I’ve sailed a number of boats with in-mast mainsail reefing, including Speedwell of Rhu on her delivery trip. I’ve developed a strong dislike of this system, to the point where we had the masts on Speedwell replaced so that we could fit a slab reefing system.
If I was a purist I’d have also replace the roller reefing genoa with a set of hank-on headsails. That set-up would give better performance, especially to windward, but I don’t believe that the problems associated with a roller genoa are as bad as those of an in-mast furling main and we mostly sail the boat two handed so we stuck with a roller reefing genoa.
Here are the reasons behind our decision. These are based on our use of Speedwell as a long distance cruiser, if we had different plans we may have come to a different conclusion:
Sail Shape
The basic shape of an in-mast furling main is compromised by the need to be able to wrap it around the reefing mechanism. Traditional horizontal battens are out of the question so it’s difficult to support any roach in the sail. Speedwell had a simple triangular sail with a hollow leach, giving less sail area than a slab reefing sail. It is possible to fit vertical battens to the sail, enabling the sail-maker to add some roach and give a better sail shape, but these don’t control the draught of the sail in the same way that horizontal battens do.
Sail Trimming
It’s difficult to control the shape of an in-mast furling sail, especially when it’s partly reefed. Often you end up with too much draught in the middle of the sail and if the sail is partly reefed it’s not possible to adjust the halyard tension to control this. Working to windward in a blow you want the sails to be nice and flat, not baggy.
A roller geona suffers the same problem when reefed, through a good quality sail with a foam luff is a big help. In heavy weather we have the option of furling the genoa away and hoisting the storm jib.
Some in-mast reefing systems are very sensitive to boom height. I’ve sailed boats where I’ve been given strict instructions not to adjust the kicker or topping lift for fear that changing the angle of the boom will give problems when rolling the mainsail away.
Topweight
The full weight of the sail and the reefing system is always up the mast. The reefing system adds topweight that wouldn’t be present on a slab reefed boat and in addition you don’t get any the reduction in topweight as you reef.
The increased topweight reduces the righting moment at any given angle of heel, so to limit the angle of heel going to windward you need to reef sooner, which slows the boat down.
In our case we fitted a wind generator to the mizzen mast which added some topweight, so we don't get the full advantage of losing the weight of all of the roller reefing gubbins, but we still gain something and at least we haven’t made things worse.
Ease of Use
When Speedwell of Rhu was built, in 1988, a slab reefing sail would probably have had a set of plastic sliders in the mast’s luff groove. On a large sail this sort of system can introduce quite a lot of friction, especially if there’s any wind in the sail, so an in-mast furling system would probably have been easier to use.
We replaced the in-mast rig with new masts from Selden using their MDS batten car system which consists of a set of wheeled cars running up and down in the mast. This is a very low friction system so hoisting or lowering the sail is much easier than with an old-fashioned plastic luff slider system.
My experience with in-mast reefing systems has been that winding the sail in and out involves quite a lot of winching, normally on a coach-roof mounted winch under a spray hood where the person winching has a limited view of the sail. Often there’s an endless loop that needs winching to operate the reefing roller and an outhaul that needs controlling or winching out, if these both come to the same winch then it becomes quite difficult to manage. On our delivery trip we found that it took some time to winch the mainsail away, much more time than it takes to drop a fully battened slab reefing sail into a stack-pack.
Reliability
In the early days of in-mast reefing reliability was often cited as a major negative point. If the reefing gear were to jam with the sail partly reefed then in the worst case the only way of reducing sail would be to cut the sail away. Modern in-mast systems are actually very reliable and complete failures are rare so this isn’t as big a worry as is often made out, but for a long distance cruising boat there is always that nagging doubt about what will happen if the reefing gear jams.
Of course the same argument can be made against roller reefing headsails, but in this case if the system jams there are options for tidying the sail away. In the case of a complete jam I’d consider sailing the boat in circles to wrap the sail around the forestay, something that’s not on option for a jammed mainsail.
Noise
This one came as something of a surprise on our delivery trip as we were sitting out windy weather in Brighton marina. The wind was blowing from the stern quarter and as it blew across the throat of the in-mast reefing the whole mast started to resonate loudly, rather like blowing across the mouth of a bottle. The noise carried on through the night giving the crew in the forward cabin a poor night's sleep.
I mentioned this to the rigging manager at Fox’s and he told me that in certain wind directions all of the in-mast reefing boats on the hard-standing pipe-up, making quite a noise.
Speedwell came with a mystery strip of sailcloth with a set of sliders attached which we took home before the delivery trip. When we were in Brighton marina we realised that this was intended to be winched up the mast to blank off the throat of the reefing system when the sail was furled away to try to stop wind induced noise. I’m told that this approach isn’t always effective and we didn’t get to try it as we didn’t have the device on the boat.
Our slab reefing mast has a much narrower luff grove than the throat of the old in-mast reefing one we replaced and there isn’t the large cavity behind it that’s needed on an in-mast system to contain the furled sail. The boat has proved to be much less prone to wind generated noises when we’re not under way.