Decisions, Decisions: Selecting the Right Hullform

[@flutterbyeflutters]

Thank you Nick for bringing me from totally ignorant to a novice beginner.

[@worldwyn]

I always learn so much from your videos! I stumbled across your channel about nine months ago while trying to learn as much as I can about moderate sized blue water sailboats. “Why You Want a Trimaran” moved my focus to cruising tri’s. Then I stumbled across proas and Harryproas. A Harryproa sounds very appealing, but I am having trouble finding technical assessments. I would be very interested to see your analysis of proas and Harryproa designs compared to sailing catamarans and trimarans.

[@hyperkineticvp]

Where do you source your math from? I’m looking for technical calculations for a project and I’m in need of formulas to validate my design choices.

[@kurtdobson]

Ezra thank you for your response on the beneteau air hull. I had looked i to this a few decades ago while cruising on lake powell in my 28 foot twin v8 cabin cruiser at 32mph burning 18 gal an hour. Seemed like there must be a way to reduce drag. Fancy cfd codes were just a dream back then but taking a simple model i quickly came to the conclusion that any air cushion would need to be under a lot of pressure since water is about 1000 times denser than air. In any case the shear force of the water wrecks the idea. So i think angled hydrofoils might be the way to go for a powerboat in this size range. I've watched one of your hydrofoil video so thanks. Any rough idea of the improvement in efficiency? Thx Kurt

[@kurtdobson]

Ezra, I really like your informative videos... very difficult subject and the explanations are clear. One question I would like to ask is that Beneteau has a new hull design they call the 'Air Step Hull'. It injects and traps air in the planing section of the hull, and in theory this lowers the friction between the water and the hull. But, of course they get a magazine to do a review which says 'It feels better... It's stable, etc.' But they don't provide the critical information, which is 'how much fuel efficiency is achieved with this? I have Solidworks CFD on my computer with a big GPU, but I wouldn't know how to model both the air and the water at the same time. I bet you have an idea on this, so I'd appreciate any information. Best, Dr. W. K. Dobson SLC, Utah

[@DatawaveMarineSolutions]

You want multiphase modeling from solidworks. I checked the features list, and they claim Solidworks has the feature. It may be called VOF, Multiphase, or just adding in a second fluid. I did a whole video about multiphase modeling here: kzbin.info/www/bejne/haDUoX9pbdqFoNk The basic idea is to create two fluids: water and air. And you will have air inlets under the hull of the ship. The problem is that multiphase modeling won't accurately capture the air lubrication effect. CFD assumes the bubbles of air run along the hull until they can escape. But we have physical model tests that showed a different story. In reality, the water pressure compresses the air bubbles. The bubbles collapse and dissolve into solution with the water. And water with slightly more air dissolved in it still acts like normal water. So it is not an easy CFD modeling problem. But definitely fun to work with. Good luck.

[@myparadiseonbantayanisland9030]

Why do most trimarans have the outer hulls higher than the center hull?

[@DatawaveMarineSolutions]

For optimum performance, we don't want an even distribution of buoyancy between the three hulls (the technical term for the outer hulls is ama). By having the outer amas higher than the center hull, they contribute less to buoyancy, and less drag in the water.

[@Zarcondeegrissom]

this also is interesting in the angle of what is a good hull shape for plucking people out of a stormy ocean. I've seen lots of vids describe someone being within reach of deck crews, then a wave drops them down 40 feet or so out of reach. granted thats also a wavelength vs ship length thing, it is a curiosity. probably something best for after I've had my first cup of coffee and for others with the funds (I don't have) to do a proper investigation into that. I suspect that may be why EERV's are the shape they are, especially with the stair-case-like side ramps they have (for easier pulling people out of the water in the rough north sea.) great vid and diagrams. B)

[@kurtdobson]

Ezra thanks. Most of my work has been in optimization, nonlinear problems, inverse problems and more recently artificial intelligence. However I've mostly worked in electromagnetics and wireless. I've done a fair bit of multiphysics work with comsol and later with ansys. But again mostly wave propagation through materials. I appreciate your knowledge and guidance. I'll let you know if i get anywhere with this. I supect air isn't going to do much despite beneteau marketing hype. Intuition says hydrofoils are probably what i should be toying with. Best, Dr. W. Kurt Dobson Slc, ut

[@kaifailo1452]

It depends on what kind of missions & amount of load taking to determine which kind of hull.

