Very small propane powered live aboard

Hi folks,

The attached started as a doodle (very small cabin). And then it turned into a boat. And now I'm thinking of building it for exploring the southern gulf and rivers etc.
I'd like to have any opinions / suggestions etc.

 

How did you come up with the stability calculations? With one hull flooded it will capsize and not float as in the drawing. What is the cardan (double u-joint) for? You can get a pontoon boat, build a cabin on it and have a better boat. The profile shows a lot of rocker which will make it very sensitive to longitudinal loading.

 

The "boat" is too small for all that gear. In particular It is way too short for the intended purpose. It would be a barf maker in any sort of a chop.

The estimated price for materials is pretty high. I cannot imagine spending anywhere near 13 large for such a boat.

 

It's explained under 'power systems'. They are to steer the boat, as there are no rudders.

 

Hi:
First of all, happy 2013 for all of you.
After having a sight to your drawings I'd like to make a few comments.
I agree with "Gonzo and Messabout" about the weak longitudinal stability of your design. The sectional areas curve for your hull (SAC) seems to result too stepped. It would be wise to flatten it at the midship section, providing a better longitudinal response for weights displacement and waves.
From another point of view, I also agree with the post which points, that pontoons volume looks to be too small.
Hence, at first sight, both longitudinal and transverse stability have to be improved. It could be achieved by modifying your hulls desingn in two ways.
1-] Flattening the hulls bottom and making the "heads" transition stepper. I mean shorter transition curves between hulls sides and heads.
2-] Making hulls wider.
As a sequrity concern, each pontoon MUST be able to withstand the whole weight of the boat without getting submerged.

Hence, the displacement of each one MUST be equal to the total boat weight + the freeboard regulated by rules suitable for your navigation zone and conditions.

From another point of view, for manouverability, for such "Floating house" devices, if total lenght allows for it, two outboard motors, fitted at two wells between the hulls, at each head of the boat, will allow for better manouver ability, and for better weight distribution.
Its also important to be said, that watertight compartements, have to be included at each hull in order to provide for flotation enough to grant for stability in damaged conditions.
For your design, I think, four compartments, would be enough.

NOTE: All above at first sight. No calculations performed.

Regards

 

Although the information we have is not enough to say anything conclusive, I would like to comment the following (do not take my words as absolute truths):
- It is not possible to know what the curve areas of transversal sections is. I also can not say how it should be, not knowing the longitudinal distribution of weights.
- The draft at each hull should be enough to hold half the weight of the boat fully loaded, nothing more. In that draft would add the statutory minimum freeboard (if such a minimum exists), or it may seem prudent under the conditions of navigation, to get the minimum depth of each hull.
- Since there is not a passenger vessel, does not have to meet any requirement of stability after damage.
- Therefore, it is likely that three watertight bulkheads per hull is sufficient.
- Probably the ship is stable enough to meet many (not all) of the criteria that any rules would apply to her.
- The fuel-gas cylinders should go on the main deck, in a well ventilated place.
I fear there are other various aspects, from the point of view of safety, make the boat not readily available candidate to get the building permit in any maritime authority. But this is my impression, I can not prove.

 

Dear Tansl:
I appreciate your comments related to my post, but must point that, no weights distribution is needed for knowing what the SAC curves look like, as far as the designer has drawn the floating line.
As I wrote in the NOTES, at the end. I've performed no calculations, but in fact, are not needed for arriving to my conclusions.
About safety sonditions:
I dont know were you are located, but here, safety regulations are compulsory for all ships, no matter the size.
Of course, those rules are not the same for all of them.
My comments about floating conditions and regulations are not an invention of mine, but a point related to our National regulations which are very rigorous when human life is involved.
If yours are lighter, then .. better for you.

Regards

 

Dear Crowsnest, I would not turn this post into a discussion between you and me.
I am located in Alicante, Spain, about 450 km from Madrid. I have over 40 years fighting against the Spanish government regulations imposed on vessels navigating under its flag and are as rigorous, but not more, as any other administration. I think in Alicante and Madrid are obliged to meet the same standards. If yours are lighter, then .... I'll change to Madrid.
What I have said, among other things, is that "I can not say how it should be" the curve of areas because I don´t know the weight distribution. I can not know neither how this curve is because I have not a body plan. If you know how to derive it, using existing information, would you do me a big favor if you told me.
Surely you know, and if not I tell you, that all the rules are not applied indiscriminately to every boat. There are rules that apply, or not, depending on the type of boat, navigation areas, etc..
Sincerely

 

Dear Tansl:
I was going to say the same about the "Discussion between you and me". First agreement.
About regulations, of course are the same. I must point that ITS ME the one specially rigorous when choosing the rules to be applied to my designs. Once again my apologizes.

This year I have been involved in two similar designs to the one porpoused here, but a little bit bigger. (12 persons onboard).
My apologizes if I sounded too harsh, it was not my intention.

From another point of view: Spanish regulations, or better said, the way those rules are applied, are, from my point of view a nosence.
What would you say if I tell you about a 80 years old wooden fishing vessel, around 9m lenght, transformed into a kind of little tourists boat for 40 passengers, with no project, and no Architect involved, that has been aproved here ?

Well, back to the subject. Of course I give this discussion as finished, and, of course, pleased to meet you.

Best regards