Masthead versus Fractional Rig

I have no doubt that since even before the inception of the Bermudan sail plan, that there were arguements in pubs along the Solent, Clyde and Hudson about which type of mast rig was best: the forestay and back stay meet at the top or never shall be united?

Now I must declare that I am partisan when it comes to considering the merits of the masthead rig, prefering the fractional rig. However since I have sailed with some fairly advanced mast head rigs and a couple of quite unweildy fractionals I will try to moderate my antipathy for all things which lack a frac'.

The evolution of the two rigs is worthy of a blogg from some other anorak, and no doubt discussed in some annal of sailing. However the masthead design on a bermudan (or multiple there of) is of course a no brainer- you have one fixture in a mast top plate /crane and the rig is under full longditudinal tension and vertical compression. For a stick made of the organic stuff, then this makes for a somewhat more reliable life time, with there being fairly even pressure given spreaders are correctly spaced and shrouds are also correctly tensioned. A wooden fractional is exposed to a far more uneven loading, and can necessitate running back stays on sportier more powerful rigs in order to hold the mast in column and give it the support to control sail depth in both sails.

The no-brainer masthead design though really came into its own with the advent of aluminium rigs. Here a designer could simply over engineer the mast diameter, stick spreaders on at 90' and a big, simple over dimensioned plate could be welded on the top of the mast. Cruisers then from the 1950s onward had big old pole-like masts which actually respond very little to additional backstay being applied underway. The genoa became unfortunetly more important than the mainsail and it all resulted in some ruddy aweful cruisers, and worse when masthead was prefered by some racing designers perhaps for handicap reasons, resulting in stubby rigs with masses of winching to do on over sized foresails (IMHO!)

The aluminium revolution did however also enable the revolution in powerful fractional rigs firstly in sailing dinghies. Uffa fox was one of the first boat designers to employ an alloy mast on the flying fifteen, and in turn the bend characteristics relative to the trust in the mast and its' longevity. Boats could now be made with highly controllable sail shapes and more power could be deployed from larger sail areas (without the need for reefing in dinghies for example). Basically the kicker on dinghies, mainsheet and forestay tension could facilitate a flatter or deeper sail plan, and this be done underway. Coupled to easy to adjust off race shrouds and forestay legnths, and also cunninghams, traveller, jib cars then the degree of adjustability for dinghies became far greater than with simpler wooden masts at an affordable price.

Masthead Strikes Back!

Meeting at the top however does by no means exclude all the above advantages which aluminium engendered upon fractionals.  It was rather that there became a bit of a three way split as I mention above: alloy fractional for dinghies and many sub 40 foot racers, simple alloy masthead poles for cruisers and some handicap or performance optimised masthead designs. The latter was a fashion particularly in some meter designs (8m, 8m cruiser for example) and then in "tonne" designs (although most small quater tonners were fractional I believe)

Masthead then, has never procluded higher performance. There are just some pre-requisites and oddities about sportier masthead rigs, which we can return to later. Meter and Tonne designs were for their respective eras, the pinnacle of wealthy gentleman's yacht racing, and above 30 feet I would place a bet that there was either a majority rigged masthead or a very large minority. So you can hardly write off mastheads as being something for cruisers. Also as the new era of CHS and later IRC there were some designers such as John Corby who favoured the all up at t'top solution.

 In terms of meter and tonne development rule designs, a designer had the freedom to tweak some rating advantage or a better righting moment for a given hull and ballast concept by placing the sail area lower down. Then in fact they can choose to have a very tunable mast with check stays, mast rams, adjustable forestays and the like. The epitomy of this was to my mind some of the One Tonne designs which had multiple spreaders and quite tunable mast bend, both pre-race and by the use of their running rigging. These no doubt influenced the Maxi designs, with famous boats like Drum being masthead.

I was lucky enough to sail a few seasons in ISORA and other races on the Corby 35 "Converting Machine" which was a serious bit of racing kit, and mast head to boot. She had triple spreaders if I remember correctly, most images being off the net now and my shots being cut short most often. The mast was quite bendable due to the design with a degree of prebend, and a powerful hydraulic muscle box on the backstay.

Having raised the profile of the masthead to what may seem a "cult" status, let me now then knock it down a hack or two speaking from personal experience:


Drawbacks of Masthead Rigs vs Fractional Rigs

Firstly you can of course say that masthead is just laziness and penny pinching in many boat concepts and executuions: for example the ertswhile Maxi 77 and her kin: an alloy telegraph pole with little bend and little adjustability for rake. A cheap way of getting a one design in at a price point. But as mentioned some very expensive per foot yachts indeed are still being built today for IRC with mastheads. So what are the drawbacks, qaulity being equal in racing terms ?

1) Controllability of Sail Shape  with Running Rigging and Prebend

For the same quality then you do not have absolutely the same ability to control sail shape with the sails you have up. Backstay is quite critical here, when on the frac' it will bend off the top section of the mast above the "hounds" where the shrouds and forestay enter the mast. Further More mast bend is not as controllable in relation/combination to other factors, the main one being : Twist

2) Contol of Twist and Closing the Slot 

This is my main bug bear with masthead rigs. On a fractional you can use twist to open up the top third of the sail, which on fractions of around 75%-85% means that you have a forward driving force high up in the wind where you want it, without closing the slot as you would on a mast head rig. Basically the twist at the top of a given genoa will not fall open as far as you would be able to benefit from the twist in a foresail which is set.

