[Amel Yacht Owners] Re: Props and rpm


Patrick McAneny
 

Bill, Thank you for your detailed reply. If I understand you correctly and correct me if I am wrong, Amel purposely over pitched my fixed prop to restrain it from attaining higher rpms and Volvo is fine with that. So, can owners with Yanmars obtain max rpms? I can't imagine I would want to hear my engine running higher than 3000 rpm , I feel as though I am over stressing it at that , I know it stresses me . So whatever prop I should buy , I should have them sell me a prop size and pitch that keeps my TMD22a under 3000 rpm. I know you were involved in the charter business , do you have any experience with Flexofold or Max Prop ?
Thanks Again,
Pat
SM #123


-----Original Message-----
From: greatketch@... [amelyachtowners]
To: amelyachtowners
Sent: Sun, May 13, 2018 10:12 am
Subject: [Amel Yacht Owners] Re: Props and rpm

 
Pat,

It is totally "normal" when picking a prop for a diesel engine to do exactly as Felxofold suggests.  You pick a propeller that allows the engine to turn its full rated RPM at full throttle. (which is where the engine power rating is specified). The way a propeller power curve is shaped, there is no advantage to operating the engine at its "maxiumum torque."

Most engine makers will insist on speed matching as part of the proper installation.  In fact, Volvo does on their other engines.  If you installed most marine diesel engines propped to run at 1500RPM below rating at full throttle, they would struggle, have significant maintenance issues, and have a shorter than expected lifespan.

With THIS engine in particular, Volvo did not insist. They even suggested in the engine manual that there are advantages to "over-propping" the engine and having it peak at lower RPM than its full rating. In fact you have to look really hard to even find Volvo mentioning the 4500 RPM number! I am not completely sure WHY Volvo felt this appropriate for this engine, but Amel took advantage of this flexibility in full throttle RPM, and propped it to full-throttle at about 3000RPM.  

I think the history of this engine in Amels supports that decision.  We do suffer from some issues (minor carbon build up in the turbo, and constant black soot on the hull) that come from it, but but they seem to have a long and relatively trouble free service life, as a rule.  Mine just turned 8000 hours.  If I figure 12,000 hours as a reasonable lifespan, that gives me another... 15 years :)

This is one of those places where someone coming from a long history with other boats looks at the Volvo installation in an Amel and decides right away that it is wrong...  but it works exactly like it is supposed to.

My wild speculation with what happened on this engine, is that that Perkins specified the max RPM with an eye to the Automotive market.  It was a popular engine in Land Rovers, among others. A redline RPM means something very different in an automobile, where running at maximum rated RPM is an unusual and short term event.  (At least the way I drive.) In addition, automobile engines that last 5000 hours are the exception, not the rule.

In a marine installation, an engine operates very high up on its power curve--all the time.  Volvo probably felt that operating the engine at 450 0RPM continuously wasn't a good idea for service and longevity, but for some reason didn't want to change the injection pump to lower the peak RPM and HP rating of the engine.  I suspect because they wanted to keep the 74HP rating as a sales tool--even if it was unrealistic for a typical marine installation.

Long and short of this is: Have flexofold specify a prop that will load your engine enough that it tops out at something between 2900 and 3300RPM.  You'll motor at 8 knots (full throttle), and be happy.

Bill Kinney
SM160, Harmonie
Rock Sound Harbour, Eleuthera, Bahamas

---In amelyachtowners@..., wrote :

I had flexofold suggest a prop and pitch that would allow the engine reach its max rpm , in my case 4500 . I now ju st read on the Max prop website , that their prop would also allow the engine to reach full rpm ,"in flat water." I wrote back to Flexofold that this did not sound correct , as my fixed prop does not allow me to get beyond 3000, and I have not read about anyone else able to reach rpms that high. I would think  reaching max torque would be the goal . Should a prop/ pitch allow an engine to obtain max rpms ? I don't know what to think or what is correct on this subject, and I may owe Flexofold a retraction.
Thanks,
Pat
SM #123


Craig Briggs
 

Hi Pat,
Just to add a couple of points to your cogimatations, you can adjust the Max Prop pitch to what you prefer, fine tuning as necessary as you go. You may also want to check out the AutoStream by Australian company Seahawk, distributed in the US by Martec.  It's a beautiful stainless steel feathering prop similar to the MaxProp and the pitch can be adjusted without removing the prop, as I believe the MaxProp requires (perhaps just some models). Much less expensive than the MaxProp, too.
Cheers,
Craig SN68 Sangaris


---In amelyachtowners@..., <sailw32@...> wrote :

