Course How To

Weight and Displacement of a Houseboat

by Keith Fung
(Trinidad)

Calculate weight and displacement of houseboat pontoons

Calculate weight and displacement of houseboat pontoons

What is the average weight of a houseboat per square foot in plan? I plan to design and build my own houseboat and for starters I need to calculate how much displacement I need.


Keith Fung from Trinidad.



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Reply - Answer


Great question Keith, since the displacement of a houseboat is important to calculate before building.

I don't have the figures right off the top of my head, but I remember seeing a chart that showed the average weight of some sample houseboat sizes and equipment.

What I can help you with is the buoyancy and displacement that twin pontoons of different sizes and diameters can hold. The chart shows houseboat pontoon diameter by length, and by capacity in pounds.



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Lastly, hopefully some of our readers and visitors will share and post comments about their sample weight per square calculations and their houseboat building experiences and tips.

Feel free to use the "Click here to post comments." link found near the bottom of this page.

Thanks again for sharing, IAN from all-about-houseboats

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Comments for Weight and Displacement of a Houseboat

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Rating
starstarstarstarstar 		Weight of a steel hull houseboat
by: Mickey

Does anyone know how much a Stephens 16' x50' steel hull house boat would weigh?
Rating
starstarstarstarstar 		Question
by: Anonymous

I understand the cilindr shaped pontoon effect and the box shape. Where do fin U and V shaped plastic & foam filled?

I am building a houseboat with large sleeping loft. How does the extra height get factured in. Is there an equation for building? Is extra width needed for the size of the deck or pontoon capacity. The peek is off-centre. I am over-estimating in pontoon capacity and am having pontoons across the bottom of the deck.
Rating
starstarstarstarstar 		Reclad
by: Anonymjoeous

Hello to all new to the house boating . Not to boating past owner 2 hp jet boats . Jet skis 3 pontoons .? Today is .I bought a 47x12 drifter 72 model just 2 years old when that was manf . 350 Chevy engine mercruiser drive Bye the way I need parts !!! Going into it I new I was going to redo the entire vessel dismantle the entire hull factory came 1/16 metal shocked me mighty thin. It was neglected then some one installed 3/16 plates right over the old now it looks like a screen door I'm adding new 3/16 back to hull new wood removing old hand rails heavy carbon steel installing aluminum rails one inch redoing every room in the boat new floors 3/4osb advantac also new floor on the fly bridge /dance floor total 28 sheets. All in a projected time of 3 months sand blast and painted Bye my self !!!! Oh yeah just me how much does my boat weigh will I use the same water line or will it go lower or rise ? Any and all info wood lessen my stress level thanks to all another late night tonight oh is it a good ideal to install fiber glass on top n bottom of floor with a moister barrier
Rating
starstarstarstarstar 		50 ft houseboat steel hull. 60s model, fully furnished. It sunk in the boat slip beside mine. It's in about 10 feet of water. How can I help this lady out and raise her boat to have the marina pull ot
by: Mike

Any help please, she has no insurance and I want this thing out of the slip beside me.
Rating
starstarstarstarstar 		A quote regarding "weight carrying capacity"
by: boatfan

: Quote :
A slab sided box maintains the same carrying capacity for every inch of immersion. All other hull types increase the capacity to carry weight for every inch of immersion with the exception of a cylinder that lies sideways on the water.

Once you are past midpoint of diameter your ratio decreases at an accelerated level, where at a certain point a very small increase of weight will result in a sinking.

This is also an alarming situation when the vessel is subjected to a sudden shift of weight to one side as for example people on the upper level rushing to one side because of some interesting situation.
: Quote :

Please take note people, that is a very good summation. Ignore it at your peril.
Rating
starstarstarstarstar 		in process.
by: Bobby J

I'm trying to turn a 31' trailer into a houseboat. Any help would be appreciated.

Bobby.
Rating
starstarstarstarstar 		Aluminum Pontoon Houseboat Weight
by: Anonymous

I am new to houseboating and recently purchased a 21m x 6.10m, with 1m Dia pontoons, which is an aluminum twin pontoon houseboat, single deck ht of 3m and open party top deck made by Sea Spray.

The year of manufacture is 2009. The company here in the UAE has gone defunct and i am trying to get the weight specifications, and any other specifications as i wish to have it lifted to dry dock for anti-fouling.

