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#1
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What I've Learned About Props
Hi,
After the "What prop should I use", I've done some research and thougth I'd post what I've learned about various props. Fixed-blade prop: This is the simplest and least expensive option. The blades are fixed at a certain pitch. They also give the most drag under sail. To reduce this, most sailing props are thinner, "high-aspect-ratio", and usually have more advanced foil designs like "cupping" to increase drive in forward. The downside of THIS is that in reverse, the advanced foil is going through the water backwards, reducing effectiveness. Examples: Michigan Wheel "Sailor" series and Campbell Sailor props. Cost: around $500 CDN Folding Prop: This is the ultimate sailing-compromise prop. Under sail, the blades fold down to become hardly more than a giant "teardrop" on the end of the shaft, giving virtually no drag. Under power, the rotation pushes the blades out, and the backward force pushes the blades out completely. The downside of this is that in reverse, the force is trying to FOLD the blades, and centrifugal force is all that's keeping them out. This means VERY poor performance under power in reverse. Examples...? Cost: ?? Feathering Prop: Instead of the entire blade folding down under sail, they rotate, ("feathering") so that the leading edge is all that is presented. This is not QUITE as low-drag as a folding prop, but far lower than a fixed prop. When under power, the blade rotates to a fixed pitch angle. The side benefit is that it rotates the opposite way to reverse, so the leading edge is leading in both forward and reverse, meaning any cupping or advanced foil design is used in both directions. Another side benefit is that most props allow you to adjust the "fixed" pitch, some easily enough that it can be done underwater, eliminating the need to haulout to get that "perfect" pitch. Examples: Maxprop and AutostreaM Cost: About $2000 CDN Auto-prop: This is the same as a feathering prop, but instead of a fixed pitch, the pitch varies with speed, torque, etc. similar to the "torque convertor" on a ski-doo. This allows max power at all settings, best fuel economy, fastest cruising and WOT speed, etc. The downside of course is the cost. Example: AutoProp (don't know of any others) Cost: $3000 CDN Lloyd Sumpter "Far Cove" Catalina 36 |
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#2
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What I've Learned About Props
In "Lloyd Sumpter" writes:
Hi, After the "What prop should I use", I've done some research and thougth I'd post what I've learned about various props. Fixed-blade prop: This is the simplest and least expensive option. The blades are fixed at a certain pitch. They also give the most drag under sail. To reduce this, most sailing props are thinner, "high-aspect-ratio", and usually have more advanced foil designs like "cupping" to increase drive in forward. The downside of THIS is that in reverse, the advanced foil is going through the water backwards, reducing effectiveness. Examples: Michigan Wheel "Sailor" series and Campbell Sailor props. Cost: around $500 CDN Folding Prop: This is the ultimate sailing-compromise prop. Under sail, the blades fold down to become hardly more than a giant "teardrop" on the end of the shaft, giving virtually no drag. Under power, the rotation pushes the blades out, and the backward force pushes the blades out completely. The downside of this is that in reverse, the force is trying to FOLD the blades, and centrifugal force is all that's keeping them out. This means VERY poor performance under power in reverse. Examples...? Cost: ?? Looks like you have not learned much about props. Some fixed blade props are very poor on reverse, especially if they are optimized to give the best performance forward and some (good) folding props are as good on reverse than forward and much better than some fixed props on reverse. An example for you is the Danish Gori, but there are others. The centrifugal force has no problem in keeping the Gori open on reverse. There are some poor ones, but why buy a poor one, as there are good ones available? Feathering Prop: Instead of the entire blade folding down under sail, they rotate, ("feathering") so that the leading edge is all that is presented. This is not QUITE as low-drag as a folding prop, but far lower than a fixed prop. When under power, the blade rotates to a fixed pitch angle. The side benefit is that it rotates the opposite way to reverse, so the leading edge is leading in both forward and reverse, meaning any cupping or advanced foil design is used in both directions. Another side benefit is that most props allow you to adjust the "fixed" pitch, some easily enough that it can be done underwater, eliminating the need to haulout to get that "perfect" pitch. Examples: Maxprop and AutostreaM Cost: About $2000 CDN If you have a good three bladed propeller it can be much more quiet while motoring than a two plade folding propeller and can be worth the exstra cost. Auto-prop: This is the same as a feathering prop, but instead of a fixed pitch, the pitch varies with speed, torque, etc. similar to the "torque convertor" on a ski-doo. This allows max power at all settings, best fuel economy, fastest cruising and WOT speed, etc. The downside of course is the cost. You might not be able to recover the cost difference in the fuel saving, especially if you are sailing a lot. - Lauri Tarkkonen Example: AutoProp (don't know of any others) Cost: $3000 CDN Lloyd Sumpter "Far Cove" Catalina 36 |
