How to trim a genoa sail

I recently had two new sails made by Sanders Sails, based in Lymington UK. The first to arrive was the new genoa and it took me a little while to get to know it and learn how to adjust it correctly. Here is an aide memoire for getting to know how to trim a genoa so that it will deliver the best performance.

It is easier to get to know your sails in moderate conditions, ideally in winds up to Force 4.

Step 1. Getting started

Sailing upwind in 10-14 knots of breeze, sheet the sail in until the leech is just off the shrouds. Look up to make sure the sail is not hard up against the spreaders. In lighter airs, ease the sheet a little further.

Sheet lead position determines the relative position of the leech and the foot. Here there is even tension in the foot and the leech. The sail is well set and will create maximum drive.

The sheet lead position is forward, allowing the foot to sag, which makes the sail fuller. This is ok in light airs but when the breeze increases less power will be needed.

The car is moved well back, pulling the foot tight. The leech is open and there is twist in the top of the sail, de-powering the sail.

Step 2. Check the telltales

Telltales tell you whether the wind is flowing smoothly across the luff. The aim is to have all of them, on both sides of the sail, streaming together – but it is not always easy and takes practice. Here are a few tips to help you practice:

Your first check is to luff gently from a close-hauled course while watching the windward telltales.

If the top telltale lifts first this means the leech is too slack and the sail has too much twist. Moving the car forward along the track.

If the top telltale starts lifting first, the sail has too much twist, meaning the leech is too slack because the sheet lead is too far aft. Move the car forward a little along the track.
If the bottom telltale starts lifting first, the sail has too little twist. Move the car aft a notch or two.
When they all lift together, you have got it right. After that, you only need to watch the bottom one while sailing. It is a good idea to mark the track with an indelible pen in order to remember the optimum settings in light, medium and high wind strengths.

If the bottom telltale starts lifting first, the sail has too little twist – move the car aft.

Other telltale signs:

If the leeward telltales are lifting, you either need to ease the sheet or sail closer to the wind.
If the windward ones are lifting, you should sheet in or bear away.
In strong winds when you are beginning to get over-powered, you will probably need the windward tales lifting slightly all the time.
Once you have freed away from a close-hauled course, the top of the sail will tend to twist open so the telltales will no longer stream.

Step 3. Adjust the fullness

In light to moderate winds – especially in a chop – you need a relatively full sail for power. That means minimal backstay tension to induce some forestay sag and not too much halyard or sheet tension either. If you find you are not moving, try letting everything off a little.

Tightening the backstay increases forestay tension, which reduces the fullness of the sail. So, increasing forestay tension helps to improve speed and pointing ability in strong winds.

When the breeze picks up, you need less power or you will be sailing on your ear with terrible weather helm. The problem is that the extra wind pressure increases forestay sag and makes the sail fuller. So, to flatten it, tighten the backstay, increase the halyard tension and sheet in harder. You may also need to move the car back a hole to flatten the foot and de-power the top of the sail.

Step 4. Adjust the draft position

Draft position plays a major part in determining pointing ability and ease of sailing. Moving it forward (increasing halyard tension) means you won’t point so high, but reduces the heeling force in fresh conditions. The boat will also be more forgiving to sail, especially in a chop. So, if you just can’t get those telltales to settle no matter how hard you concentrate, make the sail a little rounder in the luff by tensioning the halyard.

A slack genoa halyard results in a fuller sail with the draft further back, which will help performance in light airs. Tightening the halyard will move the draft forward, better for stronger winds.

Boat interior varnishing

Most boat interiors have a combination of varnished and painted surfaces including solid wooden joinery, plywood laminates with thin hardwood veneers and glass reinforced plastic. When making your assessment of what you are going to do, bear in mind that the varnishing process consumes a lot of time, especially if the existing surfaces are in poor shape.

