Pontoon design

Hey all,

I am design student and i am designing a boat for my studio project, i am a graduate student in ID and i wanna ask you people on this forum a few questions, this is my first boat design project and i am not too familiar about boats.

i was looking at pontoons and i noticed its made mostly from aluminium, is there a particualar reason for that , why is plastic not used or fibreglass as in most hulls and also i found out that pontoons are more used in shallow waters and does it have anything to do with the buoyancy that the pontoons are made of aluminium

also what is a difference between a catamaran and pontoon boat.....is the catamaran an ocean going vessel while the pontoon is restricted to shallow waters....

You gotta forgive me for my poor knowledge in boats, thats why i am here for ...to get more and from people who have tons of experience...

thanks

pontoon freak

 

Pontoons are aluminum, almost always round (cylindrical) because that is an easy way to form them. In short this is a quick way to build a "pontoon boat" but far, far from the most efficient hullform.

Ordinary pontoon boats are not seaworthy. They work well enough in calmer water but will be suicidal at sea. No aluminum does not add to bouyancy any more than fiberglass or wood construction. The aluminum pontoons that you see are simply a cheap and dirty way to build.

The catamaran is simply a boat with two floats that are parallel at some distance from one another. The pontoon boat could, technically, be called a catamaran. Cat sailors would choke at such a description. Cats are usually well designed and engineered, unlike the barge like pontoon.

Cats are made in different sizes and larger ones are quite capable of ocean travel. The smaller ones are not intended for offshore operation and many of them are purely for racing or pleasure boating inshore.

The people on this forum are generous with their time and knowledge, however they are hesitant to educate people who are starting from square one. There are mountains of books,that you can consult,that will be most informative. One such book that springs to mind is "The Nature of Boats" by Dave Gerr. Do some reading and then get back to us if you have technical questions that are of interest to you.

 

Pontoons = freshwater, Al hulls are good your beaching and duarablity, and abrasive use were fiberglass cannot take punishment like Al or metals. Al is used because of it density.

 

Thank you so much

messabout and captain RAh,

That was awesome , the differenciation between catamarans and pontoons were not clear at first , but they looked and functioned the same.

Messabout, i will go through that book and get back to you , once again i am speechless in the way u have so easily explained it ...

hats off mate...

 

Can I chuck a couple of cents in here, I no nuthin, but, the statement that pontoons are not sea worthy, I feel is questionable.

Catamarans are in my un-knowledgeable mind designed to travel as efficiently as possible in one direction, hence the hull design.

Pontoons are designed mainly as work platforms so travel is not the main criteria, it's the ability to do something when you get there especially with stability in mind.

Oil rigs are often built as pontoons, floated out to site then the legs are extended down onto the ocean floor.

Most people think of pontoons as the aluminium party boat, but they also have a role as work platforms made mainly in steel.

Does aluminium add to bouyancy, contrary to a previous thread, yes it does. The lighter you make a craft, the more bouyant it is.

Poida

 

No they do not add to buoyancy. You are confusing buoyancy and displacement. Bouyancy is dependent solely on the interior volume of the pontoon. Displacement is determined by the weight of the entire craft regardless of whether it is a pontoon boat, catamaran, monohull or barge. Buoyancy is the upward force on the boat as it sinks lower into the water. Displacement is the volume of water displaced.

 

G'day Ike

You are correct bouyancy is the upward force of the water which remains the same.

If an object has a mass heavier than water then it is known to have a negative bouyancy, less, it has a positive bouyancy and equal a neutral bouyancy.

OK the upward force of the water remains the same on all objects regardless of the mass but it is the mass of an object that makes it more bouyant or not.

Thus using aluminium rather than steel of fibreglass due to less mass makes the craft more bouyant.

Me thinks

Poida

 

Catamaran Hulls

So if he choses he can either build it using the standard or if he had say 2 18' cat hulls from a sailboat say a hobie, he would be able to build on that ? Or , would that not work?

 

Yes platforms built on surfcats as they are called here is quite popular in our estuary system.

Surfcats used to be a popular item a number of years ago but have recently lost popularity, hence they are a good cheap means of floatation for a few people. They are hired out as BBQ pontoons.

I have one in my backyard that I built a transome on but then bought a boat.

To save weight all the structure should be built out of aluminium.

Poida

PS. Next I'm down the estuary I'll take a photo of one and post it.

 

Poida:
The thingies that we Yanks call pontoon boats are not work boats. They are pleasure/fishing/picnicing kinds of things that are appropriate for their politely presumed intent.

The cause of my derision is that they are commonly overpowered in an effort to go faster. Think of a 20 foot pair of pontoons with a platform in the middle, carpeted of course. Now think of a 150 HP outboard attached to the back end. The lunatics in my area, reckon that they must go 30 knots in order to be socially acceptable. If it can not go that fast they get a 200 HP motor.

The original pontoons here in Florida were made of stolen aluminum irrigation pipes. There used to be miles of it laying about in orange groves. The owners of the irrigation pipes were not much amused at the loss of their property. Our orange groves are pretty much wiped out these days because developers have built condos and convenience stores where the groves used to be. So there is very little need of the irrigation piping. And we get our orange juice from Brazil.

Any fabrication shop with a roll former can build cylindrical pipes in short order and they do. Well the fab shop/welding shops saw an opportunity to build pontoon boats. And they did. The welders are very good at what they do but not very good at hydrodynamic things. Who cares ? People still buy the ill begotten travesties. Round pipes do not plane very well. But what the hell ? If you apply enough power a dumptruck will plane. There have been so many of the things built and sold to unsuspecting party boaters that cylindrical floats have become acknowledged as the correct hullform. That is an example of how mistakes beget more mistakes until ill concieved activity becomes the normal order of things.

As for seaworthy; That is a relative term I suppose. A round tube with closed ends has an increasing amount of bouyancy as the waterline rises to the mid point of the pipe. Gain in bouyancy is impressive because displacement change is exponential. When the waterlines rise above the mid point the bouyancy gain diminishes at the same exponetial rate that it had increased before. Not an issue in calm water but a deadly issue in a sea way.

 

hi there...me back with more questions after research

Hey guys;

i was wondering is it possible to make the pontoons telescopic, i mean modular.....will the structural integrity of the hull hold if u are trying to telescopically move the pontoons like shrink and elongate them....is there a technology available to do tat.....

I dont wanna piss u techies out there...but just thinking of possiblilities....

can it be done,.....

cheers

Pontoonfreak.

 

amazing....wooww

messabout.....

you should i mean it , you should write a journal or so on the history of pontoon boats or in general , boats...that was an awesome bit of information...

cheers

Pontoonfreak...