MacGregorSailors.com

Hi Gents,

I need to measure the typical angle the Mast rotates when the boom is over the stanchions (next to the winches) I have measured it to be around 20 degrees but then I realised that the mast does it's "airplane wing thing" too and turns a few more degrees than the boom. I didn't have time to raise the mast today and measure it properly but my rouge measurements came out at 15 degrees. Making the total mast rotation 35 degrees.

Just wondering if anyone has done this before or actually knows the mast rotation angle at this point?

Thanks for your help gents.
Neo

I have no idea and my boat is on the hard. But it does rotate a lot MORE than the boom angle. Mine swings way over. Gravity seems to play a big role.

Why do you need to know this? Sounds like you are moding something.

--Russ

Hi Russs,

Here's my post from the thread "Finally, a wind instrument that will work with a Mac!" (Page 9) ... viewtopic.php?f=9&t=24758&start=120

Neo wrote:I'm working on other solutions now and looking for thoughts feedback.
Firstly I want to display things on my iPad using applications like Wifi MID - https://itunes.apple.com/cy/app/mid-wif ... 95285?mt=8
I found a reasonable cost NEMA to Wifi adaptor made buy a small company and I got chatting to the guy that designs and builds them. He told me he had found a very good generic wind instrument and was working on an adaptor device that would output NEMA. I got very excited about having a low cost anemometer display on an iPad but then remembered the directional issue with anything mounted on a rotating Mast
So I got thinking that on an when sailing upwind, the boom just swings over to where the stanchions are (can't go much more because the Mainsheet hits the Lifelines) and the Mast follows suit. So for the most part the swing angels are wrougly known (ie. 20deg - 0deg - 20deg) and for cruising does the exact angle even matter?... So I requested if I could have a couple of offsets put into the adaptor box. Here's what he came back with ...
Definitely food for thought... I had a rotating mast on my cat so I know exactly what you mean. It requires software modification as well as hardware.
I could put 2 little tilt sensors in, one tilted to starboard and the other to port, each by say 10 degrees. The sensors are simply a binary (on or off) mercury switch of the type you'd find in a bilge pump float switch. The device would be mounted abeam and could be positioned anywhere out of the weather. When the boat is at less than 10 degrees heel then both sensors would be open circuit. When the boat heels more than 10 degrees either way then the device would detect the direction of heel apply the 20 degree offset in the appropriate direction. That would be the simplest and cheapest solution. I don't think there's any need to use an accelerometer that can sense precise heel angle. There would be no way to detect the exact angle of mast rotation in any case, and as you say it's just for cruising purposes so you don't want to invest huge dollars.

The 10 degrees of heel is arbitrary and could be adjusted by physically changing the angle of tilt of the sensors on the board. The mast rotation offset could be set initially to 20 degrees. The device already has 2 push-buttons (up and down) to tune out any misalignment of the installation. There is a reset push-button and a data LED as well, so I could incorporate a system of holding the reset button for a certain number of seconds to enter either alignment mode or rotation offset adjustment mode. The modes would be indicated by the data LED either blinking slowly or rapidly.

All this sounds great to me and I have already placed my order for the Wind Instrument he done testing with .... Does anyone else like the sound of this concept?

All the best.
Neo

Ahh.. I see.

As I recall the mast can only rotate a fixed amount before the rigging stops it. Again, boat is in storage with mast down so I can't check.

--Russ

Ok, looks like this idea is busted!! .... After sailing in high winds I realised that the boom angle is somewhat fixed/limited but the Mast rotation does vary a lot (upto 45 degrees) depending on wind angle.... having 2 simple angle offsets simply won't work so it's back to the drawing board

You could mount an analog radial position sensor on the leading edge of the mast at the level of the shroud connector, where the curved spreader holder piece is mounted that doesn’t turn.(think of attaching a little pointer to the front of the mast that passes over a curved sensor that can tell where the pointer is)
For simplicity, you could test it with a wiper style variable resistor (rheostat) just like what is used for a car fuel tank level sensor. That’s how they work...

(Thinking...)
Locate the center point (zero) where the mast is straight ahead and measure resistance there, measure the resistance at one full angle, measure the resistance at the other angle, and map out the resistance curve vs angle (sensitivity or slope). The programmers could use this signal to determine the needed offset in the program to correct the wind angle for any mast angle. It would be called a split range signal. Adds to the signal when goIng one way from center, subtracts when going the other way.

(Thinking more now...)
There are actually rotary position sensors for this prupose that use a tiny cable to spin the shaft on a drum as the cable is pulled one way or the other. The cable makes several wraps around a drum in the middle of the cable, the two ends are free. Pull the cable one way, the drum turns one way, pull it the other, it spins the other way. Internally, it varies linearly with rotation. You mount this device on the fixed spreader holder, shaft vertical, and pin the two ends to the mast. As the mast turns, it pulls the cable one way or the other. Same setup - find center, span in each direction, and set up a split range for the programming so it knows how much to add or subtract.

Search something like “analog rotary position sensors for industrial automation”.

Thanks vizwhiz... These are great ideas but the guy making the "Anemometer to NEMA" convertor was not keen to do too much more development and he wanted a solution he could promote to any yacht with a rotating mast, not just a Mac .... Without his support I don't have the resources or knowledge to knock up an electronic solution that works with his convertor

I am however investigating a mechanical solution .... It's just a concept at the moment so will speak of this when after I've conducted a beta test ... wish me luck

Okay, I found some stuff that I’m sure would work pretty well. One question - what wind indicator units are you using? Or are you plugging this into a multipurpose autopilot / trip computer (Raymarine, Garnin, etc.)? What I’m wanting to check into is what auxiliary inputs these devices have available, and what setting/parameter options could be used to apply said input as an offset to the wind angle calculated by the computer... Also will need to see what power source/supply they can offer on the aux input.
This can be done...

Hi Vizwhiz,

I'm using the Davis Weather 6410 Anemometer with a custom made Davis to NEMA adaptor. That's then connected to a NEMA to Wifi Bridge and the readings are displayed on an iPad app "EDO Instruments" or "MID Wifi". https://www.ebay.com.au/itm/NMEA-to-WiF ... :rk:4:pf:0
The Davis to NEMA adaptor currently has two built-in tilt switched (which I'm going to remove) to + or - 30 degrees when heeling.

It's a neat solution. If only I could get it to work at the top of the Mast.