Prop Scan

[REBrueckner]

What's been the experience of owners with flo scans and prop scans. Does the computer scanning of props ACTUALLY get reflected in any improved efficiency?? I'm not talking an old wobbly prop out of aligned and vibrating, but a comparison between one working reasonably well then computer scanned.

 

[Fanfare]

Ten years ago I repowered with 550 hp. 6-92TAs. Had to go to stronger shafts and went from 3 blade props to 4. So all new, seemed to work fine, except I could never get the stbd. packing gland to stop leaking. Last year I decided to go with dripless shaft seals. Shafts had to come out, to do that props have to come off. So I figured I might as well have the props scanned while they were off. (Also ended up having shafts remetalized in bearing areas due to rust.) Props were not far off, but had some adjustments. Shaft seals seem to be a big improvement (only 50 hrs--we'll see) but props much less vibration, less noise in master stateroom at speed. A considerable improvement. However, I didn't notice any improvement in efficiency. I wasn't looking for one, maybe I didn't notice it. I think the cutlass bearings will last longer though.

All in all, I think it was a good investment. Even though I hadn't hit anything hard with my props, they still get small nicks and scrapes from stuff I don't even see in the water. If I had bent a prop I would surely have it done.

Jim Grove, Fanfare 1966 50MY

 

[Maynard Rupp]

We have two sets of 3 bladed props. When we bought the boat the previous owner had changed from the set that was on from the factory to the new condition spares. He said he had a slight vibration and hoped the newer props would cure that. I could not get within 200 RPM of the recommended for our Crusaders so last winter I pulled the props for re-pitching. The shop was to remove 2" of pitch and scan the props. I then pulled the old props out and was shocked to find they were re-stamped with the pitch I was having put in the newer props. I went to the shop with these in hopes of saving money and just switching props. He scaned the old props briefly and said they were way off. He said they used to just beat the props to shape with a mandrill and mallet, and when they scan the props that were done that way they always find them off. I guess each blades pitch would vary from others and the twist wouldn't agree from blade to blade. He re-pitched our good props and scaned them, told us to keep the others for spares, and expect a vibration when we use the old props. Hmmmm, seems that was why the last owner changed them. So, I guess the prop scan system works. We paid $500.00 for our 26" 3 blade props and the checking of the spares. The props look like new, are smooth, and the RPM is now in range.

 

[Trojan]

I had mine scanned 2 years back on my old boat.Three times. I'm also in a quam about wether or not I gained any efficiency. I know the boat ran smoother with less vibration. Seemed to get on plane faster. How they are checked gives you a warm feeling knowing they are correct when you put them on. I plan to get my spares reworked and then checked by proscan. I guess it is more of a question to me as to how good my present prop guys are verses the prop scan. I don't know what the other guys use to check theirs if they use hammer blocks to fix an shape them. I know how Propscan checks them and how they repair them. It does work. But is it worth the additional monies. I guess quality is an issue here. You would tend to think that if the boat ran smoother overall. That it stands to reason you would have to gain some efficiency. Its just seems hard to prove. If I find any hiccups after Proscan checks them. I will have them go through my props forever. At my age. I like that warm feeling. Bill

 

[Nonchalant1]

PropScan is just a high accuracy blade pitch measuring device run through a computer. They'll do a PropScan for free if you bring in your props. Of course, they expect to find problems frequently and make their money fixing what they find. They can do one of my 28X31s in 5 minutes and print out a report. I have taken in a 28X31 that they said was OK as is, so at least they tell you if they're OK. They still have to heat and beat to get the blades into the correct pitch at 6 radius points for the propscan 1srt class spec.

Having out of tune props makes a big differrence. My spare props were bad (small cracks halfway to the shaft) so I bought new Michigan Wheel nibrals (Ouch - $1900 ea) and had my good set brought up to 1st class spec so when I hit something, my spares can just become my primaries until the next time I have to change props. Saves time and hauling $.

The other high quality measuring technique is Hale MRI. I have had that done and you don't get as fancy a report as PropScan (BFD) and they only measure at 4 radii instead of 6.

