Thoughts on this drive system

[Willallison]

Any thoughts on this drive system?

http://www.dbdmarine.com

Compared to an Arneson drive, why is the gear housing and prop hub so large in diameter (there are no gears in there, right?) Is it just to accept merc/omc/volvo standard props? Are these "stern drive" props ideal for a surface drive ???

I also don't understand how the steering works - where is the leverage?

[Willallison]

The blurb on the site states that the drive is not intended to be surface piercing as such, though some of the images on the streaming video show the drive trimmed to the point where the prop is clearly visible.
I suspect that the reason for the girth is indeed to allow the use of standard merc etc props. It would certainly make prop selection easier - not to mention availability and cost.

I always thought that a Mercruiser outdrive went to the trouble of placing the prop below or even with the bottom of the hull to make sure the prop had a flow of undisturbed water (and also why an inboard places the propshaft at an down angle vs. just going out the transom.) Doesn't this drive deliver a "worse" flow of water to the prop? If not, why has the prop been placed below the boat vs. just behind the boat for so long?

And continuing, when you mount a mercruiser outdrive too high, you get cavitation. With a similar prop, what allows this drive's prop to be mounted higher - a larger anti-cavitation plate?

[tom28571]

Good questions, Guest. I thought the same but was waiting on an expert in drive systems to comment. A couple of other guesses: The drive probably does not steer but relies on a separate rudder as a normal inboard would. It would need a CV joint to stop vibration from varying rotation. Maybe the vertical adjustment is just for raising the prop out of the water at rest.

[Willallison]

If you watch the short streaming video on the web site, the drive does indeed turn to steer the boat. The film shows a ski boat turning quites sharply with little or no apparent ventilation.
I'd have to agree with the loss of efficiency ideas - not so much because the drive is located aft of, rather than under the transom (Arneson, Buzzi etc have managed with that configuration very nicely...) but because - unlike a sterndrive or outboard - there is significant shaft angle involved. Though this is decreased as speed is increased and the drive is presumably trimmed up.

[Portager]

Very interesting drive. It is essentially an Arneson Drive with conventional props instead of a Rolla prop. In addition DBD Marine has incorporated a top plate that appears to provide the function of trim tabs and help prevent cavitation. I think the conventional prop should work better for lower performance boat designs.

The Arneson Surface Drives http://arneson-industries.com/Arneso...e%20Drives.htm have proven the performance and the corrosion resistance of the concept so the risk should be relatively low. I like the manual steering back-up. We lost a hydraulic line on our Arneson Drives and had to call for a tow .

You could also consider an Arneson Drive with a conventional prop adapter as an alternative or back-up. http://arneson-industries.com/Perfor...20Upgrades.htm. Another option would be to design for the Mercury Bravo™ Stern drive and use either the Bravo™ or the Arneson drive with the Bravo™ to Arneson conversion kit. http://arneson-industries.com/bravo_...conversion.htm. Arseson offers a proven track record and a wider range of power options. I don't know if the cost is competitive or not.

Have you gotten any pricing information yet? Based on it's simplicity, the DBD should be cheaper than a conventional stern drive, but then the stainless steel materials will drive the cost up, so ...

Cheers;
Mike Schooley

[Willallison]

Oooh! Now they are some sexy links!
Mike, for a fella so keen on the semi displacement cruiser, I never would have picked you for an Arneson owner....! Tell us about your boat.....
As for the pricing, the price of the CD300 model is AUD $9500 (+10% GST) - so around US $4500. I don't know how that compares with Arnesons etc.

[Willallison]

Mike,
One aspect of surface drives which rarely seems to get comment is their mid-range efficiency. As someone who has owned one, how do they compare when you have to run at slower speeds?

[Portager]

The company I work for has a deep vee Magnum 44' with Arneson drives and twin 600 HP Cats. It does 45 knots but it won't plane below 27. This makes for some rough rides in the Pacific swells. : mad:

I tried to attach a pic, but it does not seam to show up in the preview, so it this doesn't work I'll read the FAQ (although the shame would be unbearable)

I am the responsible engineer for the fire control system and the 30mm cannon on the bow , so I ride the boat out to the shooting range a lot . The Phantom is responsible for my love of displacement boats.

The efficiency of the boat at low speed isn't something that we worry too much about. It would only show up at the gas pump and the companies plastic card takes care of that. I get the impression that our fuel consumption more a function of miles than conditions but I'll check with the boat driver.

Cheers;
Mike Schooley

[Willallison]

Bloody hell Mike - who do you work for - and where can I get one of them there boats!!

[Portager]

Used to be McDonnell Douglas but they merged with Boeing. Then Boeing sold my division to DRS Technologies.

Unfortunately the Phantom boat isn't available to the general public or drug lords, otherwise we would sell a lot more.

Cheers;
Mike Schooley

[Willallison]

It wasn't so much the fuel consumption that I was interested in (though that would be worth knowing too) more about how the boat / drive performs as the speed is reduced.
In the case of the Magnum it obviously doesn't go too well - you said it won't go below 27 knots. I wonder if that's the case with all surface drive boats.......
'nother question for you......what's the big thingy sticking up behind the radar?

[Portager]

I think the problem planning below 27 knots is a function of the weight and the deep V hull not due to the drives. In addition we have oversized trim tabs since the Cat engines are heavier than the original SeaTec engines.

The drives actually get too much bite at start-up (when the stern is so deep in the water that you can't raise the props out of the water). Since the Rolla props are designed to operate only partially submerged and at start-up they are fully submerged, we have to use cavitation tubes that allow the props to suck air to reduce the loads. Despite this, Phantom gets up on step very quickly and relatively easily.

Our experience with the Arneson drives is that you can adjust the height of the drives and optimize the engine loads much like a controllable pitch prop. Phantom performs quite well at moderate speeds, which is where we generally operate because of the swells and our electronics don't like to get airborne (or actually the landings after).

The ball behind the radar is our electro-optical sight. It has an infrared sensor, 2 near Infrared low light TVs and an eye safe laser range finder (wouldn't want to damage the eye sight of the people you are about to shoot ).

Cheers;
Mike Schooley