The Top Twenty-Five Design Errors
Commonly Found in Boats of All Types
by David Pascoe, Marine Surveyor
The following is a list and brief discussion of the top twenty-five major design errors that I find in boats of all kinds, power and sail. It was based on my experience with over 4000 surveys conducted over 30 years. You can use it as a guideline as to what to look for when trying to see beyond all the glitz and glitter of the surface appearance, to make a preliminary self-survey before you make an offer. (Text 32K)
it's hard to believe that a builder would try to get away with building a 32 foot boat with only one structural bulkhead, but a lot of them do. Or, what is proffered as a bulkhead is really nothing more than a partition that separates one space from another. A boat that lacks adequate bulkheading suffers from all sorts of problems, starting with the fact that the hull will twist along its longitudinal axis, so that what you end up with is a sort of "flexible flyer." From there hull/deck joints start loosening, guard rails loosen and fall off, the boat leaks, stress cracks appear all over the decks and superstructure, and engine alignment problems occur which are rarely ever correctly diagnosed.
In teaching a marine survey class, I would use a 30" long plug for a boat model hull that had 12 station, full 3/32" plywood bulkheads and skin, but no deck. That's very thin and light, but to demonstrate the tremendous strength that bulkheads give to a hull, I would put the model down on the floor and stand on it. I did this dozens of times and it never broke.
A series of small partitions, bonded to the hull like a series of frames usually will not do the trick. Look for wide open spaces and substantial lengths of the vessel which have no bulkheads. When dividers are found, check to see whether they are really bulkheads or just space partitions; check for signs of movement or working of the interior components. Look for evidence of splintered wood, parts rubbing together, gaps in joints where there shouldn't be any, screws backing out and misaligned components.
Insufficient bulkheading often goes hand in hand with flexing decks. For express cruisers particularly, where the fashion is to provide large open interior spaces unbroken by bulkheads, the lack of support not only causes the deck to feel like walking on a mattress, but the flexing of the deck results in serious leakage problems. Hatches, port holes and windows mounted in a flexing structure will develop leaks that will be impossible to fix. It should go without saying that large decks need to have adequate framing, yet far too many designers and builders overlook this obvious point.
These conditions can be easily checked by walking or jumping
lightly on the decks to see how much they sag or flex. Look
for leakage around windows, port holes and most particularly
inside of cabinets, lockers, under berths and so on for signs
Without a framing system, hull sides pant (flex, bend) and put stress on the hull/deck joint, shearing off screws and resulting in the deck joint opening up and rails loosening or falling off. The inability to keep rub rails on is a chronic problem for many boats, and so are leaking port holes that can never be sealed because of the hull sides panting. Bear in mind that when a hull slams off a wave, extremely powerful shearing loads develop in the hull sides that are primarily responsible for deck join problems. And for cored sides, the problem can be even more critical because these loads are highly conductive to causing core separations. One way to check is to just pound on the hull side and see if the whole structure flutters. If it does, you'll know what you've got.
Check for loose rub rails, screws backing out, cracks along the deck joint, loosening of components attached to the hull sides on the interior. As with #2 above, also check for signs of leakage at the deck joint on the interior.
Here's a design faux pas that's been around for a long time and one would think designers would be more alert to it. Cabin tops and flying bridges need a bit more than window frames to hold them up, and when the structure is inadequately designed, the boat owner is left holding the bag for all sorts of serious problems. First is chronic window leakage that, no matter how many times the frames are pulled and recaulked, simply will not stay sealed. Another problem is cracking window glass which, on warranty claims, builders claim that the owner abused the boat. In most cases it's not pounding that broke the windows, but stress on the glass because the window frames are the primary means of support.
Design mistakes like this can be difficult, if not impossible to repair or correct. The problem with buying a boat like this is that the unrepairable leaks will ruin the boats interior, causing a substantial loss in resale value. In newer boats the leaks are usually small, but develop over time to a serious and chronic problem. Occurs most often in 25' to 45' motor boats of all types. Easy to diagnose by simply examining all windows from the interior. If the exterior frames are smeared with caulking, you can be sure there's a problem.
