Houseboat weight

Discussion in 'Boat Design' started by dragn, Jul 13, 2016.

  1. dragn
    Joined: Apr 2015
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    dragn Junior Member

    Hey there. Pretty new to this .. im building a houseboat and was looking for some input on the weight and flotation. I went as big as i could on my pontoons wich are 30"×28" 37feet long. Out of 0.100" aluminum. . My building however i did not skimp..all regular building methods..with 2×4miles walls. And 2×9 trusses for the top deck.. 5 /8 " plywood for the floor and top floor (deck).. ive calculated that my floats can safely hold about 16000lbs. But id love some more input. Wish i knew how to post pics for a better idea?
     
  2. JSL
    Joined: Nov 2012
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    JSL Senior Member

    0.10" aluminum sound pretty thin for this size of boat.
    allowing for the max draft as being 1/2 pontoon depth in fresh water I get a max displacement allowed of about 13,500 lbs. (assuming there are 2 pontoons)
    What you need to do is a weight estimate (weights, centers of gravity, on all axis) which takes into account everything on board and in the boat- the pontoons, framing, outfitting, stores, etc. right down to the nails, screws and paint. It is tedious, boring, and requires a fair amount of patience and concentration. Or.... you can just 'wing it' and be prepared to make corrections after launching day. I assisted a fellow who took the latter approach, needed extra buoyancy, so he simply added another pontoon.
    I am sure other members will add some useful tips
     
  3. messabout
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    messabout Senior Member

    If your pontoon section dimensions are 28 x 30, then we will assume that they are rectangular, not round. JSLs estimate of displacement for half immersion is in the ball park if you have two pontoons. I calculate a little bit less but 13,500 is near enough.

    You have used some robust materials for the top sides. Robust: spell that h-e-a-v-y. A lot of the answer depends on how much 5/8 ply, how many 2 x 4 and 2 x 9s that you have used. It matters what kind of wood you have used too. You will need to do as JSL says and account for every last item that you have used plus an estimate of passenger weight, fuel, water, beer don't forget beer, and everything else.

    On a boat that size I would expect you to use some amenities...maybe a shower, refrigerator, generator, and other stuff whose weight will add up to a plenty. Yes a laborious process but worth the trouble. Do it before it is too late.
     
  4. JSL
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    JSL Senior Member

    That reminds me. I assume this houseboat will be powered and out on the water (ie: not a float-home). One other matter to address is the structure- it must be suitable. If not, your first 'cruise' could literally be a "shakedown" cruise.
     
  5. SamSam
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    SamSam Senior Member

    I took the bathroom scale to Lowe's once and spent an hour or so weighing the different parts I was going to use in a boat I was contemplating. I weighed 3-4 of each item and averaged it out. While I was at it I weighed alternatives like thinner and thicker plywood, different sizes of lumber in case I had to cut down the weight or something. I weighed 10' stuff and figured out the weight per foot, so if I needed an 8' or a 16' 2x? I just ciphered the weight on paper instead of weighing separate 8-10-12-16' boards.

    Divide the pontoons into a number of water tight chambers so if you get a hole in one the boat maybe won't capsize. Put hatches in and use the space for tanks, storage etc.
     
  6. JSL
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    JSL Senior Member

    One handy source for outfit item weights is a good marine catalog like West Marine. They have all the shipping weights for each item.
    And when dealing with metal, allow about 5-7% for over-rolling and welding.
     
  7. dragn
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    dragn Junior Member

    Thanks for the help. Yes they are square. Ive done a base idea of the materials so far. About 6000lbs. . So should be ok for now. I think i will put it in the water as is. And this way i can judge as i add weight.. also as a crazy idea.. i had access to free water cooler bottles. So i sealed them up and have been throwing in my pontoons. Got about 100 over em already. Lol as for mobility. It is more of a floating cottage than a boat.. but wouldnt mind being able to move it around. But not priority. .
     
  8. jdehart
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    jdehart Junior Member

    Hi there - I'm new to the site but we are planning to build a floating home/camp and in doing some research on the weight of a home I came across some sites for home relocation and demolitions and it seems the average weight per square foot living area was 60 lbs. Does this seem like a legitimate estimate? If so it may help when calculating your cabin.
     
  9. JSL
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    JSL Senior Member

    You're on the right track for weight. House moving firms have to know.
    A friend recently had a 'weight experience' on a float home. Lovely, 2 level, decent size but not sure if anyone did a weight estimate. Launching day it had a pronounced list. Rather than add buoyancy they added ballast to the 'high side', thereby reducing the freeboard & reserve buoyancy. Not dangerous but a bit inconvenient: Some added weight (heavy winter snowfall ?) could make life 'exciting'.
    Just in case: Check with your city/municipality bylaw office to see if they have any requirements.
    PS: saw an article in the Seattle Times re house weights. Mentioned Lbs/sq.ft. at 200# for single level and 275# for 2 level. [The 60# mentioned could be floor loading.]
     
