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Solo DMD+ Sail Tuning Guide

By David McGregor Introduction This tuning guide works for both the Rooster DMD+ Dacron/Mylar mix sail and the straight Mylar  DMD+ Solo Mainsail .  I use the all Mylar sail as it responds better to changes in cunningham tension and is lighter.  It is more difficult to “read” than the Dacron/Mylar version which may be …   Read More

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By David McGregor

Introduction

This tuning guide works for both the Rooster DMD+ Dacron/Mylar mix sail and the straight Mylar  DMD+ Solo Mainsail .  I use the all Mylar sail as it responds better to changes in cunningham tension and is lighter.  It is more difficult to “read” than the Dacron/Mylar version which may be better suited to lighter winds and shifty, inland conditions.

I prefer to have one setting that works well for all conditions. If you know that conditions are going to stay windy or light you can loosen or tighten the shrouds and/or forestay but I find it easier to use mainsheet tension, cunningham, outhaul, traveller and centreboard position to move “through the gears”. Having only one rig setting gives you less to worry about and it’s nice to have full power “on tap” when you need it (starts, when the wind goes light).

Mast Foot Position

I use a Boon FRP solo and have the mast on the Medium Setting. This has the front of the mast heel 3052mm from the outside of the centre (measure through the transom ports). My mast (D+) has the track cut out in the area of the mast gate. If you don’t have this you will need to move the mast foot 8mm forward.

Forestay Tension

Without the sail up the forestay should just be in tension (better to be to slightly loose rather than to tight) with the mast resting on the back of the mast gate. As the wind increases you may want to ease the forestay adjuster 1-2 holes. I prefer to leave it in one position and rely on the Cunningham.

Shroud Tension

The shroud tension seems to have just as much effect on power and pointing as forestay tension. I have experimented with more or less tension and now use quite tight shrouds. As the mast doesn’t have spreaders and can “pivot” around the hounds, the middle of the mast can move forward and to windward as leech tension is applied. This makes cutting the sail very difficult! Without the sail raised the shrouds should be in tension when the mast is pushed forward and there is a 10mm space between the front of the mast and the front of the mast gate. If you are overpowered or want the rig to “breath” more, ease the shrouds so the gap is reduced to 5mm. This is fast but will adversely effect pointing.

Mast Chock

I do not allow the mast to move at deck level so I put all the chocks in front of the mast. Removing the chocks does depower the rig but it takes power from the lower section of the sail rather than the top.

Outhaul

I leave the outhaul quite lose to generate power low down. I never pull the outhaul tight even in 30+ knots. Measured at the mainsheet blocks on the boom the depth of the sail is approximately 120mm. I tension the outhaul to reduce the depth to 80-100mm on flat water or very high wind.

Cunningham

The secret weapon! Once you are overpowered you should start to pull the cunningham on.  As well as dragging the fullness in the sail forward the Cunningham frees the leach and ultimately reduces the drag of the upper part of the sail. You need to use more cunningham tension than feels good for the sail. I judge the Cunningham tension by looking at the top 2 battens. When you pull tension on both battens should straighten. In extreme conditions the top of the sail can be completely flat. Some boats have a 6:1 cunningham rigged so that it is easier to get the required tension. REMEMBER TO LET THE CUNNINGHAM OFF WHEN YOU BEAR AWAY. You will damage the sail if you don’t.

Traveller

Most people prefer to use the kicker to control the leach tension but I prefer to use the traveller and mainsheet tension. There are advantages and disadvantages to both methods and lots of people go very fast using the kicker. My reasons are:

1.     The kicker pushes the boom/mast forward and creates low down mast bend which I don’t want.

2.     It is quicker to change the leech tension by moving the mainsheet rather than altering the kicker.

3.     With the amount of mast rake now being used there is less room under the boom. With no kicker the boom moves up when you ease the mainsheet to tack – saving your head!

I never bring the boom closer to the centre line than the inside edge of the side tank so the traveller is always eased at least 100mm from the centre. As I pull on more mainsheet the traveller is eased progressively and is usually 150mm from the centre. The Boon boats have a very long traveller track so you can ease the traveller a long way out and it works very well on a close reach.

Centreboard

I have a 2:1 control line led to the side deck so that I can control the centreboard rake whilst I am hiking. In light winds I have the leading edge of the centreboard vertical. I don’t rake the centreboard forward. As the wind increases I rake the board back and once overpowered I try to have no weather helm at all. This can meaning raking the centreboard 30-40%. You will not point very high but you will go fast and I believe the efficiency of the foils at speed more than makes up for the lack of pointing. I have 6 positions marked on my centreboard – Leading Edge vertical, trailing edge vertical, 15% rake, 30% rake, 45% rake and a light wind running position.

Downwind

Cunningham off. Outhaul off – the elasticised foot makes this really easy. Kicker on for reaching and eased for running to make the boat more lively! Downwind speed seems to be more dependent on technique than rig settings. Take Steve’s advice and watch the Boat Whisperer Downwind DVD.

David MacGregor Wins the Solo End of Seasons with the Rooster DMD+
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5 comments

  1. John Nixon Reply

    I would be interested to know how you actually measure C/B rake at the % points you define

    John

  2. David McGregor Reply

    Hi John,

    I measure the C/B rake by rolling the boat on to it’s side and measure the leading edge of the C/B relative to the underside of the hull. Leading edge vertical and trailing edge vertical are obvioulsy easy but I my children’s protractor to measure the other angles. I mark the angles on the C/B handle where it enters the case and have a 2:1 adjustment on the uphaul and downhaul so that I can more the centreboard whilst going upwind.

    David

  3. Russ Hopkins Reply

    Hi,
    i am a 95kg and until recently have been using a cumulus rig. However i have recently dusted off my wavelength that came with the boat. Its the first time i have used it and loved the mast and sail as it gave me much better off wind performance. However i am looking at upgrading to a different sail. My first question is how does the rooster sail perform on a wavelength mast? I found the wavelength sail very full which helped my downwind performance. I would really appreciate some feedback before i shell out for a new sail, or even worse should i be looking to change to a D+?

    1. Profile photo of Steve Cockerill

      Steve Reply

      Hi Russ,
      I think you should be looking for a Cumulus, perhaps the front taper version which is currently in vogue.
      The Rooster sail is cut for a stiffer section. I think that you are on the heavier side of the weight spectrum, then you should firstly change your mast.

  4. Rooster Blog » Blog Archive » MXL Loadpath Sail in 20 Knots Reply

    […] was used successfully to win the end of seasons with Dave Mcgregor in 2010.   David shared his tuning guide on our blog for this sail; his thoughts are in keeping of how I would prefer to use a Solo sail. […]