Pontoon Design

[Ducktoon09]

I am designing a pontoon that I plan on using for fishing, hunting, partying, and river floating. My initial plans are for a 16x7 boat. It will seat six and hold more. I dont have approx. numbers on weight of boat, havent got the weights for all materials. But it will have to hold at least 1000-1500 lbs. of people and equipment. I was wondering if anyone would have any advice on the possibilities of this working? Also how do I figure out how much weight each pontoon will be able to float?

[robherc]

hmmm...it sounds like you still have a LOT of blanks to fill in.

1. Good news first: Frest water weighs 62lbs/square foot, therefore, your pontoons will be able to keep about 62 lbs (boat and cargo/people) afloat per each cubic foot submerged. Keep in mind, you'll want to have a GOOD "margin for error" here to keep the boat a bit above the water, instead of fluch with the surface & getting your feet wet with every ripple! A good rule of thumb (I think) is to give yourself about 2x the displacement you think you'll really need (i.e. for 1500 lbs cargo/people, 1000 lbs boat, and 350lbs motor...I'd double that 2850 lbs and make it 5700lbs/92cu.ft. displacement to submerge both pontoons [figurative numbers only there]).

2. For us to answer any of your other questions, we'd need a good deal more information on the craft you intend to build.

What will you build it out of (wood, fiberglass, aluminum, steel, ...)?
Where will you be using it (fresh water lake(s), streams, rivers, coastal saltwater, all the above)?
What kind of superstructure will you, or will you not, be wanting to build on it?

A BIG recommendation would be to spend a few hours scouring google...see if anyone's already built something that might work for you; then see if there are any plans available. Having proven plans is a BIG advantage when undertaking a build.

[PAR]

Frankly if calculating hull volume is out of reach for you, at this stage in the design process, you need a fair bit of education to expect reasonable success from a self designed boat. Buy a set of plans. The math and hydrostatics have been worked out, plus the boat likely will not flip over, dunking friends and family on launch day.

It's not my intent to offend, but calculating how much submerged pontoon you need to support he loads you anticipate is a fundamental prerequisite. It's not especially difficult stuff to do, but you do have to have a clue about the principles involved, particularly if farther from shore then the weakest swimmer aboard can swim back too.

[messabout]

A 16 foot by 7 foot boat is too small for six people unless they are very friendly. Even if friendly, the size and movable load have some serious issues with respect to safety. Do as Par says. Get a set of plans for a pontoon boat that has been built and thoroughly tested.

If you are up to the math involved then calculate the displacement of the floats as if ALL the total weight is resting on one pontoon only, then add the safety factors. Sooner or later all six of those people are going to rush to the same side of the boat to view whatever has attracted their rapt attention. You will need to do the calcs in the fore and aft direction also.

[Ike]

Here is the way to calculate capacities for pontoon boats from the Canadian Regulations. The US Coast Guard does not regulate this for pontoon boats. But the AMerican Boat and Yacht Council has a standard for Pontoon boats that is pretty much as described by everyone above, and is very similar to the Canadian Standard. So this should get you in the ball park.

4.3.2 Recommended Maximum Load Calculation
4.3.2.1 Where a power-driven small vessel is of multihull construction and is not over 6 m (19 ft 8 in) in length,
the maximum recommended load in kilograms is determined by the lesser of the following (a) or (b):
(a)
Where
GL = Gross Load
b = constant buoyancy factor of 1000 kg/m3
Vt = the total volume in cubic metres within all of the pontoons of a vessel
W = the dry weight in kilograms of the vessel, deck, railings, console, seats, and any other
permanent Structures and fittings, excluding the outboard engine or portable fuel tank
We = outboard engine weight, as determined from Table 4–1
(b) Maximum load as defined in paragraph 4.3.1.6
4.3.3 The Recommended Number of Persons
4.3.3.1 Where a small vessel is of multihull construction and is not over 6 m (19 ft 8 in) in length, the
recommended number of persons shall be determined in relation to the volume of pontoons, the
volume of the largest compartment of the pontoon, gross load, and engine weight as follows:
Where
GL = gross load in kilograms
Vlc = volume of largest compartment, in cubic metres, defined as the largest volume between
separation bulkheads in any pontoon
Vp = total volume in cubic meters of all pontoons
75 = assumed weight of one person in kilograms
Number of Persons = –G––L– X ( 1 _ –V––lc– )
75 Vp
( (Vt x b) – W GL = –––––––––––– ) – We
2
C O N S T R U C T I O N S T A N D A R D S F O R S M A L L V E S S E L S – T P 1 3 3 2 41
H U L L D E S I G N R E Q U I R E M E N T S 4.0
4.3.4 The Recommended Maximum Power
4.3.4.1 Where a small vessel is of multihull construction and is not over 6 m (19 ft 8 in) in length, the
recommended maximum power in kilowatts shall be determined in relation to the squared length and
the diameter of the pontoons as follows:
Maximum Power (kW) = 3 X L2 X Dp
Where
L = length of the pontoon in metres
Dp = diameter of the pontoon in metres

Here is the link to the whole standard. http://www.tc.gc.ca/publications/EN/...HR/TP1332E.pdf
You need to use the engine weights in the table in the standard. It is the same table the ABYC uses and The USCG uses.