Why does a cutter rig point higher & sail faster?

We can point higher (10+ degress) and sail faster in light winds (up to 80% of true wind speed!), after converting our O'Day 37 to the cutter rig version. I fly a 110% high clewed Yankee and 75% Staysail.

Can anyone explain this phenomenon or share their similar experiences?

 

You changed one old genoa for two new sails. Possibly re-tuned the rig in the process. Maybe the main is too full to work properly with the old genoa. But if cutters were always better, at least some of the racing boats would be rigged that way. Ten degrees is a big difference.

The jib(s) are there to divert the air that passes thru the foretriangle, creating drive. The two rigs should divert just about the same amount of air about the same amount and get about the same amount of drive.

 

Are two sails more efficient?

You're right about the two new sails replacing the old Genoa, but wouldn't the extra surface area of the staysail result in more lift, since there are two airfoils vs one? Does a bi-plane have more lift than a mono-wing aircraft with the same airfoil shape? Could it depend on the design of the sailboat, in that a "headsail driven" boat could derive more benefit?

Thanks for your thoughts,

Captain Rich

 

Re cutter headsail rigs.

The cutter rig I have found is an excellent rig.

If your yacht was designed as a cutter its mainmast will be further aft. I have found that Cutters rigged with a single headsail don't point as well to windward in a good breeze.

You can gain some ground when tacking with a self tending staysail as it continues to drive the boat throughout the tack.

SeaDrive
Don't ever use the argument that if it worked well racing boats would use it!
You are forgetting that what you see on racing boats is that which gives the best advantage in the rules. There are many good sailing boat configurations that are simply penalised out of existance for racing.

 

When power was limited aircraft were bi planes or even tri planes.

A large amount of work (lift) is generated by the area just behind the leading edges.

With almost 2X as long a luff the cutter does better.

And the slot accelerations of the sails do better at feeding the main.

Illingworth & Primrose ,"Offshore" or "Furthur Offshore" is still the Bible for Cutter folks not involved with go slow "racing " rules.

FAST FRED

 

The only problem with the "it's all the racing rules' fault" is that IRC doesn't rate cutters (unless I'm very much mistaken) and open rules like the Open 60s have nothing against them either. I don't think the rules actually rate the staysail at all, so it's all "free" area.

In fact, not even IOR had anything against cutters. The "double head rig" was quite popular down here in the early 1970s, on boats like Fastnet winner "Ragamuffin" (S & S 48). Then it became obvious that, in reality, one headsail was better in almost all situations. The cutter's reign was a reaction to the stretch in old sailcloth.

Since that time, rating rules and offshore racing sailors have tried full battens, wing masts, ketches, schooners, cat ketches, fractional rigs, long overlaps, no overlaps, unstayed rigs....to think that they are conservative and to think that racing rules are too restrictive doesn't seem right.

In fact, as far back as Uffa Fox designers have noted that there is a REDUCTION in the number of headsails (after all, if you really think that more is better you'd have a triple-headsail rig like boats of the 1920s wouldn't you?)

When you see a cutter rig upwind in the Vendee Globe, or in the really fast boats like cats etc, then there's some evidence that they are more effective.

 

One of the problems with modern "cutters", e.g. Island Packets, is that they are set up with a staysail set up inside a masthead genoa. In that case the staysail really just adds drag. The (upper and outer) jib needs a high cut foot in order to allow the (inner and lower) staysail to do some work.

The point about the air flowing thru the foretriangle is that all the business about leading edge and slot effect and whatever is all detail. The big picture is Newton's law, and the exchange of momentum as air is diverted back. Given that, it's hard to see how any sail set on the forestay could be more efficient than a good genoa.

The most popular cruising rig nowadays is a masthead sloop with a sizeable (150%) genoa on a furler. This is very limiting when the wind is too strong for the whole genoa. A well thought out cutter rig gives some options for reducing sail.

 

Aerodynamic Models for Cutter Rigs ??

Is anyone aware of an aerodynamic model for cutter rigs? US Sailing's Velocity Predictor Program won't handle the twin headsail configuration.

It would be interesting to see if the model predicts that the combined length of the Yankee and Staysail equates to an equal sized Genoa. If it did, that could explain the performance increase.

