Some ideas

It isn’t easy trying to make the best of a “small” swath, I guess this boat has to be at least 3 to 4 ton and have its legs as far apart as possible. Stability and moving people (say 150 kg=150 liter) can be compensated by the progressively giving more buoyancy keel (400liter?) on the 1.2 cubic meter (1200liter hull)(s) giving 1200kg uplift.

Infolding legs on the “house” (max 4m wide for special transport) spread to a max 10m beam. Waterpumps and tanks operate the retractable legs. Also intended for manoeuvring and berthing. Having the engine(s) down the struts in the submerged hull(s) doesn’t make it easy in design and accessibility. Has nobody ever attempted to place some sort of a engine into a bulbkeel before in wonder? It’s always possible to go back to a cat. With legs? Middle hull carrying the engine? I just like this design better…

The calculator graphs for wsa hullspeed times 3 I assume, plus wavedrag on the 3 keels show, as I see it, a swath running comfortably on minimal swa can do economic speeds up to 40kt !? (I’m more than satisfied with 20kt) Formdrag may be giving the highest resistance than? Is hydrodynamic drag 10 times higher a aerodynamic? This wing hull form will come up with speed I hope to create a minimal swa on the keels. Work out the leg designs? How to figer out what forces are involved, see also http://boatdesign.net/forums/showthread.php?s=&threadid=1178&highlight=swath Anybody in mechanical engineering with some advice? I started making a polyester model (3 legs) of a meter, have weights, and want to do some dynamic testing on a sunny day soon.

Just keeping you informed, please correct me if I’m wrong.

Yipster

Still thinking of the “how big” option 1 tread, a scalar engine, or maybe a “steam engine” as in the powerboats tread might make a big difference…

 

Sounds great - low CG, very quiet etc - but how do you provide access for servicing and repairs? If the 'legs' are big enough to provide access, then they will have too much surface area - or the boat will have to be much bigger.....

 

quik service, easyer said than done i realise (but wouldnt it be nice!)

 

Like to see you engineer that one (at a reasonable cost ) and still leave room onboard for people moving about etc.
Plus you've put the engine at the front of the 'boat' - not too keen on that idea either!

Please don't take my criticisms personally - you just gotta convince me that the concept is viable in this size range.....

 

Thats why i asked -premature- for help. As a swath is a displacement, steel and weight wont be a problem i assume.

Got 1 model hull sandpapered. Got to do the mold than the 3 scale hulls. For testing weights and behavior have to fix 3 of those together, think of ways to propel or tow and wait for a warmer day.

I've recently seen small sloops having the eng. up front and a hydrolic (seems to become populair and chieper?!) powered -rear-prop. And why shouldnt a prop be placed all the way up front? All that is still open in my mind. Must confess that the drawing above dont have that leg tapered as i like. But many things are still to be figered out.

The swath concept i like, unlike a hydrofoil it can -but not that fast- cruize at any speed, having good economy and ride at the same time. Its using its own constant trick on mother nature doing that.

In my opinion well worth giving it a try. But please do stay critical!

yipster

 

I'm only hypothesising here, but I can't see that just because you use SWATH, weight doesn't matter. No matter the hull configuration, the weight of the vessel is equivalent to the mass of the water displaced - the heavier the boat, the more water it will displace. In the case of a swath, a heavier boat will require bigger floats / pods / whatever you call them, or it will simply sink deeper until that equivalent displacement is reached.

In fact with swath, I'd have expected that as you're trying to minimise wetted surface, weight would be a major issue - but probably not as great a concern as variations in weight between light ship and full load conditions.

 

I am a little bit disappointed that only a few are sharing some thoughts on other boat design ideas. I would have expected at least some catamaran plans or other design ideas here in O2 but maybe that is still to come. I’ll keep talking swath ok?

Its good to be critical, but swath isn’t a max. load design. Calculating some of your questions is easy and may convince you better than I can. I did not say weight doesn’t matter, I said a swath is a displacement boat with a constant all speed range “trick”. It’s not like a hydrofoil, wig, cat or planning boat design. But maybe the keels and/or floads must be bigger, that’s possible. Its not so much the WSA as it is the SWA (small waterplane area) that makes a swa(th) very interesting. Its not “my” swath either since all sorts of early SWA patents are way back. What I’m aiming at isn’t even a true swath, I’ll like to mix it with tapered legs that more submerged come in as ama’s. The “floads” use a little foil action etc. All still to calculate, model build and test. Now making the model floats / pods / whatever you want to call them I have to use double moulds (and sealings) design a legframe inside etc. and I fully agree it is more complicated, expensive etc. but also see great gains. Calculate the difference between wave and wsa drag in a broad speedrange and you’ll see! Got a –still to add- formdrag formula for me? I’m back to sandpaper.
yipster

 

The poly shell of the first half leg came off real nice. As discussed in the “scratch build models” threat this “model” is now for a (2 pers) water bike. Displacement of one complete leg should be 80 liter. 3 legs would carry 240 kg. Weight can be added easy, buoyancy not. For a whistle I got a 30 kg 7.5 hp mercury outboard with worn out short shaft bearings. Must be repaired and plan to mount it on the backside of the front leg. With a high pitch prop I only hope its enough to make some speed. With pipes making a plm. 3 meter flat A frame (wont torque) to mount the legs on. Want to keep the front leg vertical adjustable to change the angle of attack, balance a seats basket on the bar and allready asked my wetsuit back. A pic of half a leg I’ll post later. Still far from testing and only wondering about behavior. yipster

 

Gotta hand it to you Yipster - you sure don't muck around do you!
How about posting some pics in the Gallery of the buil as it progresses....

 

thanks will, its sort of work do! http://www.conceptboat.com/ i found elsewhere in the forums, think i''ll enter that competition (who else is designing?) with "my" swath. foto's follow. yipster

 

I was going to enter last year - but couldn't find the time in between my Westlawn stuff. Might have a go this time around....

 

5 axis plotter

at http://www.boatdesign.net/gallery/showphoto.php?photo=733&papass=&sort=1&thecat=506 a pic of my sandpaper work. what a joy it must be to have acces to a 5 axis foam miller plotter, 3 axis can even be great i imagine...

 

t(w)o difficult questions..

1e
the advantage of having a single prop outboard on the forward leg has the theoretical advantage of easy steering. by cornering fast (>40 knots) i get doubts on heeling on this non-liniar design. does anybody know how this may have been solved before? maybe better to have (also) horizontal rudders on the stern legs or what?

2e
wsa power, as ther is only a minimal wavedrag, is hard to calculate. 3 torpedo shaped pods of 100 kg displacement would need what sort of power to reach what sort of speeds on what economy? i know i'm asking a lot, than again, i promise cookies when this wins something in the http://www.conceptboat.com/ competition.

yipster

 

amazing diagram for this 3*100 kg/liter displacement isnt it!
friction/wsa resistance is very much lower as wave drag here.
the questions above i'm working on and have one more here:

the horizontal A frame that must hold the legs on the corners might not torque, made from aluminum pipes it may bend and swing. a carbon frame easely sets me back a grand i figger and may bend as well. maybe wise to extrude the A in the way the pic shows?
yipster

 

and some answers...

From the wetted surface area you can use the ITTC formula:

cf = 0.075/(logRn - 2)**2

where rf = 0.5 rho v**2 S Cf

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from the forum on "the society of naval architects & marine engineers" sname i'll get more worry's: "this tri-cat is close to some existing notable designs, please caution!!"

i am not aware of that and only hope my designbrief in total is an original swa concept. if its within the concept boat competition rules (have to check) i'll post my designbrief and drawings here as i go along...

yipster