Newbie question: would this trimaran folding system work? (parallel hinge)

Hello everyone,

I'm new to boat building and just signed up to this forum to ask my newbie question. I've been reading quite a lot about folding trimarans (also on this forum) and right now I'd like to try and build a W17. There's just one thing: I really need the amas to be foldable on the water, so the boat should still be stable enough while in the folded mode (for paddling or a small motor, with the sails down of course). Here in Berlin there's really only little space to get into the water. Also, it would be really good if the boat can stay in a berth in folded mode during the summer, so the amas should not be rotated too much.

Today while day-dreaming at work I've figured out the parallel hinge system as seen in the attached pdf. The unique features it offers are:

• Foldable while on water
• Amas are not rotated, the top side stays at the top
  
• Amas are lowered a little bit for increased stability (can be adjusted by the length of the inner and outer board pairs)

Let me explain the system also in words. The pink circles resemble rotatable joints. The blue and green rectangles represent pairs of boards, not tubes, which form the akas. These boards should be as broad as the original akas. The purple part on top is a connector which provides the parallel faces for the parallel hinges.

The blue boards are forming one parallel hinge, while the green boards are forming another one. You can imagine the boards as the long sides of two parallelograms, while the short sides are formed by the ama / the main hull and the purple part. In this way, the ama cannot rotate while moving to and from the main hull.

In the extended state (top sketch), the blue boards are on top of each other as well as the green boards. This is a natural end stop, the akas cannot unfold any further. In the folded state (bottom sketch), the outer bottom and inner bottom board are touching; this is a natural end stop, the akas cannot fold any more.

A (small) problem is, in both states, chafing as to be prevented. I imagine rubber parts would help here.

Another problem I see is that the top boards may act as levers to lever out the joints. Special caution would need to be taken here.

A third problem: The ama on the windward side will not stay extended if the pairs of blue and green boards are not fixed together by a locking system. This would have to take a lot of force to keep the system from folding.

Room for improvement: I think it should be possible to have the amas rotate by a defined small angle by adjusting the distance of the joints on top of the ama and tweaking the relative length of the blue boards. In this way the top side of the amas could be rotated slightly by a fixed angle to be perfectly parallel to the water.

I'm looking forward to your comments! Has anyone employed a similar system? It's quite simple and for sure I'm not the first one to make it up - there must be reasons why it won't work...

 

For a more simple folder check out the Brown/Marples Seaclipper designs. There is a 16 and 20, among others.

 

How will you lock the joints?
That many joints will have a lot of freeplay.
Getting the akas to hold the ama in one place will take a lots of weight and mechanism, and will still be floppy.
As illustrated, the akas will flex a lot, compare the depth of each element to the depth of the original mechanism. Perhaps that is just the illustration.

Why are you so insistent about keeping the ama vertical?
The Ferrier system is well documented and used for 30+ years.
If it ain't broke don't fix it!!!

This was brought up some years ago, either here or on Woodenboat forum. You might search for it. Nothing was ever published about it being actually designed.

 

It's true, a lot of joints potentially mean a lot of wobbling. Self-made joints wouldn't be enough, commercial joints would have to be used, which can get quite expensive given the number of joints.

I want to keep the amas vertical because I would worry about water entering through the inspection hatches while berthing for months on end.

Another problem I realized: the joints of every axis of rotation (at least four joints per axis) would have to be aligned perfectly for both akas, otherwise the folding mechanism won't work. This is a very difficult task! In my opinion it is too difficult for the beginning builder, I think I wouldn't be able to do it as I don't have any boat building experience.

 

I use to work for an aircraft manufacturer.
We had significant trouble keeping 3 hinges in line, and the tolerance or free play of the joints was a continuing problem.
This was on very expensive structure.

You can make such a structure fold even with some alighment problems of the joints, if you have enough power.
But I don't really understand how you will force this to fold - what would be the mechanism.

I think you could easier fix sealing the ports.

 

The middle of he beam would be the worst place to have a join. Rapido have a much more sound looking solution. Rapido 40 - Rapido Trimarans https://rapidotrimarans.com/rapido-40

 

If that fold system would work without other elements it would be interesting.
Is there a better description on how the ama stays upright, and how the aka ends up taking that path?

Funny, the original W17 beam has a joint in the middle and it seems to work.
Same as the old Cross 18.

 

The Farrier system can be replicated fairly easily - see pictures of the mock-up that should certainly be done before cutting and fitting the real thing. The key is getting the angles and fixing points right - the mockup will prove that.

Sure this does not answer your wish to have the amas remain vertical plane, but it does work. It would still be working if some helpful soul has not stolen everything moveable, then torched the boat

 

Hi Matthias S
Just got a heads up from a buddy to look at this. As he said, it's hard for me to understand why you would not first ask the designer if he/she has a solution. Surely, ALL designers deserve that respect and opportunity IMHO.

Anyway, I would like to help solve your issue as the design you suggest is definitely not one I would support, being FAR too full of joints and connections that are inherently weak, as 'Mr UpChurch' has wisely pointed out.
I designed a horizontal swing-arm system for a W32 design about 3 years ago and at least 3 W17 builders (Norway being your nearest) and the prototype W19 builder are all now using this design, adjusted down to size. It's inevitably somewhat like the Dragonfly design but it is designed to use the existing main beams of the W17 without structural change and the outer curved beams will look just as good, but are revised to suit the required circular pad interface. While the Dragonfly system is of S/S and uses 1 pivot bolt, my system can use simpler S/S or Fiberglass link plates but then has double bolt connections to add more security. Initially at least, it is being recommended that the forward beam also has a waterstay (as does the Dragonfly for all beams) but in my case, this is as a back-up as the system has been designed to be as strong as the present one, which has proven itself after 2000+ miles over 8 years of regular use on the prototype and now, many more miles from others that followed.

As far as where joints should be. They can in fact be just about anywhere as long as the loads are calculated correctly for that location and being in the middle of what is effectively a cantilevered beam, is certainly not the worst place.
Hope this helps but please write me if you want more clarification. Once you purchase plans, then you would get access to the SwingArm system anyway. Glad I caught this in time.
Best to all and please .... stay Covid free.
Mike
www.smalltridesign.net

 

fyi

bad link above

Small Trimaran Design | Home Page https://smalltridesign.com/

 

Oh geez ...thanks fg ... must be getting tired with age ... dot net is my email server.
Just noticed the Aussie mock-up of the Farrier system and his comment. Are you serious that someone actually stole the boat ! That must be the most discouraging conclusion to hours of work that I've heard ...my heart aches for anyone with that sort of luck.
But the mock-up does serve to show a weakness of the system .. the relative lowness to the water of all the framework and protuberances that makes boats so fitted, wetter than they need/should be. Scarabs are the same and both systems take considerable cost, time-to-build and set-up to work properly. It's no wonder that Ian sold the system as a working set, but many years ago it was quoted at $6000 when I once inquired. Once set up, the Farrier original does work well though if the added spray doesn't bother you. The Pros and Cons are covered in an article on my website if needed. Cheers

 

Hello, I am that very Norwegian having a W17 built with Waters swing arm system; scheduled to be ready some time in 2021. My W17 will have the carbon rotating mast and racing rig.