazarette would have to be chopped up into impractically small compartments.
But by using a combination of foam and compartmentation in the design phase, any boat can be made, if not unsinkable, highly resistant to sinking. Absent foam or extensive compartmentation, most boats will sink like a stone with a small hole anywhere below the waterline.
However, just because a boat can’t sink (easily) doesn’t mean it won’t capsize if swamped. In fact, the likelihood of swamping goes up with the sea state because of the stability-robbing free surface effect. To keep your boat afloat it’s also important to make sure the seacocks, hoses and related hardware below the waterline are kept in good condition.
The cockpit should be high enough above the waterline to provide adequate reserve buoyancy for the scuppers to drain overboard when the boat is fully loaded or even somewhat overloaded. The hull itself must be strongly constructed to resist damage and subsequent penetration from hard wave or object impact. Scuppers should be large enough to free any water from a boarding sea quickly.
The more freeboard, the better when it comes to keeping the ocean out of the boat. A tall bow is especially important. Some wakeboard boats and open-bow runabouts are, in my opinion, inherently unsafe, unseaworthy designs in rough water, especially when the water shipped over the bow ends up in the bilge instead of draining overboard through scuppers. Keep such boats on smaller lakes and bays, but watch the wakes.
I often run open-bow boats, such as center consoles and dual consoles, but I do so fully aware that such a boat is more vulnerable to a boarding sea forward than a closed-bow boat, which will shed most or all of the water right back overboard if the bow stuffs. In a center console, be assured that the wave will end up around your ankles if it is breaking when you stuff your bow into it (a rare occurrence with the right hull shape and adequate freeboard), so your scuppers and deck height better be engineered to send it overboard post haste. And while you have a foot of water on deck, make no sudden course changes that could cause a capsize, and keep her heading up sea until the deck has drained, for the same reason.
There’s also the condition of the drivetrain and its ability to provide reliable propulsion when it’s needed most. Having adequate horsepower to accelerate away from a breaking wave or to turn quickly between wave peaks is important. And it’s not just horsepower; it’s also how the power is delivered to the water that is important, with steeper gears and larger-diameter props providing far more traction at slow speeds than shallow gears and eggbeater props. Also, the engine needs a clean fuel supply, with clean tanks and adequate fuel filter/separators.
The boat should have a sound electrical system that is properly designed and maintained — and stays dry and corrosion-free — and adequate batteries for starting the main engines, with isolation and cross-connect capability.
A pilothouse with excellent visibility so you are aware of what’s going on 360 degrees around the boat is vital to situational awareness and safe operation. Pull those drapes back or take them down so you can see what’s going on astern. This is an area in which many of the enclosed-pilothouse boats being built today are weak, with as much fiberglass as glass between you at the wheel and the horizon. This need for unbroken all-around visibility is particularly important in heavy seas, especially when crossing a rough inlet when inbound so you can gauge and time the seas for safe passage.
Stay in charge
With a boat that’s in good structural and mechanical condition and is capable by design of running in rough seas, let’s look at some handling tips that might be of use in heavy weather. If your track takes you into the seas, tacking 20 or 30 degrees to either side of that track is a good way to minimize the time it takes to get home while decreasing the stress on your vessel and its passengers. That’s largely because you won’t be launching so far off the wave peaks with each encounter; pitching and heaving motions are more gradual when taking waves at an angle. Also, keep a very sharp watch forward of the beam so you can learn the wave patterns and steer around the roughest patches.
xIf you can’t outrun waves, you must be even more aware of what’s going on behind you, as you could be overtaken and swamped by a breaking wave. It’s ironic that displacement trawlers often have the poorest visibility astern from the helm; these are precisely the boats that most need to know what’s going on astern.
When running down-sea, you are most apt to get into trouble (trouble is spelled b-r-o-a-c-h if you missed that earlier) when you’re moving faster than the waves because crossing the wave crest can make for dicey going. Make sure you are on the right boat and on your game if you’re attempting to overtake heavy seas.
It might be that the safest strategy is to get on the back of a wave (a 150-foot-long wave travels reliably at 12.2 knots in deep water) and ride it in if your destination is downwind. If you are in a hard-riding, wet, underpowered boat with poor directional control and stability, God bless you. A wet boat is a dangerous boat because it keeps you from seeing as well, and seeing and reacting quickly and correctly is staying alive in very heavy seas.
My ideal rough-water planing sea boat has a moderately sharp bow with generous freeboard forward and a warped-vee bottom tapering to 20 degrees deadrise aft. It will get on plane at low speed, and the deadrise at the stern is enough to give the hull the directional stability it needs. One of the reasons Down East hulls can be a real problem running with the waves is their flat sterns, which may help them with load-carrying ability but do nothing to keep them going in a straight line in a following sea. That’s where the keel usually helps a little, and the barn door rudder, with power steering making a tight steering ratio possible, helps a lot.
