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

Tranona said:
Exactly what it says. Taps its own thread in the material. As opposed to threads already tapped in the material. Difficult to think of any term that is more explicit to describe the process.
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Except how does a person without knowledge of engineering jargon know the verb "to tap" in that sense?. To the average person a self-tapper is just "a screw". Wood screws are "those screws without the screwy bit at the top". And what's with the arcane numbers which only the power of google reveals represent gradations of 0.013 inches "major diameter" (starting from the blindingly obvious 0.06 inches, and just when you think that using the imperial system must mean they think like antique FORTRAN programmers, No! they start the numbering at 0!). Screws took me a while to get the hang of. The amount of jargon that goes on is probably lost on people who've owned a lathe since they left school, don't ask whether it can do BGP before purchasing a router and assume that everyone understands common woodworking and metalworking terms. "filleting and fairing" for example. Where have you ever seen anyone define "filleting" when using the term to answer an evident novice's question? Many people will then wonder exactly which bones need to be removed to complete the task.
 
A forward sloping transom (sometimes known as a duck billed transom) reduces the water drag on the hull. It is used on several designs of ship where speed is required. Some ships such as P&O's cruise ship Aurora or, What was, P&O Containers Jervis Bay class have the entire transom sloping forward. Some ships, such as some warships, only have a small duck bill at the bottom of the transom.
 
jerrytug said:
Another design point I can't get my head around is overhangs. I can read that overhangs give greater waterline length when heeled. Fine, but why would you not want the 'extra length' when NOT heeled? Tumblehome on the topsides is another design feature I don't get. Why?
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Tumblehome on wooden warships is also supposed to have made it less easy for boarders. I understood that in GRP boats, it was expensive because it required the hull to be moulded in two parts longitudinally.

For a discussion of overhangs, see here: http://www.ybw.com/forums/showthread.php?359941-Bow-shape-and-characteristics-under-sail-Overhang-v-straight-stemmed
 
laika said:
Except how does a person without knowledge of engineering jargon know the verb "to tap" in that sense?
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Thanks Laika. It's true, asking a very qualified person is frequently not very helpful...the longer it is since they learned themselves, the less they'll recognise that it isn't obvious.

I can perhaps show how true that is, by inferring from the explanation that almost all screws are self-tapping...because they're usually pointy enough to be driven into whatever material they're designed for...in my unschooled mind, if a screw isn't pointy, it's a bolt. So why are self-tappers always described as such? What does a non-self-tapper look like?
 
I should make the effort, but I have never really understood the effect that land has on wind direction and speed when coasting or going past islands. I just take what I am given.
 
dancrane said:
What does a non-self-tapper look like?
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As vyv_cox said, there's wood screws for example, but for those of us without a kindly old uncle to whip out a tool to show us in his workshop, there's always t'Internet:
http://en.wikipedia.org/wiki/Screw

These are self-tappers:
(hmm..forum doesn't load images from remote urls now it seems and the gag is somewhat spoiled by putting an explicit url in...)
http://upload.wikimedia.org/wikipedia/commons/6/69/Astaire%2C_Fred_-_Never_Get_Rich.jpg
http://upload.wikimedia.org/wikipedia/commons/4/40/Gene_kelly.jpg
 
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Romeo said:
I should make the effort, but I have never really understood the effect that land has on wind direction and speed when coasting or going past islands. I just take what I am given.
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Similarly, I probably know less about weather than I should.

Pete
 
How does the thermostat control the temperature in a raw-water cooled Volvo? I have aired this one several times, last time only yesterday, but nobody seems to know. I was previously put in contact with several Volvo repairers/servicers but they had no idea either.
 
Tranona said:
Maximum beam of the hull is not at deck level, but lower down. So looks fat from ahead or astern. Partly driven by rating rules and partly by (IMHO misplaced) aesthetics. Very popular with some designers about 40 or more years ago!
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And with Contessa 32 fans to this day, though I'm afraid they always look like fat women sitting down to me.
 
laika said:
These are self-tappers:
View attachment 37209 View attachment 37210
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Excellent! ;)

I think I do understand, now. Basically, what I call a bolt, needs a female hole to screw into...no sniggering at the back there!!...whereas what I call a screw, goes into the material without needing much, if any, pre-drilling...and is therefore a self-tapper.

It certainly was not obvious, to me. I'd thought the phrase meant that when the screwhead is flush with the surface, it simply rotates without continuing in, deforming the thread.

Still makes me wonder why the phrase 'self-tapping' continues in such common and frequent usage. We don't often refer to our vehicles specifically as 'horseless' anymore, do we?

That Wikipedia page on screw-types is helpful...it accepts that the definitions and usage of the terms is quite variable and inconsistent. So hopefully no room for pedants! :)
 
laika said:
Except how does a person without knowledge of engineering jargon know the verb "to tap" in that sense?.
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Guess they could do the obvious and look the word up in a dictionary. There they will find that if the term is used in relation to screws it can have only meaning - that is creating a thread. Not difficult then to work out what the "self" bit might mean.

Agree there are plenty of confusing and obscure jargon terms around in all sorts of fields, but would not put the chosen example among them.
 
vyv_cox said:
How does the thermostat control the temperature in a raw-water cooled Volvo? I have aired this one several times, last time only yesterday, but nobody seems to know. I was previously put in contact with several Volvo repairers/servicers but they had no idea either.
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I don't know but I do know that it does. I also know what happens when it doesn't!
 
dancrane said:
Thanks Laika. It's true, asking a very qualified person is frequently not very helpful...the longer it is since they learned themselves, the less they'll recognise that it isn't obvious.

I can perhaps show how true that is, by inferring from the explanation that almost all screws are self-tapping...because they're usually pointy enough to be driven into whatever material they're designed for...in my unschooled mind, if a screw isn't pointy, it's a bolt. So why are self-tappers always described as such? What does a non-self-tapper look like?
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Screws are usually tapered. Self tappers are straight and as said the thread is designed to cut a thread into the hard base material.

A bolt has a plain part of the shank as a bearing surface. A Set Screw hasn't got a point but is threaded full length of the shank.
 
Tam Lin said:
I don't know but I do know that it does. I also know what happens when it doesn't!
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No doubt it does. Not only that but the engine is perfectly capable of driving a calorifier, which Volvo said it couldn't without spending a bomb on additional equipment. Do you think Volvo know how it works?

What happened when yours failed? and did it fail open or shut?
 
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