[@petercooke2115]

I have for a long time had the idea of a large diameter (8’ plus) circular tube hull for a catamaran Of course forward sections would tapered to som extent Is the idea flawed? Thanks .

[@DatawaveMarineSolutions]

It doesn't sound flawed. The idea should work, with some reinforcement for concentration points. The pure circular section just is not optimal for a catamaran. If you look at the current catamaran yachts, only the bottom 3 ft or so of the hull is shaped for passage through the water. The rest is just vertical height so we can fit people inside the hull.

[@petercooke2115]

Thank you, I was thinking more of underwater section than above,with a larger type radius.I think it would have a low surface area if profile was a long water line.It would also be less effected by load

[@Arnob_111]

So I'm just curious.. how about Trimaran for a hospital ship? We need high stability, large deck space and moderate dead weight capacity. Also, it would certainly need a large helipad to accommodate a few helicopters.

[@DatawaveMarineSolutions]

A trimaran would work very well for a hospital ship. Especially consider the transit mode for a hospital ship. In general, hospital ships need to respond to aftermath of a battle, or disaster relief. In either case, the ship needs to transit into a region quickly. They need fast speed, plus moderate deadweight capacity, as you mentioned. The trimaran hullform would allow all those.

[@dchiffy]

Great lecture , i think context is super important.

[@stevekang573]

Does the boat go better with the bow lifting or cutting which is better if piercing is better why not add a foil under the catamaran or winglets on a mono haul

[@DatawaveMarineSolutions]

Excellent question. I don't think there is a simple answer. In general, the SHIP should always ride over the waves. Sometimes that means the bow only is better driving through the waves. And some cats and monohulls do have foils.

[@welliguessimwhateverusayia8533]

That would be a great boat for the Mississippi River

[@jerrywilson589]

If I was to email you a rough sketch of what I wanted, what would you charge me to design a 40 ft trimaran for a home build project?

[@DatawaveMarineSolutions]

It depends on a variety of factors. Email me the sketch and I can provide some rough pricing guidance. ([e-mail]) We can go from there if you are interested.

[@jerrywilson589]

@@DatawaveMarineSolutions ok, thank you for your response. I am working on a sketch now and will send it to you upon completion and reference this conversation in the subject line. Thanks again.

[@myeflatley1150]

Nick, be honest. You know that wave action has a very large effect upon which hull to pick. For example catamarans do well in flat waveless waters, such as lakes in good weather. However, the same catamaran in the open ocean will roll and pitch more and more as the swells increase in height. Even in good weather, swells in the ocean can reach 15 feet.

[@DatawaveMarineSolutions]

True that seakeeping is one of many factors that we need to consider when picking a hullform. (Sadly, I can't fit all the factors into a nice simple graph.) There are several projects where I ignored this graph due to other practical considerations like seakeeping, propulsion requirements, or simple owner preference. That said, catamarans get a bad reputation. If we are talking a standard recreational yacht, I agree that a catamaran has limited options for seakeeping in the open ocean. But when we go to the commercial marine sector, the naval architects have several additional tools we can apply. First, the catamarans get much bigger. A 15 ft swell doesn't look nearly as big when the catamaran is 200 ft long and made of steel. Additionally, there are several devices such as bilge keels and control fins that we can add to actively reduce the motions further. I just completed a concept design on a 50 ft catamaran that employed a seakeeping hydrofoil, which was another advanced motion control device. This reduced the pitching and rolling down to only 1/3 of what you normally expect on a catamaran of similar size. In the end, catamarans can be comfortable, if you can afford the advanced engineering.

[@myeflatley1150]

@@DatawaveMarineSolutions Toroid monohulls forever, at least on something small to medium size.

[@richardhenson8499]

What about using a trimaran hull for an aircraft carrier?

[@DatawaveMarineSolutions]

I agree that the idea has merit, and I do not know why we have no trimaran aircraft carriers. I think it would take an expert in naval strategy and procurement to explain that. The only explanation I can think of: if there is no advantage to having a wider flight deck. A wider flight deck is the main advantage that a trimaran provides, but that also comes at a larger cost for the ship construction. Like I said, it would take an expert in naval strategy and flight operations to explain why we have no trimaran aircraft carriers.

[@steveburch5113]

Completely off-topic - I need advice on possible modification on a 14 X 60-ft houseboat sitting on two fiberglass pontoons. Are you available for hire for discussions?

[@DatawaveMarineSolutions]

Sure. You can find my contact information on my website: dmsonline.us/about/contact-information/ Just give me a call.

