Aluminum Anchors provide a lightweight alternative to steel. Some, like the Fortress can be disassembled for stowage. These are reasonable factors for tackle selection. One important and less discussed attribute of these anchors is density and their actual weight under water. Design and size have much to do with the ability to set and holding power. Weight does too. A 32 lb. Fortress (FX-65) is about the same size as a 60 lb Danforth (60H). At 32 lbs. the Fortress weighs all of 19.8 lbs. when immersed in salt water. Under 20 lbs. The Danforth, being more dense as well as starting out heaver is 52.2 lbs. A Danforth of compatible dry weight, the 35 lb. High Tensile comes in at 30.5 lbs when submerged.
In some bottoms and in certain weather this may not make a big difference. If you boat primarily in the Chesapeake and ICW, smaller and lighter anchors may suit you. If you need an anchor to bite into weed, grass or hard bottom, you may want to consider steel. I am simply raising this point to, hopefully, enable better decision making.
While I discussed the Forterss/Danforth style, this goes for all aluminum anchors. They loose approximately 38% of their weight in salt water. Steel looses 13%. Subtract the percentage from the dry weight(DW) and you get the wet weight (WW). For aluminum - DW-(DWx0.38) = WW. This is for salt water which is 1.025 the density of fresh so the difference would be minimal.
I tend to run to the heavy side for a 41' sailboat. We have a 73 lb. Rocna on 3/8" D7 chain and a 55 lb. on 5/16" BBB on the bow. At the stern we have a 43 lb. Danforth with 3/4" nylon double braid. We anchor in a lot of different bottoms and in a lot of different exposures. We do sleep well at night.
All that said, choose ground tackle that you will be able to handle. If your windlass dies in a deep anchorage, will you be able to get anchor and chain back up? Make sure you try in good conditions before you need to in bad. All input is welcome!
In some bottoms and in certain weather this may not make a big difference. If you boat primarily in the Chesapeake and ICW, smaller and lighter anchors may suit you. If you need an anchor to bite into weed, grass or hard bottom, you may want to consider steel. I am simply raising this point to, hopefully, enable better decision making.
While I discussed the Forterss/Danforth style, this goes for all aluminum anchors. They loose approximately 38% of their weight in salt water. Steel looses 13%. Subtract the percentage from the dry weight(DW) and you get the wet weight (WW). For aluminum - DW-(DWx0.38) = WW. This is for salt water which is 1.025 the density of fresh so the difference would be minimal.
I tend to run to the heavy side for a 41' sailboat. We have a 73 lb. Rocna on 3/8" D7 chain and a 55 lb. on 5/16" BBB on the bow. At the stern we have a 43 lb. Danforth with 3/4" nylon double braid. We anchor in a lot of different bottoms and in a lot of different exposures. We do sleep well at night.
All that said, choose ground tackle that you will be able to handle. If your windlass dies in a deep anchorage, will you be able to get anchor and chain back up? Make sure you try in good conditions before you need to in bad. All input is welcome!