Frequently Asked Questions
 
1.   Do I need to order spare blades?
    You can order a full set of spare blades (10) for a remarkable low price, if they are ordered at the same time you order your prop. This program gives the yacht owner the equivalent of four props at a competitive price to the best metal. Imagine traveling with your spare props in a sac or box. Blades weigh around 5 lbs. each for a 80' yacht.
2.   How much do extra blades cost?
    Extra blade sets (5 blades) are approximately 1/3rd the price of a new propeller.
3.   How do Contur® props react to impact injury?
    Whether you run aground or hit a submerged object the Contur props do not bend. Portions of a blade make break off and leave the remaining blade to propel you safely home.
    Example:
Damaged carbon fiber propeller This vessel accidentally ran aground, but continued to operate for a further 1800 miles without realizing that the propeller blades had been damaged - the Skipper only wondered why the speed
had dropped off.
 

These broken blades will get you home without shaking your boat apart!
4.   What is cavitation burn?
    Cavitation is caused by turbulent water impacting the prop hub and leading edge. These photos demonstrate the deteriorating effect of CavitationCavitation Burn Burn eating away at the bronze base of the prop blade.
Carbon fiber props can be designed to minimize this effect, however analysis of the boats bottom and the cause of turbulent flow is equally important. Boats cruising at 25+ knots should be especially aware of their bottom configuration as blades have been known to separate from their hub as a result of Cavitation Burn.
5.   Absorbing the Energy of Cavitation
    Numerous methods of handling the energy of disintegrating cavitation bubbles. "Here is a method of absorbing the energy ideally suited to Contur props since it can be applied in the mold."  (See video and power point)
Cavitation Video                    Cavitation Power Point Presentation
   
Get Windows Media Player 10 Get Microsoft Power Point Viewer
Get Windows Media Player 10 to view the video above. Get Power Point Viewer to view the Contur Prop Presentation.
    What kind of blade injury can be repaired?
   

Carbon Fiber Propellor Blades
Superficial injury that does not involve
the carbon fiber. The special epoxy
coating is impact resistant.

 
6.   What other advantages of impact injury over metal?
    The blades are light weight and elastic. They take the impact force usually sparing the shaft and transmission.
7.   How do Carbon Fiber Props result in better fuel efficiency?
   
This chart demonstrates carbon fiber props. Because carbon fiber props are flexible and custom designed for your boat, they approach the ideal load for each RPM. Note on the graph the difference in height between the red & green graph. That difference is the increased fuel efficiency. i.e. Greater torque using less fuel.
8.   How large can a composite prop be?
    The largest propeller ever made is one of Carbon Fiber Composite. The 2.9m diameter composite propeller is on the RV Triton triple hull warship.
9.   Why are the small size props so expensive?
    These are custom made props and the set up costs for a small prop is virtually the same as a large one. Multiple identical props do reduce the costs. Several owners with identical hulls and power could combine to purchase several sets thereby reducing set up costs.
10.   Do I need to put antifouling paint or prop-speed on the props?
    We do not recommend any other coating. The polyurethane paint is not conducive to barnacle attachment and marine growth can usually be wiped off with a gloved hand. Light sanding and repaint, brush, roller or spray is recommended at the time of hauling for a bottom job.
11.   After ordering, how long will it take to get my props?
    Our standard delivery is approximately 8-10 weeks. Please note that propellers are manufactured in Germany and we have a great relationship with customs, but cannot control their time frame.
12.   What if I can't get all my measurements?
    We are here to assist in any way that we can and if at all possible we can assist you with the measurements and accompany you on a sea trial to help you gather your performance information.
13.   Can the blades be changed underwater?
    Yes  
 
 
 
 
14.   Will I still be able to use my boat if I damage a blade?
    Yes, you will be able to get home or to a convenient place for a diver to remove the prop for repair or blade replacement. Running with damaged blades will not extend the damage.
15.   Can I use my present metal props as spares?
    Yes, but if you change one, be prepared to notice a tendency to turn away from that side because of increased efficiency of the Contur propeller. (US Naval Academy project - two identical props, one Carbon, one Bronze, had trouble keeping a straight course).

