Analysing Upwind Performance

Hi,

I guess it is because I can only manage about 50` to the wind in my small catamaran, but I am obsessed with trying to understand why other boats point better than me.

The contributors for this performance would be:

1. Sails
2. Windage
3. Daggerboards
4. Skipper
5. Others?

How can one analyse the problem logically to identify the area(s) on which one can work on, to effect an improvement?

best regards

 

Someone else will have to tell you whether an improvement on 50 degress is possible in a small catamaran. A lot of small boats don't achieve the nominal 45 degrees from the wind in practice. However...

Your symptoms are either
1) you can't point higher because your sails no longer draw and start to luff, or
2) the sails stay full when you point higher, but the boat slows way down, or stops.

Probably the first. In this case, the most likely culprit is the sails, or the way the sails are set and trimmed. For example if the jib lead is wrong, some part of the jib luff will lose the wind too soon. If the lead is too far forward, it wil be near the foot. If the lead is too far aft, it will near the head. If the lead is too far outboard, it will be the whole luff. If the lead is too far inboard, it will backwind the main too much. It's easy to find instructions for trimming sails. The big sail lofts have pamphlets for free, and there must be web sites for Hobies and other popular catamarans. Sorry to say, if the sails are old there may be no cure short of new ones.

Case two where the sails draw but the boat stops would be due to the centerboard(s) or daggerboard(s). Foils have to have enough forward motion to work, and the higher you point, the more force they have to generate, and the faster you have to be going. Once the boat slows down, it starts going sideways. Make sure your foils are not damaged and the proper size. There may be some technique involved. To get to better performance grooves, it may be necessary to get moving fast on a close reach and then point up. Look for material on 'changing gears' on sites about sailing catamarans.

 

Thanks for your reply.

I myself tend to think that the main culprit is probably the jib. This is because I point mainly using the tufts. At 50^ the top one is lifting up frequently. Any closer and the sail starts to backwind. The sail is fairly old but seems comparable with others which do better upwind. I tend to blame it on 2 things:

1. the jib is set on furling gear and and it's luff is tightened at the top and the clew some 50mm behind the forestay. The luff tape, which is of the type with double luff rope and is about 50mm wide seems to add extra camber right up front.

2. The mast has no backstay and therefore the forestay can only be tightened by pulling on the mainsheet. However this cannot be pulled too tight since you will end up with no twist in the main and the leech telltales curling back. This also tends to add extra camber up front.

I say the above, well aware of the old saying that "a bad workman quarrels with his tools"

Regards

 

"Nominal 45 degrees". Hmmmm. Some time ago I was firmly told in this forum that modern 12 metres can point well upwind of that - 35 degrees off the true wind was mentioned. I am still waiting for someone to give me a full technical reference which DOCUMENTS scientifically that it really is possible to sail closer to the true wind than 45 degrees (anecdotes don't count).

Any takers?

Tony.

 

Tony, what do you call "anecdotal" evidence and what is "scientific"? Is a VPP, (which is just a computer programme's attempt to take information from a wind tunnel and from a tank test and then ally them according to formulae constructed by someone) more "scientific" than something written by someone who sails 12 metres?

I've only done one 12 metre regatta, but man do they point.....

Fajoe, in light conditions even high-performance cats don't seem to point at 45 degrees. We seem to need 8 knots or so to get pointing. I don't really know why; maybe in light airs, boatspeed is such a high degree of the apparent, that the apparent shifts waaaay forward?

 

The 50^ I give is the average angle I do over a leg and I measure it at home by downloading the data from my GPS onto my home computer and taking the average on each leg. I think that is a good measure because it weeds out theoretical angle improvements due to wind shift. When i spar against my friend on a J80 I know for sure he is doing better than I because I see him pointing better by about 15^ consistently.

Finally to the assertion that multihulls point worse especially at low speeds...I don't understand why it should be so and hence the reason for my original mail.

regards

 

Well, at the cat club I sail, we have a couple of former world champs who don't point much higher in light airs than we do, so it can't be the skippers.

They sail low-windage boats like A Classers, so it can't be windage - and in light airs windage isn't important anyway, is it?

They have very good daggerboards (like those on last year's world A Class champ), so it can't be bad foils....these are not Hobies we're talking about.

They have superb sails, so it can't be the sails.

The As are about the fastest thing there is upwind in light airs, so it's not that they are bad designs.

So it can't be any defects in these particular boats....so (unless I'm very much mistaken about the angles, which may be the case) it must be that cats just don't point too well in light airs. We know they are footing well, so that's why I think it may be that they have the apparent a long way forward - but I'm probably wrong.

But that's cats in general. How do you find out how your boat is going? Well, have you looked up the class tuning guide? Have you asked the top skippers how high they are pointing, using telltales as a guide? What's your twist like? Many fast cats don't need much because their sails are so flat. What sort of boat is yours?

One thing that is noticeable in our class, which comes in cat-rigged singlehanded and sloop-rigged doublehanded versions, is that the cat rig points much higher in the light airs.

 

<>>>We know they are footing well, so that's why I think it may be that they have the apparent a long way forward - but I'm probably wrong.<<<

My boat is a 24ft Micro called Strider. When I am comparing to the J80 which is more or less the same size, the 2 boats would be going at the same speed in winds of 8knots or under but he would be going tighter. Therefore the reason cannot be apparent wind.

