twin keels as an option

[tomcostin]

What do ya''ll make of this? It could at least make for interesting discussion.

http://www.brayyachtdesign.bc.ca/html/twinkeels.html

[Jeff_H]

That web page has been around for a while and has had a lot of discussion. While the author makes a lot of hyperbolic claims for bilge keels (aka- twin keels), the realities are that bilge keels only offer an advantage in terms of shallower draft and the ability to ''dry out'' and remain standing.

They offer the disadvantages that they offer significantly greater drag in most sailing conditions (which is confirmed in the chart on that webpage where the bilge keels are shown as having 44% greater drag at low speeds up to about 23% greater drag ar higher speeds and heel angles). In the side by side sailing that I have done in identical models except that one had bilge keels and the other a fin keel, the fin keel had greater speed, pointed higher, tended to roll less, and made less leeway.

While a lot has happened to optimize both fin and bilge keels, the increased drag of having the extra foils in the water is hard to overcome. While bilge boards (operable) have been used on race boats these have generally been raised and lowered on each tack, (Talk to nay scow sailor). Bruce King''s bilge boarder was banned in IOR along with a all moveable foils. In the 1970''s IOR gave boats with low stability and operable foils a real rating advantage. These boats were not expecially fast on a boat for boat basis but had gift ratings. IOR''s problem with these boats is that they had moved into a realm where stability was a serious problem and with several major knockdowns, IOR moved to close the door on extreme low stability and operable foils. Bruce King''s bilge keeler was included when that ban was imposed. Open class boats use bilge daggerboards today in concert with an operable keel that can swing a big weight to windward. The tremdous stability gains of an articulated keel allows enough sail area to overcome the greater drag of the extra bilge foil. That said the boats with moveable water ballast and a single foil are faster in lighter conditions.

Another big issue is that when you run a bilge keeler aground, you are seriously aground and there''s no easy way out. You better hope you''ve grounded on a rising tide.

Unless they suspend the laws of physics, I doubt that a boat with fixed bilge keels will ever offer the performance of a single fin, (even a shoal draft single fin with a Scheel keel or a wing.)

Jeff

[aasault]

Hey Jeff_H,

What do you think about the Shannon Shoalsailer?

[Jeff_H]

I find this a very confusing boat. When I look at the boat and listen to Walter Shultz''s explanation I am frankly baffled. The boat appears to defy almost everything principle that I think is important in a coastal cruiser. Here is this boat with enormous wetted surface,inefficient foils, high form stability, blunt entry. It should be an uncomfortable dog to sail, but I have spoken to a knowledgeable sailor who has sailed one and he swears that he was very pleasantly surprised at how well it sailed. he says that she may not live up to the hype, but she sails a lot better than you would guess just by looking at her. Its important to understand that she was not intended as an offshore boat, but for poking around back corners of a shallow venue, and where performance is not all that critical, this should be a reasonable choice. Of course Iam still gagging over the price that they get for this boat. (I know that this reflects my own personal taste but for that kind of money you can buy a Farr 395.)

Jeff

[garyp]

Bouncing off the Shoalsailor: any opinions/experiences with the Hake Seaward Eagle lift-keel?