What jet pump should I order?

The size of the boat, the loads you carry on an average trip, the type of water you primarily run in and the level of performance desired should factor into your choice of pumps.

American Turbine SD 309 – Small Block 350

This is a good performing pump for boats 18′ – 21′ in length and primarily carrying lighter loads (2-4 people + day gear) in deep water.
Engine Recommendation:


  • Lowest Cost
  • Fastest Top Speed


  • Stock aluminum impeller is prone to damage from debris
  • Debris lodged inside pump tends to hamper performance
  • Inferior slow speed control compared to higher volume pumps

Hamilton 212 – Fuel Injected Small Block or Big Block

The most appropriate choice for boats 21′ – 35′ in length which carry heavy loads (6-8 people + gear) in a variety of water conditions.
Engine Recommendation:


  • Superior load carrying capabilities
  • Excellent slow speed control and reverse
  • Stainless steel impeller for superior durability
  • Lower cruising RPM (better fuel economy)


  • More costly than other choices

What is cavitation and or ventilation?

As a shape passes through water at an increasing speed, the pressure that holds the water to the sides and back of the shape is lowered. Depending upon water temperature, when the pressure reaches a sufficiently low level, boiling (the formation of water vapor) will begin, The collapsing action, or implosion, of the bubbles releases energy that chips away at the blades, causing “cavitation burn” or erosion of the metal.

The initial cause of the low pressure may be nicks in the leading edge of the impeller resulting from debris passing through. Massive cavitation by itself is rare, and it is usually caused by an impeller that is severely bent or has had its blade tips broken off resulting in an impeller far too small in diameter for the engine.

Ventilation, often mistaken for cavitation, occurs when air from the water’s surface or gases from the exhaust outlet are drawn into the impeller blades through the jet intake. The normal water load is reduced and the impeller over-revs, losing much of its thrust. This action most often occurs when turning, particularly in conventional aluminum jet boat hulls (not using a reverse chine). Ventilation can also be caused by aerated water from extruded chine hulls and simulated reverse chines by welding 1?x3? angles along extrusions. Thunder Jet’s Exclusive Reverse Chine Hull allows for less impeller ventilation than these conventional hulls.

How does weight distribution affect performance?

Weight distribution is extremely important to boat safety as well as performance. Weight can affect a boat’s running angle, attitude, performance and ride. For the best top speed with a moderate to fast planning boat, passenger loading in most cases should be evenly distributed. Each boater should seek out what weight locations best suit his or her needs. Always remember that weight distribution is not strictly confined to fore and aft locations, but also applies to lateral weight distribution.

How does altitude affect performance?

Altitude has a very noticeable effect on the wide open throttle (WOT) power of an engine. Since air gets thinner as altitude increases, the engine begins to starve for air (oxygen) and horsepower is lost. If the boat has been set up at a lower altitude and then moved to a much higher altitude, there will be a noticeable reduction in power. All Thunder Jets are available with port fuel injected motors. This, combined with our efficient reverse chine hull, will usually solve any altitude problems.

How does climate affect performance?

Summer conditions of high temperature, low barometric pressure, and high humidity all combine to reduce engine power as much as 15%. This, in turn, is reflected in decreased boat speeds of (in some cases) 3 -5 miles per hour. Nothing will regain this speed for the boater except the coming of cool, dry weather.

How should I maintain and service jet pumps?

Essential to good Jet Drive maintenance is periodic inspection and lubrication to the jet’s thrust bearing. If you boat in shallow and silty waters, you may want to inspect your pump more frequently for excessive wear. Always remember to refer to your maintenance manual for proper lube and maintenance of your jet drive.

Why is the stainless steel on my boat rusting?

Stainless steel is just as its name implies – it “stains” less than normal carbon steel. Only the highest quality stainless steel available is used on Thunder Jet boats. Rust can occur under numerous circumstances, including polluted water and galvanic corrosion. The rust can be removed with rubbing compounds. A scotch-brite pad is OK, but do not use steel wool.

Why do most boats drive from the right side?

Nearly all recreational boat manufacturers place their operator’s position on the right-hand side and use right-hand rotation propellers to compensate for the boat roll resulting from propeller torque. Jet pumps do not produce boat roll, therefore Thunder Jet is simply following the “right” tradition.

What affect does trim have on boat performance?

The trim angle of a boats drive has a distinct effect on the planing angle of the boat, which significantly alters top speed and handling. The engine/jet drive should be trimmed in at the factory for best start-up acceleration and shortest time to plane. If trimmed “in” (under) too far, the bow drops and the boat runs too wet. In this condition, top speed drops, fuel economy decreases, and the boat may over-steer in one direction or the other (otherwise known as “bow-steering”).

If trimmed “out” too far, the jet may lose its hold on the water. In conventional extruded chine hull designs, the boat may start to “walk” from right to left to right, etc. (“chine walking”), and getting on plane may be difficult or labored. Porpoising may also occur.

Why do I need a tachometer?

A tachometer (“tach”) measures engine RPM’s. An engine is designed to run at certain RPM limits. Without a tachometer, the operator has little opportunity to know if the engine is at a dangerously high or low RPM level. Any deviation from the established RPM levels other than those associated with climatic conditions, elevation, or gross load changes, is an indication of a possible performance problem.

