Why does a cutter rig point higher & sail faster?

"and insufficient luff tension, will have terrible trouble pointing high."

Not so, the sailmaker can cut a sail that points almost as high IF he knows there is no backstay adjustment.

A properly built sail for a boat that uses less luff tension is only a sail cut modification.

I.m still waiting (40 years now ) to find a sail that works as well half rolled up as a correct sized & built hanked on sail.

0.5K to 55k and functional is a lot from one Universal window shade!.

FAST FRED

 

I will likewise claim my inexperience ahead of time. I have 200,000 sea miles in as small as 30 and large over 100. I am an avid racing addict and started racing in order to extend my cruising range on the weekends. I now race more than I cruise. I have made my living at sea and now work ashore. I am still a novice without a doubt but have seen and experienced most rigs.

Personally I will never own anything else but a fractional rig "fast" boat again. I have been able to get out of a storm more quickly and have been able to avoid two hurricanes by flat out outrunning the storm. I have roler furling on my boat for cruising and when the weather gets badd offshore a roll the jib. Depower the main and never leave the cockpit. In fact with my new remote for the autopilot I don't even have to leave the dodger area if the weather is foul.

You are very correct luff tension can be accounted for however headstay sag which was spoken of as being a problem without a backstay can not be recut. Too much sag will affect pointing. Many boats I have seen that struggled with pointing usually had a 1-2 foot sag in the head stay. These boats are just not able to get the boat moving close to the wind due to the entry, forgive my lack of technical explanation but it is a very common problem I have seen many times. In fact in my own boat we were pointing 10 degrees lower than another boat we have always outpointed. The runner was brought on along with a bit of halyard and bang we started climbing up. 6 inches of head stay sag makes a huge difference.

My observation during this thread is that it is likely that if a real pointing difference was found on the new cutter type set up, it is most probably due to the smaller headsails not inducing as much sag and maybe the luff could have been a bit tighter on the genoa resulting in a little fuller entry making it easier to drive higher.

 

Window shade?

Hi Fred

Very interesting point. Maybe thats the main vertue of a twin headsail rig. You can reduce the headsail area by either 55 or 45% by just dropping one of the sails. This can easily be acomplished without even leaving the cockpit. All that is needed is a downhaul. The 3/4 fractional sloop that I now use has one (it cost about $5). By relieving the halyard and pulling on a string, the jib comes down. Always. It may get a little wet as a fold or two may end up in the drink, but the sail area is efectively reduced 35% within a minute or two with no help from the crew.

Now back to your point. I propose a race.

Take two identical masthead sloops.
Rig one with a 120 jib (for a trully fair comparison)
and a roller furling set up. (and I mean a good one that doesn't jamb)
Rig the other one with twin jibs with a down haul only on the outer jib.
Now make them race upwind on a day when the wind strength is constantly varying from force 4 to 6 and back again.

To keep this as fair as possible, numerous such races would be needed. I would say at least seven. And the results would have to be averaged.

Now handicap in accordance with the cost of their rigs. In so doing, assume that each boat was designed originally for the rig it is wearing. (the cost of retrofitting is not counted, but the cost of extra headstays, making two sails, as well as the cost of the down haul and the roller furling gear is counted)

The winner is. The boat that delivers the most bang for the buck (or euro).

For instance. If one boat beats the other by 10%, but its rig costs, say, 13% more, it can still be considered the loser.

I would predict a close race. And I wouldn't dare predict a winner.

How about it?

Bob

 

Rich,

Getting back to your original question, I think the answer is a combination of new and improved sails, retuning, and added sail area, but also the nature of that sail area.

First, of course we know what new and improved sails can do to a boat, especially these days -- your sails are not just new, but more modern. Sailmaking may have advanced more than anything else WRT to sailboats in the last 20 years.

We still don't know how your boat was tuned before. You said the Navy guys twiddled with the jib and staysail leads, moving them out to the rail. But where was your genoa lead to begin with? How straight was the headstay? Being sorted by really good sailors is always a great help.

Next, was your old genoa really an upwind sail, or compromised for reaching and roller reefing -- and therefore unable to take advantage of a tight sheeting angle anyway? I've been on plenty of boats where you could do anything you wanted with the jib lead, but the sail itself wouldn't let the boat point any higher. In that case, if there's room for a staysail to draw cleanly without interfering, it can only help.

