Swath Boat building Plans

[blackdaisies]

There are tons of boat building plans on the internet, but I found none for Swaths. They are the most durable boat for rough water, stable on water, energy efficient with a 60 percent increase in mileage in fuel compared to other boats, fast, and look as easy to build as a pontoon. Can I assume any pontoon pattern can be used for a pattern? Does anyone know the measurment between the pontoons and the walls leading up to the boat platform? I looks like for a very small concrete boat, the pontoons would be 1 foot wide and there should be a 1 to 2 foot rise from the pontoons to the platform.

Also what is the greatest length of boat for this type of boat that one sail can move through water efficiently without a motor?

If anyone would even take a guess, I would appreciate it.

[yipster]

in a small model test you can find the principal idea but swath's are not ment for still waters and structuraly it is a tough boatdesign were concrete wont work as building material. ah, a sail, how nice but have you considered the exesive heeling in smal waterplane area displacement twin hulls? read more on swath under the search button!

[clmanges]

Blackdaisies, I was looking at this just yesterday, and I wouldn't put a sail on one; one of the problems is their dangerous behavior when heeled.

You ask about foot-wide pontoons, but it's a meaningless question, since you haven't said anything else about the boat -- length, width, displacement, other dimensions.

As to materials for the pontoons, large plastic pipe is a good place to start looking, but do the search, as Yipster says, and you'll get a better idea.

Curtis

[blackdaisies]

I wanted to be within trailering width, very small at 8 foot wide and 33 feet long because it will fit the multi hull trailer I plan to buy before I even start thinking to make this. This is a beginner project. There is more stability on the ocean on a swath. Catamarans are supposedly more able to handle harsh weather and with the weight put in proportion can act like a swath, but the swath is more stable in the waters.

Which do you think is more important on a small boat on the ocean? Better harsh weather handling or better stability on the ocean water? I know a small boat of less than 36 feet would never be good for ocean traveling. The farthest I could possibly go is down the Mississippi and if there's time into the gulf and on the ocean. I want a good boat for both waters.

It looks like the pontoons would be 2 feet wide and the wall heading up from the pontoons would be 4 feet long, then the platform would be added. The boat would have to be heavy enough to make the pontoon sink 4 feet and then the platform could be up to 7 feet? Tell me if this sounds off.

On the internet I've seen huge swaths with three floors, but the swaths are probably 10 feet wide or at least 6. The boat itself looks like a huge rectangle box shape long end vertical, so its a wonder how they don't fall over. I would imagine self righting them would be hard.

Hollow concrete pontoons wouldn't be that hard to make even for a beginner, but how would the pontoons do holding all the weight of the boat from the bottoms? They may crumble if they are kept on a trailer.

If I had a company that just sold easy do it yourself plans for mini small swaths, I wouldn't have a problem. I just thought there would be something out there on the internet already about one that size.

Thanks for the advice!! I appreciated the help!

[Infinitus]

This is a topic I, too, am interested in. Are there any technical design books on SWATH boats?

[masalai]

That wont be nice - have a look at my gallery - I had a go at a power boat - made a model after going for a trip on the 30ft C10 designed by Robin Chamberlin (about 2 ft hull beam best for coastal or semi sheltered waters.

Have a read of The Coastal Passage about 2 editions back - all about "Foreign Affair" which was motored from Brisbane and back filling up twice and also driven across to New Caledonia and Vanuatu (14 meters LOA) http://www.thecoastalpassage.com/ for the New Caledonia trip
http://www.icecat.com.au/objectives.htm for the story - look at all the links for the full story. of the trip Brisbane to Tasmania (Hobart)

there is a 12 metre version being built in Brisbane now... this is not for amateur design or build...

[blackdaisies]

http://www.sailingcatamarans.com/wiz.htm

I think it would be better to stick to something already available. There is no current plans available on the internet for swaths the size of a small houseboat or mini cruiser. The only thing that comes close to a trailerable 8 foot clearance is this one when folded.

http://www.dixdesign.com/3fold6.htm

It's a trimaran that folds in 4 positions, one for storage in the dock, one on the trailer, one in its full position, and a self righting position, but it's for somewhat protected waters.