How to read nautical charts

Whilst most sailors today rely on GPS to find their way at sea, nautical charts are a crucial tool for any sailor to navigate safely and effectively. Here is a reminder of some of the basic steps involved in reading a nautical chart:

An explanation of the IALA maritime buoyage systems – IALA A and IALA B

What are the differences between the two IALA buoyage systems, IALA Region A and IALA Region B, and where are they used? As recently as the 1970s...

How to use tides and currents to your advantage

If you are contemplating a cruise through tidal waters and strong currents, then planning your trip carefully in advance is essential to enable you to take advantage of favourable tides rather than constantly fighting against them.

Rudders and steering systems – Part 3

In the third of our three blog articles on rudders and steering systems, we look at how to replace rudder bearings and repair a water-saturated core.

Wooden Hulls – Part 1

Traditional wooden boats have a plank on frame construction, a centuries old boat building method that is still in use today. Variations of the traditional method include carvel, clinker and strip planking, which all relate to the way the planking is attached to the frame.

Sailing at the touch of a button

Easier and more controlled sail handling can also be achieved by powering up a furling mast. I came across some interesting solutions at the Southampton Boat Show this week on the Selden Mast stand, where they were running demos of their E40i electric winch and SMF furling system.

Tidal terms and definitions

Getting to grips with tidal terms and definitions can seem a little daunting, even to the most experienced sailors! Here we look at some of the key terms and definitions associated with the language of tides.

How to improve a yacht’s upwind performance

There are several ways to improve the upwind performance of a sailing yacht. Read on for some useful tips including headsail reefing, heavy weather jibs and motor sailing.

Gybing a sailing boat

Gybing is the sailing manoeuvre used to change a boat's direction through a following wind. As with the tacking manoeuvre,...

Weather forecasting resources and tips

All competent sailors need to have a good basic understanding of how to interpret a weather forecast. They also need to be able to interpret the actual conditions they are experiencing.

Learning about diesel engine maintenance

Marine diesel engines are internal combustion engines that are designed specifically for use in maritime applications. These engines are commonly used in a variety of watercraft, ranging from small boats and yachts to large ships and vessels. Learn about marine diesel engine maintenance courses.

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Part 6 – Communications

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the sixth of a 10-part post where solo sailor, Bernie Branfield, shares his first-hand account of his single-handed, 2022 Jester Challenge, from Plymouth, UK to the Azores, in his 26′ Invicta Mk2, Louisa.

You Need To Understand The IRPCS ColRegs To Pass Your Yachtmaster, Master of Yachts and Coxswain Certificate of Competence

IRPCS ColRegs Rules of the Road at Sea and Yachtmaster Learning, understanding and remembering the International Regulations...

Wooden Hull Repairs

While wooden boat hull maintenance is mostly straightforward, it is always a good idea to take expert advice on any repair job needed doing to a wooden boat, unless you have done the job before and know what you are doing.

How to Avoid Collisions At Sea With The ColRegs

Every Skipper Needs Accurate Knowledge of the IRPCS ColRegs As a responsible skipper it is every skipper’s duty to learn and apply the IRPCS...

Boat Improvements

My Boat - practical improvements Author - Mike Rossiter Most boat owners who have had their craft for any length of time will have made what they...

Leaking decks

Leaking decks are perceived as a nuisance by some boat owners, but if leaks are ignored a much more serious situation may well be developing, especially in the case of boats with balsa or plywood deck cores. So deck leaks do need to be investigated and dealt with.

Understanding tides

If you are used to sailing in tidal waters, you will know that tides can be both a benefit and a hindrance to the sailor. In many ways,...

Tools and spares for your boat

Tools and Spares to take to sea!

You won’t regret taking a look at our essential tips and checklist to make sure you’re prepared for routine maintenance and those unexpected jobs that come up whilst you’re afloat!

Essential Knots: Sheet bend

Essential Knots: Sheet bend Use: Joining two ropes together. A sheet bend is particularly useful for joining two ropes of different...

Steel and Aluminium Hulls

The two metals used for hull construction are steel and aluminium. These are both very strong materials and will last a long time as long as they are cared for, which primarily means protecting steel boats from rust and aluminium boats from electrolytic action.