The February issue contains an abbreviated answer from Nigel Calder to a reader's query about the pros and cons of lifting keels and twin rudder - learn more here
The February issue contains an abbreviated answer from Nigel Calder to a reader’s query about the pros and cons of lifting keels and twin rudders.
Following a reader’s letter Nigel Calder offer further thoughts on lifting keels and twin rudders to supplement the feature on keels and rudders in the October 04.
* Lifting keels add an element of complexity beyond that associated with fixed keels. They should only be considered where shoal draft cruising is contemplated. There is then a choice between a ‘low aspect’ long keel with shallow draft (such as those found on Island Packets) or else some kind of a centerboard or lifting keel (such as is found on Southerleys). The former will seriously impair upwind performance relative to the latter, so which to choose is a function of what kind of upwind performance you are looking for. If you are going to have a centerboard/lifting keel, in the ‘down’ position it should result in a relatively high aspect, deep-drafted keel (otherwise, why not have a long, low aspect, keel?).
* If you are going to have a centerboard/lifting keel, for obvious reasons the rudder draft must either be less than the ‘keel up’ draft, or else it must also be possible to reduce the draft of the rudder (with a kick-up section, or something similar). This makes it difficult to fit a rudder with sufficient size and ‘lift’ to maintain control over the boat when well heeled, or hard pressed. An excellent way to get over this is with twin rudders. In any event, if I was thinking of buying a centerboard/lifting keel boat, before committing myself to this kind of design, I would want to press it hard to ensure there was no loss of control (I do this for any design; there are far too many keel boats with inadequate rudders).
* Centerboards/lifting keels have to be hinged at some point, and need a lifting tackle. Both are potential failure points, and so must be accessible for regulator inspection and maintenance. Damage is more likely if the boat is run aground than with a conventional fixed keel.
* If a centerboard/lifting keel is a loose fit, it can result in annoying knocks and rattles. It may also be difficult to get up in some circumstances.
* There must be a housing into which the centerboard/keel lifts which may have a significant impact on the interior accommodations (on some boats there is a substantial trunk; on others, such as the Southerleys, the keel is substantially below the cabin sole).
* In some cases, the ballast is in the boat itself and the centerboard/keel is more-or-less unballasted, in other cases the centerboard/keel contains a high percentage of the ballast. In the former case, when the centerboard/keel is up it will not have much of an impact on the boat’s stability (and its Angle of Vanishing Stability, or AVS) whereas in the latter case it may.
So… for me the key questions are how shallow do I want to go in draft, how important is it to maintain good upwind performance with a shallow draft, and what’s the boat’s AVS with the centerboard/keel up? Assuming it is decided a lifting keel is appropriate, I want to know the rudder will maintain control at all times without becoming the first thing to hit the bottom, and that the keel hinge and lifting mechanism are rugged, troublefree, and easy to access and maintain.