I have often heard the fastest point of sail is 120 degrees from sailors. All of my reading has indicated that 90 degrees apparent to the boat would be the fastest. This would make sense being 120 degrees true wind would be about 90 degrees apparent, depending on forward speed.
The reason for my questioning is, I can sail fastest with apparent wind 90 degrees up to 45, but once I fall off and get the wind at anything aft of 90 the boat slows down.
I have often read about sailors "screaming downwind", but have never even come remotely close.
Fastest point of sail?
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Posted: Aug 05, 2009 - 08:52 AM
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Posted: Aug 05, 2009 - 09:02 AM
there is a trick (or 2) to doing it... (Screaming downwind) -
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Posted: Aug 05, 2009 - 09:06 AM
speaking of screaming my cat screams when i nearly top out on speed. i think that is a high tension cable exposed in my rudder that does it. it really scares new people.
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Posted: Aug 05, 2009 - 12:06 PM
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Posted: Aug 05, 2009 - 12:11 PM
Great chart Andrew. Do you know if that actual or apparent wind direction?
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Scott,
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Posted: Aug 05, 2009 - 01:08 PM
i really dont know
i have seen it in many books
i actually think it is old, based on monohull speeds and not take apparent wind into the mix at all. it only goes to 8knots.. that is a nice drift in my world... :)
and few if any mono's have the ability to really harness apparent wind... (as far as i understand).. with the exceptions of under spin and super race mono's can do 30 knots...
edited by: andrewscott, Aug 05, 2009 - 01:10 PM -
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Posted: Aug 05, 2009 - 07:38 PM
right across the wind is what most polars say
check the one in the hobie university pdf -
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Posted: Aug 05, 2009 - 07:48 PM
To go screaming downwind, the wind also must be screaming. Try sailing dead downwind in 20-25 plus and you will be the one screaming. -
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Posted: Aug 05, 2009 - 10:10 PM
I thought in my reading that cats are not know for their down wind performance, thus the use of the spin.
My preference is 90 degrees to the wind with a slight outhaul of the travel car. Enough to get the standing rigging singing.
Anyone have time and interest to get a new topic going on tell tales (including interpretation and boat adjustments) for optimal speed and performance? -
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Posted: Aug 06, 2009 - 03:48 AM
for best sail performance/boat performance you want all tell-tales streaming cleanly aft on both sides of the sails and top and bottom of the sails
mainsail on a cat - use the traveller to get both bottom sides streaming cleanly and use the main sheet to get the top tell tales flowing well (correct twist off)
the jib is a little more complicated to put into only a few words because of the range of jib block fixing options, (no adjustment at all to 4 way adjustment)
today i came downwind:o) screaming up behind 2 noobs on a h16, they couldn't work out why i was closing so quickly
as we got within hailing range i yelled out that they should let their traveller out (it was locked in center)
they did, only halfway, but they started pulling away from me
obviously my traveller was too far out so i pulled it back halfway and started closing on them again
the point being that speed depends on many things not just point of sail. even the tell-tales can be telling lies as when you have the jib pulled in too far and are also pinching all the jib tell-tales will usually flow well and the air being fed by the jib past the back of the main can make those tell tales flow even though the main is not in the best position to produce best power/speed
the best way is to try and follow people who have the same boat as you and seem to sail faster
watch what they do and try to copy, if you are not sure what they are doing, ask
edited by: erice, Aug 06, 2009 - 03:29 AM -
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Posted: Aug 06, 2009 - 02:03 PM
I understand it to be the broad reach. Where the energy wasted in lifting a hull is transfered into forward speed. It makes sense. I have hit my fastest speeds in this orientation.
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Posted: Aug 08, 2009 - 11:34 AM
Can I expect to have my tell tales trimmed to perfection every time I'm on the lake or will there be conditions that will have an effect? I struggle to get them collectively behaving the way that the books describe.
Always a student....... -
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Posted: Aug 08, 2009 - 07:54 PM
been thinking about how the theory, fastest - 90degrees, has differed from my experience, top speeds - 100-120degrees.......maybe time for some definitions
90degrees to the wind should offer the best efficiency or fastest speeds at low wind strengths for day to day sailing
most of the polars you see tend to show 10mph winds
on my 5.2, once the wind picks up enough to lift my hull, even with my 75kg/170lbs fully trapped out, the boat is reaching it's max hull speed? on a true reach of 25kph/16mph/15knots and it will do this in about 12knots of wind which is most windy days where i sail
at those speeds the windward hull is just out of the water and the wind on the rig is forcing the leeward hull as deep (draggy) as it can safely go. this deep bow sends back a bow wave big enough to hit the outer edge of the forward beam as it is tilted into the waterflow.
