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Old 28-01-2010, 23:35   #1
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Sea Anchor Size Recommendations?

Can someone help me re conciliate the difference in the size recommendations by these two sea anchor manufacturers?
Sea Anchor and Para Anchor Size Chart
Sea Anchor: Your First Line Of Defense When Facing Heavy Weather
It's seams to be quite different. What's up with that??
Oddly, the one made from the lighter material is the one suggesting the larger size, which could potentially put more load on it. I guess this would only come into play if it was undersized which would change depending on Sea conditions. Hmm, a circle I can't get to the end of .
Anyone?

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Extemp.
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Old 29-01-2010, 02:50   #2
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I seen on YouTube one that was made with alot of small cups all in a row along the line. It looked very nice and easy to recover.

one Trip I made the winds picked up on me very fast and had to cut a spinnaker sail down, man it was so hard to recover and yes it did stop the boat on a dime. Now I have the deploy sock but when I looked at that one chart it made me think of that sail.

From the one chart I would need a 15' yes I agree that is much smaller than a spinnaker sail but still think about the recovery.

Before you decide please look around for the one with small cups in a row.


Dutch
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Old 29-01-2010, 05:08   #3
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Loading on the sea anchor is a complex function of it's total area, simplified, the larger the canopy, the lower the loading per square bit of what ever you measure it in. The attachments to the canopy are a different matter. All the load is transmitted from the canopy to the strops etcetera so these need to be large (strong) enough to take the total load. When I investigated this before I bought an sea anchor and a drogue, I realised I didn't have sufficient expertise to calculate the loads so I settled for accepting that the manufacturer should know what they are talking about and accepted their recommendation after talking with one of their technical peeps. For the drogue, I realised that I needed to install stronger anchor points but with a sail boat I'd imagine you already have winches far enough aft to be able to use them, if you get a drogue as well. Don't overlook the need for anti chafe gear for either solution.

Hope this helps a little.

P.
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Old 29-01-2010, 08:57   #4
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I think you may be talking about a drogue which trails from the stern of the boat.

Regards,
Extemp.
Quote:
Originally Posted by johnar View Post
I seen on YouTube one that was made with alot of small cups all in a row along the line. It looked very nice and easy to recover.
Before you decide please look around for the one with small cups in a row.
Dutch
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Old 29-01-2010, 09:36   #5
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Hi again Extemp,

I'm sorry, I was in a rush and didn't quite finish the thoughts I had. You noted that the larger chute was made of lighter material compared to the smaller one. That's because the load per square area is lighter, the larger it is. For those who don't quite get the concept, imagine me walking across your nice strong teak deck in high-heels. I'd mark it and then get keel-hauled. If I wear sneakers or deckshoes, I spread the load and you may let me come on board again

P.
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Old 29-01-2010, 09:43   #6
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Quote:
Originally Posted by Extemporaneous View Post
Can someone help me re conciliate the difference in the size recommendations by these two sea anchor manufacturers?
Sea Anchor and Para Anchor Size Chart
Sea Anchor: Your First Line Of Defense When Facing Heavy Weather
It's seams to be quite different. What's up with that??
Oddly, the one made from the lighter material is the one suggesting the larger size, which could potentially put more load on it. I guess this would only come into play if it was undersized which would change depending on Sea conditions. Hmm, a circle I can't get to the end of .
Anyone?

Thanks,
Extemp.
Never used one... never will.....
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Old 29-01-2010, 10:59   #7
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I absolutely agree except ......
As the area of the chute increases, the potential load increases as there is more resistance. A smaller chute will slip through the water once overcome by force where the "Larger Chute" will continue to try to hold the boat. There must be a ratio of sorts that may change as the forces increase compared to the chute size??
I'm guessing that if the chute is sized properly, then all will be well.
Hence the question regarding size. Obviously there is differences in opinion by these two Companies.

Cheers,
Extemp.
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Originally Posted by fishwife View Post
Hi again Extemp,

I'm sorry, I was in a rush and didn't quite finish the thoughts I had. You noted that the larger chute was made of lighter material compared to the smaller one. That's because the load per square area is lighter, the larger it is. For those who don't quite get the concept, imagine me walking across your nice strong teak deck in high-heels. I'd mark it and then get keel-hauled. If I wear sneakers or deckshoes, I spread the load and you may let me come on board again

P.
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Old 29-01-2010, 23:39   #8
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The load on a chute is a function of wind speed not chute size.

Rate of drift downwind is a function of chute size.

Depending on who you want to believe the load imposed on a 40 ft boat in 60 kts of wind is 1400 to 4800 lbs
at 120 knots it is 4 times greater or 5600 to 19,000 lbs.

