As part of my research for a story I was writing, I once asked a fellow marine writer, who was also a well-known naval architect, to explain the basics of hull design. Well, whether you subscribe to this metaphor or not, you can’t deny that the subject of powerboat hull design starts out pretty simple and quickly gets complicated.
But if all you really want is a working knowledge of those basics so you can be a more informed boater, a good place to start is not erotica but rather with a knife and a box. Clearly this comparison has limitations, but hopefully these two objects illustrate the basic concerns hull designers must deal with to create practical, efficient hulls.
You can intuitively see that the easiest boat to power through the water would be one with a fine, sharp entry with minimal frontal area that therefore produces minimal resistance.
So the next step in the evolutionary process of hull design is to bring the pointy part farther aft so that the front part of the hull isn’t totally flat but rather somewhat V-shaped. But suppose that you’re not as interested in speed as you are in a smooth ride and efficiency.
As noted above, the lift that a planing hull experiences due to the upward force of the water on its flat surfaces is a double-edged sword. Some hull designers are loath to accept the limitations inherent in these two hull types and so attempt to combine the best features of the planing hull and the displacement hull by creating a design that can exceed theoretical hull speed yet provide the kind of stable, soft ride in waves that a displacement hull is famous for.
Obviously this explanation is highly simplified, and there are plenty of other design nuances that I haven’t covered. Trim Tabs on a well designed hull allow the hull to run at its optimum running attitude over a broader range of speed, sea conditions and weight distribution. For example if the boat can plane at lower speed and still keep its bow down cutting an oncoming chop it is essentially running on its lines and the good characteristics of its hull design are working. Calling Trim tabs a crutch for bad design (if it is a good design to begin with) is like faulting an aircraft designer for including flaps for low airspeed performance. I think what we have here is an engineer who is accustomed to having an extra 25% runout of any adjustment beyond what should be needed.
I'm not sure what 'philSweet' is getting at but I would state its obvious that you need no more trim than that required at WOT. Location: united states A boat that requires drives to be fully tucked in at WOT and interceptors down at WOT is unusual.
Can you describe in more detail what happens if the drives are not fully tucked in and if the interceptors are not mostly down approaching WOT? Location: Australia Worth trying bigger, wider tabs as an experiment, doesn't necessarily create more drag either.
Originally Posted by Mr Efficiency Worth trying bigger, wider tabs as an experiment, doesn't necessarily create more drag either. Originally Posted by tunnels How can more surface area in the water not create more drag ?
Originally Posted by tunnels What is the better trim tab and wide one across the boat ?? I've uploaded several pics of a very successful one of the French Navy, a bit too big, but a good example of the results obtained when a boat is designed for efficiency and not fashion.
The boat is very heavily built (Lloyds A100) as shows its displacement of 41 metric tons full loaded. When making potentially dangerous or financial decisions, always employ and consult appropriate professionals.
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As more and more fishing effort to be diverted to areas beyond traditional fishing limits, the expertise available with the Project has to be deployed to conduct intensive fishing operations in grounds where sizeable resource potential is indicated through exploratory surveys by vessels of Fishery Survey of India. Location: india Can anyone help me with the basic fundamentals of Ship Hull Detail Design? The Societys premier reference work, a revision of the 1967 publication on naval architecture covering ship's geometry, stability, flooding, strength, resistance and propulsion, vibration, ship controllability and motion in waves.
Being a Naval Architecture Student you shoud be able find answers to all these questions by yourself from basics you have learnt over last 6-7 semesters.


To create space to locate a big diameter propeller, if I understood your question correctly. If you use a rudder, you usually use skegs to support it with this type of vessels, if I properly understood your question.
Location: gold coast Water Dynamic Hull Form Which hull stern is more water dynamic (has less drag) in a forward motion, taking into account the anti foul line is about 50mm above the water line? Location: Australia Gawd, hard to get a clear sense of what we are looking at there. Location: gold coast Sorry forgot to mention, non planing full displacement hull average speed 8 knts.
Location: Italy (Garda Lake) and Croatia (Istria) It's Bauhaus applied to boat design!
As Ad Hoc and PAR said, none of the above forms are really efficient at low displacement speeds, the biggest problem being the high wetted surface area and the transom stern. But I guess your bauhaus was probably not intended for voyages anyways, but rather for short trips from one (more or less) permanent mooring to another.
Location: Australia The one with the anti-fouling certainly would have went better with a shallower angle of departure, or a curved exit, than what looks to be at least 30 degrees at the stern, but pottering around at sedate speeds should be OK.
Location: Okinawa, Japan For the purpose of that craft, both cutaways are a waste of time and take away useful buoyancy.
Originally Posted by Delane For the purpose of that craft, both cutaways are a waste of time and take away useful buoyancy. Originally Posted by Mr Efficiency The cutaway idea is sound enough, but not the way it was executed.
Location: Eustis, FL Both transition types suck at the speeds you'll be traveling at. For example; if you took the tapered section and started this taper several feet forward of it's current position, you might see this very modest improvement.
You compromise a lot in any way you look, wrt flotation, speed, hull interior, comsumption etc. And you can also see that the boat that could carry the most people and cargo would be a box—a barge. First of all, since the entire bottom except for the very front is flat, it’s still going to pound and slap when it is headed into waves of any size, especially if it achieves any significant speed. In that case you probably don’t want a planing hull but rather a displacement design. Generally speaking, the resulting number is the fastest in knots a displacement hull can go, regardless of the amount of horsepower applied to it.
At slow speed, a swell or chop will also exert lift on these surfaces and make the boat rock and roll. The result of their effort is the semi-displacement hull form, and it generally has either truncated hard chines or other relatively flat hull surfaces on the after part of the hull that generate some lift as the boat moves through the water.
Good thing if you're designing a packaging machine, but hydro doesn't really degrade over time the way machines do (I haven't seen gravity break yet). But do you run your boat at maximum negative sterndrive and tab trim to optimise WOT and still not achieve a good pitch angle for maximum speed?
Your comment about critising aircraft design is wrong as that's exactly what flaps are for, to improve low speed performance(like a boat) and your comment overlooks the fact that planes don't usually use flaps to correct wing profile at WOT maximum speed for a light load. My comment are about a boat designed very recently by a well known designer with an International boat builder.
The question would be 1)has it got enough at WOT and 2) Is it achieved with a satisfactory balance of organic inbuilt hull trim as opposed to external devices.
As you can see, there is nothing fancy but just optimization born from years of experience at sea. This could restrict some functions on this site and impede your overall enjoyment perusing it.We highly recommend that you update to the latest version that is compatible with your operating system. MoreTENDERS AND TOYSKiwi duo design 100% electric tenderJP RIBS and Kit Carlier have collaborated on a 100%-electrically powered superyacht tender, which can be recharged when docked on board the mothership.
Bulbous bow for long rangers, but as you are talking about a 1 day trip , you really don't need it.
The top pic looks like it might be intended to plane - but without more info as Mr E said, hard to make a good guess.
I'd be more concerned about strong headwinds, which should see you doing 2 knots backwards ! So the obvious solution to traversing the water with maximum comfort and cargo is to combine the two shapes—a box-like body with a sharp bow.