Bill, Thank you for your detailed reply. If I understand you correctly and correct me if I am wrong, Amel purposely over pitched my fixed prop to restrain it from attaining higher rpms and Volvo is fine with that. So, can owners with Yanmars obtain max rpms? I can't imagine I would want to hear my engine running higher than 3000 rpm , I feel as though I am over stressing it at that , I know it stresses me . So whatever prop I should buy , I should have them sell me a prop size and pitch that keeps my TMD22a under 3000 rpm. I know you were involved in the charter business , do you have any experience with Flexofold or Max Prop ?
Thanks Again,
Pat
SM #123


-----Original Message-----
From: greatketch@... [amelyachtowners] <amelyachtowners@...>
To: amelyachtowners <amelyachtowners@...>
Sent: Sun, May 13, 2018 10:12 am
Subject: [Amel Yacht Owners] Re: Props and rpm

 
Pat,

It is totally "normal" when picking a prop for a diesel engine to do exactly as Felxofold suggests.  You pick a propeller that allows the engine to turn its full rated RPM at full throttle. (which is where the engine power rating is specified). The way a propeller power curve is shaped, there is no advantage to operating the engine at its "maxiumum torque."

Most engine makers will insist on speed matching as part of the proper installation.  In fact, Volvo does on their other engines.  If you installed most marine diesel engines propped to run at 1500RPM below rating at full throttle, they would struggle, have significant maintenance issues, and have a shorter than expected lifespan.

With THIS engine in particular, Volvo did not insist. They even suggested in the engine manual that there are advantages to "over-propping" the engine and having it peak at lower RPM than its full rating. In fact you have to look really hard to even find Volvo mentioning the 4500 RPM number! I am not completely sure WHY Volvo felt this appropriate for this engine, but Amel took advantage of this flexibility in full throttle RPM, and propped it to full-throttle at about 3000RPM.  

I think the history of this engine in Amels supports that decision.  We do suffer from some issues (minor carbon build up in the turbo, and constant black soot on the hull) that come from it, but but they seem to have a long and relatively trouble free service life, as a rule.  Mine just turned 8000 hours.  If I figure 12,000 hours as a reasonable lifespan, that gives me another... 15 years :)

This is one of those places where someone coming from a long history with other boats looks at the Volvo installation in an Amel and decides right away that it is wrong...  but it works exactly like it is supposed to.

My wild speculation with what happened on this engine, is that that Perkins specified the max RPM with an eye to the Automotive market.  It was a popular engine in Land Rovers, among others. A redline RPM means something very different in an automobile, where running at maximum rated RPM is an unusual and short term event.  (At least the way I drive.) In addition, automobile engines that last 5000 hours are the exception, not the rule.

In a marine installation, an engine operates very high up on its power curve--all the time.  Volvo probably felt that operating the engine at 450 0RPM continuously wasn't a good idea for service and longevity, but for some reason didn't want to change the injection pump to lower the peak RPM and HP rating of the engine.  I suspect because they wanted to keep the 74HP rating as a sales tool--even if it was unrealistic for a typical marine installation.

Long and short of this is: Have flexofold specify a prop that will load your engine enough that it tops out at something between 2900 and 3300RPM.  You'll motor at 8 knots (full throttle), and be happy.

Bill Kinney
SM160, Harmonie
Rock Sound Harbour, Eleuthera, Bahamas

---In amelyachtowners@..., <sailw32@...> wrote :

I had flexofold suggest a prop and pitch that would allow the engine reach its max rpm , in my case 4500 . I now ju st read on the Max prop website , that their prop would also allow the engine to reach full rpm ,"in flat water." I wrote back to Flexofold that this did not sound correct , as my fixed prop does not allow me to get beyond 3000, and I have not read about anyone else able to reach rpms that high. I would think  reaching max torque would be the goal . Should a prop/ pitch allow an engine to obtain max rpms ? I don't know what to think or what is correct on this subject, and I may owe Flexofold a retraction.
Thanks,
Pat
SM #123


Patrick McAneny
 

Craig, I will check it out, they all sound good according to their propaganda . But which is the best,how do you know. Yachting Monthly did a prop test, but then that was brought into question. 
Thanks,
Pat SM#123


-----Original Message-----
From: sangaris@... [amelyachtowners]
To: amelyachtowners
Sent: Sun, May 13, 2018 11:11 am
Subject: Re: [Amel Yacht Owners] Re: Props and rpm

