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Old 20-09-2010, 21:42   #1
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Safety Netting

Just curious of how bad windage would be with my boat if i were to attach safety netting to my lifelines from fwd to aft? Would anyone know?
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Old 20-09-2010, 23:32   #2
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not much IMHO

although racing boats tend to try avoid because of a small amount of drag...
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Old 20-09-2010, 23:46   #3
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I agree that windage would be minimal. We just removed ours because it kept try to rip my toes off.
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Old 20-09-2010, 23:46   #4
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If you want an absolute measurement you can do the math with some calipers, measure out how much square inches of surface area in a square foot, and multiply. I did it with my rig once and there's a heck of a lot more windage than you'd imagine.

On the plus side it's balanced with lifelines so the affect on the bow should be roughly the same as on the stern. And if you look at a center cockpit boat with a dinghy on davits, you can safely bet that you have less windage than they do.
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Old 21-09-2010, 06:13   #5
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Not a major point, but it seems that wind at or near cabintop level is going to be pretty turbulent to begin with, so adding drag in that tumbling mess of air won't produce as much windage as the same netting set up higher in more laminar flow air.
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Old 21-09-2010, 07:15   #6
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Safety netting along your lifelines is put there to help preserve the lives of your young children and/or animals/pets. It is not strong enough to stop a full grown adult from falling off the boat. So the question about "windage" is strange since that would raise the question of the value of boat performance over the value of human or pet life.
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Old 21-09-2010, 08:55   #7
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We had netting on our life-lines for the first 7 years after our daughter was born. There was no difference in the performance of our boat. The very first weekend after we removed them, one of our dogs took an unscheduled dive over the side during a tack. Fortunately, the air was light, she was wearing a dog life-jacket and recovering her involved nothing more than heaving too and calling her. (I have never seen a Springer Spaniel swim faster in my life!).

FWIW...
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Old 21-09-2010, 09:25   #8
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netting

Does anyone have input on netting color. I will be installing for next season as our baby will be walking by next season and we'll all feel more comfortable with netting.
I saw a boat which seemed to have black netting recently. It was not nearly as visible. This has been found in hockey arenas where netting behind the glass is mostly black now to reduce its visibility.

Any ideas from personal experience on 1. aesthetics of dark netting? 2. availability of dark netting? and 3. UV stability?

Thanks!
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Old 21-09-2010, 11:35   #9
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My reasons are not for saving lives of people or pets, mainly if something were to come loose that it might not role overboard such as with gear whil cruising, but I might have answered my own question with gear on the deck and windage ratio.
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Old 21-09-2010, 12:58   #10
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We bought our boat with safety netting, and within a few months, had removed all of it. We both commit the dangerous crime of sailing with no shoes on; numerous occasions did we catch our toes on it, especially when stepping out around the dodger, but also everywhere on the boat. A couple of bad stumbles when going forward. Stepping off the boat onto the dock it wanted to grab at fingers as well. I nearly went for a swim when I caught my finger and was thrown off balance. I absolutely hated it. Our boat does also have lee cloths (I think they may also be called dodger cloths in the UK - they're made of black sunbrella surrounding the cockpit to just forward of the cockpit) which are great, and were originally added to keep kids and dogs aboard.

I understand why you'd want them for small kids/pets, but I think we'll do all we can so as to not have to add it again.
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Old 21-09-2010, 13:10   #11
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I wouldn't go without it

For twenty years I've used netting, it started out as a kid thing but as with any small boat cruising, the deck becomes storage and I hate that blooop sound. It has to be replaced occasionally and should be the knotted nylon type as I've gotten at Fisheries Supply in Seattle. West Marine has gone to a woven type that I quicly returned as it failed as soon as it was installed. Done right it will stop anyone from going over and the dog likes to lean on it underway.
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Old 21-09-2010, 13:22   #12
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With respect, some of these answers seemed to stray from your original question.
I just went thru this subject of windage while helping a new owner prepare hes C&C 41 for Igor.
Windage is surprising under-considered generally. While deck level netting may not be a major problem in 10-15 knots, it can become a not insignificant factor when the wind is up to 25-30 and you are jockeying into a slip or berth.
Try holding a piece of screen wire 4 x 4 up to 25knts of wind, you'll be surprised at the force. screen wire is 42% open area.
Not to stray from the original ?, but I was pointing out to my friend that his 50ft rolled jib x 6" diameter, was 25 sq ft. Hold 2/3 of a sheet of plywood up to 30knts of wind, and let me know your thoughts.
Enough of my rambling mind
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Old 22-09-2010, 14:36   #13
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Humm...

Induced Wind Loading

F= (A*Sf*Gf*V^2)/390

Where:

F = Horizontal Force in Pounds
A = Projected Area in Square Feet;
Sf = Shape Factor (.90 for round, 1.10 for Flat Plate);
Gf = Gust Factor (1.10 at Sea Surface);
V = Wind Velocity in MPH (Knots x 1.15)

Netting sold by West Marine, Defender et al is a 2½ in mesh made of DuPont’s #36 Nylon line that has a diameter of 2.5mm. Aligned at 45º, there is a total of 9.8 feet of line per square foot of netting or roughly .0804 SF of projected area per square foot of mesh. With 24” high life-lines and a .9 shape factor there is roughly .1447 SF of area per running foot of life-line.

Assuming the yacht is running across the wind in 15 knots of wind with no heeling angle and (generously) assuming that both the leeward and windward life lines forward and aft of the coach roof are fully loaded and the top one-half of the windward life line in the area of the coach roof is loaded, the effective loaded length of life-lines assuming a 110% curvature factor for the shear is approximately 49 feet (on an Irwin 28.5).

Given the foregoing, in 15 knots of wind the netting adds a whopping 5.94—call it 6-lbs of load on the yacht’s topside due to wind. In 50 knots of cross-wind, with the yacht heeling due to loading on the spars and rigging, the effective loaded length of lifeline falls to 24.44 feet due to the shielding of the leeward lines by the windward shear and the sheltering effect of the coach roof on the windward side along its length. Accordingly, the load induced by the netting increases to only 33 lbs.

The netting only begins to become significant in hurrican force winds when, at 100 knots, it would add, roughly, 120 lbs of transverse loading loading. In fact, however, at that windspeed, the yacht's bow or stern will be facing the wind most of the time hence the netting will add virtually nothing, eh?

FWIW...
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Old 22-09-2010, 15:07   #14
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nice scientific approach HyLyght...this simplistic formula seems make sense as an approximation...The key to any aerodynamic force is typically calculated as a factor of exposed frontal area and of course wind speed squared.

Factors like the type of air flow (turbulent or laminar) as suggested could farther make this less significant. The total drag of the netting being the sum of the form drag, the skin drag and (The netting is fairly rough so this would add to the drag)

...but this should be insignificant if your area calculation is correct....the area calculation is the only part I question because a roll is definitely not see through when rolled up so it seems the total equivalent sf would be closer to 2 sqft (the roll is 2 feet long and about 6" across and seems to be overlapped multiple times)

Regardless the drag is insignificant compared to the top sides of the hull!!
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Old 22-09-2010, 16:54   #15
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Originally Posted by osirissail View Post
Safety netting along your lifelines is put there to help preserve the lives of your young children and/or animals/pets. It is not strong enough to stop a full grown adult from falling off the boat..
Really? I was considering adding netting where we leave the cockpit onto the deck just in case. But it will not keep an adult in the boat?
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