What is marine fouling?

Fouling is a kind of unwanted build-up (usually animal/vegetable derived) occurring on the boat’s bottom and jet drive. Fouling creates additional drag, which reduces boat performance. In fresh water, fouling results from dirt, vegetable matter, algae or slime, chemicals, minerals and other pollutants. In salt water, barnacles, moss and other marine growth often produce a dramatic build-up of material rather quickly. So it’s important to keep the hull as clean as possible in all water conditions to maximize boat performance. Severe cases of bottom fouling can prevent planing by adding too much drag.

How can I protect my engine from corrosion?

The leading cause of corrosion damage is galvanic corrosion (the electrochemical interaction between different metals). It is most hazardous where drive units are immersed in salt water, brackish water and many inland waters with high conductivity caused by pollution.

The corrosion reaction occurs when electrons flow between dissimilar metals connected or grounded through water. In the process, one of the two metals is eaten away. The damaging corrosion can be eliminated by providing sacrificial metal-zinc which will preferentially corrode to protect the drive unit.

Sacrificial anodes are installed at the factory by the engine and jet drive manufacturers that Thunder Jet uses. Additional transom mount zinc anodes are available for optimum protection, if deemed necessary. The anode’s main purpose is for corrosion protection. By their very nature, they deteriorate very rapidly and must be constantly inspected and regularly replaced if you are an avid salt water boater.

How will salt water affect my boat?

The use of marine grade aluminum, zinc anodes, and freshwater cooling in combination with respected name brand components such as Faria, Morse Controls, Detmar, PPG, Heatercraft, Lawrance, Redline Marine, Marine Power Corp, Hamilton Jet, Guest, Teleflex, Mecury Marine – to the premium grade materials such as “rot not” treated marine wood products gives Thunder Jet boats as much salt water protection the industry can offer.

What is a reverse chine?

Unlike typical extruded chine construction that most aluminum boat manufacturers utilize today (a displacement hull that simply pushes water out of the way), Thunder Jet’s exclusive Reverse Chine Hull utilizes the energy available in the bow spray to create lift beneath the hull. This will cause the boat to achieve quicker planing speeds and have superior performance characteristics. What happens is that the hydrodynamic forces overcome the static buoyant forces sooner and the hull reacts by moving forward and up out of the water, reducing draft and creating less drag. The smooth flow of water generated by this design allows more water into the jets intake during both straight line speed and hard cornering maneuvers. This increases fuel economy. The reverse chine also will not allow the rear end slide (typical characteristic of extruded chine hull boats).

What type of aluminum is used?

All Thunder Jet boats are constructed with 5086 H116 and 5052 H32 corrosive resistant marine grade alloy.

How much gas will my boat burn?

Although mile per hour numbers are usually how boats are judged, Thunder Jet has taken the time and energy to convert the savings by using our Exclusive Reverse Chine Hull vs. the typical extruded chine aluminum hull into actual dollar savings at the gas pump. Depending on the models/brands used for comparison purposes, Thunder Jet claims to save boaters with standard 5.7 Liter Jet Drive power as much as $600 -$900 per year (based on 100 hours of operation). These savings increase the more hours you boat.

What purpose are the planing strakes?

At planing speeds, strakes serve several purposes. Primarily, they provide additional lift, acting somewhat like an extra chine and helping to get more hull out of the water. This reduces drag and increases overall performance. Strakes also tend to break up the flow of water beneath the hull to eliminate some of the surface tension that develops between the water and the bottom and help the hull to track well through all speed ranges.

What is the difference between an axial and a mixed flow jet pump?

Mixed flow (pressure) pumps such as the American Turbine, Legend or Berkeley, draw water in through the intake in the bottom of the boat, compress it and discharge the water through a small diameter nozzle at very high pressure. Generally single stage (1 impeller) and produce the fastest top speeds.

Axial flow (volume) pumps such as the Hamilton or Kodiak 2 and 3 stage draw water in through the intake in the bottom of the boat and accelerate it through chambers that remain a constant size in diameter. The water discharged through a nozzle at higher volume and lower pressure than a mixed pump. Generally have better load carrying capabilities than mixed flow pumps.

What type of top should I order?

If you want to maximize versatility, a folding top is the best bet. It provides good weather protection but is a little noisy on a windy day. In just a few seconds it can be folded up or taken off to enjoy the sunshine or provide more fishing room.

If you want maximum weather protection, a hard top with sliding windows is the way to go. Boats with hard tops (cabin style) are very popular in the Northwest where the weather can change from fair to mild to wet and windy in a few short moments.

A good compromise between the two is a fixed frame canvas top. It provides good weather protection yet does not add the weight or expense to your boat.

What size boat should I order?

You should always consider a boat slightly larger than what you think you need. 21′ is a very popular size because it is large enough to carry a sizeable group (up to 8 people quite comfortably), yet is highly maneuverable and easy to trailer. Buying too small of a boat often results in an upgrade the following season.

What type of engine compartment should I order?

A 1/2 Deck is similar to a Dog House in that it has a padded motor cover to sit on, but it also has storage compartments on either side of the engine cover and taller side rails for protection. You stand approximately 10? off the floor on either side of the engine.

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