Welcome to the Maunie of Ardwall blog

This is the blog of Maunie of Ardwall. After a six-year adventure sailing from Dartmouth to Australia, we are now back in Britain.

Sunday, 25 October 2015

Day 6: The {D,V} Equation and Other Calculations

Ok, so regular readers will be itching to know if the optimism of yesterday's blog, vis-a-vis flying the Parasailor, was justified. Well, we had wonderful sailing through the night as the wind increased a little and swung from behind us to a broad reach (i.e. over our right shoulders) but at 3.00am Dianne woke Graham up from his off-watch dreams for a review. Maunie was charging along at 7 –7.5 knots but was becoming a little more difficult to keep in a straight line.
Di was right to make the call so we sat and did a quick calculation of the D > V/2 equation (where D is Discretion and V is Valour)  and decided that we should drop the sail and move back to white sails. This is always an extra challenge at night but with good planning and care we achieved it without dropping the sail or lines in the water and were soon back sailing at about one knot less. At 125 sq m the Parasailor is 70% bigger than the combined mainsail and yankee so it certainly makes a difference and the wind did continue to build as we reached a weather front at about 7.00am. It would have been a challenge to manage a neat drop of the wet spinnaker if we'd still had it flying in those conditions so we patted ourselves on the back for Di's good call.
Once we were though the front with about 3 hours of drizzle and variable winds, we've popped out to the west of it so have lovely sunshine but with the wind light and moving steadily to the SW, which is the direction we are still trying to go.  We've been looking at all the weather information that we have and it seems that the forecasts are continually changing for the low pressure systems converging on NZ as we do the same. The good news is that the low pressure that threatened to whack us on the nose on Wednesday seems to be moving more slowly so we might escape a bashing. However the bad news is that we've had to do some more maths.
It now seems as though we are going to get lots of very light wind over the next 3 days so Bob's latest routing model suggests we'll need the engine for about 65 hours (ugh!). We've been working out our usage so far (an estimate based on previous engine runs as we don't have an accurate fuel meter on board) and we think we have enough fuel for about 72 hours at slow speed (5 knots). That speed should be fast enough (just) to get us into Opua before the adverse winds arrive but our estimate is probably accurate to only +/- 10% so it could be very close on whether we run out of diesel.
It could be a lot worse, of course, we could be bashing into a head wind now and feeling decidedly uncomfortable so we'll just have to take what comes and keep a light hand on the engine throttle.

No comments:

Post a Comment