I nicked the Idasailor rudder last year while camping in Georgian Bay. To prevent that from happening again, I just fabricated a SS prop guard. $20 for 1 in x 1/8 in x 4 feet Stainless Steel and $20 for a machine shop to weld it together. I did the cutting, bending and buffing.
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Nice
I need to do something. I've seen everything from a trimmed mudflap screwed to the cavitation plate to the Powerthruster below:
I need to do something. I've seen everything from a trimmed mudflap screwed to the cavitation plate to the Powerthruster below:
Power Thrust theory
Justin, Power Trust implies they use the ducted propeller theory (see link). It was originally invented by Stipa and Kort in 1934. But the prop must be very close to the specially shaped duct to make any improvement. So don't waste your money. Power trust also place high load on the cavitation plate and may break it off. A band with support down in the bottom is a more robust construction.
Justin, Power Trust implies they use the ducted propeller theory (see link). It was originally invented by Stipa and Kort in 1934. But the prop must be very close to the specially shaped duct to make any improvement. So don't waste your money. Power trust also place high load on the cavitation plate and may break it off. A band with support down in the bottom is a more robust construction.
thanks Kaizen
My 9.9 Merc has plenty of power and I don't see the need for the Thruster. It's overkill as a propguard.
My 9.9 Merc has plenty of power and I don't see the need for the Thruster. It's overkill as a propguard.
Ducted Fan
I only know what works, and my prop guard works great. Let me be specific: it creates way more thrust than without it, it protects my rudder yes and possibly protects a swimmer unlucky enough to be in the area, and it totally protects my prop and engine from the negative effects of striking the bottom or rocks. If you have more thrust, you can back off the throttle, and that translates into fuel efficiency. (And less pollution, if you care). I drilled four 1/4 inch bolt holes in my cavitation plate, I have motored a lot since then with my ring, over Spring Break alone I motored over 150 miles on Lake Powell, and there are no cracks in the metal casting. Why don't more engines have these ducted fans? Why don't the manufacturers install them? These ducted rings are not for boats that plane, or go more than 20 MPH (from the website read). Every high thrust submersible I have ever seen had ducted fans. For our application, I can't think of a downside, can you? You can see a picture of my ring at the link below. John S Boise
I only know what works, and my prop guard works great. Let me be specific: it creates way more thrust than without it, it protects my rudder yes and possibly protects a swimmer unlucky enough to be in the area, and it totally protects my prop and engine from the negative effects of striking the bottom or rocks. If you have more thrust, you can back off the throttle, and that translates into fuel efficiency. (And less pollution, if you care). I drilled four 1/4 inch bolt holes in my cavitation plate, I have motored a lot since then with my ring, over Spring Break alone I motored over 150 miles on Lake Powell, and there are no cracks in the metal casting. Why don't more engines have these ducted fans? Why don't the manufacturers install them? These ducted rings are not for boats that plane, or go more than 20 MPH (from the website read). Every high thrust submersible I have ever seen had ducted fans. For our application, I can't think of a downside, can you? You can see a picture of my ring at the link below. John S Boise
Band width
By the way, Kaizen, very nice. What criteria did you apply for selecting the width of the band? My outboard is a mid 80's Evinrude 2 stroke. My band is about 4 inches wide. John S
By the way, Kaizen, very nice. What criteria did you apply for selecting the width of the band? My outboard is a mid 80's Evinrude 2 stroke. My band is about 4 inches wide. John S
Band width
The length of the unsupported (108 degrees) portion determines the width of the band. In other words, the larger the diameter the stiffer or wider the band. You don't need much if it is a circle because once you bend it and bolt it in place, the tension will just stiffen the band up. An archway is very strong. Unlike the Powertrust dedign which is supported on one side, it needs to be wider to provide the same stiffness.
The length of the unsupported (108 degrees) portion determines the width of the band. In other words, the larger the diameter the stiffer or wider the band. You don't need much if it is a circle because once you bend it and bolt it in place, the tension will just stiffen the band up. An archway is very strong. Unlike the Powertrust dedign which is supported on one side, it needs to be wider to provide the same stiffness.
Ducted Prop
John S, How close is the prop blade to the duct? The attached web site indicate close fit so the water don't go around the tip of the blade. The duct need some pressure differential between the outside and the inside. Do you have two bands welded together to make an airfoil?
John S, How close is the prop blade to the duct? The attached web site indicate close fit so the water don't go around the tip of the blade. The duct need some pressure differential between the outside and the inside. Do you have two bands welded together to make an airfoil?
Blade Clearance
Hi Kaizen, When I made this ring, I did not think about efficiency as much as assured clearance. My band clears by about and inch all around. I have a new band that will just clear the prop I'd like to try when I get a chance. Even with the large blade clearance I have now, the effect is really remarkable. Besides reduced tip clearance and band width, it is possible to experiment with converging and diverging ducting. My band is just a curl of metal my brother rolled for me. Besides my curiosity, I am very cheap! John S Boise
Hi Kaizen, When I made this ring, I did not think about efficiency as much as assured clearance. My band clears by about and inch all around. I have a new band that will just clear the prop I'd like to try when I get a chance. Even with the large blade clearance I have now, the effect is really remarkable. Besides reduced tip clearance and band width, it is possible to experiment with converging and diverging ducting. My band is just a curl of metal my brother rolled for me. Besides my curiosity, I am very cheap! John S Boise
Prop ring
Hi John S, I like you pics a lot. I am an engineer and like to mess around with things. Please Stay connected with the forum. You got a good boat. Kaizen is the name of my boat which is Japanese for "constant improvement".
Hi John S, I like you pics a lot. I am an engineer and like to mess around with things. Please Stay connected with the forum. You got a good boat. Kaizen is the name of my boat which is Japanese for "constant improvement".
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