So you see a thunderstorm coming...

trainmanjess · May 16, 2013

Hello

and welcome to the family of Macs... i too am new to sailing... i have a 86 Mac25... just remember your mast is like a giant lightning pole out there... i do not have eny experiance with thunderstorms yet... but i am sure i will learn... it is just my opinion being a survivalist... seek shelter fast and make your boat as small as possible...

i wish you all the best with your mac26... all the Macs are good boats...

again welcome to the Mac family... the forum here has alot of friendly people and a load of information and experiance, we newbies can draw on to help us... good luck and happy sailing...

sincerely
Jess

Jackdaw · May 16, 2013

Get off the water if you can. Its safer, not just from a lightning perspective, but from wind/waves. I know dozens of people that that have been hit by lightning while sailing on Lake Superior. No one hurt in these thankfully but it scares the crap out of you, and usually kills most of your electronics.

Sadly a family sailing a Mac25 was struck on Lake Superior last year. They beached to get off the water, but were struck when trying to get back in the boat. A young boy was killed.

http://minnesota.cbslocal.com/2012/08/19/9-year-old-dies-after-lightning-strikes-sailboat/

MrBill_FLL · May 16, 2013

paging WALT!

dropping the main sail will not help. dropping the mast would, maybe.....

when you start reading about lighting there are 2 camps, those that want the boat grounded and those that don't.

waterballast boats are hard to ground since there is not a lead keel.

I'm in the ungrounded camp. and feel lucky.

Its surprising we don't have more strikes down here... we get thunderstorm almost every day from june to september. but its very very rare to hear of a strike on a boat.
-(and we have thousands of boats on the water daily)

I've been out many times and thought we should have been hit but weren't....

justsomeguy · May 16, 2013

Mast up in my "driveway" on the trailer, easily 50% higher than the nearby tree that got struck. FWIW.

P.S.- The tree, a big 'ol mesquite, is okay, it seems.

walt · May 16, 2013

The lightning accident referred to above I’m fairly sure happened to a newer water ballast 26 foot Mac (26M I believe). Also, the advice to get off the water is questionable. Keeping away from the mast is good advice and easier to do off the water but the act itself of getting off the water and being right there at the water/land interface in my opinion could put you at higher risk than just staying on the water and away from the mast and shrouds.

One day I’d love to explain why but I’m in the camp that Dr. Ewens solution of discharge electrodes at the water surface is the best way to dissipate charge from the mast. I also am in the camp that thinks that “grounding” a sailboat has about equal chance of helping or reducing your chance of taking a strike and it’s overall likely insignificant.

Folks that have been around for a while know that I had developed an aftermarket lightning protection system based around Dr. Thomson’s patent (Im an EE and had an additional patent) but I backed off this after looking into liability insurance and my own financial risks. In todays lawsuit happy world, this sort of product is larger business stuff.

I do think this makes my boat safer if I were to get a strike, here is my Mac http://zenpole.com/pictures/26_store.html (not an advertisement – I do NOT sell these nor does anyone else). There is a brochure pdf file a here http://zenpole.com/

RonRelyea · May 16, 2013

Head Back! It's not just the lightning!

I was out on Long Island Sound in June 2010 and heard the NWS alert on VHF. High tailed it back to my mooring in Manhasset and 5 minutes later it hit! I'm thankful for the free transienent moorings in Manhasset! Here's the NWS summary for the storm ....

...SUMMARY...
THE NATIONAL WEATHER SERVICE IN NEW YORK NY HAS CONFIRMED A
MICROBURST /STRAIGHT LINE WIND DAMAGE/ NEAR GREAT NECK IN NASSAU
COUNTY NY ON JUNE 24 2010.

AS A SEVERE THUNDERSTORM MOVED RAPIDLY SOUTHEAST ACROSS NORTHERN
NASSAU COUNTY...IT PRODUCED SIGNIFICANT STRAIGHT LINE HIGH WINDS
THAT DOWNED MANY TREES...SOME THAT FELL ON POWER LINES...HOUSES
AND VEHICLES.

