A plan ... a sail plan!

Our regular reader (you know who you are) will know that I do like a plan.

And the big plan right now is the new sails we have on order from Dolphin Sails.

Having finalised the dimensions &c., after full and extremely useful discussions with Ben at Dolphin, I've now been able to tackle something I've been meaning to do ever since we bought Pagan.

And that is to start working up a clear understanding of the reefing options and getting properly set up to put the right reef(s) in at the right time without all the guesswork that's been the way of it so far.

Now I must emphasise from the top that the following drawings and calculations are MY drawings and calculations, not the drawings of the new sails supplied by Dolphin. And to further clarify, these are the initial starting scenarios based on the theoretical calculations on sail balance that I've carried out. In practice, it won't be quite like this - the genoa reefs, especially, will probably not be as deep as I've indicated as the more of the genoa is rolled away the less efficient it becomes.

A further factor is that the centres of effort of the sails are (as is the traditional way) calculated on the flat two dimensional plan of the sail (and are equivalent to the centre of mass). In the real world, a sail is not two dimensional, it is an aerofoil, and the centre of effort (the axis along which the lift generated by the sail operates) will not be the centre of mass.

This axis of effort is affected by various factors and whilst it could, with sophisticated software and very accurate modelling of the sail, be calculated, that is well beyond the tools I have available and not actually necessary for my purposes.

Anyway, enough of that! The first and most critical step in producing new sails for a yacht is to measure the critical dimensions on the boat in question. The old sails are never measured, there's no guarantee that they were spot on in the first place and in any case they'll be worn and distorted otherwise there'd be no need for new sails! Dolphin duly came out and measured up and a couple of days later I received the first draught plan of the new sails.

That led to some further discussions about reefing points, the size of the genoa &c. and Glen and I made a flying visit to Pagan to check up on a couple of things we weren't 100% sure about. Following a further exchange of ideas with Dolphin, the design was finalised and the new sails will hopefully arrive in about 8 to 10 weeks.

So what's the crack then?

Well let's have a look at the original Westerly sail plan ...

One notable feature of the Laurent Giles designed Westerly ketches is the absence of a rigging wire (a stay) between the top of the main mast and the top of the mizzen mast. This stay, called a Triatic (don't ask me why) serves the function of a back stay for the main mast. Laurent Giles did not, apparently, like triatic stays and preferred to fit a conventional backstay on the main, albeit split into two about a third of the way up in order to clear the mizzen mast.

That's an aside of no real relevance other than that the existence of the back stay limits the amount of "roach" - the amount by which the leech, the trailing edge, of the sail extends beyond a straight line from the clew ... ugh, for the uninitiated ...

The basics of sail nomenclature (an image I half inched from somewhere ages ago and I can't remember where it was from so apologies to the owner!)

Roach is useful to some extent as it's "free" sail area but remember that a sail is an aerofoil and increasing the area is only useful if the aerofoil shape isn't compromised. Too much roach, whilst useful downwind (the only time that the driving force is generated by the wind hitting the sail) can compromise the efficiency of the sail on a reach and close hauled ...

Oh heck, this begs some better explanation too doesn't it?

There's a pretty good article on the subject - Forces on sails - Wikipedia which covers all you need to know.

The diagram on the right illustrates the essentials of how a sail works. It also illustrates something I'll be coming to a bit later.

As you can see, the lift is generated at an angle of 90 degrees (roughly) to the sail which is not the direction we want to be going in! However, the underwater profile of a yacht (the hull and keel) resists going sideways like anybody's business and really really wants to go forwards. So most of the lift from the sails is translated into forward movement. However, there is always a certain amount of sideways movement, which is called leeway. How much depends on the design of the boat, the set of the sails and the conditions. It can be as little as two or three degrees off the way the boat is heading up to as much as ten or more degrees.

Right, where was I ... this is not going to be a short article!

So what we discovered, which was critical, is that the rig on Pagan has the standard ketch masts however the main boom is slightly shorter and the mizzen boom is both slightly longer and set slightly higher up the mizzen mast. Why? Who knows! This is the very reason that sailmakers do not rely on manufacturers sail plans, even better quality original drawings by the designer.

In practice, that means that both our main and our mizzen sails have to be slightly smaller than the original drawing suggests. However, they end up being a little bit bigger than the original specification! You pays your money and takes your choice! As long as they fit, who cares?

