Yellowfin Vairable Pitch Surface Drive

[Willallison]

Yellowfin are producing what must be one of the only commercially available variable pitch surface drives. The advantages are numerous - not the least of which is lower speed efficiencies and no engine overloading.

Any thoughts?

www.yellowfin.com

[Frosty]

I didnt see anything about variable pitching. Infact I didnt see much about any thing exept how wonderfull it is and a lot of pictures of boats.

I have read about surface drives being trimed automaticaly---is this another one.

[Willallison]

Yes - I have to agree - a great deal of marketing hype and not a lot else.
There was a piece on the VSD in the Nov/Dec issue of RINA's Ship & Boat International.
There was also a picture of the unit - which was annoyingly absent on their web site!
The unit has a large diameter hub that allows for a stronger blade attachment - the archilles heel of VP surface drives up until now, as the blade loading varies by so much.
The VSD is available for units 60 - 2000hp and they claim everything from increased efficiency to the lack of need for bow thrusters.
It's an interesting concept so long as the complexity doesn't too much of an issue.....

[Frosty]

Yes a picture of the thing would be helpfull. There was a sketch of it placed amongst other sketches of drives ie jets ,conventional and surface drives. This however seemed to depict a very compact unit with the prop very close to the transom. A measurement that seems illusive and secret.

[marshmat]

Well, the website is sadly lacking in any sort of real information. It looks like it was tossed together by a $7-an-hour high school student and I see precious little data on what the thing actually is, or how it works. Or what their claimed "Total drivetrain and propulsive efficiency 80 to 85% ( Standard in the recreational market 30 -50%)" is based on.... the term 'efficiency' is MEANINGLESS unless you specify how it is defined, and on what basis the comparison is made.
Bottom line is, I'm skeptical. I see a lot of marketing hype, and no engineering data to back it up. I see fanciful claims with not a word as to their basis. And they don't even post a photo of the very thing they're trying to sell. Ordinarily I like new ideas such as this, at least until they prove themselves unworthy, but the Yellowfin VSD drive strikes me as less than worthy.

[Willallison]

Here's a pic of the unit - apologies for the poor quality
A few more details -
Blades can be rotated to vary both pitch and angle relative to the hub. It allows, for instance for the blades to be folded flat against the hub for beaching. It also allows for trimming of the vessel, by varying the angle of the blades top to bottom. Side to side variation provides steering.
They say it produces significant side thrust, making it unsuiatble for single installation. To overcome this they offer a dual output, single input unit.
Cost is supposed to be comparable with a sterndrive, when you take into account the lack of need for bow thruster and trim tabs....

All very complicated, but still rather interesting, I think.

[marshmat]

Taking surface piercing to the limit, eh?
Weird way of steering.... and side thrust would be beyond killer....
I don't quite get the sterndrive comparison though... 'cheaper once you account for not needing a thruster and trim tabs', well, a sterndrive setup doesn't mandate either of those if it's well designed and properly balanced.
Curious how the device will perform under objective testing.... and how it'll hold up after a couple seasons in warm saltwater.

[Willallison]

They're suggesting that with a twin installation, the VSD will give you the same leevel of control as if you had tabs and a thruster, for about the same money.

[Frosty]

That picture posted looks to be on a display of some sorts. I cant see how it works and i cant see the conection with the transom.

So its a swivel steering, up and down trim, reversing blades, pitching blades, feathering blades. probably automatic and conected to the engine management system. Claiming that you will no longer need a bow thruster is exagerated. No matter what you do with your stern it will not do what a bow thruster will do to your bow.

[marshmat]

I'm not sure if it actually swivels or trims, really.... (does anyone know for sure?) it looks from their descriptions like steering, trim are accomplished by changing pitch and rake at different points on one revolution, much like a helicopter steers and trims itself by cyclically adjusting the pitch of its blades.
Still don't get how it can possibly be as manoeuverable, or more so, than a sterndrive with bow thruster.... or how it can possibly be as efficient as they claim when a cursory glance seems to indicate that much of the applied power goes into side thrust.

[Frosty]

Oh,- Ok so you think that the blades are constantly changing pitch and rake to obtain steering by side walk? Well it would explain the huge hub wich probably has some kind of adjustable cam arrangement.

This control (I guess) must be 'fly by wire' Mmmmm electronic stuff!!!

It would be nice to know. Poor management here on some thing interesting. I hope they are listening, Its all very well saying it does 30% this and that at 40% but how?

[marshmat]

More from their website:

# Simple integration of a wide variety of navionics and other equipment into the VSD’s data bus as options
# Minimum of high-integrity service parts, with high-level swap-out of sealed assemblies

It has a main data bus, and their literature seems to indicate all control is fly-by-wire over this data bus. It has a lot of black-box assemblies, apparently not serviceable, that are simply replaced (probably expensively) if they break.
This page, http://www.yellowfin.com/efficiency.html is what really peeves me off and has me convinced that it's going nowhere with the current marketing scheme. Speeds and accelerations are listed in percentages, among other childish mistakes, and what's more interesting than what's provided is what isn't: there is nothing technical, nothing at all about the drive itself or any of its technology, that they're talking about. That's a good sign that someone is pretty clueless. Another good line "compatible with any engine type, even non-marinised engines". Since when does marinising have anything to do with the propeller? It may be a useful device, in some specialized applications, but I can pretty much guarantee that with error-riddled literature and clueless marketing it will go nowhere even if it is a decent machine.
I will have to see some independent tests and results, not stuff from their own press department, before I can come to any conclusions on the technology itself. I can safely say right now that the marketing sucks and their publicists are doing a great job of spreading manure.

[RANCHI OTTO]

Bed website...I have nothing undestud about this system and the figures indicated seam to be unrealistic.

[Willallison]

Proof that there is indeed rarely anything new in engineering...
I was playing in the bath last night (as one does!) when I noticed that the drive unit on Ernie's boat bore a striking resemblance to the VSD....

[gonzo]

Outdrives don't require trimtabs. The trim feature is enough to control boat trim. As for bow thruster, this design is still applying power from the stern. That means it can't provide thrust in the bow, which is what a thruster does. A lot of unsupported claims and manipulated data.