Questions and issues surrounding in-mast furling mainsails and their potential to jam or cause problems have come up multiple times with many owners I have spoken to. Inevitably, I have both current and potential owners asking me if I like it and (predictably) does it jam?
There are many horror stories out there about jams.
Most of these stories have been blown out of proportion and I find many perpetuated by those who have never even had in-mast mains.
Some of the concerns are viable. The two biggest are that you will lose some performance with an in-mast.
For racers, unless appropriately handicapped, this probably is not the best option.
Another major concern is that if it does jam in a storm, you cannot blow the halyard to drop the main. Nightmare scenarios and reports of cutting down mains in a storm have surfaced.
I have not heard of a Catalina C400 (my current boat) having to do this, but have heard others report it from other manufacturers that perpetuates the concerns of this system.
For the record, I have thousands of miles on both traditional slab (or jiffy) reefing mainsails and in-mast furling systems. I've been offshore more times than I can count with my in-mast and been stuck in some pretty nasty storms and squalls – one lasting three days.
With my knowledge of both systems, I will heartily say that I would never go back to slab reefing unless I was racing. And I also believe the performance lost is minimal between the two - and most of us not doing distance races would never know.
Most of us were never instructed on it or because we are seasoned sailors, use it as we would a traditional main.
Therein is the problem and why in-mast furling systems often get a bad name. For the record, I have never, not in many thousands of miles, had one single jam.
Note the location of the clew in the pic below. It does not go horizontally into the mast. It travels up at an angle into the mast. This is critical to understand.
Why? Because as a traditional (slab) reefer, you would point into the wind, tighten down the mainsheet to keep the boom centered - some even tighten down on the boom vang to help - haul up the main halyard until you have reached the top, then fall off and begin adjusting the vang, sheet, outhaul and halyard to the appropriate point of sail and conditions.
We effectively reverse these to drop the main, again keeping dead to wind or close to, and keeping the sheets and typically the vang taunt. If you do that with an in-mast system, sooner or later it will jam.
On In-mast, you MUST allow room for the car to travel down the boom and for the clew/sail to enter and exit at its proper point.
If you cinch down on the main sheet and vang and then begin to haul in the reefing line, you will see that you cause tension down the leech of the sail. This often results in crinkles forming as you reef. These crinkles are what cause jams.
So, when reefing your in-mast, you must release the tension on the main sheet and vang. Take the tension off so the sail can roll into the slot as designed. Also, keep some tension on the outhaul as you reef it to prevent any unwanted crinkles and a smooth roll.
Lastly, you will notice the mast is slotted more to one side than the other. Depending on where your sail rolls, one point of sail may be easier to reef than others. For us, ours is a starboard tack. This is because the sail rolls out away from the mast and does not rub against it while reefing.
Don’t forget to put some McLube on the boom track to reduce the friction on the car. I do this about once a month.
We almost never use the winch to reef our sail in normal conditions… and NEVER use the electric winch.
If you reef the sail by hand, you can feel any potential jams before they happen and can pull them back out. If you gorilla-arm that sail in with the winch or the electric winch, you can create a jam that will be very difficult (if not impossible) to get back out.
If you find yourself in a situation where you have to winch in the main, at least go slowly and keep staring up the slot for crinkles going in.
I am a fan of in-mast furling mainsails for most sailors. It keeps the crew safe and in the cockpit instead of tidying up sails on deck. It also gets a lot more use than traditional mainsail reefing systems because it is so easy to use and reef.
Keep in mind what I said above when operating the sail, and you too should get thousands of trouble free miles.
S/V 'Sea Mist IV', Catalina C400 #289