Submitted on October 8, 2004 by Eric Swanson

Question: I read your response back in January to a question about an in-mast furling main on a 38’ boat. I am considering purchasing a new 45 footer and am having troubles deciding on whether I should seriously consider in-mast furling or not. It’s obvious that there is a trade off between convenience of hoisting/sail handling and overall sail performance, but are there any numbers on how much performance is lost with such a main? At some point it makes sense as you get larger but just not sure when that point is.

Thanks
Eric Swanson

Answer: Hi Eric, it is not really possible to quantify the difference between an in-mast furler and a conventional mainsail in general terms, because there is no "standard" in-mast sail or conventional sail these days. In-mast sails are being built with battens which allow straight leeches or leeches with positive roach and conventional, horizontal batten sails can be built with a wide range of leech roach and batten configurations. Also, the weight and windage of a stow mast are both significantly greater than a conventional stayed mast, and the range of bend and bend controls can be much greater on a conventional mast. Because of all these variables, you would need to look at the two specific rigs that you want to compare. Then it would be easy to quantify the difference in area in the two mainsails. A calculation of the difference in theoretical driving force between the two mast and sail combinations would require a more costly Computational Fluid Dynamics (CFD) analysis. The yacht builder or designer might be able to give you quick estimate by providing two sets of "polar" performance curves, one for each rig. If the manufacturer is offering either rig, they should have a weight estimate for each one, as well as two sets of righting moment data.

Regards,
Dan Neri

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