What is the correct trim of the mainsail when flying a spinnaker with the wind dead astern? Some of my crew feel that the boom should all the way out to the spreaders, just as if you were flying a genoa and running wing and wing. Others believe the boom should be kept closer to the centerline of the boat so that it doesn't blanket the spinnaker. Who is right? What if the angle of the wind changes?
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Why on earth would you want to run with the wind dead astern? This is almost always the slowest point of sail. Reaching off about 15 degrees will be a much better line. But to answer your question, running is a simple matter of sail area. Expose as much sail area to the wind as possible. Run the main way out with a slight ease on the halyard and tension on the vang. An ease on the spinnaker halyard of about 3' and the pole square to the aparent wind.
Main position with Spinnaker
A simple rule of thumb is that the boom and spinnaker pole should form a continuous line. In other words, visualize the spin pole as an extension of the boom, right through the mast; and yes, for sailing dead downwind the boom should be as far forward as possible. As for why anyone would want to sail DDW, maybe that's where the mark is!
A simple rule of thumb is that the boom and spinnaker pole should form a continuous line. In other words, visualize the spin pole as an extension of the boom, right through the mast; and yes, for sailing dead downwind the boom should be as far forward as possible. As for why anyone would want to sail DDW, maybe that's where the mark is!
oh no.... not dead downwind
As Alan states, dead-down wind with a spinnaker (or any other combination) is the slowest thing you can do to a boat (other than heaving-to). Whats going to happen is all the aerodynamics involved with the sails will be essentially ZERO. What propels a boat in this 'mode' is all drag forces and little aerodynamic lifting force ..... therefore the largest cross section you can expose to the wind is best: mainsail against the spreaders, etc. This is a VERY inefficient mode of sailing - s.....l.....o.....w. Broad reaching and tacking/gybing downwind (usually at 45 degrees off the (true) wind for most boats) is the fastest because (an important because) the ***apparent wind*** over the sail will be at a maximum (versus VMG). The faster speed will be **CREATING** faster apparent wind !!!!! With higher apparent wind on a broad reach the 'aerodynamic mode' of sailing is possible/probable. True, that the total distance sailed is vastly greater but the increase of speed and sail aero efficiency is so much greater. Only when the boat can reach 'hull speed' is going dead down wind useful. The 'great' Buddy Melges was one of the first to 'tack down wind' when on the super fast sailing inland lake scows and also ice-boats ... and it 'revolutionized' those classes of boats. It also got him a medal in the Olympics on the Soling class. .... and ALL top racers the world-over have been 'tacking downwind' ever since. It used to be before the 70s that most boats when dead down wind would use: Main, spinnaker, spinnaker staysail, genoa staysail, blooper, etc. all flying at the same time (and from a SINGLE mast). After Buddy Melges, all those complicated downwind sails went to the wastebasket. Unless the boat is at 'hull speed' going dead down in a severe 'blow', the FASTEST course will be to broad reach ... using the higher apparent wind *over* leeside of the sails. If you have a GPS onboard the answer is simple and profound: Track or activate the VMG function to a waypoint that is dead downwind and sail by varying from dead-downwind to a (tacking/gybing) broad reach (setting sails perfectly, of course) ... and watch the VMG value. Run a few trials between two fixed marks .... a stopwatch will prove the point !!!!!! If your boat is regularly raced you can get the polar diagrams of speed vs. wind velocity vs. sailing angle from USSailing (for a fee) .... and you will probably find your boat is fastest (to the next dead downwind mark) at near 45 degress off the true wind when going downwind. hope this helps
As Alan states, dead-down wind with a spinnaker (or any other combination) is the slowest thing you can do to a boat (other than heaving-to). Whats going to happen is all the aerodynamics involved with the sails will be essentially ZERO. What propels a boat in this 'mode' is all drag forces and little aerodynamic lifting force ..... therefore the largest cross section you can expose to the wind is best: mainsail against the spreaders, etc. This is a VERY inefficient mode of sailing - s.....l.....o.....w. Broad reaching and tacking/gybing downwind (usually at 45 degrees off the (true) wind for most boats) is the fastest because (an important because) the ***apparent wind*** over the sail will be at a maximum (versus VMG). The faster speed will be **CREATING** faster apparent wind !!!!! With higher apparent wind on a broad reach the 'aerodynamic mode' of sailing is possible/probable. True, that the total distance sailed is vastly greater but the increase of speed and sail aero efficiency is so much greater. Only when the boat can reach 'hull speed' is going dead down wind useful. The 'great' Buddy Melges was one of the first to 'tack down wind' when on the super fast sailing inland lake scows and also ice-boats ... and it 'revolutionized' those classes of boats. It also got him a medal in the Olympics on the Soling