Archive technical articles

Sailing the Alerion Upwind

The most critical thing to remember when sailing an Alerion upwind is that you are trimming four foils.  First we will look at the underwater foils. What you do with the sails affects the angle of attack of the keel by either increasing or decreasing leeway. Take a look at the diagram below:


Think of the wing shown above as your keel or rudder. Note that as the angle of attack increases, more and more of the flow over the keel or the rudder surface becomes detached or “stalled”. This results in decreased lift and increased turbulence, which is slow. There are two factors that influence leeway. One of the most important is boat speed. Think of gently putting your foot into a pool. There is almost no resistance. Now do the same off the high dive. There is lots of resistance. The faster your boat goes the more resistance there is to side slipping. One thing that is often forgotten in the “pursuit of pointing” is that in order to “point”, you first have to minimize going sideways.  So first you have to get speed, then you point.

Sail trim affects the amount of helm on the rudder when sailing up wind.  You always want to sail the boat upwind with minimal helm / rudder angle. A little bit of rudder angle is actually beneficial, since our underwater foils are symmetrical.  Use your tiller extension, even if you are sitting in the cockpit. If you can’t easily steer the boat using two fingers on the extension, you have too much helm. The cramp in your fingers will be your first clue that you are not trimmed correctly.

Your sails function just like wings. See the diagram below:


Think of the bottom of the wing as your boom. Note that the “Lift” is perpendicular to the boom. So, one of the challenges of sailing an Alerion upwind is to get those lift arrows pointing as far forward as possible, without sacrificing pointing. The reason we sail faster on a reach is because those arrows are aiming further forward as the boom is eased from the centerline. So, here are a few basic tips:

1) First of all, remember that we do not sail a boat with an overlapping jib. The conventional wisdom does not apply. So, never sail the boat with the traveler centered. It should always be between ½ and 2/3 of the way down.  In lighter air it should be 2/3 down and the mainsheet relatively tighter than if the boom were on centerline. As a result, the force vectors on the lower parts of the main are facing further forward. A key thing to remember is that you do NOT want to change the angle of attack of the top third of the main, only the bottom two-thirds, hence the relatively tighter mainsheet. The big difference is that there is no overlapping jib to keep you from letting the traveler down. So, you benefit by getting the force vectors facing further forward on the lower parts of the sail and thereby reducing leeway.

2) One of the most important lines on the boat is the backstay. The backstay allows you to control the power in the main. More backstay tension will yield a flatter and therefore less powerful main. If you have helm and your telltales are indicating that the sails are not stalled,  pull in on the backstay! (if the telltales are stalled, the traveler is positioned correctly, and the boat is not over heeled, then try easing a tiny bit on the mainsheet) An airplane pilot lowers the flaps to create a “deeper foil” for the lower speed conditions at take-off and landing. The pilot then “flattens” the wings as the “apparent wind” increases due to the thrust of the jet engines or props. Likewise, when sailing, as the apparent wind increases, you need a flatter wing (sail) in order to reduce lift. Too much lift translates into excessive heeling and helm on a sailboat. See the diagram below:


As you pull on the backstay, you bend the mast. As the mast bends, the main will get significantly flatter, there by reducing lift. Below is a series of photos showing a mast with no backstay and about 3/4 backstay on. The photos immediately below show what happens to the mainsail with the identical amount of mast bend.


If the backstay were fully on, the top of main would be board flat and therefore generating no lift / heeling.

3) The other really important line is the jib outhaul. The jib outhaul allows you to control the twist of the jib and therefore the slot between the main and the jib. The slot needs to stay open to promote good air flow between the main and the jib. If you are carrying a big bubble in the main it could be because the main is too full, but more likely it is because you have the jib boom too far inboard and/or are carrying too much tension on the jib outhaul, thereby preventing the jib leach from twisting. The aft end of the jib boom should never be more than an inch or two inside the edge of the cabin top. If it is you are guaranteed slow. Just like the main: You want to keep the lift vectors facing forward.

Apparent Wind

There is a common misconception that there is not much you can do about the wind. While we do not have the ability to play god and turn 4 knots into 15, we do have the ability to tweak the wind, just a bit.

First, we need to define two types of wind. The “TRUE” wind is defined as the wind speed and direction that you or an anemometer would feel when stationary. That part is pretty simple.

The “APPARENT” wind is defined as the wind felt by a moving object. Think of the difference between walking into a stiff breeze and walking with the breeze. Even though the “True Wind” remains the same, it is much easier (and warmer) to walk with the wind as opposed to walking into it. The difference is the “Apparent Wind” felt by your body. Please look at the diagram below:

Apparent-Wind copy

 Notice that as soon as the boat’s direction changes from dead downwind, not only does the Apparent Wind Speed change, but the Apparent Wind Direction does too! For simplicity, the diagram above, assumes that the boat speed will remain constant. In real life, an increase in Apparent Wind Speed will almost always result in an increase in boat speed, which is the goal. As boat speed increases, unless the boat is dead downwind, the Apparent Wind will move forward.

So, what is the practical application of all this? The answer is that in lighter winds, when our boats are a bit under-powered, we can help the situation by getting the boat to “feel” more wind.

