Sunday, March 13, 2011
Hawks Channel & The Fla Keys
We departed Ft Lauderdale and traveled south via the ICW, it was way too rough on the outside for a comfortable passage. Winds were out of the N/NE 15-20 kts and building, this close to the gulf stream winds in opposition to the 2-3kts gulf current can give big steep waves close in.
The inside run is certainly stimulating with much to see and lot's of activity. Tedious because of so many "go slow" manatee zones and bridges. You can count on it taking twice as long as it should. We had a worry at the intersection of the ICW and Haulovers inlet. A notoriously skinny spot, which we were relieved to find had just been dredged. The last time we went through this area there was a TowBoat US and Seatow on site knowing that inevitable groundings would occur. For some a bad day for others a rather good living. We crossed without incident but held to the greens which had a tad more water and a softer sandy bottom. The reds have rocks near them and the winds were blowing such that you were being pushed towards the reds & out of the channel and we needed to compensate.
Our plans were to anchor all the way to KW, with the first anchorage in Key Biscayne.
This was also the first anchor attempt with the new Rocna 55. Our initial and every attempt since has been met with fast setting and great holding. Our last anchor, a CQR would take 20-30ft and sometimes up to 60 feet to set properly depending on the bottom type. While the Rochna would almost set where it first lands. Quite an improvement.
We did not have really strong winds, rather an average in the mid teens most nights. Retrieving the anchor was straight forward but it did bring up a bit of the bottom with it, which was strangely reassuring to me to see how well it had set, buried might be more apt. On our first retrieval we found an old phone handset in the muck with a cord & plug, including a sea slug. Quite a trophy. The waters were clear and beautiful and we cooked dinner on the grill, enjoying the tranquility of the setting.
When we anchor at night we set an anchor watch. Which is a common feature of chart plotters, we have 3 separate for redundancy. We mark our location and draw a radius around the boat. If we were to slip anchor and drag outside of that radius an alarm will sound to alert us. Been there and done that in high winds & it is not fun. We set up a baby monitor in the pilot house and the other in our stateroom to be certain we would hear it. The display also shows, as a track, how the boat moves while at anchor making it easy to see how the boat moves as it is pushed by winds or tides. We ended up with a nice tight arc. Both reassuring and helps make a quick assessment of how we are doing. And of course we always set our snubber lines to take the stress of the anchor windless and it is much quieter. This is an interesting picture in that it shows the snubbers taking the strain and the slack chain going aft to the bow pulpit. Also it shows how well the anchor is set because as the wind blew, the chain came out of the water during a gust as the boat pulled against the set anchor. In this picture we were in 8' of water and had about 110' of chain out.
Some confuse scope as meaning chain from bow pulpit to sea bottom, that would mean in 8' of water would be 56 ft of chain/line which would be incorrect for a 7:1 scope.
L= length of rode from anchor ring attached to the anchor to the bow pulpit,
d= from the water line to the bow pulpit
D= water line to the bottom
For example in the case of 10 ft depth and 110 ft of chain is deployed, assuming the bow pulpit on Seabright is 10 ft above the water line:
110/10+10 = 5.5 scope
Minimum scope on an all chain rode is 4:1 solving backwards that would be a total of 60 ft of chain. For a 7:1 would be 140 ft
The holding power of an anchor is highest when the force on the anchor shaft is horizontal and weakest when it is vertical. Chain gives more pull down on the anchor shaft, keeping it horizontal than rope and is therefore preferred.
Min anchor rode is 4:1 for all chain rode and 10:1 all rope, combo is 7:1.
Chain however adds nothing to the shock absorbing capabilities like rope and once stretched taut and it can be broken, a very good reason for snubbers or additional anchor in a really bad storm.
Posted by John and Jeannie Coyle at 7:46 PM