Volvo Composite Stern Drive

[Jeff]

Interesting - a new composite non-corrosive stern drive has been introduced by Volvo Penta.

In addition to being impervious to corrosion (a big deal if you’ve ever had to spend hours and hours refinishing aluminum stern drives to get them back into good condition after they were corroded – that’s not a fun job I can tell you), Volvo claims their new composite lower unit has a hydrodynamic profile which reduces drag by 10 percent. Volvo unveiled the drive at the Miami International Boat Show on Feb 15th and says it is targeted exclusively at the saltwater fishing series. It may not have the sexy look of their metal drives, or Mercruiser’s new performance series drives for that matter, but if the mechanical durability proves to be satisfactory, for boats left in the water it is a nice possibility.

http://www.boats.com/content/default_detail.jsp?contentid=15316

[tom28571]

Very interesting Jeff. I wonder how the 10% drag reduction is achieved. It is not obvious. Of course Volvo has been claiming that their units did not corrode for many years. Do you know just how much of the outdrive is composite?

[Jeff]

I also really wonder about the 10% drag reduction. I don't know much about aluminum casting, but I would have thought that an aluminum/metal drive could be cast into a finer/thinner profile and the same shape as a composite drive. It seems unlikely that they would have applied a better design to this drive than their performance drives, unless materials + analysis happened to coincide at the same time. I don't have much information on this - I happened to see the boats.com news release an hour after coming in from looking at a little corrosion I have to take care of on my Mercruiser drives for next summer, so I found it timely to (re)post here :)

Hopefully I'll have some more information soon (though I'm not sure I'm sold yet - after all, it's only because I bought my current boat used and it was corroded by electrolisis which ruined the factory finish on the drives that I have this constant maintenance chore.)

[Willallison]

A little more info on the drive:
The first I saw of the leg was a short article in a UK mag (MBY) published late last year. Subsequent articles all seem to refer to the reduction in drag coming from a slimmer profile and the units rather distinctive shape.
As far as the amount of composite used, I seem to recall that the actual drive train - shafts, gears etc - are still made the traditional way, it's just the casing and some of the ancillary parts made from the composite

[Guest]

Composite material are stronger than thier metal counterparts! Therefor less materials needed therefore a smaller smaller profile with the resulting reduction in drag is possable!
This would explain why composite rigging is all the rage now!
I have no idea if Volvo have done this succesfully but twenty years experience with these materials tells me that this is more than possable!
As i'm now a resident of Volvos home land, Sweden(ex New Zealand) i'm looking into Volvos composite capabilitys and should know more soon

[gonzo]

The drive has two composite halves around an aluminum alloy tube. The metal part is machined for bearings and other mechanical parts. They tested them at the Virginia Beach facilitie by hitting semi-submerged telephone poles at 45 mph. They couldn't break it. The reduction in drag is a redesigned more efficient shape.