position of boiler and engine in new launch

[Lopez Mike]

And are there any of those stinking jet skis or equally horrid wake board boats on those lakes?

I'm not quite clear about what you are trying to determine. If it is fore and aft weight distribution, adding another hull will likely not affect that.

If it is to what degree the hulls (tubular?) will be submerged, then a fairly straight forward calculation will take care of that. Water is about eight pounds per cubic foot.

A decent safety rule is that such a tubular hull should not be submerged more than, perhaps, 40% of it's diameter. It needs to be on the positive side of the submergence v.s. flotation equation. In other words, if it is most of the way under water, you are on the side of diminishing returns as far as getting the boat back on an even keel.

It's a fairly known thing that a hull shaped like most modern submarines has much less drag when submerged. It is less known that such hulls are completely dependent on the location of the center of gravity to stay upright. They roll like pigs in a seaway when at or near the surface.

It has also been demonstrated, with loss of life, that a pontoon boat, once a hull is submerged, has little to keep it from rolling over and then is very happy to stay that way. This seems to happen every few years. The wind catches the canopy and people are trapped underneath and die.

Were I in your shoes, I would worry much more about getting your pontoons as far apart as possible and your weights as low as possible and not worry as much about fore and aft weight distribution.

Pontoon boats are usually propelled by outboard motors with a low center of gravity. Machinery and oafish passengers have a singularly high center of gravity. I have this awful imagination that sees the whole show tipping over when all of your guests decide to step to the dock side at once to disembark.

I sound like such a Cassandra. But do think about these things.

[DetroiTug]

A real danger with pontoon boats used with an outboard, is people moving to the front to disembark as the boat is coming in to dock. It's happened quite a few times if the helmsman decelerates quickly with a lot of weight forward, the front will submerge - bite in forward and flip. The shorter they are, the more apt they are to do that. The general attitude on the lake I lived on was 24 feet was the suggested minimum safe length. The marinas would not livery anything shorter.

Using a pontoon for steam power, it is most likely going to need a center pontoon. My buddy has one and he added a pontoon in the center that runs about two thirds the way back. I think it is a bit larger diameter than the other two. His boiler only weighs about 400 pounds and the engine about 250. 1000 pound boiler a few hundred for the engine, passengers, wood, gear. I'd be looking for another pontoon.

As Mike points out, the displacement is easy to determine.

Area of a circle = pi 3.1416 X Radius X radius

That times the length in inches

divide by 221 square inches per gallon

water weighs 8.12 pounds per gallon.

Then multiply X 40 that is the percentage of wetted hull area.

Subtract about 400 er so for the weight of the pontoons.

-Ron

[cyberbadger]

Lopez Mike, DetroiTug, fredrosse, etc,

I appreciate the posts, but I feel like I'm hijacking lighthousekeeper's thread!

A real danger with pontoon boats used with an outboard, is people moving to the front to disembark as the boat is coming in to dock.

The previous hull owner (2 stroke gasoline 10+ HP outboard). Told me a similar story. 15 people. They gunned it, luckily they managed to recover.

For the Nyitra I I was thinking about 2 crew and 2-3 passengers, and give them a lecture about the limitations...

Maybe I should start a new thread?

I appreciate the input - but I don't want to hihack other folks threads??

-CB

[DetroiTug]

I was replying to Mike as he referenced trim and buoyancy conditions with pontoon type watercraft. Whereas, "trim and buoyancy" are the the subject of the thread.

[Oilking]

To All,
Christiansen Yatchs in Vancouver WA, builder of the kind of boats God would have if he could afford it, moves the boats into a drydock where the props & rudders are installed along with the final outfitting. With the tanks filled the boat is floated, the waterline is marked, the boat lifted again and the boot top painted. So I was told buy workers as I watched a boat being moved into the drydock.

Dave

[DetroiTug]

General rule of thumb: Locate machinery such that the boat floats level with the design waterline. Then when one or two persons run the boat from behind the engine, pitch is slightly high forward, this is OK and typical. Added passengers in the forward area can bring the boat back to level. Pitch with bow down should be avoided for all typical load conditions.

The hull lines, if available, will show the Center of Bouyancy for various draft conditions. Freeware like Freeship or Deftship (I am sure there are many others) does all these calculations without effort on your part, but you need the hull lines modeled.

Yes, a reliable bit of software should typically get it very close. All things known and considered, a result should be arrived at with a high level of accuracy. Naval architects are not using free shareware off of the internet though and what they use probably costs more than one of our boats.

I sell Cad Cam software. I explain to customers that there are three types of software: Good software that costs money, and is very powerful and provides accurate results, Good software that is cracked/stolen and free software. And the free type is typically worth exactly what it costs. Free software is generally written by programmers that are doodling or simply took it on as a class project or to test an internal architecture. Who knows, maybe it's as good as any professionally written software? I wouldn't trust the results of free software when a mistake it creates could corrupt perhaps a years labor. When a software is purchased there is a warranty provided that the software will provide an accurate result and the author assumes some level of responsibility, with freeware there is neither a warranty or an obligation to produce anything.

-Ron

[fredrosse]

I generally agree with what you are saying about "Free Software", caution is prudent. However there are exceptions, for example, much of the very high end software is offered on a trial basis, for a limited time period, and for free.

Other offers from high end software producers comes in the form of their professional software with limited functions. This gives the user unlimited time to try out the software, but it does not have all the features that a professional designer would want. This is the case with the freeware like Freeship or Deftship. These programs (in the professional and costly versions) are used as design aids for much larger craft, including large ocean going ships, but the free versions are just missing several features, such as list and pitching calculations. They are as correct as the professional versions for giving areas, shell expansion drawings, centers of buoyancy, metacentric height, etc. In my experience, very adequate for the purposes we steamboaters might want.

The Cad Cam software you sell, tell us more. I still make drawings with software from the early 1990s, and would like to get an idea of what is out there from someone who I can communicate with.

[mtnman]

And this is why you put it in the water...

[Lopez Mike]

Not to put down these wonderful computational tools (and they are powerful) but I think I'll stay with floating the boat. I would easily spend more time learning and using one of these applications than I would steaming. And I don't get enough steaming time as it is!!!

[DetroiTug]

Fred,

Good point, I was under the impression these were small stand alone programs for free.

Yes some of the software companies offer stripped down versions of their programs for demo use which generally expire or no work can be saved/printed and involve annoying sales attempts to get the user to upgrade to a licensed copy.

I'll PM the rest of my reply as I'm a dealer and I don't want to post anything here resembling a sales ad.

-Ron