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#3
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What I've Learned About Props
"Lloyd Sumpter" wrote in message news  Hi, After the "What prop should I use", I've done some research and thougth I'd post what I've learned about various props. Folding Prop: This is the ultimate sailing-compromise prop. Under sail, the blades fold down to become hardly more than a giant "teardrop" on the end of the shaft, giving virtually no drag. Under power, the rotation pushes the blades out, and the backward force pushes the blades out completely. The downside of this is that in reverse, the force is trying to FOLD the blades, and centrifugal force is all that's keeping them out. This means VERY poor performance under power in reverse. Examples...? Cost: ?? I think Martec has their prices on their web site. I have a 27'er and the 12 x 10 folding prop I need is about US$550. Gori was in the same price range, if you're willing to bargain. Both these companies make geared props, where there is an intermediate gear between the blades that forces them to open at the same rate. This keeps vibration to a minimum. In general I agree that folders don't function as well in reverse as a fixed, but if you just increase engine RPMs you can get the thrust you need for most situations. |
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#5
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What I've Learned About Props
We took a three blade Max-Prop around the world on Swee****er and I
would never use anything else for serious cruising. Low drag, excellent thrust in forward and reverse (you really care about thrust in reverse when maneuvering in a tight marina), can be adjusted to exact required pitch. On the other hand, the boat I race on uses a folding prop. The key there is absolutely the lowest possible drag -- nothing else matters -- and only a folding prop will do it. The fact that it's kind of anemic going forward and even worse going backwards, and that you have to set it with the hinge horizontal when you shut off the engine, are secondary to the lowest possible drag. For a serious race boat, I would have nothing else, but I see no other use for one. The standard sailing propeller used to be a two blade with relatively low blade width that would hide behind the keel of the typical long keel boat. Now, with virtually all sailboat propellers out in the open, I wouldn't want a fixed prop under any circumstances -- it's just a big drag. As for AutoProp, it sounds like snake oil to me, and unecessary to boot. The propeller law curve drops off at roughly the third root of RPM ie, HP ~=~ RPM^0.3333). Once you throttle back a little, the HP goes down very fast, almost always a little faster than the engine's ability to produce HP. This protects the engine beautifully -- choose a prop to absorb the HP produced at max revs and you know you have enough HP at all lower revs. Why mess with Mother Nature when she's making life easy? And on our current love? 59"x39" three blade cast iron. Jim Woodward www.mvFintry.com "Matt/Meribeth Pedersen" wrote in message link.net... "Lloyd Sumpter" wrote in message news Hi, After the "What prop should I use", I've done some research and thougth I'd post what I've learned about various props. Folding Prop: This is the ultimate sailing-compromise prop. Under sail, the blades fold down to become hardly more than a giant "teardrop" on the end of the shaft, giving virtually no drag. Under power, the rotation pushes the blades out, and the backward force pushes the blades out completely. The downside of this is that in reverse, the force is trying to FOLD the blades, and centrifugal force is all that's keeping them out. This means VERY poor performance under power in reverse. Examples...? Cost: ?? I think Martec has their prices on their web site. I have a 27'er and the 12 x 10 folding prop I need is about US$550. Gori was in the same price range, if you're willing to bargain. Both these companies make geared props, where there is an intermediate gear between the blades that forces them to open at the same rate. This keeps vibration to a minimum. In general I agree that folders don't function as well in reverse as a fixed, but if you just increase engine RPMs you can get the thrust you need for most situations. |
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#6
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What I've Learned About Props
Lauri Tarkkonen wrote:
Looks like you have not learned much about props. Some fixed blade props are very poor on reverse, especially if they are optimized to give the best performance forward Lloyd mentioned that. and some (good) folding props are as good on reverse than forward and much better than some fixed props on reverse. An example for you is the Danish Gori, but there are others. The centrifugal force has no problem in keeping the Gori open on reverse. There are some poor ones, but why buy a poor one, as there are good ones available? When I looked for a feathering/folding prop, I'd never met anyone with a folding prop that could depend upon the blades opening fully in reverse every time, particularly in an emergency; they all seemed to have to baby them and learn tricks. I also wondered whether the more modern transmission gearings make it worse: Our 2GM swings at a maximum of 1200 rpm, quite a bit slower than the anemic engine it replaced. If you have a good three bladed propeller it can be much more quiet while motoring than a two plade folding propeller and can be worth the exstra cost. We had to replace our fixed two blade because of harmonic vibrations at high power. The whole boat shook, which can't have been a good thing. The 3-blade is MUCH quieter and smoother; not quite as efficient, but not as bad as I expected. Auto-prop: This is the same as a feathering prop, but instead of a fixed pitch, the pitch varies with speed, torque, etc. similar to the "torque convertor" on a ski-doo. This allows max power at all settings, best fuel economy, fastest cruising and WOT speed, etc. The downside of course is the cost. You might not be able to recover the cost difference in the fuel saving, especially if you are sailing a lot. Overall cost savings don't much enter into this sort of purchase. Cheapest by far would be a fixed prop. It would take us a very long time to consume $1500 worth of fuel, much less save that much on fuel. (In 1067 hours, we consumed 341 gallons.) If you want to save $$, slow down. We normally power at 5.7+/- knots and consume 0.36 gph. That's not an unreasonable speed with our 6.6 knot hull speed. When we went 6.2+/- (enjoying the new prop), consumption was 0.69. When I backed off to 5 knots for a month, consumption over 43 hours was 0.20. To gain just over a knot, we used 3.5 times as much fuel. -- Jere Lull Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD) Xan's Pages: http://members.dca.net/jerelull/X-Main.html Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/ |
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#7
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What I've Learned About Props
Why wouldn't you use anything else for serious cruising? What others have you
used and dismissed for serious cruising? Lots of serious cruisers switch props for different portions of their voyage. BTW, a Martec Autostream feathering prop costs 2/3 of a Max-prop and works just as well. John S/Y Truelove (Jim Woodward) wrote: We took a three blade Max-Prop around the world on Swee****er and I would never use anything else for serious cruising. |
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#8
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What I've Learned About Props
I've raced, cruised, and voyaged, here, in Europe, and around the
world, on deliveries, charters, other people's boats, my own boats, and boats I have built for others. I've talked to a lot of people in a lot of different places, many of whom like MaxProp and some of whom prefer other brands. I have not done anything like a proper comparative test, ala Consumer Reports or Practical Sailor. So all I have is impressions and opinions based on experience. The problem with assessing the goodness of many marine items is that you can look at two of them, side by side, and they both look fine. The fit and finish appears to be the same. Yet one of them is the name brand and the other is 2/3 the price. If you manage to take them out and test them, one may perform better, but is it the good long term choice -- hard to tell. It's hard to make a choice. You can't test longevity easily. Ours is a difficult environment. Corrosion is an issue. Will they both last ten years? Twenty? What is the failure rate likely to be? Are they both built out of the best materials or did one maker cut corners -- and, of course, the corner cutter might be the name brand? Sometimes word of mouth tells you. On our circumnav almost all the voyaging boats had watermakers. About half were a common brand, widely sold. Most of their owners bragged about the wonderful warranty service they got. It turned out that most (maybe all) had had to use it. I have no clue how good Sea Recovery's warranty service is -- we put 700 hours on ours without incident. Which watermaker won't I buy for Fintry? One guess. On feathering propellers, the issue is less clear cut. I've had good experience with MaxProp on a variety of boats. I've used others and had one or two failures. People I respect, who are just as careful with their money as I, pony up the extra for MaxProp. Is this definitive? Absolutely not. But in selecting carefully machined bronze that's going to sit under the boat, occasionally slam back and forth between forward and reverse, now and then take hits from logs and tangles from nets, I take into account everything I know. And, BTW, PYI (the USA distributor for MaxProp) are good people. ------ I don't understand, "Lots of serious cruisers switch props for different portions of their voyage." I can understand changing pitch if you were going up a strong current, for example, and wanted to use all of the engine's short term horsepower rating instead of the more usual use of the continuous rating. I can also imagine a really performance minded person taking off a MaxProp in Panama and