Anybody know how to figure this out
- Thread starter Scary
- Start date
The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
If you have answers, please help by responding to the unanswered posts.
Bob Cofer
Guru
On my first ship we were anchored in a 4 point moor with 10" Sampson braid rope. We snapped two of the during a heavy storm that blew in on the beam. 4 20k anchors with 12" chain on 6 ton buoys that never drug. They weren't Rockna's.
cappy208
Guru
No worry. There's 11 and a half months left to do the calculations when they will be needed.
The simple answer is: "Don't anchor where you will have to short scope (like at Mandeville) under extenuating circumstances." More is better. Heavier chain is better. Using the engine to ease the load until the anchor sets and the boat heads into the current/wind is key also.
The simple answer is: "Don't anchor where you will have to short scope (like at Mandeville) under extenuating circumstances." More is better. Heavier chain is better. Using the engine to ease the load until the anchor sets and the boat heads into the current/wind is key also.
Britannia
Wannabe
FF
Guru
- Joined
- Oct 12, 2007
- Messages
- 22,552
The hassle is it would take lots of tending to STAY at a 90deg angle to the current.
Any side loading causes the boat to move (think sailboat) which will cause one set of anchor lines to have a higher load.
Even a SQ barge will surge one way or the other.
Any side loading causes the boat to move (think sailboat) which will cause one set of anchor lines to have a higher load.
Even a SQ barge will surge one way or the other.
caltexflanc
Guru
Ok, did I miss something here? Is the OP using two anchors "bow and stern" ?
OP
OP
Scary
Guru
I was trying to discuss how rapidly we can increase anchor load,
It's all exploring how quickly anchor loads can ramp up with current, wind and way you set up your anchors. As soon as you get away from just dropping a single anchor how adding a second anchor can actually add to anchor loads. Something I hadn't really thought about. Another point I wanted to make is how rapidly current and wind velocity increase anchor loads.
It's all exploring how quickly anchor loads can ramp up with current, wind and way you set up your anchors. As soon as you get away from just dropping a single anchor how adding a second anchor can actually add to anchor loads. Something I hadn't really thought about. Another point I wanted to make is how rapidly current and wind velocity increase anchor loads.
Britannia
Wannabe
7/16" Grade 43 (G4). 350' - that's 700lb in weight (21,600lb breaking strength).
Thanks for making me check - now I know!
Richard
Last edited:
OP
OP
Scary
Guru
Britannia
Wannabe
It's an Ideal Windlass. Slow but effective. We won't say what kind of anchor is on the end of the chain...
Richard
Attachments
JDCAVE
Guru
- Joined
- Apr 3, 2011
- Messages
- 2,902
- Location
- Canada
- Vessel Name
- Phoenix Hunter
- Vessel Make
- Kadey Krogen 42 (1985)
Straightforward enough. Measure the tension with a custom tensiometer. I'm sure some engineering firm would be happy to do the study for a fee. Figure on the mid 6 figures.
Another option: contact one of the big oil companies. I'll bet they have already done fairly in depth studies on the forces of currents and waves on their moored structures.
Jim
Sent from my iPad using Trawler Forum
Another option: contact one of the big oil companies. I'll bet they have already done fairly in depth studies on the forces of currents and waves on their moored structures.
Jim
Sent from my iPad using Trawler Forum
caltexflanc
Guru
Or 0 as the case may be, and usually is. Unless of course you are trying to pull the boat apart.
Paul Swanson
Veteran Member
I thought the attached drawing would clarify the anchoring across a current situation. It is impossible to keep the boat in line with the anchors since the rode tension would be infinite. The tension can only be determined when the angle is known.
Nomad Willy
Guru
Right on Paul.
Nail on the head.
Nail on the head.
We have had to deal with this situation once a few years ago. This was a Labor Day raft of about 10 boats. The raft was set up by a fellow who is very experienced at doing this, and it was oriented to the prevailing wind. There were six anchors used: at angles off the bows and sterns of the boats next to the end boats and straight off the bow and stern of the center boat.
However, the wind shifted after the raft was set up until it was blowing relatively hard 90 degrees to the boats.
We were the upwind boat, so the "raft master" had us deploy our Fortress FX23 stern anchor 90 degrees off our starboard side from the midships cleat. The pressure on that anchor and rode was considerable but it kept the raft in place. Some of the load was picked up by the angled anchors off the boat inboard of us.
So no calculations or hard numbers, only the evidence that whatever the pressure is, it can be a lot. This was from wind, not current.
However, the wind shifted after the raft was set up until it was blowing relatively hard 90 degrees to the boats.
We were the upwind boat, so the "raft master" had us deploy our Fortress FX23 stern anchor 90 degrees off our starboard side from the midships cleat. The pressure on that anchor and rode was considerable but it kept the raft in place. Some of the load was picked up by the angled anchors off the boat inboard of us.
So no calculations or hard numbers, only the evidence that whatever the pressure is, it can be a lot. This was from wind, not current.
BruceK
Moderator Emeritus
- Joined
- Oct 31, 2011
- Messages
- 13,347
- Vessel Name
- Sojourn
- Vessel Make
- Integrity 386
Our Maritime Authority decreed fore and aft moorings, more boats in a given space = more mooring licensing fees, but there was an outcry, and some expert opposition based on the loadings imposed, it got dropped most places. I`ve seen it at Angel Isl in SF, can`t be much fun hooking up.
markpierce
Master and Commander
- Joined
- Sep 25, 2010
- Messages
- 12,557
- Location
- USA
- Vessel Name
- Carquinez Coot
- Vessel Make
- penultimate Seahorse Marine Coot hull #6
The fore-and-aft mooring in Ayala/Hospital Cove at Angel Island is designed so boats face incoming wakes (mostly from ferries) but cross-wise to the currents.
http://angelisland.org/visitor-information/boating-camping/
Raises the difficulty in hooking up, but I've always had help from a fellow TFer in a dinghy. Note current pushing boat away from the photographer:
Last edited:
Similar threads
