Boat Prop Calculation Tools

Propeller calculators are software that helps determine the ideal diameter and pitch for a specific boat motor that is put to a specific use. There are also calculators that determine the power each rotation of a propeller will provide the boat. Beyond prop selection tools like welders, polishers, sanders, hammers, screwdrivers and spanners are useful when replacing or repairing boat props.
The software available to calculate pitch or diameters of props come with a preset integrated database. They calculate the speed, slip, pitch, rpm and drive gear ratios after the required information is entered into a query section. The software has useful, ‘Help’ options and the reports given by the calculator are printable.
Calculators determine the requirements for all types of propellers. Calculations can be obtained for outboard and inboard motors, gasoline and diesel motors, 2 stroke and 4 stroke engines, 3 blade, 4 blade and five blade props, stainless steel and aluminum props and for different types of boats like flat bottomed boats, cruisers, speed boats, skiers, fishing boats and pontoon boats.
The various measurements provided by these calculators include propeller sizing, pitch adjustment, shaft tapering, slip and speed calculations, the gear ratio and rpm of the propeller. Calculators are useful modern methods of calculation with near perfect accuracy. Since calculators are computer software they are easy to use. The digital reading on calculators has made calculators even more user friendly. They help to give precise information on propeller sizing and performance.
Another useful propeller tool is the propeller scan. This is a computer based propeller inspection system. The scan reduces the time spent in diagnosing the performance problems of a propeller. The problems are quickly detected and the prop can be modified or repaired accurately. The scan gives an accurate reading of the problem and this helps to correct vibrations and slippage when repairing the prop.
The tools required for removing and repairing props are screwdrivers, ratchets, hammers and many other automotive tools. It is important to keep a spare prop for possible collisions with underwater obstacles and to learn the basics of prop replacement as a safety measure. A pair of rubber gloves is necessary when handling a boat propeller because the blades can be very sharp.
The digital age has impacted the boat prop industry and online tools are available to help boaters choose the right propeller for their unique needs, diagnose problems and repair propellers with great accuracy. For repairing and replacing propellers traditional tools are adiquite. However, experts believe that props should not be repaired by the boater. Expert technicians will have the expertise and experience in repairing the propeller to precise specifications. Boaters should carry a spare emergency propeller with the same configuration as the propeller in use and replace the propeller rather than try to repair the propeller.
A propeller having precise computer calculated specifications and fitted carefully with traditional tools to the specifications in the engine manual will give hours of excellent propulsion for the boat.

INCREASING YOUR PROPELLER’S EFFICIENCY

Typically, a minimum space of about 10% of the prop diameter is needed between the hull and the tip of the propeller blade for a displacement boat; for a high-speed planning craft the clearance should be 15 to 20 % or more. Ideally, a boat’s props should be ‘fine-tuned’ to suit the boat’s hull shape and displacement. A quick way to determine prop’s performance is to listen to the engine. If the engine cannot get to its maximum rpm, the prop may be over-pitched or oversized in terms of diameter or aggregate blade area-meaning that it is like trying to start a stopped car using the third gear.
If the engine reaches its maximum rpm easily and may even over revolution, but the boat doesn’t get to its maximum speed, the prop might either be too small or under-pitched. This is like driving down the highway in first gear. Other characteristics indicate other problems to an experienced prop mechanic. If a boat is suspected not running at its optimum, have it checked out by an experienced prop shop, which markets, repairs and tunes propellers.
If decision is made to get a new propeller, first take a number of dimensions from the boat, starting with the distance from the shaft centerline to the hull bottom at the fore-and-aft center of the intended propeller location. This dimension will tell the largest diameter prop that can be fitted to the boat. The displacement of the boat should also be known, ideally, boat condition when it’s in sailing condition, known as half-load condition in naval architecture. This means the tanks are half full, half of the stores are onboard, and all the crew is onboard.
The maximum rated horsepower are also needed, in addition to the maximum rpm speed of the engine, the reduction gear ratio, the diameter of the prop shaft and whether the prop is to run clockwise or counterclockwise.
When a prop comes from the manufacturer, it is pitched reasonably accurately but not fine-tuned. The fine-tuning is done by the prop shop along with any additional needed work such as cupping and balancing. This is to make sure to get the right prop for the boat.