Quadrant

[Jim Ledger]

Re: Quadrant

Johnno, thanks for posting the picture of the quadrant. I have seen it and believe it to be made by the Port Townsend Foundry. It's a quadrant for a smaller catboat. It's useful for study and understanding the general arrangement of the components.

Here's a link to a picture of the steering gear of a twenty-eight foot catboat, more in line with our requirements...

http://www.yachtworld.com/core/listing/photoGallery.jsp??access=Public&currency=USD&units=Feet&boat_id=2476150&back=boatDetail.jsp&boat_id=2476150&noOfPic=20

[Jim Ledger]

Re: Quadrant

I'm not sure what the final part will look like, but if anything like a 4:1 spur gear, look up "involute". I'm not sure you're going to get that in a casting, but maybe a secondary operation?? I don't think you want to hob a custom gear. Any chance of finding a 4:1 anything in a close size and integrating it with the rest of the quadrant? Perhaps you don't need a true involute tooth profile, but whenever I hear someone talking about custom gears, my mind immediately goes to the tooth profile. I'm very interested to hear where you take this.

Thanks, doctor, I have been hoping to get some information on tooth design and would welcome any advice in this department.

From what I see the teeth on the above linked picture appear to be triangular in cross section, thirty degrees off vertical, the gullets filleted and the top points of the teeth rounded off. An easy enough thing to mock up in wood, a straight section with a parallel gear. to see how the action works.

The tolerance would be fairly loose, by which I mean there would be a fair amount of play between the rack and the pinion.

[hokiefan]

Re: Quadrant

Thanks, doctor, I have been hoping to get some information on tooth design and would welcome any advice in this department.

From what I see the teeth on the above linked picture appear to be triangular in cross section, thirty degrees off vertical, the gullets filleted and the top points of the teeth rounded off. An easy enough thing to mock up in wood, a straight section with a parallel gear. to see how the action works.

The tolerance would be fairly loose, by which I mean there would be a fair amount of play between the rack and the pinion.

I will dig in my boxes of books. At one point I had a very good book on mechanism design which included gear teeth. Almost always formed by casting, then machining. I'll see if I can find it.

It was written by a professor who had worked long enough in real life that he told us, "Sometimes the math won't work. You just have to draw something out that looks like it will work, then try it. See what doesn't work and fix it." One of my favorites.

Cheers,

Bobby

[PeterSibley]

Re: Quadrant

Being slack and lazy I'd just run radii out , that will give you the tooth shape, I'd make those up , then do a few calculations about the diameter of the wheel. You need root diameter and pitch diameter , I'll have a look through my old trade school literature if you'd like me too but it's pretty obvious if you draw up a scale cross section..

[Jim Ledger]

Re: Quadrant

Here's my plan.

The quadrant itself won't be a large single casting with a yoke attached. Such a thing would be far beyond my casting capabilities, too big a pour.

What I have in mind is a built-up assembly consisting of four curved laminations of Locust timber.

The first lamination would be the tiller itself, strapped to the top of the rudder in the usual fashion and extending through a hole in the transom. Roughtly three by three at the transom it would extend forward to the quadrant.

The second lamination would be the quadrant itself, bent to the radius determined by its distance from the pintle center. The tiller would tenon into the center of the quadrant arc.

The other two laminations would be a pair of knees to reinforce the joint between the tiller and quadrant arc.

I see no problem being able to build this structure to a suitable degree of strength.

The quadrant teeth would by cast bronze, made from of one flat-back pattern of a quarter of the arc, thus four required. These would be trimmed and bolted to the top of the Locust lamination forming a continuous run of teeth.

The pinion would be cast bronze...not a difficult casting once the design is right and the pattern made. As it's beveled the draft is built in. It could be cast in the drag as one piece with a core for the shaft.

Beyond a little cleaning up the bronze parts would require no machining other than boring out the cored hole to fit the steering shaft...and a keyway.

The steering shaft will be a piece of one inch propeller shaft, already on hand. In fact, all the materials are already on hand.

The thing to keep in mind is that this piece of gear is more akin to windmill technology than anything from the Twentieth Century, robust, slow moving, overbuilt and fairly loose.

[Ian McColgin]

Re: Quadrant

I'll try to get detailed shots of the underside of the rack and pinion. There are some details that are really important and might be hard to make work if the bulk of the quadrent is wood.