Now the added area. IIRC the O'Day was not overcanvassed to begin with. Plus it had a relatively low-aspect rig. You've added sail area, which improves the SA/D ratio. But you've also added luff length, which I guess you could say increases the effective aspect ratio. Plus a jib has a better lift/drag ratio upwind, with no mast interfering with airflow. So besides adding sail area, you've also improved the overall lift/drag ratio.

Your cutter rig looks like it might be a hot tip for this boat. A friend of mine had one back in the 70s, and raced it extensively (PHRF). He had a full compliment of sails, including a blooper. I'll mention this discussion to him the next time we get together, and see what he says.

 

Efficiency in a rig is about more than speed per dollar, just as it is also about more than speed per square foot of sail area.

 

I would change that to read "IF he knows how much the headstay will sag." The problem is that the amount of sag in a (relatively) slack headstay varies a lot, so a sail that looks good in a moderate breeze is a bag when the wind is strong and a flat sail is preferred. The reason racers do better with a tight headstay is that the sag is more nearly the same so the sail sets better, on average.

 

Cutter Rigs, Summary Replies

Interesting observation experienced by many sailors in actual practice, particularly when the staysail was not located so close to the headsail as to effectively cut off the slot.

Only partially true statement…..you haven’t accounted for the efficiency of this flow diversion. The cutter rig may perform this driving function with less overturning moment and less leeway inducement….and maybe even requiring less overall sail area.

The extra staysail area will result in more lift. The bi-plane does have more lift, but not necessarily as a result of airfoil shape, it just produces more lift in a lower aspect ratio form (not as long a wing required)

“Cutters rigged with a single headsail” have created an inefficient slot…..the throat of the slot is SO large at its opening and so comparatively small at its exit. I feel this is also a significant inefficiency with the std sloop rigged vessel at the lower panels of the rig. If we are assuming just horizontal air flow over the rig we see a very large receptive slot at deck levels and in these lower panel regions (ie; large distance between forestay and mast), but then necking down into a very restrictive slot between the leech of the headsail and the mast/mainsail….more on this later.

And I agree Mike, many innovations have been ‘rated’ out of existence

Not true. Exactly the same old explanation that just won’t die. The air flow in the slot is slowed. (the slot effect)

Lets distinguish between our discussion of the pointing capabilities and the performance capabilities. The cutter rig, like the bi-plane, does possess more aerodynamic drag than the higher aspect ratio foils.

I’d say a lot of this depends on the proper separation of the headsail and staysail, and the sheeting angles and base available.

I would tend to agree with you there.

In a very brief statement, I think you captured the essence of it!

I’ve always felt this parallel leach situation was a very desirable configuration….a uniformity to the slot, vertically speaking. I seek this uniformity of both the ‘slot’ exit and entrance with my ‘aft-mast cutter/ketch’. And elsewhere on this forum, aftmast

The sheeting points on a cutter rig with its staysail reasonably spaced away from the headsail would very likely not end up “on the same toerail”. This would of course depend upon the cut of the two headsails. Certainly it should appear a lot easier for the sailmaker to cut the two ‘parallel’ headsails to work in harmony than the ‘triangular slot’ of the headsail/mainsail of the Bermuda rig.

And finally in the broad reaching situation, the wide sheeting base available to the multihull craft permits a larger overlapping headsail to be sheeted properly, rather than pinched in, closing up the shot and backwinding the mainsail.

This ‘combination’ of the sails is the key word. I think your combination (I fly a 110% high clewed Yankee and 75% Staysail) is the correct one for a cutter rig that utilizes a conventional mainsail. On my unconventional main-less rig I include more overlap of the two headsails as my staysail becomes my mainsail.

Interesting observations from a long time sailor.

We should always be open-minded enough to factor in first-hand practical experiences in conjunction with the scientific theory.

That’s a pretty broad statement that “cutters are not as effective upwind”. Guess we would have to get into defining “effective”. Effective for the racer could be slightly different than effective for the cruiser. In this forum we’ve seen a few experienced sailors come forward with very definite experiences of pointing higher with a cutter rig. And the bonus is they did this with a lower aspect rig (or it could have been), with smaller size sails, and more versatility in the deployment of sail area. I would call this effective.

Granted there might be a higher drag associated with the cutter rig (maybe not as fast upwind), but the greater stability, and or decreased draft, etc could all be advantages for the cruising sailor.

I don’t believe this was the inference when the bi-plane subject was brought up…..rather more lift at a lower aspect ratio.

