OK - we have two numbers being calculated (thanks, Andy)
Required rode length = (Depth of water(t) + height of cleat)* (Scope Factor)
Where Depth of water(t) is a function of time (ie tides)
Scope factor = 7:1 recommended, 3:1 often practical limit
Swing factor = Length of rode+chain+height above waterline of cleat (approx) + 25 feet 10 inches ( )
Note that as the tide goes down your swing radius will increase ....wonder how you work that one in??
>> It is amazing isnt it.....Chapmans says 7:1, but in a crowded anchorage 3:1 is 'acceptable - its a wonder we dont hear more stories of loose boats at anchor and collisions.
Shameless pitch for the Bullwaga anchor Ive used for several seasons in grass, muds, rocks, and sand with very good results.
Cuttyhunk MA is the most crowded place I have anchored for a week - but Ive found that magical 3 foot depth in the back of the pond that no one else can get into...
Chain on your rode is counted when you calculate the recommended 5:1 or 7:1 scope. I can't recall for certain but I believe Chapman's recommends a minimum of 10% of your maximum rode length be chain. More chain is better only up to a point. Chain does not absorb shock as does nylon rode. It's heavy to haul and store as well.
The formula given which adds in the length of the boat is for calculating rode length, not total swing. Total swing is not a particularly useful calculation. It's only good to determine the likelyhood you'll hit a stationary object or a boat tied to a mooring ball. In a normal anchorage, you must assume that when your boat swings, the other boats will as well, and under this assumption it's typical to anchor closer to other boats than your total swing would indicate. If you don't, and assume there must be clear area for the entire radius of your total swing, there won't be room for you in many anchorages. If you're by yourself, go right ahead. Otherwise, don't.
The Mac is notorious for sailing at anchor and you must take that into consideration when calculating how close you can anchor to other boats. I use an anchor riding sail to reduce this effect, and depending on whether wind or tide induced, it makes my boat lie at a different angle to the anchor than most other boats. This figures in to my proximity calculations as well.
Interestingly, I have never seen anyone use the famous, two anchor Bahamian moor in the Bahamas, nor in the FL Keys for that matter. In fact, anyone who uses one would probably be considered a moron and can expect to have another boat crash into you when the tide reverses and every other boat in the anchorage swings, but yours doesn't.
I've never heard of not adding in the height of the cleat above the water and instead using the rode length mark to where the rode enters the water. It could work in dead calm water where the rode enters at a fixed and constant angle, but in heavier weather wherin the boat is bouncing and sailing as you're attempting to anchor, it's not possible, nor will it work if there's slack in the rode. The calculation is no easier either way and it's real easy to simply cleat the rode at the mark, so what's the point?
You back down on your anchor "gently" as stated above only to take up the slack. Actually setting the anchor requires serious pull. Based on their more conservative HP to size ratio, it is recommended that most sailboats set their anchor at or near full reverse throttle, for 30 seconds to a minute. For a 50HP Mac, that could be considered overkill, but "gently" simply won't do it for setting. BTW, it's also recommended that you let out full scope of 8:1 or even 10:1, back to set, then shorten the rode as necessary to put the boat at 7:1 or where it needs to be.
BTW, it's also recommended that you let out full scope of 8:1 or even 10:1, back to set, then shorten the rode as necessary to put the boat at 7:1 or where it needs to be.
And another addition - Ive read in logs that you set at short scope and then let out to longer scope - a procedure which makes no sense to me whatsovever (ive posted this question here too)
I set at long scope and shorten to the scope required by the mooring field as Chip notes above.
Catigale wrote:Shameless pitch for the Bullwaga anchor Ive used for several seasons in grass, muds, rocks, and sand with very good results.
Cuttyhunk MA is the most crowded place I have anchored for a week - but Ive found that magical 3 foot depth in the back of the pond that no one else can get into...
Okay, so I googled Bulwagga anchor and found it. Most interesting anchor. Gets great reviews and apparently the thing is fantastic in grass. http://www.navstore.com/bulwagga.aspx
The video clip where they demo it is on the beach in sand. It would be great as a shore anchor as well.