A frequent problem with 30 -40' fly bridge sedan models where the stringer height is reduced to unacceptable levels in order to achieve headroom and styling considerations. The objective is to place the engine as low as possible to achieve this by reducing stringer height. Most often it is the outboard stringer aspect ratio that is so low that the hull bottom and stringer are flexing. In other words, the stringer is too weak to prevent the bottom from flexing and so the engine is moving up and down! I have measured stringers moving up and down by as much as 1-1/2". A condition like this will wreck the engine mounts and often cause transmission and propeller shaft damage. I've had cases of boats going through three and four transmission failures before the source of the problem was finally discovered. Requires a professional surveyor to evaluate.
If the proper ratios of strut arm length-to-width to cross-section are not achieved, under the load of the propeller that strut will flutter. Many struts also have a base that is too small so that the strut applies too much leverage to the base, causing it to loosen. When the proper design parameters are not met, the entire drive train starts to self-destruct. Symptoms are constantly leaking stuffing boxes, vibration, rapid cutlass bearing wear, loose and leaking strut bolts, engine mount damage and occasionally leaking transmission seals or damaged output shaft bearings. A design error that can be very costly to correct.
A typical example is a 28' aft cabin style cruiser which has the cabin sole only a few inches above, or even literally on the bottom of the hull. Then the bilge pump is installed in the only place that it can be, under the engine where it cannot be reached for testing the float switch or servicing. When the float switch inevitably fails, the cabin floods, and can cause considerable damage.
Most commonly a problem on motor boats under 35 feet and most sailboats in small to midsize range. A boat left afloat, unattended has to have a reliable pumping system. Every year hundreds, if not thousands, of boats sink because of reliance on bilge pumps that are too few in number, too small in size, or pumps that are simply improperly installed. Bilge pump system failure is a common problem because (1) float switches can easily jam with debris, wire connections get wet, or the switches come loose and lay on their sides, effectively rendering them inoperative.
Forty years of trying have proved that a single pump cannot be made reliable. Therefore, the only effective solution is redundancy, i.e. back up pumping systems. Be sure the boat has an adequate number of, and properly placed, bilge pumps.
No one would take their living room furniture and put it outside in the rain, and yet boat builders seem to insist on putting non-weather resistant upholstery on the exterior of the boat. After a few years, the plywood base structure rots and it all begins to fall apart. A typical 32' express cruiser can have as much as $3,000 worth of upholstered items in the cockpit area, a high price to pay for such perishable luxury. If you're not willing to put the covers on after every use (as most people aren't) then you'd be better off avoiding all this upholstery. The best bet is to look for boats that have removable cushions that can be stored in the cabin. Otherwise, you'll pay a high price in rapid deterioration and loss of resale value.
A boat's exhaust system has to be designed in such a way that water cannot flow back up the exhaust pipe and into the engine. Again, because we have so many untrained people designing and building boats, this continues to be a common problem with boats of all types. Result of design error is costly engine damage, the cause of which is frequently overlooked or misdiagnosed.
The problem here is that you have a very costly piece of machinery located under a non-watertight hatch. Most often, the hatch has poorly designed gutters and drains that easily clog up with debris, causing the gutter to overflow and pour water onto the generator. The result can be the ruination of a $4-8,000 generator, a very high price to pay for a piddling design mistake. Generators located under cockpit decks should have large and deep gutters, large drainage systems and lock down, gasketed hatch covers. Problem is most prevalent with entry level boats; more and more top end builders lately have been addressing the problem.
This web site contains several articles on this subject so I won't go into much detail here. Suffice to say that some builders having been building blister-free boats without the use of more costly materials for a very long time. So why don't they all? Mainly because they find it cheaper to try to fend off warranty claims than to institute the kind of quality control that is well known to prevent blistering. Only the boating public can prevent this problem by refusing to tolerate blistered bottoms.
Switches, circuit breakers, engine instruments and other controls located on an exposed helm panel. Either the equipment is not water proof, of the panel leaks water so that all the terminals and connections under the panel get wet, corrode and fail. You know what would happen if you left your convertible car out in the rain with the top down. Why expect it to be any different with a boat?
Welded aluminum fuel tanks can last darn near forever, but not if they're not improperly installed. Aluminum tanks corrode and fail, not because they get wet frequently, but because at some point they trap water in a place where it constantly stays wet. Most common problems are foamed in place fuel tanks and tanks mounted directly onto a plywood deck. The foamed tank can trap water between tank and foam, while the plywood deck on which a tank sits stays wet and never dries completely. Problem is most prevalent on small cruisers and runabouts.
