Wooden Houseboat Design stability

Discussion in 'Stability' started by AwJees, Aug 30, 2021.

  1. AwJees
    Joined: Aug 2021
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    AwJees President of He-Man Woman Haters Club

    I purchased plans for a 27 foot garvey dory then stretched it kept the same beam, beefed up the frames and designed a cabin. This lets me keep it trailerable. I'm curious where im at with stability. If someone could help. Ive drawn what i want now i need to make some compromises. I will answer any questions.

    Web capture_30-8-2021_45226_spirainternational.com.jpeg houseboat side.png Houseboat stern paint.png
     

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  2. bajansailor
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    bajansailor Marine Surveyor

    Have you asked Jeff Spira for his opinion yet? He designed the Mobile Garvey dory.
    Spira International Inc - Mobile Garvey Dory Plans https://spirainternational.com/hp_mobi.php

    I am wondering why you want to have a traditional peaked roof like on a house ashore?
    One positive aspect is that the hot air inside rises, and can be vented out, but on the negative side it is extra weight and materials high up, and the centre of gravity will increase, compared to if the roof is flat.
    And you already have 6'6" of headroom if this is to the top of the sole - or is it to the inside of the bottom shell?
    More likely to the inside of the bottom shell, which reduces your effective headroom (if you have a ceiling, or a flat roof) to about 5'8" (if we allow 4" at top and bottom for framing structure).
     
  3. AwJees
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    AwJees President of He-Man Woman Haters Club

    Some important information i forgot. The hull weighs about 2600 pounds and the cabin weighs 700 pounds. I like the peaked roof over a rounded or square roof. the peak of the roof is only 2 feet above the 6foot 6 inch mark at the center. The cabin is also built very light but strong. It is measured to the inside of the bottom of the shell
     
  4. TANSL
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    TANSL Senior Member

    The boat , in its original version, has a high L / B ratio. As the length increases the stability will undoubtedly present problems. It is also possible that it is necessary to add some longitudinal reinforcement on the bottom and / or sides. Do you have a detailed list of all the weights that make up the full load and their centers of gravity? You may have to reconsider the overall length the boat can handle.
     
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  5. fallguy
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    fallguy Senior Member

    The height is a problem.

    There is no reason to do stability analysis when so clearly too high.

    When considering the heights, you need to realize; you do not stand where countertops are or in the settee.

    windage is always an issue in houseboats, where you plan to sail?
     
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  6. TANSL
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    TANSL Senior Member

    But someone will have to check what can and cannot be done with the boat from the point of view of its stability, don't you think it is convenient? Even saying that the weight is too high is not enough, it would be necessary to know how high it is and how much it should be lowered. Frankly, I do see reasons, many and important, for a stability analysis. And you are absolutely right, windage, in this boat, can be critical.
     
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  7. AwJees
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    AwJees President of He-Man Woman Haters Club

    I havent loaded the boat yet. I have considered a 150 hp outboard on the back about 450 to 500 pounds and up to 70 gallons of gas split between 2 tanks at the rear of the cabin for simplicity picture 2 , 5cubic ft tanks 1 on each side. The motor will draw from both keeping it fairly balanced. I can understand windage being a problem with the surface area of the sides. I am a little surprised at having stability issues. with the hull weighing roughly up to 2700 pds and the cabin weighing 700. The sides of the cabin sit on the outer edge of the hull so they will be 4 foot 6 inches in height. Now swithching to a view from the stern, consider that a parallelogram from a rear view giving me 6 foot 6inches head clearance when standing in the boat The ceiling is a simple triangle truss reaching 2 feet higher in the center. If i changed to a flat roof it doesnt appear to gain much. But I will yield to the experts. I posted this for help and to make compromises to what i want. The boat remaining trailerable is pretty important and I am going to build i just have to get the design safe and comfortable. The 20 foot cabin seemed comfortable. I couldnt get a comfortable cabin and a fishing deck on the 27 foot design.
     