I've read that the way they are building the hulls bigger or deeper, they might be almost the same as a swath, but a different shape altogether. I think that's the closest I will get before plans are available for a swath for mainstream beginners on such a small boat. These boats are usually over 60 feet.

[clmanges]

I think it would be better to stick to something already available. There is no current plans available on the internet for swaths the size of a small houseboat or mini cruiser.

I think there's a good reason for that. Near as I can tell, SWATH design has a rather limited range of applications, and none of these seem to be recreational.

[blackdaisies]

They are for stabilizing the boat mostly, but are better than a conventional boat on the ocean. It's mostly been used for platforms for drilling oil and diving. The size of the boats can be smaller and still be stable on the water. Normally on a small boat you will be bounced around. They were created so they could use smaller boats to do jobs normally done on larger ones. A ship is much more expensive than a swath boat, so it must have saved a lot of money.

That is why I would think if you compared a 36 foot monohull's stability and sea worthiness to a 36 foot swath, it wouldn't compare very well. Plus the swath is faster. It's more expensive to build, but if you do it yourself for a small boat, it would be worth the extra money. Even to buy one, it would be worth the money.

I have only read good things about swaths and catamarans except they cannot read the wind very well. In a traditionally boat you get better sailing because of it.

I wish I could get this same plan, but in a longer form. The trailer will only take up to 33 feet, but this plan is for 22 unless it comes with a way to lengthen the hulls. The small 8 foot width is important to me anyways because I want to use normal means of trasnprotation to get the boat in the lake. I know the "Wizard" is small enough a fist time builder could get it done.

They should have more plans available for swath boats. I know they are fairly new, but they would go like hotcakes if they were introduced to mainstream boaters for better platform boats. I'm sure a fisherman would love the stability more.

[masalai]

33 ft long and 8 ft wide sounds like an impending disaster and to put it bluntly f***ing stupid, as that beam = no stabulity.... just look at what has been built and demonstrated to work....

[blackdaisies]

I definitley don't know much about boat building, but canal boats are somewhat that size, large canoes, and Gondolas are similar too. I have also read the longer narrower boats are better on the water. Not to say my dimensions are right because I don't know myself for sure, but they seem to be in the same category and there are many out there. Maybe not on those dimensions, but some are.

http://en.wikipedia.org/wiki/Narrowboat



The plan I mentioned opens up to be about 13 feet. I want something like this canal boat, but see it as adding those underwater swath pontoons to make it more stable.

[masalai]

like a wooden horse.... wont work....

[blackdaisies]

What do you think of canal boats at all? With Hydrofoils in the back? Install some swath pontoons underneath them? That would be the same thing as what I was talking about.

Here's an oversized canoe that does well.

http://www.blackfishwilderness.com/canoebuild1.htm

http://www.blackfishwilderness.com/canoehistory.htm

I guess if I want to make a safe boat a long ocean going boat it will have to be with outriggers on simple longboat type patterns. The outriggers can be swaths? That sounds more solid and it would work.

These are ocean going rowboats, so if they can make a boat capable in such a small area, a swath or cheap imitiation of a swath should be worth a shot.

http://www.row4water.org/index.php/view/3

There are those boats that I don't know the name of that have those long poles attached to the bottom of their boats with a pontoon like shape. They say those are for stability. Have you ever heard anything about those?

[Munter]

With due respect, I think you need to do a lot more reading before starting a swath project. Its easy to see some of the advantages of that type of craft while forgetting the disadvantages. Start with a consideration of the centre of bouyancy and the center of gravity and think about what happens when the boat heels. Also think about the ability of a swath vessel to handle changes in load and trim.

