~~ Compass Question ~~

I was looking at various sites for a RITCHIE Dash Mount compass. I saw one that said that it was for boats up to 16'. (Bass Pro)

I didn't realize that a compass was only good for certain lengths of boats.

On iboats, I found one that was like the one in Bass Pro, but doouble the price. The $ don't bother me, just confused about the lengths, and how that all works.

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I may be wrong but i doubt the size of the boat would matter.
It probably just rates the size of the compass. Like why would you need a huge compass on a smaller boat...just my guess..

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a compass is a compass. weather your walking, driving in a car, or a boat or a plane....
there is much to understand about a compass, but they work whatever your navigating. assuming you understand compasses.... deveation, variation, true or magnetic... and theres a bunch more to it than that. if were to say much more about them, i'd have to look in book...

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Gotta be some kind of advertising ploy, Bassmaster huh, guess what probably 90% of bass fishers have 16' boats.

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Better compasses are bigger, with finer markings on the card and usually greater damping, and cost more (sometimes a lot more). As said above, a compass is a compass and will work the same on any boat/ship.

Most people with 16' boats don't want a 8" diameter compass and most folks with 50' Hatteras don't want a dinky little compass. That is the only reason I can see for designating a compass as suited to a particular size boat.

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Ayuh,...

As Usual, I fully Agree with JB,...

The differences in the per foot of boat ratings are mostly about what kinda compass quality,+ features you'd expect for that sized vessel...

'ell,....

I've got an old Boy Scout Compass bouncing around the boat somewhere,...
Just as a back-up for those times you're foolish enough to Doubt your compass,......

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JB is correct.

Here is the selection chart from Ritchie. No mention of length per say. For the most part its divided up into type of craft and its primary usage.

http://www.ritchienavigation.com/products/selectionguide.html

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I bought a small Richie and have learned a couple things. The mounts are different so If you are going to use the Bracket make sure you have clearence between the dash and windshield. The other mount is 1/2 in the dash. Only the bubble/clear lens sticks above the dash. Make sure you have the surface space should you go this route.

The second thing I learned is the smaller compass is much more sensitive than the larger ones. Sensitive to adjust and sensitive to use. They all work, but I believe the smaller one would be harder to hold a true course with than it would be with the larger one. If I had it to do over again I would buy the bigger one. Plus the bigger one is much easier to see and read. Just my two cents.

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THANX, for all the input.

Smaller = More sensitive, really makes sense, along with all the other input. As usual from this board.

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I've got the Ritchie Trek on our Triton Bass Boat. It reads within 2 degrees of the GPS Magnetic heading.

We went with the size of the compass, not much room on a 16 foot boat.

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204 Escape said:

THANX, for all the input.

Smaller = More sensitive, really makes sense, along with all the other input. As usual from this board.

Click to expand...

I wouldn't call the smaller compasses more sensitive, Escape.

The real difference is the damping, how fast they can respond to changes in heading.

Small compasses can turn faster to keep up with the more maneuverable small boats, but they may wobble a bit in their indications. That is light damping.

Large boats turn more slowly. The more heavily damped large compasses are more stable but can keep up with the slower maneuvering of large boats/ships.

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I really never herd of one for a certain size boat either but smaller boats that bounce and vibrate more need a card with more damping. A compass on a small boat without enough Damping may spin all the way around but the same compass on a larger boat may work perfect.

A smaller boat that tends to pitch and roll more needs compass card or mount that can also pitch and roll more.

An aircraft carrier does not need a compass that can handle a lot of pitch and roll but a 16 foot high speed rubber raft does.

In general I think smaller compass are designed for smaller boat.
Not many people put a compass with a 8 inch card on a small boat.
also not many large boats use a compass with a 3 inch card.
Compass I have on my 14 foot boat would be unacceptable on my 21 foot boat and one on my 21 foot would a poor choice on the 14 footer.

In selecting a compass I think important to get one that functions the same way as your brain. In My case I need one that you read off the part of the card toward the bow. For me much eaiser to know weather to turn the wheel to the right or left without having to think about. When reading off the ones that you read off the side of the card closest to pilot I always want to turn the wheel the wrong way.

Also for me I never try to hold a course closer than 5 degrees offshore. In general I will steer a little different climing the swell and the opsite way on the back of the swell. Also look 3 to 5 swell ahead to steer around the Breaker. A small change in course can make a big difference in the ride and saftey of the trip. With Loran C or GPS it makes it so easy to go around the nasty swells and get back on course.

Inland it pretty much put it on course then check it now and then to keep your course.

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Part of the reason for using a smaller compass on a smaller boat (besides just not having room for a larger compass) is that it is impossible to steer an accurate compass course on a small boat. A small boat is influenced by wave action, wind, wakes, and current more than a larger boat. In many conditions, it is impossible to maintain a heading closer than 5 to 10 degrees of the desired compass heading. If you cannot steer more accurately than that, what good is a compass with 1-degree markings and accuracy down to a percentage of a degree. For the most part, I use the compass as a "general" direction indicator on my small boat. If it gets me within 10-degrees, I am happy. I then use the GPS for fine tuning or visually look for a landmark or buoy to steer toward.