[@nobody46820]

May I suggest the Americans Cup vessels?

[@jkg6211]

Can this concept be applied to the hull design of a vessel made for 3 to 6 inches of water, a hull weight of less than 600lbs (total weight of around 1,500lbs, engine, passengers, etc.), and a speed of 30+mph?

[@DatawaveMarineSolutions]

In general, yes, but that only forms the starting point for the hull design. Based on your description, I suspect you will want a planing hull. Is this some type of air boat?

[@jkg6211]

@@DatawaveMarineSolutions No, it's an idea for an outboard driven hull around 16ft long with a 7ft beam, made to get back in extreamly shallow saltwater flats. As shallow of draft as possible?

[@MrAmerican]

Hey, can you help me with a project? I have a few questions.

[@DatawaveMarineSolutions]

Probably. What are your questions?

[@ezraboren2069]

Oh here I am 4 weeks later What would be the best deadrise for the biggest wake possible. 26ish foot long boat

[@DatawaveMarineSolutions]

@@ezraboren2069 For the biggest wake? I would go with 2 deg deadrise. The ideal theory would be zero degree, but you want a little deadrise to maintain directional stability. Though I have never heard of a case where someone wants to maximize deadrise. The only thing I can think of that is close is wave energy applications. If that's the case, remember that planing hulls are governed by different physics that displacement hulls. And wave energy tends to conform better with the rules of displacement hulls.

[@kurtdobson]

Ezra just saw a youtube video on navys new boat Juliet marine systems ghost. Swath ridez below water with props on front that are designed to cavitate... flies thru foam 45mph.

[@yashmanwani6232]

I wish this video included foils too.

[@henningklaveness7082]

Great video :-) thanks a bunch!

[@welliguessimwhateverusayia8533]

Ok I've been thinking, I've made 275,000 in the stock market this year and I have a large container and a small container in my yard. Think it's possible to build a house boat out of a container, storage container.

[@DatawaveMarineSolutions]

It is possible, but not recommended. Storage containers are only designed to be strong at the corners. Everything else is fairly weak, to keep the container light. And they are not built to be watertight. A hull needs to be strong over the entire surface to hold back the water pressure. (The water pressure builds up fast with a deeper draft. This is why your ears can pop when diving in a swimming pool.) I would not trust your life to this, or anything valuable.

[@welliguessimwhateverusayia8533]

No, what I ment was, like build plywood catamaran pontoons a big houseboat

[@welliguessimwhateverusayia8533]

Set it on top

[@DatawaveMarineSolutions]

@@welliguessimwhateverusayia8533 Ah. That is a lot more reasonable. The structure of most ships is divided into two sections: the hull that needs the strength, and the deckhouse that is far less critical. Using the containers as the deckhouse (the part you set on top) should be fairly reasonable. Of course, you still need to check for leaks in the container and all the usual interior buildout. But yes, that idea could work. Nice idea.

[@joskojansa1235]

Wow, you must have lived all your life on oceans and seas. I'm in awe of you. You wouldnt make for a rope catcher. Even with wifi

[@EdmundRobinson]

What about the three types of proas; Pacific proa, Atlantic proa, and HarryProa?

[@DatawaveMarineSolutions]

Proas really have their own special category. I need to eventually do a separate video on them.

[@Dave_Sisson]

On the basis of the way things are presented in this video, I'm wondering why all passenger ships over 12,000 GT are monohulls? Despite ambitious plans, the two companies that build large catamarans (Incat and Austal) have never been able to sell anything bigger.

[@DatawaveMarineSolutions]

I don't have a solid answer on that subject. I have actually seen a case of a SWATH cruise ship. But that was a single experiment that died quickly. I should note that those cruise ships do carry a large amount of heavy machinery below decks to support the passengers. It's basically a floating city with fresh water plant, sewage treatment, HVAC, etc. But I think a catamaran or trimaran would still be potentially feasible from a pure physics viewpoint. I think a lot of it comes down to image. The hull shapes of those ships are very important to the cruise lines. That ship is their marketing image. I think conventional monohulls tend to conjure more association with traditional luxury yachts.

[@Dave_Sisson]

Thanks. Just before you uploaded this video I was browsing Incat Tasmania's website and they show plans for 130 metre vessels, but the biggest they have been able to sell is 112 metres. I thought the reason might be related to physics, hydrology or engineering, but it's interesting that the reason may be more related to image.

