# Hull Design

Discussion in 'Boat Design' started by RichardBoatBuild, Apr 11, 2021.

1. Joined: Apr 2021
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### RichardBoatBuildJunior Member

Hello all, I am a newbie here, thanks for having me. I hope I can learn and share as much as possible on this forum.

I am a designer and builder and have been designing a houseboat I plan on building in the next year.

I am quite happy with the design and am now looking for advice from experienced builders.

My question is on the hull design. I wanted to design something that is in my ability to build and keeping in mind this is not a boat meant to be driven at high speeds. I think this will work. I am not sure about buoyancy and knowing if the engine will be submerged enough.

Richard

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### gonzoSenior Member

What is your weight calculation for the complete boat plus passengers and gear?

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### RichardBoatBuildJunior Member

Great question, I think I have a homework assignment.

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### TANSLSenior Member

I totally agree with you, you still have a lot of work to do and it is likely that the design, with which you are now so satisfied, will have to be changed in several respects when, to mention just one variable, you have calculated the weight total and the position of its center of gravity. If you need any help, just ask.

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### RichardBoatBuildJunior Member

I do what help. I really do not know how to calculate weights except with some guests. I would be open to hiring an engineer... Not sure.
I am building this solar and have guessed I would need about 9 batteries that weigh about 130 pounds each. I can always make two compartments under the deck one for storage and one for batteries and decide once the boat is in the water.

What do you suggest?

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### TANSLSenior Member

I think it would be important to have a good General Arrangement plan with everything that the house boat is going to carry on board and where each thing is located, a descriptive report that explains what the boat should do and in what conditions, while detailing the materials, equipment, services and regulations that the ship must comply with. Then, after making a very preliminary first estimate of weights, define the structure and calculate the scantlings. With this, the weight of the structure could be calculated in more detail and thus approximated much more the total weight of the ship. Then it will be necessary to check their stability, for example.
You see, there is work to be done. In the end, if everything is correct, make some beautiful drawings like the ones you have now, but the really definitive ones.

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### bajansailorMarine Surveyor

Richard, do you know the basic principle of calculating the volume of a cube?
It is Length x Breadth x Depth.
You apply the same sort of principle to calculate the volume of displacement of your boat.
The easiest way might be to initially calculate the profile area of the hull between keel and waterline in the side elevation view above.
You can do this by breaking it down into rectangles and triangles.
Once you have the area of the immersed side elevation, then multiply it by the average beam between keel and waterline (as the hull sides are flared out), and you will have the volume of displacement.
Multiply this by the density of the water (I presume you will be using it in fresh water, and that you use metric, so it is 1,000 kg / cubic metre density) and you will have the weight in kilos.
How does this compare with the weight estimate that you will have carried out?
If the weight estimate is a lot more, then she will float deeper than the calculated waterline.

The more accurate your weight estimate is, the better it will be. Try to think of everything that will go into the boat. Not just the outfit items, but all the plywood, 2 x 4's and 2 x 6's and all the other timbers that you will be using for framing, also all the fibreglass..... - it all adds up very quickly.
Re how big you should make your frames - it might be worthwhile buying an existing houseboat plan to use as a reference guide?

Edit - maybe something like this could be a useful reference?
20' & 24' Water Lodge - flat bottomed houseboats-boatdesign https://www.boatdesigns.com/20-24-Water-Lodge-flat-bottomed-houseboats/products/899/

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### RichardBoatBuildJunior Member

I forgot to include the floor plan. I have thought that through.
I would need to calculate the materials but I am not an engineer and do not know how to calculate the load disbursement.

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Richard you will need to calculate the weight of all the timber used as framing, calculate the weight of the skin, the weight of all the furniture, plumbing, electric items, fuel for the outboard if it is gas powered, and anything else that the boat will contain including passengers, food, water, and so forth.
That is not too difficult to do but it is laborious. Absolutely essential for your or anyone else's design.

You need these figures to do appropriate design work on the bottom. For example, one of your pictures shows the aft end of the bottom below the surface of the water. That will cause excess drag and sap up a lot of power from your propulsive machinery.

Good luck with the project, but do all the calculations before you settle on the final design.

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### RichardBoatBuildJunior Member

Thatâ€™s great advice, thanks so much.

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### RichardBoatBuildJunior Member

i think it would be helpful for me to hire an engineer.

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### bajansailorMarine Surveyor

Be careful if you go down this route - professional boat designers probably have more integrity than your average lawyer, but even so, the costs could quickly add up.
Have you found any existing house boat designs on the internet that appeal to you?
Even if they don't appeal 100%, nothing in boat design is perfect - everything is a compromise - so you could use an existing design as a reference basis, and use the general arrangement that you have shown above (but you should still do a weight estimate for all the furniture etc in your design, that would be extra to the reference design).

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### RichardBoatBuildJunior Member

Thanks mess about, would A, B or C be better options?

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### RichardBoatBuildJunior Member

What are you saying about layers lol yes and no, I do want to have fun with the design since I am a designer I want to have some input. I know some engineers maybe that can help me. I need to digest all this good advice. Thanks again.

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### RichardBoatBuildJunior Member

There is someone building a boat off a 1950s popular mechanics article on YouTube. I was taking some inspiration from here.

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