You can read all of our comments on FloScans on the floscan thread here recently.

Doug Shuman

 

[Akyla]

I had black dog props in MD do my wheels several years ago using the prop scan system. they needed straightened out anyway...
I was very surprised at how smooth the boat ran afterward, much better than before and they were brand new wheels for the year before I bent them. The short freq vibrations all went away. I had them tuned up this spring after four years and they again did a great job, though they were not off by much. I think a system like that is they way to go, otherwise you are just beating on the blades until they closely fit a pitch block - not too scienctific.

 

[Mike36c]

I had mine scaned and tweaked two months ago here in Stuart, FL. The props were 2 year old Hy-torque's and undamaged, basically new issue. We're not done playing with them yet but this is what I've found so far. Three advantages 1. They are absolutely MUCH smoother. 2. The props can tweaked so both engines are loaded exactly the same. 3. The blades will be exact when changing pitch. Are they more efficient? Unless your wheels are WAY off to start, I mean miss-matched for the application(way over/under pitched) I don't think you'll see much.

 

[SeaEric]

Dave, Did you think the pricing at Black Dog was fair? Since my boat is out of the water this winter and since Black Dog is right up the road from me I was thinking of popping my wheels off and getting them checked out. Some of the old timers around here poo poo the computer prop balancing in favor of the traditional methods. The last few results I have had from the heat and mallet guys have not been satisfactory to me. Time to try the high tech method for my otherwise low tech boat.

The majority of what I wish to accomplish with her out of the water is a complete review of bearings, packing, trim tab operation, bottom fairing, removal of unused thru hulls, etc. Jim Rosenthal has counseled me that with a carefully performed "tweaking" of hull, running gear and machinery that I can probably pick up a knot or 2 in cruise speed, with minimal investment. He provided this speech when I started talking about repowering.... Anyway, I'm going to give his advice a try. Then of course I will probably add stabilizers and lose the speed I have picked up!

 

[captddis]

I used to ship props to Blackdog from FL. They are one of the best. There is now a excellent propscan shop in Cape Coral I use.
I am a big believer in propscan. However the computer does not lie but be sure the shop has techs who can read it and apply it.
As anexample on my 46 HP , back in the late 80s the PO hit hard and had the props done and redone many times . The boat was smooth but the speed never was the same. fast forward to 03, I tried both sets of props and sent the better set to be scanned. They call and say that they measure out OK but the blades are out of shape. He says it looks like the blades were folded and bent back ,but not twisted back into shape. Now the boat is smooth and the long lost speed is back.

 

[Capten]

We have had very good results working with Steve King at Black Dog Propellers here in Maryland over the past 8+ years. We have had new and used wheels tuned by Steve and have noticed much improved performance as far as speed, RPMs, and vibration are concerned. The cost is probably twice the cost of old traditional methods but in my opinion well worth it. I would never go back.

As far as fuel efficiency goes, I am installing FloScans this winter and since I will never be running a set of "non-prop scanned" wheels again I will not have anything to compare to.

BTW - Black Dog's facility is pretty impressive and some of the monster wheels he works on are really incredible. In fact, I think he does a lot of new props for boat builders such as Hatteras and Viking.

 

[SKYCHENEY]

Doug,
$1900 each? Now that's a good price. When I took my props to PropScan, they wanted $785 each to repitch and tune. I said okay, but then started to think about how that might compare to just buying new props. When I inquired at Michigan Wheel, they quoted me $3000 each for new 28x30x4 Federals. I guess I made the right choice to just go with PropScan.

 

[Nonchalant1]

Yeah, I scoured the internet for a week and then negotiated back and forth. I wound up buying them from the East Coast and they shipped them to Chicago (free if I remember right, because I was comparing landed costs). That was 18 months ago. They were 28X31 4 blade Michigan Wheel Nibrals.

Doug

 

[REBrueckner]

For clarification: my understanding is that even with computer reading of props, PropSCan or whoever, they are still corrected via "heat and beat", meaning manually, then rechecked for compliance to specs. Is this how it actually works?? When I checked last year at a big prop shop in New Bedford, Mass, I was amazed to find they did NOT use any computer aided assessment!! I wanted to watch one being done..This shop serves the commercial fishing boats at D.N. Kelley and Fairhaven Shipyard, two BIG operations. go figure.

