Yellowfin Vairable Pitch Surface Drive

[ylpmisfin]

I noticed there has been some debate about the yellowfin drive system.

I can tell you that from first hand experience that the things they claim are true, after all all the claims will have to be substantiated by the relevant bodies before being put into production.

Any craft that has the drive fitted will be much easier to handle, will be able to steer side on and dock side on and the craft can turn on its own axis. There is fantastic effeicency and fantastic control. The website does show a small video clip with the docking on however this is slightly speeded up.

I am available to answer any questions you may have on the drive system apart from the intricate details that make it work as these are top secret.

[RANCHI OTTO]

What about the ratio hub diameter/ prop. diameter?

It seams to be very low...this means turbulances at the hub end.

[Willallison]

RO - I gather that as the drive is mounted much closer to the transom than most other s/drives, the hub runs clear of the water at speed.

ylpmisfin (gotta get yourself a better username! ) thanks for the input. I'd be interested in the units performance at intermedite speeds - where surface drives are traditionally poor performers, being optimised for high speed as they usually are....

[RANCHI OTTO]

We have carried out some test in a Model Basin with different hub diameter and we have noted the turbulances behind the hub itself.

The Maierform has patented a bulb installed to the rudder just in front of the hub.

The reduction in power was of 3% abt.

I suggest you to lengthened the hub..nothing else.

I'm interested about this system even if the web is not very cleare (for me!)

[ylpmisfin]

there is very little turbulance in the water as the hub does not sit in the water, only one blade will drive at any one time. The hub will sit directly on the transom giving a much more compact design, after all theres no need for it to hang out any further. Regards the testing you have done i dont think you have understood that the hub is not in the water so your test would not of given the right results if thats how you set it up. You suggested that the hub should be lengthened, well once in production the hub will acctually be much smaller. Thanks

[gonzo]

By your answer, I assume you are related to the manufacturer or you are it. How do you explain your claims that a drive mounted on the stern does the job of a thruster?

[ylpmisfin]

No i am not related neither am i he. I think you have an impression of a very small company, well its quite the contrary. What you have to remamber is that the vessels will be fitted with two hubs twin engine or single engine still two hubs. Side movement can eaisly be acheived using two drives, it can be done using conventional drives but it is very difficult and involves alot of paddle shiffting the yellowfin takes all that trouble away. The thrusters are no longer required. Alot of people do not belive this claim from the looks of this website have a look at www.yellowfin.com and search out the video shows contained on the site they will show a test vessel carrying out these manouvers. thanks

[PetterM]

Some new photage on the website:

http://www.yellowfin.com/video_0.asp
http://www.yellowfin.com/video_1.asp
http://www.yellowfin.com/video_2.asp
http://www.yellowfin.com/video_3.asp

This is a single engine boat....

Some press coverage:
http://www.yellowfin.com/media_coverage.asp

[marshmat]

Interesting system.
Still a lot of unanswered questions, though. And a lot of marketing hype that appears to have very little engineering basis. My comments on one particularly grating slide:

Other new-generation drives VSD
Total drive train efficiency 35% > 45% (another slide says 80-85%)
On what basis? Efficiency can mean a lot of things, and engineers ALWAYS specify how it's defined.
Engine power reduction for the same speed 30% 50%
Again, compared to what?
Increase in speed for the same power 45%
Fuel consumption 30% 50%
No point of comparison given, therefore the percentage is meaningless. Sounds cool but there's no basis given for the claim.
Speed limit 45 knots no speed limit
What competitive surface drive is capped at 45 kts? What's it being compared against? Volvo IPS maybe, which was specifically designed for fat heavy boats?
Acceleration (with a smaller engine) 30% 50% (potentially 75%)
Acceleration... as a percentage?

