Rick,
More on trim.
Using Flotsam, with 700 lbs down and 240 lbs of driving force at 10.53 ft (3.21 m) above the hull bottom (not waterline) I get a pitch angle of 1.75 degrees. If I understand what trim down is... the hydrostatic portion would be 140 mm down. So you're ~94 is good news.
Dennis
From: Dennis Cox <dec720@att.net>
To: harryproa@yahoogroups.com.au
Sent: Thu, September 9, 2010 7:38:18 AM
Subject: Re: [harryproa] MLM Trim
Rick,
Any trim up is a good thing in my book... I'll take whatever I can get.
I just double checked my COE.
The area centroid is 3.21 meters above the bottom of the lee hull. This includes the main with roach and jib.
I have a paper theorizing the wind speed gradient as a function of height which would drive the COE up. But since the sail warps, it would seem that the top portion doesn't produce as much lift as it would normally... thus driving the COE down. So are there some other fudge factors used based on the area centroid?
Would it be possible for you to run that curve using 3.21 meter COE? BTW - Does Flotilla do all this processing... or do you have to do some subsequent analysis to get this curve?
Also, if I put depth marks on the lee hull, do you think they'd be visible and worthwhile if I video'd them at speed? It would be good to correlate your numbers with testing. We might be able to come up with some empirical method to describe the dynamic lift contribution of planning.
Dennis
From: Rick Willoughby <rickwill@bigpond.net.au>
To: harryproa@yahoogroups.com.au
Sent: Thu, September 9, 2010 5:44:55 AM
Subject: [harryproa] MLM Trim [1 Attachment]
Dennis
Attached shows the trim you can expect from MLM with respect to speed.
The curve is based on CoE at 4m above waterline (maybe low) and all weight carried on lw hull - so a limit condition but not necessarily the worst state particularly if you articulate the ww hull and it has its aft end bouncing along. This will push the lw hull even more bow down.
If you ever see the top end of the speeds shown then nosedive will be a possibility. In the range 7 to 12kts MLM should run with almost level trim.
The trim will be a limitation for the height of rig you can use effectively. So this brings up efficient low aspect rigs
It is common to see airfoil fencing in some applications like these:
http://www.carversation.com/wp-content/uploads/2009/07/formula-1-cars.jpg
http://i12.photobucket.com/albums/a222/bamamom40/7061SchatzMcMahan.jpg
But fencing or winglets are not so common on yacht sails although there are a few keels with them.
Rick Willoughby
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