 
Hi Pat,
Just to add a couple of points to your cogimatations, you can adjust the Max Prop pitch to what you prefer, fine tuning as necessary as you go. You may also want to check out the AutoStream by Australian company Seahawk, distributed in the US by Martec.  It's a beautiful stainless steel feathering prop similar to the MaxProp and the pitch can be adjusted without removing the prop, as I believe the MaxProp requires (perhaps just some models). Much less expensive than the MaxProp, too.
Cheers,
Craig SN68 Sangaris


---In amelyachtowners@..., wrote :

Bill, Thank you for your detailed reply. If I understand you correctly and correct me if I am wrong, Amel purposely over pitched my fixed prop to restrain it from attaining higher rpms and Volvo is fine with that. So, c an owners with Yanmars obtain max rpms? I can't imagine I would want to hear my engine running higher than 3000 rpm , I feel as though I am over stressing it at that , I know it stresses me . So whatever prop I should buy , I should have them sell me a prop size and pitch that keeps my TMD22a under 3000 rpm. I know you were involved in the charter business , do you have any experience with Flexofold or Max Prop ?
Thanks Again,
Pat
SM #123


-----Original Message-----
From: greatketch@... [amelyachtowners] <amelyachtowners@...>
To: amelyachtowners <amelyachtowners@...>
Sent: Sun, May 13, 2018 10:12 am
Subject: [Amel Yacht Owners] Re: Props and rpm

 
Pat,

It is totally "normal" when picking a prop for a diesel engine to do exactly as Felxofold suggests.  You pick a propeller that allows the engine to turn its full rated RPM at full throttle. (which is where the engine power rating is specified). The way a propeller power curve is shaped, there is no advantage to operating the engine at its "maxiumum torque."

Most engine makers will insist on speed matching as part of the proper installation.  In fact, Volvo does on their other engines.  If you installed most marine diesel engines propped to run at 1500RPM below rating at full throttle, they would struggle, have significant maintenance issues, and have a shorter than expected lifespan.

With THIS engine in particular, Volvo did not insist. They even suggested in the engine manual that there are advantages to "over-propping" the engine and having it peak at lower RPM than its full rating. In fact you have to look really hard to even find Volvo mentioning the 4500 RPM number! I am not completely sure WHY Volvo felt this appropriate for this engine, but Amel took advantage of this flexibility in full throttle RPM, and propped it to full-throttle at about 3000RPM.  

I think the history of this engine in Amels supports that decision.  We do suffer from some issues (minor carbon build up in the turbo, and constant black soot on the hull) that come from it, but but they seem to have a long and relatively trouble free service life, as a rule.  Mine just turned 8000 hours.  If I figure 12,000 hours as a reasonable lifespan, that gives me another... 15 years :)

This is one of those places where someone coming from a long history with other boats looks at the Volvo installation in an Amel and decides right away that it is wrong...  but it works exactly like it is supposed to.

My wild speculation with what happened on this engine, is that that Perkins specified the max RPM with an eye to the Automotive market.  It was a popular engine in Land Rovers, among others. A redline RPM means something very different in an automobile, where running at maximum rated RPM is an unusual and short term event.  (At least the way I drive.) In addition, automobile engines that last 5000 hours are the exception, not the rule.

In a marine installation, an engine operates very high up on its power curve--all the time.  Volvo probably felt that operating the engine at 450 0RPM continuously wasn't a good idea for service and longevity, but for some reason didn't want to change the injection pump to lower the peak RPM and HP rating of the engine.  I suspect because they wanted to keep the 74HP rating as a sales tool--even if it was unrealistic for a typical marine installation.

Long and short of this is: Have flexofold specify a prop that will load your engine enough that it tops out at something between 2900 and 3300RPM.  You'll motor at 8 knots (full throttle), and be happy.

Bill Kinney
SM160, Harmonie
Rock Sound Harbour, Eleuthera, Bahamas

---In amelyachtowners@..., wrote :

I had flexofold suggest a prop and pitch that would allow the engine reach its max rpm , in my case 4500 . I now ju st read on the Max prop website , that their prop would also allow the engine to reach full rpm ,"in flat water." I wrote back to Flexofold that this did not sound correct , as my fixed prop does not allow me to get beyond 3000, and I have not read about anyone else able to reach rpms that high. I would think  reaching max torque would be the goal . Should a prop/ pitch allow an engine to obtain max rpms ? I don't know what to think or what is correct on this subject, and I may owe Flexofold a retraction.
Thanks,
Pat
SM #123


greatketch@...
 



Yes, Amel overpitched the prop on the Volvo on purpose. Volvo suggested that one of several reasons that you might want to restrict the top speed of the engine was "reduced noise."  

