New Drive

[PROPELLER]

Just received January issue of Motorboating & there is a new drive in town. Its called Inboard Performance System or IPS for short by Volvo Penta. It looks like a sterndrive only its mounted on the bottom of the boat where a typical inboard shaft is mounted & the Propellers face forward to pull the boat through the water instead of pushing. It has many advantages like better maneuverability, faster acceleration, higher top speed, greater range (better fuel economy by as much as 30%), less smoke, less noise, easier installation, safer underway, more usable space. There are very few disadvantages like more moving parts, twin installations only (at least at this time) & vulnerable below the water line. But it is designed to shear off without hull damage if you hit something.

[Charlie T]

There has been a ongoing thread on this on the "BOAT ED" forum for a couple of weeks. Look here http://www.boatered.com/forum/topic.asp?TOPIC_ID=63508

[Mee-n-Mac]

It's an interesting concept though I'm not sure what it accomplishes beyond what a normal stern drive (I/O) would do. It appears to be aimed at the big boat market, to replace inboards with this new IPS, giving them the advantages of a stern drive. I'm guessing that packaging / space concerns prevent the usage of a normal I/O in these boats ? One thing I noted was the lack of an anti-cavitation plate and then upon further thinking (duh) I realized that one wasn't needed because the bottom of the boat is serving that purpose. I wonder then if we'll see a "puller prop" (you have to see the pic @ the above link) configuration on future "normal" stern drives given that Volvo claims better efficiency due to undisturbed water flowing to the props ?

On another note my first thought was that this was the "stern drive in a box" concept that I had previously seen. The "STiB" packaged an engine and outdrive in a separate floating box that attached to the transom in lieu of a OB. I thought this (STiB) was a solution w/o a problem.

[madrasahs]

Very nice, but they ought to include an EPIRB in the lower unit.

(Maybe carry a small 2-stroke outboard to get you home?)

[Will]

Biggest thing you will notice with these drives is the inability to shift like an inboard. With a lower shift cable just like an I/O that silky smooth shift is just not as silky smooth anymore. I think it is a great idea however these loose the ability to swing a big bore prop, also in saltwater conditions there is a lot more to go wrong as far as corrosion goes. Another thing we have to deal with now is gear lube. Before there was no worries about gear lubw with an inboard but now once again you are back to square one. Id take a straight shaft inboard anyday over one of these, at least with a straight shaft the stress is dispesed over your struts, shaft universal and closest to your stuffing box where as with this drive the four bolts which hold it to the hull are taking a lot of the stress. Since the shaft is also inside of a tube so to speak from early reports on this. I believe there will also be a good chance of corrosion in a salt or brakish environment.

Just not my thing, sorry Volvo


Will

[gtxrider]

I looks strange but people say the same thing about anything new. Progress?
Read the article from "Motor Boat and Yachting"

http://www.ybw.com/auto/newsdesk/200...42mbynews.html

[madrasahs]

Originally Posted by Will

Biggest thing you will notice with these drives is the inability to shift like an inboard. With a lower shift cable just like an I/O that silky smooth shift is just not as silky smooth anymore. I think it is a great idea however these loose the ability to swing a big bore prop...at least with a straight shaft the stress is dispesed over your struts, shaft universal and closest to your stuffing box...Just not my thing, sorry Volvo. Will

This is "oats and buggy-whip" talk.

Just like the cavitation plate is gone, the NEED to swing a Big Bore prop is gone.

The efficiencies are just too great with tractor drive. You'll need less horsepower (and fuel, and pollution) to go as fast (and have a greater range) as Big Bore.

I was impressed with the drive before I read Motorboat and Yachting's report posted by gtxrider.

Consider the "modern" aircraft designs that have "pusher" drives (B-36, Lake Amphibian, Buccaneer, Colonial Skimmer, Republic Seabee). All are hampered by too-great a horsepower requirement, engine-weight, inefficient power use, or all the above.

The Seabee (in which I've got some time) could barely stay aloft with its original 174HP engine. "...Cruising speed: 90. Stall speed: 90. Landing speed: 90..." was a common complaint. (Seabee image, below).



Volvo has millions invested in development costs, and it's appearing at a very bad time for the American market -- the dollar being what it is today.

This would be a very expensive retrofit for the Big Bores that need to go even faster. Underwater exhaust is another disincentive.

Too bad, as there will still be too many over-horsepowered, noisy, inefficient boats -- with obsolete drives -- on our waters.

[Will]

Mad, I hate to break it to you but no. I have already seen these drives on Doral cruisers being put out for 2005. There have been numerous complaints already. The drives take much too long to respond dockside. The drives can not take bottoming out like a regular sterndrive can, and the biggest thing, you stilll have the pesky problem of shifting a sterndrive. They shift like a bear from what I have heard. These boats all have the 370 Volvo TAMD's in them, which is a wonderful motor however this drive just doesnt do it. Every person I've talked to has said they would love their vdrives back or straightdrives.


W

[Dave R]

I would expect teething problems with a new design. The concept is brilliant though, having nothing ahead of the props to disturb the water makes so much sense. Nothing stopping them from applying the same concept to a stern drive in the future either.

[Cal]

Great idea for deep , clean water. But having TOTALLY exposed props could get REAL expensive REAL fast it you hit something. Standard outdrive is much more forgiving