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-   -   Where to attach the sea anchor? (http://www.sailnet.com/forums/general-discussion-sailing-related/84322-where-attach-sea-anchor.html)

MedSailor 02-25-2012 02:06 PM

Where to attach the sea anchor?
 
Even though I've read between 2-300 sailing books by now, I've somehow missed one of the greats: Adlard Coles, "Heavy Weather Sailing." Reading it now and learning a great deal.

Personally I've always thought that, for my boat/crew/situation a parachute sea anchor will be the first line of defense for a survival storm if heaving-to is no longer a viable option.

On S/V Fairhaven, I have a wonderful/awful 8ft long bowsprit, with associated rigging, hanging off the pointy end of the boat. This presents challenges to figuring out the best place to lead a sea anchor from. Ideally I should choose a spot that is immensely strong, has a minimum of chafe, and will hold the boat at a good angle with the rode. See picture below.

https://lh6.googleusercontent.com/-T...attachment.jpg

I have a bridle set up to the stem (blue arrow) that I use for my main anchor. It's great as it reduces the needed scope and is quite strong as it is attached to the bobstay attachment point. On my rig, the bobstay is the most loaded stay. This seems like a good possibility for leading the sea anchor. It might assist the bow rising over a wave due to it's low aspect, and the fitting is man-enough for the job, but every time I would be nose-down the line might chafe (or bend) on the bobstay and dolphin striker. Also the boat might yaw quite a lot as there is quite a bit of windage (furled headsail) forward of this point.

The Anchor roller I have installed at the end of the sprit (green arrow) is pretty beefy but I have some doubts. It's 3/8 welded aluminum and uses a 5/8"stainless bolt to bolt the roller through the cranz fitting (the collar at the end of the bowsprit where all the rigging is attached) so it is, by way of the bolt, part of the rig. The lead would be free of chafe, except at the roller itself, but I worry it might try and pull the bow down, instead of helping it up as the lower point of attachment might do. Also being part of the rig means it's strong enough, but the way it attaches to that 5/8"bolt makes me worry it could shear off under huge loads.

Lastly is the red arrow, pointing to the fairlead up forward. This is a bronze fitting through a hefty bulwark in the bow. Since it is part of the hull/deck, I expect it is man enough for the job. It might help hold the bow slightly off center as the fairlead isn't centered. On the other hand if the boat veers the other direction, the anchor lead will be chafing across, and trying to destroy, the bowsprit and it's rigging.

Thoughts?

MedSailor

Bradhamlet 02-25-2012 02:47 PM

I'm thinking the red arrow with a fair lead or bridle would be where I would start with. Maybe us it in a 20-25kt day and see what your results are.
Lancer 36
Brad

killarney_sailor 02-25-2012 03:49 PM

Have you read the Pardeys book on storm tactics? Their approach it use a second line from the parachute anchor rode to amidships so that the parachute is off to the side of the bow. this would work very well with the fairlead you have and eliminate any possibility of chafe forward (except for the fairlead of course) and help you stop forereaching.

jimmalkin 02-25-2012 04:15 PM

I would suggest Kilarney has it right - lying head to sea and yawing through the wind is uncomfortable and unsafe as you are bow into breaking waves. The advantage of the heaving to solution of the Pardey's is the ease of motion in the vessel as the slick created by the hull eliminates/significantly reduces the breaking tops of the waves. With your fairlead and a midships line from a well bedded cleat to a large block pulling your para aft to produce an approx 30 degree angle to the wave trains, you should be well set.

Try it out in moderate conditions as every boat needs a slightly different set of rudder and/or sail combination to keep balanced at 30 off the wind. In our 50' cutter, we found that we didn't need any sail up at all as the hull and trunk cabin structure provided enough force to keep the rudder active.

The Pardy book also has a video which is helpful. Their suggestions have worked well for us.

billyruffn 02-25-2012 04:16 PM

Given all the gear you have on the bow, you might consider using a bridle to hold the boat at a slight angle to the wind / seas. You will probably run the rode out one of the closed bow chalks and then put a snatch block of the rode with a bridle line leading aft to the cockpit. You can then use the bridle line to adjust the angle of attack.

One of the advantages of using the bridle over simply running the rode from the bow is that you may find that the seas and the wind aren’t necessarily coming from the same direction (or you may have seas coming from several directions) and so you may find it necessary to adjust the boat’s heading to reach the most comfortable riding angle.

Lin and Larry Pardy have a video for sale (and rent on You Tube) that explains how they use a para-anchor in heavy weather. An intro to the video is at Featured Authors :: Lin & Larry Pardey :: Pardey Videos - Paradise Cay Publications - Nautical Book Distributor. Retail and Wholesale, maritime books, boating, sailing, pirates, fishing, lighthouses, mermaids, boats, navigation, charts, noaa training
and if you double click on the introductory video it seems to take you to youtube where you can rent it for 48 hrs for $2.99.

I bought the video several years ago and found it very helpful. I use it as part of the crew briefing if we’re heading offshore and it seems like we might have need of the para-anchor.

The Pardy’s boat has a bowsprit like yours and so it might be helpful to have a look at how he sets up the para-anchor.

MedSailor 02-25-2012 04:55 PM

I appreciate the bridle suggestion, and I do own the video and book by the
Pardeys. My concearn is that the loads on the bridle line would be beyond what anything on my boat could cope with.

This concearn is borrowed from Mr. Adlard Coles, after reading his book. He is a big fan of sea anchors, and the pardey method in general, but his research shows that the pardey method may only be acceptable to small boats. He notes that the bridle line is under tremendous load, and doubts that larger boats could have the gear to cope with bridle loads.

Chapter 25 of his book documents a 45ft Tyana Surprise Ketch of 13tonnes displacement (mine is a 41ft ketch of 14tonnes displacement) whereby they deployed their 28ft para-anchor and set up a bridle of 3/4" line per Lin and Larry Pardey's instructions. They say the bridle "broke as soon as it was tensioned."

Of course I could use an amsteel bridle line, but then the snap shackle and my Lewmar 44 winches might not be up to the task. Ideally I would like a setup where I "could" use the bridle method, but would also function with a single rode if I were unable to get the Pardey method to work.

MedSailor

MedSailor 02-25-2012 05:01 PM

Biliruf,

What gear did you choose for your bridle? What is your boat's displacement?

MedSailor

gershel 02-25-2012 05:01 PM

Here's 1 more book, probably the most informative on sea anchors.
Drag Device Data Base

drag device data base

Marc

Flybyknight 02-25-2012 05:10 PM

My concern about running a sea anchor from the bow is that as the ship is going astern, there is a tremendous load on the rudder if you are not able to positively lock it centered in place; no easy task.
I always thought the ultimate survival mode was trailing warps astern, as K Allard Coles suggests.


Dick

MedSailor 02-25-2012 05:27 PM

Quote:

Originally Posted by Flybyknight (Post 836749)
My concern about running a sea anchor from the bow is that as the ship is going astern, there is a tremendous load on the rudder if you are not able to positively lock it centered in place; no easy task.
I always thought the ultimate survival mode was trailing warps astern, as K Allard Coles suggests.


Dick

Can you point me to where he suggests that?

He does say that for those who do trail drogues astern (I don't think he has a low opinion of warps for their lack of drag and large stowed size) that keel profiles like mine are ideal. He mentions, and I take heed, that this technique usually requires multiple skilled helmsmen, which I am unlikely to have. I also worry about crew fatigue with active tactics such as this.

If the anchor is of sufficient size there should be little load on the rudder as there is little drift backwards. Correspondingly though, the loads on the line and bridle are massive.

MedSailor


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