THE DAMAGE EXTENDED OVER A BROAD AREA EXTENDING FROM OLD POND ROAD
EAST TO HAMPSHIRE ROAD...WITH DOWNED TREES FACING SOUTH AND EAST IN
THOSE AREAS RESPECTIVELY IN A FANNED-OUT FASHION INDICATIVE OF A
MICROBURST. THE MOST SEVERE DAMAGE IN THIS SWATH WAS CONCENTRATED
ALONG OLD POND AND STRATHMORE ROADS...WITH DOZENS OF HEALTHY
HARDWOOD AND PINE TREES UPROOTED OR SNAPPED IN TWO. THIS DAMAGE IS
INDICATIVE OF MAXIMUM WINDS OF 100 MPH.

SEVERAL OTHER NEARBY AREAS ALSO EXPERIENCED WIND DAMAGE...INCLUDING
KINGS POINT...THOMASTON...KENSINGTON AND MANHASSET. WINDS GUSTED TO
74 MPH AT 245 PM AT THE KINGS POINT NOAA/NOS TIDE GAUGE ON THE SHORE
OF WESTERN LONG ISLAND SOUND.

FourPoints · May 16, 2013

RonRelyea said:
I was out on Long Island Sound in June 2010 and heard the NWS alert on VHF. High tailed it back to my mooring in Manhasset and 5 minutes later it hit! I'm thankful for the free transienent moorings in Manhasset! Here's the NWS summary for the storm ....

...SUMMARY...
THE NATIONAL WEATHER SERVICE IN NEW YORK NY HAS CONFIRMED A
MICROBURST /STRAIGHT LINE WIND DAMAGE/ NEAR GREAT NECK IN NASSAU
COUNTY NY ON JUNE 24 2010.

AS A SEVERE THUNDERSTORM MOVED RAPIDLY SOUTHEAST ACROSS NORTHERN
NASSAU COUNTY...IT PRODUCED SIGNIFICANT STRAIGHT LINE HIGH WINDS
THAT DOWNED MANY TREES...SOME THAT FELL ON POWER LINES...HOUSES
AND VEHICLES.

THE DAMAGE EXTENDED OVER A BROAD AREA EXTENDING FROM OLD POND ROAD
EAST TO HAMPSHIRE ROAD...WITH DOWNED TREES FACING SOUTH AND EAST IN
THOSE AREAS RESPECTIVELY IN A FANNED-OUT FASHION INDICATIVE OF A
MICROBURST. THE MOST SEVERE DAMAGE IN THIS SWATH WAS CONCENTRATED
ALONG OLD POND AND STRATHMORE ROADS...WITH DOZENS OF HEALTHY
HARDWOOD AND PINE TREES UPROOTED OR SNAPPED IN TWO. THIS DAMAGE IS
INDICATIVE OF MAXIMUM WINDS OF 100 MPH.

SEVERAL OTHER NEARBY AREAS ALSO EXPERIENCED WIND DAMAGE...INCLUDING
KINGS POINT...THOMASTON...KENSINGTON AND MANHASSET. WINDS GUSTED TO
74 MPH AT 245 PM AT THE KINGS POINT NOAA/NOS TIDE GAUGE ON THE SHORE
OF WESTERN LONG ISLAND SOUND.

I was out that day on my way back to Stamford when it hit. The forecast had said it wasn't going to reach us until about 3pm, but it really started to come in fast and hard at 1pm, when I was still 4-5 miles out from the harbor. Had the storm jib up, and main reefed initially but took down all canvas after blowing out the stiches on the leach when rounding up to take the main down. Motoring into the wind at full throttle we were only making 0.5-1.0kts SOG for over an hour. We eventually made the last 4 or so miles back to the dock, but not until around 4:30pm.

Lesson there is never assume the time table until the storm arrives given by the NWS to be accurate, cut the safety margin they give by half...

