Trimaran crossbeam calculations

Okay Daiquiri, here's another one - the North American canoe and the Greenland kayak are thousands of years old, designed and developed by stone age people - to an excellence that can only fractionally be improved upon today (computers and high technology materials) - in fact it is debatable that they are an improvement - since materials for the original, classic designs were gathered from the natural environment, and not from elaborate manufacturing - how does that compare/counter your pyramid analogy? Cheers.

 

Hey Gary, don't misinterpret me. I'm not saying that old design means bad design. I'm simply in love with traditional wooden boats.

And am also convinced that thousands of years of evolutionary trial and error process can only produce good and functional shapes. Vice-versa, a boat designed with the ultimate computer and the ultimate software by a person with no clue about boat usage or about life at the sea will generally produce much worse results.

But the kayaks you have mentioned do have their place in the pyramid analogy, by the simple fact that the stone age people had to break many boats and possibly loose many ancient sailor's lives in the sea depths before finding out the best kayak shape, materials and scantlings for their vessels. Today we have a knowledge and technology which allow us to anticipate many problems and possible dangerous design details. We usually don't need to send people to death to learn which things work and which ones don't.

Venturing into the open ocean just few centuries ago still mostly meant putting sailors' life to the mercy of ancient Gods. The modern materials, electronics, engines and weather satellites have made our lives safer than ever. When someone loses his life at sea nowadays, it becomes a breaking news. But not so many centuries ago the big news was when the bloke managed to survive.

Cheers!

 

FT's crossbeams

Gary - Thought I'd post another 2 pages from the David Palmer book about FT because they tell the story so well. You're absolutely right about how the crossbeams came to be. The FT 4 page sets it out exactly. Classic. The FT 3 page is Palmer's description of the overload and the effect on the WL, not any interpretation of mine. In the end, it's the story of a good boat for her time suffering badly because of problems with....her crossbeams. Hmmm..

 

Of course the quick reply that people make is that the Titanic was designed by professionals. Some say humans were designed by God, others that they evolved by trial and error. For sure they weren't designed by computer.

FT was just a couple of years before my time working for Derek Kelsall. I did see it sailing and knew David Palmer quite well when we served on the same safety committee. And having met Mike Birch a few times I'm sure if the skippers swapped boats the results would have been different.

For the record. FT was designed and built in a hurry during the three day week crisis of 1973/74. Basically Derek had to build it with the material available that week, or not at all. Hence the original metal truss beams bolted together.

The beam design I liked that he did was on boats like Triple Fantasy. Basically a truss beam but made all in glass/epoxy.

The real problem with trimaran beams is designing them so that they don't slam and stop the boat when sailing into waves. A truss beam does that nicely as there is a big hole where most of the wave impacts are.

I did sail GB4 a lot. The beams were strong enough but the fairings needed rebuilding after the first few sails (one repair I saw being done was with the boat on the beach in Crosshaven during the 1978 RB race)

I am currently designing a trimaran. I haven't got as far as drawing a lines plan or even deciding on the weight estimate so that I can do that because I am still working on the crossbeam design and until I have an idea of how that will work (and thus a rough idea of their weight and C of G) I cannot know how heavy the boat will be or where I need to put the C of B

Also of interest are the two recent Iren's near sister ships. One broke its beams, the other did not. One had curved foils in the outriggers, one did not.

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

==================
Richard, which Irens boats are you referring to?

 

Richard, Oman broke and she didn't have foils - that will confuse the punters.

 

Nicols need good glue joints. In all cases designing an idiot proof construction is pretty hard with the wide range of skills builders have. Modern composite boats raise the bar in many ways but for amateur construction some over engineering is a good idea because of the wide variety of build quality. Don't racers say if it didn't break you made it too heavy? Many of the pre epoxy designs are really tough when made with epoxy which takes the pressure off good fitting.

 

Gary: I know; I didn't say the foiled boat broke.

Interesting though. If the two boats were otherwise identical then potentially the lift from the foils put less load on the beams than the foil-less outrigger did when burying itself into the waves

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Or the builder had a bad day..... or if the foils helped the designer didn't allow enough of a margin for the impact/shock loads ....

 

Not so fast, AH

It may be OK if I speak for Catsketcher because I know him very well and I'm familiar with some of his research.

He referred to Nicol and Piver and he's probably got just about every word written by them and about their boats, dating back to the '60s - and he does know Nicol's failures and he mentioned them.