Nice tip. I may have to get one of these things.
I've never been to Cuttyhunk, but Naushon Island was very quiet when I was there. We went ashore to be met by a man on horseback explaining that it's a private island (owned by the Forbes family) and we were free to use the beach, but not to come inland. It was the darkest place at night that I've even been in my life. So magical.
One of the selling points of the Mac was it's shallow draft and ability to get into places others can't.
Tarpulin Cove is where we spent a couple nights last summer - indeed, beach is public, politely signposted that the rest of the Island is off limits.
Bullwagas are pricey but I have been happy with mine. You could fab this yourself if you are torch handy, but I not unhappy the large gross margin on my anchor went to support a local company in upstate NY <std.io.disclaimer=I have no financial interest in this company>
As catgale mentioned in an earlier post,i go with an anchor drag alarm,i have a navman chartplotter and its got the facility
Ive gone for overkill on the anchor and chain but i still like to have a backup,i sleep heavy,so im fitting a buzzer to my chartplotter,if my boat moves i want to know
bastonjock wrote:As catgale mentioned in an earlier post,i go with an anchor drag alarm,i have a navman chartplotter and its got the facility
Ive gone for overkill on the anchor and chain but i still like to have a backup,i sleep heavy,so im fitting a buzzer to my chartplotter,if my boat moves i want to know
I sleep heavy as well. Maybe I could fit electrodes to my body instead of a buzzer.
That Bulwagga anchor looks like a good investment. Storage might not be as simple as a danforth in the locker, but for something that works well it's worth it.
Fabricating one isn't worth it IMO. The designer has tested this well and knows the exact specs. A genuine unit will be zinc coated and I believe in supporting good ideas. It's only 2 1/2 boat bucks. For peace of mind, it's a good deal.
On the original post I overstated the primary anchor weight, it's a 13 lb. danforth. But it's the biggest one that fits the M anchor locker. I had a mud bottom. Looks like the anchor(s) pulled on the tidal swing and the flukes were packed with mud when I pulled them up to reset them. I set the primary anchor by backing down and the smaller one by yank and pull till it bit solid.
My position and the small number of boats on the hook makes me not a problem on my swing cirlcle with 100 feet of rode. I am probably at least fifty yards away from the closest boat on a 360 swing.
I put another anchor out aft and it held good last night with similar conditions. Originally, I had had two anchors on the bow about 45 degrees apart and that's when she drug. She drug a little then bit down and held about fity feet from her original anchor point.
I thought my original anchor plan was overkill for the situation. I don't think I would anchor this way if I expected winds over 10 knots.
O.25 boat bucks for the Bullwaga, unless boat bucks have been dropping like the greenback
Seriously, I believe a boatbuck is 1000 USD as used here...as in
Break
Out
Another
Thousand
>> I dont think hand setting an anchor is prudent - you need some HP to dig that anchor in, then make sure it is holding by watching some marks for some time. I pulled into the Great Harbor in Woods Hole MA last summer in 20kts, with just me and the girls on board, and had to anchor to windward of the mooring field in 8 feet at high tide. I only had room for 3:1 scope. I wasnt happy. Luckily its a sandy bottom where the Bull excels. Caitlin took the helm, I went forward, lowered anchor and laid 15 feet of chain and 20 feet of rode, cleated off while the boat blew back. The boat jolted to a stop as the Bull dug in - took the revs up to 3000 and the boat didnt move - counted to 5 slowly. We spent rest of the day on that hook with no problems.
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of the mooring field in 8 feet at high tide. I only had room for 3:1 scope. I wasnt happy. Luckily its a sandy bottom where the Bull excels. Caitlin took the helm, I went forward, lowered anchor and laid 15 feet of chain and 20 feet of rode, cleated off while the boat blew back. The boat jolted to a stop as the Bull dug in - took the revs up to 3000 and the boat didnt move - counted to 5 slowly. We spent rest of the day on that hook with no problems.