Quadrant

[Jim Ledger]

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...

[jsjpd1]

Re: Quadrant

That's going to be a big casting. How much do you think it'll weigh?

[Jim Ledger]

Re: Quadrant

Edsons weighs in at forty pounds but they don't use any Locust in theirs...or Lignum Vitae.

[Ian McColgin]

Re: Quadrant

I'll get you that pic and the measurements Jim. Really. Just been stuck doing stuff in Hyannis the last few days.

[Ian McColgin]

Re: Quadrant

What you've drawn does not look right.

[Ian McColgin]

Re: Quadrant

Anyway, you've got to do the planking before worrying about the rudder.

[Jim Ledger]

Re: Quadrant

What you've drawn does not look right.

It's a work-in-progress, Ian, just the begining of a process, putting something down on paper instead of just kicking it around in my head. It doesn't really matter if it's the final form, in fact it will probably change quite a bit before any building begins. There are a number of complexities that will have to be sorted out in little mock-ups, tooth design mainly but there may be more.

Any input from your boat would be invaluable at this stage, no rush, you understand, as this is a little back burner projectand as such will be done in spare moments.

[DoctorB]

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.

[Matti]

Re: Quadrant

Not the perfect, but reduction gear from electric motor, proper size, or steering gear from truck is common solution, or is it?

Matti

[johnno]

Re: Quadrant

Jim, I'm guessing you might have already seen this?

https://www.facebook.com/pages/Port-Townsend-Foundry-LLC/168103826554894

[andrewpatrol]

Re: Quadrant

Just when we are getting SO bored with his other thread WHAM out comes something even better!

And he hasn't even finished showing us his boom yet!

i can't wait to see this. Wish I had half your capabilities Jim

[Ian McColgin]

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.

Most of the time in most conditions a seven ton catboat with over 500 square feet of sail has a perfectly manageable helm, but if you're sailing off the wind in a Gale (Force 8, winds up to 40 knots) you will feel some very serious rudder feed-back.

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.

[Ian McColgin]

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.

[Duncan Gibbs]

Re: Quadrant

Okay Jim! Once more you have my full attention!

I'll have to hijack that Sibley fellow one day: Your exploits in casting have convinced me of no other avenue available to me.

[PeterSibley]

Re: Quadrant

Lessons available Duncan.