sharrow propeller. a revolution?

[rslifkin]

Wow. One whole prop comparison published. What if the conventional props were the wrong fit for the test boat? No one has ever cherrypicked tests to make their product look good? Color me skeptical. I honestly hope they find a true step change in performance.

I absolutely agree that they didn't test a wide enough range of props for a good comparison. But even still, showing that big a gain with the same size prop is still significant.

 

[LarryM]

That does seem to be true... as they mentioned it was speed through water and not speed over land. I'm not in knowledge of water sensor type that is 100% accurate. Guess there may be some. Interesting they did not mention [or show] water sensor used nor its reputed %age of accuracy??

They are pretty accurate. The Airmar ultrasonic sensor accuracy is ±0.1 knots for speed under 10 knots and ±1% for speed above 10 knots.

The B&G sensors are rated at ±2%.

They didn't state which brand they used, but there a number of manufacturers now producing them and most have decent reputations for accuracy. Airmar seems to be the most common as they supply them to most of the majors.

 

[Art]

Although I find the posts interesting, I am certainly not an engineer and can offer no observations that could be technical in nature. I can, however, offer a "first thought" after seeing a photo of the subject propeller. It looks like it could attach itself to all kinds of fowling material, quicker than most other propellers! Seaweed, fishing tackle, lobster trap lines, plastic bags, etc.

Keen observation!

Makes me think... if seaweed [or other items] were to become tangled... would simply going into reverse thrusts [such as with standard props] be able to untangle the attached item?

 

[Nomad Willy]

Walt, Art I agree.
Could turn into a ball of kelp quickly.

 

[diver dave]

I will predict that a real 10 to 15% improvement in range/fuel used will trump any fouling issues; and also will overcome the straightening die issue that will be interesting to see.

 

[Art]

Walt, Art I agree.
Could turn into a ball of kelp quickly.

That Codger Walt! Taint his first day on the beach!!

 

[Codger2]

I will predict that a real 10 to 15% improvement in range/fuel used will trump any fouling issues; and also will overcome the straightening die issue that will be interesting to see.

Geez, I did not think of that but the tool to straighten that prop will be the next revolution!

 

[OldDan1943]

Vibration? Note the RPM or range of RPMs, tell this to the prop shop ... One can have the prop tuned to different levels. Mine is tuned to level 3 which I am told is a bit over kill for a trawler/tug. So this is where I would start... Then, get out the Prushin blue and verify the proper contact between the tapper of the prop and the shaft, replace the nut. Got a key way and key? At least replace the key after close inspection of the key way. Pull the shaft and have that check for straightness and alignment. While you have it pulled, change all the bearings and couplings. Dont check them, replace them even if the look good. Once inside the boat, I think all that is left is, the transmission support and then engine motor mounts.
This will take lots of time and and a few out of the water activities.

But, I would start by tuning the prop first.

 

[stubones99]

Vibration? Note the RPM or range of RPMs, tell this to the prop shop ... One can have the prop tuned to different levels. Mine is tuned to level 3 which I am told is a bit over kill for a trawler/tug. So this is where I would start... Then, get out the Prushin blue and verify the proper contact between the tapper of the prop and the shaft, replace the nut. Got a key way and key? At least replace the key after close inspection of the key way. Pull the shaft and have that check for straightness and alignment. While you have it pulled, change all the bearings and couplings. Dont check them, replace them even if the look good. Once inside the boat, I think all that is left is, the transmission support and then engine motor mounts.
This will take lots of time and and a few out of the water activities.

But, I would start by tuning the prop first.

Dan, if you had watched the Sharrow propeller video, you would see that one of the many advantages is it has less vibration...

 

[Aquabelle]

If you measure with a bent stick, so long as both measurements are taken with the same bent stick the differences measured will be valid.

Wow. One whole prop comparison published. What if the conventional props were the wrong fit for the test boat? No one has ever cherrypicked tests to make their product look good? Color me skeptical. I honestly hope they find a true step change in performance.

 

[OldDan1943]

Dan, if you had watched the Sharrow propeller video, you would see that one of the many advantages is it has less vibration...

One can eliminate the vibration long before he has props ready for a trawler.
Plus, if there is a mechanical reason for the vibration, better to find out now before it does additional damage to the running gear.

 

[OldDan1943]

I think right now he is aiming at the outboard market.

 

[Bluto]

I wonder how he is building those. That would be a tricky thing to produce.
Repairs may be almost impossible once it's damaged. Those loops smoothly change in pitch.. A curvy blade is one thing, these curving arches have me stymied for a theory of "How'd he do dat??"
I imagine he's using aluminum over stainless because stainless is very hard to work compared to softer aluminum.


This is an exciting advancement if it works as reported.

 

[wfleenor]

They cast the basic form and then use a multi-axis milling system to complete it.

 

[Nomad Willy]

Don’t see it being repaired the usual way.

 

[Haloo]

I think right now he is aiming at the outboard market.

If all you fellas want to fund a couple of these Sharrow props for me, I'd be happy to try them out on my outboards and report back. I promise to be unbiased.

 

[LarryM]

I think right now he is aiming at the outboard market.

