Why do multis (supposedly) not point as high?

[EarthBM]

Not starting any tribal wars here, just a simple boat design question.

Is this because of leeway? So with effective foils this goes away?

Is this because of the geometry where the lateral resistance (from the leeward hull) is leeward of the center line? Why would this matter with balanced helm? (This reason would explain tris pointing better than cats)

 

[Doug Lord]

That's pretty much an urban sailors myth IF you're talking well designed high performance multi vs well designed high performance mono hull. C Class and other performance cat's point very high- at least equal to a mono. In some conditions, speed made good(vmg) upwind is enhanced by footing off a bit in a cat.

 

[weightless]

Often the answer is that they choose not to point as high (wrt the true wind) because it's faster not to. I think you may be confusing "getting upwind" with "sailing close to the true wind".

 

[glowmaster]

Glowboat, our F24 tri can point as high as most any boat, but the VMG is not as high, so it is often better to bear off a few degrees.

 

[Lost in Translation]

Hi. It is not an urban myth but a reflection of history with older boats that did not have good could for upwind work. On my A cat I can sail over a Melges 24 by out pointing but it is faster to sail roughly the same angle as the Melges and be double their speed. No problem to match upwind angles of any dinghy or keelboat that has been I the same course as me. Other modern multis may not be quite as close winded but can still preform well. Peter Johnstone wrote a nice article on heavy weather tactics that discuss this question too.

 

[Groucho Marx]

Simple answer; they're sailing faster than any mono to windward ... therefore multihull apparent wind is carried further forward.

 

[βhyde]

I think that is pretty much a myth based on old designs or big, heavy cruising cats (without boards). I can't speak for high performance cats, but on the more modern F-25/F-27/F-24's I've sailed we've never had a problem with pointing with the monos if we choose.

The other myth you'll here a lot, is that multis don't do well in light conditions. Complete B.S. Most multis have much, much higher SA/D ratios than monos of the same length and much narrower hulls.

 

[plywoodboy]

Agree with all this for modern multis, but thing that makes us look low pointing often is that if we are on same smaller cans course and go around a bottom mark close behind one (they start 10 mins ahead at my club so we can have fun), our width (and clear vision if you are driving from the happy hull) makes it difficult to roll them from windward side. If you are successful they are not happy, and in club racing it is not polite for most of us to lose friends like this. Easy way is foot off and come back up until you find another one. Their understandable perception is that they have outpointed you.

Peter H

 

[Rantifarian]

I think that is pretty much a myth based on old designs or big, heavy cruising cats (without boards). I can't speak for high performance cats, but on the more modern F-25/F-27/F-24's I've sailed we've never had a problem with pointing with the monos if we choose.

The other myth you'll here a lot, is that multis don't do well in light conditions. Complete B.S. Most multis have much, much higher SA/D ratios than monos of the same length and much narrower hulls.

There is a bit of a divergence in multi design, on the one hand there are lots of designers making lovely boats with boards that point well and keep moving in the light. Then there are companies like fountaine pajot building floating condos that reinforce the old ideas that multihulls stop in light air, tack through 120 degrees, won't sail in above 15 knots etc. Not really a myth, just an overgeneralisation from people who very rarely see a well sailed racing multi

 

[Trovão]

it was true when the multi in question was something like a hobie14.

 

[SCANAS]

Back the bus up a bit. EarthBM what type of Multi's are you talking about? Sure C-Class or racing multis point well but is that the question?

 

[DDW]

Simple answer; they're sailing faster than any mono to windward ... therefore multihull apparent wind is carried further forward.

^^ that is under appreciated by most sailors. I'm sure this will stir up some s**t:

Any sailboat's most efficient pointing angle (relative wind angle) is the sum of the aerodynamic and hydrodynamic drag angles (arctan(L/D ratios)). This by itself isn't a revelation or even controversial, it is simply a mathematical consequence of the definition of the terms. However the L/D ratios are inherent (mostly) in the design of the boat - efficiency of the rig minus the windage of hulls, efficiency of the foils, etc. - so its most efficient pointing angle is built into the design. It varies very little over normal wind strengths. As a boat picks up speed, the apparent wind pulls ahead, to maintain the more or less fixed efficient pointing angle the true wind angle gets wider. The increase in speed must be enough to overcome the extra distance sailed.

