Trimaran Design Concept with longer foils than the main hull

Ah, good onyer, Ad Hoc, maybe we'll smuggle in some Belgian beer from the Trappist Monks to celebrate. Cheers.

 

I that case, I'm coming too !

 

I thought I was already there but realized there is no such thing as hell or heaven for the atheists but what they allow for themselves......Like good beer!

 

http://www.liveleak.com/view?i=71f_1350498880

 

Oh Yes.

Classic, loved it !

 

We're not taking the piss, Boradicus, well, a little bit - but in no way am I knocking your enthusiasm and excitement for multihull design.
But those other cruel, heathen and savage ******** here .... off to s thermostatically out of control laminating oven with them.

 

Books...

I wish I had seen this earlier, because I just ordered SAILING THEORY AND PRACTICE by C.A. Marchaj, without having the chance to compare your recommendations... I'll look at them later, however. Marchaj didn't set me back a lot, so there is still room for more subject material I think... In the end it is more what is practicable in terms of actual usage in my opinion. I love books, but how many books have I purchased and never used versus those few tomes that are an essential part of my soul and livelihood? Don't worry, I'm not a judgmental man except perhaps when it comes to other Christians :*) - but I try hard to overcome my shortcomings because we are not even supposed to judge each other! There is a difference between sharing your faith and trying to use it as a measuring stick for other people. The latter hardly ever works out in my perspective - but never say never, because I came to my faith in spite of how I had been treated by people that I had run foul of in the church. I am not saying that churches are bad, or trying to be critical of other Christians in church, but when we set ourselves to a standard of loving others, including those we might not want to prefer, I have found myself coming short of the mark so often that I am truly humbled by my own short coming. So how can I be too critical of someone else who is a Christian? And if someone isn't a Christian, what right do I have to be critical at all??? Last Sunday's sermon was all about how we ought to be critical of ourselves instead of others. I don't know about you, but I think that is probably a good foundation for any belief system. Thanks again, and in the short time I have known you on here you have been most kind and generous toward me!

 

Getting more books...

Gary, I am looking at these three titles with a view to supplementing what I have already ordered. I used to have a great little book from the UK on various general things to do with sailing, including navigation, flag flying, storm preparation and weathering, etc. I think I sold it or left it somewhere - which is too bad, because it was rather handy to have around. I have not been able to get much information from reviews on Amazon for these three, except for the first one (Jim Brown's). I can get either or both of the others relatively cheaply, but what I am wondering is what would make the better supplement what have already ordered.

As I stated above, I have already ordered SAILING THEORY AND PRACTICE by C.A. Marchaj, and I have also downloaded the free PDF from Cornell University Library of
Skene's Elements of Yacht Design

I know the Skene book is quite old, but I have seen it recommended on the Naval Architecture Thread and it is also free, so unless I am wasting my time reading it, it would seem to be profitable to see what I can learn from looking while I await my book orders .

If I had to pick one or two of the three you listed as supplemental material, inclusive of general information for yacht handling, which, in your opinion would be the better or most critical of the three to get?

I am also curious about Marchaj's "Seaworthiness : The Forgotten Factor" and "Aero-hydrodynamics of Sailing," although I am concerned that the latter one, as interesting to me as it sounds, might prove very technical.

Anyway, back on topic, I am looking at Skint For Life's second post on his Multihull Collision Survivability thread, and the sketch he provided is quite similar to the type of design that I am talking about, except for the fact that his main hull appears to be above his inflatable pontoons or amas, depending on how he has decided to make them.

His idea of using inflatable amas brings to mind the potential benefit of having amas that are lighter in general - although not necessarily inflatable - in order to lessen some of the structural requirements for the beams. There would, of course still be the mass of the main hull to consider when calculating for beam strength, but lighter longer amas might prove a viable way to increase the effective LOA and seaworthiness of an otherwise smaller craft. My understanding from looking at Skint For Life's thread is that there would be potential for considerable drag if the amas were inflatable, not to mention the fact that the safety considerations of having a raft in the event of a puncture would be close to nil.

But the idea might not be entirely without merit. I have read about airtight collision bulkheads, and I have seen some structural pictures such as the one posted on page 4 of that thread, posted by SabahCat, and took note of post #14 by OldSailor7 on the same thread where he talks about the installation of air bags as a preventative in case of incurring damage to both the main hull and amas.

I thought briefly about the possibility of incorporating a derivative of these ideas in order to achieve a light-weight, yet somewhat survivable design of the amas. Taking the idea of breakaway bulkheads at the bow I am wondering about creating a light weight netted sock to hold and form up inflatable internal bulkheads, where the netting attaches to an outer geodesic shell that is a light weight laminated design, with more reinforced FRP at the bow, and waterline. This might provide both a light weight solution for amas as well as a way to soften collisions and to manually cut away damaged areas by cutting through the netting.

I am wondering if it would be more beneficial to use modular netting as opposed to one long sock, however, otherwise, after impact, if part of the wreckage is caught up it might continue to pull apart the remaining of the structural skin of the amas.

