Amateur trimaran design critique

@rberrey I have several reasons why.

First and foremost; I would like to make the trimaran such that it can be shipped in a standard 40ft container. The door opening of a standard container is 7'5"×7'6", this limits the maximum beam and height to the same measurements.

Secondly, I would like it to be able to be moored in a standard size berth at a marina. So while the idea is that the amas and akas WILL be demountable, that will only be done for shipping. For trailering I want it to be "foldable"(telescoping) for ease of use in a marina and to minimize set-up time when trailering. I have read that ease of use greatly affects the amount of use a trailerable boat gets, and minimizing the fuss from trailer to water is essential.

Lastly; additional beam increases weight, and the trimaran is already bulky for its length, especially in height. I also don't see right now how I would utilize the additional space effectively. Does that answer your questions?

 

Mr Millard. Multihull Structure Thoughts thread page 102 has a Canadian home designed "Peter Walford trimaran W24 Pocket Cruiser" (use the line in google for fast access) which may be of interest, Some jpegs below. Also there is hull design software at Hullform 9P now working with windows 10 - download links https://www.storerboatplans.com/boat-design/hullform-9p-now-working-with-windows-10-download-links/
This software does a lot of the hull fairing and calculations for you. The package is free. A near professional hull design software package is at: https://www.delftship.net/
search the site as Delftship has a free version with less capability. Both take time to learn but after you play around you will learn a lot about hull shapes, center of buoyancy etc. The only thing required after that is a detailed weight calculation, a structural strength analysis, an aerodynamic analysis etc. Free standing masts are very viable, look at the Harryproa web site.

 

To design and build an ultralight sophisticated multihull it is necessary to get very technical. I have worked with shipwrights that were illiterate but were excellent at building a particular type of boat. They learned through a lengthy apprenticeship and years of trial and error. However, they did not have the knowledge to design or build a boat that was outside of their narrow area of expertise. Claiming that someone with no experience is the equal to an experienced shipwright disregards all common sense and is simply facetious. Further, $200 boat plans are not comparable to what a NA will provide in the way of technical advice and customized design. You get what you pay for. I am not discouraging the OP from designing or building a boat. I do point out the difficulty and time it will take.

 

I am not a NA, but a shipwright and mechanical engineer with over thirty technical certificates. I have taught marine technology and wooden boatbuilding (for free). Maybe you should look at my credentials instead of making snide remarks on what I should do, when in fact I am already doing it.

 

I only have a technical certificate and it took me more than 8 years to get it. How can you get 30 technical certificates in the short time of a lifetime? Amazing, my hat is off to so much talent.
A question corrodes me, mechanical engineer or just a mechanic?

 

Both, I am a mechanic and a mechanical engineer. I also have a liberal arts degree.

 

Nothing wrong with the liberal Big D..

 

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Guys/gals/friends/members: I appreciate that you are reading this thread, keeping yourself updated and are showing interest, but please don't derail it with irrelevant posts.

While I try to compile a more accurate and complete list of structures, parts and other things and calculate their combined weight I have adjusted the design of the bottom part of the hull to allow a draft of up to 50cm/1'8". At that new waterline, the total displacement becomes 3068 liters/108 cubic feet or 3068 kg/6764lbs. The goal is still to make a lightweight boat, but that gives me a huge margin to work with. The major drawback with that, beside the draft itself, is that the proportional displacement of the amas/outriggers to overall displacement decreases significantly.

 

This is essential.
I wouldn't do any more work until you get a good grip of the weights.

For the structure too, err on the side of caution. Never assume you'll hit your targets.

And don't forget to add a healthy margin, minimum 10% to your lightship weight.

 

Here are some rudimentary waterline/draft sketches with the modified hull form.

P.S. I have added some preliminary drawings of the athwartships bulkheads.

 

Nice sketch.

Your measurement conversions don't coincide.
50cm is closer to 20" if you're rounding off.

And what happens to the vaka stern hull...?

Do you have a top or bottom view?

 

@BlueBell. 20" just so happens to be the same as 1'8"... Or did you misread 1 foot 8 inches as 18 inches (18")?

There is no bottom sketch yet. Additional sketches, including a top view, are available in the first post of the thread. Not sure what you mean about the stern of the vaka...?

Thank you for responding!

 

I misread, thanks.

Okay, I understand the rest now.

Cheers