Does anyone know the righting moment (30deg heel) of a Venture 22 (no water ballast, keel down) or the angle of neutral stability (ideally around 110 deg)?
loudemartelly@comcast.net
loudemartelly@comcast.net
Stability
- Thread starter SeamanLou
- Start date
- Status
If McGregor didn't calculate them at design time (which I really doubt) you are on your own. Happily there are some standard formulas that will get you started. Good thing you wanted to leave out the water ballast, it usually messes this up.
http://www.sailingusa.info/cal__avs.htm
http://www.sailingusa.info/cal__avs.htm
This sailcalc capsize ratio is pretty useless as it only takes into account beam and weight. It doesn't even look at where the ballast is located. The US Sailing avs link is a lot more accurate, although still just an estimate.
Every boat can capsize. The Center of Gravity (CG) gets over the Center of Buoyancy (CB) and over she goes. This is the so-called Point (or Angle) of Vanishing Stability. Once it gets to this point, she will usually continue to fully invert, and the boat is normally pretty happy being upside down. Self-righting is simply a term used to describe boats with very high AVS numbers. Above 145 will usually do it, but ideally you look at the whole GZ curve. The smaller the part under the line, the less likely to capsize, and the more likely she will self-right.
As Mitiempo points out, this full calculation is very complex. Done correctly, it takes into account the shape of the keel to calculate the actual CB, and factors in things like cabin area above the deckline (which helps the boat roll back over, and adds extra buoyancy when heeled over more than 60 degrees.
Guess Fedom 77's is the easiest reply. Roughly same as in Mac Manual, but it warns against removing flotation. Blocks that came with mine don't seam to fit and are only about 12 cft. Thats about 800 lbs. Boat displaces 1800 (+ motor & extra stuff). Doesn't it still sink anyway?
Jackdaw, Cool diagram on capzising. Too much math for me. I usually hit an Angle of vanishing stability after about the third beer
. Venture will sink to a certain point and then the built in foam is supposed to keep it afloat although very wet, assuming all the original foam is there. MacGregor actually flooded a boat and it only sank up to the deck. Your V-berth should have flotation blocks and there should be some under the settee seats and in the aft end. If not you might think about adding some. Every time I buy a piece of electronic equipment I stuff the foam packing into the boat wherever I can find unneeded space. Also, Always keep keel locked in down position or you could capsize and the keel will make a very ugly move into the trunk...
Most parts of a boat are very close to neutrally buoyant. Just like people! Normally additional flotation just has to offset the weight of the dense keel to make it unsinkable.
But boats don't have to fully capsize to sink. Most go down when they downship water thru the companionway at 90 degrees. Keep your lower board in while sailing!
But boats don't have to fully capsize to sink. Most go down when they downship water thru the companionway at 90 degrees. Keep your lower board in while sailing!
Last edited:
- Status