Originally Posted by bluewater1953
Just went from the Fortress to the Rocna. What a difference! When you shift with wind
and tide you might have a problem with the Fortress type.
That would depend, of course, on the anchor
model and bottom type. There are certainly sea bottom conditions (ex. harder soils) where a denser anchor with a narrow single
fluke will have an advantage over a larger, two fluke design. In softer soils, where an anchor can penetrate more easily, the larger surface area of two fluke offers a huge holding power advantage.
To illustrate this point, there are three holding power tests that I can immediately think of (West Marine-USA, Voile-France, Pakryss-Sweden) which were conducted in softer soils whereby a Fortress out-performed much heavier steel
anchors, including the Rocna.
Regarding the wind & tidal shift and re-setting issue, I have posted this before: It is our firm contention that a properly set Fortress anchor, with its two massive precision-machined and sharpened flukes, is not more likely to break free from a sea bottom during a wind or tidal shift than other anchor types, particularly those with far less surface / resistance area.
This contention is based upon the opinion of a 40+ year US Navy
soil mechanics and anchor design expert, the 25 years of testimonials we have heard from Fortress owners all over the world, particularly from those in our hurricane
region here in south Florida
, as well as from independent test results (Practical Sailor, Sailing Foundation).
All of that noted, we will readily acknowledge that sailboats oftentimes do not have the engine
power to back down hard enough on the more massive Fortress anchor to bury it deeply, and therein lies a key issue in how it performs (or not) during off-center loads.
Here's an interesting comment from the Sailing Foundation test, after they put 4,000 lbs of load on a 24 lb Fortress in straight line, 90°, and 180° directions which illustrates this point:
The Fortress set so deep that the rode had to be hauled in to 1:1 and significant power applied to rode by the 83,000-pound tug to break it free. It is doubtful that a sailboat would have windlass power to break it out. Perhaps large primary winches or a rising tide might be adequate. However, it is also doubtful that a sailboat could have set the anchor that deep in less than a full hurricane.
So for a sailboat, the Fortress anchor would certainly serve you well as a storm anchor when the wind force and load are expected to be extreme, and the anchor will be buried deeply as it is designed.