I’ve always thought bilge keels or bilge fins or twin keels or whatever you want to call them were a good idea. They are very practical for a number of reasons but bilge keels never caught on in American for reasons I’ve never quite understood. However, I was reminded of how practical they are when I was in Britain recently and it’s rekindled my interest.

Photo 1 - Portsmouth Quay

Photo 2 - St Ives Harbor

I was at Portsmouth Quay on my way to visit the Museum and the HMS Victory when I noticed almost all the boats by the ramp had bilge keels, even the power boats. Photos 1 and 2 are of Portsmouth Quay in Portsmouth England and St Ives harbor on the Southwest coast of Britain. These photos, taken at low tide, demonstrate the need for something to keep your boat upright on the hard. I’m told that on the East coast of Britain the problem is even more extreme. The same large tidal range (8 to 10 feet or more) combined with a gently sloping bottom. This is where Maurice Griffiths, a British designer very fond of bilge keels, was from (more on Griffiths later).

Photo 3 - Portsmouth Quay

Photo 4 - Falmouth

Of course bilge keels aren’t the only solution for the hard; the boat in photo 3, a 35 to 38 foot trawler type, uses pilings for support and the boats in photo 4 and 5 use removable legs. However, using pilings means you must come back to the same mooring or another set of pilings. The legs, of course, have to come off and on. Bilge keels, on the other hand, are always there ready to take the hard even if you are not.

Both the trawler and the cruiser have keels to protect the prop from the bottom. Dories and other flat bottom boats generally lack keels and here is where bilge keels help as well. In the Northeast coast of American and on the Canadian East coast tunnels were and are built into the bottom and the shaft and prop are lifted up inside the tunnel as the boat goes aground. The Boat in photo 6 has solved this problem with bilge keels or what might be more appropriately called twin skegs. This boat, which looked something like a Cobble, could just run up on the beach or tie off to a mooring and not have to do anything.

Photo 5 - Falmouth

Photo 6 - Portsmouth

For power boats bilge keels can do more than just protect the prop or keep the boat upright- they also help dampen roll. The boat in photos 7 and 8 has bilge keels and while they help keep the boat up right they also dampen the roll. There seems to be various opinions about how much they dampen roll but everyone agrees that there is a noticeable effect.

So for power boats bilge keels help the dampen roll and help keep the boat upright but for sail boats they also provide lateral resistance. Ted Brewer wrote a great article in the January/February 1995 issue of Boatbuilder Magazine on the use of “bilge fins”. He used the term “bilge fins” because the “keel of a boat is the structural backbone and runs from stem to stern; the part that sticks beneath the hull to resist leeway in a modern sail is the fin.” He points out in the article that a bilge fin boat can have the same shoal draft as a keel/center board boat without all the problems of the center board. He also points out that when the boat heels over the bilge fin increases its draft because the fins are angled out while the single fin has less draft. He states the “Bilge fin hull is obviously more efficient under sail” than a shoal keel of the same draft.

Photo 7 - Portsmouth

Photo 8 - Portsmouth

This agrees with the opinion of Peter Thomas of Select Yacht Group in Britain. The Select Yacht Group are builders of the Cornish Crabbers, Cornish Shrimper and the British Hunter 20, a “twin keel” sail boat, among others. Pete says “People seem to associate the name bilge keels with poor performance so we use the term “twin keels”. “We don’t tell people they’re sailing on a twin keel boat and they always comment on how well the boat points.” Pete isn’t the only one that feels twin keel boats can sail to the windward as well as single fin boats of the same draft. I spoke to several sailors at Falmouth, England who feel the same way. They felt pretty strongly about it, actually.

Photo 9 - Falmouth Harbor

Photo 10 - Falmouth Harbor

Sailing well to the windward isn’t the only positive performance trait the bilge keels have. According to Eric Hiscock in Cruising Under Sail, Maurice Griffith’s Lone Gull ll, a bilge keel yacht, tracked very well and was able “to hold her course unattended for long periods even when running, and this is something which one does not usually associate with shoal-draught vessels.” Another very positive trait of Lone Gull ll was her “refusal to build up a rhythmic roll under any conditions of wind and sea.” Other bilge keel boats seem to exhibit this very desirable trait as well and don’t show a tendency to broach in a following sea. Certainly tracking well, not rolling, and resisting broaching are what we all want in a good cruising boat.

Photo 11 - Falmouth Harbor

Photo 12 - Falmouth Harbor

There are some down sides to bilge keels, of course. For example; they have more wetted surface than a single keel boat, bilge keels don’t lend themselves to all types of hulls, and they require hull support where the bilge keels attach to the hull. These are small points, in my opinion, compared to the benefits…. however every feature has its advantages and disadvantages….everything is a compromise. The main question is; do the advantages outweigh the disadvantages?

When I was at the harbor in Falmouth a boat count showed about fifty percent of the boats had bilge keels. That means a large number of sailors in Falmouth felt bilge keels had more advantages than disadvantages. Photo 9 and photo 10 show a nice little cruiser with a LOA of 22 to 24 feet and a draft of about 36 inches. It’s sitting on a simple flat bed trailer that would be very easy to launch and retrieve. In photo 11 a similar sized bilge keel sail boat sits on another simple easy to build trailer. Photo 12 helps demonstrate some of the reasons bilge keels are so popular; the boat on the right must have jacks and supports or some kind of cradle to stay upright while the boat on the left requires nothing to stay upright.

Photo 13 - Falmouth

Photo 14 - Falmouth

Aside from the popularity of bilge keels I noticed that there was a wide range of types and shapes of the bilge keels. There was even variation in how the keel or fin was attached to the hull. Some seemed to have no fairing at all, as in the close up detail of photo 13. The opposite extreme is photo 14, where the keel is faired into the hull like an airplane wing. There were very thin fins (photo 15) to very fat keels (photo 16) and this very shoal draft wooden lapstrake boat in photos 17 and 18.

Photo 15

Photo 16

What all this variation says to me is that bilge keels can be very tolerant and will do the job in a wide variety of shapes and configurations. This may be one of the reasons bilge keels are so popular in Britain and one reason American builders should take a look at bilge keels. Are they right for every boat? Of course not, I certainly wouldn’t use them on an around the buoys racer. But a coastal cruiser or an open daysailer, where shoal draft and good sea keeping abilities are important, would be good candidates.

Photo 17 - Falmouth Harbor

Photo 18 - Falmouth Harbor

Seeing the large number and variety of bilge keels was an unexpected but educational part of my trip. And it certainly has reminded me of all the advantages of bilge keels or bilge fins, or twin keels or twin fins or whatever you wish to call them.