Sailing XTC

[doug748]

An excellent YouTube channel and great resource for students of yacht design. Each Zoom session hosts a different top designer. Here is Julian Everitt with some trenchant views on:

Fractional rig - Fashionable because of rating advantage not fundamental performance.
Keels - Questions popular engineering design and the way racing boats are used outside their design envelope.
Chines - Often used because they are expected or purely to put more accommodation into a boat.

Anyway here he is:

Others in the series include Kevin Dibly, Ron Holland etc.

.

 

[msangel]

Interesting. I'll watch it definitely. The channel's hosts seem very experienced in yachts.

 

[Laser310]

Fractional rig - Fashionable because of rating advantage not fundamental performance.

Rating advantage..? ..a meaningless statement unless he specifies which rule - probably some but not others. IRC - yes.., but the various performance based rules maybe not so much.

Anyway.., both masthead and fractional rigs clearly have performance advantages and disadvantages that are unrelated to rating rules.

 

[dunedin]

Rating advantage..? ..a meaningless statement unless he specifies which rule - probably some but not others. IRC - yes.., but the various performance based rules maybe not so much.

Anyway.., both masthead and fractional rigs clearly have performance advantages and disadvantages that are unrelated to rating rules.

Another video from somebody with lots of opinions but perhaps less facts.

To say that a fractional rig is driven by rating rules not performance, without any supporting evidence, is a major leap into personal opinion.
The fact that
* almost 100% of model racing yachts use fractional rigs
* almost 100% of racing dinghies use fractional rigs upwind (many use masthead kites downwind)
* most racing day boats use fractional rigs
* Americas Cup yachts of every variant use fractional rigs
* most cruising yachts now use a slight fractional rig
There must be a message in there somewhere.

 

[Wing Mark]

Is it possible to have a rating rule which is completely 'neutral' about fractional rigs?

Do you compare on the basis of a given height of mast? triangular sail plan area? True sail area? Sail and spar area to include wing masts?

Or maybe we should compare rigs with no limits at all, what's the fastest rig on a given hull over a range of wind conditions?

Should we think more about rigs being efficient in terms of drive vs heeling moment?

 

[KompetentKrew]

I corrected the video's URL (removed the :537 from the end) so, if you watch it below, it starts at the beginning instead of 9 minutes in:

 

[flaming]

You can't just look at fractional and masthead from a "for the same sail area, which is best" point of view, as it is a lot more complicated than that.

For a given sail area a fractional rig will require a taller mast, and a proportionally larger mainsail than the equivalent masthead rig with large overlapping genoa. The fractional rig has a small disadvantage upwind, in that it has a higher CoE, and probably higher centre of mass, so will require a bit more righting moment.
However, it is well known that higher aspect ratio sails are more efficient, which helps to counter this. Added to the fact that it is practically easier to depower a fractional rig than a masthead rig.
Reaching traditionally favoured the masthead rig with a big powerful genoa, but the modern code zero sails flown off a masthead halyard and bowsprit are even larger and more powerful.

And then, when you turn downwind the fractional boat can set a substantially bigger spinnaker as its mast is taller, and in addition the mainsail is larger, making for far greater potential sail area. As the wind increases the fractional boat also has the option to use a shorter hoist, just above the forestay, to allow for a smaller kite set lower, and even a smaller code sail. Where the masthead boat has to keep all spinnakers at full hoist, giving only the option of going for a narrower kite to reduce area, which brings its own issues in terms of stability and ease of trimming etc.

Realistically the most up to date race boats are really operating in a kind of hybrid mode. Upwind they are using fairly high aspect rigs, but with the mast set well back in the boat the genoas are actually not much smaller than the traditional big overlappers. But because they are not overlappers they can be flatter sails sheeted at much tighter angles. Then off the wind the deployment of large code sails, then spinnakers, coupled with a large squaretop main, mean that the rig carries more, and more efficient, sail on any point of sail than the traditional masthead rig, but also retains the flexibility to reduce downwind area by using the shorter hoist point.