Second, because the bottom is flat, such a hull would be hard to control; it will wander from side to side, requiring constant correction to the helm.
But only up to a point, for as you extend the V aft, you reduce both the hull’s interior volume and the lift that was created by the flat surfaces passing through the water.
The best of these boats go fast and ride well because their designers have figured out how much V to employ forward, exactly when it should begin to flatten out, and how quickly.
A shape that generates lift also produces resistance, and a wider hull that has more interior room also has more hull surface in contact with the water, and therefore experiences more resistance.
Instead of that flat hull bottom and hard chines, it will have a round bottom and rounded chines that don’t react so severely to pressure generated by waves. So if you have a displacement hull with a waterline length of 36 feet, its maximum speed is 8.04 knots.
There's no reason to provide more trim capability than that required at WOT with full tanks. If so there's really no value in these trim devices, because if they don't achieve a relatively flat pitch at WOT with maximum negative trims then they'll be very little use to adjust for sea conditions.
The classic looking tenders feature plumb bows and deep V-shaped hulls for better performance. MoreTENDERS AND TOYSLynx comitted to YXTLynx Yachts appoints Filippo Rossi as sales and marketing manager and looks to build on the first YXT sale.
I don't think the loss of bouyancy is an issue, the thing is clearly not going to plane with the kind of installed power it has.
Considering what this vessel is, there's very little you can do to improve over all efficiency. But of course a knife doesn’t float, and being very narrow, has little internal volume in which to carry anything. Such a vessel would not only carry a lot of stuff and slice through the water, it also would be able to achieve relatively high speeds because its flat bottom will be pushed up out of the water as the speed and thus the force of the water increases.
This creates port and starboard flats that create lift and help plane the boat and keep it on an even keel.
If a good planing trim is achieved at cruising speed, typically trim is too low at top speed.
Even if you elected to carve up the bottom aft half of each pontoon and reshape them to a more efficient form, there's so much windage, you'll not see much more then a fraction of a knot improvement.
At the same time, increasing the V increases the total surface area of the hull coming into contact with the water, and that increases resistance. But these flats also react to the lift created by waves moving under the boat, causing it to rock and roll. So virtually every displacement hull also has a prominent keel that keeps it headed in a straight line. As you increase waterline length, you also increase the potential top speed, which is why multihulls and boats with bulbous bows are able to go faster than simple monohull displacement boats.
If the specification is interceptor, then surely one that occupies a greater wide of the hull could be the ticket. Everything has its price, and in the end it’s up to you to decide what you must have and what you are willing to give up to get it. Mostly trim tabs and low stern drive trim are needed while getting to plane or at (low) cruising speed. Thanks to the wider chine in the bow section and the spray rails, guests can enjoy a dry trip.”The smaller model can carry 12 guestsThe new models feature bow thrusters, a deck shower, a removable ski pole, a carbon fibre swim ladder aft and are finished with teak decking.
It would have been better to start rising, preferably in a smooth arc, from somewhat further forward.
But when it’s choppy, the box will begin to rock and roll, especially at rest, and as you move it forward, it will bounce, slap, and wander to either side. They also share the same construction approach and will be built from E-glass and carbon fibre using a sandwich and resin infusion method, complying with EU RCD requirements and will be CE category B classified.  While the owner model includes a single windshield aft of the small cabin, the open tender has two individual shields, allowing guests to walk the length of the boat. There looks to be a penalty in hull drag, as well as having your prop working in water being dragged along by the boat, which is not ideal at all. Based on Class rules, find minimum bow height required & decide if u need a forecastle deck.



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