In combination with a high degree of control of mainsail depth (without necessarily check stays) , rig tenstion aiding this if set up right, then the added twist open top and drive you get is more easily controllable.  There is of course a counter agruement, but masthead devotees fall upon their own sword here in number 3:

3) Masthead Slot and Twist Necessitates more Frequent Sail Changes

This is the one major difference in crewing a performance masthead versus a fractional. Due to the effects above, and the desire to increase twist in the main, while reducing heeling moment, masthead boats like the corby, the IMX38 and say the venerable j35 change headsails more often than comparable frac's. Serious racers "need" a larger wardrobe of headsails.

Serious frac' racers will of course also make necessary sail changes, especially from the light Genoa 1 to the heavy Genoa 1,  but by in large you will find that a No. 2 sail in any fractional sail locker is a little used sail because many can survive with their H1 genoa by twisting the sails off more and more, and reckon that in round the cans a change down is more painful than being overpowered. In squally conditions this means that on a typical frac' between three-qaurters and seven-eigths, you can keep drive on in the sails by having the top of the mainsail open. Also on most sail plans on fracs and egometries of fore-triangle, often the longer triangle on the genoa opens ( twists or is set outboard on barber hauled boats)  more than the steeper trianlge  of a masthead

Finally in my experience you can avoid a reef longer when you do change down to a number 3 for example. You can twist off the top of the sail and open it on the backstay more on a frac.

4) Necessity for Masthead Kites

If you are not setting a small, ugly inside forestay spinnaker, then on a masthead you are also limited to setting a masthead spinnaker. This means you have a much larger sail area, which is all the rage for many, but means that after a certain wind strength the boat becomes unweildy and broaches become more spectacular.

Big spinnakers and assy's have played their part in the inexorable rise of the windward-leeward race format, but this does not of course exclude frac' rigs: take for example many Mumm 36s have been converted to masthead, and the FF 15 and 505 have trialled bigger, DDW spinnakers. Many new IRC optimised designs feature too a high, tall aspect spinnaker to the mast top on frac's.

Although this is a point which can be taken from two angles, if you have any amount of reaching to do and a twitchy tonne hull shape or light ballast, then a masthead kite can be a handful compared to one on or around the frac'.

5) P.s. Critical Set Up for Pointing
If you read my later blog on Pointing, there is an example of the Figaro Masthead confirguration which is very critical to mast set up, and we are talking just an inch at the foot of the mast on the hogg, and a few inches on the forestay to acheive better rake and 'windward lever'. Because the genoa/jib has a larger sail area and it is higher up, its lee-lever effect has to be monitored and because you may want a taught forestay to reduce luff sag, you may pull rake out of the mast and hence reduce pointing. Having said that boats like the J 35, j29 and Corby 29, 35, 36 you name it, with masthead point like no body's business and that is due to a good rig set up and a powerful, full height slot- see below now for the benefits of masthead.

Plus Sides of Masthead

Well to try and for the sake of a reasonable discourse, what are the advantages of masthead ?

Really by in large they are all the flip side of my points above:

1) No Brainers, no skills : for a once a month cruiser captain, there is nothing to think about, especially with roller reefing genoas and in-mast reefing. You can get a cheap, stiff, overengineered and therefore lifetime reliable mast.

2) You can have the same or larger sail area on a lower mastheight. This can be important for a design, where a powerful genoa is taken into account for example, or a low aspect , low heel sail plan is desirable for some reason. I have not found out if CHS and later IRC penalises higher mast height relative to overall sail area, but I suspect it does!

3) Power the Slot All the Way Up: The converse of using twist is when the boat needs to be fully powered up and pointing. For their waterlegnth and general power to weight ratio, the j35 and the Corby masthead designs pointed higher and acheived a better VMG in so doing. Remember the slot effect is two plus two equals five in terms of the lateral acceleration along the outer surfaces, while in addition the latter day development of square-top mains shows that there is a lot of power being spilled off the top of the sails.

A racing mast head with the right foresail up for the windstregnth, most likely captures a little bit more than you would imagine that extra few meters of jib triangle would due to the combined effects of slot and training the vertical air a little more before its' exit by the trailing vortex from the top of the main.

4) Masthead Kite on a More Mechanically Stable Rig : the fore-aft mast top triangle is inherently more stable than a frac' and this has it's greates advantage in supporting the pressure exerted by a mast top spinnaker. Side forces when reaching are supported more by the forestay, the shrouds and the total compression effect of the "sealed" topped rig. I dare say that a j35 holds its spinnaker in more wind than the fractional predecessor the j36.


At the end of the day........ it comes down a bit to personal choice and budget. A masthead performance racer will most likely be more expensive in new purchase and sail wardrobe. Also far more one designs are fractional perhaps because they often are built to appeal to racers who do not want to budget a big sail wardrobe, but I say more likely because the designer is free of handicap or rule configurations and can opt to place more power in the mainsail where it is more controllable on the simplist running rigging available to those at the back of the boat where decisions are made.

 That is my last tuppence worth on the matter! Make your own mind up!