class. .... and ALL top racers the world-over have been 'tacking downwind' ever since. It used to be before the 70s that most boats when dead down wind would use: Main, spinnaker, spinnaker staysail, genoa staysail, blooper, etc. all flying at the same time (and from a SINGLE mast). After Buddy Melges, all those complicated downwind sails went to the wastebasket. Unless the boat is at 'hull speed' going dead down in a severe 'blow', the FASTEST course will be to broad reach ... using the higher apparent wind *over* leeside of the sails. If you have a GPS onboard the answer is simple and profound: Track or activate the VMG function to a waypoint that is dead downwind and sail by varying from dead-downwind to a (tacking/gybing) broad reach (setting sails perfectly, of course) ... and watch the VMG value. Run a few trials between two fixed marks .... a stopwatch will prove the point !!!!!! If your boat is regularly raced you can get the polar diagrams of speed vs. wind velocity vs. sailing angle from USSailing (for a fee) .... and you will probably find your boat is fastest (to the next dead downwind mark) at near 45 degress off the true wind when going downwind. hope this helps
Agree with Alan
I have a feeling that 15 degrees off DDW in moderate conditions is often times at least in the ballpark, depending upon the boat and windspeed, but 45 sounds higher than any I can imagine, besides the possibility of maybe a catamaran or scow or other easily planing boat which could reach extraordinary speeds to make up for the additional distance. I seriously doubt if any displacement keelboats reach max VMG in that range. In looking at a San Juan 28 polar, in its case, to reach max VMG, it never needs to head up higher than 11-12 degrees off DDW under any conditions- even light. I suppose it depends on each boat and its specific polar chart, but as a rule of thumb for keelboats, 45 degrees off DDW sounds somewhat out of line.
I have a feeling that 15 degrees off DDW in moderate conditions is often times at least in the ballpark, depending upon the boat and windspeed, but 45 sounds higher than any I can imagine, besides the possibility of maybe a catamaran or scow or other easily planing boat which could reach extraordinary speeds to make up for the additional distance. I seriously doubt if any displacement keelboats reach max VMG in that range. In looking at a San Juan 28 polar, in its case, to reach max VMG, it never needs to head up higher than 11-12 degrees off DDW under any conditions- even light. I suppose it depends on each boat and its specific polar chart, but as a rule of thumb for keelboats, 45 degrees off DDW sounds somewhat out of line.
Sometimes DDW is fastest....
Any time a displacement vessel gets close to hull speed (e.g. with a spinnaker or other efficient downwind sail combination) while DDW is the shortest route to target, there is obviously little or nothing to be gained by trying to "heat it up" in any other direction(as VMG will tell). In fact, under these conditions one's best chance of breaking through the hull speed limitation is to try and surf as long as possible on passing waves. In general, surfing conditions will require your vessel to be more or less squared off on the waves (in order to avoid being broached). In short, you may find yourself mostly sailing DDW under these exhilarating conditions...... Have fun Flying Dutchman
Any time a displacement vessel gets close to hull speed (e.g. with a spinnaker or other efficient downwind sail combination) while DDW is the shortest route to target, there is obviously little or nothing to be gained by trying to "heat it up" in any other direction(as VMG will tell). In fact, under these conditions one's best chance of breaking through the hull speed limitation is to try and surf as long as possible on passing waves. In general, surfing conditions will require your vessel to be more or less squared off on the waves (in order to avoid being broached). In short, you may find yourself mostly sailing DDW under these exhilarating conditions...... Have fun Flying Dutchman
I'm with Alan and Rich
Dead downwind is perilous without a preventer, and off the wind is faster. That said, here's a proven bowsprit to throw the spin away from the main, enabling a tighter angle of sail without blanketing. Note: 2 pages of pix here...
Dead downwind is perilous without a preventer, and off the wind is faster. That said, here's a proven bowsprit to throw the spin away from the main, enabling a tighter angle of sail without blanketing. Note: 2 pages of pix here...
re
DW
The original question Kevin asked was the preferred position of the boom WHEN running DDW. Most of the responses since then have been telling the author how wrong he was to even be thinking about DDW. In fact , there are a great deal of variables involved when choosing off wind courses, as the post from Flying Dutchman said. Type of boat, wind speed, sea state, etc. all play a part in determining optimum VMG. But then again, that's not what he asked.
DWThe original question Kevin asked was the preferred position of the boom WHEN running DDW. Most of the responses since then have been telling the author how wrong he was to even be thinking about DDW. In fact , there are a great deal of variables involved when choosing off wind courses, as the post from Flying Dutchman said. Type of boat, wind speed, sea state, etc. all play a part in determining optimum VMG. But then again, that's not what he asked.
