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Old 19-08-2009, 12:43   #1
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Improving Capsize Ratings?

Hi all,
New to the forum, such a great site and very happy to be here!
Forgive me if this is a topic already covered, but does anyone have thoughts on how to improve a boats capsize rating? I have a Moody 33 C/C. a very sturdy boat, 4-1/2 cast iron bolt-on fin keel, 11.8 beam, 29 LWL, deck stepped mast, weight is 10 tons. Boat is Lloyds certified (for offshore?) The capsize rating is approx 2.1, however...I suspect due to the wide beam. My thoughts are that I might add some weight in the engine room (I have a 400lb mooring anchor that perhaps I could attach to the engine stringers?) or maybe lengthen/redesign the keel? I am very happy with the boat, (it's almost paid for) and it has crossed an ocean or two, but Not with me at the helm. I am a relatively inexperienced sailor but do have my sights set on a future pacific voyage. I am wondering if the boat could be improved or should I consider selling and moving on to something else when it comes time for the pacific voyage? Perhaps the boat is fine the way it is and I am just too inexperienced to know?
Any thoughts on this would be much appreciated.
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Old 19-08-2009, 13:00   #2
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There are all kinds of calculations you can make based on the dimensions of sailboat. I believe capsize rating is essentially the same as capsize screening value. Go here:

Sailboat Design and Stability

Many of these formulas either do not take account of other important variables or are more or less accurate only for older classic boat designs. The short answer is that if you are going to go cruising on your Moody, you'll be adding way more weight than a 400 lb. mooring anchor.
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Old 19-08-2009, 13:01   #3
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The capsize rating relates to the total area under a vessels stability curve. (righting moment (GZ) versus angle of inclination). In technical terms, when the GM (metacentric height) goes negative, the boat has no ability to right itself without any external forces acting on the boat. The compromise is that the larger the metacentric height, the stiffer the ride is, meaning it would be very uncomfortable from what are called snap rolls. Common to all boats, they are a compromise of many factors. Boats with a positive GM at all angles of inclination can be made, but you would not want to live a boat that is that stiff.
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Old 19-08-2009, 13:10   #4
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Not sure why you want to mess with a good boat. Adding weight to a boat that was designed with that generous beam just defeats the purpose. and wow, that is one heavy 33 footer! Are you sure you're not focusing on the numbers too much? Your boat should have excellent intitial stability due to the beam and of course at some point would reach to point of no return and go over. But a few hundred pounds, in the hull probably wont make much difference. About 80 lbs (two large zinc bricks) at the bottom of the keel would do more than 400 lbs at the floor boards.
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Old 19-08-2009, 13:19   #5
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Agreed, if righting moment (stability) is what you want, then you want to maximize the moment arm which is weight times the length of the distance from the center of buoyancy. This would mean that in terms of stability 100 pounds times five feet, (500 foot-pounds) would have more effect than 400 pounds at one foot (400 foot-pounds) away from the LCB. The drawback of doing the latter....you would have added 400 pounds to your boat and received virtually nothing for it by putting weights in your bilge, not to mention the added drag of an additional 400 pounds.
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Old 19-08-2009, 13:29   #6
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One of the reasons I submitted this question was that I was hoping to not have to do anything with this boat. But I have read that this is not a great boat for blue-water single-handers from an author of some note. (can not think of the author or exact title at the moment) I know this boat has crossed an ocean or two, know that the designer had succesfully raced the same model in early bluewater race events, etc, but also know that he capsized it in less than extreme conditions and later died crossing the gulf stream in it. Got me to thinking...did I not buy a seaworthy enough boat? I have sailed her in the Keys in brisk conditions and she handles and rides beautifully. Overall I am very happy with the boat but am worried this may not be the best boat if caught out in extreme conditions thousands of miles offshore.

Really appreciate the input folks!
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Old 19-08-2009, 13:36   #7
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So perhaps a small modification of 100lbs or so at the bottom of the fin keel might be helpful and would not hinder performance? I would think that lengthing the keel to say 6ft might also help? obviously this would add more than 100lbs! She's a heavy boat but carries a load rather well. Good sailor when it's blowing 10k or more. I never liked the idea of extra weight on the stringers, just happen to have a good mooring anchor!.
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Old 19-08-2009, 13:38   #8
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10 tons?

Quote:
Originally Posted by Rvrratt View Post
I have a Moody 33 C/C. a very sturdy boat, 4-1/2 cast iron bolt-on fin keel, 11.8 beam, 29 LWL, deck stepped mast, weight is 10 tons.
wow. that would be a heavy 33 footer. I looked up the specs on that boat, and came up with 11,000 pounds loaded. That's 5.5 tons.
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Old 19-08-2009, 13:50   #9
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Hi, Rvrratt, and welcome to the Forum!

I sure wouldn't add 400 lbs of dead weight to your engine room. It might make things worse, not better, and would tend to set her off her lines since the weight would be toward the stern.

Perhaps the best thing you could do is make sure you have a decent set of sails that can be reefed way down. Then get your heavy weather sailing skills up to snuff. Invite some friends who've got some experience to go out with you in a blow and see how she handles. In addition, consider a parachute anchor or a series drogue if you plan to sail across oceans in bad weather. Learn about weather forecasting so you can avoid conditions that might roll your boat.
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Old 19-08-2009, 13:52   #10
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I stand corrected.
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Old 19-08-2009, 13:59   #11
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To add weight to the bottom of the keel a naval architect will be needed to determine if the keel to hull connection can handle the additional torque.
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Old 19-08-2009, 14:21   #12
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Realistically, HUD is right on, sail the boat within it's limits. IF it is truly a tender boat, consider sail mods to bring it back in line. Taking the roach out of your main not only reduces area but eliminates sail wear etc at the batten pockets and makes it easier to sail short handed.. (A few years a go this was a trend in World Cruising) I believe you said you have a cast iron keel. Would it be possible to drill and tap into that? Put a 1.5 x 4 x (keel length) strip of Lead on each side of the keel at the bottom. (like a bulb) This could add great ballast in the right place. possibly just a few bolts and high strength adhesive. then fair it all into a bulb with epoxy paste...
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Old 19-08-2009, 14:25   #13
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That's what the racers do...have bulb keels. The difference is they have this all engineered ahead of time. You don't change one characteristic of a boat without changing other characteristics, and sometimes the other characteristics can be negative ones. Get a naval architect involved if you are going to be doing this.
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Old 19-08-2009, 14:40   #14
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Yea, that would be the best advice, but NA's tend to use rules of thumb also... after all.... his boat was likely designed by one! 400 additional foot pounds distributed over approx... 12 ft of 1" thick glass adds what... about 3lbs of stress per inch?
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Old 19-08-2009, 15:29   #15
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I agree that experince and time out on the water is the best way to gain confidence in the boat. I believe the name of the publication that specifically pointed out the shortcomings of this boat was "the seaworth offshore sailboat" and being relatively inexperienced thought that perhaps I bought the wrong boat. I appreciate everyones input.
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