Volvo Penta IPS revealed

[kach22i]

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

[Deering]

I understand the advantages of the prop placement and the other features, but this still looks like a crazy design to me. With no skeg or keel protection, every piece of floating net or line will foul your props. And since they're way under the boat how do you free them w/o a swim?

Maybe boating out of North Carolina or Florida is different, be we have a lot of crap (logs, big stuff) floating in the water here in SE Alaska and in the PNW. Since these are designed for high speed travel, when (not if) you run over something the damage is going to be expensive. Fortunately, Volvo thought of that - they've designed the lower unit to rip right off, hopefully leaving your hull intact. Great marketing plan - put really expensive gear in a location where it's really likely to be damaged, and then have it fall off. I bet the insurance companies will start charging boats with these units a higher premium.

What will they think of next? Put the prop sticking forward off of the bow?

[kach22i]

Originally Posted by Deering

With no skeg or keel protection, every piece of floating net or line will foul your props.

Are conventional pusher designs setup to deflect or cut lines/nets?

Touching the bottom at low speed shouldn't be a problem as the skeg on the bottom extends below the propellers. The subsequent vertical force is transmitted into the robust GRP mounting ring inside the hull and assuming the engines are put into neutral promptly, no damage should result.

In the high-speed scenario, the leg and pod will shear off flush with the hull. The lower bearing carrier has been engineered specially to break at a point below the O-ring seal between the fixed and steerable parts of the drive. As the leg bends backwards, the vertical drive shaft simply pulls out of its spline. The inside of the transmission is now open to the ocean but no water can escape into the boat and the vital mounting joint between transmission and hull will remain not only intact but undamaged thanks to the energy absorption of the big twin O-rings.

They could of defended their design better - seems like a quick/short version. What would one of these do to a manatee in Florida?

http://myfwc.com/manatee/prop/

http://www.manateeworld.com/research.htm

[Deering]

"Are conventional pusher designs setup to deflect or cut lines/nets?"

Not necessarily, but... from what I can tell you can't install one in line with a keel or with a skeg in front to provide some protection or you lose that "undisturbed water". They're hanging out there completely exposed. Of course, a couple of exposed shafts/props probably aren't much better, but I don't like them either.

Even if the props aren't fouled, floating stuff (kelp, line, plastic bags, branches) will hang up in the appendage area above the props. Look at the picture and tell me you can't envision that happening again & again.

I had the same thought as you, except substitute "whales" for "manatees" in this part of the world.

This seems like one of those ideas that works great... until it doesn't.

[kach22i]

There is a photo in this gallery of the drive system installed on a real boat - some other fun pictures as well.

http://www.boatdesign.net/gallery/sh...00&ppuser=1988