UK Sailmakers Ireland: The Ins & Outs of Inhaulers

September 12, 2021

Setting the inhaulers is often discussed before a race yet rarely changed on any boat once set. Maybe it’s too hard to adjust them once the sail is trimmed, or maybe they aren’t considered once the gun goes off? Neither case is an excuse not to adjust your inhaulers in the same way you adjust your headsail leads.

Inhaulers are an important tool that need to be adjusted as the wind speed changes between light and heavy.

Inhaulers: how do they work?

Classic boats have long tracks on their decks along which jib cars give the proper sail shape. You know, the telltales are twittering in unison. But newer boats, particularly with non-overlapping jibs, can get an extra bit of speed by installing inhaulers that move the lead position inboard or outboard rather than just fore and aft. Optimizing the width of the slot between the sails can do a lot for speed. Next time you sail behind some high-tech race boat, look at how close to the mast their jib is trimmed to. If they are using such tight sheeting angles, there must be some good reason to do it…and that’s not because it makes you go slower.

Inhaulers were invented to pull the clew of the genoa or headsail inboard to control/close the slot between the main and headsail. Inhauling has two main effects. First, the tighter slot redirects the airflow around the back of the mainsail at a better angle, increasing the amount of airflow attached to the back of the main.

Second, the airflow is compressed into the slot between the main and headsail. This compression and slight slowing down of the airflow forces the airflow on the leeward side of the headsail to accelerate into that void, increasing the airflow speed over the two sails much like how the airflow accelerates over the wing of a plane.

You can see on the Uni – Titanium headsail and main. The slot is nice and open, with lots of twist in the headsail. This is perfect for building your boat speed.

Note that when inhauling a headsail to work effectively, both the main and headsail have to be adjusted in concert, so the slot is between them is balanced. The traditional set-it-and-forget-it approach isn’t good enough any longer.

That said, compressing the airflow has both good and bad effects. Too much compression (inhauler too tight) overloads and chokes the slot. You can see this in real-time as the luff of the mainsail starts to backwind. You can use backstay to flatten the mainsail in 12+ kts to allow the slot to open, but this is not possible to do in light airs below 8 kts. You will generally notice this effect happening in the 8-12 kt range on most boats.

Top Tip: If you feel the boat is sailing sluggish, don’t be afraid to ease the inhauler a bit and see if that increases speed.

Too little compression has the slot too open, so the airflow is not being directed around the back of the mainsail, and the symmetry of the two sails won’t be working together, causing the boat to sail slower.

Knowing how much inhauler is the key; it takes time and practice to figure it out on any boat. Don’t be afraid to play with your settings during a race or while doing a boat-on-boat pre-race tune-up. Most boats have the tracks set on the deck at about 10 degrees or more, but you will find this inefficient for racing. We inhaul to close the sheeting angle down to 7 or 8 degrees. You can easily do this on any boat by measuring the sheeting point from the centreline out to the working angle of the sail.

Top Tip: Keep an eye on the lines that control the inhauler. They can be under significant load and may be prone to wear. So overbuild instead of underbuild this system.

An important point for the uninitiated; sheeting the inhauler in shouldn’t be made with just any headsail. The sail must be designed to have extra twist in the leech to be inhauled harder. If you don’t have the twist designed into the leech, you will completely choke the slot, and you won’t be fast. You will notice this when you inhaul, and the leech is straight from the clew to the head because the sail wasn’t designed with extra twist in the leech. Most inhauled headsails have twist between 13 – 15 degrees.


Here you can see the FSI study of the slot on a J/109 with the leech twisted open at the top.

Precisely how much you inhaul and in what conditions are different for every boat. Well, that’s the real question, isn’t it? A boat with a long keel, for example, shouldn’t go inside 9 degrees, or the boat would stop. The speed of the boat through the water also greatly affects the inhauler. The Cape 31, for example, can go into 5 degrees as the balance of the lead allows the boat to do it. It would help if you had a well-designed boat with the sails, keel, and rudder working perfectly together to do this angle. An older designed boat would not maintain this sheeting angle without the boat coming to a complete stop and sliding sideways. For example, a J/109 can have a sheeting angle of 7 degrees, whereas a First 44.7 would have a wider angle.

Now that we understand how inhauling works and what happens when you don’t get it right, we need to look at the different types of inhaulers and how they work.

There are two main types: direct and X/Y inhaulers. The direct inhaulers move the lead in or out, whereas the X/Y inhaulers allow you to move the sheeting point in all directions. Being able to make a wider range of adjustments (with the X/Y inhaulers) is very useful for boats with a narrow sheeting angle.

Here are two photos of direct and X/Y inhaulers.

Here you can see the J3 Titanium headsail on the J/109 is sheeted in hard to get the max pointing and boat speed.

So how do you know if your inhauler is too tight or too loose? It all has to do with the amount of airflow that sticks to the back of the sail. You don’t want the flow to split away from the sail too soon. It’s critical to keep the airflow attached to the back of the sails as much as you can. I personally put my hand on the back of the sail around the clew and up to head height to see how much airflow is sticking to the back of the headsail. I do the same with the mainsail. I also feel the front of the mainsail with the airflow is being compressed between the two sails, so I can see how much airflow is directed onto the mainsail at the front of the slot.

Top Tip: When you set one side’s inhauler, consider if the other side should be adjusted to the same setting. Consider the sea state, and you may need more punch through the waves on one tack vs the other.

Over inhauling in light airs is a common mistake. If the inhauler is too tight, this airflow will separate too early in front of the clew patch on both sails. This is most noticeable in sub 8 kts. The airflow will split away from the sail, causing turbulence and drag. This is the reason in lighter air, you move the inhauler out again, so the airflow sticks to the sail. When the wind speed is fast enough, you can trim the inhauler inboard and close the sheeting angle, so the max angle with the main and headsail is achieved.

Here you can see a Titanium headsail on the J/109; the car is moved well forward, so there is lots of foot round, but the inhauler is not too tight.

One of the most noticeable things when you over inhaul is the backwinding of the mainsail. If your slot is efficient, you will notice the leeward side of the mainsail close to the mast will have a tiny flutter in the slot. That is a great indication that the slot is full, and the airflow is redirected onto the mainsail. Too much of this will have backwinding on the luff of the main. Again, too little flutter will have the airflow spilling off the back of the jib, similar to being on a reach and having the airflow want to take a 45 degree turn off the leech.

Here you can see on the pogo 30 the X/ Y inhauler so the clew can move in every direction. For the best sheeting angle.

Have your sheets and lead rings the right size, so they don’t affect your tacking. The lines should move freely so they won’t develop wear points; this is also critical to the system working properly. Having an X/Y track on the cabin top is the best option of all, but this is not possible for most cruiser racing boats as they can’t add a track on top of the cable.

In the end, when you have determined what works and what doesn’t, put marks on the deck and record your settings for next time. There’s no need to “recreate the wheel” if you already have proven the right settings for each wind speed and sea state.

If you have any questions or need any advice, please feel free to contact us a UK Sailmakers Ireland. or WhatsApp us some photos of your set-up, and we would be happy to help.

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