Back to the drawing board: Design flaws I've noted - Soundings Online

Back to the drawing board: Design flaws I've noted

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Most boats have intelligent ideas worth noting, along with areas that need a little more thinking through. It’s rare to see a boat that gets it all right — or all wrong. My intent here is to provide some of the insight needed to distinguish what works and what could be better.

No boat is perfect, so consider a multitude of features when assessing safety and seaworthiness.

For example, I’ll take a look at a specialized class of boat, the tournament sportfisherman, and show how creating a pure fishing machine to the angler’s specs can compromise seaworthiness. A Coast Guard Motor Lifeboat, of course, is far more seaworthy, but it would be tough to land a bluefin tuna from a 47 MLB, which could also be more seaworthy with a few design changes.

Stepped bottoms

The stepped hull has several positive attributes: reduced frictional drag, increased speed and fuel efficiency, quicker planing and better sightlines because of a flatter running angle. But in order to function, in my experience and that of stepped-hull designers I’ve spoken with, the boat needs to be capable of a 25-plus-knot cruise. In other words, stepped hulls don’t help below these speeds and can actually add drag because of the turbulence at low planing or semiplaning speeds.

In addition to the need for speed, the boat’s center of gravity and weight must be kept under control — too heavy or too top-heavy, and the boat can have problems with instability. On some so-called stepped boats, you might see a notch in the chine that looks like a step cutout where there is actually no effective step under the boat. It’s just a marketing gimmick to make the boat look like something it’s not. If you think the steps are gimmicks, ask the builder for evidence that they are hydrodynamically appropriate for a particular application.

Love me tender

Boats that sell based on their interior volume tend to do well at boat shows, but out on the water they can be a problem. Voluminous boats have a full bow, which makes them hard-riding and wet in just a moderate seaway. A 35-footer such as this, with a queen-size berth and his-and-hers lockers in the bow, might be just the ticket for people who rarely cast off, but it’s not a good cruising boat, which will limit people who want to travel any distance offshore in comfort.

This brings up the importance of the sea trial. Be sure to take a boat out on a long test ride in rough conditions before buying it. Wait until the wind is blowing because most any boat will have good manners when conditions are calm. On boats smaller than 40 feet, in particular, it is also important to have a full load of fuel and water, as well as a full complement of crew and guests. That way you can see whether the boat is underpowered, whether it climbs up on plane easily, whether you can see the horizon when seated and coming up on plane, whether there is enough standing room and seating for everyone, and so on.

This plumbing setup could sink your boat if the raw-water inlet and bilge pickup are open and the engine shuts down.

Sea-trial results that the builder posts are often in absolutely ideal conditions, with an unpainted bottom, no canvas up, 20 percent fuel and water, and two people in medium-size shirts on board. Take the time to check the boat yourself.

Voluminous boats also tend to have a lot of sail area and get blown around at the dock, so make sure you can comfortably handle it in a strong wind. If you are apprehensive or embarrassed every time you bring the boat in or find yourself yelling at your crew — who is probably closely related to you — you will regret buying the boat. These boats also tend to have a high center of gravity, so they can be tender. Watch how far a boat lists when people step aboard from the dock, compared with other boats of the same size.

Safety first

This bow rail projects so far beyond the gunwale that it's difficult to reach and impossible to lean against without being off balance.

Another thing to pay close attention to is the bow rail. Ideally, it should be 30 inches tall, yield very little under 400 pounds of pressure and be directly above the outer walking surface. Some railings are nice and tall, but they’re canted so far outboard that they’re almost useless in keeping you safe. Some project so far beyond the gunwale that they would be impossible to lean against without your being off-balance, and difficult to reach even with your arm extended.

When you come up against a piling, the rail also will try to act as the rubrail, with unsatisfactory — and costly — results in the event of anything more than a gentle bump. This design also eliminates the ability to maneuver using a piling on the bow as a fulcrum, which is a very handy trick when maneuvering in close quarters.

When you inspect the engine room, all is not as it may appear. What is widely accepted in the recreational marine industry would not fly in commercial and military applications.

An example can be found in the photo above. It’s an example of high-quality plumbing hardware made of marine bronze alloy that could potentially sink your boat. Note that the main engine raw water inlet through-hull fitting has its own seacock — so far, so good. But integral to the raw water inlet are a pair of “bilge pickups” — inlets that can be used to dewater the bilge in the event of flooding, using the main engine’s cooling water pump, which has a far greater pumping capacity than the bilge pumps. (Note: An actual boat would not have both bilge pickups as seen here. This is a mockup to show the possibilities.) Whichever bilge pickup you choose, when it’s opened to take suction it creates a path from sea to bilge.