From what I observed it was less than 10,000 lbs at 100 knots (40 ketch, 28,000 lbs disp.) as the sacrificial line I rigged from the rode to the foredeck held.
On a 14 ft chute that works out to 60 lbs/sqft of chute.
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Old 30-01-2010, 02:00   #9
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Originally Posted by mesquaukee View Post
The load on a chute is a function of wind speed not chute size.
Hmmm . . . perhaps for 'average load', but not for 'max load'. Max load would be a function of wave size and shape. If you were unlucky enought to get two monster breaking waves, spaced so that the first stretches out the rode and then the second hits, you could get a temporary load essentially equal to vessel displacement.
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Old 30-01-2010, 08:34   #10
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Quote:
Originally Posted by Extemporaneous View Post
I absolutely agree except ......
As the area of the chute increases, the potential load resistance increases as there is more resistance. A smaller chute will slip through the water once overcome by force where the "Larger Chute" will continue to try to hold the boat. There must be a ratio of sorts that may change as the forces increase compared to the chute size??
I'm guessing that if the chute is sized properly, then all will be well.
Hence the question regarding size. Obviously there is differences in opinion by these two Companies.

Cheers,
Extemp.
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Originally Posted by mesquaukee View Post
The load on a chute is a function of wind speed not chute size.

Rate of drift downwind is a function of chute size.

Depending on who you want to believe the load imposed on a 40 ft boat in 60 kts of wind is 1400 to 4800 lbs
at 120 knots it is 4 times greater or 5600 to 19,000 lbs.

From what I observed it was less than 10,000 lbs at 100 knots (40 ketch, 28,000 lbs disp.) as the sacrificial line I rigged from the rode to the foredeck held.
On a 14 ft chute that works out to 60 lbs/sqft of chute.
Thanks mesquaukee,
Yes of course you're right regarding Load having nothing to do with chute size. What I was trying to say is its potential to resist load increases. Of course this is complicated because there is slippage in water.
Ya and I don't really care where the load comes from. It comes from lots of places.
The heavier cloth and support structure has to be the way to go. The size is still in question.
Put another way. What (BESIDES RETRIEVAL) problems are there if your chute is over sized? Would it not just allow LESS movement of the boat through the water? And potentially increase loads at the fastening points of the parachute to the boat due to increased stopping power of the larger chute. I would think that one would want to err in this direction due to the negative affects sliding backwards on a wave would have on your rudder with very little that could be done at that point.

Any more thoughts on this?

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Old 30-01-2010, 09:21   #11
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Originally Posted by Extemporaneous View Post
Put another way. What (BESIDES RETRIEVAL) problems are there if your chute is over sized?
I am not sure they are right, BUT, Lin & Larry (Pardey) think that a smaller para-anchor, that will slip/slide a bit thru the water under heavy load, is better than a bigger para-anchor. They believe that the 'slick' caused by the boat sliding thru the water disturbes the waves and prevents/avoids the worst breaking waves.

The sliding also reduces/minimizes the shock loading on the rode and deck hardware. By far the most common failure mode with para-anchors is rode breaking. Mostly by chafe but some by simply overloading in wave shocks. A smaller para-anchor could reduce even the chafe by making the loads more constant and less cyclic.
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Old 30-01-2010, 11:01   #12
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From what I experienced using a chute is if nothing else is done the boat will sail back and forth just as it would as if it were anchor. Obviously this would obviously increase shock loads, increase chaff on the rode and eventual breakage.
Keeping the boat on one tack is a must. I used a deeply reefed Missen, the reefing line of which chaffed through in a few hours. I ended up lashing it tightly to the boom with 1/8' line.
The slick caused by slowly sliding back (full traditional keel) did smooth out the waves somewhat when the wind subsided, it did not significantly reduce the wave height.
At 100 knots it was impossible to see if any slick was produced or see anything at all.

We endured numerous shock loads, the boat being violently picked up and dropped. Shock loads are a killer of hardware and lines (chaff). Obviously the rode should be as elastic as possible to reduce loads created by shock loads.
The rode going over the bow is where the rode would break. Chaff gear can do only so much to protect the rode and it needs attention. Letting the rode out a little bit now and then seems like a good idea to control any chaffing, the bow is not a pleasant place to be.
Attaching multiple lines to the rode using an Prusik knot forward of the bow and leading them back to the boat is more secure. Should one line chaff and break there are others to carry the load.

The choice of a chute size, rode size, length of rode, chaff protection, etc., has no one answer.
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Old 31-01-2010, 17:46   #13
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Before buying a sea anchor you may want to read more on series drogues.

Specifically the US coastguard report that concluded "A series type drogue provides significant advantages over a cone or parachute type drogue."

Drogue Information
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Old 31-01-2010, 19:37   #14
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Extemp, Yes you are right a Drogue, I hope you take a little time to look into them they seam much safer and you have controll to recover them.

The point here is to keep the boat pointed into the weather and not stop it on a dime, every time I think of any Sea anchor I think of the Jaws movie were the shark rips the stern right off the boat.

best of luck,

Dutch
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Old 31-01-2010, 19:50   #15
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Extemp, Yes you are right a Drogue, I hope you take a little time to look into them they seam much safer and you have controll to recover them.

The point here is to keep the boat pointed into the weather and not stop it on a dime, every time I think of any Sea anchor I think of the Jaws movie were the shark rips the stern right off the boat.

best of luck,

Dutch
Thanks Dutch.
I think ...... I will end up getting both a parachute sea anchor and a series drogue. I thing they both have uses at different times and in different sea states.
"best of luck,"
Keep that coming please.
We could all use the best luck.

Thanks,
Extemp.
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