I thought I'd try to contain tip losses on my outboard, so I came up with this kind of shroud. It uses 5 bolts to mount it so I am not apt to remove it and reinstall it just to find out before/after. However, this 8 HP engine pushes my 26D with full ballast and 2 adults/2 kids with a whole bunch of crap onboard up to 7.3 MPH with GPS readout. It does not cavitate in forward like it used to do (if you rapidly opened the throttle, from a dead start, it would often suck air). It does not seem to help cavitation in reverse. Efficiency-wise, from a seat of the pants kind of feeling, there seems to be way more push than before. As a by product of the installaion, the prop is protected at all times and it is now not possible to chew up my IdaSailor rudder with the kicker.
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gary
thrusters
that is one BIG ring you have there. mine is alot smaller, the prop tips just clear the ring. i am able to get 9 knots at full power with my 10hp honda. it's nice not to have to worry about chewing up the rudder.
that is one BIG ring you have there. mine is alot smaller, the prop tips just clear the ring. i am able to get 9 knots at full power with my 10hp honda. it's nice not to have to worry about chewing up the rudder.
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Steve Paul
Priceless
These thrust rings are very nice guys. I've often thought the hydrofoil wings would do the same thing for those not able to make or buy the full rings. Have you had any experience with the ring hitting bottom and being deformed? Guess the other question would be does the ring attach to the skeg as well? Did you buy these or are they home-made? Made of stainless? You're so right, not worrying about the rudder is priceless. Steve
These thrust rings are very nice guys. I've often thought the hydrofoil wings would do the same thing for those not able to make or buy the full rings. Have you had any experience with the ring hitting bottom and being deformed? Guess the other question would be does the ring attach to the skeg as well? Did you buy these or are they home-made? Made of stainless? You're so right, not worrying about the rudder is priceless. Steve
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John S
Ring Details
Gary, You can get 9 knots or about 10-11 MPH? Wow, I have got to do better. This is the first iteration of an ongoing attempt to make better power from my kicker. Yes, it is homemade. It is approx a 12 in circle that is 4 in long with the band centered over the prop. The reason I selected 12 in is that is half the distance from the center of the prop to the anti-cavitaion plate, to which I mounted this entire circle of metal. I picked up a mount on the skeg after having the band move off center till the prop rubbed on the inside of the band (not catastrophically, just noisily). Just thinking about the turbine engines that I look at every day: there design has a very close fitting shroud that meets a squared off blade end. I was going to look for a bigger prop diameter that would fit on the shaft and then cut down the prop tip ends to a square end shape that would just clear the shroud. Balance and see how it does. Even like it is now, the engine pushes much better than before. I am in the process of obtaining a thicker ring, but I'd like to ask a question, Gary, how is your ring mounted? Is there a block or spacer mounted between your anti-cavitation plate and your ring? Thanks John S
Gary, You can get 9 knots or about 10-11 MPH? Wow, I have got to do better. This is the first iteration of an ongoing attempt to make better power from my kicker. Yes, it is homemade. It is approx a 12 in circle that is 4 in long with the band centered over the prop. The reason I selected 12 in is that is half the distance from the center of the prop to the anti-cavitaion plate, to which I mounted this entire circle of metal. I picked up a mount on the skeg after having the band move off center till the prop rubbed on the inside of the band (not catastrophically, just noisily). Just thinking about the turbine engines that I look at every day: there design has a very close fitting shroud that meets a squared off blade end. I was going to look for a bigger prop diameter that would fit on the shaft and then cut down the prop tip ends to a square end shape that would just clear the shroud. Balance and see how it does. Even like it is now, the engine pushes much better than before. I am in the process of obtaining a thicker ring, but I'd like to ask a question, Gary, how is your ring mounted? Is there a block or spacer mounted between your anti-cavitation plate and your ring? Thanks John S
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John S
Bottom Strike
Steve Paul, My daggerboard or rudder would ground out first before my outboard ring would hit. I have only used this setup once with the new skeg mount, but surely I'd rather hit the ring than my poor outboard if it did come into contact with an object. John S
Steve Paul, My daggerboard or rudder would ground out first before my outboard ring would hit. I have only used this setup once with the new skeg mount, but surely I'd rather hit the ring than my poor outboard if it did come into contact with an object. John S
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Steve Paul
No argument
No argument there John, I'm the one not afraid to ask the d....ss question. I was thinking if my 26S rudder hit something and folded up like it's supposed to then my prop could hit "it" too. Just thinking out loud. I actually think it's pretty neat. Again, did you make this or buy it? Steve
No argument there John, I'm the one not afraid to ask the d....ss question. I was thinking if my 26S rudder hit something and folded up like it's supposed to then my prop could hit "it" too. Just thinking out loud. I actually think it's pretty neat. Again, did you make this or buy it? Steve
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John S
Kicker Details
