snomobile skis on a PWC

[Village_Idiot]

Here is an idea whose time hasn't come...

I noticed some of the snomobile videos on youtube where they are running across ponds for several hundred yards to get to the other side, using just a snomobile. The power-to-weight ratio, power from the propulsion (paddle) belt and planing forces of the skis and bodywork are the only things that keep these things going. Lose any momentum and they sink like a rock.

That got me thinking... what if you had all of the force that is going to the propulsion (paddle) belt instead going to a prop? And what if you had proper buoyancy for the thing so that it would float while sitting still?

Oh, they kinda have that with a PWC. Except the PWC uses a jet (inefficient) and a bulky monohull. What if we mounted snomobile skis to the PWC? Would that give it some fantastic planing/ride capabilities? Maybe they would have to be pretty small skis. Would be nice to have a prop on the thing, too, instead of a jet. Maybe a surface-piercing prop...

Anyway, I'm just playing some mind games and giving you engineering types some ideas to think about...

Cheers

[kach22i]

Look in this thread, lots of links and images related to the concept:
T-Craft

[Village_Idiot]

Cool... some interesting concepts there.

I'm picturing snomobile skis on a PWC as maybe being more of a planing surface than a hydrofoil, with the smaller surface area improving ride as well as the associated suspension components also helping to smooth the ride, at least in a chop.

Off on a tangent...
It would appear that part of the problem with using hydrofoils is keeping the prop where it would have a good bite in the water when the craft is up on the foils, at least when the waves get deep. Seems the appropriate fix would be a jackplate of sorts that could move the prop up and down vertically in the water column (with or without the engine), thereby achieving good water purchase at all elevations, higher efficiciency in calm conditions, and still retaining some shallow draft.

Off on another tangent...
I wonder if anyone has tried pocket tunnels on large planing craft. They work quite well on small boats once the characteristics are dialed in. What are the practical limits in how large a fully-planing craft can be, with, say, 12-1500 HP at its disposal? I know I can carry 13 people in a 26-foot pocket tunnel hull and still get on full plane with a 115hp outboard...

[kach22i]

Originally Posted by Village_Idiot

I know I can carry 13 people in a 26-foot pocket tunnel hull and still get on full plane with a 115hp outboard...

No way dude, are you serious?

Do you have pictures?

I don't think hovercraft of that HP can carry 13 people (on hover/plane), and they are pretty efficient.

[marshmat]

The largest full-planing pleasure craft I know of is a Millennium 140, "The World is Not Enough. 140' LOA, 165 tons, 20600 hp (2x5300hp diesels and 2x5000hp turbines) and reportedly does 70 knots. If anyone knows of a bigger and/or faster full-planing yacht, please post.

Floating snowmobile = brilliant. It would save the guys at Rotax from having to design engines that can survive being dropped into 0-degree water at 7,000 RPM. Which, reportedly, some of them can in fact do.

[Village_Idiot]

Yep, 13 people (including me, the captain). However, it is a flat-bottom boat (more efficient planing) mod-V jon boat. It is a 26-footer with a five-foot bottom width (long narrow boat). I put a lot of thought into the design layout to maximize storage and seating.

Engine is a 2007 Mercury 4-str. 115hp. Originally had a Trophy Plus four-blade 17p prop on it, but I switched it out for a custom Baumann tunnel prop (3-blade 13p). I'm not sure I would've gotten on plane with the Merc prop.

Also, with that much weight in the boat, I don't think I could run much shallower than a foot of water (although I didn't try). The hull itself was drafting about nine inches with 13 people aboard.

Apparently long skinny boats are efficient as a planing hull as well as a displacement hull.