Masthead, or Fractional Sloop?

[Will Gilmore]

Offwind unsteady aerodynamic analysis of flow around a yacht. Taken from https://www.totalsimulation.co.uk/marine-aerodynamics/
Several articles I just read mention or show a tremendous amount of turbulence and air loss at the foot of the sail. Some treatments include closing the space between sail and boat, and sewing a shelf at the foot, to prevent spillage. The picture above is of a broad reach, I think, and shows how much turbulence is caused at the top half of the main. I don't know what the implications are for a fractional vs masthead rig. It may be that all that is achieved with a taller headsail is more heeling force. However, there is a lot of air loss at the foot, as well. This doesn't seem to be rig specific but, a long footed Jenny may help.

Here is an article I came across about setup and reading telltale.
http://www.jasperandbailey.com/tech/news.html

I wonder why no one has mentioned cutter rigs as having the best of both worlds. A fractional forestay and a masthead stay.

One more point to ponder or question to answer: in a larger boat where the mast is not designed to drop for trailerring, is the mast set hard upright or does it articulate for rake adjustment? Because, a rigid mast step might mean the ability to flex the mast shape without a fractional forestay. Like holding one arm of a bow stiff and pulling on the bow string.

- Will (Dragonfly)

 

[Jackdaw]

Offwind unsteady aerodynamic analysis of flow around a yacht. Taken from https://www.totalsimulation.co.uk/marine-aerodynamics/
Several articles I just read mention or show a tremendous amount of turbulence and air loss at the foot of the sail. Some treatments include closing the space between sail and boat, and sewing a shelf at the foot, to prevent spillage. The picture above is of a broad reach, I think, and shows how much turbulence is caused at the top half of the main. I don't know what the implications are for a fractional vs masthead rig. It may be that all that is achieved with a taller headsail is more heeling force. However, there is a lot of air loss at the foot, as well. This doesn't seem to be rig specific but, a long footed Jenny may help.

Here is an article I came across about setup and reading telltale.
http://www.jasperandbailey.com/tech/news.html

I wonder why no one has mentioned cutter rigs as having the best of both worlds. A fractional forestay and a masthead stay.

One more point to ponder or question to answer: in a larger boat where the mast is not designed to drop for trailerring, is the mast set hard upright or does it articulate for rake adjustment? Because, a rigid mast step might mean the ability to flex the mast shape without a fractional forestay. Like holding one arm of a bow stiff and pulling on the bow string.

- Will (Dragonfly)

Lack of “plate effect’ on the main or jib results in about a 1% loss of efficiency.

No one mentioned cutters because they’re not that efficient. It’s a sail area management technique, not done for performance.

Deck stepped masts naturally lean back. Keel step masts have an adjustable plate, that allows the rake set between the foot and the deck, which effects the entire mast.

 

[Barnacle Bill]

I think where you sail and what conditions you have may have an influence on your decision. Example: J/Boats made the J/29 in either a masthead or fractional rig design. Also with inboard or outboard. There is no question if sailing on inland bodies of water, where the wind can be lighter, the masthead rig is faster than the fractional rig. The outboard model was also faster than the inboard model (but that is another topic). One thing about fractional rigs for those who don't race (or for those who do as well), is that headsail handling is easier. You are not muscling a large headsail every time you tack. With a fractional rig the mainsail is larger and has more horse power than say the old IOR designs (where the horsepower was in the headsail). Most well found boats that are fractionally rigged will sail with a good balance under main alone. The other thing about fractional rigs is they are usually tapered and easy to bend for better sail trim. The masthead rig usually is like a telephone pole and not so bendy, which limits some sail adjustment. To the extreme, you might ponder a Star boat which is a hard-chined 22-footer used in the Olympics. It has a very bendy (noodle) mast which has as many as 6-8 adjustments to control the shape of the mast alone - depending on her vintage. There were upper AND lower running backstays (no permanent backstay), butt adjustment, mast rake adjustment and rotating (forward even) very long spreaders. One of the coolest boats I have ever sailed/raced. Most modern racing boats have non-overlapping headsails and because of the design of the boat, they sail extremely high and fast. Off the wind they depend on spinnaker speed (usually Asymmetrical). Even modern cruising boats like Hunters use headsails no larger than 135% on a fractional rig in their attempt to keep sailing easy and to decrease heel. As a matter of fact, in some of their models, if you wanted to add a 150% headsail, because of the design of the deck, there wouldn't be anywhere to install a longer track or a track further back on the deck to accommodate the bigger headsail. Of course not all of their designs were like that, but the trend has headed in that direction. There's no question if you sail in a lighter wind area, the masthead rig will move the boat faster on those lighter winded days. It also has something to do with the higher aspect of the masthead genoa too, which can reach winds that are off the water more where the smaller boats or boats with a lower combined center of effort cannot.