No problem, Steve Paul, I ask the really stupid ones all of the time, but then I often have others tell me they were too shy to ask the same. Anyway, yes, I made this trial ring. But no, I did not roll it into a circle: my sheetmetal worker brother does the custom work for me as I dont use my sheetmetal skills all that often and I don't have access to the neat machines he has. I have already asked him to make a 9 inch circle for my next test. I am going to fab up a HDPE spacer to fit between the cav plates and the circle to more closely enclose the prop tips. As far as hitting something goes, I think that the forward part of the outdrive would hit something first, as the ring is very aft on the outdrive assembly. But if the situation occurred that just the ring was struck, I think that the prop and the ring would get tangled up. I already have experience with this as my first try with the 12 in ring was not braced correctly and the ring moved over into the prop, and all it did was make a bad noise, scratch the prop tip and inner circle. We are talking about 7 MPH here as well. I wonder if my kicker outboard will kick up if it strikes something, I have never really looked at that to see. I'll post another pic as soon as I get the new ring. John S
No problem, Steve Paul, I ask the really stupid ones all of the time, but then I often have others tell me they were too shy to ask the same. Anyway, yes, I made this trial ring. But no, I did not roll it into a circle: my sheetmetal worker brother does the custom work for me as I dont use my sheetmetal skills all that often and I don't have access to the neat machines he has. I have already asked him to make a 9 inch circle for my next test. I am going to fab up a HDPE spacer to fit between the cav plates and the circle to more closely enclose the prop tips. As far as hitting something goes, I think that the forward part of the outdrive would hit something first, as the ring is very aft on the outdrive assembly. But if the situation occurred that just the ring was struck, I think that the prop and the ring would get tangled up. I already have experience with this as my first try with the 12 in ring was not braced correctly and the ring moved over into the prop, and all it did was make a bad noise, scratch the prop tip and inner circle. We are talking about 7 MPH here as well. I wonder if my kicker outboard will kick up if it strikes something, I have never really looked at that to see. I'll post another pic as soon as I get the new ring. John S
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MrBill
Details?
Hey JohnS, Can you tell me what the ring does for cavatation? I've seen these before but only as a river prop guard. I though the drag was an issue... I dont think I have cavatation problems in forward, but huge problems in reverse. almost non existant... a side profile photo may help... does the ring help funnel the water?
Hey JohnS, Can you tell me what the ring does for cavatation? I've seen these before but only as a river prop guard. I though the drag was an issue... I dont think I have cavatation problems in forward, but huge problems in reverse. almost non existant... a side profile photo may help... does the ring help funnel the water?
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John S
Ducted prop
I have a cavitation problem (without this ring) when I ask for full power from the engine when the boat is at a standstill. I also started thinking about the losses of water displacement from centrifigal movement of the water by the propeller. So I thought I'd try to contain the displaced water in a duct. Since I can get metal bent anyway I'd like, I decided to try a ring around the prop to see what effect it would cause. I was very happy that the engine pushed the boat more with the ring installed. I also noticed that the prop did not cavitate anymore in the conditions described above. I happened to try the engine in reverse yesterday, and the prop cavitated excessively when full reverse power was asked for from the engine. While the ring forms protection as a secondary effect, I am primarily interested in more thrust from the outboard. I am going to mount a smaller, closer-to-the-prop ring in the near future and then I'll record the results. I think that drag is not so much a consideration at the speeds that I will see with an 8 HP, at less than 10 MPH. The body of the lower end of the outboard surely presents more drag than the edge of the ring. My next variable after that will be a longer length of duct. John S
I have a cavitation problem (without this ring) when I ask for full power from the engine when the boat is at a standstill. I also started thinking about the losses of water displacement from centrifigal movement of the water by the propeller. So I thought I'd try to contain the displaced water in a duct. Since I can get metal bent anyway I'd like, I decided to try a ring around the prop to see what effect it would cause. I was very happy that the engine pushed the boat more with the ring installed. I also noticed that the prop did not cavitate anymore in the conditions described above. I happened to try the engine in reverse yesterday, and the prop cavitated excessively when full reverse power was asked for from the engine. While the ring forms protection as a secondary effect, I am primarily interested in more thrust from the outboard. I am going to mount a smaller, closer-to-the-prop ring in the near future and then I'll record the results. I think that drag is not so much a consideration at the speeds that I will see with an 8 HP, at less than 10 MPH. The body of the lower end of the outboard surely presents more drag than the edge of the ring. My next variable after that will be a longer length of duct. John S
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mrbill
re-hub kits
I would be cautions about using max throttle. -I spun a hub on a kicker a while getting back to port on a powerboat w/ primary motor dead. as you probably know, the metal prop has a pressed in rubber HUB that connects to the drive shaft. (I guess this is to not break the shaft if you hit a rock) anyway, if you put a lot of torque on the prop, you may spin the hub. not a huge deal, once the hub cools a bit, it will get some grip and you should be able to limp back home. I had a new hub pressed in by local repair shop, but think they also sell a field install kit. fwiw, I was not full throttle, when it spun, just under the point where it would cavatitate....
