The 57sq.m rig on Bucket List can overpower it above about 12kts depending on the crew weight. Reducing sail area while maintaining mast height improves the rig efficiency so it sails faster upwind. You will note from the polars that at 5kts wind the full rig is faster upwind but not by much.
A high aspect sail can produce a Cl of about 1.2. In the boat model I allowed the Cl to get lower to reduce lift but if all the sail is still up there is a lot more drag than needed to produce that lift making the efficiency low. The same situation exists if the mast top is bending off so there is no drive from the top of the sail but it still has all the drag.
Clearance and windage are not particularly incompatible for a HP. It is mostly to do with the clearance of the beams at the lw hull. They are the first part that will plough waves.
A proa still has a port and starboard tack. It can be confusing for sailors on an approaching boat on starboard tack who have not seen a proa before. They expect the proa to tack through the wind but it stops before heading off on the new tack - it typically gets a reaction. So the angle separating windward tacks is what counts. By the way it still makes sense to place green and red telltales on the sails.
Yes BL should have been capable of windward tacks 60 degrees apart.. Probably not easy to tack through the wind though because it was so light: meaning little momentum relative to the drag on rig, hulls and beams. Once the load comes on the ww hull, as sail load drops, it acts like a water brake on the ww side and the rig acts like an air brake on the other side - wide beam of two loaded hulls and long, low rocker hulls do not turn easily. I do not know if Rob tried to tack BL through the wind with the little test rig.
BL should keep sailing up to 30 degrees to true wind but there would not be much point unless trying to make some mark on the current tack.
Polars are useful to know how the boat should perform on different points of the wind in different wind strength. Reasons for differences, inevitably on the slow side, are worth understanding; whether a modelling error, incorrect input or poorly sailed. Polars can also be used to assess the merit of changes before making them. I can set up a reasonable computer model of a sailing boat in a couple of days. That is usually a lot lower cost than spending money on changes that often do not achieve the desired result. If there are three or more variables involved, most humans cannot figure out the interactions. A sailing boat has a lot more than three.
Polars based on fundamental physics yield all the forces needed to design the boat and rig. They give insights into the limits such as when a hull lifts. They provide guidance on the best way to operate the boat such as when to reef; how much rudder immersion should be required under given conditions or when to lift the dagger board; what angle to true wind and apparent wind will give the best VMG etc
Rick
On 26 Mar 2019, at 1:14 pm, '.' eruttan@yahoo.com [harryproa] <harryproa@yahoogroups.com..au> wrote:Excellent!
Rick, if I may impose, can you explain why less sail makes on the wind faster? Anyone is free to answer if they like.
Did Rob not just suggest that typically reefing reduces pointing?
So, one wants clearance, but windage is a problem. These are competing priorities?
So, the Endeavour crew sucked, but got better? Please do not ban me Rob!
Does the language of 'Tacking through some degrees' make sense for a HP? Does a HP 'shunt through some degrees'? Or is it called a tack, even if you don't actually tack the boat?
Can we say that bucket list could have tacked through 60°?
Is it typical for a sailor to have memorized his boats polars?
Do sailors do test sailing to fill out polars?
Thank you for your patience.
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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