Te-PK work in progress
I still don’t see how the parallel hull has more wsa as the faired hull for = disp.
Beyond “performance” - for a cruiser - what is the real difference?
If it is easier, quicker and cheaper to build - then such differences as they are - are negligible at best?
More volume = more load - and all cruisers want to load their boats…..
I am computer challenged and rely on maths and pictures. Water moving in a straight line has less resistance than water moving against something and drag as it is sucked in again…...
A parallel hull will track better than a faired one.
A faired hull will turn (tack) better that a parallel one?
Curious as to what an asymmetric hull does - one side straight and the other faired?
As to tankers - fully loaded they do 16-17 knots - knot bad for the hull form/short bows/weight ?
The pioneering naval architect Froude showed that a hull with a parallel midbody has the wavemaking resistance characteristics of a hull which is equivalent to that of the tapered ends removed and stuck together. The parallel midbody provides only frictional resistance. What this means is that the ‘hull speed’ of a hull with a parallel midbody is lower than that of a fully faired hull of the same length. For hulls with the same length to beam ratio, the hull with the parallel midbody will generally have less wetted surface than a fully faired hull.
What this means for hull resistance in general is that a hull with a parallel midbody will have less resistance at low speeds due to its lower wetted surface area. This is why we see this type of hull used for oil tankers where the speeds are very low relative to the size of the vessel, and where the cost of the vessel vs internal volume is an important factor. The photos of the large double canoes posted above are also examples of load carrying hulls that travel at relatively low speeds relative to their length. Barges are another example.
This is very interesting! This makes a lot of sense to me, and partly explain why i think Bolgers Advanced Sharpies and Fredrik Ljungströms Arch-bow hulls sail so fast. Its a much more scientific way of discribing what i tried to write in my thread about my Advanced Sharpie Proa.
Thanks for this information!
Johannes.
As to tankers - fully loaded they do 16-17 knots - knot bad for the hull form/short bows/weight ?
It’s relative. In resistance terms,16-17 knots for a tanker several hundred metres long is equivalent to around 3 knots for a 10m boat. Wavemaking resistance scales according to the square root of the waterline length.
the power to weight ration on those ships is infinitesimal. check out the technical documentation here
http://www.portrevel.com/3734-the-model-fleet.htm
some of these models have 1/3 hp for 10 tons of weight on a hull thats @ 40ft.
Tom
Beyond “performance” - for a cruiser - what is the real difference?
If it is easier, quicker and cheaper to build - then such differences as they are - are negligible at best?
More volume = more load - and all cruisers want to load their boats…..
Alex,
referring to your sketch of the camp cruiser with very blunt bows, here the resistances of three variants. The loss of speed for a to blunt bow is evident, independent if the hull is faired or parallel. Are these values really negligible?
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“For hulls with the same length to beam ratio, the hull with the parallel midbody will generally have less wetted surface than a fully faired hull.”
I have checked this declaration with Freeship/Delftship/Michlet, and all says, that a parallel hull with same length to beam ratio AND same displacement has more wetted surface as a faired hull. Who’s right???
the power to weight ration on those ships is infinitesimal. check out the technical documentation here
http://www.portrevel.com/3734-the-model-fleet.htmsome of these models have 1/3 hp for 10 tons of weight on a hull thats @ 40ft.
Tom
Yes, and that is because, in relative terms, they are travelling very slowly. That is why it is eccononical to build very large ships that carry huge loads. Using large ships is a very efficient way of moving cargo. But as soon as you begin the incease the speed in terms of speed/length ratio, the resistance rises rapidly. High speed ferries, for instance, are a relatively inefficient form of transport and can only be justifed ecconomically if saving time is an important criteria for the service of the vessel.
Mal.
No not negligible. Thanks for the graphs!!