If you must make headway beam-to in big seas, keep a very close eye upwind and be ready to maneuver to avoid breakers or, better yet, pick a different destination. Running with the seas just 10 or 20 degrees abaft the beam can be especially treacherous. Even when running along at a good 20 or 25 knots, the waves from that relative direction can overtake you one minute and you overtake them the next. This hazard can be especially pronounced in a boat with poor steering response.
One misconception is that displacement trawlers are necessarily the most seaworthy boats because they have such a high range of stability. However, not all displacement trawlers have all that great a range of positive stability (360-degree stability is sine qua non here), especially when windows start breaking and water floods the boat. Also, you’re going to need all the stability you can get if all you can make is 7 or 8 knots upwind.
I would much rather be in a well-designed planing hull that can maintain 16 or 20 knots in rough water, for two reasons. First, I can get home a lot faster and be tied to the dock and sipping a piña colada while the seas are still building and those 37-by-15-foot planing barges and 8-knot displacement trawlers are still slogging it out at sea. Second, if I can keep up a good turn of speed, I can avoid the breakers and the roughest patches of water by simply driving around them with my excellent hull form, plenteous power and agile steering.
On the other hand, if you have an ocean-crossing 8-knot trawler, pay close attention to your weather fax or other reporting service and avoid the high seas well in advance. If you are prudent and pay attention and have chosen and maintained your boat well, risk is reduced, and you should be fine.
Something else I consider whenever venturing offshore, regardless of the weather forecast, is who I’ll have with me on the boat. There
are many days when I would bring a couple of young guys (like me) along for a run through the inlet and offshore when I wouldn’t consider bringing my wife and small children or grandchildren. Again, it’s a matter of risk management, which by the way is what seaworthiness and seamanship are all about — mitigating, minimizing, controlling and understanding risk.
I have gained new insight from Ben Golub, a client of mine — he is having a Tiara 5800 built — who is in the financial risk-management business. So in the case of my wife and small kids, Pleasant Bay on Cape Cod, Mass., is great and appropriate on most any day, while there are many (even most) days when I would not take them through Chatham Inlet.
Why? It may be nice and calm when we head out, but by the time we get to the tip of Monomoy and back, things can change pretty quickly. Risk management means I take them no more than a few miles offshore from the inlet, and only on gentle days when my VHF radio and cell phone — more risk attenuation — are working. Then, as my wife, Sarah, pointed out on our last ride near the Chatham Inlet, there are great white sharks lurking offshore, waiting for one of those thousands of seals to happen by, which does you-know-what to the risk formula.
If it starts getting rough, put everyone in a life jacket, including yourself, and keep them down low in the boat, especially if it’s a small boat with a lot of big people on board. Don’t go aft or let anyone get into a vulnerable position topside in very rough water; it will be difficult to fish out someone who goes over the side, and you will be endangering the boat and the rest of the passengers when you do so.
Make sure the VHF with digital selective calling is working — DSC transmits your identity, nature of distress and position to the Coast Guard upon activation — and a handheld VHF backup is a great idea. If you head offshore beyond VHF line-of-sight range, you should have an HF radio, as well, for reliable communication.
Also, make sure you have plenty of flares, a working and registered EPIRB and, if you venture well offshore, a life raft that will automatically inflate and that has enough room for everyone on board. Survival suits can mean the difference between living to boat another day if you wind up in cold water.
Make sure someone knows where you’re going — in other words, file a float plan — so they can come look for you when you don’t come back as expected. If you change your destination and expected time of return, tell one of your contacts ashore. Know what the tide is doing so you know what to expect when coming home across the bar that evening. Make sure your running lights and bilge pumps work. It’s all common-sense stuff.
There’s lots more to talk about, but my pen is running dry. For now, your best bet when things get dicey is a boat that’s intelligently designed, soundly built, resistant to capsizing and sinking, has reliable propulsion, is capable of relatively high speed in rough water, and has good steering control and the ability to accelerate quickly (good traction and plenty of power). Don’t push it; if you wonder whether it’s time to turn around and head home or time to put on the life jackets, it is. Boats are only seaworthy for the conditions for which they are designed.
Buy a copy of “Chapman Piloting & Seamanship.” It’s in its 66th edition and is still the best text I know of on this subject. You can always learn something, no matter how much salt runs in your veins.
See related articles:
- Situational Awareness
- Watch your wake
This article originally appeared in the July 2012 issue.