Plastimo Compass Compensator

[Joe_Cole]

Looking through the Plastimo catalogue I see that they supply a compensator to correct for deviation on their compasses. It looks as if it needs simple screw adjustments for East/West and North/South correction. Depending on the compass it has a list price of £5 to £8.

Has anyone any experience of using these on a DIY basis? As I have up to 17 degrees deviation on my compass I'm tempted to say that I couldn't make it any worse!

Joe

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[isandell]

I recently replaced my Plastimo Contest. The old one had compensator but I never felt the need to touch it. The new one did not have compensator and I had to cut the case of the new compass a bit to get the old compensator to fit.

The two screws (N-S and E-W) are quite sensitive, a fraction of a turn to compensate for a few degs. so maybe 17 deg is possible but it seems a lot and I would try to reduce that before using a compensator (but I expect that you have tried already).

I cant remember whether the instruction give any guidance on max allowance.

Ian

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[john_morris_uk]

The compensator is for exactly the circumstances you describe. Assuming you can't move any of the magnetic fields/ferrous metals that are giving you the deviation, then have a go.

You will need a handbearing compass and some space to turn the boat in a reasonably calm water with some objects a couple of miles away on the N/S and E/W (approximately) bearings.

If you want the full details, it has been described in several magazine articles. If you haven't got access to them, ask and I (or someone else I have no doubt) will try and write a concise explanation of how to go about it.

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[Joe_Cole]

Thanks guys. I'll get one and have a go. Something useful to do when there's no wind!

Joe

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[cliff]

Did my new plastimo last year - took a bit of fiddling about but achieved reasonable results in the end.

17deg is quite a lot but you should be able to reduce that considerably. I would check the fitting of the compass before starting down the road of compensation. When I changed mine it was upto 35deg out yet the old compass was as near as damn spot on. Checked everything for a reason and eventually found the Stainless Steel screws I had used were magnetic. Changed the screws for bronze and deviation came down to 3~5 deg which although Plastimo say there is no need to apply compensation I had a go and got it down to next to nothing.

As for the SS screws, I took them into work and had a look at them turned out to be 410 grade not 316 hence they were magnetic.

Below is an excerpt from the Plastimo compass instructions

3. Deviation
- Deviation is an error in degrees on some compass headings due to magnetic disturbance (it can be either a positive or a negative value).
- It depends on the compass heading. As it may reach high values and make navigation dangerous, it is essential that you know the deviation difference before putting to sea.
- To draw the deviation curve (which gives the deviation values for each compass heading) measure deviation at compass courses at intervals of 30° (N, 30°, 60°, E, 120°...).
The deviation curve can be drawn on the enclosed table.
- This curve must be checked each year. Each time you put to sea, it is best to check that the compass and the curve correspond by means of a transit of two objects ashore. On a sailboat, we recommend to draw two diagrams, the first one with the engine off and the second one with the engine running in neutral.
Deviation measure method :
Check that compensation screws are in neutral position (according to the compass the cuts in the screws head are horizontal or they coincide with the hyphen - see figures D-E).
- Use a handbearing compass (ex Iris 50). This compass must be perfectly positioned along the longitudinal axis of the boat, it must be maintained in a horizontal position and placed in an area not subject to magnetic disturbance (example: the rear of the boat).
Note the heading of the handbearing compass.
The deviation value is obtained by subtracting the handbearing compass indication from your compass indication.
Example : If the handbearing compass indicated 30° and your compass indicates 34°, the deviation is - 4° for 34°
4. Compensation
- Some compasses can be fitted with a compensation device (according to models compensation is delivered as standard or is optional).
- If the deviation is between 7 and 20 degrees at some headings the compensation device will reduce the errors of your compass.
If deviations exceeds 20°, change the place of your compass.
If deviation is not more thon 7°, if is not necessary to correct the compass with the compensation device, but the values must be counted when laying a course (see formula paragraph 2).
- Warning : compensation is a very delicate operation, it is therefore advisable to call for the assistance of a professional compass adjuster.
Compensation Method :
With a handbearing compass like the Iris 50 model, place your boat successively at every cardinal point: North, East, South and West.
- By means of compensation screws, suppress deviation on headings North and East, and reduce deviation by half on headings South and West.
- North and South screws are for North and South heading corrections and East and West are for East and West heading corrections.
- Warning : when correction has been completed, a new deviation curve must be drawn.

Hope this helps.

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[Joe_Cole]

Thanks. I hadn't thought about the screws. That's another job you've found for me to do!

Joe

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[cliff]

Sorry about that but with me being a simple person I look for the simple things first. I learned the hard way - deal with the easy things first then worry about what is really wrong!

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[ongolo]

I have four articles or sources of info from the net, how to adjust a compass.

The easiest (if I remember correctly) was from Ritchies website.

If you dont come right, let me know your addr and I will mail to you or give you a yahoo group which we use for storage space for just such things.


regards ongolo

<hr width=100% size=1>1000 dream about it, 100 talk about it, 10 start and 1 completes it