I would be cautions about using max throttle. -I spun a hub on a kicker a while getting back to port on a powerboat w/ primary motor dead. as you probably know, the metal prop has a pressed in rubber HUB that connects to the drive shaft. (I guess this is to not break the shaft if you hit a rock) anyway, if you put a lot of torque on the prop, you may spin the hub. not a huge deal, once the hub cools a bit, it will get some grip and you should be able to limp back home. I had a new hub pressed in by local repair shop, but think they also sell a field install kit. fwiw, I was not full throttle, when it spun, just under the point where it would cavatitate....
you can buy one
You can buy a "Power Thruster" from the chandlery on this site. I bought one and can't wait to try it out! click the link and chek it out, heck of a lot easier than making one.
You can buy a "Power Thruster" from the chandlery on this site. I bought one and can't wait to try it out! click the link and chek it out, heck of a lot easier than making one.
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John S
Power thruster
Yes I did look at the Power thruster and I thought that they did not go far enough with the idea, just far enough to make the claims. Don't get me wrong, I think it is a great item, but I want to wring every bit of thrust that I can out of the kicker. They say in their description that the prop should be at least 1 inch from the prop blade, which I find interesting. I would like to have the blade clear my ring by the least amount of clearance and then test that set-up. As far as easier goes, I am a fabricator and I like to make things. The cost of this project so far is $0 and I am having a great time brainstorming. I would like to have a close fitting ring with a propellor with squared off tips like a turbine engine. This principal is just like the ideas that put those winglets on the ends of the wings of airliners. The high pressure areas want to run over to the low pressure areas and I am trying to stop that. Eventually I will have to quantify the difference with and without the ring if only for my own curiousity, but I am lazy and the water is sooo cold... John S
Yes I did look at the Power thruster and I thought that they did not go far enough with the idea, just far enough to make the claims. Don't get me wrong, I think it is a great item, but I want to wring every bit of thrust that I can out of the kicker. They say in their description that the prop should be at least 1 inch from the prop blade, which I find interesting. I would like to have the blade clear my ring by the least amount of clearance and then test that set-up. As far as easier goes, I am a fabricator and I like to make things. The cost of this project so far is $0 and I am having a great time brainstorming. I would like to have a close fitting ring with a propellor with squared off tips like a turbine engine. This principal is just like the ideas that put those winglets on the ends of the wings of airliners. The high pressure areas want to run over to the low pressure areas and I am trying to stop that. Eventually I will have to quantify the difference with and without the ring if only for my own curiousity, but I am lazy and the water is sooo cold... John S
R
RichardL
More info from John
John S - please keep us informed and let us know how your project progresses. Gary from Edmonds, you tell us that yours is smaller (prop ring that is!), and I would be interested to know if you bought the ring or made it, and the details.
John S - please keep us informed and let us know how your project progresses. Gary from Edmonds, you tell us that yours is smaller (prop ring that is!), and I would be interested to know if you bought the ring or made it, and the details.
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RichardL
A whole bunch of prop guards
Check out the site below, I came across it after reading this thread and then searching for "prop guard" on the net. There are a whole bunch of prop guards, although some are too big for our small outboards. I did not have time to look at all of the sites, however, I did see one that went down to 7" diameter blade, and they do cover the subject of cavitation and thrust increase in several of them.
Check out the site below, I came across it after reading this thread and then searching for "prop guard" on the net. There are a whole bunch of prop guards, although some are too big for our small outboards. I did not have time to look at all of the sites, however, I did see one that went down to 7" diameter blade, and they do cover the subject of cavitation and thrust increase in several of them.