I was reviewing the chart which is published on your forum regarding calculating weights etc, however I could not identify anything longer than 60ft?

Is it possible through this website that somebody can point me in the right direction to calculate the overall weight for lifting.

Many thanks and appreciation in advance, Keith
Rating
starstarstarstarstar 		Re: Caveat
by: Anonymous

The comment posted by beached is one of the best articles written about pontoon buoyancy. It shows a thorough understanding of the issues involved.

Anyone thinking of using round section pontoons needs to be aware of this. I would urge anyone to also Google what is known as the PONTOON EFFECT ....
Rating
starstarstarstarstar 		Archemedes Princible to calculate weight of houseboat
by: Anonymous

The weight of a floating object is equal to the weight of water displaced. I calculated the volume of one tube and divided the sum by 2 so the tubes will sit at half submersion. See Archiemedes Princible.

To calculate the volume of the toon I used (Volume = pie times Radius squared times length.) For each cubic foot of volume you can pack on 62.4 lbs of weight.
Rating
starstarstarstarstar 		A question for Keith?
by: Anonymous

Hi Keith, I'm thinking about building a barge to lift boat moorings, if the total load including mooring, lifting gear, hull material, motor, etc, etc, (everything) came to perhaps 20 tonnes.

If I want the waterline to be half way up the flat bottom hull, based on what you've said, I presume I'll need a hull volume of 40 cu meters, have I understood you correctly? Thank You.
Rating
starstarstarstarstar 		Weight and displacement of some Houseboats
by: Scotty

My 2 cents worth....whatever houseboat you build will be heavier than what you had planned! My aluminum 35ft estimate was 5.5 Tons and I ended up with 7 Tons.

A friends steel 45ft is 17 Tons. I have a 16 ft beam and his is 17 ft. Both are probably "well furnished" so hopefully this will give you a calculation.

Also think of the water traffic where you intend to use your houseboat- it's pretty easy for a large cruiser to send a wake in your direction that is 3 ft high.

To not have the wave come on board, you need to make sure you have enough freeboard. To my mind you need at least 2 ft out of the water.

Good practice is to have maximum of half your pontoon diameter in the water, which means 4 ft minimum pontoon diameter.

Don't forget to be realistic in your live load, EX: people, food, and water/fuel.... Say 1 week onboard- 700 liters of water, 150 liters of fuel, 200 liters of sewage you didn't pump-out last trip, 80kg of food, dishwash liquid, wine, beer and potatoes (you weigh your groceries next time!).

And 3 people on board, plus the 4 friends who stop in... all of this adds up to say about 1.8 Tons on top of your estimated hull weight to be kept in reserve.

Hull volume (m3)= max weight(Tonne) x 2 to have your hull or pontoon half submerged at max loading. If you said 10 Ton of boat load max (say 40ft alloy or 35ft steel) you need 20m3 of hull -2 pontoons of around 1m square or a flat bottom hull 0.5 m deep.
Rating
starstarstarstarstar 		caveat
by: Beached

I'd like to add my 3 cents worth of opinion here.
I am aware that these prefab aluminum tubes are popular to provide floatation in pontoon boats and houseboats.

Popular because I presume they are factory made, cost effective and your floatation calculations are simple.

I can see them in application of a dock and in the smaller pontoon boats, but would not consider them in any sort of serious houseboat.

Any floatation design that has reduced buoyancy at a certain point of the immersion is not something I would want to depend on.

A slab sided box maintains the same carrying capacity for every inch of immersion. All other hull types increase the capacity to carry weight for every inch of immersion with the exception of a cylinder that lies sideways on the water.

Once you are past midpoint of diameter your ratio decreases at an accelerated level, where at a certain point a very small increase of weight will result in a sinking.

This is also an alarming situation when the vessel is subjected to a sudden shift of weight to one side as for example people on the upper level rushing to one side because of some interesting situation.

The total weight on the boat may very well be within the carrying capacity as long as it is relatively equally distributed and supported by both tubes but will become quickly dangerous when the load shift to mostly one tube.

All boats will heel under that situation and can be made to capsize, however the houseboat with circular tubes is especially prone to that situation.

If I would need to use something other then a single hull similar to a barge I would recommend a U or V cross shaped unit.

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