In the event this information might prove helpful or interesting*to someone, here is what we learned this week at Kruger & Sons marine propeller shop in Seattle where we took our two 22" diameter, 18" pitch (supposedly)*props in anticipation of having to buy two brand new props.* Kruger & Sons had been recommended to us by several people in the local marine industry as the best prop shop in Seattle if not the Puget Sound area.
Two years ago a different prop shop in Seattle had checked our props and said they were worn out and needed to be replaced.* After conferring with the yard we use, it was decided we could get another year or two out of them, at which point we would buy and install new props.
Kruger performed an initial visual and sound inspection of the four-bladed props*when we brought them in on Monday and said they were definitely*not worn out. They were pitched too coarse for our engines and*they could see*at least one slightly bent blade.* We've never hit anything that we know of so it may have been this way when we bought the boat.
They said they would repitch the blades from 18" to 16" as well as true up the blades, balance the props, etc.* This represented a major saving in dollars for us, which is good since the price of diesel will continue to climb.
They confirmed what I had been told---*fewer blades are more efficient than more blades, more blades generate less vibration than fewer blades.
They also said that, contrary to what I had been told, a three-bladed prop will generate more prop walk at low rpm than a four-bladed prop. I have been impressed with the responsiveness of our current props in kicking the stern around when maneuvering to a dock. So I guess three-bladed props would be even more responsive in this respect but we're not going to spend the money for new props just to gain this advantage.
Kruger & Sons carries two makes of new props in the size range for boats like ours. There are "economy" props from Taiwan or China*and "quality" props from somewhere else. As a point of reference, 22-16 props for our boat would be about $800 each for the "economy" prop and about $1,400 each for the "quality" prop. They did not say if our current props were from the same manufacturer who makes their "quality" props, but they did say that our current props are from a*high-quality manufacturer.
I asked if the finer 16" pitch would mean that we'd have to run at a significantly higher rpm to achieve the same boat speed. They said we would have to run at a slightly higher rpm BUT... the engines will not be as loaded down so we'll get the same boat speed at a lower fuel consumption. They compared the props*as they were currently set up*to running a car up a hill in too-high a gear.
I got a call today that the props are ready for pickup.* They said that whoever set them up before had*done a terrible job (their words).* Some of the individual blades were slightliy different in size than others on the same prop.* One prop was pitched an average of 18", the other an average of 17."* (There could have been a*legitimate reason for this, but the important point was that none of the blades on any one prop*were exactly matched in pitch.)* Some of the blades were bent slightly, not from striking something but from being improperly set up.* The hub of one prop was even out of true.
The blades are now all sized the same, they are all pitched the same, there are no more bends or "wows" in the blades, the bad hub has been trued up, and they have been computer scanned and balanced.
Since we are putting the same props back on the boat instead of a new set, it will be very interesting to see how they compare in terms of smoothness, performance, etc.* I'm curious to see if any of the*minor vibrations that*we simply chalked up to the boat being three decades old are no longer with us.
These props were on the boat when we bought it ten years ago, so we have no idea when they were installed.* Nor do we know who*set them up, other than it would have been someone in the San Francisco Bay area since the boat spent its whole life there until we bought it.
Anyway, if anyone in the Seattle area has questions about props, I would sure recommend at least including Kruger & Sons on their list of prop shops to talk to.
Two years ago a different prop shop in Seattle had checked our props and said they were worn out and needed to be replaced.* After conferring with the yard we use, it was decided we could get another year or two out of them, at which point we would buy and install new props.
Kruger performed an initial visual and sound inspection of the four-bladed props*when we brought them in on Monday and said they were definitely*not worn out. They were pitched too coarse for our engines and*they could see*at least one slightly bent blade.* We've never hit anything that we know of so it may have been this way when we bought the boat.
They said they would repitch the blades from 18" to 16" as well as true up the blades, balance the props, etc.* This represented a major saving in dollars for us, which is good since the price of diesel will continue to climb.
They confirmed what I had been told---*fewer blades are more efficient than more blades, more blades generate less vibration than fewer blades.
They also said that, contrary to what I had been told, a three-bladed prop will generate more prop walk at low rpm than a four-bladed prop. I have been impressed with the responsiveness of our current props in kicking the stern around when maneuvering to a dock. So I guess three-bladed props would be even more responsive in this respect but we're not going to spend the money for new props just to gain this advantage.
Kruger & Sons carries two makes of new props in the size range for boats like ours. There are "economy" props from Taiwan or China*and "quality" props from somewhere else. As a point of reference, 22-16 props for our boat would be about $800 each for the "economy" prop and about $1,400 each for the "quality" prop. They did not say if our current props were from the same manufacturer who makes their "quality" props, but they did say that our current props are from a*high-quality manufacturer.
I asked if the finer 16" pitch would mean that we'd have to run at a significantly higher rpm to achieve the same boat speed. They said we would have to run at a slightly higher rpm BUT... the engines will not be as loaded down so we'll get the same boat speed at a lower fuel consumption. They compared the props*as they were currently set up*to running a car up a hill in too-high a gear.
I got a call today that the props are ready for pickup.* They said that whoever set them up before had*done a terrible job (their words).* Some of the individual blades were slightliy different in size than others on the same prop.* One prop was pitched an average of 18", the other an average of 17."* (There could have been a*legitimate reason for this, but the important point was that none of the blades on any one prop*were exactly matched in pitch.)* Some of the blades were bent slightly, not from striking something but from being improperly set up.* The hub of one prop was even out of true.
The blades are now all sized the same, they are all pitched the same, there are no more bends or "wows" in the blades, the bad hub has been trued up, and they have been computer scanned and balanced.
Since we are putting the same props back on the boat instead of a new set, it will be very interesting to see how they compare in terms of smoothness, performance, etc.* I'm curious to see if any of the*minor vibrations that*we simply chalked up to the boat being three decades old are no longer with us.
These props were on the boat when we bought it ten years ago, so we have no idea when they were installed.* Nor do we know who*set them up, other than it would have been someone in the San Francisco Bay area since the boat spent its whole life there until we bought it.
Anyway, if anyone in the Seattle area has questions about props, I would sure recommend at least including Kruger & Sons on their list of prop shops to talk to.