This used to be a very common problem with big, expensive diesel engines. When riser failure occurred, resulting in water entering the engine, the repair costs on warranty claims was so high that larger boat builders resolved the problem fairly quickly so that poorly designed risers on big diesels is much less of a problem today. For gas engines, it's another story altogether. The worst offender is Mercruiser, whose thin wall, poorly designed risers fail by the thousands, often after only 3-4 years, usually resulting in severe and costly engine damage. Crusader Marine solves this problem by placing the riser within the fresh water side of the cooling system so that the risers are not salt water cooled, unlike Mercruiser whose risers are seawater cooled.
Top quality engine mounts are very expensive and this provides the motivation for builders to use the cheapest mount they can find. Unfortunately, if the engine mounts aren't going to hold the engine steady, then the engine can't possibly stay in alignment. And when the engine goes out of alignment, bad things start to happen. This is why most surveyors pay close attention to engine mounts and conduct a load test to ensure that the mounts are doing their job.
This includes bilge pump discharges, cockpit drains, shower sumps, heads, sinks and the like. Builders often seem to forget that when you make a hole in a boat to let water out, it can just as easily - often more so - bring water into the boat. More boats sink from improperly designed plumbing systems than any other cause.
Despite all the hype by manufacturers and marketing people, foam cored structures still experience high rates of failure. There is no escape from the fact that foam is a very weak material, and why anyone would want to use it in boat construction is a mystery to me. The number of companies that have used it, and have subsequently gone out of business, is inordinately high. If you are contemplating buying a boat with a foam cored hull, beware that it is not without risk of encountering extremely costly defects.
Because rear engine boats are stern heavy, it doesn't take much water in the hull, which runs aft to where the engine is, to sink. Every year thousands of small boats in the 16' to 30' range with either outboards or stern drives sink. Most often, the culprit is improperly designed cockpit decks and drains (scuppers) located only a few inches above the water line. This can mean that many boats only have an effective freeboard of only several inches. Don't be fooled by those flimsy plastic hatches in the cockpit deck that rely on a small O-ring to seal them. Most of the time those O-rings do not seal tight and allow water to leak into the hull. Nor will flappers on the scuppers keep the water out.
Most frequent offender is the hole cut low in the motor well for the control cables. The purpose of the motor well is to keep the water out of the hull. But when you cut a hole in the motor well . . . well, guess what will happen? The same applies again to our little plastic hatches or inspection ports installed at the bottom of the well. They're not water tight and can end up sinking the boat. A motor well should have no holes in it whatever below the level of the transom top where the engines are mounted.
Most common in outboards or stern drive boats. Plywood transom cores rot out because the builder cuts the stern drive opening but does not seal the exposed edges of the plywood that then sucks up water and rots. Particularly a problem for fresh water boats, less so in sea water. Glass encapsulated wood stringers are inevitably going to get wet, and that's usually not a problem as long as the wood used is rot resistant. Most often a problem in lowest price boats where cheap materials were used, like cheap, untreated C-D plywood.
Typically, this problem manifests itself as the vessel ages. Not having adequate support, the cabin top begins to sag and rigging loosen. Often times the deck is supported only by an interior partition, usually the head compartment, which is sitting on a fiberglass sole or inner liner, with no support between the sole and keel. Look for: sagging cabin top, head door won't close properly, partitions loose, joinery work spreading apart, gaps in moldings or a sagging cabin sole.
The primary cause of all water saturated cored decks. So many stanchion bases have such a small foot print, that when pressure is applied to the stanchion, it simply prys all the fasteners loose. And when that happens, water leaks into the core and into the interior. Cored decks should be designed with a fillet around the stanchion bases, an area where there is no core but only solid fiberglass. Stanchion fasteners should NEVER go through the core. Look for soft, spongy feeling decks, primarily at midsection, and water stains on the underside, usually within cabinets.
Leaking chain plate causes bulkhead to rot or serious interior water damage. When chain plates go through the deck, there should be a raised boss or fillet in way of the chainplate. That's so that the caulked seam does not end up submerged in water standing on the deck and leaking gallons of water into the boat.
Very common in low cost boats. Look for water
stains on inside of hull at mid and bow sections, inside cabinets
and lockers; also lots of rust stains from wet steel cans
and other steel objects that rusted, usually in galley or
under dinette. Another sign is a boat that has too much mildew
First posted on October 14, 1997 at David