If you’ve ever anchored a boat, you can likely anchor a seaplane. Some things to think about when anchoring your plane is where to tie the anchor line to, and how much “scope” to use.
The scope is the ratio between the depth of the water and rope length to the anchor (the anchor rope is also referred to as “rode” which generally means the rope and chain that connects the anchor to your boat or plane). A 3 to 1 scope in 10′ of water requires 30′ of rode (or total rope/chain length). Remember the chain gets attached to the anchor if you want to use any, and the rope to the plane. The purpose of chain attaching to the anchor is to prevent the rope from chaffing on rocks on the bottom, as well as assist with holding strength of the anchor. Generally, we use only rope, as chain is very heavy to carry in your aircraft. A 3 to 1 scope may be fine for a brief anchoring in very light wind, but depending the holding force of the anchor, and the type of bottom you are over (sand, rock, etc.) you may want to use the recommended 7 to 1 scope (70′ of rope for 10′ between your tie off point and the bottom). Note: “depth” when it comes to scope is measured from where you are tying of the rope to down to the bottom. I.e. if the water is 10′ deep and you are tying off to a cleat on the float 1′ above the surface of the water, then for a 7 to 1 scope you would need 77′ of rode to account for the extra foot above the water and maintain the same shallow pulling angle on the anchor. For this reason, anchoring in shallower water is preferable.
While lightweight aluminum anchors are great for weight and balance, they may not have the same holding power of heavier anchors. Research which anchors will work best for the bottom type you intend to anchor on.
Keep in mind the clearance you will have with other vessels and obstacles if the wind shifts as the aircraft will swing around in a large arc depending upon how much rope you let out. Be aware of the water becoming too shallow if the aircraft were to swing at anchor.
Be sure to comply with maritime rules for displaying daytime or nighttime signals such as an anchor light if remaining at anchor overnight.
It is best to have the rudder neutral and elevator down to keep the AOA low on the wing if the wind picks up. If possible, lock the controls with ailerons neutral, elevator nose down, rudder neutral.
Mooring is a bit easier since you just have to worry about reaching the buoy and tying off to it. You will still want to ensure the aircraft will not swing with the wind into a dangerous place or pose a hazard to other vessels, but the concern about holding power and scope is generally moot. When approaching a mooring buoy, always approach to the side so you do not cause damage to the propeller or the hull. It helps to have an extra person to use a boat hook or be able to stand on the float and grab the buoy. Use extreme caution if your helper is unfamiliar with seaplanes, many “good helpers” want to walk to the front section of the float to catch the buoy as soon as possible, and can easily be struck by the propeller. Ensure your helper remains away from the propeller, and if possible, drift or use a paddle to maneuver the aircraft with the engine off to moor or anchor the plane.