Prop tip velocity

I was going to say that. If the prop is too big, ventilation will set in. If the prop is made smaller, tip cavitation starts. If RPM cannot be reduced or out of the equation because the marine gear is already in place, why not increase MWR (mean width ratio) or increase the number of blades to reduce blade loading?

Further, with so little draft available in shallow water, ship squat can be a problem.

 

This prop diameter/waterdepth/thrust requirement was always going to be the major problem. consequently I left this to last after some accurate constraints on thrust were established. Average results on thrust are 600 kg/unit carrying 60 ton @ 4 Kts

Initially a train will consist of 2 units + a tug. The tug will draw about 500 mm

While ultimately this thrust should be while operating in 1 m water depth, in practice because the shallows are less than 5% of total system it would not matter if the train slowed to 1- 2 knts in shallow water.

Therefor I am now thinking a retractable shrouded prop of around 800 mm which will be allowed to break the surface where necessary. This is much better that a small prop that will effect efficiency (and cost) through the entire range.

There are 2 ways to provide relatively undisturbed water for a prop behind a hull in these water depths: Tunnel hull (cat) is one.

But, I know that in some tunnel designs a single central-mounted prop's performance will drop significantly. Any one here got info on this? Jets hate tunnel hulls apparently.

Jets are not an option for this operation: Debris, weight, and cost. I read yesterday that jets in the Arabian Gulf are chewing out within 3 months because of grit in the water.

cheers

M

 

DCokey: I think that you are adding up the dimensions of the containers, but not the extra hull size to have enough volume to float in no more than .5 m of water. If you do, maybe a third will fit. A fully loaded container is 44,000 lbs or 19,960 kg.