Jackdaw · May 16, 2013

walt said:
The lightning accident referred to above I’m fairly sure happened to a newer water ballast 26 foot Mac (26M I believe). Also, the advice to get off the water is questionable. Keeping away from the mast is good advice and easier to do off the water but the act itself of getting off the water and being right there at the water/land interface in my opinion could put you at higher risk than just staying on the water and away from the mast and shrouds.

The boat in question was for SURE a older 26C. As for getting off the water, unless you are in a CE 'A' rated boat I recommend seeking shelter. These storms can generate 60 MPH winds and that will overcome a Mac 26 or similar sized boat.

As for the boy, the family got to shore (a remote beach) and huddled under a cover as the rain and high winds pelted them. Sadly when they could take that no more, they moved to get back in the boat. The boy was struck as he climbed back to the boat.

My understanding says that once a bolt gets to 200-300 feet off of the ground on its downstroke, it can strike almost anywhere in the 45 degree angle cone under that point. It explains why its often not the highest point around that gets hit, but is always close to it.

walt · May 16, 2013

Not that it matters that much but all the 26 foot macs are water ballast. When this really tragic event happened, I saw a picture of the boat and "was sure" it "was" an M model - but I did a google search and found a bunch of news on that accident but none with the picture of the boat I saw. So I cant confirm (the original post said Mac25 - it was a 26 foot Mac).. But.. not that important anyhow. From a lightning standpoint, the old Mac 26C's are very similar to the 26M (ungrounded mast, no metal center post, water ballast).

My comment about staying on the water was more related to lightning stike, not related to the CE rating, wouldnt want to argue with that.

finding41 · May 16, 2013

After the next thunder storm in your area check these: http://www.intellicast.com/Storm/Severe/Lightning.aspx
http://www.accuweather.com/en/us/national/severe-weather-maps
http://thunderstorm.vaisala.com/explorer.html
I can't find the link to the one I'm thinking of. It allows you to get closeup type maps of any area.
So; I would check and see if the strikes are on the water on shore.
That's just lightning.
Don't disregard the other dangers stated above. (wind, waves, etc!)
Those are just my ideas. I'm not an expert. (I'm a mailman that walks around in thunder storms. It's a living.)

chp · May 17, 2013

If I had that big engine I would get into shelter as quick as possable. I wouldn't be so concerned about the lightening as the wind. Storms always produce a gust front with very strong winds. Even a very heavy rain can produce some strong winds. If I see a line of heavy rain I reduce sail before it hits.Check out the Chicago-Mac race a couple of years ago when the fleet got hit with a storm and the wind was clocking 60-100knts. I've been hit with a few storms, always at night on anchor and do worry about a strike. I just unplug all the electronics and don't touch any metal and hope for the best.

RonRelyea · May 17, 2013

your mast isn't necessarilly a lightning rod!

here's a video of a strike at a marina just down the river from me ... if you look closely, there's a sailboat not too far from the strike, but it was a power boat that got hit.

http://www.youtube.com/watch?v=oqzjk1kp5Ug

Piotr · May 17, 2013

I read an article explaining that the lightning travels strait down to the foot of the mast. If it is not grounded via keel (grounding stays does not work), the electricity will seek it's own path to water via hull. For the fiberglass boats, it means multiple pathways along the surface ("spiderweb"). It means that there is NO safe place on the boat during a thunderstorm, unless you ground your mast (see Walt's links - that's EXATLY what I would do, unless you can run a heavy gauge cable from the mast to your keel).

kito · May 17, 2013

Piotr said:
I read an article explaining that the lightning travels strait down to the foot of the mast. If it is not grounded via keel (grounding stays does not work), the electricity will seek it's own path to water via hull. For the fiberglass boats, it means multiple pathways along the surface ("spiderweb"). It means that there is NO safe place on the boat during a thunderstorm, unless you ground your mast (see Walt's links - that's EXATLY what I would do, unless you can run a heavy gauge cable from the mast to your keel).