1) When attempting to sail downwind in light air, we can temporarily sail at an angle that would be closer to a broad reach. The change in angle alone will give us a bit more Apparent Wind Speed. The real benefit is that with the increase in apparent wind speed, boat speed will also increase, thereby moving the Apparent Wind Angle even further forward. So, you can slowly bear off, until you go too far. Then apparent wind speed will decrease, the apparent wind angle will go aft and you have to start the process all over. The bottom line is that your downwind course will look like a very elongated series of S’s. Your tiller movements should be very slow and subtle so as not to have the rudder slow you down.

2) When sailing upwind in light air, resist the temptation to point. First bear off a tiny bit to build speed. The increased boat speed will significantly increase the Apparent Wind Speed that the boat feels and the boat will accelerate. Note, that this acceleration comes at a price; you won’t be able to point quite as high.  While the other boats are aiming high, you’ll be going fast.  The speed will get the keel and rudder generating more lift. The trade off is well worth it. (see the sailing upwind section above)


A Polar Diagram is a theoretical map of likely performance parameters for a given boat over a range of true wind speeds and  directions. The diagram below was given to us by the Alerion Builders at US Watercraft. Looking at the downwind numbers, it appears that the values assume a symmetrical spinnaker, so don’t get too upset if you fall a bit short. The upwind and reaching numbers seem pretty realistic.



If you want to fly a spinnaker on your Alerion, and don’t want to have a symmetrical spinnaker because you don’t want to be on the foredeck during a gybe, then a asymmetrical spinnaker is the way to go.

Fortunately, Selden has what you need; Selden 72mm Gennaker Sprit and a Deck Ring for Selden 072-072-70, for the aluminum version. A carbon version is also available. 076-076-70. The aluminum sprit comes about 6′-6″ long. Don’t cut it down, but use the full length, which will provide about 3′ extension beyond the bow. The carbon sprit is longer; don’t cut it either. The additional length can be of help when running.

You may have to modify some things to allow the sprit to clear you running lights. I relocated both the starboard chock and cleat, by attaching each so that their forward fastener now used the aft hole. Lizbeth was able to install her sprit without moving deck hardware.

The Selden Deck Ring was raised using a 1″ thick teak block. The block is 3-3/4″ X 2-1/2″, which is the size of the base of the ring.  The only difficult problem is having someone climb way up forward to install shims and the fastener nuts.

The Selden kit comes with two pad eyes, which you locate on the deck so that the forward one is used when the sprit is fully extended, and the aft one is used when the sprit is in the stored position. I located the forward one so that when the sprit was extended, the forward end was on the centerline of the boat. I took measurements of the location of the two pad eyes, but I think it best if you locate them yourself.

The spinnaker tack line is led through the sprit, through a Harken bullseye and then to a clutch on the cabin top. I use 57mm Single Harken Carbo blocks for the spinnaker sheets. Their location should be determined after you get your spinnaker unless you plan to install adjustable twings, as was done on Lizbeth. Mine were attached to two pad eyes located 10-1/2″ forward of the forward edge of the winches.  I already had my spinnaker halyard installed, which I also use to hoist my jib sock.

Most sailmakers will be able to provide an asymmetrical spinnaker. If given a choice, you will probably benefit more from a sail that is shaped more for running than for reaching.

We hoist the chute out of the turtle, and have installed a small ring on a shroud to clip the top of the bag.

After 40 years of flying symmetrical chutes on a Rhodes 19, it took a while to fly it properly, especially during a jibe.

Enclose are photos which should help you out.

Deck Ring on Dream
Deck Ring on Dream
Dream with the Sprit Retracted
Dream with the Sprit Retracted
Lizbeth with Deck Ring Removed
Lizbeth with Deck Ring Removed
Lizbeth with Deck Ring
Lizbeth with Deck Ring
Dream with Sprit Extended
Dream with Sprit Extended
Lizbeth showing Tack Line
Lizbeth showing Tack Line
Lizbeth Twing Setup
Lizbeth Twing Setup
Dream Under Sail
Dream Under Sail
Lizbeth Under Sail
Lizbeth Under Sail

Alerion 28 Masts

With Hall Spars going out of business and the builder changing mast suppliers, the following table of measurements might be of use to anyone needing to either work on their rig, or replace it.

Alerion 28 Mast Measurements

All Distance Measurements are taken from the butt of the mast towards the Masthead with the exception of the actual extrusion data.

Component Data:
Extrusion fore/aft 5″
Extrusion Athwartships 3-1/8″
Length Overall 40′ 8-1/4″
Bottom of Upper P Band 40′ 1/4″
Center of Headstay Pin 33′ 5-3/4″
Upper Spreader (Center of Bar) 25′ 3/4″
Intermediate T-bar Plate 24′ 8-1/4″
Lower Spreader (Center of Bar) 15′ 8-3/4″
Lower T-bar Plate 15′ 4-1/2″
Top of Upper P Band 7′ 1/4″
Mast Weight* 89.5#
Mast Balance Point* 19′ 3-1/2″
Upper Spreader** 1′ 11-7/8″
Lower Spreader** 2′ 10-3/4″
Spreader Weight 3.875#

*Mast was weighed without standing rigging or spreaders. Tag lines were led in place of halyards. All factory installed halyard turning blocks were in place. Spreader bars were installed, but spreaders were removed. Balance point was determined in this configuration.
** Measured from center of mast bearing surface to spreader tip.