I don’t think this is “chat based on a single experience”, but rather a look back thru a lot of history of sailing will bring up a VERY considerable number of such references. Besides, those other positive attributes you bring up aren’t insignificant in there ‘effectiveness’.

Boy, here’s two conflicting views. The narrow sheeting base of the monohull, and too-close forestays could account for Dreamer’s observation…..(not sure that he was on a similar Island Packet cutter).

I would interpret Too-Sweet’s observation thusly; I believe he is of a performance vein, and thus would be dissatisfied with the ability to sheet the genoa in closer than the outer shrouds to effect pointing capability. What he experienced by inserting the staysail was creating a more uniform upwash to the genoa that allowed higher pointing by the genoa (the slot effect). If he refrained from overtightening up on the genoa, hopefully he left the slot open enough to not degrade the flow over the trailing staysail and mainsail.

Not necessarily is the sheeting angle still horrible. There is a fine line between enough slot, and not enough slot. Anyone with a rotating mast (particularly on a small cat) has experienced this phenomenon…..rotate the mast too much (in a desire to flatten the main) and you severely ‘choke off’ the slot between the jib and the main….performance drops immediately.

Simultaneously keep in mind that the trailing sail is providing the beneficial upwash to the headsail that promotes the headsail being able to point higher and drive harder (and this is true whether the trailing sail is a staysail or a mainsail). The shape of the headsail, both airfoil and entry angle are critical in meeting this extra capability to point higher. And these two features need to be accounted for under some different operating conditions between the top of, and the bottom of the sail plan. I am continuously amazed at the art of sailmaking that allows these guys to shape the headsail (fractional or masthead) and the mainsail of a sloop, to work together, considering the wind gradient and the widely divergent slot that exist in the triangular Bermuda sail plan. No doubt the shape of the genoa for a single headsailed boat should be shaped differently than one for a twin headsailed vessel. And with these different shapes there likely would exist different sheeting arrangements.

An interesting aside topic as I continue to research my twin-headsailed, mast-aft rig proposal, is that I feel a need to provide a less than optimum leading edge foil (furler foil) to the two headsails in order to defeat their extreme sensitivity to entry angle wind variations caused by the inconsistent wind and/or the inconsistent helmsman.

Good analysis

 

Re Brian's note re cutters pointing higher; "Interesting observation experienced by many sailors in actual practice, particularly when the staysail was not located so close to the headsail as to effectively cut off the slot."

Ummm, dunno about the number of sailors who have found a cutter rig pointing high in actual practice in a reasonable test. For example, the Whitbread Round the World winning maxi ketch Stienlager used a cutter rig BUT ONLY WHEN CLOSE REACHING. Today, researching another topic, I found an article by America's Cup winner and Olympic medallist John Bertrand, about the Peterson Admiral's Cup racer Superstar of 1977. John referred to the cutter rig as being a CLOSE REACHING RIG. It certainly was, in that style of boat; we used to use them in masthead one and two tonners in the late '70s and early '80s.

So we were NOT biased against cutter rigs. But they were NOT better upwind. They were used only for REACHING. At one time, in the very early '70s, Australian boats sometimes used cutter rig upwind, but as soon as sails improved the sloop dominated upwind.

It's fairly simple. Staysails were not rated at all under IOR. It was totally free area. So if cutter rigs were higher upwind, people would have used them. They weren't, so people didn't.

Either all of the world's best sailors were wrong, or this one case (with no controls re two-boating against another O'day, the state of tune etc) is wrong.....I know which one I'd choose, it's fairly logical.

Re "I don’t think this is “chat based on a single experience”, but rather a look back thru a lot of history of sailing will bring up a VERY considerable number of such references."

Yes, and almost alll of those references have fallen by the wayside now that modern sails and rigs have arrived. Cutter or double-head rigs were used at some times by many of the world's best ocean racers. Those sailors now use sloop rigs. Are they stupid? No.

Re "And I agree Mike, many innovations have been ‘rated’ out of existence".

Dunno....how many innovations are rated out of existence under IRC? How many are rated out of existence in the Open 60s, Mini Transats, ORMA multis. etc????

If you look at many of the innovations that were rated out under IOR, you'll see that many of them actually only produced a marginal improvement in pace, if any at all. Look at Cascade, for example. For a 37'er, it was dog slow.....it just rated like a 30. That cat ketch wasn't "rated out of existence", it was just rated properly, and Cascade and Denali and L'effraie kept on winning. Terrorist's and Hawkeye's bilgeboards were only marginally faster, if at all.

rE "Anyone with a rotating mast (particularly on a small cat) has experienced this phenomenon…..rotate the mast too much (in a desire to flatten the main) and you severely ‘choke off’ the slot between the jib and the main….performance drops immediately".