[@Georgewilliamherbert]

@@DatawaveMarineSolutions My impression has been one where operating cost is factored versus other cost aspects. When I see cruise ship economics breakdowns, it seems like hull purchase (distinct from hull fitout / passenger spaces fitout) and fuel costs are very small compared to staffing, supplies, the capital cost of the passenger spaces, etc. The savings you'd get with more efficient hulls isn't valuable compared to doing bigger (scale efficiency); when bigger hits limits like vertical clearance under bridges and depths of harbors that are uneconomical to dredge deeper, cost savings in hull might drive it then. Or, fashion; if people start seeing trimarans or catamans or SWATH as "cool" they'll demand it...

[@KuraIthys]

That's an interesting question. I've taken a trip on the Devilcat when it was still in operation between Tasmania and the mainland. (it's since ended up somewhere near canada) The devilcat is the name of one of Incat's largest catamarans. Or at least, it was while it was in service in Australia itself. Meanwhile it didn't last long, and the only remaining service on that route is a more conventional ferry 'the spirit of tasmania' In spite of the fact that it could carry 900 passengers and 240 cars, in my experience it was quite small relative to conventional passenger ferries I've been on. The main passenger decks were extremely wide, easily comparable to any large ferry but there wasn't much length to the ship, so it comes out looking very strange. I have to say it was a pretty unpleasant trip because there were a LOT of passengers that had bad sea-sickness. And it's not just your own tendency to get seasick you have to consider in a scenario where like 100 passengers are ill; The smell of vomit alone will make other people who wouldn't otherwise be seasick feel quite sick... So, yeah, I wouldn't call it a pleasant experience. This may be one of the contributing factors as to why catamaran passenger ferries and cruise ships aren't more popular. Even if the actual probability of getting seasick on such a ship isn't as great as all that, the perception alone would not do you any favours. When it comes to vehicles that carry passengers, there's a lot more to it than the practical qualities of a ship. Perception, reputation and appearances can be as important as any actual practical performance of the technology. For whatever reason, both catamarans and hovercraft have suffered largely the same fate, when it comes to passenger transport. - Especially at larger scales. (even though hovercraft, by the very nature of the technology function better at larger sizes than smaller ones) Having said that, while large ocean-going catamarans are rare worldwide, with the Incat's devilcat being one of the largest, and given it's australian made and was originally operated near the place it was built... It's interesting to note how widespread catamaran ferries are in Australia - not these large ocean-going designs, but smaller ones used in rivers and bays. The Brisbane river passenger services are run almost entirely using catamarans. Sydney harbour is also about 90% catamarans, with only the very largest ferries being more conventional in design... For some reason, catamarans are popular for passenger services on relatively calm waters and for relatively small ships (though some of the Sydney harbour cats are still on the order of 30-40 metres long), but large ocean-going designs don't seem to have the same level of popularity. Speed is another consideration; A catamaran is quite fast as far as ships go, which is desirable for ferries (for which the primary goal is to get people from point A to point B), but may not be innately useful for cruise ships (where the trip itself is the major appeal)

[@sharatchand3027]

Hey Nick, I am a fanyour videos, I have a request...... Can you make a comparision video on RIB or a Composite boat

[@DatawaveMarineSolutions]

I'll add it to the list.

[@fredio54]

You are SO weird, but quite addictive to watch :-D

[@muhammadadibabwahab2446]

how about semi displacement?

[@DatawaveMarineSolutions]

Those generally get set by the speed range. If you have a ship that needs to operate routinely between Fn = 0.60 - 1.0, then I would consider semi-displacement. Also useful for higher deadweight coefficients, when it may be difficult to maintain a vessel on plane.

[@It-b-Blair]

👏👏👏👏👏👏

[@terrenceklaverweide6356]

‘Moving thousands pounds of concrete...’ by boat. Hahahahahahaha

[@welliguessimwhateverusayia8533]

I ain't even sold my ginsing yet, I got some money to burn

[@Georgewilliamherbert]

Didn't I see this before?

[@DatawaveMarineSolutions]

You may have caught it on one of the playlists. I upload several videos at a batch and leave them unlisted. But I discovered that they still show up if added to playlists, even if unlisted.

[@Georgewilliamherbert]

@@DatawaveMarineSolutions That's probably it. I did really like it; as a lapsed Naval Architect who keeps a finger in sometimes, it's good to see explanations of where the boundaries lie in choices like hull design, based on requirements parameters and more current design thinking. Thanks!