# Slender non-planing foil assist catamaran?

Discussion in 'Hydrodynamics and Aerodynamics' started by S V, Dec 28, 2020.

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### S VJunior Member

Ok, what is your solution to ship on riverway 50 passengers at 35 knots, using up to 170kg/hour of fuel?

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Firstly.... why 170kg/hour of fuel?

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### S VJunior Member

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All i can do.. is reiterate the question.

But if you're not able to provide the answer.. there is little I can do to assist.

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### S VJunior Member

Can anyone tell me, what is "S" in foil lift formula?
z = ( rho / 2 )* V^2 * Cl * S

Is it total surface area of the foil - top AND bottom or just one side??? For example 0.2m x 1m foil has S fro this formula of 0.2 sq m or 0.4 sq m?

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### S VJunior Member

It is approximate fuel burn + ~10% of comparable soviet hydrofoils, of similar passenger quantity, 45-50-60 passengers (although heavier), operating at ~60kmh . There are no very accurate data, but this is all is available. If you know, "Raketa" type hydrofoils - take them as example and add 10% to fuel burn.

The fuel bill from ship operation has to be in that range.

7. Joined: Oct 2008
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Well, this is where you're starting to go wrong.
Whist this value MAYBE an approximate, it is relating to a design that is known and fixed.
You have yet to mature your design to actually know what is what..? Thus until you design it...you wont know.
As you're putting the cart before the horse!

Whereas:
That is an objective to aim for...a real world constraint.

So, what restrictions are there on the river regarding:
Max draft?
Max wash height
Speed restrictions
Length/beam restrictions
Emissions restrictions
Noise restrictions
Berthing restrictions
Bathymetry of the river restrictions
Bunkering ability on route

These are just a few variables that shall dictate the design.

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### S VJunior Member

Imagine me as a businessman/enterpreneur, as I look at it 70% from business perspective, 20% from passenger, 10% from naval engineer. I see body of water, which is accessible only by ship and people on the opposite sides who have the money for transportation. There is infrastructure on the both sides. The amount of money they are willing to pay is limited. Do you think it matters for me or for people is it monohull, trimaran or catamaran as long as it meets their expectations or simply gets the job done on the predefined conditions? Does it matter how many engines it have? Everything suits as long as it fits or almost fits to the business plan you made. By meaning almost that means few percent difference.

Max draft - 1.1m to the deepest part of ship, that is the most draft allowable during any operation point. It is much deeper water on berthing places. There is advantage for every centimeter of less draft.
Max wash height - no restrictions. I tripple checked - really no restrictions, there is not a single government paper available for this route.
Length/beam restrictions - 5m beam, length - no restrictions
Emissions restrictions - standard EU, none additional
Noise restrictions - stndard EU, none additional. If you talk about passenger NVH... Well they have to be relativelly comfortable for 3-4hours trip.
Berthing restrictions - the berths are vertical made of concrete of various height, some have floating docks, so from 20 to 50-80cm height from water surface, everything fits. There are means to dock ship.
Bathymetry of the river restrictions - have no idea how to translate it
Bunkering ability on route - none. Fuel for 7 hours cruise + 0.5h reserve. That is 7h round trip Point A- Point B - Point A.
Passengers - 50, 1 toilet, 2 sq m area for luggage.

I think that is more than enough to suggest at least the type of the ship. Target fuel consumption I already mentioned. Cruise speed - mentioned. Approximate price for the ship - mentioned.

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### BMcFSenior Member

Ahh, but how will you control the craft when it is on foil? All foil-assisted craft I've ever been involved with with foil lift fractions greater than about 50% required a fairly sophisticated flight control system to maintain constant flying height, list and trim, and, in many cases, to stabilize the craft in yaw as well. The foil-assisted trimaran that we built was almost impossible to fly "manually" once it was up on foil and the amas were clear of the water surface. A foil-assisted cat hull is a bit more forgiving in that respect, at least with regard to list stability.

One of the neat things about Dr. Hoppe's foil systems is that their lift objectives are conservative and lift fractions relatively low....thus removing the necessity for active control.

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### S VJunior Member

Tandem passive foils, as much far form CG as possible. 75% lift is not 100%. From the theory papers Hysucat has the exact problem you mentioned: one single foil at around CG which is sensitive to weight shifts, like people movement. Soviet hydrofoils and I think many other passive tandem hydrofoils nave no such thing as active control, there is nothing "active" there at all: throttle and rudder control, that is wheel, not much else. Hoppe Hysuwac system seems to differ, it uses foils as far one form other as possible, also he mensions some custom projects where exactly "tandem foil" in his words system was used. And from his papers there are projects where is more than 50% of foil lift used.

EDIT: paper form Migeotte, student of Hoppe:
At semi-planing and planing speeds the main foil is designed to carry between 40% and 75% of the weight, depending onsize and displacement of the vessel.

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### BMcFSenior Member

Many Soviet hydrofoils (and similar designed Rodriguez hydrofoils) had active control even though their overall stability was largely a feature of the surface piercing foil designs. At the least, they had trim flaps. I've worked on/with a number of them. I'm fairly certain that you are not going to be incorporating surface-piercing foils on a cat. The old ladder-foil concept maybe....

Most of the Hysucat packages I've seen have the main lifting foil just forward of the CG and much smaller trimming foils aft. We were approached at one point by a builder that was interested in obtaining titanium foils for their Hysucat project...something we design and build.

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### S VJunior Member

If you want I can drive one day to place and make a photos of two of the different ships of that soviet era, to be more exactly their foils form all the available angles - there are none of such devices, except rudders. Nothing moves there, everything passive. And their foils are made from 3 vertical struts and 1 horizontal wing. It is Raketa and Polesje type. One of the photos you can see in earlier posts. Maybe some other seagoing hydrofoil had that.

Yep. But there is another system: Hysuwac and even custom projects which do not fall into Hysucat or Hysuwac categories as Hoppe specifically mentions, that it is custom system, for example Rheinjet does not fall into HC or HW systems.

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### S VJunior Member

Maybe we can close a discussion, as I probably know the answer about why and how it will work on super slender cat operating in Fn 1-1.2 region.
In short - it will work.

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### BMcFSenior Member

Good luck with it.