# Speed Boat on skis

Discussion in 'Boat Design' started by Poida, Apr 28, 2011.

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### DCockeySenior Member

2. Joined: Oct 2009
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### DCockeySenior Member

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### tom kaneSenior Member

Patents pending are not published so there is a lot going on that you do not know about
and hundreds of inventors can be working on the same ideas.

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### BertKuSenior Member

My apology, I overlooked that one. Certainly ideal for offshore taxi's.
Bert

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### DocScienceWishful builder

Here is a chart of -
(Wind Speed (mph) vs. Stagnation Pressure (Pa))
http://buildingscience.com/documents/insights/bsi-057-hockey-pucks-and-hydrostatic-pressure

50 Pa= 20 mph =32 km/hr =.0073 psi =1.05-lb/sq.ft.
100 Pa= 30 mph =48 km/hr =.0145 psi =2.09-lb/sq.ft.
150 Pa= 35 mph =56 km/hr =.0217 psi =3.12-lb/sq.ft.
250 Pa= 45 mph =72 km/hr =.0363 psi =5.23-lb/sq.ft.
500 Pa= 65 mph =105 km/hr =.0725 psi =10.4-lb/sq.ft.
1000 Pa= 90 mph =145 km/hr =.1450 psi =20.9-lb/sq.ft.

At 75 km/hr you would get a maximum pressure underneath of about 5.3-lb/sq.ft.
At 90 km/hr you would get a maximum pressure underneath of about 8-lb/sq.ft.

If the rear of the boat is not touching the surface of the water to trap the pressure in, the air would escape fairly fast, to lower the pressure underneath.
I am guessing that air escaping underneath, would lower the pressure underneath by at least 2/3
If that is the case, your pressure underneath will not exceed 3 -lb/sq.ft. at 90 km/hr .
If the rear of the boat is more than a foot off the water, I actually would expect a much lower figure of lift.
If the effective underside of the boat is about 6ft x 10 ft, that would give a lifting pressure of 60*3=180-lbs of lift, at 90 km/hr .
With the weight of the craft being more than a ton, it may not be overly helpful to leave the sides of the supports for the ski, solid.
That would mean that you could use strut support attachments if there was a good reason to do so.

There might be someone who can check my figures to see if they look in the ballpark.

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### keroseneSenior Member

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### DocScienceWishful builder

To- kerosene
You would have to read back in the thread. The first boat was built on very low budget, just to get it in the water, as fast as possible, to test the ski profile.

.
As far as the newer version, I think that another design modification is being tested.
As to my last post above, I just checked one of the more recent videos.
At 0:20, The news reporter calls it a "mini-hydrofoil" . She must have made that up on her own.
In this last video, I see that they have changed the design to be more like a hovercraft, using ski sides.
The faster speeds of 100km/hr now increase the air pressure underneath by a good margin.
I still do not know how the back end has been modified.

.
By looking at the angle of the lifted front end, I think a lot of pressure is lost there.
I would expect that they now have pressure sensors to tell us exactly what the maintained pressure is underneath.
I do like the new modifications, but think that both the original and new designs might lead to interesting crafts.

.
On this page, look about 8 posts above my posting, to see the design of a hovercraft with somewhat ski sides.
.

Last edited: Oct 30, 2015
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### DocScienceWishful builder

My explanation of the inefficiencies /efficiencies of hovercraft.
The water will still take more energy to pass through than the air, but I wanted to talk about the air resistance here.

When you look at the front profile of a hovercraft, it is somewhat similar to a mac truck cab driving down the road, returning home, without a trailer or load.
Aerodynamically it is pushing air out of the way as it drives. This takes a lot more energy than a car.
At the hovercraft, very little air goes through. That air must go over, and around the sides to get past the hovercraft.
Unlike a mac truck cab, no air can go underneath.
If you want the hovercraft to be able to go through larger waves, you need to make the height higher, and what you end up doing, is making the front profile of the hovercraft even larger than the mac truck, making even more resistance to the air.

When you are not going top speed, there is not enough air entering the front of the hovercraft to provide lift, so it must either be done through inefficient pumping of air under the hull, or some other form of water interaction.
If you increase the speed of the hovercraft so that it provides its needed air pressure, you are pushing through all of that frontal area, at a higher speed, which takes even more energy.

You can not allow air to flow through underneath, because if it does, you loose your lifting air pressure underneath.

What this means.

Since the stern is very near the water level to preserve lift, you can not go over waves well, but this boat is good for inland water ways and lakes. When you go over more rough water, I can observe more lift or bounce as the hull is lifted a small amount, as it rides over the small waves.

In large lakes and ocean, that bounce will become very noticeable.
In the older model boat, with more clearance underneath, it goes over the waves better.
To use the newer model boat, it would need to have a major revision in the rear, to make more clearance for bigger waves.
That would also mean more frontal area with more wind resistance.

To make or revise a boat for use in the open ocean water, I think it would be more efficient and better, to use the skis alone, and skip the hovercraft modification.

Feel free to point out errors in my composition.

Last edited: Nov 1, 2015

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### myarkSenior Member

Quote
http://www.gizmag.com/marine/
Boats are as old as human civilization, but that doesn't mean there's no room for improving the design. Case in point is the SkiSea, a new hull concept out of Australia that uses special skis to provide hydrofoil-like lift. SkiSea creator Trevor Payne says this approach allows for greater fuel economy, stability in rough waters, a shallow draught, and higher speeds while generating minimal wash or bow waves. Gizmag spoke with Payne about his design.

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