Rick,
Thank you so much for all the time you spent doing this, much appreciated! Very impressive what you can achieve with simulation.
There was a lot of info in these to digest.
I must say that I liked the speed numbers much better on the first set of charts :-) Seriously I understand these are dynamic analysis and not VPP.
I had a mail writen up when I got your last post ... had to delete my answer and had quite a lot of reading since. I understood before that the higher aspect ratio have a better Cl but I also understand now that the higher Cl/Cd move to a lower angle of attack which I guess is the reason for better pointing ability of the 40 sqm sail.
Since the chart do not account for the ww hull and the speed is lower than I would like, I am considering now a higher aspect ratio 50-60 sqm sails to compensate.
I think now a little more bow volume would be good ... but as you have shown, bigger sails is not always better !
As for going close to dead downwind, as you pointed out, it would be uncomfortable (wallowing) and best VMG is reaching.
I read that high AR sail are not good when going off wind but what is not clear to me is how far can a proa use sail lift going downwind or at what true wind angle does it only uses sail drag (since there is no shroud the sail can be set at a much higher angle to the boat and still give higher forward forces than using drag only) ?
It maybe could be sailing best VMG using lift all the time ? Then high AR is good all the time :-) No more questions about big downwind sails.
I was thinking that such a light boat, a 15m hull and a 6 ton-m moment, I could be sailing very close to wind speed ... maybe the schooner rig max Cl is the limiting factor.
Agreed that this hull is overpowered at 10 m/s and 50 sqm ... the bow do not come up much! Very good to see also the 10 m/s 40 sqm graph.
The other thing this tells me is that in good wind but not much waves, the limit will be the overturning moment, not the pitching. Did more research about water ballast and found the Gougeon 32 Cat does this ... definitely will be added to the design. It could help very much when sailing a much lighter boat since the chart are at full displacement.
I installed Autodesk CFD so will try to get a Cd out of it, may take some time to make this work though. Would be very interesting to have a good VPP but these plot is more than I could ask for at this point :-) Again many thanks!
Luc
__._,_.___
Posted by: lucsimard@ymail.com
| Reply via web post | • | Reply to sender | • | Reply to group | • | Start a new topic | • | Messages in this topic (27) |
.