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John S
Prop Guards, rings
RichardL, Thank you for the link. I see a couple of products there that look quite like my own fabrication. From other research I gather that propeller ducting has been going on for many years. One major gem I have found is that the effectiveness of the duct is mainly felt at low speeds and heavy torque, like when we push our boats through the water. At higher speeds, the ducts have less effect and their drag factor goes way up. Another interesting variation is having the duct either taper larger or get smaller, or have the duct's smallest ID right at the propellor and open up before and after that point. Another refinement is to have a radial slot cut around the duct just downstream of the propeller to allow outside low pressure water to be drawn into the exhaust flow and thereby increase the accellerated mass. Another solution is to attach the ducting ring right to the prop blades and let it whirl around as one piece. I saw one assembly that had squared off propeller tips that just cleared the shroud, so my ideas have already been thought of, created and marketed long ago. I'm still hanging onto the cheapness idea for my ring, some of these propeller ducts or shrouds are very exspensive!
RichardL, Thank you for the link. I see a couple of products there that look quite like my own fabrication. From other research I gather that propeller ducting has been going on for many years. One major gem I have found is that the effectiveness of the duct is mainly felt at low speeds and heavy torque, like when we push our boats through the water. At higher speeds, the ducts have less effect and their drag factor goes way up. Another interesting variation is having the duct either taper larger or get smaller, or have the duct's smallest ID right at the propellor and open up before and after that point. Another refinement is to have a radial slot cut around the duct just downstream of the propeller to allow outside low pressure water to be drawn into the exhaust flow and thereby increase the accellerated mass. Another solution is to attach the ducting ring right to the prop blades and let it whirl around as one piece. I saw one assembly that had squared off propeller tips that just cleared the shroud, so my ideas have already been thought of, created and marketed long ago. I'm still hanging onto the cheapness idea for my ring, some of these propeller ducts or shrouds are very exspensive!
S
Steve Paul
Original Thought
John S, I learned long ago that "original thought" is a very rare thing to find in our society. I know I've had thoughts of inventions and improvements only to find I'm years or centuries late. Improving on other's thoughts is another story. Don't stop playing around (with props). Look at bow thrusters, they are engineered for max thrust at low speeds and also have the props squared off for close tolerance to the guide tubes. It's still a lot of fun for me too. Steve
John S, I learned long ago that "original thought" is a very rare thing to find in our society. I know I've had thoughts of inventions and improvements only to find I'm years or centuries late. Improving on other's thoughts is another story. Don't stop playing around (with props). Look at bow thrusters, they are engineered for max thrust at low speeds and also have the props squared off for close tolerance to the guide tubes. It's still a lot of fun for me too. Steve
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RichardL
It was just FYI
John S - I wasn't suggesting you should stop the development of your thruster as there are others on the market (but way too expensive), however, I thought it may give you some insight into what is already out there. After all where would the world be if people stopped trying to improve on products that were already available. Hopefully with your expertise, you can come up with something even mnore effective for a much lower price. When that time comes, I will be one of the first in line to buy one from you. Keep us posted!
John S - I wasn't suggesting you should stop the development of your thruster as there are others on the market (but way too expensive), however, I thought it may give you some insight into what is already out there. After all where would the world be if people stopped trying to improve on products that were already available. Hopefully with your expertise, you can come up with something even mnore effective for a much lower price. When that time comes, I will be one of the first in line to buy one from you. Keep us posted!
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Tom S
Good idea
John S, Good idea. I was thinking of something similar but you've done the R&D for me so I'll be picking up some stainless and shrouding my 26s prop too. Our lake has some shalow spots that I can only motor through with the keel and rudder up and I've touched the prop a couple times so this would help quite a bit. 7.3 mph is good for a 8hp. Even with a 10hp you'd be hard pressed to hold 7.5 mph. I think that gary's 9 knots was in a strong current as a 26 will exagerate no more than 6.5 knots through the water no matter how large the outboard feels or how poor the gps tracks. A macgregor 26d will only exceed 6.5 knots while on it's trailer. Thanks for sharing the good tip.
John S, Good idea. I was thinking of something similar but you've done the R&D for me so I'll be picking up some stainless and shrouding my 26s prop too. Our lake has some shalow spots that I can only motor through with the keel and rudder up and I've touched the prop a couple times so this would help quite a bit. 7.3 mph is good for a 8hp. Even with a 10hp you'd be hard pressed to hold 7.5 mph. I think that gary's 9 knots was in a strong current as a 26 will exagerate no more than 6.5 knots through the water no matter how large the outboard feels or how poor the gps tracks. A macgregor 26d will only exceed 6.5 knots while on it's trailer. Thanks for sharing the good tip.
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MRBILL
RINGS AND REVERSE?