Not so; some world-class guys in some high performance small cats classes over-rotate their mast dramatically to depower; others in the same class de-rotate to depower. They often end up side-by-side around the course. We're talking guys who are top 10 in the world's most popular cat classes, here. They are NOT stuffing up.

I remain puzzled by "I would interpret Too-Sweet’s observation thusly; I believe he is of a performance vein, and thus would be dissatisfied with the ability to sheet the genoa in closer than the outer shrouds to effect pointing capability."

How could anyone expect to sheet a genoa inside the outer shrouds, unless in an extremely unusual boat?

 

Cost for performance dosen't matter?

I couldn't agree more. If we went only by speed for dollar, I could propose a bed sheet and a broom stick for a forty footer. If it moved the boat at all, I could claim it won.

Like wise, I could put an articulating wing (ala Little Americas Cup) on the same forty footer and, with the greater performance, claim it won.(never mind the fact that it probably cost many times more than the boat and couldn't be reefed)

The forgoing are obviously ridiculous examples. But they really illustrate how silly things can get if one takes worthwhile concept too far.

In the case of the race I proposed, I do not think the results would be lopsided enough to lead to any such outrageous out come. I imagine that the two rigs would be quite comparable in price.

One would need the expensive roller gear (I have no idea how much it costs, but my guess would be a certain amount for each square foot or something like that) and two powerful winches.

The other would need: two head stays, two back set shrouds (or running back stays) to keep the inner stay tight, two jibs, and probably four winches. I don't know if four small winches cost more, the same, or less than two large ones, but I do know the extra shrouds and the exra stay as well as the chainplates for each will definately cost more.

I have a feeling that the two rigs would be within 10% of each other in cost. Maybe 15% at the most. The performance of each in varying wind strengths should pretty much cancel each other out.

In light to moderate winds, I would expect the roller reefing sloop to do better. After all, it has the one large jib. In stronger winds, I would expect the two jib rig to do better. It could drop one of its jibs and, presumably, the other would still be setting good. (as well as giving the main some slot effect help.)

The single jib, on the other hand, would by then be rolled to a small fraction of its original size and have lost most of its three dimensional shape. Its main purpose by then would be to act as windage to keep the bow from rounding up. With The weekender type that I had, I sometimes used the spool furling jib for pretty much the same purpose. I used it mainly to backwind the bow over when changing tacks. My light beamy cenerboarder just didn't have enough momentum to come about reliably in strong winds and a chop.

That being said, wouldn't it be nice to know if one rig had a definate cost or performance advantage over the other. What if one were slightly better than the other, but significantly more costly ?

I, for one, have never known a boat owner that didn't have to watch his wallet. If most boat owning households are anything like mine, the boat is the first thing thought about and the last thing con$idered .

Bob

 

A point of interest here in ratings, IOR did allow staysails and the mighty blooper as free area. Even today the blooper is free area in many rating systems but is not seen on the course as its benefits are not great enough to justify the hassle. Staysails are allowed also free but we have very few people who use them as we have found that the speed increase is only in a very narrow wind range and direction. Specifically beam reaching and forward of the beam reaching.

My boat is close winded (24 degrees apparent) the sheeting angle is 7 degrees. It will not point higher or go faster upwind as a cutter. It is highly refined and while it is a quite old design it still points with the modern boats showing up. It would not point higher or go faster with a cutter rig, but add a staysail when we crack off to 40 degrees apparent moving the leads outboard and the boat jumps up .5 knots in speed. No doubt the cutter rig is extremely effective on a reach and has some handling advantages especially with roller furling for weather.

I do think 249 is correct it is not as effective upwind, race or cruiser doesn't matter, it is not as fast upwind. Other benefits may make it preferrable for an individual but that does not make it more effective on a point of sail.

 

I wonder if there might not be a lot of complex issues here, size of the boat, hull design, course sailed, wind strength, crew numbers, size of the sails. There are so many factors that need considering.

Consider a large cruiser short tacking to windward up a channel with a small crew ( look at the prior post by the chap Kennedy ), the cutter ( with self tacking staysl ) on a meagerly crewed heavy sailboat will outperform a single headsail and will work her way efficiently to windward (providing her Cp is not too high).
So will a 3/4 rigged racing sloop flying the appropriate sail. The racing sloop will go faster but that doesn't mean that the twin headsail is not the better rig on the cruiser.

