TECHNIQUE The keel speaks to you: can you listen to it?

With the help of expert Davide Zerbinati, we tell you everything you need to know about your keel and reveal what are the “warning signs” that could hide problems, even serious ones

When we had the chance to go “for a lesson” from Davide Zerbinati, owner of the firm of the same name, we did not let the opportunity pass us by: in 20 years of activity, he has designed several hulls, appraised about 3600 boats (1000 models) and possesses a very high-profile know-how.

AT “KEEL SCHOOL”
We “went back to school,” sitting at our desks and taking notes as Davide told us what to check on your boat’s keel and how to interpret the signs that hide a potential problem-a key operation especially if you are buying a used boat because Zerbinati’s word, “statistically 54% of the surveyed hulls were likely to have experienced bottom impacts.”.

But first a bit of history: until the 1970s, boats were equipped with structural or semi-long keels (with a heavy ballast of 42 to 45 percent of the boat’s weight) made of cast iron, scrap and even concrete: innovations began in the 1980s with the first keels with semi-long bolted trapezoidal fins made of cast iron and lead.

Ten years later came the trapezoidal shapes with greater dive (35 percent ballast), and between the 1990s and 2000s here came the great popularity of bulbous fins, with increasingly thinner blades (and ballast equal to 28 to 30 percent of weight). The initial righting moment has improved over time, both through the introduction of the bulb (thanks to which, among other things, gliding at the lift is possible) and the shapes. Whether the future for cruising boats will be under the banner of foils (the appendages that lift the hull out of the water) or systems such as DSS is still too early to tell.

THE RIGHT MATERIAL
Let’s start with knowing the materials your cruising boat’s fin is made of to understand how it will perform. If you are buying a used boat, inquire about the fin material and specifically ask if it has been damaged or repaired, in which case have an appraiser analyze it with ultrasound.
One of the cheapest solutions is cast iron (iron-carbon alloy 2-6%), which is harder and more abrasion resistant than steel, but has less resilience (ability to absorb a shock without breaking) and greater brittleness.

The best cast iron is austenitic spheroidal cast iron (GS550): however, some yards use a medium-low grade cast iron, ferritic spheroidal cast iron, which is often porous (i.e., with widespread presence of small voids) and not free of casting. Therefore, be aware that in the event of bottom impacts, the fin may have cracks in the structure or dangerous internal fractures. It is generally glued to the hull with soft sealants.

Somewhat more expensive is the lead fin: this is a softer and more ductile material that can absorb shocks well. But it must be “hardened” with antimony (usually at 4/5%) to prevent it from deforming under its own weight, and there must usually be a cage inside it that acts as a skeleton preventing deformation of the profile. The problem with lead is bonding to the hull so what you will need to check periodically is the attachment of the keel, the condition of the pins and studs (i.e., the “tie rods,” immersed in the fin during casting, that are used to “hang” it to the hull). Usually the best bonding to the hull is with resin: watch out because history speaks of frequent water seepage when bonding with soft sealants (polymers).

SPECIAL AND METAL
Leaving aside fins for racing boats, with special or “Weldox” steels (machined with numerically controlled machines), whose profiles are perfect, one of the most popular solutions is the hybrid one: the wing part made of cast iron with the torpedo made of lead. This is because cast iron provides profile rigidity, while lead offers more stability, impact resistance and less volume since it has a higher specific gravity.

Aluminum and steel are used only when the fin is structural: ballast, usually lead, is cast from within or from special holes and then occasionally insulated. This ensures a monocoque structure. Inside the hull, the fin studs are attached with nuts to a perforated metal plate: usually bonding is done with araldite (epoxy resin) and finished with soft sealant. The choice of using a soft glue with cast iron fins makes it easier to disassemble and faster to assemble.

WHY BOATS LOSE THEIR KEEL
After the necessary “smattering” of materials, let’s move on to the problems that can affect what is underneath your boat and, precisely because they are not immediately noticeable, very dangerous. Every year, there is no shortage of cases of boats losing their keels with more or less serious consequences. This can happen because of a structural problem in construction or design (the lost keel of the Oyster 825 Polina Star III recently came to the forefront), and in this case it will be up to the surveyor to determine which.

One of the most common reasons for this is corrosion of support pins (often for cast iron fins) or studs (which in this case are part of the lead fin cage): rust “eats” one or two of them, the others give way later through fatigue.

Brown side drippings on the fin are an early warning sign. Check periodically, by opening the dunnages and accessing the bilge-if there are fiberglass encapsulations they should be evaluated-that there is no rust and that they are of the right materials. Stainless 304, 316 or 316L, cadmium-plated steels are okay (A2-grade austenitic steels are not good, because they do not resist chlorides and thus salt water): check that the washers are also made of the same material, or at most galvanized iron. Generally, the pins should be cleaned, tapped, and brushed well so that an assessment can be made as to whether the rust is only superficial or whether the material crumbles between the fingers and becomes black-colored rust: of course, replacement of the pins will have to be done on site.

If the pin is found to be in good condition, shiny and not deformed, it should be treated with ferox or primex epoxy and then coated with lithium grease or similar. You understand how critical it is to keep the bilge perfectly clean to avoid upstream corrosion and poor visibility of “suspicious signs.”
S

and you hit the bottom (you, or the previous owner if you are buying a used boat), know that the hit may have caused the pins to break or damage to the planking laminate where the keel is attached.

This could fail completely as a result of delamination (i.e., the total disconnection between two adjacent layers of the laminate. A delamination is considered to be a disconnection of more than 6.5 square cm) that is not perceived over time.

THE “NAKED EYE” CONTROLS
As you may have guessed, the keel is one of the most delicate parts of the boat: placed that, if you are buying a used boat or if you want to be even more reassured before launching your new boat, the overriding advice is to go to an experienced technician, here is what you can check “with the naked eye” to avoid getting ripped off and more important, not to find yourself in dangerous situations.

Definitely, when the boat is dry, check for excessive separation between fin and hull and that the planking does not show abnormal flexing aft (a sign of a high-speed impact): also pay attention to any cracks in the structure; a small split could hide a huge amount of damage inside the fin.

In the square be suspicious if the dunnage is not well aligned and that there are no abrasions at the base of the furniture caused by sudden raising of the dunnage. A blow or structural failure could have raised the keel. Do not even trust if you understand that the bilges have been blatantly repainted or if they are very dirty, they may be hiding a crudely fixed problem or there may be water seepage from the fin. Finally, check, as we have already anticipated, the condition and shape of the studs and that the bolts grip the entire thread.

Eugene Ruocco

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