 I don't know what Amel did on the Yanmars.  I am sure somebody here can answer that...

I wouldn't tell them "under 3000" but rather give them 3000 as the target.  Lower speeds will result in lower net power output from the engine, so you don't want to drop much.

I have owned two boats with a "Classic" 3 blade MaxProp (including Harmonie) and have been very happy with them.  They work, they are easy to care for, no bearings, seals, or other parts that wear out.  Every haulout I take mine apart and clean and grease it.  I keep a zinc on the end, and all has been good.

I have no experience with Flexofold specifically.  My fleet experience with folding props is limited to Martec brand props on racing sailboats.  Not applicable to a SM installation, but I didn't particularly like them, both from a maintenance and a performance under power standpoint. The maintenance issue was wear of the pivot pins. They needed regular replacement.

In the real world, I very much doubt there is anything other than a theoretical performance difference between any of the major brands of folding or feathering props.  Certainly in sailing performance, and even in motoring the differences aren't really going to be significant. Many folding props struggle a bit with reverse, but I suspect that is more a case of the helmsman needing to rev the engine more than he was used to.

One nice thing about a Maxprop: Based the experiences of other SM owners who have them installed by Amel in the early production run, you know exactly which one to get and where to set the adjustable pitch without trial and error. No need to pay the premium for the model with in-water pitch adjustment.

And as a total aside.... Speaking of "premium," the new 5 blade Maxprop is a beautiful piece of machinework!  Priced like fine jewelry, but I imagine it is runs really, really smoothly.  Certainly not worth it for the two or three hundred hours a year I have the engine running, but it would certainly make me the star of the boatyard at haulout!

Bill Kinney
Sm#160, Harmonie
Rock Sound Harbour, Eleuthera, Bahamas

---In amelyachtowners@..., <sailw32@...> wrote :

Bill, Thank you for your detailed reply. If I understand you correctly and correct me if I am wrong, Amel purposely over pitched my fixed prop to restrain it from attaining higher rpms and Volvo is fine with that. So, can owners with Yanmars obtain max rpms? I can't imagine I would want to hear my engine running higher than 3000 rpm , I feel as though I am over stressing it at that , I know it stresses me . So whatever prop I should buy , I should have them sell me a prop size and pitch that keeps my TMD22a under 3000 rpm. I know you were involved in the charter business , do you have any experience with Flexofold or Max Prop ?
Thanks Again,
Pat
SM #123


Jose Venegas
 

I did some studying when I was buying a prop for my previous Beneteau 361.  I found that selecting the type of folding prop depended on the objective.  If it is to reduce drag while sailing the Flexofold or Max prop are pretty good doing that, and better than the Auto-prop which, at low wind conditions tends to take strange configurations causing extra drag. In the category the Max prop because its blades are flat has the lowest drag.
If the objective is to minimize fuel consumption during motoring, the blade of the Flexofold and the Autoprop are better shaped with an angle of attack that is reduced from the center outwards (twist).  This is important because the speed of the blade relative to the water increases with the radius of a rotating object.  The Autoprop blades have a constant angle of attack (flat blades) which is less efficient and can cause flow separation, turbulence, and possibly cavitation reducing their efficiency. 

Finally, if optimizing fuel consumption while motor-sailing is the objective, the  Autoprop is best as it adjusts its angle of attack as the wind increases and keeps the prop working efficiently.  Fix pitched props like the Flex or Max as the wind increases they end up spinning adding little power.   

In summary,  If cost is not the issue, I find that the Autoprop is Ideal for those of us that tend to motor-sail when the wind is low or comes from the nose.

My 5 cents.

Jose Venegas
Ipanema SM2K 278
Boston


karkauai
 

I’m very happy with my MaxProp. It’s not as persnickety as the AutoProp about growth.  I service it at every bottom paint job when I change the shaft seals and WOB.

They make a model that can be repitched in the water.  It’s a lot more expensive than the standard model that you have to haul out to repitch.  I had to do one quick haul to repitch when I reported with the Yanmar.



Kent Robertson
S/V Kristy
SM243


Patrick McAneny
 

Kent, Didn't know you had bought the Max prop , glad you are happy with it, I think I am going with it. I may give you a call.
Thanks,
Pat


-----Original Message-----
From: Kent Robertson karkauai@... [amelyachtowners]
To: amelyachtowners
Sent: Sun, May 13, 2018 12:58 pm
Subject: Re: [Amel Yacht Owners] Re: Props and rpm

 
I’m very happy with my MaxProp. It’s not as persnickety as the AutoProp about growth.  I service it at every bottom paint job when I change the shaft seals and WOB.

