The Articulated Sailboat

Yes, I am-and looking forward to your updates...

 

Similar things have been done and worked well. A lot of the speed sailing boats use various tricks to prevent overturning by aligning the under water and above water forces. Sail rocket is one example. Your Bruce foils will have to get further apart as the mast gets taller, but that's a question of design and compromise. It might also tend to tip over if it gets hit by a gust before it starts moving. The foils get their lift with motion - no motion - no lift. Small amas above the foils might make it a little more forgiving.

 

Thanks for the input Peter.

I don't want the Bruce foils to get too far apart as the whole thing will become ungainly and too sensitive to heeling angle. In a tight turn the inner foil may lose lift. The objective is to keep the force vectors acting on the foil(s) and sail close where they meet the weight/buoyancy vectors at the centerline of the boat, since the area of the triangle translates into heeling moment.

In past experiments I have found that inclining the sail to the vertical has the same effect as inclining the foils. It is actually possible to overcompensate so the boats heels into the wind - a strange sensation. The lateen sail provides a wind force vector that is angled downwards where it crosses the centerline and it should, I hope allow me to keep the foils closer to the hull.

However, you are incorrect regarding the need for forward motion: when a gust hits the boat almost immediately moves to leeward and the foils generate a moment countering the heeling force from that instant. Previous rigs using Bruce foils heeled a few degrees when hit by a beam gust then quickly righted before the boat acquired forward motion. Of course in this case the counteracting moment was not provided by lift as the foils are completely stalled, but it did the job!

I plan to have small amas above the foils as you suggest. These increase the static stability of the boat and help counteract all that weight high above the W/L.

 

Progress is slow on the demo build as I am having to fabricate a lot of metal parts, not my favorite activity nor what I am best at. However I expect to have a pic or 2 soon to illustrate where this is all going.

In the meantime I have rethought the potential "front wheel steering" problem as addressed in this and several subsequent posts:

Form the post referenced in the quote" ... if you get into irons then it is almost no chance of backing out as you can with a stern rudder ..."

I have realised that this problem is very unlikely to arise with the proposed rig. It is not merely a front-mounted rudder that is turned to initiate a change of tack, it is the pair of hydrofoils and also the raked mast. So the sail will generate power on the new tack almost immediately.

This of course was the design objective of the proposed innovation from the beginning, which I lost sight of.

 

At last, some images

I am getting through the metal bashing part. The tubing is 1" (25 mm) dia 6061 T6 (or similar) Aluminum, 0,058" (1.4 mm) wall thickness which I think is adequate for this lightly loaded structure; I have smaller diameters which fit snugly together allowing me to make the mast telescopic and the other long parts modular so they will fit in my van.

The first pic shows the basic Tee-shaped structure: it is rotated slightly to port to distinguish the rotating assembly from the fixed plywood deck. The beam for the starboard ama and Bruce foil is sticking out to the left in the photo and the bowsprit, which will carry the raked mast, is on the right. The port ama beam has not been made yet, the stub that it will mount on can be seen better if you zoom in.

I would have preferred to use bent tubing for the crosspiece but I haven't found anyone local who can do it; the auto exhaust guy can't bend tubing this small, and my buddy with the machine shop has closed down and sold off all his equipment due to the economy. So for now I had to cut and fabricate as best I could.

The ama beams slope down at 15 deg to bring the amas closer to water level; the bowsprit is (more or less) horizontal although it seems tipped up in the photo.

The second pic shows the bearing structure; the ply wood plate carries a 6" (150 mm) lazy susan bearing, it is upside-down and normally rests on the deck. The smaller (3", 75mm) bearing on the right goes under the deck with the smaller ply backing plate and the whole thing is held together by a 1/4" (6 mm) bolt with the deck sandwiched between the bearings. This keeps the bearings under pressure since they are not designed to withstand load in tension.

The bearing arrangement may seem a bit overdone considering how little moment is required to flip a a kayak, but the main load will occur if/when I hit a submerged object. When the ice melts various tree parts drift down the river into the lake and wander around for the first month or so of Spring until they fetch up on a bank.

This project shares parts with the http://www.boatdesign.net/forums/sailboats/sailing-directly-upwind-29981-6.html thread; for that project the rotating part constitutes the "Sailing Machine" and will be mounted on the Link Beam shown in the last post of that thread. For that application the bearings on the deck will be more heavily loaded. We will see how they stand up!

 

Argghhhh...

It's starting to look like something from a 1950's horror movie.

"As the handsome, gun-toting hero discusses recent reports of awful happenings with his old professor in the isolated old house, his clueless girlfrined stretches out in sunglasses and bikini on the lawn outside. Half-hidden in the shadows, the ancient creature stirs, green and ghastly, dripping slime and ichor ..."

"Cut!. I don't see slime and ichor people! " the director stormed, hurling the screenplay across the set.

Hmm, I'm not too good at novel writing either. Better work on my boat-building skills a bit more.

 

I'm not sure if this is entirely relevant to this thread. I built a model proa a few years ago which had an articulated cross beam. The sail was fixed 90 degrees to the cross beam and the cross beam could be moved +- 40 degrees to the main hull to trim the sail. Also, the ama could be rotated independently a further +- five degrees relative to the main hull, and this was used for steering. There were no fins or keels. Lateral resistance was provided by deep V hulls. It worked quite nicely, but I think the steering would have worked better if I had provided a high aspect fin or centreboard on each hull. A photo and a short quicktime movie are attached.

 

I have just found this thread. Interested in the results.

 

Mal: interseting concept! It deserves its own thread.

Magwas: I will report results, good or bad. I hope the performance is good, as the whole thing is starting to look more complicated and heavy than I had hoped.