Houseboat Stability

Seattle house barges are a gem of lakefront living and certainly a very special lifestyle for those who choose to love them.  The alure of the custom architecture, the instant access to kayaking or boating, the close knit neighborhoods which make you feel like you are living in a small town, all of these factors draw Seattle residents to Lake Union living and I have very much enjoyed working with these customers.

One issue that has come up on a few surveys of these magnificent floating homes is that of stability.  This is a topic which is often forgotten but of great importance especially during home remodels or for homes which have never had these calculations done.  Vessel stability is quite simply the factors that go into the angle of heel (how the barge leans side to side) and how this relates to final vessel trim as it sits in the water.  It probably does not need to be said that disregard for barge stability can have negative consequences but often stability issues can be easily remedied with a solid plan.

Stability graph for different angles of heel.

There are two main factors to consider when planning for stability, static and dynamic forces

Static – Static forces are  those related to the distribution of the mass of the boat.  Ballast (weight added for stability), structural height and width, weight of building materials, etc.  This is an interesting calculation as we don’t get to take the boat apart and weigh each component so surveyors conduct a heel test with calcuations in order to accurately model the static forces.

Dynamic – These are forces which change over time and might include tank water sloshing, a large number of guests on the rooftop deck or even a winter storm cross breeze pushing on the exterior wall.

Overall there is a lot to consider when dealing with the stability of your house barge.  How the center of bouyancy changes given the shape of the hull, how the center of gravity relates to all else to create the righting arm (the force that rocks your boat back upright).  All of these factors go into calculating a number of figures which inform the current state and safety of the home and reveals great info about the stability of the barge.  If you are super interested about the specific of these then feel free to contact me and I can send you some more detailed info but for now I am trying to prevent this article from becoming a Naval Architecture textbook.

Stability Tips:

  1.  Consider getting a stability survey – I have to say this first of course as getting professional help on this matter is the best way to have a great plan.  Keep stability in mind especially if you are planning additions to your floating home.  A stability plan can help to make sure your project results in a fully functioning and safe home.
  2.  With a shallow draft barge hull that is common for house barges, simply adding more ballast does not always help.  I did some consulting on a very narrow and tall houseboat that the owner had been adding a huge number of concrete sacks to the bilge for ballast but with no change to the shockingly slow roll that the boat had.  With calculations we were able to determine in this case that his placement of ballast was reducing the metacenter of the boat slightly faster than it was reducing the center of gravity.  To paraphrase, his ballast plan was actually a detriment to the stability of the boat.  An easy plan was made to solve the ballast issue.  Ballast is normally as low as it can be and with shallow draft house barges this sometimes means the ballast is under the barge rather than in the bilge.
  3. Ballast should be secure in place.  Loose ballast will tend to shift when it is being most challenged by dynamic forces with the effect of making things a lot worse.
  4. Avoid using uncured sacks of concrete as ballast.  It is a cheap soluction but powder concreate is a chemical which becomes hot and caustic when wet and these factors are not good neighbors for your hull.  I have seen these concrete sacks sitting inside wood hulls with severe degradation in the area where the concrete bag was sitting on the wood hull.  I have also seen lead tire weights in use as ballast and this material can tend to leach toxins into the bilge water where it eventually gets pumped overboard.
  5. Stability considerations are not only for the tall, high risk barges.  If your boat has a fast and uncomfortable roll in weather that tends to make your guests uncomfortable, then a stability plan can actually help slow this roll down while still maintaining ultimate safety.  Recommendations might include ballast, trim weights, outboard floatation, flopper stoppers, and a number of other tactics to dampen the roll.
  6. If you are replacing or doing significant work on an old wood or fiberglass over wood hull then consider replacing the hull with a lightweight and wider footprint aluminum hull.  They last a long time and often this change tends to add significant additional stability AND value to the boat.

If you have questions in general about houseboat life then you can contact Kevin and Linda Bagley at Special Agents Realty, two people who have been a tireless supporter of houseboats in Seattle and knows everything there is to know about them.

I fostered a great interest in this question while stationed up in Juneau, Alaska for the US Coast Guard.  One heavy snow storm up there resulted in two houseboats having major stabity issues due to rooftop snow load and the additional weight this caused up high on the barge.  After the snow was removed and the houses made right again I was able to help these owners create a plan to keep their homes safe for the future considering all dynamic loads to be expected in Alaska.  This is a topic for which I have great passion and If you have questions about houseboat stability then feel free to contact Eric at Tasman Boat Company.