Hard to tell. Here is the Sharrow Website where Custom Inboards, Commercial and Military are already available. Recreational is coming soon. Looks like they are starting big (custom) and working their way down in size. I just signed up for the Recreational updates. Might be interesting to try on my sportie. I'll likely need a gofundme to do it though

 

[FF]

15% better is the usual claim for counter rotating props , and even std shaped props with a ring around them.

Price and ability to repair may count for more to rec. boaters.

 

[Art]

How often [i.e.how many times] have you actually needed to replace your prop(s)?

Props on my boats are currently in fine condition. Props on boats I've owned since the mid 1960's to early 70's have always been kept in darn good condition.

Only time I recall changing props [due to needing to] was way back in my mid teens through early-20's; on smaller boats I had, when I was not nearly careful enough about prop collisions with bottoming as well as avoiding flotsam.

So... although I am very interested in this new prop design... I will continue eating popcorn for quite a while watching the Sharrow prop market evolve.

It appears to me the biggest and immediate [pleasure boat] market for Sharrow [pretzel like design] props will be as added cost feature opportunities on new boats. Pleasure boaters who do 1000 hours [that's 125 8hr. travel days] or more cruising per year may want them for fuel savings... if they save as much as is being predicted. Working boat market may be similar in their new boat arena... yet somewhat different for also changing props on existing boats; as long as cost-savings work out over the long run.

Hoping to see more tests and stats provided on these "new fangled", screw-propulsion Sharrow prop units that will each attach to the end of power shafts... just like the old props have always done!

I love new and better designs for all items. Wishing Sharrow the best luck!

 

[Codger2]

I love new and better designs for all items. Wishing Sharrow the best luck!

I'm with Art & others on this one.....I've tried many new component designs on my boats over the years but I will wait until the dust settles on this one. (Pass the popcorn, Art!)

 

[Art]

I'm with Art & others on this one.....I've tried many new component designs on my boats over the years but I will wait until the dust settles on this one. (Pass the popcorn, Art!)

Need plenty... could be a long movie!

I joined in the update sector of their website. Will be great if this new design really grows legs by providing robust prop-design improvements. They just might have something here!

 

[OldDan1943]

I figure I will be dead and buried before the prop hits the Rec market. Then, as we all know, different boats need different props etc.

 

[Art]

Did Noah have a get home-engine?

If he did - bet it did't have a Sharrow prop!

 

[Shrew]

This statement has me curious:

"The SHARROW PROPELLER™ generates more thrust and uses less energy for a given RPM than a standard propeller design"

The same can be achieved by increasing pitch, however that also translates to increased load.

How does one achieve an increase in thrust (forward movement) with the same or lower RPM and NOT increase load in the process?

I could literally make the same claim by increasing the prop pitch until it was over-propped. I see no mention of impact to Max RPM at WOT.

 

[rslifkin]

A prop isn't 100% efficient. Some energy is wasted throwing vortices off the blade tips, some is wasted as skin drag, etc. So if you can reduce the drag of moving the prop blades through the water and reduce tip vortices, you need less energy to produce a given amount of thrust.

 

[LarryM]

This statement has me curious:

"The SHARROW PROPELLER™ generates more thrust and uses less energy for a given RPM than a standard propeller design"

The same can be achieved by increasing pitch, however that also translates to increased load.

How does one achieve an increase in thrust (forward movement) with the same or lower RPM and NOT increase load in the process?

I could literally make the same claim by increasing the prop pitch until it was over-propped. I see no mention of impact to Max RPM at WOT.

Rslifkin just beat me to the reply

I think the answer is ultimately less slippage and lower drag. More of the power from the engine in translated into thrust because the design is more efficient. RPM and load remain the same, but thrust increases, and boat speed goes up. Or, boat speed remains the same as before, but RPM and load are reduced. At least theoretically.

 

[Art]

I think Sharrow prop design holds merit. I'm not clear on just how much merit... hopefully a lot!

 

[rgano]

The design's merits might have more impact on me had they just left out that first prop as a comparison. Comparison between a tanks and a sport car comes to mind....

 

[diver dave]

Rslifkin just beat me to the reply

I think the answer is ultimately less slippage and lower drag. More of the power from the engine in translated into thrust because the design is more efficient. RPM and load remain the same, but thrust increases, and boat speed goes up. Or, boat speed remains the same as before, but RPM and load are reduced. At least theoretically.

Pretty close. It's actually power efficiency at the root of this chase. IE; power out / power in. Power in can be expressed at RPM x Torque. Power out can be expressed as thrust. Its the losses in the prop to be minimized. For instance, the water flow that is radial, and not axial. And, these bubbles that had been presented as cavitation losses. Boiling water with low pressure areas (excessive blade loading) is not essential for thrust! And, lastly, water heating is not appreciated here (blade friction). These are few that come to mind.

ps: thrust is not a good measure of work, actually, force is not a measure of power or work at all. You need to consider a force over a unit of distance. But, I propose it is a valid unit of measure to describe efficiency, and fairly easy to measure in real world, using a shaft mounted strain gauge.

pps: the tugboat bollard test comes to mind. Engine at WOT, lots of torque and thrust. But, zero speed and 100% slip for 0% "efficiency". So, speed needs to come into the equations at some point.

 

[OldDan1943]

If he did - bet it did't have a Sharrow prop!

Maybe, remember, 'everything old is new again.'