They make a model that can be repitched in the water.  It’s a lot more expensive than the standard model that you have to haul out to repitch.  I had to do one quick haul to repitch when I reported with the Yanmar.



Kent Robertson
S/V Kristy
SM243


greatketch@...
 

Jose,

I completely agree with the engineering theory of your analysis.  

Where we might differ is I simply do not believe that a on a boat like an SM the drag difference between an Autoprop(worst) and a Maxprop (best) would be at all noticeable to anybody cruising. Especially since people who would chose the Autoprop for the promise of its improved motoring performance are most likely to be motoring at the times when the difference would be largest.

All of these options have drag an order of magnitude lower than a fixed three blade prop, and that difference is most certainly easily noticeable!  But the differences in drag between the various folding/feathering options simply isn't significant given all the other variables involved.

In the real world, an Autoprop costs about $1000 more than a classic Maxprop of similar size. If I accept on faith the maximum fuel economy improvement that Autoprop claims in their marketing (30%), to generate a positive payback would require more miles of motorsailing  than I will likely do in the rest of my cruising life.  Other people do motor sail a lot more than I do and might come to a different conclusion.  

Bill Kinney
Sm160, Harmonie
Rock Sound Harbour, Eleuthera, Bahamas



---In amelyachtowners@..., <jvenegas@...> wrote :

I did some studying when I was buying a prop for my previous Beneteau 361.  I found that selecting the type of folding prop depended on the objective.  If it is to reduce drag while sailing the Flexofold or Max prop are pretty good doing that, and better than the Auto-prop which, at low wind conditions tends to take strange configurations causing extra drag. In the category the Max prop because its blades are flat has the lowest drag.
If the objective is to minimize fuel consumption during motoring, the blade of the Flexofold and the Autoprop are better shaped with an angle of attack that is reduced from the center outwards (twist).  This is important because the speed of the blade relative to the water increases with the radius of a rotating object.  The Autoprop blades have a constant angle of attack (flat blades) which is less efficient and can cause flow separation, turbulence, and possibly cavitation reducing their efficiency. 

Finally, if optimizing fuel consumption while motor-sailing is the objective, the  Autoprop is best as it adjusts its angle of attack as the wind increases and keeps the prop working efficiently.  Fix pitched props like the Flex or Max as the wind increases they end up spinning adding little power.   

In summary,  If cost is not the issue, I find that the Autoprop is Ideal for those of us that tend to motor-sail when the wind is low or comes from the nose.

My 5 cents.

Jose Venegas
Ipanema SM2K 278
Boston


Patrick McAneny
 

Jose, I would have already bought an Autoprop and almost did, until I was informed that the shaft housing had not been modified as on later models to accept the Autoprop.
Thanks,
Pat
SM#123



-----Original Message-----
From: jvenegas@... [amelyachtowners]
To: amelyachtowners
Sent: Sun, May 13, 2018 12:24 pm
Subject: Re: [Amel Yacht Owners] Re: Props and rpm

 
I did some studying when I was buying a prop for my previous Beneteau 361.  I found that selecting the type of folding prop depended on the objective.  If it is to reduce drag while sailing the Flexofold or Max prop are pretty good doing that, and better than the Auto-prop which, at low wind conditions tends to take strange configurations causing extra drag. In the category the Max prop because its blades are flat has the lowest drag.
If the objective is to minimize fuel consumption during motoring, the blade of the Flexofold and the Autoprop are better shaped with an angle of attack that is reduced from the center outwards (twist).  This is important because the speed of the blade relative to the water increases with the radius of a rotating object.  The Autoprop blades have a constant angle of attack (flat blades) which is less efficient and can cause flow separation, turbulence, and possibly cavitation reducing thei r efficiency. 

Finally, if optimizing fuel consumption while motor-sailing is the objective, the  Autoprop is best as it adjusts its angle of attack as the wind increases and keeps the prop working efficiently.  Fix pitched props like the Flex or Max as the wind increases they end up spinning adding little power.   

In summary,  If cost is not the issue, I find that the Autoprop is Ideal for those of us that tend to motor-sail when the wind is low or comes from the nose.

My 5 cents.

Jose Venegas
Ipanema SM2K 278
Boston


karkauai
 

I didn’t notice a significant difference between fuel consumption between the AutoProp and MaxProp.


Kent Robertson
S/V Kristy
SM243


karkauai
 

I still have my old AutoProp if anyone wants to buy it.  It’s just taking up space now, so you can have it for a good price.
 I think a good prop shop can modify it to fit your shaft.



Kent Robertson
S/V Kristy
SM243