[northoceanbeach]

Where do the forces go sailing downwind?

I don't know exactly why I thought about this. I was just thinking about reefing and stuff.

If the wind is at most angles you heel. The more you heel the less force there is on your rig.

If you are sailing dead downwind you don't heel. Plus your boat has a max speed. So what happens to those forces as the wind increases? It seems it would tear your mast off the most easily although I am not sure this is the number one way to get dismasted.

I know as the wind picks up you lessen sail and at some point you may be sailing dd with just a storm jib. But while it is picking up. Say a squall hits fast, until you have the chance to lessen sails is this a particularly dangerous time?

 

[sailingfool]

.. So what happens to those forces as the wind increases? ...

The boat starts to bury the bow. At some point, the drag upfront may cause the boat to decide its time to head up (or down)...

 

[Faster]

A serious squall from DDW is most likely going to require you to round up and take down a lot of sail. It's difficult, if not impossible, on most boats, to dropped a powered up main while holding your downwind course.

Since up to that time you were subtracting your speed from the windspeed when you do turn around it will seem alarmingly windier, and indeed be a struggle to get the sails down, and, if you're alone, keeping the boat under control as you do so.

The trick is to keep your head on a swivel to give you the most reaction time, and to sail conservatively/reef early in a building breeze downwind. This is probably one of the main reasons for the popularity of sailing on headsail alone when going downwind.. much easier to reef down/roll up a genny and deal with a full mainsail in those conditions.

Even a hanked on headsail is likely to collapse down the forestay if the halyard is blown when downwind, whereas that same sail can tend to climb the stay pointing upwind in a big breeze.

 

[Tim R.]

How is it that the rig has less force when heeling? I can guarantee you that your rig has more force on it at 10° of heel than at 5°. When sailing DDW your boat is moving forward thus reducing force on the rig. On a beam reach your boat moves very little laterally other than heeling.

 

[joethecobbler]

when you heel the wind dumps as the angle og heel increases.don't know if it would be less tension overall, but I have 1backstay as apposed to 3 shrouds.
my guess.
rounded up in a gust w/ my spinnaker up this fall and it almost took the rig down. had to go aloft to place the starboard shroud back in. the spreader an re-sieze it.
oddly, my daughter who was 9 told me I had too much sail up.She was not happy when it happened as she was at the helm and I was forward on deck.
she won't let me forget it.

 

[Tim R.]

It takes more force to make your boat heel more. Wind dumping helps but it is still more force on the rig than at lower wind speeds..

So if what the OP is saying is that there is more force when DDW then beam reach why does the boat not settle down once it is forced to turn 90° from DDW?

The bow starts to bury and the boat leans forward to one side or the other and initiates a violent turn towards the wind. I would bet that the strongest force on the rig in that maneuver is when the boat is beam to.

Should not be hard to figure out if you have a decent Loos gauge. Measure the static tension on the rig at rest and then measure it at DDW and beam reach in consistent force winds. You will have to measure each shroud on the one side and combine them. You would also have to measure each backstay if you have two like my boat. It will probably take a decent amount of wind to overcome the static tension. I would do it but my mast is down for the winter.

 

[Faster]

I think for the same apparent wind speed and the same sail area, your rig will be more loaded DDW simply because the boat cannot bury the bow and 'spill' as easily as it can heel laterally and reduce the apparent area.

Sort of like comparing the force on the rig with the wind on the beam and the sail overtrimmed.. at sea the boat can heel, reduce the presented area and 'reduce' force.. try the same thing on the hard where the boat can't heel and the forces should be greater.. until you flip the boat off it's stands!

 

[SchockT]

I don't know exactly why I thought about this. I was just thinking about reefing and stuff.

If the wind is at most angles you heel. The more you heel the less force there is on your rig.

If you are sailing dead downwind you don't heel. Plus your boat has a max speed. So what happens to those forces as the wind increases? It seems it would tear your mast off the most easily although I am not sure this is the number one way to get dismasted.

I know as the wind picks up you lessen sail and at some point you may be sailing dd with just a storm jib. But while it is picking up. Say a squall hits fast, until you have the chance to lessen sails is this a particularly dangerous time?

Just because the boat is heeling doesn't mean there is less load on the rig. DDW is the slowest point of sail, and will also result in the lowest apparent wind speeds, and the least power in the sails. The biggest hazards to your rig when running is the potential for shock-loads due to uncontrolled gybes. If the boom is allowed to slam across violently stuff can get broken. If you are flying a spinnaker, and you round up, the loads on the rig rapidly increase from what they were when you were sailing a deeper course. If the chute collapses and fills again the shock load can be extreme. That is when things cam break. Having said that, the rig should be able to withstand those forces. If your upper shroud came off during such an event then your rig is in serious need of professional attention! How would you and your 9 year old daughter have handled a dismasting that day?

 

[northoceanbeach]

Yes. I wasn't trying to say that overall there are less forces on the rig at 10• vs 5•. I mean. You wouldn't be heeled over farther.

Just that at most points of sail the boat can heel to reduce pressure ad spill the wind. So at least it has a way to reduce pressure as pressure increases.

So the only way to reduce pressure downwind is to reduce sail.

 

[Tim R.]

...So the only way to reduce pressure downwind is to reduce sail.

Or go faster. Obviously there is a limit but going faster reduces the forces going DDW more than on a beam reach.

Increasing speed on DDW reduces apparent wind while going faster on a beam reach increases apparent wind.

 

[SchockT]

I get what you are saying, but you are over estimating the amount a sailplan will depower as the boat heels. Sure, the heeling motion might "cushion" the impact of a sudden gust, but the load on the rig is still going to be much higher taking the gust on the beam vs taking the same gust on the stern. You have to remember that sails are at their least efficient when running. They produce a fraction of the power they could on a beat or a reach. That is why spinnaker were invented: It takes a whole lot more sail area to produce the same amount of power down wind.

 

[TQA]

Be aware of the false sense of security you can get sailing a fast boat DDW. Say you have 30 knots true and the boatspeed is 12 knots. That means the apparent wind on deck will be 18 knots which will feel sort of OK. However turning around into wind to reduce sail may be a dangerous maneuver.

 

[SchockT]

Be aware of the false sense of security you can get sailing a fast boat DDW. Say you have 30 knots true and the boatspeed is 12 knots. That means the apparent wind on deck will be 18 knots which will feel sort of OK. However turning around into wind to reduce sail may be a dangerous maneuver.

Absolutely! All it takes is one mistake on the helm like punching the bow into the back side of a wave and stopping the boat....All at once your butt is in the air and the breeze behind you has just doubled!

 

[Alex W]

This is the only time when I can get my boat to sail well above hull speed. It is hard on the boat and hard on the skipper, but a lot of fun. I have limited experience in these conditions, but have been trying to learn more from sailing in them. All of what I'm writing is from my experiences on my Pearson 28-2, a "racer/cruiser" that is more cruiser and not designed to plane.

You are only asking about wind pressure, but in these conditions you'll also typically be sailing downwind with following waves.

In my (again, limited) experience when I'm overpowered and going downwind in these waves the boat will want to broach as it crests a wave. There is less directional stability on the hull and it will want to turn sideways with respect to the wave.

If I reduce sail then the boat won't want to turn up so dramatically and it is a lot easier to keep it pointing downwind. Then it can start to surf and that's when things really get moving and fun. I've gotten my boat going about 10 knots (hull speed is more like 6.5) in 20 knots apparent and 3-4' following waves.