    Last edited: Jul 29, 2016
  10. jdehart
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    jdehart Junior Member

    Hmmm... I wonder if that weight includes the foundation? Would be interesting to know. The floating house we are thinking about is 27'L x 16'W for a total of 432 sq ft. If those calculations are correct it would be 86,400 pounds - I'd have to do some serious re-planning!
     
  11. JSL
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    JSL Senior Member

    you can google Seattle Times - ask the expert: what does a house weigh.
    Oops. They did say the foundation was included but not other 'heavy' stuff like roof tiles, etc. House movers mentioned 80,000 to 160,000 lb. Of course, don't forget the contents and furnishings..... a stone fireplace could ruin your day!
    You could also check mfrs of Pre-Fab houses.... they have to be 'shipped'
     
  12. jdehart
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    jdehart Junior Member


  13. Petros
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    Petros Senior Member

    most of my work in my engineering consulting firm is designing building structures, and I know intimately what floor, wall and roof assemblies typically weigh.

    When I do calculations for loading on typical light wood framed residential structures I use 10 lb per square foot (10 PSF), for typical walls and floors. this includes insulation and incidental wiring, plumbing, HVAC, etc as well as surface finish (gypsum wall board interior, wall sheathing, and siding/trim). Roof structures range from about 10 PSF to 15 PSF, depending on roofing material, clay or concrete tile is 20 PSF. These are for the whole assembly, and average over windows, doors, as well as wall surfaces.

    Interior walls are typically about 6 or 8 PSF using GWB. I would not advise using Gypsum wall board in a boat, so using interior wood paneling would be better, and much lighter too. they also make some decent looking plastic panels in 4x8 sheets for use in bathrooms, which would be good in a house boat for halls, kitchen and bathroom areas.

    If you use 2x3 wall studs, wood panel interior walls, 3/8" cdx plywood with either cedar, metal or vinyl siding, and all vinyl windows, it should be much lighter. Vinyl flooring too, light, druable and inexpensive. I would also put a vapor barrier on the inside, and house wrap on the outside of the framing. Metal roofing would be light and durable, conventional asphalt/fiberglass composite shingles costs less but weighed a lot more. Rigid foam insulation would be excellent, but costs much more than fiberglass.

    There is no reason using home construction methods would not work for your plans, but there are a few minor changes I would suggest (I have built some 26 boats, as well as my own house and garage, and design buildings for a living): use all galvanized screws, (or stainless!) rather than nails, add some galvanized metal strapping horizontally around windows and doors directly on the framing (it will be under the siding so it will not show), and screw the plywood sheathing to the framing with plated or stainless screws at 4" spacing (rather than normal 6"), and attache each roof rafter to the wall top plate with galvanized metal straps, and cross over the ridge line from one rafter to the other with the metal strap. you can get a Simpson heavy galvanized continuous meal strap CS-16 in a large coil fairly inexpensively at Home Depo or similar store, or you can special order it in stainless for quite a bit more cost.

    Also, do not use any particle board, it will absorb moisture and swell, use only plywood or solid swan lumber. also if you use vinyl flooring get the kind with synthetic backing, the lower cost material has a heavy paper like backing, which holds moisture and will mold. Us only water resistant adhesives and caulks of course.

    Using this construction methond will make it more durable and weather tight: heavy weather, occasional haul out, or grounding, will not cause all the joints to work loose. I would also caulk all of the joints to keep moisture from getting into the structure.

    You also need to consider the "Live load" as well. In a home the code requires 40 PSF for living areas (this includes the weight of furniture, storage areas, as well as human occupant loads), but only 30 psf for bedrooms. these are good numbers to use but will likely be overkill for a smaller house boat (it is not like you will be filling it with your 60 year collection of National Geographic magazines or pack the boat full of wedding guests which happens occasionally in a home). I think this lower number of 30 PSF would be fine for all floor areas in a house boat, and than estimate the weight of storage areas separately. Unlike a home, you have to balance both structural weight and storage/cargo and equipment weight to keep it on an even keel.

    You should also use this 30 PSF (or 40 if you want) for all open decks and horizontal surfaces outside the house as well. And than apply a roof snow load as well, so a heavy snow fall does not sink it. Typically 20 PSF for being on the coast is enough (about 3 ft of wet snow), though you might check with your local building department for what they use for homes. Make sure you ask for "roof snow load", they typically give you ground snow load with is about 30 percent higher. You can also go with the min of 20 PSF for the roof, and just assume you will be shoveling snow off the roof and decks if you get more than a foot anyway (which does not happen that often). OTOH, if you do not live on it full time, you will have a hard time getting to it if your town has more than a foot of new snow on the ground anyway.

    about ten years ago we had an unusual heavy snow fall in the Puget Sound area of Seattle, and there are lot of people that live in house boats around the area. There was one particularly desirable marina that had all covered slips, so the boats are not exposed directly to the weather. Some brilliant planner did not think about snow loads and when we got 3 ft of wet snow on the roof, the floating docks all sank, pulling with it all of the yachts in the marina. Hundreds of boats were ruined. Much of the roof structure also failed and dropped tons of snow on the boats under it, as well as swamping them all. I guess they did not permit the covered docs since the building department only permits structures built on land.
     
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