this acts as a big brake with almost a fire hose of water spraying up
on that point of sail - (90 degrees), on that boat - (1975 designed 17foot beachcat without spin), with only my righting moment - (75kg/180lbs), the boat seems to be hitting a wall
any more wind at 90degrees just lifts the hull higher and over into a capsize, or buries the leeward bow deeper into a pitchpole
to avoid either i have to either dump sheet so the rig dumps power, or i have to steer upwind
on the rare occasions that the winds are reliably blowing the waves into white caps, 15-20knots?, it is will also moan through the rigging and send everything humming
that's the sign that it would be suicide to try and sail a reach with only my 180lbs to hold down 19m2/220sqft of sail (that when i usually remove the jib before going out and blow the traveller in tacks to prevent being weather-vaned into irons every tack)
those are the conditions where i recorded my absolute top speed of 30kph/18mph/16knots and that was hiked out as far aft as possible on a deep reach. seems you gotta have both bows working for you on a 17foot beach cat in the white caps
that was once 3 years ago when i first bought the boat
perhaps if those winds come again and i get some foot straps aft i could trap out well aft and tighten that reach up a little to get a bit faster and still have both bows buoyancy to balance the huge tipping moment on the rig
another way to go faster for me might be to fit a spin so i could make more use of the wind while sailing deeper
edited by: erice, Aug 08, 2009 - 07:11 PM -
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Posted: Aug 09, 2009 - 07:18 PM
OK, as I read your notes, you might as well have been on my P16.
In strong winds (mid teens to low 20's) and hitting true wind at 90 degrees, my perception is that I should be getting more speed out of the boat. But, as you describe, I hit that wall. The rigging is humming but I'm not getting the forward motion proportional to the wind. The point where the harder I drive it, instead of reaching more speed, I push it closer to a wreck (usually pitchpole in my case).
Does the boat reach a point of equalibrium between the push of the wind and the drag of the leeward hull?
Thus the tell tales. My thought is if I can erad and understand them and trim the sails accordingly, I can get past that wall. It's an ongoing process.....always learning.
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Posted: Aug 09, 2009 - 09:44 PM
Deepsees is correct, it is a broad reach,135 degrees off the wind. You'll need a bridle wind vane (kept perpendicular to hulls), barber haulers to bring jib blocks outboard, main traveler all the way over, and crew almost sitting on top of you on weather hull rear to keep bow out. And I know you have enough wind on Muskegon Lake. Pete -
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Posted: Aug 09, 2009 - 10:01 PM
I think the answer is NO. It depends on weather conditions. But in moderate air you should be able to get them fairly consistent. I was out today in 25-30 mph and I didn't give a darn what they were doing, I was concentrating more on keeping the pointy side up, but had a lot of fun doing it. Also wasn't racing, just having a good time. Water was cold too, back to about 57 degrees they said.
Yes at some point there is a max hull speed and an equilibrium point. You max speed on a given day will however change with water conditions (waves etc) and crew weight.
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Posted: Aug 10, 2009 - 08:38 PM
I agree completely with deepsees and pbegle. The fastest speed I ever achieved, was on a H14 last summer. I was about 30-40 degrees off dead down. No jib, just the main sail and going like hell. I haven't been able to duplicate it since.
One very interesting thing I would like to point out. When I was doing this, both of my rudders kicked out. This even made me go faster. The hobie sat very high in the water due to the planing. There was very little weather helm on the rudders due to the fact that I was heading mostly down wind.
This got me thinking (yes, there was smoke)
I know that there must have been a lot of testing and research that went into designing various beachcats, but from the day I first seen a beachcat til now, the rudders on these things seems all WRONG to me. IMO
In my opinion, rudders should be swept back NOT plunging nearly straight down for 18"....two of them. Talk about putting the brakes on!!!! Why can't they be swept back?....Weather helm? better leverage design can fix that. I realize there will be a lot of pressure on them.(I can see them bend on my H14 when they are swept back) carbon fiber should give them the strength needed. I'm just very puzzled over this. The only difference between water and air is water is far denser....soooo this would make it even more important that everything reaching into the water needs to be swept back. The faster a jet is the more the wings are swept back.
Maybe I should have made this a new topic.
Jim
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Posted: Aug 11, 2009 - 03:11 PM
you can not have rudders swept back..
if you look at EVERY rudder system (ever) they all have the same design... a vertical trailing edge
you couldn' turn them by hand if you did... they would cause unmanagable helm, you would cause unmanagable drag and the center of effort would change depending on the depth of the rudder (which changes when a hull goes up)
and you would break them off...
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Posted: Aug 11, 2009 - 04:14 PM
Jim,
The best way to ensure that you have huge amounts of weather helm is to sweep the rudders back slightly.
The center of force will move further away from the pivot point and the force of the water against the rudder will be ampilified. You want the center of effort to be slightly behind the pivot axis so that the boat slowly turns into the wind when the skipper releases the tiller.
If you get the ceneter of effort too far forward, you end up with lee helm and the boat disappears if you ever fall off. The biggest problem with this is that it usually takes our beer with it.
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Posted: Aug 12, 2009 - 12:17 AM
I went digging to find out more about the points of sail. The link below to the National Geographic site allows you to control the rudder and sails in a simulator to achieve maximal speed under various wind conditions.
Experiment.....are you reaching max speed with a beam or broad reach with the simulator?
http://www.nationalgeogra…tives/sailing/index.html