putting on a folding two blade for the next 7,000 miles where there's good wind and little motoring -- but I don't know anyone who's done it. What did you have in mind here? ----- Finally, FYI: Martec AutoStream 6000 series $3,000 MaxProp 70322, $3,035 (Both three blade, bronze, 22" for 1.375" shaft) Other sizes may differ. Martec's stainless series are cheaper, but I'm not sure I'd want a stainless prop. http://www.martec-props.com/prices-feathering.htm http://www.pyiinc.com/?section=brows...sku=70322&sn=5 Jim Woodward www.mvFintry.com (Truelove39) wrote in message ... Why wouldn't you use anything else for serious cruising? What others have you used and dismissed for serious cruising? Lots of serious cruisers switch props for different portions of their voyage. BTW, a Martec Autostream feathering prop costs 2/3 of a Max-prop and works just as well. John S/Y Truelove (Jim Woodward) wrote: We took a three blade Max-Prop around the world on Swee****er and I would never use anything else for serious cruising. |
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#9
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What I've Learned About Props
On Sat, 25 Oct 2003 18:07:58 +0000, Jere Lull wrote:
Lauri Tarkkonen wrote: Looks like you have not learned much about props. Some fixed blade props are very poor on reverse, especially if they are optimized to give the best performance forward Lloyd mentioned that. Of course all the data I have is theoretical - YMMV. The "testimonials" I read about how much better even some fixed-blade props were in reverse against folding props were written by folks who replaced their folding props - so obviously they were not happy with them, or at least felt they had to justify their decision. If you have a good three bladed propeller it can be much more quiet while motoring than a two plade folding propeller and can be worth the exstra cost. We had to replace our fixed two blade because of harmonic vibrations at high power. The whole boat shook, which can't have been a good thing. The 3-blade is MUCH quieter and smoother; not quite as efficient, but not as bad as I expected. I will never go back to a 2-blade, period. A writeup at WestByNorth tells why: http://www.westbynorth.com/choose.htm Auto-prop: This is the same as a feathering prop, but instead of a fixed pitch, the pitch varies with speed, torque, etc. similar to the "torque convertor" on a ski-doo. This allows max power at all settings, best fuel economy, fastest cruising and WOT speed, etc. The downside of course is the cost. You might not be able to recover the cost difference in the fuel saving, especially if you are sailing a lot. Overall cost savings don't much enter into this sort of purchase. Cheapest by far would be a fixed prop. It would take us a very long time to consume $1500 worth of fuel, much less save that much on fuel. (In 1067 hours, we consumed 341 gallons.) Agreed! I can see some non-monetary reasons for going to a feathering or folding prop, but can't see the advantage of the auto-prop. I'm now torn between the 3-blade fixed Campbell Sailor and the AutostreaM. I like the AutostreaM's stainless-steel: at the very least, it would Look Kewl on my SS shaft (and I know the corrosion and marine-growth characteristics of SS). I also like the ability to change pitch - I now feel that PITCH is the primary variable to get optimum power/speed from the prop. I suspect that a C.S. fixed would give marginally better performance than an AutostreaM AT OPTIMUM PITCH. But since the A-S is easily adjustable, I think I'd be able to achive optimum pitch much faster and more easily. I'd also like the feathering advantage, although I was jokingly adding up all the "fasters" I could get: feathering gets me 1-2 knots faster, the Sail Guy said a new headsail would get me at least a knot, clean bottom would give me an extra 1/2 to 1 knot...and I was going 6 knots in an 8 knot breeze. So add that all up, and I'd be going about 9-10 knots!  Lloyd Sumpter "Far Cove" Catalina 36 |
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#10
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What I've Learned About Props
On Tue, 28 Oct 2003 07:31:12 +0000, Jim Woodward wrote:
Finally, FYI: Martec AutoStream 6000 series $3,000 MaxProp 70322, $3,035 (Both three blade, bronze, 22" for 1.375" shaft) Other sizes may differ. Martec's stainless series are cheaper, but I'm not sure I'd want a stainless prop. http://www.martec-props.com/prices-feathering.htm http://www.pyiinc.com/?section=brows...sku=70322&sn=5 First, I wonder if the popularity of the MaxProp is because it is US made, whereas the AutostreaM is made in Australia. Check out: http://www.seahawk.com.au/ (the REAL website for AutostreaM) Second, why not a SS prop? Most powerboaters regard a SS prop as "top of the line" (of course they're usually comparing to aluminum...). The SS prop has no "give" so it can utilize advanced foil designs like cupping better (again, mainly compared to aluminum, but I'd probably add composite to this). Also, my SS shaft seems to be less susceptable to electrolysis, corrosion, and marine growth than my Campbell Sailor bronze. Not saying you're wrong, just wondering why you wouldn't want a SS prop. Lloyd Sumpter "Far Cove" Catalina 36 |
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