   
16.   Industry Competition?  
    Many companies are working to develop Composite Propellers. To the best of our knowledge, Contur Props are the only inboards with replaceable blades. Contour is the only one certified by Lloyds Shipping, ISO 9002 and in use on civilian yachts and large military vessels including submarines.
17.   How does the shaft and strut position affect water flow?
   
18.   Characteristic Comparison Table
    Bronze vs. Carbon Fiber Propellers
   

Style

Bronze

Carbon Fiber
     
Cost
    

Initial cost

  

Quantity cost

  
     
Repair
    

Easy to repair

  

Time to repair

  
     
Characteristics
    

Weight

  

Variable pitch

  

Replaceable blades

  
Performance
    
Acceleration  
Fuel economy  
Noise  
Use in an emergency  
   

Title Explanations

Cost

Initial

Carbon fiber propellers are more expensive than bronze props for a one off application if compared on a like for like basis, but if all other factors in the table are taken into consideration future costs and savings out way the initial cost.

Quantity

During manufacture of first propeller a mould is made, this is then reused for future blade manufacture. The large the quantity ordered at one time the cheaper they are.

Repair

Ease & Time to repair

Any competent person can replace a full set of blades for 2 props within half a day.

The propellers do not need to be sent away, thereby avoiding 2/3 weeks or more out of commission. This is particularly relevant for vessel that may be chartered as a quick replacement of blades can save the loss of a charter, which in some cases can be many thousands of dollars

A quantity of spare blades can be carried for replacement of damaged blades.

Characteristics

Less weight

Blades are 70% lighter than conventional bronze propellers, this equates to less strain on the shaft, p. brackets, cutlass bearings, and gearbox. This also allows ease of manhandling

Variable pitch

The way these props work is very much like a non mechanical variable pitched prop. With a standard bronze prop the optimum pitch is at wide open throttle so as soon as you throttle down the bronze prop becomes inefficient.

Our props are at their optimum at all times, hence the flexing. They are highly pitched at the bottom end, which gives good acceleration and efficiency and normal pitch at the top end same as the bronze prop. As the pitch is the same no slippage occurs.

Performance

Acceleration

This is a notable feature of our Carbon Fiber propellers. There is less propeller weight, which allows quicker rotation, and optimum bottom end pitch.

Fuel economy

Due to optimum pitch better fuel economy is achieved particularly at 60% to 80% engine load. Normal cruising can be achieved at less RPM.

Noise

Thinner blade tips are achievable which makes the Carbon fiber propellers quieter especially if our seven bladed propellers is chosen.

Emergency usage

Even if the blades are damaged the boat can still be used, as there is no excessive vibration of a bronze prop.

Conclusion

Though the one unit cost of Carbon Fiber propellers seem more expensive than a Bronze propeller for a yacht builder, where quantities are involved, this is not the case. 

For an individual one off purchase, the propellers still have so many advantages over the standard bronze propellers that such an expense can be justified.  They provide a financial benefit immediately when the props are installed. Such improved fuel economy, resistance to impact reducing costs of repairs, reduction in repair delays, and the ability to replace the blades by a competent owner or engineer without the need to be sent away to specialist propeller shops where the turn around could be between two to three weeks.

For leisure yachts a swiftly repaired propeller can save a family vacation, which would normally have to be abandoned with much upset form friends and family, who would have taken pre booked time off work.  Similarly a swift change of blades can save a charter and the huge charter fees involved. 

In the commercial world - time laid up under repair is time and money lost.

In our opinion Carbon fiber propellers are already replacing conventional bronze propellers and it is only a matter of time before they are the first and only choice of the builder and commercial operators as well as individuals.