What Every Houseboat Needs

How one prop could change the industry

January 2016 Feature Brady L. Kay


I doubt we’ll ever see a day when people will drag race houseboats or put them through some type of a timed water course. Face it, these crafts aren’t exactly made for top-end speed and if you disagree you might not truly be in tune or be able to appreciate what the houseboating lifestyle is all about. But just because most houseboats will never be mistaken for a high-performance cigarette boat, it doesn’t mean you should settle for poor handling.

Houseboat magazine first discovered Piranha Propellers over 10 years ago while researching the best propellers in the industry. While on assignment in California I stopped by and visited with the Piranha crew and was extremely impressed with what this company was offering the marine industry at that time. Fast forward 10 years and I was once again lured back to the Golden State to test a houseboat-specific propeller that had just been released.


Piranha Propeller owners Brad and Cathy Stahl were anxious to show me how their new Reverse Thrust propeller works on a houseboat, but first they wanted to demonstrate what makes their props different than anything else in the industry.

Each Piranha propeller is made through an injection molding process and what makes the modular design unique compared to similar props is that the individual blades are designed to be replaced due to damage or to be re-pitched, while keeping the same hub. The center hub is made from a high-strength aluminum core, over molded with Piranha’s specially-formulated composite material.

The Piranha blades are designed to absorb the shock of a propeller strike, which virtually eliminates lower unit damage. The Piranha boat prop hub is so strong that the manufacturer actually guarantees it for life, which should not only interest houseboat owners, but marinas who rent houseboats as well. 

Damage Testing

The replaceable blades are manufactured from a specially formulated high-strength aerospace composite material. A boat propeller is a critical component to the performance of a boat. Damaged propellers will not only degrade performance, but can cause excessive wear on the lower unit. Spare Piranha prop blades are easily stored, and replacement of a damaged blade only takes a few minutes. With the replacement prop blades on hand, it is simple to restore a damaged propeller to factory new specifications in minutes.

To demonstrate this process, Brad set up a course on Lake Comanche in Jackson, Calif., that would allow me to feel first-hand what it’s like to break a blade or two. Can you imagine purposely running over a log just to show how easy it is to fix a propeller? It sounded like a good time to me.

Using Brad’s ski boat I got up to around 3000 rpms and drove over the top of the log and based on the immediate thumping noise I knew I had hit it good. I limped the boat to the shore and got out to see the damage. We trimmed the engine up and discovered one of the blades was completely missing. Mission accomplished!

Brad simply reached into the boat, pulled out one of the inexpensive replacement blades and in a minute had the old broken blade out and the new one in its place and ready for another run.

Being able to fix a broken propeller on the fly can be the difference between a fun houseboat vacation and a miserable one.

Thrust Test   

To run numbers for the new Reverse Thrust propeller, the Piranha team rigged up a torque system using a Jeep and Brad’s boat.

With a 15 X 15 aluminum prop, the reverse thrust measured at 265 pounds, while the new 15 X 15 Reverse Thrust Piranha propeller came in at an amazing 625 pounds of thrust, which more than doubled the aluminum. Prior to the release of this new Reverse Thrust prop, 500 pounds was the maximum amount of thrust any Piranha propeller had ever achieved.   

Onboard Testing

While the thrust numbers were impressive, we were anxious to see how the propeller would feel in a real world application—on a houseboat—so we made the three-plus-hour drive north to Silverthorn Resort in Redding, Calif. This marina has created a solid reputation on Shasta Lake by offering a wide range of rental houseboats.

We went out with Craig Lockwood, the mechanical and service manager at Silverthorn who has been on Shasta Lake for over 30 years. We were also joined by Mike Reha who is the general manager. When the Reverse Thrust propeller was first released, Silverthorn began testing the propellers on its fleet of 60 houseboats.


“One of our regular renters noticed a big difference in the speed and handling and we didn’t even tell him we switched props,” says Reha. “He spends more time on the water than I do and could instantly tell we had done something to improve the handling.”

As we headed out on Shasta Lake the difference in performance was noticeable, especially when reversing and slowing down the large houseboat.

“It stops a lot better than an aluminum propeller,” said Mike. “And that’s something I would think all houseboat rental companies would be interested in.”

As the maintenance manager, Craig sees the main advantage with saving both time and money.

“To get an aluminum prop repaired you have to remove it and take it into town to the only shop that repairs them. It’s going to take them about 7 business days and it will cost roughly $50 to $60 a prop to fix,” says Craig. “If we have 10 houseboats out, on average three of them will come back with propeller damage because on Shasta the water levels change so much. Renters aren’t typically experienced at being able to identify water hazards.”

With a Piranha propeller the labor costs go way down, so it’s more than just a more efficient propeller. In less than 5 minutes you can knock out the broken blade and swap it with a new one.

“It’s a lot more practical and cost-effective to keep spare blades on hand than a full fleet of backup aluminum props that you have to store,” adds Craig. “I could easily run out of props waiting for some to get back from the repair shop.”

Even with the well-publicized drought going on in California, there is still plenty of water to houseboat and enjoy this beautiful lake and we proved it during our test.

“There has been a lot of negativity with the drought being the biggest topic this summer, but there is still a lot of lake to enjoy,” says Mike. “Our lake is just as much fun as when it was full.”

Plant Tour

After seeing how well the props held up during our testing, I was curious to see how the props were manufactured so I concluded with a trip to Piranha headquarters in Jackson, Calif.

Jason Nakken demonstrated the injection molding process that starts with small pellets that are moisture-free when they enter the hopper. Heated pellets form in the molds and then are ejected into a pan of water where it will take the next 75 seconds or so to cool down. The manufacturer will run the same mold for up to two days before switching out and the machine runs basically five days a week from 8 am to 5 pm, although the JSW machines were built to run non-stop.

“We bought the injection molding machines used and we’ve probably put 4 million cycles on them just ourselves,” says the owner.

The raw material comes from PlastiComp in Minnesota. From the raw material to the full manufacturing process, everything is 100 percent made in the U.S.A.

“Even our mills are made in the U.S.,” adds Brad with a smile.

Next, each propeller is trimmed and grinded and de-burbed and the prop includes exhaust ports that are built into the design.

Hydrobite Blades

Hydrobite Blades are something unique you’ll never find on an aluminum prop, but with injection molding it’s possible to add three raised grooves to each blade for better control. This design has been incorporated into Piranha’s line of props, including the new Reverse Thrust prop.

Flex Fit

Designed to flex under a load, the Piranha propeller is exactly where it needs to be at the correct moment. The difference between an aluminum prop is the aluminum flexes, but it doesn’t bounce back. The highest loads on a propeller are just before the boat gets on plane, which is part of the reason the Piranha propeller outperforms a lot of aluminum props.

Brad demonstrated this by recreating the flex points with both his propeller and an aluminum propeller, both of which he took to their breaking points.

“It’s truly amazing the amount of strength you get from a composite.”

Moving Forward

In December 1989, the first Piranha propeller was displayed at the San Francisco Marine Boat Show and the company has been going strong ever since. Brad’s idea for the prop actually came from talking with his brother Eric who lives in Oregon and was always breaking props on the shallow Willamette River. Using his degree in Aerospace Engineering from Cal Poly in San Luis Obispo, Calif., Brad has taken that idea and created a one-of-a-kind prop that you truly have to test to believe. And through research, he’s created a Reverse Thrust propeller that is ideal for houseboat applications.

For those marinas tired of fixing aluminum props after renters bend them or for houseboat owners who are looking for more control, Piranha Propellers has what you’re looking for.

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