With all the engineering tools at our disposal we still use gut instinct, based on years of experience, to size ground tackle systems. The wind speed graph above provides a glimpse at one end of the benefit spectrum. Grey Wolf II is cruising in Tierra del Fuego at the bottom of the world, and recently experienced wind gusts in excess of 100 knots, more than 116 mph, at anchor.
The screen shot above followed a message from Peter Watson aboard his FPB 78-2 Grey Wolf II to FPB 78-3 Iron Lady II, also cruising in Southern Chile: “Pick your anchorages with care. We had 100 knots at anchor last night in gusts. We were in 15m with 90m of anchor chain out. Dashew anchor good!!! Bit bumpy but safe.”
The Manson Supreme anchors aboard the FPB 78s are 150kg/330 lbs, connected with 12mm/15/32″ chain. Adding the height of the bow to water depth (15m depth + 3.3m distance of chain roller off the water) is a scope ratio of 90/18.3= 4.9 to one.
In more benign conditions this setup can be used with much less chain veered, resulting in a smaller risk of fouling and dramatically reduced swinging room.
Our old scientific proof of anchor suitability still holds. To wit: if the experts in your marina laugh at the excessively huge anchor on your stem, you know you are on the correct path.
When you see these anchors in their chocks the size is not immediately apparent. But with a model for scale you can see the FPBs use BFAs…
For more details on our anchoring system logic click here.
And for data on FPB 78-1 Cochise at anchor in 75 knots of breeze click here.