Compasses?

swginn · 28 April 2004, 13:01

Went to my local chandlers today to buy a compass for my new rib. They stocked three different types.

Danforth Skipper 2 Global Balance
Plastimo Offshore 75/90
Silva 70

Has anybody got any experience using any of these models. Which is the best for use on a 6m Rib? Any reccomendations or advice? It will be mounted off to the right, to allow for GPS mounting on the flat horizontal surface in the pic.

Mark Halliday · 28 April 2004, 13:13

Just fitted a Ritchie B-51 bracket mount. Good clear 120mm card, back lit, well damped and can be adjusted up to 30º to alow for all the cabling, metal & RF around a console. Available with black, white or blue card.
£47.99 from Aladins Cave.

Alan · 28 April 2004, 13:14

Gonna stick my neck out here and say none of 'em & you should get a digital one with a handbearing compass (e.g. Plastimo Iris) as ultimate backup. Proper compasses in my experience are damn near useless in a RIB at speed and in a chop. Steering a course to +-20 degrees is the norm. A digital one such as KVH azimuth or 'praps one of the tacktick solar powered ones gives a much easer to read and use display. I know its another piece of electrikery to go wrong hence the thought of the solar powered tacktick (costs about £180). In real extremis e.g. if all your electrics go wrong, the GPS satellites go down etc etc you can get your hand bearing compass out and use to navigate even if you have to do it slowly or stop every so often for position fix and new course to steer.

Of the three you have mentioned I've only used the Plastimo 75 which seemed as good as any.

Cheers,
Alan

Daniel · 28 April 2004, 14:22

I'm inclined to agree with Alan... i realy regret selling my KVH with grayswish. I do feel a 'budget' fixed compass is good enough, because it will be just as useful as a 'good' one. I've fitted a small £30 one to my rib... it allows me to tell which way i am pointing and that is about all.

swginn · 28 April 2004, 14:42

I suppose I should have said that the main reason that I'm buying a compass is as a backup for my GPS which will be my primary navigation aid and so don't really want anything electrical. At the end of the day there's not much that can go wrong with a conventional compass.

Alan, did the plastimo 75 have adjustment to allow for electrical interference (GPS, VHF, Sonar).

By how much (degrees) does electrical interference generally affect a compass?

Jackwabbit · 28 April 2004, 14:58

Don’t under estimate to power of a conventional compass.
We were diving off the Mulberries in Pagham bay one weekend in fog, we had no problem getting there & back to Bognor using the GPS on the first trip. We managed to get back out again on the second trip using the GPS with no problem, it was when we went to come back the GPS wouldn’t initialise it couldn’t find any satellites. We later found out they switched them off for re-calibration,

so we had to use the old clockwork compass. As land came into sight we were only 100yds away from the slipway.

Alan · 28 April 2004, 15:35

Quote:

Originally Posted by swginn

I suppose I should have said that the main reason that I'm buying a compass is as a backup for my GPS which will be my primary navigation aid and so don't really want anything electrical. At the end of the day there's not much that can go wrong with a conventional compass.

Alan, did the plastimo 75 have adjustment to allow for electrical interference (GPS, VHF, Sonar).

By how much (degrees) does electrical interference generally affect a compass?

Well yes and no. I'd assumed that you wanted the compass for backup. Whilst there is not much that can go wrong with the compass itself you are right that you need to compensate for effect of electronics and swing it to understand deviation on particular headings. If you read the installation manuals for compasses and electronics they say that they should be some distance apart. Can't recall exactly how much but generally more room than is available on a RIB console. Especially a small one like yours.

The thing that attracts me with the tacktick kit is that it is completely self contained and self powered. 200hr battery life with solar charging. So it is an independent back up system.

and no I dont sell em its just what I would fit on a new RIB myself!

check out http://www.tacktick.com/products/vie...ct.asp?prod=29

thorper · 28 April 2004, 15:42

Hi - this is the setup we've got on our Tornado (comes from Barnet marine like your rib), using a plastimo compass. It works well, and is pretty useable even if the boat is moving around a lot.

Ricky

swginn · 28 April 2004, 16:01

Thanks very much for the input all. Alan while I value your experience and opinion, I prefer the conventional glass ball approach. It just comes down to personal preference. I can see the advantages of the Tacktick system, but would prefer to see North South East & West instead of digital numbers. If they made a model with a more traditional North South East West display I would definitely consider it. Not sure if this makes sense, but I just like the glass ball compass.

Thorper, what model is that?

Scary Des · 28 April 2004, 16:21

A word of caution, the conventional compasses are badly effected by electronics and lumps of metal and the effect might not be same throughout its range (sometime a few degrees off, sometimes more). With the previous boat I owned keying the fist mike would swing the compass 20 deg. To get the compass set properly is a comparatively expensive operation involving a compass swinger (that least that is what he called himself) and driving around in circles for what seemed like hours.

