10 foot SWATH

[yipster]

think you guy's are to hard and its taken out? i saw the picture and thought of it as a small swathie cat with a bit diablo shaped hulls

Originally Posted by dskira

Apex 1 you are very sceptic fo no reason. You should explain me why (a little more than "just to fat") this hull is not a SWATH.
Being skeptic should be accompanied with some input of the picture at hand, perhaps you participate to the testing, not posting what ever picture suit your purpose of negation.

First let me say if there is a reason for being sceptic is to be judged by myself only!
Second: if there are doubts (plural!) it would be your turn to backup a simple statement with facts.
Third: if that picture did in fact show a SWATH, why did you remove it so fast? Maybe others (real experts on the subject, like Ad Hoc) would have resolved our doubts?

Richard

[mydauphin]

I want to see picture to see if Apex is wrong... I got to get him sometime...

Originally Posted by mydauphin

I want to see picture to see if Apex is wrong... I got to get him sometime...

Jaja,
you have to cue, there are quite some others around here..............

[Ad Hoc]

dskira

That is not a swath...some like to call it a semi-swath. But in reality it is neither. Since it looks like the width of the hull at the waterline is constant down to the keel.

[Ad Hoc]

dskira

What is the waterplane area to displacement to 2/3rds power, ratio for this vessel?

Originally Posted by dskira

I started testing SWATH concept in the mid sixtees and we made twenty different very rough and small model. It was interresting.

Another statement i seriously doubt!
The US NUC started testing in 1970 and launched the first vessel in 1973, and you did in the mid 60ies? Although the Dutch built a exploration vessel in the late 60ies I dont believe there have been any private studies at that time (or even earlier) in the US.
Thanks for the lesson in SWATH techniques, though misadressed to Ad Hoc.
One point in describing a SWATH is the ability to decouple, no matter how broad the general concept description might be. The picture you provided does NOT show this ability, therefore it is NOT a SWATH in terms widely agreed and used by the industry. Just small waterplane and twin hulls do´nt make a true SWATH!
Et basta!
When you claim to contribute to a topic you have to accept that your contribution is valued. It was.... and you failed!

Regards
Richard

[Ad Hoc]

dskira

So, to explain the bigger picture, can you answer my Q in post #55 please?

[Guest625101138]

Originally Posted by amaurer

........
Question three:

-In the end, I need ~1000lbs to achieve 4kts on 30lbs of thrust. My calculations for a SWATH tell me I might juuust make it, while similar calculations for conventional (say, monohulls) say its a little hairy. From experience with trolling motors on my old Capri 16.5, this seems ambitious. Has anyone else heard of a SWATH being more efficient at slow (<4kt) speeds, or do I have a systematic error in my approach?

amaurer
It has taken me a while to get back to this.

I have done a comparison of a surface hull for minimum calm water drag at 4kts and a twin hull vessel with majority of the buoyancy submerged. Both displace 450kg. The surface hull is 6.6m long and both of the hulls on the submerged buoyancy vessel are 3m long.

The comparisons are for calm water. The submerged buoyancy craft would be much less affected by waves of course. In fact the reserve buoyancy in the surface skimming hull may be too little to avoid total immersion in waves as I have drawn it.

The water drag on the different vessels at 4kts is:
Submerged buoyancy - 51N (11.4lbf)
Surface Hull - 30N (6.7lbf)

You would need to iterate these two concepts with the actual payload and operational requirements in mind but this gives a starting point. The drag of either craft is well within your 30lb thrust limit in calm conditions.

The wave drag on either vessel at 4kts is very low but around 4.5kts the wave drag on the surface vessel starts to climb rapidly. The wave drag on the submerged buoyancy vessel remains low.

Email me if you want to go into more detail on the possible iterations.

Rick W

Originally Posted by dskira

If you know how to read, SWATH means what it means, not something else you want to make believe. Your credentials what ever they are seams not well put at work.

So, dear dsikra apart from your very nice and exhaustive diagnosis of my character and knowledge (especially the geographical one I like), what is your problem in telling the audience why the vessel shown in your picture is a SWATH?
And where are your problems in answering such a simple question as Ad Hoc´s?

Knowing so much as you do about our industry, how do you like my statement:
"the Swath concept includes tri hull configurations too!"
What means, it is wrong when you say you just can translate the acronym and thats a swath!

Regards
Richard

Originally Posted by dskira

If you know how to read, SWATH means what it means, not something else you want to make believe. Your credentials what ever they are seams not well put at work.

So, dear dsikra apart from your very nice and exhaustive diagnosis of my character and knowledge (especially the geographical one I like), what is your problem in telling the audience why the vessel shown in your picture is a SWATH?
And where are your problems in answering such a simple question as Ad Hoc´s?

Knowing as much as you about our industry, how do you like my statement:
"the Swath concept includes tri hull configurations too!"
What means, it is wrong when you say you just can translate the acronym and thats a swath!

Regards
Richard

[Ad Hoc]

pictures gone again....oh well easy come easy go...

[Ilan Voyager]

Boring Thread...

I'll put my grain of salt. I going to make some semantics so we will see if we are discussing of the same things.

The boat of the pic is not a swath. It's a catamaran with "a bit peculiar" hulls, mainly in the purpose to have very slim hulls. Very slim underbody and the topsides flare immediately above. Passing in a wave the immersed volumes will vary, as like any ordinary boat.

The first purpose, if I'm not wrong, of swaths was the comfort of the passengers by minimizing the vertical accelerations and the lateral ones also.
To minimize the vertical accelerations you have to decouple the rotations induced by the variations of the immersed volumes at the bow and the stern.

In every day language that means:

1- the volumes must be totally immersed so the center of volume does not vary with the waves and stays aligned with the center of gravity. The whole boat remains horizontal. The stabilization of the underwater body comes from the surfaces of this body, plus the direction of pushing of the propellers, plus some dynamic devices (governed by computer).
That means if the track of the body is perturbed, he must be able to return in a stable state in a little number of cycles (phugoïde in french) without diverging or the boat will be very shaky or worst totally unstable.

2- consequence of the 1- the platform must be above the height of the average waves expected to be encountered. Thus a 10 foot swath, unless it's extraordinary high, is only a swath with waves in proportion of its size, ie very small waves of a few inches. In real world, very small boats follow the surface of the sea...

3- consequence of the 1- and 2- the volumes of the pods or connections must be as small as possible, while having a sufficient strength and good hydrodynamics. Hard exercise...
It's why the catamaran showed in the evanescent picture is not a true swath as we see with the Inca catamarans or boats like the Slice. To much volume immediately above the immersed body.

I hope that my english is enough understandable.

[Ad Hoc]

I.V.

yes becoming tedious and totally missing the point.

[Ilan Voyager]

Yes Ad hoc I hope we'll come back to the subject.
Out of subject of this thread and more about slim hulls:
dsikra, the shape of the catamaran on the pic was interesting and looked simple. May we know more about this cat? Size, displacement etc? Other pics?