How to know if you need more power or less drag?

[danstanford]

Just got this result in a search for other trim items and it reminded me to reply with the results of our experimentation. In the end we found we had too much forestay sag causing a too deep jib with the aft end of it rounding up into the main. Once I got that under control the boat woke up going to windward.

I have a new boat now but am still wrestling with the topic of the original post. We can get to our polar targets once the breeze gets up over 9 kts but below that we struggle to get to them. We are planning to get the whole team involved in the difference between needing power when we are slow on the starting line or after a tack to escape bad airs and then lowering drag as we come up to speed. Playing the backstay is the one tool we tend to ignore in this transition and so it will be a focus.

 

[shemandr]

I’ve never sailed a J99 so take that into consideration of my reply.
It is a fractionally rigged boat with a bendy mast, I presume. In that case I would employ the backstay to add power or subtract drag quite a bit. I think tell tales on the main a few feet back from the mast would be helpful. If they show stall then there is too much camber in the main and it should be flattened. If the are streaming there is the minimum drag. They will stream even if you are under powered. So you want them on the edge of breaking. When it’s windier they will probably not be useful.
I like adjusting the backstay because it can be done much faster than adjusting the outhaul and it affects the middle of the sail and not just the foot.
And, of course, avoid bad air at almost all costs!

 

[danstanford]

I’ve never sailed a J99 so take that into consideration of my reply.
It is a fractionally rigged boat with a bendy mast, I presume. In that case I would employ the backstay to add power or subtract drag quite a bit. I think tell tales on the main a few feet back from the mast would be helpful. If they show stall then there is too much camber in the main and it should be flattened. If the are streaming there is the minimum drag. They will stream even if you are under powered. So you want them on the edge of breaking. When it’s windier they will probably not be useful.
I like adjusting the backstay because it can be done much faster than adjusting the outhaul and it affects the middle of the sail and not just the foot.
And, of course, avoid bad air at almost all costs!

We have several tell-tales in various places on both main and jib to insure we are not suffering from stall and they are great to show just that as you say. The fraction is quite high and the mast is aluminum so bending the mast is not a piece of cake but for sure the backstay does work in this manner but perhaps less than desired.
This photo has the backstay on full and I will post another photo with the backstay off.

 

[danstanford]

As you can see, the various tell-tales are flying where we need them to be (you have to trust me that the leeward side look the same) even though the leech telltales are diverted a bit to leeward in this photo we do know to keep them in the air.

 

[shemandr]

For the above two photos how was the boat performing relative to the polars and what was the windspeed?
To my eye for each the draft is pretty far forward (Good for a wide steering groove) and a bit deep. Although the tell tales show no hint of stalling t that depth. How well were you pointing?

 

[danstanford]

For the above two photos how was the boat performing relative to the polars and what was the windspeed?
To my eye for each the draft is pretty far forward (Good for a wide steering groove) and a bit deep. Although the tell tales show no hint of stalling t that depth. How well were you pointing?

These were taken before the race as we were poking around making sure we had good trim for the conditions. The boat points quite well though if you look at the photos for the windex you can see we were a bit below our normal beat angles.

I would say we are generally happy with our performance but looking to eke out that last half a knot. The outstanding question for me is how to know when you should be lowering drag and the best current answer I see is when we need to manage heel. The answer may be difficult to ascertain because I want it to be not too nuanced.