I think Tacktick is a good option or Autohelm who used to make a fluxgate compass with a conventional display. Alternatively an Iris 50 handheld £40 (more in euros) and worth every penny (cent) but remember to stand up when you are using it.

Lester McCarthy · 28 April 2004, 16:25

You will find the compass easier use if it mounted in front of the helmsman, not off to one side otherwise you might have a tendancy to steer around in circles.

Mark Halliday · 28 April 2004, 16:30

[QUOTE=Jackwabbit]Don’t under estimate to power of a conventional compass.
QUOTE]

Absolutly right.
In my young and foolish days I navigated a 32ft yacht from St Malo to Hamble with only with a compass and depth sounder. Thick fog all the way and the log died 5nM out of St Malo. It took a while and we did some extra miles to be sure we did not get run over or hit something. BTW this epic voyage predated DECCA let alown GPS.

Alan · 28 April 2004, 17:43

[QUOTE=Mark Halliday]

Quote:

Originally Posted by Jackwabbit

Don’t under estimate to power of a conventional compass.
QUOTE]

Absolutly right.
In my young and foolish days I navigated a 32ft yacht from St Malo to Hamble with only with a compass and depth sounder. Thick fog all the way and the log died 5nM out of St Malo. It took a while and we did some extra miles to be sure we did not get run over or hit something. BTW this epic voyage predated DECCA let alown GPS.

Don't get me wrong a compass is an essential aid to navigation for yachts, mobos etc as is the ability to do "steam" navigation with charts, tidal diamonds, leeway, eps, dr etc etc. However there is a world of difference between that and an open and high speed boat like a RIB.

SWGINN you are welcome! At the end of the day it comes down to personal preference and if you want a traditional compass fit the largest and best damped one you can. And as Lester says fit it in your line of sight for easy viewing whilst driving. Mebbe on the front of the console on a gimbal mount so you look over the top of the console at it?

Cheers, Alan

Alan Priddy · 28 April 2004, 17:55

And Lester should know, I have followed him in circles on more than one occasion! Alan P

Alan · 28 April 2004, 18:02

Quote:

Originally Posted by Alan Priddy

And Lester should know, I have followed him in circles on more than one occasion! Alan P

Isn't there a quote from Clive in his book about the compass being a convenient thing to hang your baseball cap on and thats about it or am I imagining things Alan?!

John Kennett · 28 April 2004, 19:53

Quote:

Originally Posted by Alan

Gonna stick my neck out here and say none of 'em & you should get a digital one

Well I would just get the biggest Plastimo Offshore that you can fit on the console. I would have it directly in front of the helmsman too, with the GPS and other bits and pieces relegated to the sides.

I used to have an electronic compass (a Ritchie as far as I can remember) and didn't get on with it at all. I have heard good reviews of the KVH one though.

John

Richard B · 28 April 2004, 20:06

Quote:

Originally Posted by John Kennett

Well I would just get the biggest Plastimo Offshore that you can fit on the console. I would have it directly in front of the helmsman too, with the GPS and other bits and pieces relegated to the sides.

I'm with John on this one.

Alan - the Plastimo 105 on Blue Ice is really excellent - Used it properly last year when the chartplotter was on the blink. IMHO it's a good idea to have at least one instrument that's not dependent on the 12v system.

Also see: http://www.rib.net/forum/showthread....light=plastimo

swginn · 28 April 2004, 20:09

Thanks all!! I was thinking along the lines of a Plastimo after seeing them today. I can probably mess about a bit with the GPS and make room to mount it in the middle. I was thinking of getting the Offshore 90 (its on special at my chandlers!!) I'll have to have a look at the 105 though and see what size it is first, if I can fit it I'll get it. Is there any advantage in using a bracket mount compass instead of a flush mount bearing in mind that I'm going to mount it on horizontal surface. The only one I can think of is that the bracket may damp vibrations, or am I being too particular.

thanks guys,

Steve

Richard B · 28 April 2004, 20:14

I'd go for flush mount if possible - brackets can only add to the wobble. Good compasses are well damped with their fluid.

Hightower · 28 April 2004, 20:25

I too am looking to buy a compass. Can't fit one on the console but was restricted to a 45 deg angle on the front LH side of the console (like fiirst photo).

The only option was for flush mount and the only compass I've found that'll fit there is the Mini C from Plastimo. What I'm worried about is the lack of compensation this budget compass has.

Do I need compensation if using a GPS? I've got GPS Chartplotter, could I work out from the heading on the GPS what the deviation is, to make a note of it and use the correction when I come to use the compass?

Andy