ANY THOUGHTS TO FIXING THE REVERSE CAVAIATION? THATS THE AREA I WORRY ABOUT... HITTING THE DOCK AND OTHER BOATS.... AGAIN, I MOVE ABOUT 6 KNTS AS IS, WHICH IS FINE FOR ME. (MERC 9.8) IF I COULD GET REVERSE TO WORK, I'D SACRIFICE SOME FOWARD SPEED. -MOVE THE RING AHEAD OF THE PROP? THINK THAT WOULD WORK? I FIGURED I'D LOOK FOR A NEW PROP THEN TRY CUPPING/RE- PITCHING IT. -ANYONE ELSE HAVE REVERSE SOLUTION? THANKS IN ADVANCE....
ANY THOUGHTS TO FIXING THE REVERSE CAVAIATION? THATS THE AREA I WORRY ABOUT... HITTING THE DOCK AND OTHER BOATS.... AGAIN, I MOVE ABOUT 6 KNTS AS IS, WHICH IS FINE FOR ME. (MERC 9.8) IF I COULD GET REVERSE TO WORK, I'D SACRIFICE SOME FOWARD SPEED. -MOVE THE RING AHEAD OF THE PROP? THINK THAT WOULD WORK? I FIGURED I'D LOOK FOR A NEW PROP THEN TRY CUPPING/RE- PITCHING IT. -ANYONE ELSE HAVE REVERSE SOLUTION? THANKS IN ADVANCE....
J
John S
Putting it all Together
All right, this project is part of my evil (to some) ideas about the plane-ability of the 26D hull. The fact that multiple persons posting on this list have gotten their 26D's to go faster than the theoretical hull speed should raise the suspicion that this hull shape is NOT a "pure" displacement hull. Anyone who squats down and looks at the hull when it is on the trailer will see a hull that looks pretty similar to any other planing fisherboat. Now here is where it gets a little weird: what if the 26D would plane or at least go faster than 10 MPH with the ballast tanks empty and on the kickers push alone? Yes, it might be tippy, but so is my brothers aluminum boat. Yes, the boat might not be suitable for (take your pick): insurance agents angry about flotation foam removal, little children who are so trusting and vulnerable and can't swim and don't have on their PFDs, your mother-in-law, etc. I am not inviting any of those onboard. I am very concerned about cavitation of the kicker in either forward or reverse. Maybe not cavitation, but the phenomenon wherein the motor seems to suck air at the prop, and is less effective. I just realised how ineffective my kicker is in reverse, I have to test the reverse performance some more to see what is happening there. Last night, my brother dropped off a Stainless Steel shroud with a 9 in diameter and a 4 inch length. I will be fabricating spacer blocks out of HDPE to center the ring around the 8 inch prop, as I can no longer just mount the ring on the anti-cavitation plate. It is very thick SSteel, but I still want to pick up a brace on the skeg as long as I have already drilled a clearance hole for a #10 machine screw. By the way, some shrouds are put around props to protect the propellor, some are there to protect swimmers and even manatees, not all are performance enhancers. I think I probably do more damage to my prop while removing the engine from the transom and transporting it, than I ever did by hitting something under power.
All right, this project is part of my evil (to some) ideas about the plane-ability of the 26D hull. The fact that multiple persons posting on this list have gotten their 26D's to go faster than the theoretical hull speed should raise the suspicion that this hull shape is NOT a "pure" displacement hull. Anyone who squats down and looks at the hull when it is on the trailer will see a hull that looks pretty similar to any other planing fisherboat. Now here is where it gets a little weird: what if the 26D would plane or at least go faster than 10 MPH with the ballast tanks empty and on the kickers push alone? Yes, it might be tippy, but so is my brothers aluminum boat. Yes, the boat might not be suitable for (take your pick): insurance agents angry about flotation foam removal, little children who are so trusting and vulnerable and can't swim and don't have on their PFDs, your mother-in-law, etc. I am not inviting any of those onboard. I am very concerned about cavitation of the kicker in either forward or reverse. Maybe not cavitation, but the phenomenon wherein the motor seems to suck air at the prop, and is less effective. I just realised how ineffective my kicker is in reverse, I have to test the reverse performance some more to see what is happening there. Last night, my brother dropped off a Stainless Steel shroud with a 9 in diameter and a 4 inch length. I will be fabricating spacer blocks out of HDPE to center the ring around the 8 inch prop, as I can no longer just mount the ring on the anti-cavitation plate. It is very thick SSteel, but I still want to pick up a brace on the skeg as long as I have already drilled a clearance hole for a #10 machine screw. By the way, some shrouds are put around props to protect the propellor, some are there to protect swimmers and even manatees, not all are performance enhancers. I think I probably do more damage to my prop while removing the engine from the transom and transporting it, than I ever did by hitting something under power.
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