Apparent wind

Right, lets get back to basics – apparent wind, what’s that all about?

The concept of apparent wind is largely unknown to non-sailors but if you sail a boat it’s a fundamental fact of life: apparent wind is what you sail in.

Apparent wind is the wind you experience when the boat is moving – it’s the true wind modified by the boats motion. A 15-knot breeze coming at you from 45 degrees off your bow when you’re stationary becomes a 20-knot breeze at about 35 degrees off your bow when you’re moving forward at around 6 knots. The boat speed adds to the true wind speed, and modifies its angle of approach.

Conversely, when the wind is from behind its speed is reduced by the speed of the boat. A 15-knot breeze from dead astern is an apparent wind of just 9 knots when the boat is moving at 6 knots.

When you’re sailing you don’t really think about apparent wind – it’s the wind you’re sailing in and that’s that. However, there is a time when you really need to consider the effects of apparent wind and that’s when you change from a course off the wind to a course on the wind. If you’re running downwind in 20 knots true wind it might feel like a perfectly manageable 14 or 15 knots apparent. But as you slow and turn onto the wind things will become a bit more of a handful, unless you’ve anticipated it.

Apparent wind – the wind you sail in.


No, no, I’m not referring to activities in the book 50 Shades of Grey and nor do I mean forming meaningful relationships; I’m referring to the connecting together of your boat’s non-current carrying metal components to form a common ground for your DC electrical system.

Bonding, that’s the word.

The bits we’re talking about are the engine, gear box, fuel tanks, water tanks, the external casings of pumps and motors and so on. Typically, in a bonded boat these items would be connected together with copper conductors to a common bonding conductor which usually runs fore and aft down the boat. Not bonding your boat means leaving all those big chunks of metal isolated from each other.

The idea is that bonding everything together with appropriate copper conductors provides a large common ground for the electrical system, it provides lightning protection and it controls corrosion.

There are some who prefer not to bond. These isolationists aren’t necessarily anti-social; they just think that bonding leaves the boat vulnerable to stray-current corrosion outside the hull even though it is protected from stray current corrosion within the boat.

An important issue is the question of whether or not to connect your through hulls into this common grid. Personally, I prefer plastic (Marelon) through hulls and seacocks so, for me, it’s a moot point. But with metal through hulls you have to decide whether to connect them to the other components or to leave them isolated to look after themselves. The predominant view is that you should leave them isolated.

So, research the subject and make your choice – to bond or not to bond, that is the question. Bondage, that’s something else.

Troubleshooting your VHF antenna system.

It’s that time of year when some boat owners realise their vhf radio or their AIS unit is not performing up to scratch. The boating forums are full of appeals for help and some of the responses are good, some a bit fanciful. Here’s a link to some advice on troubleshooting your antenna system:

Troubleshoot your antenna system

I hope this helps.

Note that I wrote this in 2011 when we’d been the Metz UK and European agent for six years, we’re now in our thirteenth. My, how time flies.

Comments etc.

Have to turn off comments for a while – life’s too short to spend time deleting idiot spam comments. Back later, I hope, when the spammers move on.

While I have your attention, remember Sailing Snippets is still available to download for FREE. You’re welcome.

Here’s a picture of a fleet of racing boats:

Goings on

I notice a great many of you, over 300, have availed yourselves of the free book offer, I hope you all enjoyed it. If you haven’t downloaded your copy it’s still available and still free, help yourself.

Just back from Houston, Texas, which is a huge sailing centre – not many people know that. We’re introducing the CableDorade (formerly the Cableport in UK) to the US market. Soon there will be a website where North American customers can buy in dollars and have it delivered from Texas.

The CableDorade is a great way to get mast and other above deck cables through the deck without leaks, high-maintenance glands and plugs and that snaggiest of things, the swan neck.

All for now, folks.

Last Post

I’ve decided this will be my last blog post.

I’m finding it increasingly difficult to generate fresh material to interest my boating audience. I suppose this is mainly because I don’t get out on the water as much as I used to. I can’t bring myself to just re-post YouTube links and I don’t want to become a bore regurgitating the same old stuff, so I’m bowing out now. I’ll leave the site active for a while so newcomers can browse the archives.

Site traffic has declined a bit recently but is still very good for a boating blog, more than 250 unique visitors a day, so a big thank you to my faithful followers!

The Salty John on-line boat business is in its thirteenth year and flourishing as a supplier of communication antenna systems, including the fantastic Metz antenna range. I’ll continue to devote my time to that enterprise for many years to come.

I wish you all fair winds!