The primary difference in the design would be that if there were a collision, the main hull would still be at risk, and therefore require the amas for additional flotation (whereas Skint For Life's design has the main hull riding high above the water line, as a sort of separate mono hull in case the amas are completely destroyed).

However, when considering creating both long and light-weight amas, it seems to me to be important to include some considerable longitudinal reinforcement. I am not sure what a light-weight solution for this would entail.

Any takers or ideas on the subject?

 

Russian Designed Inflatable Trimaran

Here, Russian designers and sailors have a trimaran that is inflatable. What I notice the most is that rather than having two large beams to connect the amas, there are four somewhat smaller beams, and in turn they are connected to two longitudinal "beams" that run the length of each outrigger/ama. I would like to look at this in greater detail later, but what is interesting to me is that the longitudinal reinforcements run parallel to the upper portions of the amas, and along the inside. This would tend to make sense to me, being that the forces interior to the connection of the main hull to the amas would be the most needful for reinforcement.



(After looking at this it appears to me that only one longitudinal beam is on the inside of each ama, whereas the other runs down the center of each?? I am talking about the beams actually on the surfaces of the amas. There appears to be an additional longitudinal support beam running across the top of the beams jutting out from primary hull as well as some interesting looking angled braces connecting to the bow.)

But with a shorter main hull, I wonder how the reinforcements would be best laid out. Now I am thinking in terms of designing a truss, but as a horizontal cage for the hulls much like what was done in this boat. In house construction, trusses are made to support and span a roof across a horizontal that would not normally be capable of supporting the requisite load. I believe the same concepts would apply to frame construction in a small trimaran with long outriggers. Although I am applying a concept from an example involving mostly static forces, I believe it is similarly portable to a system involving more active dynamics.

Would that be correct, or not?

 

The USA-17



The USA-17, according to the article, has primary hull of 27M LOA and amas of 34.5 LOA. That's approximately a 1.2778 ratio, amas to main hull. It is listed as having a carbon composite hull type, and only has two beams connection the amas to the primary hull...

 

It's been discussed recently on this forum. This was his first book, very much superceded by Aero-hydrodynamics of Sailing which is the Marchaj book I would recommend. The Seaworthiness one was really only relevant to IOR monohulls

Derek Harvey was a sailor ( he had one of my 24ft Strider designs) not a designer - unlike Jim Brown and Chris White, and some of his design comments are a bit suspect

Derek Kelsall wrote a nice little book on catamarans some years ago. Charles Kanter has a few books out, but he has some ideas that are not "mainstream", shall we say.

The original Skenes was the "bible" (if I can say that to you) for self taught designers for years

You could also look at the AYRS publications.

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Richard:

Thanks a lot for the information about the books. In a way, actually, referencing the bible is a strong sign of respect for The Bible, as in The Holy Bible All sea faring men probably have faith of some kind - what do you have to lose when you are hoping against hope and it is an impossible situation??

I really think Brown's book from all I have heard ought to be next in line. I'll bump Seaworthiness and add Aero/Hydro and take a look into Kanter too.

I am finding Skene to be a little tricky due to my lack of knowledge of the terminology he is using. I am just beginning Chapter Five, on design, but I can't say that I have a firm visual grasp of calculating the lateral plane yet, or of using Taylor's Mean Secant Method for the determination of wetted surface area (although I grasp better the concept of the Prismatic Coefficient), and I am not really sure what he means by half-breadths when he is referring to calculating the moments of inertia.

I think a more visual text would be helpful in this regard. I have been taking a look at delftship software, so perhaps this can help with some of the more routine calculations that seem a little arcane - but the theory is really helpful, and seeing how he juxtaposes tradeoffs between speed and seaworthiness, for instance, is valuable in its own right. Thanks for all of your help and encouragement.

 

Hello Richard, I liked the Harvey for the overview. I found some of the math in the Kelsall odd but I'd have to look it up again, seemed like proofreading errors. White's book is alright but not unbiased either..."fish don't have chines..."?!

 

I have "Aero Hydrodynamics" and think it a great book but also think the Marchaj books have far more math than the average sailor wants to sit through. He wants to get his feet wet and that is the best teacher. The human contains an advanced computer with built in sensors even if he doesn't understand the decimals of what the formal language tells of the proceedings. For centuries the wind on the cheek and seat of the oilskins have given feedback he has compensated for with tiller and sheet, with eye on wind, current and wave. This Brown does cover, having skipped the math....Getting your heart, mind and britches united can make for faster progress when you do launch from the arm chair. As the flight instructors say....nothing beats flying time.

 

Cavalier: true. Math is a formally descriptive language, and language, when used is a reflective process that allows for an analytical evaluation of our experiences. Intuition plays a fundamental role as well, as I believe that is what you are talking about. Intuition may lead us to discover things we have not yet found a formal way to describe or quantify, and because of its capacity to do this, it is invaluable - I agree!!! Using both in concert is the height of excitement through living continually just at the bounds of discovery...