Fractional Rigs… Good bad or indifferent...

[Seajet]

The thing which doesn't seem to be mentioned so far is the SLOT EFFECT of squeezing and accelerating the air between the fore & mainsails, like a jet; this is more achievable with a fractional rig.

As for mast support, a 7/8ths rig becomes as well supported as a masthead rig as soon as the first reef is taken in.

When did you last see a masthead rigged racing dinghy ?!

Slot effect; View attachment 35762

 

[oldharry]

Plenty of Trident 24s built in the 60's with fractional rigs still going strong with the original spars - mine included! Properly set up, there should be no weakness. However the Trident has a Jumper stay arrangement to help support the mast above the forestay, an arrangement rarely seen with modern fractionals.

 

[mrming]

If the leeward shrouds on a fractional rig with swept spreaders are going slack, the rig isn't property set up, the mast will be more prone to pumping and tend to rotate around the windward shroud, subjecting to spar to twisting loads. Both are likely to encourage fatigue failures.

As far as I understand, it's okay for the leeward inner to go slightly slack upwind, but obviously the cap shroud should never be slack. Selden and Z Spars both have excellent tuning guides available on their website, and a Loos professional tension gauge is also a good thing to have.

 

[Simondjuk]

Yes, it's the caps which are most important in the respect I was referring to. The main task of the diagonals being to limit fore and aft bend and keep the mast in column laterally. If the leeward Ds are just slackening when hard pressed, that's acceptable provided that the mast remains straight. That said, I prefer mine not to go slack and tension them accordingly. The tension in fractional rigs needs to much higher than most people assume, our caps for example are tensioned to something in the region of 2000 kilos and the D1s to over 1000 kilos. Even these modest tensions feel brutal to apply with spanners. On larger boats, the loads become so high that tensioning via the bottlescrews becomes impracticable and the mast must be jacked and shimmed to achieve the required tensions.

 

[Lakesailor]

Quite apart from all the "perfect set-up" considerations. I've had both rigs (in small boats) and find the lack of downwind ability a balls-ache in fractional rigs.

 

[William_H]

Most of the pros and cons have been mentioned. Chafe on swept spreaders being one disadvantage. The lack of inner forestay is a huge advantage when tacking.
The robustness of the spreader base in the swept direction is really critical and spreader structure here should be checked.
I do not subscribe to the huge static tensions many do. You do however need to check the mast shape when uder pressure and adjust stays accordingly.
good luck olewill

 

[John the kiwi]

That may in fact be true, but it's not intrinsically obvious "if I think about it". In my head, the point where the capshrouds and the forestay meet is fixed in space. By pulling the masthead backwards above that point, I push the middle of the mast, below it, forwards. The tripod of shrouds and forestay remains the same.

Pete

Not sure if this helps, but i finally understood that if the mast is curved between cap shrouds and fore stay attachment(hounds) and the mast step then the straight line distance between those points is decreased as compared to when the mast is dead straight. This can be enough to reduce the tension in the stays as you crank on outhauls and kickers or masthead back stay which have the effect of increasing mast bend. Some yachts therefore have running back-stays to compensate for this loss of tension and retension the forestay to maintain a straight jib luff.
Cheers

 

[Sybarite]

Ditto, flappy rigging isn't a great idea on any modern boat.

You can avoid all these problems with an aerorig design. Gerard Dykstra, one of the most influential architects around said that if had to start again for his own boat (currently a Besteaver 53') he would have an aerorig. He has designed what will be the world's largest sailing yacht, 463'.

http://www.gdnp.nl/currentprojects

 

[30boat]

The tensions on fractional rigs do have to be high in order to avoid the lee caps and lowers to go slack .I had to tension my Fulmar's rig to 25% of the breaking load of the wire in order for the rig to work properly.My previous mast was very bendy because the cross section was too small (compensated by very thick mast walls) and it would pump despite high rig loads so I installed checkstays and runners.That made the rig incredibly stable and if I find that my much larger cross section new mast still pumps I'll also fit checkstays.So far it appears to be very stable and Fulmars don't have checkstays as a norm.

 

[Noahsdad]

I have a keel stepped fractional rig with spreaders perpendicular to the mast so hence runners, check stay and back stay to fiddle with.
I use the runners to tension the forestay, check stay to check mast bow and by applying more backstay can I postpone the need for a reef by moving the effort of the main aft allowing some wind to spill from the leech.
The boat (38') is great fun to sail, longer passages never get boring as we are always tweaking this and that for that little bit extra and my wife and I have no problem releasing and tensioning the runners whilst tacking though I always rig a preventer when running dead down wind.

 

[lotusman]

That may in fact be true, but it's not intrinsically obvious "if I think about it". In my head, the point where the capshrouds and the forestay meet is fixed in space. By pulling the masthead backwards above that point, I push the middle of the mast, below it, forwards. The tripod of shrouds and forestay remains the same.

Pete

I think of it like this and hope it helps:

When the capshrouds are tensioned on a fractional rig with backswept spreaders a force directed forwards is transferred into the mast at the base of the spreaders causing the mast to bend forwards. When the backstay is tensioned it also exerts a force bending the mast forwards, in effect the backstay shares the bending force with the capshrouds, the consequence is that tension reduces in the capshrouds.

If you look at a side view of a fractional rig with backswept spreaders, the capshrouds follow a direction aft from their upper fixing on the mast to the tip of the spreaders at which point they change direction and from the tip of the spreaders to the chain plates the capshrouds are close to parallel to the mast. Tightening the backstay bends the mast and the capshrouds follow a straighter line from masthead to chain plate which is a shorter distance, hence tension is reduced.

I am not sure what you mean by capshrouds and forestay meeting at a point fixed in space.

I am in the camp that believes capshrouds should not be slack in a fractional rig.

A point not yet mentioned is that a fractional mast due to its smaller section may be less suitable for fixing a radar – this was the case on my previous boat, a fractionally rigged 33’ Albin Nova.

 

[Keen_Ed]

The battle is lost, and the masthead rig lost it. A substantial majority of new boats are now supplied fractional, and the size of the genoa is slowly diminishing - less than 110% now seems to be the norm on new designs.

Overlap is a very inefficient place to put sailcloth. On a racing boat, at least, it only makes sense if it's free or cheap in rating terms. Every development / restricted class which allows different sail plans sees no or very little overlap.

 

[Laurie]

Where does all this leave the masthead rig with swept spreaders? The worst of both worlds? Yup that's my current rig.......

(And no, very true, cap shrouds should not be slack!)

 

[macd]

Another factor the OP might want to consider, not a huge one, is standing rigging replacement intervals. Because of the higher loads on fractional rigs, some insurance companies require replacement after eight years, compared to ten for masthead rig (or similar variations on the same theme). Other insurers make no such stipulations.