Fin Keel Weakness

Fin keels compliment the sails of a sailboat remarkably. High aspect ratio keels, just like high aspect ratio sails, offer gains in performance while reducing the effects of unneeded drag and weight. While these underwater appendages work astoundingly well, they do have their limitations. If you are able to sail without conflicting with these weaknesses, a fin keel can serve your yacht very well. On the contrary, if you find that these weaknesses will interfere with your ideal method of cruising, a fin keel would not be your ideal setup.

Fin keels attach to the bottom of the hull via a small contact area. This small area has to withstand all the stress placed on it by the forces acting on the hull and the keel. When your yacht catches a puff of wind and heels over, the force on the sails heels your boat over while the force on the keel tries to right the yacht. The junction of the keel and hull is under extreme stress as the hull is trying to pull up while the keel is trying to pull down. If you combine these stresses with heavy pounding seas, the loads experienced by this small area will climb exponentially. With time and stress, fatigue will set in and stress crack will begin to form around junction of the keel and hull. 

Another problem with fin keels is they are not very well protected from impact. They are, by design, a very long lever arm. If you were to strike an underwater object, be it a sunken log or the sea bed, this force is going to be multiplied and then transmitted to the rest of the yacht via a very small area. This small area will be subjected to extreme loads and can form cracks.  


In the Chesapeake Bay, most creeks are around 4.5 to 5 feet deep. Sailboats with shallow enough drafts will attempt to enter these waters, typically running aground at some point during their life. When a grounding occurs, the forces excerpted on the keel are enough to create these characteristic cracks in the front of the keel near the hull.  

These cracks are just the visible damage that occurs to the yacht, but the forces run much deeper and so do the damages. The bolts that attach the keel to the hull are located in the bottom of the bilge and are often bathed in bilge water for the life of the yacht, causing corrosion to wreck havoc on the bolts. The combination of these bolts rusting away and the forces from an impact can cause the keel to actually fall off! If the keel falls off, you now have two very major problems.  

First, the keel is gone and the keel bolt holes (which are rather large) are open and flowing a lot of water into the hull. If these holes are not plugged quickly, your yacht could sink from the in flowing water! 

Second, the keel is gone! You no longer have any ballast or righting moment to counter the sails. If a puff of wind heels you over, you will capsize! Worst of all, if you do capsize, you will not right yourself because the ballast is gone. Losing your keel is not just terrible, it is horrible! 

If you decide on a yacht with a fin keel, don't try exploring shallow waters. If you run aground, damage will occur to your underwater appendages and the repairs can be quite costly. Think of a fin keel yacht as a deep water dream machine! It will glide through the waves with ease and efficiency, but it is a fragile dream machine. If you hit it too hard, it will break along with your dreams.