 

[Nonchalant1]

Yaeh, that's how it works. The difference is the old artistry required to make the pitch match at all radii has been replaced by the computer measuring device.

 

[Akyla]

Yes, I would say they treated me very fairly.
The first time I took them in they were very mangled. 22kt across the bar will do that you know... I dont remember the exact cost without looking through my files, but it was not as much as I had expected. But remember, my 36 doesn't have really big wheels.

The tune up I took them in for three years later cost me $50 bucks a wheel and I thought that to be an exceptional value! (They didn't have to do much to them though) Plus, I've had very good customer service from them, so I think Black Dog is the place to go for me.

 

[luckydave215]

Expensive props are put on a cmm (cooridinate measuring machine) and a file generated. The tech or designer then selects the surfaces he thinks are the ones desired, and the rest of the prop is formed, welded, and 4 axis machined to that shape. This process is most effective with new oversize "blanks" but can still be helpful to used wheels. Any shop that is using blacksmith methods on your props is working in the stone (bronze?) age.

 

[Nonchalant1]

Expensive props are put on a cmm (cooridinate measuring machine) and a file generated. The tech or designer then selects the surfaces he thinks are the ones desired, and the rest of the prop is formed, welded, and 4 axis machined to that shape. This process is most effective with new oversize "blanks" but can still be helpful to used wheels. Any shop that is using blacksmith methods on your props is working in the stone (bronze?) age.

Dave,

Isn't the PropScan device just a "coordinate measuring machine". It takes computer guided measurements of 3D coordinates at six different radii of the actual blade pitch for each blade (literally thousands of measuring points) and then compares them to spec and to each other.

If a prop blade is bent it should be heated and bent back. Maybe that's what you meant by "formed"? The "beat" part of heat and beat isn't with hammers, it's with hydraulics. Just call that "formed". A CNC machine can only remove material, so they try to get it as close as possible by heating and beating it without removing any metal first.

Doug

 

[luckydave215]

Yes it's a cmm. When I talk about "expensive" props, I'm not talking about those typically found on low speed yachts. And yes, to machine a part to size, it must first be oversize. Forming a prop (heat and beat, hydrualics, bending, whatever-) will only result in an appromixate shape, with numerous random radii and thickness/shape/pitch, unless the part is "hot formed" (forged) between male and female dies. This process is prohibitively expensive, way out of reach for boats like ours. The only way to achieve the desired shape to any close tolerance other than die forming is to start with a blank or to add metal by welding and then machine to size.

 

[Trojan]

Prop scan is only the process of scanning the blades with a computer aided measuring stylist and program. After you find out what is right or wrong. They still weld, grind, beat and bend the wheel to make the repair. Depending on the size of the prop they might use hydrulic rams and pulls to bend it. The amount of scans on a blade is dependent on the size of the blade or the class of checking you want to pay for. Large props are usually checked to a class 1, 5 passes per blade. Class 2 is 4 passes per blade. Most wheels 20 in. on down are checked to a class 2. Thats about a 1/2 in. width scan on a 4 in. blade. New factory props are only checked to a class 5. I can't imagine what you get off the hammer blocks. There is one prop company that is producing a wheel from a forged blank. They CNC the blank to whatever size you want. Of course the blank must be close to the size you want to start with. I saw a few of these wheels and they sure look nice. A bit pricey but they ought to be worth it in the long run. Due to there strength and stress relief. They should have the strength of stainless and maintain there shape for a long time. I think the machined wheels will be my next purchase. Bill

 

[Genesis]

A GOOD prop guy with a set of hammer blocks can do damn near as good as the scanner guys.

I had mine scanned this spring. They were VERY close - and the last time they were done, it was the "old way."

The Propscan guys commented that they were quite impressed that they were almost dead-on. It was quite cheap to have them tune 'em for that reason - there wasn't much to fix.....