Variables
Assuming a displacement hull configuration, the downwind course to a mark should vary according to relative boat weight, wind speed, and % of hull speed that is achieved. That is, a heavier boat should sail lower than a lighter one of the same length; a given boat should sail lower in stronger winds than in lighter ones; and a boat that is at or near hull speed should sail lower than if it were not going so fast. Clearly, DDW is not the slowest (in fact it is the fastest) point of sail to the mark if the boat is at hull speed.
Assuming a displacement hull configuration, the downwind course to a mark should vary according to relative boat weight, wind speed, and % of hull speed that is achieved. That is, a heavier boat should sail lower than a lighter one of the same length; a given boat should sail lower in stronger winds than in lighter ones; and a boat that is at or near hull speed should sail lower than if it were not going so fast. Clearly, DDW is not the slowest (in fact it is the fastest) point of sail to the mark if the boat is at hull speed.
Kevin: When sailing DDW with a spinnaker the boom should not be centered. Here's why - your goal is to keep the wind flowing across the spinnaker in only one direction. with the boom centered that can't happen. If your going to sail DDW, for some reason such as it is blowing like stink, the main would have to be at the spreaders but as others have stated DDW is not the way to go. Without getting to technical, you want to sail on a broad reach and then turn smoothly to another broad reach as you move toward your destination. A lot of guys I know think it is correct to keep the spinnaker in front of the boat and to steer under it. I'm far from a spinnaker expert because most of the folks I deal with have trouble with the jib!! Sitting here visualizing what happens with a spinnaker while sailing DDW with the main all the way to the spreaders, I think there would be a tendency for the wind that gets behind the main to cause the spinnaker to wrap. I also thing the boat would have a tendency to roll a lot. I could be all wet about those observations and best shut up while I might be ahead.
jimg
I think that I covered that question in my first responce. Aside from pointing out the fact that running DDW is not usually the best course I also responded to Kevin's question as to placement of the boom....."to answer your question, running is a simple matter of sail area. Expose as much sail area to the wind as possible." These discussions are just the kind of thing that are needed to help demistafy sailing. New sailors can reap the benefit of the knowledge of more experienced sailors. No one should be taking offence at opinions expressed. This truly is an information forum.
I think that I covered that question in my first responce. Aside from pointing out the fact that running DDW is not usually the best course I also responded to Kevin's question as to placement of the boom....."to answer your question, running is a simple matter of sail area. Expose as much sail area to the wind as possible." These discussions are just the kind of thing that are needed to help demistafy sailing. New sailors can reap the benefit of the knowledge of more experienced sailors. No one should be taking offence at opinions expressed. This truly is an information forum.
good advice
Thanks for the feedback and advice. As to why I would go dead downwind, I often sail in narrow channels between islands, etc. without much room. I am usually short handed, so tend to avoid gybing the spinnaker if possible. I was in a race last summer with light air and it was essentially one long downwind leg (25 miles). Most of the other more experienced skippers went gybing off. I tried to sail as straight as possible to the next channel mark (being somewhat of a novice). The wind eventually died and we had to call the race, but I finished second on corrected time! It was during this race that I experimented with the position of the main and found that by sheeting it in a bit, I could keep the spinnaker flying a little longer, while others around me were collapsing. That's what got me thinking about the ideal position for the main. I really like the idea of using a GPS to experiment with different downwind courses to optimize my VMG. The only problem is that we won't see open water here for at least two more months! Again, thanks to everyone who chimed in.
Thanks for the feedback and advice. As to why I would go dead downwind, I often sail in narrow channels between islands, etc. without much room. I am usually short handed, so tend to avoid gybing the spinnaker if possible. I was in a race last summer with light air and it was essentially one long downwind leg (25 miles). Most of the other more experienced skippers went gybing off. I tried to sail as straight as possible to the next channel mark (being somewhat of a novice). The wind eventually died and we had to call the race, but I finished second on corrected time! It was during this race that I experimented with the position of the main and found that by sheeting it in a bit, I could keep the spinnaker flying a little longer, while others around me were collapsing. That's what got me thinking about the ideal position for the main. I really like the idea of using a GPS to experiment with different downwind courses to optimize my VMG. The only problem is that we won't see open water here for at least two more months! Again, thanks to everyone who chimed in.
A concession/eating crow
As an example, check out the following J24 link. Polar numbers indicate optimim VMG under light conditions approx 45 degrees above DDW -true wind. (OK, I see the light. Keelboats can, under the right, specific conditions, head up with success.) Still, even with this boat, under heavier conditions, it does better to head WAY down, only ten or twelve degrees off DDW. Rich- My point is, 45 degrees off the wind is too high of a number to apply as a general rule of thumb, especially for slower boats. Jimg- half the fun of this forum is the sidetracks we take- if all we ever did was stick to direct responses to questions, it would be boring indeed.
