Tips, Tricks & Rules of Thumb

[markpj23]

Thought it might be nice to share some shortcuts related to navigation and seamanship. Looking forward to hearing what tricks others have learned over the years...

Angle on the Bow - Estimating CPA

Quick trick for computing closest point of approach (CPA) for another vessel. You can do this in your head easily and with good accuracy.

Kown officially as the Radian Rule, I also learned it as "Target Angle" and "Angle on the Bow." Surface Navy types use Target Angle, submarine service uses Angle on the Bow - since EVERYTHING is a "target" to submariners

I use Angle on the Bow, so here we go. Observe the other vessel and estimate how many degrees off of his bow YOU are - assuming that you are standing on the other vessel's bow. Another way to say this is "how many degrees of the other vessel's bow can you see?" The answer will be either Port or Stbd, in a range from 0 to 90 degrees.

For a vessel dead ahead on a reciprocal course to yours, the Angle on the Bow will be zero. A vessel dead ahead running perpendicular will be either port or stbd 90 angle on the bow.

So how do we compute distance at CPA? Take the Angle on the Bow as a percentage X the present distance = Distance at CPA.

So if you are 10,000 yards apart with a Port 20 deg Angle on the Bow, the distance at CPA will be 10,000 * .20 = 2,000 yards. This is a good rough estimate you can do in your head very quickly.

For those exacting types, you actually need to divide the angle on the bow by 90 degrees to get the exact multiplier. For example, a 45 degree angle on the bow means that you will close to exactly half the distance at CPA.
45 deg AoB / 90 degrees = .5
Distance at CPA = Current Distance * .5
Distance at CPA = 10,000 * .5 = 5,000 yards

This will NOT work if the other vessel is dead in the water - you will quickly notice the dreaded Constant Bearing, Decreasing Range scenario

Here is a safety tip I tell anyone who sails with me. You would be surprised how many experienced sailors fail to do this. When handling dock lines, ALWAYS take a wrap on a dock cleat. Even if you still have to position the boat, if you try to pull from the dock, you will eventually go swimming.

[ssullivan]

We have a saying that has developed, muck like Kai Nui's: Never trust your feet.

We tell guests (new ones mostly) that when aboard you can never trust your feet and must always grab something with your hand while making your way around the vessel.

[Doghouse]

Similar but here a few.
One for you, One for the boat. - Always keep one hand on the boat to hold on.
Right 1 baby (from the commercial) right is 1 horn
Do you have any red port wine left? Red light, Port Side, Left Side.
Red is rite when returning. red nav markers on right side returning from sea
Green gets you going. The opposite of the above.

Rabbit comes out of the hole runs around the tree then back into his hole. - How to tie a bowline knot.

If he is staying you are swimming. (no not a comment from SWMBO) If another boat stays on the same position vs your boat, change course or go swimming.

[WaLiveaboard]

Don't count your eggs cuz a bird in the tree is worth 2 if you cant get out of the cockpit....--


Don't know... I think it was the rum

[SkiprJohn]

Doghouse,
I learned it as "Even red nuns are right returning." Same thing but gives you the shape of the buoy too.
In some areas of the world this rule does not apply. Reverse is true.
Regards,
JohnL

[nolatom]

Everyone's heard these, but anyway:

When in doubt, let it out..

The "3 T's" rule namely, "Tiller Towards Trouble"--useful jingle when teaching new sailors, it'll help prevent, or minimize, a jibe, a knockdown, or a collision

And for navigation, the ever-reliable (though understand no longer P.C):

True Virgins Make Dull Companions (add Whiskey)

Can Dead Men Vote Twice (at Elections)

And for a very rough measurement of angle, your fist, held horizontally at arm's length, describes about a 10-degree arc horizontally. Same obviously if held vertically to measure altitude

[coot]

The relative bearing of an object will not change if you are on a collision course.

To watch for a change in the bearing, I sit in a place where I see the other vessel right behind a shroud, above a winch, whatever, and look through one eye. What they never say in the book is that it is amazing how fast you can make the determination when you use a fixed reference on your boat. You can see a change of a few degrees even faster than using a bearing compass.

I later discovered that this is how baseball players catch fly balls -- they move themselves around so that they see the falling ball at the same relative bearing. Too bad nobody ever explained this when I was in school taking compulsory Physical Education classes...

[markpj23]

Originally Posted by coot

The relative bearing of an object will not change if you are on a collision course.

And an extension of that thought is:

To avoid a collision either INcrease the Bearing Rate,
or DEcrease the relative speed to ZERO.

Note: actually colliding in order to reduce relative speed to ZERO does not count!

[Vasco]

Worm and parcel with the lay, turn and serve the other way.

[markpj23]

Originally Posted by Vasco

Worm and parcel with the lay, turn and serve the other way.

OK I'll bite - what the heck is this one?

[Starbuck]

Vasco is splicing line.

[Vasco]

Splicing wire rope. Especially the heavier stuff used for shrouds on ships. After you have spliced the wire rope you fill the grooves in the splice with small stuff and sometimes white lead and tallow (this is the "worming"). The effect of this is to make the splice nice and smooth all around. Then you wrap the splice using about a 4 inch wide burlap strip (parcelling). These two steps are done with the lay of the rope. Then you serve the splice with marline using a serving tool which is a wooden thingmajig that you wrap the marline around. This is done against the lay. The final product is a nice clean splice that's wrapped in marline. It's been a few years since I did this. Doubt if I could splice wire rope today. Took a lot of effort, pulling the tucks through and bashing it with a marline spike. I still remember the little ditty though.

[Seaquesta1]

Never, ever try to pee over the windward rail.

Seaquesta1, that should be rule #1. Are you speaking from experience?