Imagine the mate sees water in the bilge, and the captain tells him to open the bilge pickup. Then the engine shuts down for some reason, and the plumbing pathway finishes the job. If the engine shuts down while the raw-water inlet and bilge pickup are open at the same time, the engine room will flood quickly. If the boat does not have watertight bulkheads, and enough reserve stability and buoyancy with the engineroom flooded, it will sink. A more seaworthy and sailor-proof design would have an either/or interlock so you could take suction from the sea or the bilge, but not both at the same time.

Sportfishing boats

Mates and anglers like to be standing just inches above sea level when playing and boating fish, whether in a 25-foot outboard or a 90-foot convertible. The trouble is there is little reserve buoyancy aft with such a low cockpit elevation. Losing buoyancy aft with a cockpit full of water can quickly put any big boat in trouble in heavy seas, especially if there is progressive flooding farther forward in the hull. That’s not to say a boat such as this is unseaworthy, but that compromises made to accommodate the mission can reduce seaworthiness in a way that both the owner and captain should be thoroughly aware of and ready to respond to in a cascading situation.

When this sterndrive is tilted up, it projects past the swim platform. This is dangerous to anyone jumping or sliding off the aft edge of the platform.

The same goes for adding one deck after another — an open flybridge on top of an enclosed flybridge, for instance — on a planing, shallow-draft hull form that relies on form rather than weight stability. This boat would be incrementally more stable statically and dynamically if the third-deck flybridge and the enclosed bridge were removed — this is only a thought experiment — because the vessel’s center of gravity would go down and sail area would decrease.

The ultimate stability of a shallow-draft planing hull is quite small, compared with a full-displacement vessel. The addition of weight topside is always going to cause the righting arm to decrease and the sail area to increase, both of which affect the boat’s ability to right at extreme angles of roll. This is especially the case when stability is measured not just hydrostatically but dynamically in a seaway with steep waves and high winds, where a planing hull’s stability can be reduced quickly.

Of course, this does not mean the convertible is an inherently unseaworthy design. In fact, in many ways, including its speed capability in rough water, it can be more seaworthy than an 8-knot displacement hull. However, what this means is that the boat’s design, systems reliability and redundancy, construction quality, maintenance diligence, as well as the crew’s experience, humility and judgment all have a bearing on the vessel’s ultimate seaworthiness.

Coast Guard

As a former Coast Guard surfman, I like to occasionally visit my alma mater. I used to run the 44 Motor Lifeboat and was interested in learning more about the 47 MLB that took its place. About five years ago, I saw one out of the water at a Coast Guard repair facility, and I saw then that even the Coast Guard gets it wrong once in a while. That’s my conclusion after spending some time on the 47 MLB, talking to surfmen who have graduated from the Coast Guard’s surf school and reading a caution about broaching in the boat’s operator handbook.

If the 47 MLB had axehead rudders instead of foil rudders — and they were substantially larger — I am confident it would be both less susceptible to broaching and far more responsive to the wheel when station-keeping in heavy surf.

A boat such as this, which is both light and high forward, needs all of the steering control it can get, especially at bare-steerageway speeds trying to keep the bow upwind in surf. In addition, excessive exposed rudder stock creates turbulence, reducing the lift (steering forces) generated when hard over. There is also too much space between the top of the rudder and the hull, so a good deal of pressure spills off the rudder, further reducing lift in the form of turning forces. Foil-shaped rudders create less drag at displacement speeds and are a good choice for sailboats but not for a planing hull capable of more than 26 knots.

Here is the warning from the 47 Motor Lifeboat Operator’s Handbook, pages 6-13:

“While operating the 47FT MLB stern to the seas >6’ and RPMs >1800, the boat is prone to being caught on the hardchine. Being caught on the hardchine is best described as the boat suddenly heeling over 50-80 degrees on a false keel. The coxswain’s corrective action shall be to immediately reduce power to return the boat onto the true keel.”

This is odd language to apply to what is a simple, though I’m sure extremely exciting, broach condition. A broach is a combination of a hard roll and yaw occurring at the same time, which is what is likely to happen when the boat lacks sufficient directional control down-sea. More powerful and responsive rudders would help prevent this from happening in the first place, as they would more readily prevent the yaw, which would in turn prevent the roll and subsequent broach that results when thrown beam-to in breaking or otherwise steep seas.

All boats are compromises, and the right boat for you will strike a balance. Keep these features in mind whether you’re evaluating a boat at a show or in the next slip.

April 2014 issue