Sailing and propellers.

If you think anchor selection is a controversial subject you should try talking about propellers.
I don’t know why these subjects should cause such angst, but they do. So I’ll just dive right in.

The first issue is drag: Under sail with the engine stopped does the propeller create more drag when it’s locked or when it’s allowed to freewheel? You would think the answer would be unequivocal – and it shouldn’t need rocket scientists to work it out. But just to be sure, some rocket scientists, or their marine equivalents, did work it out recently and their answer is unequivocal: There is less drag when the propeller is allowed to rotate.

Scientists at MIT and at Strathclyde University agree on this. It is fact.

So, we know we get less drag with the propeller rotating but what are the other arguments for and against allowing the prop to turn?

Noise: The rumble from a rotating propeller can be quite intrusive, particularly if you’re off watch in a stern berth. Some people can’t stand the noise whilst others find it interesting; they like to judge the speed of the boat by the level of noise.

Energy recovery: If you want to run a generator off the shaft it has to turn – simple.

Wear: Where there’s motion there’s wear and tear, if not damage, to drive train bearings and seals.

Gearbox damage: Clearly you shouldn’t be risking damage to your gearbox or losing your warranty protection just to get a half a knot of boat speed under sail or to get a good nights sleep in the quarter berth.

It seems that Yanmar became so concerned at the number of requests they received for clarification on the best practice for their engine/gearbox combinations that they issued a directive: The gearbox must be in neutral when sailing or your warranty will be invalidated. If you want to stop the shaft use a shaft brake, they say, not our gearbox.

I have to admit that I sailed for many thousands of miles with my Yanmar 3GM30F in reverse gear to stop the shaft rotating and I never had a moment’s trouble. Just lucky?

If you have a Hurth/ZF gearbox you must not select forward gear when sailing forwards. Or reverse when sailing backwards, obviously. Apart from that, use the gearbox in reverse to lock the shaft or let it run free, it’s up to you.

With a Borg Warner Velvet Drive transmission you can do what you like, it will rotate anyway.

On some gearboxes damage can occur because the engine needs to be running to provide lubrication, with splash lubrication there isn’t usually a problem, so check the manual.

It boils down to this: If you are obsessed with squeezing out the last fraction of a knot under sail you need to let the prop freewheel. You’ll be happy to accept any wear and tear on your cutlass bearing and you’ll issue ear plugs to those that find the noise is keeping them awake.

If you’re worried about wear or can’t stand the noise you’ll want the shaft stopped and whether you do that by using the gearbox or a shaft brake will depend on your gearbox manufacturer’s advice, and whether or not you’re going to obey it.

Simple, really.

But don’t worry, there are plenty more propeller issues to fight over when you want a break from anchor arguments: Folding props, feathering props, duo-props, two blade, three blade, using vicegrips as a shaft brake………

No! The other starboard!

Well, the festive weekend is upon us. May joy be unconfined and much food and drink be taken. Merry Christmas to you all.

The fashion for surrounding the helm with electronic gadgetry got me thinking about the voice-prompting, turn-by-turn, GPS sets you get in cars and I wondered how they would work on boats.

The prompt menu couldn’t just be transferred from the car sets to marine GPS units and chartplotters – a tinny electronic voice saying, politely, “You have gone too far, make a U-turn when it is safe to do so” probably wouldn’t work.

Still, it shouldn’t be difficult to devise a new set of suitably aggressive voice prompts. Amongst them might be:

“Turn onto 217 degrees now, Mr Christian, or I’ll have you flogged!”
“Ramming speed!”
“Proceed across the shipping lane on 180 degre...OH MY GOD!”
“No, you twonk, the other starboard”
“Were you thinking of making that tack I ordered anytime this week?”

I’ve just had another great idea! Why not have the boat steered by an autopilot which is controlled by voice recognition software. Brilliant. The GPS shouts the course, the autopilot obeys. Now we just need the autopilot to get peed off and sulk, ignoring further commands until an apology is forthcoming and we'll have electronically simulated the family cruise. The humans could stay home where they won't get hurt.

Garmin! Raymarine! Are you listening!

Nicknames

My office window at Salty John Towers looks out over a country lane. Off to the left the lane leads past houses, campsites and caravan parks to a pleasant inn and the river. To the right is the village with its houses, cottages, three pubs and two restaurants. And the small Post Office from which many Salty John parcels are dispatched.

Over the years I’ve given nicknames to the people that regularly walk past my window. The names are mostly of an affectionate nature and once I come to know the person involved the nickname is dispensed with.

Fifties woman is one of my longest serving perambulators. She has a blonde beehive of impressive proportions and wears straight skirts and four inch heels. I can hear the click-clack of those heels well before she heaves into view. Another one who could be heard long before he appeared was The Whistler. Two years ago I realised he’d gone AWOL. I hope he’s all right and that he’s simply taken his perpetual warble elsewhere, but sometimes I fear the worst.

Then there’s Man-woman, a bit cruel that one and I will probably feel quite guilty should I ever meet her. But her masculine countenance begged the sobriquet.

The Twins Mother is, I was recently informed, not the mother of twins. Well, they look like twins. I know who she is but as we’ve not actually met she remains in the cast. Along with The Major and Mrs Major - he of the military bearing and magnificent moustache who tips his hat at the ladies. She of the Queenly wardrobe topped by a turquoise beret which adds a certain jauntiness.

