Select Page

The job of a sailing boat’s keel is to control sideways movement through the water and to provide a counterweight to the sideways force of the wind on the sails, which causes a boat to heel over.

Keels are designed to act as underwater foils that generate lift as the boat moves through the water, counteracting the leeward force of the wind and enabling the boat to sail closer to the wind.

The most common type of keel used for sailing yachts is the bolted-on fin keel. Fin keels are usually made of cast iron, bolted through the undersides of GRP hulls with substantial stainless steel bolts. Other types of keel include bilge keels, shoal keels, encapsulated keels, lifting keels and canting keels, as used on racing yachts.

While iron is the most common type of ballast, lead is also widely used. Cement or concrete is sometimes used in combination with scrap iron as ballast for wooden and steel boats, but this can lead to steel rusting from the inside and is not considered good practice. Some modern racing yachts have water ballast which can be pumped into tanks to help counterbalance heeling.

Clearly, motor boats do not require deep keels to counterbalance the heeling effect and sideways force of a boat under sail, but nonetheless they do have keels designed to keep them stable and provide structural integrity. Displacement hulls are often ballasted to increase stability. As a result they have a low centre of gravity making them less susceptible to the wind and waves than planing hulls, which are designed for speed and performance.

Keel problems

It is very rare for a keel to fall off a boat. When this happens the incident often receives a lot of press attention as the subject is understandably of concern to boat owners, builders and designers. Marine accident investigators are usually called in and reports are published explaining the probable causes of these accidents.

There are more common incidents involving keels that require inspections and repairs to be carried out.

Keel bolts inspection

Keel bolts should be inspected once a year for signs of corrosion. Most keel bolts of modern boats with cast iron keels are studs, threaded into a tapped hole in the keel. Keel bolts can be made from either stainless steel or galvanised steel.

Lead keels often have J shaped bronze bolts cast into the lead. Bronze is only used with lead keels as bronze and cast iron create a galvanic reaction.

An inspection entails looking from the inside and outside of the boat:

Outside check

  • If there is rust appearing along the hull to keel joint then this is a clear warning sign that the studs may be corroding.
  • Look for any signs of movement between the hull and keel, such as splits in the seal or cracks in the hull area around the joint.

Inside check

  • Do a visual check of the fastenings in the bilges, making sure you take a look at all of them even if they are hard to access.
  • Dry and clean the bilge – the bilges should be kept dry at all times to help prevent corrosion of the fastenings, even if they are stainless steel.
  • Some staining and minor rust is quite common but heavier corrosion needs to be checked over carefully.
  • Surveyors tap the studs with a hammer and know what sounds to listen for. A ringing sound is good, a dull sound is not good.
  • Check for any stress cracks in the bilge area around the keel bolts, which indicate there has been movement. If you see damage like this then it would be wise to have the keel removed for further inspection.

Keel bolt corrosion

Keel bolts can sometimes be withdrawn for inspection to check their condition and for any signs of corrosion. This entails first removing the nuts one by one and inspecting the threads for signs of crevice corrosion.

Quite often, it is the middle part (the waist) of a bolt where the corrosion is taking place, which is where the hull joins the keel. This is caused by the failure of the seal at the hull-to-keel joint, which allows sea water to reach the bolts and corrode them. Under these circumstances, the seal will need to be replaced as well as any corroded keel bolts.

If you have any cause for concern it is wise to ask an expert to take a look and advise whether the keel needs to be removed for further investigation and repair.

Keel bolt and hull-to-keel seal replacement

A typical repair involving keel bolt replacement and new hull-to-keel joint proceeds as follows:

  • A frame is prepared to support the keel when it is separated from the hull.
  • The boat is supported in the boatyard hoist or crane.
  • The keel bolt nuts and washers are removed from inside.
  • The boat is hoisted a little off the cradle.
  • As separation begins steel blades are inserted into the hull-to-keel joint crack to cut through the seal. Steel wedges may be hammered into the joint to encourage separation. This can take several minutes as seals are sometimes reluctant to give way.
  • Once the hull and keel are separated the boat is lifted clear from the keel. The keel now rests in the wooden frame.
  • The keel bolt studs are inspected. If any are badly corroded or distorted then they are removed and replaced.
  • The old sealant is ground away from the flat surfaces of the hull join and keel top.
  • The fibreglass hull around the join area is checked for stress cracks. If these are found then the hull will need to be strengthened with new layers of woven fibreglass mat and epoxy.
  • The hull and keel top are prepared thoroughly for priming in order that the new sealant can be applied.
  • The boat is slowly lowered back down onto the keel, then the backing plates, washers and nuts are fastened. Excess squeezed out sealant is wiped off.
  • The nuts will need to be torque tightened according to the recommended keel bolt diameter torque settings as the seal beds down and checked again after the boat is relaunched for any signs of leakage.

