For example, a 16ft Scarab jetboat weighs 1600 lbs.
One of the most important things boaters should know before setting out on the water is the maximum amount of weight and the maximum number of people your boat can handle safely. This is not just an important safety concern, but it is also the law. All powerboats less than 20 ft in length are mandated by federal law to carry this information in the form of a Capacity Plate. A capacity plate includes information on the maximum gross load, the maximum number of adult persons and the maximum engine size that the jet boat can legally carry. The capacity plate is usually permanently fastened to the helm or near the steering area.
Before going on any boat trip, it is important to ensure you aren’t taking more people than indicated by the maximum person number on board and the total weight is not more than what is indicated in the maximum gross load.
In the event, your boat does not have a capacity plate; you can simply calculate the maximum number of people you can take onboard safely using this equation.
Vessel length (ft) x vessel width (ft) ÷ 1.5 = Number of people
Beyond that, the capacity plate usually also show your jet boat’s maximum engine power.
Maximum Person Capacity
Jet boat manufacturers generally consider several variables when determining what appears as the maximum person capacity on the capacity plate. The weight of each person is one of those variables. Typically, boat manufacturers use the average weight of about 150 pounds/person to calculate the maximum capacity. This can be a little more or a little less, but if some or all of your passengers weigh over 150 pounds, you may have to decrease the number of passengers you take onboard. You may have to reduce this number further if you are carrying heavy equipment.
If there is no capacity plate on your boat, you can calculate the engine size in the following way.
Boat square footage = Boat length x boat width
You first need to find the square footage of the boat by multiplying the length by the width. For instance, a 12-foot boat with a 4-foot transom width will have a maximum horsepower of 15.
Overpowering or Overloading
Overpowering or overloading your boat is very dangerous. Putting an oversized engine on a jet boat can cause it to sit too low in the stern, thus making it more susceptible to getting swamped by a passing boat or even its own wake. Also, it is hard to control an overpowered jet boat. Overloading the boat with either too many supplies or too many people can also make the boat susceptible to swamping. It is important always to ensure that you that you distribute the weight evenly even if you are within the maximum allowable weight. You should as much as you can to focus the weight in the middle of the boat. This will help to keep the boat stable in the water and prevent it from swamping or capsizing.
Finally, in bad weather, you should exercise extra precaution not to overload the boat. Higher waves make it harder to control the boat, and they are more susceptible to swamping. Always adjust for bad weather and follow the above guidelines for load capacity. Take lighter loads in poor weather conditions to ensure your jet boat’s stability.
Jet Boat Cooling System
In recent years, there has been a lot of misunderstanding and discussion regarding the best method to keep a boat engine cooled and plumbed properly. This article will attempt to explain the solutions to this common problem in the simplest way possible.
Problems with Jet Boat Cooling
There are several problems with the cooling system design of jet boats that have come to light over the years.
Most jet boat engines run too cool to perform optimally
There are some set-ups that are prone to excessive water pressure issues in the engine block. This is because of the high pressure that is taken from the jet drive to the cooling system.
Jet boat models with water injected headers often have the problem of using excess water which may end up contaminating the crankcase oil.
To solve these problems, it is important to understand how these jet boats are plumbed from the factory and how the set-ups of the factory are meant to work. You can regulate the engine temperature by using a bypass thermostat kits available on the market. The cheaper one is made of aluminum, and the more expensive one is made of stainless steel. They both work well with Chevy and old engines.
Once you have addressed the temperature issue, the next problem to resolve is the high coolant. If you have a blue-printed jet drive with a high RPM range at high speed, then the likelihood of having excessive pressure in the block is increased. An average jet drive can build pressures of up to 150 psi, but the jet boat cooling system is designed for a maximum of 22 to 25 psi. Excessive water jacket pressures can cause an intake of manifold gasket problems, head gasket, and water in the oil.
There has been a lot of debate over the years on how to deal with the problem of high coolant pressure, but the solution is quite simple. You should dump as much water out of the engine as you dump in it. If there is still too much pressure, you can install a pressure relief system that can help to reduce the pressure before water enters the engine. Most times, the problem of high water pressure in the engine block becomes a problem if you set the jet boat up with water injected headers.
To resolve high water pressure in the engine block, you can change some factory plumbing. You first need to take the waterline that feeds the headers from the thermostat housing and put it aside. Now add a new dump line hose and put a fitting on your thermostat housing that feeds the header. Run this line to the back of the transom so you can connect it to a new dump fitting. Get rid of the valve on the original dump line and put it aside. You should have two dumps and two inlets on the system at the end of this. The pressure on the engine block should be greatly reduced after doing this.
These are in my opinion the basic solution to most of the jet boat cooling system problems for an average boat.