Shortening Keels

[mikehoyt]

I have heard on various email lists and other areas of owners shortening keels, attaching bulbs on the bottom, etc ... to stiffen boats and lessen draft.

My question to this group.... Is this a dangerous practice? Does it affect the seaworthiness of a boat by going outside the original design parameters, etc ...?

MH

[Jeff_H]

Obviously. it really varies with the particular boat and the amount of the keel being altered. In theory if you are only shortening the keel a little and the bulb is designed to maintain so that the keel maintains the same center of gravity, then it should not affect the structure of the boat or its seaworthiness. It just won''t go to windward as well.

The problem is in the details. First of all a boat is generally designed with a certain amount of keel area that contributes to lift. When you cut a keel down you are not only reducing the area of the keel by what you cut off but also by the area of the keel covered by the bulb. You are also adding the additional drag of the bulb. All of that is bad medicine for upwind or downwind performance.

Then there are construction issues. Modern bolt on keels are constructed with ''L'' hooks in the end of the bolts. These are cast into the lead and are ''nested'' at different depths in the lead so that they do not interfere with each other''s bond to the lead. If you cut too much of the keel off, or accidently drill through one of these bolts when you drill to attach the bulb, you have reduced the strength of the connection.

With encapsulated keels the problem gets worse as you are cutting through the bottom of the encapsulation which is what holds in the ballast and then depending on secondary bonds to support your keel. You also potentially disturb the bond between the ballast keel and keel encapsulation which is quite difficult to repair.

In terms of seaworthiness, even if the boat ended up with the same stability, it would roll at a faster rate (smaller moment of inertia) and through a wider angle (because it looses the dampening affect of a deeper depth foil) with the keel depth reduced .

One minor point, asked if adding a bulb will make a boat too stiff. Stiffness generally refers to form stability rather than ballast stability and so adding a bulb may make a boat more stabile but not more stiff.

Regards
Jeff

[BigRed56]

Ahoy Mikehoyt, Yes and yes etc( what Jeff said), Next Such an expensive and risky change of a vessels performance would only be considered if the vessel were a tub to begin with or the owner had read to many articles and asked to many questions trying to talk himself into a nightmare. OK Big Red 56 the Pirate of Pine Island

[scnicklefritz]

In a recent sailing magazine I saw an article on this very subject. There''s a nice photo of the boat''s owner who has just sawed the bottom off his lead keel with a circular saw.

The keel then gets 2 big chunks of lead bolted to the bottom part, the void areas are filled in and faired and the boat now has a shallower draft and possibly a bit more weight if more weight was added than was sawed off. The boat''s now a bit stiffer and the keel is now shaped like a wing giving it better upwind performance.

A very nice retrofit.

[Jeff_H]

One mimor point, while it is possible to add enough weight to end up with a similar stability, and wings can help some with lost performance, it is not really possible to add wings and end up with the upwind performance of the original keel. Upwind performance is a real balancing act between creating too much drag to overcome the minimal drive of being close to the wind and generating enough lift in the keel to prevent leeway. Wing keels generally generate more lift that a shoal keel but they also generate a lot more drag. So while they reduce leeway, the combination of lower lift and more drag means that the shortened keel had to give up some windward performance over the original keel. That said all the windward performance in the world does you no good if you can''t get into your slip because you are too deep.

Regards
Jeff

[MaryBeth]

Oh, lord, didn''t even know that people would try to jury rig a bulb keel from their original design!!!!

Work in a boat supply store now, so should be able to say I''ve heard everything to cut costs, but not this!! Are people really doing this?

Do people just not get it, or is it the want to have a certain boat and cut the price and make it something it''s not made for?

Sorry, but this is pitiful.

Mary

[Jeff_H]

I think that keel swapping or cutting is not that uncommon. These days there are relatively few keel centerboard boats on the market and for people who live in a shallow area, the normal fin keel depths may be too much for them. Companies, like Mars Metals in Canada, make replacement keels and they make semi- stock bulbs and winglets that can be bolted through the bottom of a shortened keel. It is not that hard to do assuming you only want to take a little off of your draft and don''t mind giving up a little performance. Doing a keel cut is less expensive than paying a brokerage fee to sell your boat and many people prefer owning ''the devil that they already know''.

Jeff