Captain Rich

 

I'll be willing to bet that you changed the sheeting angle when you re-rigged, yes?

 

They have tried them yes But the measure of their acceptance on a racing boat has always been how the performance benefit stacks up against the rating penalty.

Too many new 'designers' are blinkered into thinking that racing boat form is the ultimate and everything else is a bit odd. So now we get unseaworthy cruising yachts because people want their boat to look like a rule based racer and designers and yachting magazine reviewers pander to the trend of the "cruiser-racer".

Cutter rigs remain a very good option for the larger yacht as an effective sail configuration. I would not recommend them for smaller yachts.

Many factors influence racing boat design. To add a working sail on a forestay (ie a cutter rig) the rig needs greater complexity, there are fittings stays terminations, runners or stiffer masts, added sail tracks winches, deck reinforcing... all this adds weight. Weight is a critical factor in racing boats . ( Including the Vendee globe yachts ). Performance and the rules favour light boats. Any extra weight aloft cannot be tolerated on yachts designs that chase light displacement and have such a poor stability curve.

Heavier safe stable comfortable seaworthy boats cannot be designed to the paradigm "if racing boats don't do it its a poor option" and the comparison is foolish.

 

Yes, racing boats do tend to set trends in design. But frankly are you sure that they are undesirable? Some of them are, but not all IMHO.

Secondly, all that extra stuff you mentioned that goes with a cutter rig also costs money, and quite a bit of it. So OK it may be worth it in a big cruiser, but to imply that racing rules is the reason cutter rigs are not used in other boats seems a bit of a stretch.

Re "Weight is a critical factor in racing boats.... Performance and the rules favour light boats."

Not really, surely? One of the most succesfull boats in the UK was the Sparkman and Stephens "Finnisterre" type "Sunstone", an extremely heavy boat. She won Yacht of the Year, I think (the top national offshore prize) under IOR, IRC AND IMS. She then came out here and won her class in the Hobart. She was so succesful that the ISAF's ORC had her re-measured at their expense, to see why rule favoured such a heavy boat.

Look also at recent Sydney-Hobart results, with boats like the Currawong Zeus II, the Joubert 41 and the Beneteau 40.7 doing very well. By today's standards it's hard to see those as light boats. Look also at the national IRC Offshore championship won by the Swan 48.

Considering that most racing sailors prefer light boats as they feel they are more fun, it seems quite possible that heavy boats are over-represented at the front of the fleet; after all very, very few of the old boats have crews and campaigns that are as good as those on the modern yachts. How many heavy boats have crews with proven racing skills (ie many national titles or similar), good deck gear and a full load of good sails?

re "Any extra weight aloft cannot be tolerated on yachts designs that chase light displacement and have such a poor stability curve."

Poor stability curve? If you take the Sydney 38 as an example of a typical modern racer/cruiser, I think you'll find that the modern boats have a very good stability curve. The current rule (IRC) does not penalise stability per se at all; it doesn't even measure it! One of the strongest of all trends under IRC is to optimise boats for MORE stability as the rule does not rate it.

Re "Heavier safe stable comfortable seaworthy boats cannot be designed to the paradigm "if racing boats don't do it its a poor option" and the comparison is foolish."

I suppose it depends what you call "safe" and "comfortable". I find heavy cruisers to be uncomfortable in their motion; it's a personal thing but often people just assume the slow lope of a cruiser is universally preferred.

I'm also not so sure about the safety aspect - for example in the '98 Sydney-Hobart the heavyweight long-keeled Swanson 42 Mintanta sank, as did the heavyweight long-keeled Winston Churchill. The Cole 43 Solo Globe Challenger rolled and lost her rig. Considering the very small number of heavyweight long keelers, they did very badly.

I interviewed two of the most experienced Sydney-Hobart skippers of all a while ago. Both started in the days of heavy long-keel planked and steel designs in the '60s. Both moved to S & S designs, Frers masthead riggers, IOR lightweight fractionals, IMS racers, IRC racers. Both said that their current IRC/IMS fractional bulb keelers are basically as seaworthy as their long keelers. One said that his safest boat ever was a beamy IOR boat with a very tall rig with in-line spreaders and runners, and his current Sydney 38 had the best offshore rig he'd ever sailed with.

