Sailboat design: loading conditions and factors of saftey

[catsketcher]

Gday Sean

Worrying too much about the way you build the hulls is a mistake we all have made. Researching lots to work out the best method to build the boat, that will save hundreds of hours is something us amateur builders have all done - ply sheet, strip plank, vertical foam strips, infusion from table, all good ideas but it will still take years. Say it over and over again - years and years.

The hulls will not take that long. The interior fitout will, so will the wiring, fiddling around with less glamourous parts will take you months and maybe years but hulls are probably worth about 20% of the time. The whole structure is probably only 40% of the time involved in a complete boat.

I will come across as a stale and depressed grouch but everyone should have someone who slaps them around the head a few hundred times if they want to build a large cat. Then if they still want to after that they are a little bit better prepared. You will get fed up, tired of the project and wonder why you started. You better really, really want to do this for all the right reasons.

Instead of researching online, work for a builder who builds cats in your holidays. If you can't give up holidays you aren't going to finish building your own. Try and find an amateur near you who needs a hand, help and ask questions. This experience will be gold.

As for infusion, the only amateur I know who did this still hasn't launched his boat. It may be fast but his project stalled.

And to your question as to loadings - I have asked this question of experienced and retired yacht designers. None gave me a straight answer. I think that most early multis were the result of evolution, what worked led to the next generation. It is a great way to refine anything, if you don't mind some mistakes along the way. When I designed and built my two smaller catamarans I used the theoretical method where you tie one hull to the seawall and let the tide go out - cantilever. I am pretty sure my large cat would fail this. (I built two large multis before designing my own)I am pretty sure most cats would fail this test but it seemed like a good place to use as a benchmark.

If you want to design, build a boat designed by someone else first. After the apprenticeship you will know a bit about design. Sail lots, build lots then design meekly.

cheers

Phil

[44'cruisingcat]

Originally Posted by seanjournot

Resin infused foam core construction using female molds; this method should allow for a rapid build and fast fairing of parts before layup while using a cheap and fast to build one off mold. It looks as though most of the man hours for any boat project are used during fairing, painting/ sanding/ finishing. In the end I may end up buying a license from a professional yacht designer; it will still be at least two years until I can start construction.

But we're talking about a one off, aren't we? A boat of your own design?

Which means the moulds have to be made. So they need to be taken off a plug. Which is essentially a boat, which you have to build. And fair. (Some production boat plugs were actually made into boats.)

So to use that method for a one off, you virtually have to build the shell of your boat 3 times, and fair it at least once.

[zstine]

Going back to the original question... ISO 12215 defines loading on the hull (psi) for hull panel, frame and stringer design. there's some free calculators at VectorLam.com which will help you design your hull structure and laminate schedule. Obviously point loading from rigging needs to be individually calculated. Taking the boat's righting moment and applying that load to the mast with a bit of margin is a good start.

[Tin Tin]

This should give you some inspiration, but look how long it took.
https://schionningdesign.com/the-sch...-designs-team/

[Factor]

Originally Posted by 44'cruisingcat

But we're talking about a one off, aren't we? A boat of your own design?

Which means the moulds have to be made. So they need to be taken off a plug. Which is essentially a boat, which you have to build. And fair. (Some production boat plugs were actually made into boats.)

So to use that method for a one off, you virtually have to build the shell of your boat 3 times, and fair it at least once.

Yeah what he said! I am also reminded of Roger Simpson (designer) who wrote a book "If you are 95% finished you are half way there". He was alluding to the fitting out being the longest hardest part of the job.