Mystery woman has been around for several years and is still a mystery. Attractively interesting, I’d call her. She probably leads a perfectly ordinary life but her role as Mystery woman allows for more rewarding flights of imagination.

Some of the walkers know each other and on several occasions have stopped to chat together at the end of my drive. I often wave and they wave back.

I once had the part of one of the characters, the Boy, in “Six Characters in Search of an Author”, the Luigi Pirandello tragic comedy in which six characters persuade a director to let them act out their story – the Boy shoots himself in the end.
 
Anyway, it got me wondering if my cast of characters isn’t crying out to be in a story – scandal and intrigue in a small Lancashire village, perhaps. I’ll work on it this winter.

I know this has nothing to do with sailing or boats but it’s that time of year. I’ll try to get back on track next week. Unless you’d like to hear more about Mystery woman and that bloke that runs the boating website?

I’ll take this opportunity to wish all my readers a Merry Christmas and a Happy New Year.

Waves, the wind's assassin.

It’s been pretty windy around here for the past couple of weeks. We’ve had Force 10 and 11 a couple of times in northwest England and in Scotland. 

Off Donegal they measured a wave at 67’ (20.4m), the highest wave recorded in Ireland. The Irish Met Office says the buoy that measured it is 11km off the coast, so it was generated in deep water by the persistently high winds.

I was once in very large waves, around 45 feet, off the east coast of the USA and there was a point at which I didn’t think the boat was going to make it up the face of a particularly steep wave. An illusion, of course, but pretty scary nonetheless.

The probable maximum height of wind waves is around 80% of the wind speed. So, a 50 knot wind blowing over an area of ocean with unlimited fetch would produce a maximum wave height of about 40 feet. This height is achieved after it has been blowing for a day, having doubled in height since the first four or five hours of the storm. Further maximum wave height increase is more subdued, it takes two days to get that wave up to 50 feet in height.
 
The average wave height in a storm is about half the height of the top ten percent of waves and one third of the highest wave. So, if the maximum wave height in our 50 knot blow is 40 feet, the top ten percent of waves will be about 20 feet and the overall average will be about 14 feet. It doesn’t sound so bad when you put it like that, does it? Except that you still have to survive those pesky maximums and top ten-percenters!

Outboard motor & cargo hoist.

On sailing boats, particularly ketches and yawls, you can use the mizzen boom to hoist the outboard motor or other heavy cargo aboard. If the layout of your boat doesn’t lend itself to this you can fit a dedicated cargo boom or outboard motor hoist. These are incredibly useful pieces of equipment – you’ll wonder how you managed without one.

There are various types available, some quite reasonable in price others eye-wateringly expensive. Or you can make your own from 1½” (38mm) stainless tube bent to shape, or cut and welded. The vertical section can rotate inside a slightly larger diameter tube secured to a pushpit upright with bolted clamps or hose clamps. A rubber tip or softwood plug will protect the deck from the cut end of the tube.

A three part purchase using a double block on the davit arm will give you a three to one mechanical advantage. The hoisting line can be secured to a cleat on the davit upright. A more sophisticated version might use a trailer winch and crank handle to do the hoisting. 

Whether you use the mizzen boom, a dedicated cargo hoist or simply a halyard to hoist your outboard motor you’ll need a Salty John Motor Lift™ to provide the top lifting point.

Metz Manta VHF/AIS antenna

Here’s the flyer we send out to retailers to support the Metz Manta VHF antenna, when we're wearing our Metz Europe hat.

VHF antennas are also used by AIS engines. You may see antennas described as AIS aerials (or antennas) and what this means is the VHF antenna is tuned to centre on the AIS frequencies, 161.9 and 162.0 MHz, rather than on the broader range of radio frequencies including the emergency channel, 156.8 MHz.
The Metz Manta covers 156 MHz to 163 MHz, so includes all radio and AIS channels.
Metz makes a dedicated AIS antenna but rarely is it chosen over the Metz Manta because the difference in reception is not very significant. Better to have the option to use either antenna for either purpose, I feel.

Do your's droop?

Drooping is not usually a good thing. You don’t want drooping bits. You especially don’t want drooping spreaders. Drooping spreaders are a symptom of a rig in distress, a rig on the road to catastrophic failure.

Perky upward pointing spreaders are what you want. Perky spreaders have tips that bisect the angle of the shrouds that pass over them. In this way the load on the spreader is even and the spreader is disinclined to be pushed up or down, slackening the shroud and threatening the integrity of the whole rig.

Spreaders come in lots of shapes and configurations: The racier boats have spreaders with aerofoil sections, like little aircraft wings, to reduce wind resistance. Cruising boats tend to have longer spreaders to give a broader based rig, sacrificing sheeting angle for better mast support. Old fashioned cruising boats under about 45’ tend to have single spreader rigs, for the sake of simplicity, whilst more modern boats with relatively taller masts adopt multiple spreaders at shorter boat lengths. Spreaders can be fixed at the mast or fully articulating and they come with a variety of methods of attaching the shroud to the spreader tip so it doesn’t jump out. But whatever the spreaders design, droopiness must be avoided at all costs – check your spreaders now!

A word of caution: Once you become an aficionado of the perky spreader your marina dock strolls will take on new meaning, your eye will be inexorably drawn aloft in search of droopers with the attendant risk of an early bath or a broken toe.