Boat Keels & Fins: 7 Types Explained (For Beginners)

A keel is basically a structural component of a boat or ship which looks like a fin that extends at the bottom of a boat on the center-line.

A keel of the boat is usually the first component that is constructed while building a boat. The main purpose of a keel is to offer both strength and balance to a ship or boat while it is in the water.

These keels are available in different designs, as explained below:

7 Types of Boat Keels Explained

Keels may be found in six varying designs, giving rise to six keel types.

They include:

1. Full keels
2. Fin keels
3. Bulb keels
4. Wing keels
5. Bilge keels
6. Centerboard keels
7. Canting keels 

1) Full Keels

This particular keel by design covers at least half of the boat´s length.

It contains a forward edge that bends upwards, while its aft edge usually links to a rudder. This type of keel has a key advantage of providing directional stability as well as relatively safe and strong grounding of the boat or ship.

When referring to safe grounding, the full keel is safer if the boat gets to lie on hardened ground.

The full keel offers a stable and strong balancing surface for the hull whether the boat is along the coast or while traveling.

A boat or ship which is made with a full keel rides smoothly while traveling in the water, providing great directional stability. For instance, if the full keelboat is well balanced, it enables a boat to stay in the compass direction with the keel keeping the boat in a steady direction.

A full keel design is the traditional style of older wooden boats and many newer boats.  It has many years of experience that provides a comfortable and safe boat. 

2) Fin Keels

This type of keel has a length that is less than half of the hull length. It is designed with a flat shape that is sharp-pointed at its trailing edge and resembles a shark’s fin. This type of keel is very fast, it contains less wetted surface as compared to full keels, and it also has a deeper draft than the others.

Often, the deeper the fin keel´s draft is, the better it makes a ship or boat sail.

When it comes to speed and racing, as well as performance, the fin keel is unbeatable.

3) Bulb Keels

This particular keel is often referred to as a shoal draft fin keel. Typically, a deep fin keel is made shorter and then connected with a torpedo-like bulb made from lead material at the bottom of the keel.

It is specially designed to be shallow to allow sailing or cruising within the Bahamas or the Chesapeake Bay as well as other areas with shoal water depths.

However, this design does not significantly compromise the boat´s performance since they have been used on older racing sailboats.  

If you are planning to sail over shoal waters, a bulb keel may be appropriate.  Sometimes, they are not as shallow as other special full keelboats, however.

4) Wing Keels

The Wing Keel may be used as an alternative when sailing in shoal waters.

This does not use one bulb at the bottom of the keel; instead, it makes use of two plates that are attached laterally at the bottom of the fin keel.

This type is considered by some to be better when it comes to performance as compared to bulb keels since it minimizes tip vortex turbulence while sailing. Its draft is usually less.

Additionally, since the two sides are designed in a manner that they offset each other, as the boat heels while sailing, the lateral resistance is not reduced as much as with straight or bulb keels.

However, this type of keel is hard to free in case the boat gets stuck into the muck. Their wings usually go deep and grip onto the bottom of the ground, making it difficult to release once it gets stuck.

Some of the advantages of a wing keel include:

• Minimized draught
• deeper center of gravity, which implies they have better righting moments
• re-engineered water flow above the keel foot implying that they have high efficiency and results in better sailing characteristics.

On the other hand, its disadvantages include:

• It can be more difficult to free if the boat goes aground
• this type of keel is likely to collect objects such as lobster pots as it sails
• and weed may grow at the bottom of the wings, which can become hard to remove.

5) Bilge Keels

These double bilge keel makes a boat stay upright in case of a dried out low tide.

This design results in a shallower draught as compared to fin keels. This feature makes it appropriate for sailing in shallow waters along the coastlines.

However, this type of keel does not perform as well as a single keel and is therefore used for sailing instead of racing.

6) Centerboard Keels

This is yet another alternative that may be used in shoal waters.

The centerboard keel contains a base keel, which has an internal centerboard that rotates downward to create a deeper keel when sailing.

If the waters are deep, the sailor gets better performance with the centerboard down. If you are sailing in shoal waters, you should sail with the centerboard upwards.

This feature is important as it helps to provide the boat with a performance similar to a deep keel and yet to offer improved maneuverability in shoal waters.

However, the main disadvantage of the Centerboard keel is maintenance. It is difficult and problematic when it develops mechanical issues.

7) Canting Keels

This type of keel is the most unique when it comes to performance.

It is connected onto a special (strong) hinge, and as the boat or ship heels, the crew uses hydraulics to move the keel in the windward direction.

This process of moving the keel in a different direction from your heading direction makes it possible to maximize the lateral force and the righting force, to sail faster.

The main challenging posed by this keel is maintenance due to the complex design of the canting keel.  It is usually only found in specialized racing boats.

It has a promising future when it comes to racing, but it is not recommended too often because of its complicated operations.

Common Problems With Boat Keel and Fins

First, fins and keels are not protected from potential external impacts. By their design, they are long components with lever-like arms.

Therefore, if an underwater object was to be hit, like a sunken piece of log or even the sea bed, the force that would result is likely to be multiplied before being re-transmitted onto the entire boat over the keel area.

Therefore, the small surface is likely to encounter excess loads, which may result in cracks.

For instance, on the Chesapeake Bay, the majority of the creeks range from 4.5 -5 feet downwards. Boats and small ships that attempt to get too close to shore may often get grounded at some point. The moment grounding happens, the force which results and exerts pressure onto the keel is strong enough to generate cracks on the keel or along the hull.

The cracks are only physical indications of the damage caused.

For instance, the bolts which are connecting the keel and the hull at the bottom of the bilge may be frequently wet, resulting in bolts rusting and getting corroded.

When this happens, the forces together with rusted bolts will result in the keel falling off. This is dangerous and can cause severe accidents.

When the keel is removed or damaged, and the keel bolts develop holes, it allows water to flow into the hull. If the holes remain in that condition for a while, this may cause the boat to sink as a result of the incoming water.

Also, when the keel has been compromised in some way, the ballast or righting weight, which helps to counter the sails, is eliminated. In this case, if strong wind heels over your boat, it may result in the boat capsizing!

To make it worse, after the ship has capsized, you will not be able to right it since the ballast will not be there. Therefore, when a keel is destroyed, it makes the sailing horrible!

Finally, if you want to sail a boat with a fin and keel, it is recommended to avoid sailing through shallow waters. In case your boat gets grounded, the underwater appendages may be destroyed, and repairing such elements is very expensive and time-consuming.

You should take a fin keelboat or ship as a deep water machine! In deep waters, it glides over and through the water waves efficiently and easily.