No point of comparison is given, no clue about the methods used for the calculations....
"Emissions are reduced by 50%"... again, compared to what? The claim appears to be that this thing can get by with a motor half the size of the best competitive drive, but nowhere does it mention what the competitive drive is...
"No fumes on start-up" Since when does this have anything to do with the propeller? This is a motor thing, not a drive thing.
"Minimum of high-integrity service parts, with high-level swap-out of sealed assemblies" Does this mean that when it breaks, you replace a big expensive component instead of a small cheap one?
It's a cool idea and I don't doubt that it could be very practical in some applications. But there are claims going around that are, from an engineering standpoint, meaningless. That has to be corrected if the company wants to be taken seriously by the boatbuilders. Not to mention that so far, it appears that there's only a development model actually built, and the production version (as far as I can tell) has not yet been mounted to a boat, let alone rigorously tested. There isn't even a decent quality photo of the actual device on the site.
I think it's a really cool idea that has a lot of potential. But at present it looks like naive marketing hype is going to kill what is at the core an interesting and innovative concept.

[Frosty]

I agree with Marshmat 100%. My only comment is to say that the naive marketing hype will not only kill the thing but is doing so by the minute in my opinion.
I would have thought that we would have seen some one from the company here by now to answer some of these quieries.

I also feel that the unrealistic claims show a lack of of respect for the general intelligence of the public.

People who would have the money to buy a boat with this drive would not be short of cash and will not appreciate being talked to like an 8 year old.

This type of advertising is doing more damage than good.

[Willallison]

Whilst I agree with some of the things you guys are saying, I think you're getting a bit carried away. I agree the website is rather heavy on hype and light on detail... but then they'd hardly be the first to be guilty of that:
When Volvo introduced IPS they made a great song and dance about improved performance, lower fuel consumption etc etc. Little info about what they were compared to....
They seem to be doing ok with it......

(which brings up one of my gripes... following the release of IPS, there is still an enormous amount of hype about its improvements over conventional shafts. No mention about whether larger sterndrives - without the collision risks - would have been any less efficient. But that's another story)

As to why Yellowfin hasn't appeared on this forum to defend its claims.... has anyone asked them? I mean - I know we are important, but still....

[Frosty]

Plenty of hype on soap powder adverts is fine --who cares on a 2 dollar item.

The claims this company is making is unrealistic --we have agreed upon that.

I have heard of Volvo and they have years of reputation behind them.

I have watched the film footage of the unit carefully. The driver appears to leave considerable throttle on at all times walking the boat through forward to flat( fearthered) to reverse.
Using highly pitched blades encouraging side walk with little forward thrust. With practise I have no doubt this manourvarability can be obtained.

I notice that the low speed manouveres are all to port !!! The prop must be therefore rotating opposite to engine rotation--ie right hand rotation prop.

On the high speed footage it turned to starboard, how does it do that with out a rudder?

A descent photo or 2 of the unit would settle my curiosity.

The claims of 40% this and 50% that I shall have to live with untill!!.

As Marshmat says --compared to what?

[Willallison]

The claims this company is making is unrealistic --we have agreed upon that.

Well - let's just say I'll wait to see some verification from independant tests. I neither believe nor disbelieve...

It's early days for this unit. Why not give them credit for being prepared to put the idea out in the public domain so early on in the development phase...

As to the kudos of the company, I think they've been around for quite a while and have some noteworthy developments to their credit. It may just be that you've not heard of them in your part of the world..?

[Frosty]

No I certainly havnt heard of yellow fin.

The point is ,--couldnt they show us a picture of it. Granted they have footage of a boat manouvering -- horray fantastic. How can this be early days when we have seen at least 2 boats fitted with it.

Arent we supposed to ask questions ? are we to just accept what they say? Would it be beyond our capabilities to understand?

Its this silence and distancing themselves from queries that is anoying.

Again they are conspicuously absent. Some thing fishy here.

I hope you dont think I am concerned about this in any way,---Im not.

[PetterM]

I will try to answer some of your questions from an engineering point of view.
All performance claims has been verified by running a 18 ton, 55-foot powerboat with 2 x 700 hp engines, against the same hull with similar power and shaft drives and water jet, and later by back-to-back testing vs. Bravo sterndrives.
Acceleration was taken as the time from 0–30 mph (26 knot) and the improvement as the reduction in this time as a percentage.
Obviously gains will depend on the specific application.
Some photos of the unit here:
http://www.yellowfin.com/media_coverage.asp
Check out the article in motorboat and yachting that explains rather well how this units works.

Best regards,

Petter