Sharrow prop

Siochair · 18 October 2019, 21:31

https://www.boattest.com/review/shar...gineering/3986

Has anyone seen this? If the numbers are to be believed this could have a quite an impact.

Last Tango · 19 October 2019, 07:45

Smoke and mirrors.....

It may actually be a decent prop but they could have got the same performance improvement by using a high quality 17" 3 blade and not over-revving the engine beyond manufacturers spec....

nocando · 19 October 2019, 08:53

I think the boy put name in for one or email of interest for more info atleast.

The test is still a reasonable one as it was like for like size wise. In theory all props were undersized slightly for 6k limit. With that said, as it was carried out independently (although some of the equipment was sharrows) it is a reasonable data spread from a company and captain with decent credentials to do the comparison.

Realistically some of the numbers are inflated due to not being on plane versus on plane so a boat owner is unlikely to do that. However, as it was an rpm incremental test in some ways it is understandable they included it.

I watch with interest though and see what other sizes are like in comparison.

beamishken · 19 October 2019, 08:57

Quote:

Originally Posted by Last Tango

Smoke and mirrors.....

It may actually be a decent prop but they could have got the same performance improvement by using a high quality 17" 3 blade and not over-revving the engine beyond manufacturers spec....

They tested it against two Presumably good correctly matched stainless props & bearing in mind the prototypes are aluminium it seemed to do rather well. Only time & a full production presumably stainless sharrow will tell if its a significant improvement or not.
I wouldnt discount it yet, how many people mocked when volvo introduced twin props & then forward facing props

Last Tango · 19 October 2019, 09:13

If you change the effective aspect ratio, which is what they have done, it will have an effect on the speed/rev ratio but if the engine is being revved beyond the manufacturer's recommended maximum the props aren't correctly match and it wasn't set against Mercury's premium props.

I wouldn't dismiss it but I felt the test was a "stitch-up" using two standard mediocre, under-pitched props.

Roflhat · 19 October 2019, 11:06

Pretty clever idea, I believe in the increased efficiency especially looking at the water flow compared to conventional props. The improvement in acceleration I think will be down to the increase in blade area, less slip with effectively 6 blades vs 3. Top speed I'm not sure about, a properly tuned conventional designed propeller I think would out perform the Sharrow.
Saying that a tuned Sharrow might be even better, although I wouldn't know where to start with cupping or tuning one!

nocando · 20 October 2019, 12:46

If you put on a 17" sharrow vs a 17" X then it SHOULD still outperform it, the difference in the tip and turbulence imagery they have on their site is quite something.

You hear of people getting that simply swapping out to an inertia eco for example, quite feasible to see similar with a new prop design (btw, these style props have been about over 100 years in similar guise ish)

Last Tango · 20 October 2019, 18:19

They've been around for 100 years and nobody is using them, why would that be ?

If you change the number of blades, aspect ratio, rake, cup, hub flare, trailing edge lift...etc you likely as not change it's pitch requirements.
My point is they optimised their prop for the outfit...which happened to come in at 15" and decided to compare it to a couple of standard three blade props (maybe ones they found discarded on the beach or under a wood pile in the corner of a shed that just needed a bit of hammering to straighten them out)...their only prerequisite was that they be 15" pitch regardless of whether or not 15" was the right pitch for that type of prop on that boat.
A few bubbles round the tips of a mangled three blade prop proves nothing their test does not stand up to scrutiny.
Let "Mercury" rig the boat with their choice of three blade prop as Sharrow have been allowed to do and I think the result would be very different.

Remember the E-tec V Yamaha "tug of war"

nocando · 20 October 2019, 18:44

Quote:

Originally Posted by Last Tango

They've been around for 100 years and nobody is using them, why would that be ?

If you change the number of blades, aspect ratio, rake, cup, hub flare, trailing edge lift...etc you likely as not change it's pitch requirements.
My point is they optimised their prop for the outfit...which happened to come in at 15" and decided to compare it to a couple of standard three blade props (maybe ones they found discarded on the beach or under a wood pile in the corner of a shed that just needed a bit of hammering to straighten them out)...their only prerequisite was that they be 15" pitch regardless of whether or not 15" was the right pitch for that type of prop on that boat.
A few bubbles round the tips of a mangled three blade prop proves nothing their test does not stand up to scrutiny.
Let "Mercury" rig the boat with their choice of three blade prop as Sharrow have been allowed to do and I think the result would be very different.

Remember the E-tec V Yamaha "tug of war"

The ones 100 years ago were not the same as the tips, that is the key difference. Have a look for them.

Every now and then something good comes along, vented props, duo props, contra rotating, voith etc. All have their place and largely not new ideas. Modern machine, materials and reseach techniques have perhaps made something possible that wasnt very attractive previously.

Electric cars were about before gas cars and before long flare trousers will be back

Last Tango · 20 October 2019, 18:55

Quote:

Originally Posted by nocando

........flare trousers will be back

Did they go out....?

jeffstevens763@g · 20 October 2019, 19:32

Quote:

Originally Posted by Last Tango

Did they go out....?

Might get rid of my plus 4s and try some flares.
Bet that prop takes some time to repair if dinked

Searider · 21 October 2019, 13:32

What frustrates me with these tests is that the results aren't presented in such a way that you can properly compare the propellers.

What speed and fuel consumption a boat achieves at a set of different RPMs is largely irrelevant.
I've got a selection of propellers I can put on my boat and come up with varying speeds and fuel consumption at the RPM points.

What matters to the user is:
What is the fuel consumption at different boat speeds.
Does the boat come on to the plane at a lower speed.
Does the boat run flatter.
What is the top speed with the propeller matched to the engine and boat.

The propeller has to be selected so that the engine is within its rated RPM range at full speed.

The rpm/speed/fuel consumption data needs to be plotted on the same graph with boat speed on the X-axis and fuel consumption on the Y-axis. That would tell us what we're looking at.

However, we're talking about journalists, not engineers.

It willbe great if this new propeller had some real advantages - but unfortunately this test doesn't prove it.

carldalmas · 23 October 2019, 09:08

Quote:

Originally Posted by Siochair

https://www.boattest.com/review/shar...gineering/3986

Has anyone seen this? If the numbers are to be believed this could have a quite an impact.

Yes been following the design for years throu its development
Its now nearly ready for mass sales
13%17% faster less turbulance better grip on water better fuel consumption
What i have not seen is a price !
My only concern is a log getting into the loop blades on a cruiser with tunnels props
As props have 6 blades
Oil tankers have been saving big fuel numbers good for planet eh