tag:blogger.com,1999:blog-7834826019588534175.post3665265904613911923..comments2023-09-20T06:10:29.485-04:00Comments on The Marine Installer's Rant: The Compass ConumdrumBill Bishop - Parmainhttp://www.blogger.com/profile/11554223870035485145noreply@blogger.comBlogger9125tag:blogger.com,1999:blog-7834826019588534175.post-85858965977056423832015-02-24T09:29:29.455-05:002015-02-24T09:29:29.455-05:00Anon, thanks. The nickname "Kelvin's Ball...Anon, thanks. The nickname "Kelvin's Balls" came about because Lord Kelvin creator of the kelvin temperature scale and many other things is also the inventor of the compass compensation system. Lord Kelvins Balls first appeared on binnacles in 1880.Bill Bishop - Parmainhttps://www.blogger.com/profile/11554223870035485145noreply@blogger.comtag:blogger.com,1999:blog-7834826019588534175.post-13804635149974478852015-02-19T19:22:59.911-05:002015-02-19T19:22:59.911-05:00"Kelvin balls" is also new to me, j call..."Kelvin balls" is also new to me, j call them soft iron compensators only needed on steel boats. With n/s e/w standard compensators for permanent magnetism you can nearly always reduce deviation to a few degrees on a wooden or plastic boat. Joachim fr Gothenburg SwedenAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-7834826019588534175.post-32319002208148297662013-09-05T10:21:42.622-04:002013-09-05T10:21:42.622-04:00I had a customer who purchaced a new to him boat t...I had a customer who purchaced a new to him boat that wanted to get me to set up the autopilot. I checked out the original install and all seemed well but the heading was out about 40 degrees.<br /><br />I took it out and did the circles from hell and achieved deviation just on the edge of acceptable. I fine tuned the heading to align with the compass and GPS course and the AP was working acceptably.<br /><br />When I got back to his slip, I was just about finished and was just packing up my tools when I did one last check of the system. The heading was now about 40 degrees out in the opposite direction than originally. I took the boat out again and did more circles and achieved a deviation that was a little better than the first time. Once agin I aligned the compass, heading and GPS course and the autopilot was working well.<br /><br />I got back to the dock and just before I left, I did one more check. The heading was out 40 degrees again. While scratching my head, wondering what was going on, the cutomer noticed that whenever I went forward into the V-berth, the heading would change.<br /><br />Then I finally found the problem. The boat manufacturer had used strong rare-earth magnets to hold the V-berth doors open and closed. The magnets were imbedded in the doors and every time they opened or closed, the fluxgate heading would change about 40 degrees.<br /><br />My first thought was to reposition the heading sensor away from the influence of the magnets in the doors but no matter where I could mount it there were other magnetic influences that would be just as bad.<br /><br />I gave the customer 2 options. I could butcher up his nice teak laminated doors to get the magnets out or set up his AP with the doors either open or closed but whichever way he chose, the heading would only work that way. He chose to have me set it up with the doors closed as that was the way he normally ran the boat.cr cruisernoreply@blogger.comtag:blogger.com,1999:blog-7834826019588534175.post-33386320782457248372013-09-04T09:27:40.652-04:002013-09-04T09:27:40.652-04:00Tom, you win the battle of the compasses. It is a ...Tom, you win the battle of the compasses. It is a very impressive piece of gear, and after reading the specs I now believe it provides close to perfect heading data under all circumstances. The $3600 is an ouch, but never the less it appears to be worth it given the the quality of data it's sending. It's an IMO approved heading device to boot. Thanks for pointing it out.Bill Bishop - Parmainhttps://www.blogger.com/profile/11554223870035485145noreply@blogger.comtag:blogger.com,1999:blog-7834826019588534175.post-38970995882007015772013-09-04T09:20:53.683-04:002013-09-04T09:20:53.683-04:00Rhys, the Kelvin part of the balls is Lord Kelvin,...Rhys, the Kelvin part of the balls is Lord Kelvin, aka Sir William Thompson. I stumbled upon an interesting history of the compass compilation of his written between 1874 and 1879. By 1880 his balls were so big he patented them. Here is the link<br /><br />http://zapatopi.net/kelvin/papers/terrestrial_magnetism_and_the_mariners_compass.htmlBill Bishop - Parmainhttps://www.blogger.com/profile/11554223870035485145noreply@blogger.comtag:blogger.com,1999:blog-7834826019588534175.post-15356163233013938162013-09-04T08:59:28.926-04:002013-09-04T08:59:28.926-04:00TJ, I agree completely. There is a lot of Shintois...TJ, I agree completely. There is a lot of Shintoism out there which I define as worshiping the way your ancestors did navigation,. BTW I really enjoyed reading your OTR blog. I have my own equivalent, but I haven't acquired a set of Kelvin's Balls big enough to attach my name to it... yet. Bill Bishop - Parmainhttps://www.blogger.com/profile/11554223870035485145noreply@blogger.comtag:blogger.com,1999:blog-7834826019588534175.post-49852676658467108402013-09-03T20:38:36.670-04:002013-09-03T20:38:36.670-04:00I know it's cheating but I got so upset at com...I know it's cheating but I got so upset at compasses and wandering autopilot courses a few years ago that I threw money at a Furuno SC-50 GPS compass. Best money I've ever spent. Now when the autopilot goes to a new course, it gets there precisely and without weaving. When you want to swing your magnetic "backup" compass, you can do it even in harbor as you swing around a mooring. It's a miracle!Tom Chttps://www.blogger.com/profile/16788214998768526657noreply@blogger.comtag:blogger.com,1999:blog-7834826019588534175.post-30867525501485300052013-09-02T13:14:48.253-04:002013-09-02T13:14:48.253-04:00Having a steel boat with a Ritchie Globemaster ins...Having a steel boat with a Ritchie Globemaster inside the steel-sided pilothouse, I'm used to playing with my amusingly named "compensator balls" (Kelvin's balls is new to me).<br /><br />I have made a rough deviation chart by going on a known bearing to a landmark and then going back to Start and doing a 90 degree turn and repeating until I can see if I have serious compass deviation. Currently, I haven't, but if I put the wrong gadget too close to that big compass, or forget leaving a visegrip behind it, I'm in trouble.<br /><br />I run a fluxgate and a plotter and look at the Ritchie, minus the local variation. If I get within five degrees, I feel I'm doing well, because I can't hand-steer much better than that.Rhyshttps://www.blogger.com/profile/00598445145507204424noreply@blogger.comtag:blogger.com,1999:blog-7834826019588534175.post-85414641266377108872013-09-02T12:22:40.170-04:002013-09-02T12:22:40.170-04:00Thanks. I am a recently retired professional airp...Thanks. I am a recently retired professional airplane driver now live aboard sailor. Sailor lore seems to be that the GPS system is a tool o de Debel that will crash one's boat into land at the first opportunity; better to trust a paper chart and a compass. Unless one in an absolute expert in all things compass, interpreting paper charts, and visualizing a real live picture in ones'mind of what those two things are trying to tell you, beliving a compass fix is better than a GPS fix is a complete fantasy. A "good" compass fix will set your position within a couple of hundred feet at best, more like a couple of hundred yards. The GPS will set your position within a couple of meters. A compass and paper chart is what you fall back on when everything else goes bad. A paper chart and the most basic of hand held GPSs to give a lat / long vix would be better.TJhttps://www.blogger.com/profile/03459069175481821975noreply@blogger.com