I was surprised by their answers, but they have international wins, Hobart wins and about 70 Hobarts between them so I accept they know more than I do on this subject.

 

Maybe the reason cutter rigs can point higher - all things being equal, is that the foresail makes better use of the upwash from the staysail and main.

The single foresail is more effcient as a foil overall and so developes more drive than the cutter configuration.

So although the cutter may point higher, the sloop rig has better VMG

 

Sheeting Angles ?

It's interesting that you should ask.

For maximum close reaching, I had the staysail sheet blocks 1/2 way between the mast and toe rail, with the Yankee sheet blocks at the toerail.

During the Bermuda Ocean Race this year, two expert sail trimmers from the Naval Academy and British Royal Navy experimented and found the staysail sheet block should be on the same toe rail track as the Yankee sheet, and at the same angle, to make them work together. Doing this made their leech parallel.

Their explanation for the amazing close reaching and low wind performance of the cutter rig was it's ability to create a very smooth airflow from the headsails, over the main, gaining maximum "lift" from the combination. Also, the 110% Yankee and 75% staysail combination outperformed our 180% asymetrical spinnaker from 0 to 15 knots.

The results are undeniable, since we won second place in our division, only 8 minutes behind the leader after 7+ days and 750 miles of sailing.

Captain Rich

 

Unfortunately you seem to have missed my argument here.

Remember initial stability is only part of the picture but along with it you tend to get low vanishing and a high inverted stability.

Racing boats and racing skippers have relatively large experienced crews. A yacht that is "safe" with 8 experienced sailors can be a death trap for mum dad and the kids.

Look at the Fastnet investigation, read the Southampton report.
Look at the real numbers the ratios, the crews, (and the hull conditions) for the yachts that founderd only then can you make a proper engineering analysis.

Heavier comfortable boats are much easier on smaller crews. Exhaustion and seasickness are the real enemies for a small crew in heavy weather.
Easily handled sail setups like the cutter rig have good functionality on these sorts of boats. They are not so good on a racing boat, for a number of reasons. That doesn't mean they are a poor option on other vessels.

Since much of this is an off theme debate we can discuss this later in a new thread. Please join .

 

Mike, just quicly;

"Look at the Fastnet investigation"- done it.

"read the Southampton report."- I've read the available info.

"Look at the real numbers the ratios, the crews, (and the hull conditions) for the yachts that founderd only then can you make a proper engineering analysis."

Done it; as in, I was there for many days of the Hobart inquest.

"Heavier comfortable boats are much easier on smaller crews. Exhaustion and seasickness are the real enemies for a small crew in heavy weather."

As one of the most experienced Sydney-Hobart skipper of all mentioned, light boats get their faster and are therefore often LESS wearing on crews.

I'm sorry, but I find it very hard to tell someone who started sailing with a long-keeled Robb design, competed (and was on the winning team) in the '79 Fastnet, did the '70, '77, '84, '91 and '98 Hobart, did many others and won several times, has sailed S&S, Lexcen, Peterson, Frers, Robb, Farr, Cole, etc designs that he is wrong, when he tells me that the modern boats are just as good.

I don't find heavy boats comfortable because the gear is correspondingly heavier. I agree that many modern boats have very tiring motion (modern IMS boats are horrific, much worse than IOR boats because of their higher stability and different bow shapes. I find light boats with medium width sterns and seakindly hulls and medium weight concentration to be so far ahead FOR MY PERSONAL PREFERENCE IN COMFORT that it's no contest (even compared to one of S & S's greatest heavy displacement designs).

I also find (like the most experienced of all Sydney-Hobart owner/skippers, who sails his own boat back short or singlehanded across the Strait) that the modern fractional rig is incredibly easy to handle. You can go from 0-20 knots+ wind without changing sails; just wind on the backstay and adjust the traveller, mainsheet and jib leads. As one of the few offshore owners who runs his own foredeck, I'd go for a fractional every time, and every time I do an overnighter singlehanded I bless my fractional rig and its adjustability.