>>>But that's cats in general. How do you find out how your boat is going? Well, have you looked up the class tuning guide? Have you asked the top skippers how high they are pointing, using telltales as a guide? What's your twist like? Many fast cats don't need much because their sails are so flat. What sort of boat is yours?<<<

I am afraid I cannot perform the comparison you mentioned above simply because there are no similar boats around here.

One statement I find hard to accept is that cats always point worse than monos. There must be logical reasons.

regards

 

Guest 249 - I mean measured in controlled conditions on the water or in a test tank, and not just "go look at any good boat and you will see", or "I did last week". I have been sailing myself in all sorts of boats for the last 50 plus years, and I have yet to see any hard evidence that any conventional sailboat can point (i.e. course made good) much higher than 45% to the true wind, if at all. If a good 12 metre can do this, then show me!

We all know about special craft with propellers on deck driving ditto in the water, and similar contraptions. That is a separate subject.

Tony.

 

Farjoe;

Sorry, I thought when you said "small", you were talking 16' or so.

The apparent wind COULD be a factor iin the boats I mentioned as they are 16-18 footers that go much faster upwind in the light than a dinghy like a Flying Dutchman (that's the 3 time world champ FD, not a random turkey).

 

Pointing cats

farjoe Analysing Upwind Performance
I guess it is because I can only manage about 50` to the wind in my small catamaran, but I am obsessed with trying to understand why other boats point better than me.

249
Fajoe, in light conditions even high-performance cats don't seem to point at 45 degrees. We seem to need 8 knots or so to get pointing. I don't really know why; maybe in light airs, boatspeed is such a high degree of the apparent, that the apparent shifts waaaay forward?


Hello forum! I've been lurking here for a while and you just picked the subject I'm most interested in, so I thought I would contribute. I'm not a professional designer, and I'm only an amateur sailor, but I've spent the last year or so studying sailboat design for fun, and weatherliness has always been my top priority. I like the idea of being able to cruise at a good clip on any point of sail.

First of all, my understanding is that while cats don't do their best as close to the wind as a monohull or a tri of similar length and displacement, the cat still gets better VMG than the mono by falling off and going MUCH faster. So it seems to me the answer to the question lies in what happens to the cat above 50 degs, or why it doesn't beat the tri. And I think what happens is the opposite of what happens on a reach: In a good stiff breeze, the mono doesn't have enough beam to hold the sail up, and the tri has its leeward float plowing through the water. With the cat on the other hand, the windward hull is just barely skimming along, maybe even threatening to fly. So you have the ideal situation, one long narrow hull taking almost all the boat's weight.

When you're close hauled, you have the opposite problem. You don't have enough power to hold the cat's windward hull up, so it plows through the water along with the leeward hull. The mono doesn't really do better than the cat, at least not much better, but it doesn't benefit from falling off because of the narrower beam. And the tri has the ideal situation: the boat is balancing mostly on the main hull, especially in lighter air or if you can get some ballast to windward.

Actually, there should be one situation where the cat does do the best when pointing: in a really strong gale where you can carry the windward hull even at 45 degs. But it might still do even better if you fall off just a little. The only other issue I can think of is that some cats might not have deep enough daggerboards or not have any at all, or if the boat is just too heavy.

 

249,

You don't have to apologise. I also have a 16fter so your points are still relevant anyway.

Skippy

You are right with this statement for winds above 10 knots. I can beat most monos around here except perhaps the all carbon ones at twice the length and 3DL sails.

The situation below 10 knots is another matter, at least upwind. At these wind speeds the reduced wavemaking advantages of narrow cat hulls seem minimal and I think friction resistance is probably more for 2 immersed hulls than one.

My all up weight is probably in the 1000kgs range including a crew of 2 and I always retract my daggers when not in use so their condition though not perfect are probably better than the monohull ones which are always immersed.

regards

 

Skippy;

I think you're right about the tri in light winds.

The boat I sail and the ones I sail against are performance cat; ie Tornado (current rig, 2 traps, big main and spinnaker, national champ); A Class (18' long, about 30' high wing mast, 75 kg fully rigged, all carbon, last year's world champ as skipper); Nacra F 18 (kite, 180 kg, former world champ); and the Taipans (16' long, 28' high wing mast, 104 kg fully rigged in two-person (sloop) mode and 96 kg in singlehanded mode, the fleet includes the national champ sometimes. All have deep foils by cat standards, the Taipan and A are very light.

So it's not weight or foils. Our jibs are old (2 new ones on order) but were are certainly not miles off the pace compared to the average cat sailor.

I'm still really a dinghy/windsurfer/yacht sailor at heart, but I know the cats point well in moderate and heavy air. I'm just shocked at the way we lose that pointing in the light and (as is obvious) I really don't know the reason, either!

By the way Skippy, with modern cats (which often have small hulls like an As) the windward hull is sometimes dropped in the water upwind in a big breeze. The extra wetted surface is more than cancelled out by the lee hull not being so submerged that it's driving through waves too deeply, and keeping the rig more vertical reduces downforce. We picked this up from last year's A Class world champ.

 

may be the foils at low speed don't generate enough lift to let you point so high as you do in heavy air (and top speed)

Mistral

 

The more combined drag from hull(s) and rig the lower the pointing angle.

Multihulls often have considerably more wetted surface than a similar sized dinghy particularly when that dinghy is heeled and the crew move forward to get the broad aft sections out of the water.

Certainly a single semi circular section has a minimum wetted surface for volume but when you have two of them it just don't work that way.

As the wind increases and the boat accelerates the multi has lower wavemaking drag so goes much faster.

MIK