Rob
I have an endless array of hulls in electronic form. So many that it would only be confusing. I even have an almost unlimited supply of real ones laying around my house. It is fortunate i have a large yard and lots of rafters in the garage. A few hang above the cars so my garage is still usable for its intended purpose; unlike some I know. My wife now has a rule that I have to discard an old hull each time I make a new one.
The rudders are very interesting - a lot of upside opportunity. Ever since I saw the idea of the twin rudders I knew it would be possible to avoid leeway but I did not think of the asymmetry until recently. I had some suspicion you had already thought of this after seeing what I use on the V14 pedal boat but was not sure.
When sailing close to the wind a conventional rudder will be contributing about 30% of the overall drag on the proa. So doubling the rudder efficiency could reduce overall drag by 15%. It will make a big difference in VMG. The 10% section works well for most AR. Obviously getting the highest AR within the strength and draft limitations is the way to go.
I like the linkage Todd has. With some trim adjustment between the two rudders it could be really nice. You should be able to pull a few degrees closer to the wind without losing speed by trimming them correctly.
Rick
On 05/08/2010, at 8:34 PM, Rob Denney wrote:
Fascinating stuff. Not sure if you have a repository for all the test hulls you do, but if you don't, it would be great to have them all in the Files section.
Looks like rudders have to go on my to do list as well.
rob
On Thu, Aug 5, 2010 at 6:59 PM, willoughby_rick
<rickwill@bigpond.net.au> wrote:
Curiosity got the better of me.
I have looked at the lowest drag hulls for 4t combined; with 3t on the lw and 1t on the ww. The hulls just happen to end up 21m and 13m long and total drag at 15.9kts is 2360N. The individual hulls have a drag of 1577N for the lw and 779N for the ww. So the interference is detrimental even at the optimised speed although I did have a max beam constraint of 8m and settled at 7m WOA.
There is detrimental interference maximising at 37N at 11.8kts when total drag is 1196N. Above 17kts the interference is mostly beneficial but too small to worry about. - always well under 1% of total.
This initial look suggests wave interference is a second order factor. It would pay to do a check with the ww hull more heavily loaded.
Putting time into the rudders is going to be much more rewarding in terms of performance than playing with wave interference. Likewise the selection and placement of the rig has big potential.
Rick
Rick Willoughby
03 9796 2415
0419 104 821