Choosing The Right Spearfishing Float For You – Advanced
We have already written an article going over the different methods of construction of spearfishing floats. This article is more designed to elaborate on the technical benefits of displacement and how to choose the right size float for certain species. Unfortunately there is no ‘perfect float’ out there that will land everything from small fish to world record tunas or marlin. This article will help you better understand how to build out your perfect spearfishing rig for several different targeted species and diving styles. Here are some of the technical aspects on choosing the right spearfishing float for you.
Considerations in Picking The Right Float
There are several considerations on how to pick the right float for your spearfishing trip. Most of them pertain to buoyancy, whether that be the negative buoyancy of the fish, or the positive buoyancy of the float. Other considerations include the amount of drag, and the subsequent back pressure that causes on the fish. When it really comes down to it you are just trying to balance these factors.
Negative Buoyancy Considerations
Fish are negatively buoyant when they die, especially if their swim bladder has been punctured. At the very minimum you will need a float buoyant enough to float your equipment and the fish once it had perished. How do we determine how much buoyancy we need to have for any given fish? Typically fish have a negative buoyancy of 10-20% of their total body weight. That means a 220 lbs (100 Kg) Tuna may have a negative buoyancy of 44 lbs (20 Kg). So at the very minimum we need to displace at least that much saltwater to have the spearfishing float make your fish float.
The Math on Buoyancy for Spearfishing Floats
The Encyclopedia Britanica defines buoyancy as “any body completely or partially submerged in a fluid (gas or liquid) at rest is acted upon by an upward, or buoyant, force, the magnitude of which is equal to the weight of the fluid displaced by the body”. In simple terms that means a 12 liter float displaces 12 liters of water. It has the buoyant force of that amount of water. Because the world of spearfishing is divided between Standard (American) measurements and Metric (The rest of the World) I will describe both.
Salt water is denser than fresh water as a result of salt and other particles in it. That means one liter of salt water weighs more than one liter of fresh water. One liter of fresh water weighs approximately 1.025 Kg. So a 12 liter foam filled hard float will have the buoyant force of 12.3 Kg. That means you may need more than one float to ensure large fish will be brought up to the surface, if you are targeting those kind of species. Most 3 ATM floats claim to have displacement of 25.5 Kg up to a depth of 20 meters. This makes these floats the perfect second float attached by a bungee to a hard float for those large pelagic species.
Standard is a little more complicated to measure because of conversions. 1 Kg is 2.2 lbs, so a liter of salt water at 1.025 Kg is 2.255 lbs. That means a 12 liter foam filled hard float displaces 27.06 lbs. That means you may need more than one float to ensure large fish will be brought up to the surface. Most 3 ATM floats claim to have displacement of 54 lbs up to a depth of 66 feet. This makes these floats the perfect second float attached by a bungee to a hard float for those large pelagic species.
Amount of Drag and Back Pressure
Beyond buoyancy we have to consider the amount of force these fish create when they run. All spearfishing equipment has failure points. In order to land large pelagic species we have to do our best to prevent gear failures. The best way to do this is to distribute the amount of force as evenly across all of our equipment. Fish will try and often succeed at submerging spearfishing floats. That is the ideal situation. If we just had massive floats the fish would sound or run and effectively hit a wall and tear the spear shaft or slip tip out of its body when it hit the end of your floatline. It takes the amount of force or weight that the float displaces in order to pull the float underwater.
We use bungees of various lengths to allow gradual pressure to submerge a float rather than the fish hitting the float statically. With some species it is best just to use a long bungee as a floatline. Examples of this are tuna and marlin. Other species a bungee incorporated into the floatline works just as well, like wahoo and amberjack.
All of these considerations can be difficult to manage on blue water trips. Some trial and error is bound to happen. The best advice is to talk to people that have done the trip before, or at least similar trips to help cut down on the learning curve. Hopefully this gave you some insight on choosing the right spearfishing float for you.