[blackdaisies]

http://www.swath.com/Tri-hull1.htm

While the acronym SWATH has been applied exclusively to twin-hull small-waterplane-area configurations, it is equally apt for tri-hull configurations. In fact, at least two of the early SWATH concept patents, those held by Blair (1930) and Lang (1971), included tri-hull small waterplane area configurations. There has been considerably less development work on tri-hull geometries and no tri-hull SWATH vessel has been built. However, beginning in the 1980s more research and development has been carried out than is commonly known. It has been shown that a tri-hull small-waterplane-area design can provide substantially improved speed-power performance compared with a twin-hull SWATH vessel of equal displacement. It has also become apparent that three hulls are advantageous for some design applications because they enhance the exterior appearance and vessel layout.

Why does a tri-hull SWATH have superior powering performance?

The usual powering superiority of tri-hull configurations at moderately high speeds is primarily the result of decreased wavemaking resistance, but it is also important that the hull configuration not incur a large frictional resistance penalty. By way of background, the total resistance of a twin-hull SWATH ship at moderately high speeds is roughly 50% frictional and 50% wavemaking + form drag.


SWATH ships are considerably shorter than a monohull or conventional catamaran of equal displacement tonnage. This is partly to minimize the weight penalty caused by the more deeply submerged hulls of a SWATH ship and the fact that smaller waterplane area makes necessary wider hull spacing than a conventional catamaran. Shorter length also minimizes the frictional resistance penalty from the submerged hulls' considerably higher wetted area per foot of length. Lastly, twin-hull SWATH configurations often have relatively high wavemaking resistance because their short length and greater structural weight make them less slender than would be desirable.


Geometrically similar ship forms of different sizes are called GEOSIMS. For comparison purposes it is useful to think of the 2 hulls of a SWATH ship as geosims of a single-hull small waterplane area ship having twice as much displaced volume, or buoyancy. Each dimension of a geosim, such as hull length, is related to the corresponding dimension of the reference hull by the linear scale ratio, which is defined as the cube root of the ratio of their displacements. So, the length of each SWATH ship hull is (0.500)^0.333 = 0.794 x the length of a monohull small-waterplane-area ship of twice the displacement.


An important factor affecting speed-power performance is the ratio of hull wetted area to displaced volume. For geosims this ratio follows the "square-cube law". That is, wetted area is proportional to (scale ratio)2 while displaced volume is proportional to the (scale ratio)3. The wetted area of each hull of a SWATH is 0.794 x 0.794 = 0.63 x that of the monohull, but the displaced volume is 0.50 x that of the monohull. It follows that the wetted area per ton of buoyant volume for the SWATH hull is (0.63/0.50) = 1.26 x that for a geometrically similar monohull. This means that SWATH ships have 26 percent higher total frictional resistance than a monohull small-waterplane-area ship of twice the displacement.

By extension, the square-cube law suggests it is disadvantageous to adopt a trimaran if the total buoyant volume is merely redistributed into 3 smaller but geometrically similar hulls. The wetted area per ton for such hulls would be 1.44 x that for the monohull with three times larger displacement. Total frictional resistance would be 44 percent higher than is the case with the monohull, and about 14.5% greater than for a comparable twin-hull SWATH ship. For this reason, SI's tri-hull small-waterplane-area ship designs don't have 3 geometrically similar hulls. Instead, the designs have a small-waterplane-area centerhull with 80 to 90 percent of the total displaced volume and 2 relatively short, slender vertical struts providing the rest of the buoyancy. This type of tri-hull configuration, which could be described as a "SWATH-like center hull with outriggers" was first publically advocated by William O'Neill in 1986. In general, the total wetted area (and, therefore, frictional resistance) of these configurations is no more than 5 percent larger than for a comparable twin-hull SWATH ship, but the reduction in wavemaking resistance is much greater (see comparison chart), so there is a worthwhile net decrease in total resistance.

This gives more techinical information on how the typitcal swath and the trimaran type swath behave. But I'm reasearching the questions you asked and will have some more information about them. I just thought this article was worhty of this thread since it give most of the vital information about swath building.