Swath ???

The demihull form shown is certainly not an optimum SWATH hull, nor is it a particularly good cat form, I suspect.

So you get the classic result of trying to combine the "best of all worlds". Something that is somewhere between "not good" and "really bad" at everything.

I agree, a SWATH at this size seems silly. I would go with a wave piercing cat.

Multi-strut SWATHs are also called SLICE's (AFAIK), and are not bad, but again, the struts need to be shaped.

 

No, they do not need to be shaped,

they need to be eliminated.


A SWATH is such a different animal, that the average homebuilder should forget about knowing the term!

It is more than a task for a prime builder to produce a performing SWATH. I for my self cannot! But I can produce higher quality pleasure craft than anyone else.

Why are always the least knowledgeable, those telling us how the water boils?

 

Swath

It does submerge the hulls, does that not make it a SWATH? Here is a good shot of it doing that wave damping thing. The struts cannot add drag due to they being above the waterline in Cat mode during regular transit.

 

Wont the struts create drag everytime a wave hits them causeing a surging motion?

 

Exactly that is making it a cat, not a SWATH.

It would be nice if at least the more serious members (not the ********* fraction) would agree on professional terminology, straight before discussing vessels.

SWATH is not CAT. It is closer to the opposite than those idiots like BlabberCat would think.

Seems you know a lot more than your decent behaviour would let us assume?

Regards
Richard

 

I have seen this design (and variants) before. It is as they describe…a catamaran, or multihull, that sits roughly on the blue boot top. Then when ballasted, the waterline becomes half way (hopefully) between the raft structure and the now submerged hulls, and the struts are all that is seen poking out above the water. SWATHs are very draggy vessels, and the shape of the hulls on this baby, as can be seen in the picture, when submerged would be even worse. Thus the drag would be very high, whatever speed one is sailing at, ie not very efficient at all, just to look cool.

We have designed a vessel similar to this before. It is not a SWATH. One can attempt to call it a semi-swath, or a hybrid-swath of sorts, but it is not a pure swath.

Just as a WIG is not a boat nor is it a plane, it is a hybrid, combining two known effects to produce a design that attempts to yield the best of both worlds. Just as this design does, but seems to fall short. (no supporting data).

If you take the waterplane area (at the lwl which it is floating) and divide by the displacement to the power (2/3), the value should be around 1.0. This is one way of determining how much of a SWATH the vessel really is. In the catamaran mode, it will be conventionally high, ie around the 5.0~6.0 mark. If when ballasted down to the struts, this value is close to 1.0, then by definition, in this mode, it can be considered a SWATH.

There can be several reasons why the struts are separated. Most probably by chance than real hydrodynamic ones! If the SWATH is designed for slow speed, you need to reduce the frictional drag component, as this dominates. Thus minimise the WSA, ie short struts. If running at high speed, reducing the residuary resistance component is desirable, ie longer struts. And on it goes….into directional stability etc etc. So, when designing a SWATH, struts their size and location play a big role. It is not just guess work!

 

Would the struts be separated so when one is traveling paralell to the waves they can flow over the submerged hulls???
Ad Hoc ,Do you have any renderings of your semi swath vessel ?

 

No, don't have any renderings...we only do 'pretty pictures' if the client asks for one or is required for 'some reason'. We focus on real design work, not pretty pictures.

 

Im sorry! Do u have any REAL DESIGN WORK you could share with us?

 

I think that's a pretty good assessment, Henry.

I was just trying to point out to folks that it did operate in a "swath" mode. Not sure if it fits the definition of one, but it kind of looked like one to me.

Question then for anyone:

Why is the boat at the end of my post a SWATH when the catamaran thing in the OP's post isn't a SWATH? The only difference I can see is that the real SWATH (below) has a lot of built in weight above the waterline that the lower parts of the hull keep afloat with their displacement. The small one we were talking about in this thread seems to have very little weight and uses water ballast to get it down to "SWATH mode."

So when is a boat a real SWATH and why is the the original boat not a real SWATH?

 

Why is a trimaran not called a boat...why is a catamaran not called a boat. These are all variants of 'multihull's. Why is the Titanic, or any other ship not called a monohull?....they are generically called ships or boats.

A S.W.A.T.H. is by its definitions, a noun, and being an acronym. Thus if one understands the meaning of the acronym, then all becomes clear.

Small Waterplane Area Twin Hull.

Therefore, must have 2 hulls.....and must have a small waterplane area. So in all operations, it must use the small waterplane area, for seakeeping benefits. If it does not, ie not always sitting on thin struts, then it is not a true SWATH.

How small is small (waterplane area), see my post above.

 

Uhh

Quick call those amateurs at Lockheed and tell them to stop calling their strutted designs SWATH!

http://www.lockheedmartin.com/products/OffshoreCrewTransportBoat/index.html

 

Not sure what you're refering to there, but those 2 images, are swaths.

BTW...the red swath is by A&R, not LM.

 

As I said, the multi-strut variants are called SLICE's.

 

Just wanted to contribute three pics of an icebreaking SWATH nearing completion.

Read more here:
http://www.workboat.com/newsdetail.aspx?id=4294999799