Tri with staggered beams ama slide in system...

Jetboy, how did you align the tubes in the hull so that they were perfectly parallel? It seems that those sliding systems that use four hull tubes would be that much more tricky to get aligned.

 

if it were me and i was building that kinda system on boat, I would weld the two tubes together, that way one unit lined up lines up both. Lay them flat on table clamped square and tig away!


Barry

 

I first cut the holes in my hull structure. The boat hull is significantly strengthened in those two areas with "ring frames" of additional fiberglass and bulhead to take the loading. So at those locations I cut the holes approximately 1/2 inch larger than necessary to physically fit the tube. Then I used shims around the sides to adjust the tubes to the proper position.

Getting the centerline is easy. I used a stringline down the hull matched to marks on the tubes. Then I did a lot of measurements. Both using a level front to back and corner to corner as well as tape measure front to back and corner to corner. It probably took an hour of fine tuning before I was happy enough to mix up some fairing compound to fix their locations.

Also I built the cabin top separate, so when I was putting the tubes in, I didn't have the benches or the cabin top in place. I had nice access to everything.

I think there are a few other good ways of doing it as well. One would be to build a jig. If i were doing multiple boats, I'd weld up a steel alignment jig on a welding table and ensure it was flat and true then clamp the tubes to it once they were put in place. On a larger more expensive boat this might aslo be a good option. It would only cost maybe $50 -100 in steel plus a few hours to make a nice, well braced, assembly jig. But for one time assembly of my little boat I just stuck them in and started measuring and adjusting. We'll see how final assembly works. Visually and measurement wise it's pretty close.

Also it doesn't have to be absolutely perfect. There's some play in the sleeve fit at both ends. And the floats just aren't all that rigid. They will flex enough to make up for small errors.

The biggest issue I have found so far is that the push/pull tends to bind because either the front or rear slides a bit further than the other. Making them slide out uniformly without any binding may turn out to be quite difficult in practice. The one solution I have - is not light weight - but may be necessary for practical use, is to add an additional extender mechanism. Imagine a very long set of these that have a cross tube linking them in the center so that they move uniformly. That would solve the issue, and be useful for making a tension system for the trampoline that is basically automatic. Once over center they would lock in place. I'll see as it goes whether this is necessary or not.

 

another thing that o have no clue how you could realistically engineer in would be some kinda pivot-able single point mount on float. That way pull one out it wouldnt bind the other, and when fully out lack of extra travel would not alow it to pivot anymore. So imagine a single stud mounted on float that a beam hole woud drop on, but when tight still moves a tad. Like a non Spherical rod end.

Barry

 

I think the real key to all of this is loose tolerances and then tighten everything up with water stays, rig tension, and the trampoline. The structure of those three can go a long way toward making a sloppy set of joints firm when you want them to be.

I'd like to replace mine with a farrier style folding at some point, but this was something I could build in a day for a few hundred dollars, rather than weeks. This project is getting old and I want to sail it while I design/manufacture the folding beams. I think I'll just build them to weld or epoxy into the tubes that I'll cut flush with the hull side. That should be pretty easy down the road.

 

My understanding is that Kurt Hughes uses pulleys and cables to slide the crossbeams in and out. I would think that being able to control each slider independently would reduce binding. Also, being able to tension the crossbeams outwards allows the whole setup to tighten against the water stays.

 

well not sure about the pulling them in part but, another way might be to put a channel in front edge of tube, then have lines attached to inner parts of beam that run in channel and out of boat. Now with a pulley in middle crank on lines to pull them out at same time. Solves the going out part while your on the boat floating it at least.

Barry

 

The way mine is set up with a single sleeve tube, it cannot be telescoped on the water - or at least not without some tricky gymnastics. The tubes are inserted while on the trailer and then extended and rigged before dropping in the water. As a trailer sailboat it's no big deal. If I were trying to fit in a slip I think twin sliding mechanisms are necessary.

 

The drawing shows a single beam running right through the centre hull bow and stern. The left view on the drawing is the rear beam, the right view the front beam.

'Mono Slip' has two pairs of beams that slide past each other like the Astus. I think the name refers to being able to get a tri narrow enough to fit in a standard keel boat marina berth. Seems to be an option on any of Kurts tube beam boats, although not shown on all of them on his website.

 

I've long been intrigued by the Mono Slip concept, but while such an idea seems practical on smaller narrow beam boats like the Astus, I can't imagine how one would engineer such a system to be reliable on a large boat that was kept in the water permanently. Anyone aware of a larger example, say bigger than 30' loa, built with this system?

 

It seems an ideal setup for small boats under 30, heck maybe even 25ish range tops, where your just as inclined to de mount as you are to pull them in for many reasons. For a larger boat more inclined to be constantly slipped or slipped often in varying ports I think the lift setups make more sense. Yeah there more expensive, but inline with more expensive boat and a drop in bucket compared to expensive in building a bigger boat. And big boat your just not dismantling on black or for trailer so no need for slide off.


Barry

 

Being round tubes, do you not get more than expected lift of the float tip, round tubes tend to allow the tubes to revolve inside the other tube until the inner tube deforms enough ( due to the other end being held at the float ) to jam any further movement. I think most of the sliders use square or oblong sections just to prevent this happening. ?

 

Kurt Hughes has a 38' version







http://www.multihulldesigns.com/designs_stock/d38tri.html

 

Ah, thanks, I didn't think of we're looking at a bow and stern view in the drawing, that explains the little left vs right beam height difference we see there . .

Thanks, just like we also see in Kurt's 38' Demountable Tri drawings as just posted above this post by ImaginaryNumber...

Yes, that looks to be right as Tom gave the same explanation in post #11.

Thanks Jamez, you gave a lot of good info

P.S.

Just like the 23' Daysailor on top of this post, the 38' Demountable Tri drawings also shows the front beam a little higher as the rear beam...

Note also the off center sideways angled daggerboard, to save interior space I think . . :idea:

 

Question on this discussion. Could a sliding beam mechanism be used to help right a capsized trimaran? I'm not sure it would be possible to release the locking mechanism on most to allow it to collapse - nor to do it safely in a capsized situation, but what could we design to allow this?