Concept design 25m river vessel

[micspoko]

This is my next project a 25 m concept design river vessel:
Lenght: 25m without boat at stern
Breadth: 5 m
Draft: 0,4-0,5m
Max not removable height above water at draft 0,5m: 2,7m

[Perm Stress]

Did you make weight and trim calculation? For such small draught, any of these two points could kill the whole design.

[micspoko]

For now i do only a visualisation but i think it will not by a problem. I don't calculate a weight but i think the weight it will by 30 tones (only hull) to 40 tones (max load - passangers+water+ fuel)

[Perm Stress]

0.4m draught for 25mLOA is VERY small. This proved to be a problem for many decades.
Oldest info I accidentally have (without specific search on the topic) is that it turned out to be impossible to design and build lightly armored river gunboats with draught smaller as ~0.5m in 1930 -ties, (numbers from memory some 10 years old, could be off by some 0.1m).
Newest info I have is personal experience in design of similar-sized river workboat, with design brief draught 0.4-0.5m. It ended up at 0.6m and significantly smaller working platform forward; she still trimmed stern-down in all loading conditions. Design brief was revised in the process without any penalties to the design office.

[micspoko]

trimm it will be a problem on this boat but probobly it can be solved when I do a construction project.

[cthippo]

It's a nice design, I like what you did with the curved windows. Another foot of draft probably wouldn't hurt, but I think you're on to a good design. You are going to need to watch weight limits on the upper deck though.

[BATAAN]

Is this a pump jet drive? From the concept pics the ends of the vessel seem quite sharp for the desired result and could use a larger block coefficient. A boat with 0.5m draft doesn't need sharp ends, but full to support the weight by displacement and realize the desired draft requirement. The water goes under, not around a boat like this I observe.
Just found a book "Design and Construction of Small Craft" R. Munro Smith, A.M.I.N.A. from the "Technical Section, Assn. of Engineering and Shipbuilding Draftsmen, London, 1924" with many cartoon plans of shallow draft thin light riveted iron river vessels built for export after WW1 from 40 to 100 feet, some paddlers and very interesting tunnel stern data, plans and pics. These were shipped as complete "kits" of bent iron frames and pre-shaped and rivet-hole punched long plank-like thin plates and assembled on riverbanks in Africa by cold riveting everything. The loftsmen in those days were awesome making all the holes match up when assembling the parts. I had a very old fella trained in the art try to explain it to me once, but I got lost quickly.
Anyway back to the subject, in the reference book above I see a pretty universally used midsection approaching a shallow rectangle and short, well formed ends for this type of thing, and these were successful, built and sold vessels. Of course the engines were often in the middle and 1924-heavy for the power, so that is all different in your proposed design I guess.
Also with that interior you will need to use very light and expensive materials like an aircraft with honeycomb core with veneer facings etc to get it light enough. If the engines are really under that stern deck I hope the fuel is far forward to compensate? How does she trim with empty tanks?
Nice boat and I'd love to go for a ride.
Read Weston Farmer's book "From My Old Boat Shop" for a 60-year experienced Naval Architect's instructions on how to make quick, accurate "flotational models" and how to use them for trim checking and correction. This man participated in powerboat design of all types from 1920 to 1980 and he thought this was one of the most important things he could do with any design after the drawing board and calculation (now computer ) stage. This is an essential step, especially for you with this thing which is on the edge of what is possible.

[BATAAN]

Also you seem to have seating for about 100 persons. If they're Americans that's 20,000 pounds, I don't know what to figure for Europeans, and must have stability for all to rush to one side at one time. Again, bigger block coefficient possibly, thus making the midsection longer thereby increasing stability and decreasing draft.
Weight of vessel hull and upper deck, interior (complex and heavy with many booths), engines, drives and fuel plus the above and 0.5 meter draft? Difficult but probably not impossible with very light superstructure for stability and keeping displacement down but you'd probably have to really think like an airplane designer to make it work and the cost goes up quickly that way.

[PAR]

Prettttttttty, but can it float and preform within it's expected envelop? If you didn't preform any weight calculations, how did you arrive at a draft? Guessing it's for pretty pictures, not yacht design. How well do those round ports look to hold up in a rough go?

[micspoko]

Vessel is for 50 passenger. If it is a necessary introduce a limit of persons on the upper deck. The drive is conventional propeller with a engine from mercedes. Max speed will by about 14 km/h. The basic data are taken from similar units - the more I'm afraid the weight will be lower then i expected and we need to use ballast to keep proper stability and trim. Thanks for your comments, I always like to read comments of people with more experience

[michael pierzga]

Looking great.....I like the covered aft deck passenger handling area. Back to back seating on top deck makes sense...also provides covert crowd control .

Perhaps some way to discourage tourists from all rushing to the same side for a look.... a guard rail aft so all tourist rotate single file around the bow or gaurd rails angled inward to keep them off the cabinhouse sheer ?

And perhaps some way to keep impatient , stampeding tourists from falling down the companionway steps and forming a rugby style pile up ....some kinda gate or angled deflector arrangement that only allows one preson at a time to exit down the steps.

Are the steps to the bridgedeck and the offloading gangway on the same side of the boat ? Logic says that they should be on oppisite sides to make loading , unloading fast and avoid tourist gridlock as they try to decide.. Shall
we sit Inside or Outside ?


Max visibility , waterballasted, Dutch tour boat.

http://glasshopperboat.blogspot.com/

[Alik]

Aesthetically, spacing between windows is too big, they are too distinct. I would make gaps smaller or maybe use color paint in windows area.
Then, round and elliptical windows are breaking the style.
Another issue: sheerline is curved, but roof line is exactly straight and this seems too stiff. I would suggest to make roof line softer.

And now practical issues: how to board this boat? The doors in the front/side are in worst place where geometry is too complicated. There should be some trunk with step and then door, so passengers are boarding on step, not into door opening.

There should be second exit from roof probably to front deck or to saloon. One ladder at stern only not enough for passenger boat as does not allow prompt evacuation.

Toilet doors should not open into passageway.

Hope this is of some help...

[kenJ]

Is it possible to use a catamaran hull to increase stability while keeping the draft small?

[micspoko]

yes but i think the hull should be made of aluminum to reduce weight. and now hull is designed for steel

[Perm Stress]

Originally Posted by kenJ

Is it possible to use a catamaran hull to increase stability while keeping the draft small?

All the rest being the same, catamaran will ALWAYS have more draught, as mono, as the same volume will be located under much smaller waterplane area.
More so, if structural technology is the same for both mono and cat, with same L, B, and H, cat will be heavier: first, she will have more plating area, that equal more weight, second, she will have more material (framing, increased shell thickness...) specifically added to resist torsion. Monohull, even in "box ship" form, when >80% of deck is absent, has much better geometry to resist torsion as that of catamaran.

As for stability, for same overall length and beam, mono will have more initial stability as cat.
Cats, especially sailing ones excel at having more righting moment for given weight, but their beam is incomparably bigger as that of mono. With same overall dimensions, mono will have more waterplane area, more moments of inertia of that area, and consequantly, more stability.