I reckon a keel stepped mast is safer than a decked stepped mast then? Just stay away from the mast when inside I guess.

Jackdaw · May 17, 2013

walt said:
Not that it matters that much but all the 26 foot macs are water ballast. When this really tragic event happened, I saw a picture of the boat and "was sure" it "was" an M model - but I did a google search and found a bunch of news on that accident but none with the picture of the boat I saw. So I cant confirm (the original post said Mac25 - it was a 26 foot Mac).. But.. not that important anyhow. From a lightning standpoint, the old Mac 26C's are very similar to the 26M (ungrounded mast, no metal center post, water ballast).

My comment about staying on the water was more related to lightning stike, not related to the CE rating, wouldnt want to argue with that.

Walt,

Agree with you totally on the strike issue, if wind and waves not a factor.

Also agree type of boat not important in this matter. If you watch the video in the link I posted, they show the boat on the shore.

walt · May 17, 2013

Yep.. looks like a 26S in video to me although it could be a 26D.. Both of these have a wood bulk head under the mast and are water ballast.

walt · May 17, 2013

I have always found this paper http://www.lightningsafety.com/nlsi_lhm/Radials.pdf interesting because I think it gives some insight into how a lightning strike would contact and disipate in water without a sailboat involved.

There is a term "electric field" and it is simply that if you have a voltage and a ground and you place the voltage at a distance from the ground, this creates a voltage gradient. For example, if you put a plate with 10 volts on it one foot above ground, you have created a voltage gradient of 10 volts per foot. This gradient is called electric field.

Now electrons or charge will create a voltage gradient or electric field (coulombs law) and the gradient in a material will depend on a parameter called dielectric constant. The higher the dielectric constant, the smaller the field is for a given charge.

In that paper, a model is discussed whereas the lightning column is coming down towards the water, all that charge creates an electric field and in the type of lightning we are concerned about (cloud to ground), the negative charge in the lightning causes electrons at the water surface to move into the bulk of the water and this results in atoms at the water surface missing an electron - so they have a positive charge. So the lighting strike coming down from the cloud causes the water surface to become positive charged.

An interesting thing in that paper is that that the charging of the water surface takes some time to occur - and that this rate of charging is dependent on the salt content in the water (i.e., number of charge carriers). Salt water charges very fast, fresh water can charge fairly slowly.

Of course all the electrons in the lightning strike are trying to get to all the positive charge that is at the water surface.

We also need to consider that where lighting goes is significantly influenced by an upwards leader that connects with the downward strike.
A very interesting thing about water is that even though it ionizes at about the same electric field as air, water has a very high dielectric constant - maybe 40 to 80 times higher than air. The result is that water pretty much does not ionize but the charge at the water surface could create a high enough electric field in the air above it to ionize the air above it. So it is conceivable that a leader from the water surface that uses ionized air just above the water surface could form and head up towards the downward strike.

This now gets to why I think you might be safer out on the water rather than beached on the shore but I should have said that this might apply more to fresh water. And that is that in fresh water, the charging of the water surface just takes longer and would not be as effective at sending up a leader than for example salt water - or.. the wet earth exactly where you would beach a boat or even at a boat ramp.

walt · May 17, 2013

Also... water ballast boats are about as ungrounded as you can get. Yet they get struck by lightning (as well as catamarans - also generally ungrounded)

If we look at the leader being generated at the water surface and using the mast as a "short cut", you always have to consider that a column of ioniized air apparently makes a very competitive conductor even compared to copper wire. Using ionized air, charge at the water surface would have pretty much no problem jumping to the bottom of the mast and then upwards from the top of the mast.

Granfalloon · May 18, 2013

In the summer there is a chance for thunderstorms quite often. They usually come in the late afternoon.

If the sky looks reasonably clear - no thunderstorm clouds building - go out early with plans to be in your slip by 3pm. Any sign of thunderstorm clouds forming head for home.