Bjorn
I did not play with the rig on BL to optimise windward performance. With its full 57sq.m it was overpower with 3 crew on the windward hull. The 40sq.m sail gave 9.1kts VMG but there may have been something that was faster. The beam tubes are round and offer significant windage. The Cd of a round tube is around 1 at low Reynolds #. I would need to look at details I put in the model but they alone would be significantly more than 1sq.m.
There is no reason a smaller cat is not faster upwind. It is just a matter of sailing efficiency. Slender hulls do not have much hull wave drag so length is not a factor for smooth water polars. The longer boat will pitch and plough less in open water waves than a shorter boat that is already experiencing extra drag due to pitching or ploughing.
Rick
On 27 Mar 2019, at 11:48 pm, Björn bjornmail@gmail.com [harryproa] <harryproa@yahoogroups.com.au> wrote:Rick,Nice polars. I think your VPP must take much more into consideration than the one I made in Excel (which is kind of rough). Does Bucketlist have a significant amount of windage? My VPP calculated higher VMG upwind, more than 10 knots. Mine took windage of the boat into account, but maybe I put a too low number for windage (Cd * A = 1m2). One difference is that I calculated with a higher righting moment, 2500kg*m. But when lowering it to 1800kg*m, VMG is still more than 10 knots.As a reference, have a look here:The Tornado's polar at 10 knots looks similar to Bucket list. Shouldn't a 40 feet multi be faster than a 20 feet multi?Maybe Bucklist simply was too light? Not enough righting moment to power it to speed?And this page shows around 10 knots VMG for a 45' catamaran.
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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