[Jim Ledger]

Re: Quadrant

No, a truck steering is not good in any sail boat and is spectacularly unsuited to a catboat. Look on Ted Brewer's site for the Chappaqueddic 25. You'll see that it's a massive barn door outboard rudder with a through-transom tiller leading to whatever. The most powerful and fool proof system is a rack and pinion such as Marmalade's, which will be pictured here, disassembled, in the next week or so. Cables to the tiller would not work since the tiller is long enough that the geometry won't work unless you make an arc structure to hold the cables out and tight. The strain on the cables and on the pulleys would be massive, like a good thousand pounds on the blocks since they take double the strain. It can be done, but a cast rack and pinion is more readily made strong enough.

Ted Brewers plans for the Chappaquidick did show details for cable steering. However, in a phone conversation he told me that a rack and pinion quadrant was the way to go for a more direct, responsive action. The cable steering had a drum on the wheel shaft around which the cable wound, various pulleys to direct the cable, and a wooden quadrant on the tiller end to allow the cable to have a direct pull through the steering arc.

If you wanted to tiller steer this boat, you'd want the tiller running to the front of the cockpit, giving eight feet or so of leverage, and even at that you'd want to have provison for relieving tackles. It was a much larger boat but there is no thrill quite like being one of three over two hundred pound men on a tiller when it took us all flying right to the lee rail. A few broken ribs and a collar bone later we got the tackle set up.

As the catboat design developed tiller steering became a problem in larger boats. The increasing beam of the boat made the tiller too distand for comfortable steering from the side benches. As rudder size increased the forces generated required a lengthy tiller which meant the entire cockpit had to be kept clear for steering, along with frequent changes of position for the helmsman and passengers.



Here's a picture from the files showing the rudder hung in position. The blue tape on the transom delineates the aperture for the tiller. the cut-out for the tiller can be seen on the top of the rudder, the top surface of the tiller continuing the curve of the rudder. The tiller will continue about two feet inboard of the transom, terminating in the quadrant.

[Jim Ledger]

Re: Quadrant

I'll try to get detailed shots of the underside of the rack and pinion. There are some details that are really important and might be hard to make work if the bulk of the quadrent is wood.

I understand that the quadrant is restrained from underneath in the area of the pinion, to keep the teeth meshing properly, if this is a concern.

Size-wise, I think some extra bulk could be contained within the wheelbox.

I'm thinking of running the steering shaft back to the transom, over the quadrant, to a pillow block fastened to the transom itself. The other bearing would be incorporated in the front of the wheelbox.

There is a height issue.The tiller, running in a natural line into the boat will place the wheel too low in the cockpit.

[Ian McColgin]

Re: Quadrant

Comes out the right height on Marmalade. We'll get lots of pix as it goes back together.

By the way, before taking what's turning into a five day break from Marmalade's Spring Spa, I found a nice bit of angelique where a nearby knot made for a beautiful grain sweep so the blank is cut out and ready for shaping.

[Mrleft8]

Re: Quadrant

I'll see if I have one kicking around the barn..... I know I had one at some point....

[Jim Ledger]

Re: Quadrant

If you could measure the height of the wheel hub it would be a great help. Ian.

Good luck with your Angelique tiller...keep the stones handy.

[Jim Ledger]

Re: Quadrant

I'll see if I have one kicking around the barn..... I know I had one at some point....

Good luck wit dat.

[kc8pql]

Re: Quadrant

johnno, very nice. I think when I take Marmalade's pic you'll see it's even bigger but I'll bet they have a pattern or can make it easily.

I have no doubt PTF could make one. I also have no doubt that it would cost as much as the Edson. Don't get me wrong. They do beautiful work. They cast Alaya's rudder fittings and mast band for me, but saving money doesn't come to mind when I think of them.

[Paul Pless]

Re: Quadrant

Lets make one instead.

can't wait to see this

[BBSebens]

Re: Quadrant

By far the most difficult-to-find item needed for my catboat build is the steering quadrant. Edson has one in it's catalog, a custom cast bronze item costing in excess of two thousand dollars. It consists of a yoke that bolts to the tiller, the quadrant itself, which is a pie-shaped bronze casting with teeth on the radiused rim, and a shaft for the ships wheel with a pinion gear that engages the quadrant teeth.

Lets make one instead.

The radius, measured off the pintle center, will be twenty-four inches.

There will be forty teeth on the edge of the quadrant.

The pinion gear will have ten teeth, giving the wheel four turns from stop to stop.

It's a start...

Jim, you are completely mad.

This should be pretty epic.