He mentioned Crowther and he knew Lock and his draughtsmen and comes from a family that has built and owned Crowther boats.

He mentioned Chamberlain and knows Chamberlain and has built one of his boats.

He mentioned Newick and knows Newick and has built one of his boats.

He mentioned Brown, knows Russell and I think he's interviewed Brown as well.

I'm pretty sure he's spoken in detail to Grainger, and he does know his failures as he mentioned them.

So it's not a case of not knowing about failures because of not doing research. You can't assume that he hasn't read about their failures or that he is restricted to just reading about their failures, since he's spoken to most of those guys (and Irens etc) on record about many of their failures, and read about many of the rest.

 

Ad Hoc and Dacquiri et al

I would like to say at the outset I love talking with you guys and learn heaps from it. For me a good thread like this is like getting a group of people at a party and people cutting in and going "But wait on! - What about". I know heaps more about computers now and alloys too. But I still think reverse engineering will help us a heap too.

You see until recently multihull design was done by amateurs for small boats built usually by amateurs. Usually what happened was - you sailed a multi - you built a multi or two - and then you designed a multi.

As for people dying thankfully the materials gave us a heap of clues as to possible worries. Also most of these boats were sailed close to shore most of the time and so if something started to go wrong then you could limp home. For non-racing boats structural failure was pretty much gone after Gen one boats like Nicols (sorry Cav) and Pivers. (They are great boats when built well but some had build shortcuts taken and in some few plans were given - Tryste)

So there was an evolution of design ideas and concepts that was proven on the water in real time and with real boats. That is what happened over here with the boats I am interested about. For big boats I am sure that classification societies had input.

I will go out on a limb here and say that my own boat had a very slight issue with it when I launched it. Thankfully the material - plywood is a great material and showed me it was under stress by developing a surface crack at a tight radius join. So I glassed some uni over it and kept checking for more cracking. 11 years later and nothing more has happened.

So a combination of stress relieving materials that give advanced warning - watch out for thin carbon laminates here! - understanding of the basic load paths and hands on ability is what made Aussie multis what they are today - pretty fast, light and commodious. (Kiwi boats are much the same)

For me with designer mentors as I mentioned before and with fab designers like Irens, Farr, Young, Whiting, Murray all designing boats by the seat of their pants and a bit of resin when they went wrong we got great testing all done for us.

I spend my life teaching Science so am no anti intellectual. But there is a huge amount of real life data waiting to be studied. Just like a botanist looking at the result of millions of years of evolution we can either try to replicate what happens at sea on our computers or work out what our previous generation learnt and then make a model that incorporates this.

Obviously I should now shut up and start calculating. I promise I will go away and look at the Bucc beams. I will also take the Twiggy plans to school and scan them so we can have a squiz.

cheers all

Phil

 

Richard, you've sailed on GB4 - was that after her beams were beefed up? - because she too, suffered from weight problems after the change. When James and Blyth won the Round Britain in her original form, the boat was ultra-light and in the mostly light airs of the race, GB4 flew ... but struggled in the stronger conditions.
If I remember correctly GB4 sailed in one of the French races later with Blyth as a singlehander but did not perform well and I think retired. But that was a beautiful looking tri in original form, just needed more carbon?? Kelsall extrapolated on GB4 with Riguidel's big monster, with the interesting split beams, always thought that was a good solution of strength, stiffness and no wave bashing fairing problems. I/we"d like to hear your impressions of Great Britain !V. Cheers.

 

Richard,
What size trimaran are you designing, and will it be a racing or cruising boat?

 

I really think it was build quality with the Nicols and in the case of Tryste gross overloading (acknowledged by the Haigs. 40 years on ours doesn't have stress cracks but we implemented developments from "the day" for added insurance. Nicol owners should read Pelinta by Francis G. and Joan L. Smith ISBN 0 9587538 8 1 ISBN 0 9587538 9 X(pink).If those plans were updated I'd recommend them. For affordable well proven cruising tri designs I'd recommend the Cross designs, Horstman TriStars, and the Brown Searunners. All with different proven solutions for beams. For the student You could probably buy all 3 for the price of a current design. Piver and Newick's older designs are available at printing cost from The Mariner Museum in Newport News VA.

 

Ad Hoc

6082 T6 it is, then. And welding? No way, not going there. Absolute minimum of bolt holes, no itty-bitty holes for machine screw attachments for this or maybe that, and any bolt holes there do have to be, carefully machined to .001" tolerances.