pontoon to stationary houseboat

[timycat]

I would like to take a pontoon and make it into a stationary houseboat to put in our canal. It would not need running water as we would just use it as an extra floating bedroom and the house is near for that use. What would my problems be...it would not have a motor. thanks for your help. Carol

[marshmat]

Hi Carol,

Welcome aboard boatdesign.net

This sort of boat is fairly common in Northern Ontario, for use in protected lakes with little to no chance of encountering severe weather. They tend to be built much like houses or house trailers. Nothing too sophisticated, just wood or light metal framing, wood or composite board sheathing, some kind of waterproof membrane or skin to keep the water outside, and in many cases plain old vinyl house siding to make it look the part.

The main engineering difficulty would be in making sure that the pontoon barge can handle the weight, and will remain stable with the house structure on it. It's all too easy to load such a boat down to the point where the tops of the pontoons are barely above water- this is a recipe for disaster. But as long as the pontoons have plenty of reserve buoyancy, and the thing stays at the dock or on quiet lakes, it should be doable.

[PAR]

As Matt said. Think light in every aspect of the job. You don't need 3/4" plywood for the walls, 3/8" will do. Build on 24" centers not 16". Use 2x3's not 2x4" etc.

[timycat]

Thanks Matt...

My husband and I have built many "lanai" structures out of aluminum materials such as "walk-on" 3" styrofoam roofing material where we have installed 4x16 foot roofing ourselves...not heavy, just ackward. Perhaps you don't have such material there based on snow load. The rest of the stucture will be aluminum with as you say, vinyl siding...the heaviest part will be the windows and we're thinking a sliding glass patio door off the fromt deck.

Based on that information do you still think we could use a standard pontoon platform. We can get a 24 foot basic pontoon for $1,000. We have a limited budget.

Thanks again for your quick reply...Carol

[timycat]

Thanks Matt...

My husband and I have built many "lanai" structures out of aluminum materials such as "walk-on" 3" styrofoam roofing material where we have installed 4x16 foot roofing ourselves...not heavy, just ackward. Perhaps you don't have such material there based on snow load. The rest of the stucture will be aluminum with as you say, vinyl siding...the heaviest part will be the windows and we're thinking a sliding glass patio door off the fromt deck.

Based on that information do you still think we could use a standard pontoon platform. We can get a 24 foot basic pontoon for $1,000. We have a limited budget.

Thanks again for your quick reply...Carol

[marshmat]

Carol,

You will need to know the total volume of the pontoons. (ie. take 1/2 the pontoon diameter, square that number, multiply by Pi, then multiply by the length of the cylindrical part.)

The maximum safe load for a pontoon boat is given by the Canadian standard (TP1332) as the lesser of:

1/2 * (Total volume of all pontoons, in m^3) * (1000 kg/m^3) - (Dry weight of boat)

or:
90% of the least of the weights attained in a static stability test, in which weights are added as high up and as far to one side as possible until the top of the pontoon is awash; repeat with the weights at 1/4 of the deck length from the bow and again at 1/4 of the deck length from the stern, until water is lapping at the bow or stern deck.

In short: A pontoon boat is only safe so long as the widest part of the pontoons is at or above the waterline when at rest. This should give you enough information to estimate how heavy a "house" your proposed pontoon boat would be able to handle. Keeping in mind, of course, that people tend to end up on the roof of these things, so you need to leave enough reserve stability that it won't tip when people go up top.

[timycat]

Dear Matt,

Once again, thank you for so much information. I am such a simple person I would not have thought that there was quite so much science involved.

I know I am going to sound dumb, but aren't all pontoon cylinders about the same diameter? We have a 20' pontoon boat that we do motor around in that has a 12 person capacity, would that equate to the pontoons being half in the water at rest? If that total sum of weight is 1650lbs, could I use such a figure as a total weight for the structure. Truly, with the aluminum materials that we would be using, I don't think we would come close to that figure and, trust me, NO ONE WILL BE ON THE ROOF!

Again, I thank you for all of your help...you are very generous with your time, perhaps you love this stuff.

Sincerely, Carol

[marshmat]

aren't all pontoon cylinders about the same diameter?

No, they come in a range of diameters. Anywhere from 20" to 28" are common. And the difference between a 20" and a 24" pontoon is a 44% increase in load capacity, quite significant even though you'd probably have a hard time telling which is which unless they're side by side. So for a conversion like this, you really need to know about the particular boat that you'd be basing it on. All you need is a measuring tape- get the length and diameter of the pontoons in metres, take a guess at the boat's dry weight in kg (=2.2x pounds), plug into the formula above, and you'll have a pretty good idea how much weight it can handle.