So here, in all it's confusing glory, is Pagan's new sail plan. The eagle eyed sailory types might notice the high cut of the foot of the genoa (the bottom edge for the landlubbers). That's a deliberate decision on our part after discussions with Dolphin. 

The most efficient design, especially for sailing to windward with the sail sheeted hard in, would be to have the foot as close to the deck as possible. However, there are problems with that for the coastal cruising sailor. First of all, we generally try to avoid sailing to windward! The old saw has it that "gentlemen do not sail to windward" and whilst I'm not a gentleman I concur with that notion.

With that traditional low cut foot, as soon as the genoa sheet is eased onto a close reach, the foot of the sail hooks over the pulpit rail (the solid stainless steel bars at the bows) thus compromising it's shape. So decision number one was to optimise the cut of the sail for reaching rather than for sailing close hauled to windward. The next decision, at the cost of about half a square metre of sail area, was to raise the foot of the sail another few inches above that. This is in order to give us a reasonable view under the sail. Once again, it is a compromise - we're sacrificing performance (a little) for convenience. This is motivated by the fact that we mostly sail in confined coastal waters often with a lot of other boats around and about. Being able to see the enemy is, we feel, more important than an extra tenth of a knot of boat speed (or whatever the difference would be, it matters not).

Also factored into that decision is the cruising chute which, from a reach to a run, is of considerably more use than an extra half a square metre of genoa. Of all the decisions relating to the new sails, this is the one we've agonised over the most but we've made the call and if we live to regret it hey ho (I suppose, if we've really cocked up on this one, we would have to raid the piggy bank for a bigger genoa. It wouldn't be the absolute end of the world).

So let's start breaking this down into the various reefing options ...

All Plain Sail

Yay! It's a good day with 10 to 12 knots of steady breeze on the beam (coming roughly from the side) and we're trotting along at 5 or 6 knots under All Plain Sail.

The sun is shining, the sea is shimmering with just the ripples made by the wind and we're on course, on time and "in the groove". 

Yeah, right. Happens once in a while but nowhere near as often as we'd like!

Being a 1970s classic British design, the Westerly W33 will carry all plain sail well up to the top end of F4 (16 knots) and even, if you're feeling enthusiastic, a bit more. But by the time the average wind speed hits 16 to 18 knots, it's time to reef. And we tend to reef early to keep things comfortable anyway.

So in goes the first reef.

This is achieved by reducing the size of the mainsail by pulling it down onto the boom to the first reefing point. There are eyes in the sail along this line, big ones at either end for the tack and the clew (see above) and smaller ones along the sail for the reefing cringles (lengths of, ahem, "string" used to tie the surplus sail neatly (ahem #2) to the boom.

The genoa is then reefed, by rolling some of it away on the roller reefing gear, to re-balance the boat. 

Ah, I haven't mentioned balance yet have I? Basically, the combined centre of effort of all three (in this case) sails operates on the Centre of Lateral Pressure of the hull to drive the boat forward, and (as I mentioned above) a bit sideways.

If that centre of effort is too far foward, the boat will try to turn away from the wind. This is the dreaded lee helm and it's not nice. If, however, it's too far aft the boat will try to turn up into the wind. This is weather helm. A touch of weather helm is a good thing as it helps keep the boat on track. Too much, however, is inefficient as the application of rudder to counter it creates drag and robs the boat of speed.

Far too much lee helm results in a crash gybe, where the boat turns uncontrollably and the boom crashes across from one side to the other. Crash gybes are to be avoided at all costs as they can damage the rig, even dismast the boat, and if that boom catches a member of the crew out and hits them it can easily be fatal. A gybe preventer can be rigged (and it's on my to do list) but that's not a solition to pernicious lee helm.

Far too much weather helm results in the boat insisting on luffing up into the wind. It's not as dramatic or dangerous but it isn't the way to get to your desination before the bar closes.

So having tucked away about 15% of the mainsail, if we leave the genoa alone the centre of effort will move forward potentially creating lee helm. Ugh. So we need to roll away enough genoa to re-balance the boat. Exactly how much is not an exact science and it will almost certainly be less than the theoretical amount of genoa show on my drawings. The more genoa is rolled away, the less efficient the sail gets as the shape is inevitable compromised despite the best efforts of modern sailmakers to compensate. This effect will become more pronoucned as the reefs deepen. We will only find the correct reefing points by experimentation and even then they will vary somewhat dependant upon conditions.