Everyone knows this so far. If you go on to plot the resulting VMG as a function of boat speed, with a fixed true wind and fixed apparent wind angle, you will notice that for a given set of numbers, there is a maximum VMG that can be achieved. Boat speeds above that will result in the distance sailed increasing faster than the boat speed, and VMG will fall. Due to the nature of cosines, a more weatherly boat suffers much less than a weatherly boat. So an A class cat, with very efficient rig and foils, can sail very fast and still do good VMG because its pointing angle is fine. On the other hand typical cruising cats, with a lot of windage in the hull and superstructure and maybe not too efficient underneath either, cannot do well to windward no matter how fast it sails because its pointing angle is modest.

Here are some examples. The first is a boat with an efficient pointing angle of 28 degrees (not bad for a cruising boat) in 10 knots true wind. Its maximum VMG is 5.6 knots at 11 knots boat speed and 18.3 knots apparent. Go faster than that, and VMG drops:

If the pointing angle is widened to 35 degrees (more typical of a cruising cat) in the same 10 knot wind the maximum possible VMG is 3.7 knots at 8 knots boat speed and 15.4 knots apparent. Go faster, and again VMG drops:

Cracking off of the most efficient pointing angle only makes things worse. Obviously in lots of wind the situation improves, because boat speed is smaller relative to wind speed and the apparent wind angle changes less. And as efficient pointing angles get into the teens (as they do in extreme racing boats) there is less effect even at lower wind speeds. But it is a problem for cruising cats. Cruising monos tend to have a little better pointing angle and aren't able to go very fast, so less of an issue. Note that a boat pointing at 28 degrees only needs to do less that 5 knots to beat the 35 degree boat's best possible VMG.

 

[eric e]

small tight tacking course handicap racing mixed dinghies on an old beachcat with big daggers

starting well behind, the cat could outpoint most of the poorly sailed monos with old sails

but could never shoot up the inside of a well sailed laser with flat sails

easy enough to round the outside of them

https://player.vimeo.com/video/46683503

 

[EarthBM]

Thanks. Wonder if the answers would be the same on a monohull forum. Was just going on general comments I've heard over years (eg from a guy with an Outremer 49) and my memories from learning to sail on a Hobie 16.

Some examples (A-cat, Laser) point higher because they don't have a foresail, I think.

 

[SCANAS]

Ok so you where asking about small racing boats rather than the average cruiser / racer multi.

 

[SeaGul]

sailing behind a "normal" mono - no moving keel - in a gust with a daggerboard multi shows the mono heeling a lot in the gust - then pointing higher- but don't go faster - but drifting downwards - the multi point higher and accelerates...

 

[eric e]

being the most produced multi

the dagger-less hobie 14 + 16 are probably more responsible for the the bad reputation multis have than anything else

by skilled hobie sailors they can be tuned and sailed reasonably high

but the mono sailor can only get them to reach fast, which is what they were designed to do

 

[eric e]

big cat cruisers like lagoons

aren't made for pointing either

which is why they have 2 engines

 

[Groucho Marx]

The bad pointing reputation began back in the earliest modern development multihull days and the Pivers with their too small float fins were probably the main culprits; the other point that started derogatory commentary was that they could reach much faster and pass monos of the times - and that didn't enamour them either. Also any overloaded and overbuilt multi was and is hopeless to windward.

But the smaller and near half Century old Piver designs like the Nugget can be transformed with the fitting of a decent basic daggerboard ... and then they'll point as high as any other boat. And reaching performance remains as before; this one has held 19 knots, not bad for a 40 year old boat.