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haskindm said:

Part of the reason for using a smaller compass on a smaller boat (besides just not having room for a larger compass) is that it is impossible to steer an accurate compass course on a small boat. A small boat is influenced by wave action, wind, wakes, and current more than a larger boat. In many conditions, it is impossible to maintain a heading closer than 5 to 10 degrees of the desired compass heading. If you cannot steer more accurately than that, what good is a compass with 1-degree markings and accuracy down to a percentage of a degree. For the most part, I use the compass as a "general" direction indicator on my small boat. If it gets me within 10-degrees, I am happy. I then use the GPS for fine tuning or visually look for a landmark or buoy to steer toward.

Click to expand...

Correct me if I'm wrong but this seems ok on a small lake but on a LARGE lake say 20,000 acres. The Great Lakes or Ocean. 5- 10dg is too much to be off.

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Depends on the distance. For a short distance, if you steer within 5-10 degrees you will still be within site of your goal and can visually correct. The point is that it is practically impossible to accurately steer a small boat within around 5 degrees of any compass heading. Try it sometime. Plot a course for a buoy or daymark 5 miles distant and steer only by compass and see how close you come, you may be amazed by how far you miss it. There are physical limitations that just can't be avoided and a super accurate compass with a 12" diameter card will not improve your results appreciably.

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Redsky has it right. Damping is the key. The larger the surface area of the dial, the more damping. Little boats turn quickly so less damping is desired. Big boats turn slowly so much more damping. I do it for a living so have a lot of interest. The ones we use on container ships are 7-1/2 in. in diameter on the dial. I like going one size up from the manufacturers so they are easier to read. I have tri focals.

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I don't mean to sound like a wise a**, but I taught navigation at the community college.
The rehtoric question is: Is this meant to be an ornament or is it there for somewhat seious navigation?
More $$ in a compass buys:
1. Damping
2. Larger dial= easier reading

ALL compasses work on the principle of a magnet, which aligns itself to the magnetic lines of force.So, money don't buy accuracy. There are things in a boat which alter these lines of force, and give eronious readings. This is called deviation. To do serious navigation, one must plot and make a deviation table to "correct" the errors. Consult a Chapmans for how its done.

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"Deviation" is the difference between true north and magnetic north at a particular location. It is marked on navigation charts.

Errors introduced by magnetic materials and electric field on a vessel or aircraft are just that: errors.

Corrections for error are made by "swinging", as described in Chapman's.

After swinging a compass is adjusted or the reading is modified to correct for local deviation, also described in Chapman's.

All this, of course, is necessary only if you intend to navigate a large vessel or an aircraft a long distance depending on your compass as primary or backup nav aid.

In my case compasses were backup/verification for navigating aircraft thousands of miles over water to and from islands. As little as 1 degree off course could have resulted in missing the destination that was 2,000 miles from the nearest land.

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As usual everyone has it a little bit right, especially JB, except he has variation and deviation mixed up. The original question was compass for a 16-footer and I think he was looking at the Ritchie X-21 dash mount. It fits an availaable 2-in. guage cut-out but has no correctors for Deviation. I would go one size bigger to the Trek series if there is room to mount on top of the console.

Most, but not all vessels have some sort of electronic navigation today and the compass is moving toward the "Standby" status now used in aviation. US Warships no longer carry a conventional magnetic compass, having two gyros, a heading readout from the weapons control system and a fluxgate in the pilothouse they have used the Secretary of the Navy exemption to take them off. All commercial vessels over 150 GRT must have a mechanical compass readable from the helm and also one that can be used to take bearings for position plotting. Try steering by a digital readout sometime. In Alaska, conventional compasses are more stable than a gyro for running an autopilot. A professional compass adjuster can get the magnetic compass within one or two degrees on all headings, even for steel vessels.

I know the feeling on islands. Try making landfall on Midway Island (Elev. 12 ft.) from the South at mid-day with haze.

Re: ~~ Compass Question ~~

JB said:

Better compasses are bigger, with finer markings on the card and usually greater damping, and cost more (sometimes a lot more). As said above, a compass is a compass and will work the same on any boat/ship.

Most people with 16' boats don't want a 8" diameter compass and most folks with 50' Hatteras don't want a dinky little compass. That is the only reason I can see for designating a compass as suited to a particular size boat.

Click to expand...

It may have to do with the quickness of a smaller boat as it yaws, pitches and turns, versus the same yaw pitch and turn but a lot slower and at smaller angles on a big vessel.

An abnormally big compass on a little boat will almost certainly receive damage under the bell (card) in the balance cone "if" the action overreaches the dampening speed and limits of travel, where a smaller compass won't. It has to do with "moment arms and angles" (Viscosity of fluid too.)

In the aicraft business we sometimes used different liquids according to preference (It's their Dollar!) for more or less damping quality (This of course being on small 1 to 6 seat A/C's and the older style of compass equipment.
For the small dash units on the aircraft we serviced, we used "jet A" kerosene for a secondary filler (a bit faster response) as there were no guidelines on the refills (alcohol was used too but not in aircraft, as it has a lower flashpoint than the the kerosene and could cause explosions), and the kero wouldn't freeze or contract past the bladder (expansion buffer) capacity, at 40 or 50 below zero.
PH.