 

 

What boating skills should you have before you buy a yacht?

Many people dream of owning a yacht and sailing off into the blue yonder. What boating skills should you have before you buy...

Wooden Hulls – Part 1

Traditional wooden boats have a plank on frame construction, a centuries old boat building method that is still in use today. Variations of the traditional method include carvel, clinker and strip planking, which all relate to the way the planking is attached to the frame.

Antifouling for leisure boats – Part 4

Applying antifouling. Antifouling is best applied on a dry, calm day. It is best to apply the antifouling in the middle of the day to ensure the hull is dry and as warm as possible.

Navigation safety: a quick-reference mobile app to learn the ColRegs NavLights and Shapes

 Safety at SeaSafety at sea will always remains a topical and important subject that will no doubt dominate the syllabuses of nautical...

Boat Engine Safety Checks

  Boat Engine Safety Checks Every skipper needs to make regular essential boat engine safety checks. Below you will...

Rudders and steering systems – Part 3

In the third of our three blog articles on rudders and steering systems, we look at how to replace rudder bearings and repair a water-saturated core.

Cleaning & polishing gelcoat topsides

The gelcoat topsides of a GRP boat can be pampered and restored to their former glory relatively easily when it is ashore. Gelcoat is only a very thin outer layer of the hull, often less than 1mm thick, so you should avoid cleaning it with highly abrasive cleaners, or an-ything that could potentially damage its surface.

Tools and spares for your boat

It is wise to have a comprehensive and well-organised tool kit and a supply of spares for your boat. This is both for routine...

Boat decks and superstructure

The deck of a boat is constantly exposed to the elements and should be inspected on an annual basis. Particular attention needs to be given to the overall condition of deck fittings such as the stanchions, cleats and chainplates.

Understanding your mast and rigging

The rig of a sailing boat is put under huge stresses and strains so it is important for inspections of a yacht's spars and rigging to be...

Understanding your boat’s compass

Article submitted by Mike Rossiter, Certificated Compass Adjuster. Since the magnetic compass was first used by the Chinese...

Safety Equipment Checklist for Boats

Safety Equipment Checklist for Boats   Liferaft line attached The liferaft will not work unless the trigger line is...

Pleasure craft safety equipment recommendations

Safety equipment is an important part of boat preparation and it is advisable for all pleasure craft skippers to check their vessel is...

Boat Improvements

My Boat - practical improvements Author - Mike Rossiter Most boat owners who have had their craft for any length of time will have made what they...

VHF DSC radio – how best to communicate at sea

There are many ways to communicate with others at sea. What makes the VHF DSC radio the best form of short range...

An explanation of the IALA maritime buoyage systems – IALA A and IALA B

What are the differences between the two IALA buoyage systems, IALA Region A and IALA Region B, and where are they used?   As recently as the 1970s...

Saildrive maintenance

There are less maintenance tasks to carry out on a saildrive transmission than on a traditional inboard shaft drive system with its associated stern gear. However, there are a few critical things that require maintenance, as recommended in detail by the engine manufacturers, and should be adhered to.

Keel maintenance and Repair – Part 2

If you have ever witnessed a boat colliding with a rock or other submerged obstacle you will know that there is an almighty thump and the whole boat shakes and judders. While such hard groundings seldom result in catastrophic keel failure, something has to give and even the sturdiest keels can easily be damaged by such an impact.

Essential Knots: Figure of eight

Essential Knots: Figure of eight Use: Stopper knot, prevents a rope from being pulled through a hole e.g. through a block or...

The give-way hierarchy at sea – who gives way to whom?

Whatever their size or type, all skippers have a responsibility to avoid collisions with other boats at sea.  It is...

Seized fixings and fastenings

Maintaining a boat can be a rewarding experience but at times it can also be frustrating. A prime example of this is when you come across a seized fixing or fastening that refuses to budge. Read our tips on how to release and fix them:

Hourly Checks when sailing or motoring

  Hourly Checks Get into the habit of carrying out these checks and both yourself, your crew and your boat will be...

Boat Engine Failure – what to check

Engine failure If your engine fails or is overheating there are a number of things to check immediately: • Air filter...

Wooden Hull Repairs

While wooden boat hull maintenance is mostly straightforward, it is always a good idea to take expert advice on any repair job needed doing to a wooden boat, unless you have done the job before and know what you are doing.

Boat engine fuel system

If engines are installed and serviced correctly then most marine engines are very reliable, but one of the most important parts of the engine to check and service is the fuel system.