Confessional: admit to boat-related things you've never quite understood...

[JumbleDuck]

Tomorrow you can tackle the thorny subject of head types. Hex head, socket head, slot, countersunk, raised head countersunk, cross head etc. Plus all the combinations of head type and shank type. Follow that with establishing the criteria for choosing the correct combination for each application.

I like cheese head screws. It's nothing mechanical - I just like the word.

 

[Tranona]

I like cheese head screws. It's nothing mechanical - I just like the word.

Have you been looking on the top shelf at WH Smiths again?

 

[JumbleDuck]

Sailing Smart: Winning Techniques, Tactics, and Strategies (1979) [Buddy Melges, Charles Mason]
http://www.amazon.co.uk/exec/obidos/ASIN/0805003517/dolcetto-21

Thanks, but I'm afraid it still baffles me. Is it really more complicated than "Don't go downtide if you don't have to?"

Now my question: Many sources say "tighten the backstay to increase mast bend and flatten the sail", I get the first bit, but that this flattens the sail is counterintuitive.

I believe one thinks of the centre of the mast bowing forward and thus pulling bagginess out of the middle of the sail.

 

[JumbleDuck]

Have you been looking on the top shelf at WH Smiths again?

Phwoarr. Look at the countersunk on that, eh?

 

[Pinnacle]

Now my question: Many sources say "tighten the backstay to increase mast bend and flatten the sail", I get the first bit, but that this flattens the sail is counterintuitive.

Nope - its quite logical.

On a fractional rig, as the backstay tension is increased. the top of the mast is pulled backwards. This action also has the effect of pushing the lower and middle regions of the mast forwards. This action pulls the sailcloth in the belly of the sail forwards. Hence the depth of the chord in the main is reduced ( the sail is flattened ).

 

[Simondjuk]

Now my question: Many sources say "tighten the backstay to increase mast bend and flatten the sail", I get the first bit, but that this flattens the sail is counterintuitive.

As the mast bends back above the forestay and forward below it (fractional rig), the fullness of the luff of the sail is reduced by being stretched into the forward curve of the mast, hence the sail is flattened and depowered. The leech is also opened when the mast is bent, as the distance between masthead and the aft end of the boom is reduced, which has a further depowering effect.

Edit: Seems we're all agreed on that one then.

 

[NOHOH]

Never understood how a brown cow can eat green grass and give white milk

 

[Stork_III]

Tomorrow you can tackle the thorny subject of head types. Hex head, socket head, slot, countersunk, raised head countersunk, cross head etc. Plus all the combinations of head type and shank type. Follow that with establishing the criteria for choosing the correct combination for each application.

And then think about self drilling/self tapping screws.

 

[Stork_III]

Never understood how a brown cow can eat green grass and give white milk

Or whatever you eat always comes out a shade of brown.

 

[Simondjuk]

The whole lee bowing thing is a discussion all of its own.

Whichever way you look at it though, having the tide on your lee rather than your weather bow will help to make good some of your leeway and, in some tiny degree, give you a freeing rather than heading tide wind component.

 

[chinita]

What is the difference between Phillips and Posidrive screws?

 

[Simondjuk]

The finer points of rig tuning are rather lost on me, but even most riggers seem unable to enlighten me on the aspects I'm unclear on, so perhaps I should just stop puzzling over it.

 

[Simondjuk]

What is the difference between Phillips and Posidrive screws?

Phillips is a plain cross slot. Pozi has an additional, albeit fine, cross at 45 degrees to the main one.

Worth noting that a Phillips screwdriver will happily drive a Pozi screw. The other way round, not so good as the additional points on the Pozi screwdriver have nowhere to go in a Phillips screw, hence it won't engage to its full depth.

 

[Tranona]

What is the difference between Phillips and Posidrive screws?

Different shapes of slots and, if you use the proper tools, different shapes of drivers. Positive claims to be more secure with the pointed recess at the bottom. Torx even better for easy location of the driver so preferred when using machine driven rather than hand guided tools.

Sure all this will help Dan when he comes to make his new rudder!

 

[Simondjuk]

On screws, one must also bear in mind the existence of the Phirrips head screw.

These are commonly used on items assembled in China and notable for the fact that there is not a screwdriver in existence which will fit properly, with the exception of the unique one used by the person who installed the screw in the factory.

 

[Woodlouse]

True wind is the one one you feel being stationary, apparent wind is when you are moving (true wind vector and head wind vector added).

Have a look here: http://en.wikipedia.org/wiki/Apparent_wind

findus

In the 21st century we now have Apparent wind, True wind and Ground wind. Apparent wind is what you feel on a boat that is moving. True wind is what you feel on a boat at sea that is not moving, but is still subject to tides and currents and so is not stationary geographically. Ground wind is what you feel when nailed down to the ground.

Hope that helps clear that one up. Or maybe I've just added some more dirt to the already muddy waters.

 

[grumpy_o_g]

Why people keep changing the names of things. I grew up with course (where you wanted to go), track (where you actually went) and heading (where you were pointed). Apparently we now have a course made good or something.

Oh and sail trim - I know all the theory but the practice never seems to work like that. And how people can sail faster than me by doing exactly the same thing I did...

 

[nigelmercier]

... the top of the mast is pulled backwards. This action also has the effect of pushing the lower and middle regions of the mast forwards...

As the mast bends back above the forestay and forward below it (fractional rig)...

Thanks guys, that makes sense.

 

[nigelmercier]

True wind is the one one you feel being stationary, apparent wind is when you are moving (true wind vector and head wind vector added)...

If I may rephrase that slightly: True wind is the one you would feel if you were stationary in the water ...

The True Wind does not change depending on your speed, but as your speed increases, the Apparent Wind will change in velocity or direction, or both.

 

[dancrane]

Oh, and I had a question about anchors...

Hmm, One hundred posts in 21hrs, not too bad. It seems we all have doubts to confess (or guidance to give!)...

...I sometimes wonder about aluminium as a construction material...aren't owners of ally hulls afraid of envious folk attaching a bit of some superior metal, out of sight underwater?

Wouldn't the whole boat quietly degrade in reaction to the alien bit of steel?