Right, anyway, so that first reef will likely go in as the wind gets up to 15 or 16 knots or, in other words, around the top end of F4. It might even go in earlier if we're in no particular rush especially if there's a chance of the wind picking up. Given the option, I'll go for lazy sailing every damn time!

But now the wind has picked up to a fresh breeze, otherwise known as F5 or 17 to 21 knots ...

Now it's time for the second reef to go in on the mainsail reducing it's size to about two thirds of it's full area.

And, of course, more genoa has to be rolled away to compensate although not, in theory at least, as much as you might expect due to the combination of the reduction in sail area and the movement of the centres of effort tending to cancel each other out a bit.

Under most circumstances, this is as far as we go. Being unashamedly fair weather sailors, if F6 (known as a yachtsman's gale) or above is forecast, we usually stay right where we are.

However, there are circumstances where this isn't the case. In sheltered waters such as the Solent we have been known to make a short passage in an F6 and, of course, there's always the possibility of getting caught out. Indeed, the long serving reader may remember such an occasion years ago.

Way back when, we set out on Erbas to sail round from the Crouch to Bradwell in a forecast F5 gusting F6. A bit enthusiastic for our tastes but we had a "do" to go to and it is a fairly short hop. By the time we got across the Spitway and headed into the Blackwater, we had a solid F8 on the nose! It actually turned out to be an exhilerating and very satisfying beat into the river but we had quite a few bruises to show for it and it isn't something I'd want to repeat on a regular basis.

Our next option, the one we used sailing across the Solent in a strong breeze (F6, 22-27 knots) is to dispense with the mainsail altogether and sail on mizzen and reefed genoa alone. This is our third reef.

In reality, due to the aforementioned loss of efficiency as it is rolled away, we'd almost certainly be carrying rather more genoa than the drawing depicts. We'll work that out during sea trials.

This setup is one of the sheer delights of sailing a ketch. As well as being a good option for sailing in a stiff breeze, or even a near gale (F7), it's also a handy sail plan for bimbling about when you're in no rush. Hoisting, lowering and stowing the mainsail takes a fair bit of effort so why bother if you don't need to?

Now we move into unknown territory. Our current mizzen sail doesn't have any reefing points. It's either up or it's down. The new mizzen has one reef.

Now the truth is that I don't know just how useful or otherwise that reef is going to be. It's not a cost option, it's part of the standard package, and I can forsee it being useful as there have been times when I've felt that, as we've reefed down the main and the genoa, the mizzen has been overpowered.

Once the mizzen is reefed and (probably) some genoa rolled away to re-balance the boat, we simply repeat the above options - full main, 1st reef in the main + roll away some more genoa, 2nd reef in the main and roll away even more genoa and finally no main and not a lot of genoa at all!

Just how useful these options will be remains to be seen but it's worth bearing in mind that the reefed mizzen, full main and reefed genoa equates roughly to the first reef with a full mizzen. It may be that this is a better option - keeping the full main and reefing down the ends. We shall see at sea (d'ya sea what I did there ... twice?!)

Mind you, we don't have any arrangements for reefing the mizzen at the moment. We'll have to add a cheek block, and cleat onto the mizzen boom and sort out some arrangement for the clew but that won't take a lot of doing.

One final subject I haven't touched on and I've just remembered ... and it was another critical decision.

Our current sails, as was usually the way back in the day, have a bolt rope along the foot of the sail that fits into a channel on the top of the boom. This is convenient, as the sail can't fall off the boom when being stowed, but it has little else to commend it.

A far better arrangment is to make the sail "loose footed". This means it is only attached to the boom at the clew (the outward end of the boom) and by adjusting the clew outhaul, the shape of the sail can be modified. By easing the outhaul, the "belly" of the sail is increased and moves forward. This increases lift, amongst other things, and is optimum for reaching in lighter wind conditions. Conversely, by tensioning the foot of the sail up with the outhaul, the sail is flattened (and the centre of effort moved aft a bit) which is better for sailing to windward in a stiffer breeze.

Sounds good and we decided to opt for loose footed sails. The only snag is that we don't have any arrangements for a clew outhaul on either the main or the mizzen, the clew is simply lashed to the end of the boom and whatever tension is put on when that lashing is done is what you're stuck with. I need to work out a clew outhaul arrangement for both sails, preferable one that, on the main at least, brings the adjustment back in-board. I have some ideas on that front but they're not firmed up yet.

So there you (eventually) have it - Pagan's new sail plan