  8. AwJees
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    AwJees President of He-Man Woman Haters Club

    The original 27 foot version has 12 frames at 22 inches, 3/4 inch ply on the bottom of the hull , a 2x8 keelson, 1x4 chine log, 1x4 sheer clamp. I swithched to 22 frames at 16 inches ,1 inch ply on the bottom of the hull , 2x10 keelson along with 2 2x4 along side, splitting the difference between the center of the hull and the outer edge. 1x6 chine log 1x6 sheer clamp and a 1x4 longitutdal along the side between the sheer camp and chine log
     
  9. bajansailor
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    bajansailor Marine Surveyor

    Has the boat hull been built already, and you are now designing the superstructure?
    If yes, can you post some photos of what you have built so far please?

    Apart from the weight of the superstructure high up, and the effect of a cross wind while underway, you also have to take into account the positions of the crew (How many? Maybe 2 and a dog?) and any sudden movement by them while underway - especially if (eg) two crew move to one side.
    And if she does decide to capsize, you cannot get out too easily, unlike an open Garvey.
    Hence why the stability becomes so much more important with a superstructure.

    Edit - Do you really need to have a 150 hp O/B motor? What speed are you hoping to achieve?
     
  10. AwJees
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    AwJees President of He-Man Woman Haters Club

    I dont understand the countertops and settee remark. Maybe were not understanding each other.
     
  11. AwJees
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    AwJees President of He-Man Woman Haters Club

    I havent built a thing yet still all on paper. I wont build till I get a design nailed down and have built it in my minds eye. 2 people aboard maybe up to 4 once in awhile
     
  12. AwJees
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    AwJees President of He-Man Woman Haters Club


    Here is a 24 foot version of the boat in action
     
  13. fallguy
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    fallguy Senior Member

    • You cannot stand where there are kitchen cabinets, nor is is needed where sitting, so quite a bit of the headroom is more than needed. Developing the interior layout can help. Most cabin doors are 'duckers', because you keep a 3" sill to avoid any water coming in and there needs to be a support header on top. If your peaked roof is to avoid duckers, let us know.

    The peaked roof is somewhat silly here. You don't gain anything with it; perhaps an air gap, perhaps some storage. But you gain a lot of wind area. My question about where you plan to sail was not a rip. The location is important. If this is a narrow canal boat, windage matters less than a coastal boat or a big lake destination.

    The materials also then become a factor. The higher you go, the more important each item's weight becomes. I am curious how you arrive at 700#. Figure a foam core build with some structure at 2# per sqft. Your cabin at 6'6 plus say 4" to the peak (that is short) is 10.5' per side or 21' by 20 or 410 sqft less the hullsides plus the ends or 820# in foam sandwich with minimal inside structures. I know for a fact 700# is not realistic. Doesn't include a pillow, let alone a cooktop (excuse the snark). A more practical weight for the cabin as drawn is 2500#. Perhaps very light okume can get you closer to 1500, but there is stuff inside that cabin...lots of stuff. A full cabinet of groceries up off the waterline at 5' up is not a weight to discount.
     
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  14. fallguy
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    fallguy Senior Member

    This cabin is similar width. It uses an elliptical rooftop. There is 6'3" headroom inside and 5'10" on the sides with a rapid runoff on the edge. Windage and materials are reduced this way, but we still have quite a bit of windage. If the door had to be a non-ducker, I could have made a different elliptical shape. The top is exactly 8' material, the cabin is 8'6" wide on the bottom and the walls move in 3" off vertica halfway up. This is a Wood's designed Skoota.

    Now, I am not telling you to build a Skoota, but recommending you consider that roofpeak is high and adds windage and weight for little gain and great expense. This roof structure was developed using 3-0.5" laminated timbers to get the shape...
    22B33CB9-1B44-4080-9431-D6E18645FC4D.jpeg
     
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  15. AwJees
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    AwJees President of He-Man Woman Haters Club

    I understand what you mean now. I arrived at the weight by building the cabin to scale on paper. Made a material list and waste after construction. I then used a material calcuator for the type of wood , plywood, epoxy and so on then did a calculation and added 15 %.
     
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