As an example, check out the following J24 link. Polar numbers indicate optimim VMG under light conditions approx 45 degrees above DDW -true wind. (OK, I see the light. Keelboats can, under the right, specific conditions, head up with success.) Still, even with this boat, under heavier conditions, it does better to head WAY down, only ten or twelve degrees off DDW. Rich- My point is, 45 degrees off the wind is too high of a number to apply as a general rule of thumb, especially for slower boats. Jimg- half the fun of this forum is the sidetracks we take- if all we ever did was stick to direct responses to questions, it would be boring indeed.
The difference is between True and Apparent wind.
No problem. Most boats polars optimize max speed downwind at about 45 TRUE. Onboard and due to the foward speed, the 'apparent' wind will be about 22.5, .... unless youre on an ice boat.
No problem. Most boats polars optimize max speed downwind at about 45 TRUE. Onboard and due to the foward speed, the 'apparent' wind will be about 22.5, .... unless youre on an ice boat.
RichH
Please, run that last one by me again. I read it a couple times. Not sure I understand what you're saying. A true wind angle of 45* would put the AWA at about 70 or 80 on a run, depending on speed. A TRUE wind angle of 22.5 might get an AWA of 45*. AWA is all that really should concern the skipper. The sails ONLY see AWA not true wind.
Please, run that last one by me again. I read it a couple times. Not sure I understand what you're saying. A true wind angle of 45* would put the AWA at about 70 or 80 on a run, depending on speed. A TRUE wind angle of 22.5 might get an AWA of 45*. AWA is all that really should concern the skipper. The sails ONLY see AWA not true wind.
spoke too soon
My bad. Poor arithmetic on my part. Rich, if you will reference the polar site that I previously indicated, there is a column dedicated to "true wind" and if you subtract these figures from 180 (DDW), you'll find that in lighter conditions, 6 to 8, the boat optimally heads up 39 and 34 degrees. OK, somewhat in the ballpark of your 45, give or take a few. But in anything above 10 (which is, in my book, just when the sailing is getting good and it is worth going out), the optimal heading drops under 20 degrees off DDW, and eventually clear down to 6 off DDW. I realize that this is one example, but the other polars I have seen for displacement boats have been pretty similar, with most of them benifiting bigtime from heading down when the winds pick up. For those without polars, I certainly wouldn't toss out 45 degrees as an overall rule of thumb. More like 15-30 degrees off true. For what its worth. I'll stop being contentious now.
My bad. Poor arithmetic on my part. Rich, if you will reference the polar site that I previously indicated, there is a column dedicated to "true wind" and if you subtract these figures from 180 (DDW), you'll find that in lighter conditions, 6 to 8, the boat optimally heads up 39 and 34 degrees. OK, somewhat in the ballpark of your 45, give or take a few. But in anything above 10 (which is, in my book, just when the sailing is getting good and it is worth going out), the optimal heading drops under 20 degrees off DDW, and eventually clear down to 6 off DDW. I realize that this is one example, but the other polars I have seen for displacement boats have been pretty similar, with most of them benifiting bigtime from heading down when the winds pick up. For those without polars, I certainly wouldn't toss out 45 degrees as an overall rule of thumb. More like 15-30 degrees off true. For what its worth. I'll stop being contentious now.
VPP, VMG, polars, etc.
Look at the following link: http://www.sailnet.com/collections/articles/index.cfm?articleid=carrmi0024 then.... http://www.newavesys.com/sailprod.htm Unless the boat is a planing/skimming hull the offwind boat max. *speed* (not necessarily VMG) will usually exist at somewhere near 120° TRUE... and then you have to calculate back (relativistically by vector plot etc.) to get your target AWA. THEN you must calculate for VMG.... or simply watch your GPS. The polar diagram will get you up and sailing the fastest, but you must adjust (relatistically) for optimum *VMG* Just remember that all polar diagrams are in TRUE (TWA) wind, not AWA. A GPS with VMG function takes all the 'math' out of it --- just steer for the highest number.
Look at the following link: http://www.sailnet.com/collections/articles/index.cfm?articleid=carrmi0024 then.... http://www.newavesys.com/sailprod.htm Unless the boat is a planing/skimming hull the offwind boat max. *speed* (not necessarily VMG) will usually exist at somewhere near 120° TRUE... and then you have to calculate back (relativistically by vector plot etc.) to get your target AWA. THEN you must calculate for VMG.... or simply watch your GPS. The polar diagram will get you up and sailing the fastest, but you must adjust (relatistically) for optimum *VMG* Just remember that all polar diagrams are in TRUE (TWA) wind, not AWA. A GPS with VMG function takes all the 'math' out of it --- just steer for the highest number.
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