As for IOR we saw some very odd designs under IOR, all rule cheaters but poor performers under other rating systems.
For example so many of those hulls go faster if the rule cheating scallops are smoothed out at the stern. Just a case of something that actually creates drag being worth doing because the penalty is slightly less than the rating gain. Nor was IOR (as Marchaj spent so much time pointing out) a rule that encouraged seaworthy designs.

 

For interest

Here is Wallaces "Sail Power" paragraph on 2 headed rigs.

 

Having sailed pretty much all major IOR designs from 1/4 tonners to 50's I would tend to take exception to the seaworthy comments. I have been in some of the worst sea conditions and storms on these so-called unseaworthy designs and came home everytime. What I found was the biggest issue was the loads. Because of the deep hullforms the boats did not plane and did not surf easily so when the wind increased the loads increased as the square of the wind and the loads between 20 and 30 knots were phenomenal. My current boat surfs easily and the loads are 1/4 or the loads on the old IOR boats.

When you put the boats under great load with a huge amount of sail up you find yourself in a less than stable situation. I suspect that if you put the same type of sail area up on a cruiser in 30 knots winds you would find the same type of loads and stability issues. Pushing a boat beyond its hull speed results in some abnormal behaviour.

It would seem that Wallace agrees with my assessment. The outboard sheeting angle of a cutter is the limiting factor in pointing. If you put the lead farther outboard to accomodate a staysail you harm the pointing angle.

 

Yep, Mike, it does seem to be very complex if you take it out of the straight context of pointing in a race.

Re "Nor was IOR (as Marchaj spent so much time pointing out) a rule that encouraged seaworthy designs."

As mentioned in another thread, I interviewed two of the world's most experienced owner/skippers of offshore racing boats. Both have been at the very front of the Australian fleet (winning Hobarts, nationals, representing in the Admiral's Cup and Kenwood etc) almost since the days when they had their first RORC heavyweight long keelers in the '60s; one a steel Halvorsen Freya type, the other a carvel planked Arthur Robb Lion. At least one (and I think both) did the '79 Fastnet, both (IIRC) did almost all of the bad Hobarts for the past 30 years.

Both went through heavy S&S designs of the late '60s/early '70s; into the Peterson/Frers masthead IOR days; to lightweight exotic hull fractionals by Farr and Dubois; into the IMS period with Farr and MBD designs. Both say that there was no great loss of seaworthiness and (in some ways) seakindliness through this period.

Many of the veteran boats that turn up for just about every Hobart are old IOR battlewagons, they got through the '98 and other races with no problems. When I hear names like Syd Fisher and Lou Abrahams tell me that their IOR boats were just aboout as seaworthy as their old RORC racers and their IMS boats, I have to say I give that more credence than I give Marchaj and his calculator and test tank.

Perhaps the best summation came from Lou. He said that his 42' masthead S&S boat was turned from a nice boat into a bit of a pig in some situations, when she was modified. Later, his Dubois one tonner was turned into a really good boat with modifications. I think the same thing happened to his Sydney/BH 41. As he says, it's not the TYPE of boat; it's how good an example the boat is of its type, and (perhaps even more importantly) fairly minor alterations (boom length, rudder configuration, ballasting) can make enormous differences one way or the other.

Re bumps. Yep, they seem silly and I'm glad my RORC boat doesn't have them. But any rule brings in various problems. Many RORC boats had very pinched sterns, and some (Rainbow II IIRC) had steel decks nailed over wood to reduce the rating (and stability). CCA boats got bad press at times. IMS boats can be a joke. International Rule metre boats were heavy, skinny half-tide rocks in my estimations.

And if you take away the rules, you end up with something like the unrestricted 18s of the 1980s; incredibly complex, incredibly expensive, hugely over-rigged, scary to sail. The same applies in many ways to the loosely-restricted 12' skiffs, and some of them apply to sportsboats. Moths have become very hard to sail, compared to the earlier Moths. Nigel Irens says the same things that happened to the 18s apply to the loosely-restricted 60' tris.

So IOR had its faults, but were they much worse than any other rule suffers under such pressure? Dunno.....

 

IOR fan
& 249

I suppose I should say that Marchaj spent so much time pointing out that the rules didn't necessarily reward seaworthy designs and at times rewarded some quite unseaworthy boats.
I agree it doesn't mean that they were all so.
But we are getting off the theme again.