In short, the fractional rig gives the sailor a lot more options in how to mode the boat, plus the ability to set a lot more sail downwind, and not have to winch in a massive genoa going upwind. Honestly, I struggle to see any attraction at all for a masthead rig these days.

Chines are an interesting one. I'm currently sailing a boat with a modest chine, and there is no doubt that it pays a significant part in the performance of the boat. The way the boat goes upwind in heavy air when sat on the chine is remarkable. And the ability to sit at 14-15 knots at fairly hot angles with the A5 up and in total control in a 32 foot boat.... I'm sold.... At Cowes this year we had only 1 windy day. We went round the last upwind mark off Yarmouth with the A35 who won the week. We managed to hold our A5 all the way to the finish in Cowes, hitting 15 knots at times. No other boat we saw (including J105s, Corbys, First 35s etc) managed to hold a kite, it was too hot for them. We were over 10 minutes ahead at the finish. There is no doubt whatsoever in my mind that we could hold the kite on that angle because we were sat on the chine that the other boats did not have.
And it was by far and away the most exciting sailing we had that week.

It's also true that a lot of cruising designers are using chines in order to improve accommodation, with the performance considerations being completely secondary. But what exactly is wrong with that? If the primary purpose of the boat is to accommodate people in comfort as they sail from one nice harbour to the next, then employing a design technique to maximise your accommodation seems perfectly sensible to me...

 

[doug748]

I can't speak for the man but he may well not be saying anything very revolutionary. I think his point is that, in essence, there is no magical performance advantage to fractional rig from the arrangement of sails. Pound for pound their performance is similar to masthead. The differences come on the water plus the handicapping system.
Similarly with chines, there is no particular problem in using them for decoration but, I imagine, putting more accommodation and weight into already overburdened cruising boats will not help performance or seakeeping and is a point worth making.
I assume he has spent a lot of his life thinking about this and has not just thrown it in

He made his name with chine boats in the 1970's and has used them extensively. Despite the confines of IOR, 35 years ago he was designing racers like this:



.... with wide beam carried aft, high aspect fin keels, bulbs, fractional rig and masthead spinnakers. So when he gives those opinions you have to pay attention.

25 years ago boats like this, Volante

Which, for good measure, he says is the minimum length (47 feet) at which you can actually get away with twin aft cabins.

.

 

[Wing Mark]

If you've sailed a few dinghies in the 'pretty quick' category, you will know that all the boats that behave nicely at speed have chines aft.

Designers spent the 60s trying to get plywood boats as close as possible to round bilge shapes, the 70s designing in GRP what they couldn't do with wood, then from the 90s started to realise the merits of shapes which would have been easier to make out of ply in the first place.

Of course there will always be boats just designed to 'look modern' with feature like chines which don't actually make them good boats.

But some conditions of wind and sea will find some round bilge boats performing above their yardstick.

As for rigs, affordable carbon spars have perhaps changed the optimum?
A taller fractional rig of the same area can now be made lighter, so there's less harm in having a tall mast further forwards in the boat.

 

[flaming]

I can't speak for the man but he may well not be saying anything very revolutionary. I think his point is that, in essence, there is no magical performance advantage to fractional rig from the arrangement of sails. Pound for pound their performance is similar to masthead. The differences come on the water plus the handicapping system.

When you'e talking about just using the main and jib/genoa, then yes, quite probably. But as mentioned the fractional rig opens up a lot more possibilities in both light and strong winds.

Similarly with chines, there is no particular problem in using them for decoration but, I imagine, putting more accommodation and weight into already overburdened cruising boats will not help performance or seakeeping and is a point worth making.

I don't think anyone is arguing with this....?

Which, for good measure, he says is the minimum length (47 feet) at which you can actually get away with twin aft cabins.

I must have imagined all those very comfortable nights sleep in twin aft cabins in much smaller boats then....?