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

[jerrytug]

No because once you reach hull speed the stern wave starts to fall off the back of the boat causing it to settle deeper in the water. The effect of this on a boat with overhangs is to increase the waterline length. You don't necessarily have to be heeling, though if there's enough wind to get you to hull speed there's probably enough to heel you over a bit too.

Oh yes of course.. thanks for the explanation!

 

[jerrytug]

Bermudan or Bermudian?

Halyard or Halliard?

Cutter or Slutter?

....and my Thermos Flask; keeps hot thing hot and cold things cold. How does it know?

Well a cutter has a bowsprit, but a slutter doesn't (the word is a mix of sloop and cutter)

 

[prv]

Bermudan or Bermudian?

One refers to a rig with three-cornered sails, the other to things and people from the island of Bermuda.

But in practice they are often used interchangeably, which annoys some people from Bermuda (and some pedants as well)

Halyard or Halliard?

Either - variant spellings. I prefer the former but I wouldn't say the latter is wrong.

Often claimed to come from "haul yard" (which some of them do, on a square-rigger) - but I think I remember reading an article which said that's a folk-etymology with evidence to contradict it.

Cutter or Slutter?

Cutter used to refer to a style of vessel generally; then it came to mean a fore-and-aft rigged vessel with the main headstay taken to the stemhead (implying that the bowsprit can be made to reef or steeve because the mast doesn't rely on it for support), nowadays it's mostly considered to mean a fore-and-aft rigged vessel with one mast and two headsails. Slutter is a horrible neologism and people seem to disagree over exactly what it means so it's not even a useful one, but I understand it as two roller headsails very close together so that you can choose between them by rolling one away and the other out.

Pete

 

[Woodlouse]

A cutter is a boat that flies more than one headsail.

A slutter is a boat with two headsails, only one of which can be used at any time. Usually a large genoa on the outer stay, and a more blade like jib on the inner.

 

[Alan_B]

True and Apparent Wind - never really got that. I wonder if its important.

I think I know this one

When going downwind the apparant wind speed is less than that of the true windspeed, as you are obivously travelling in the same direction as the wind. In fact I giess its the opposite when beating? Who knows, I dont like beating anyway!

 

[vyv_cox]

True and Apparent Wind - never really got that. I wonder if its important.

The illustration of this that I like is a steam train standing still with the wind blowing at 90 degrees across it. The steam/smoke from it blows away at 90 degrees - this is the true wind. The train begins to move forward, the steam/smoke trail moves back. The faster the train moves, the further aft the trail moves. That is the apparent wind.

 

[Keen_Ed]

So why not make the waterline that long to begin with?

Pete

Because that penalised your rating. Long overhangs are purely an effect of rating rules which measured waterline length by one method or another - the length and sail area rules/thames tonnage/universal/international/square metre (possible the ultimate example).

Nowadays, with box rules such as the tp52 rule, the Class 40 rule etc, where you're limited to a maximum length, despite the fact that you could if you want build a boat with lots of overhang and lower wetted surface, you don't. You build lwl to the max length, or very nearly to the max length (with maybe a little bit of stern overhang). In powered up boats, length beats wetted surface area.

99.99% of boat shapes reflect the influence of rating and box rules. E.g., current wide sterned cruising boat with twin rudders (e.g. Sense 46 YM video out today) reflects open 60 shapes (to a degree).

 

[prv]

Because that penalised your rating. Long overhangs are purely an effect of rating rules which measured waterline length by one method or another

Keep up at the back, that's the answer I already gave

Woodlouse was advancing a different (though not incompatible) theory about how overhangs make you faster regardless of rating rules.

Pete

 

[Keen_Ed]

Other advantage of stern overhang is that (should the rule give you benefit for lwl<loa), you can take advantage of the boat being measured without the crew onboard. Shorter lwl under measurement - crew gets into the cockpit = up goes waterline. In ultralight conditions, crew sits below and forwards (dogs in the kennel).

Bow overhang has struggled to be as effective. Some degree is useful in cruising boats - stops the anchor chain rubbing the topsides. And offshore, flare has benefits in waves.

 

[Woodlouse]

The thoughts behind designing modern semi displacement boats such as the TP52's are very different from trying to gain a favourable rating with the old design rules. If you're designing a boat with intention for it to frequently exceed it's theoretical hull speed you go for a different style as opposed to a boat that is just trying to get the best speed for it's length in all conditions. If you look at classes such as the now defunct IACC you'll see they still had a fair degree of overhang even in 2007.

 

[Lakesailor]

Windermere Class Yachts have a LWL of 17ft. They have a LOA of 25' 6". That's the rules.

In this picture you can see the black area is the area in the water at rest. When heeled you can see how much extra hull has been placed in the water giving a much longer LWL and more speed.

Again you can see the whole boat length is in contact with the water.

You can see in this shot how much bow and stern are available to dunk when the boat heels

 

[JumbleDuck]

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.

A bolt has a threaded portion and a smooth section.

A machine screw, often called a screw, is threaded all the way from the tip to the head

A wood screw, also often called a screw, has a much coarser thread and is tapered from tip to head.

 

[superheat6k]

My question is why do so many things boating increase in cost relative to LOA - especially finger pontoons ?

If I park my Rolls Royce in a parking space I pay the same as I would for my mini.

My answers are ...

Lee Bowing. This happens when sailing close hauled but with the tide fair i.e. Flowing from the direction of your lee side, giving you an extra lift to windward when tacking, meaning your progress is improved, or allowing you to ease off slightly to gain better boat speed, without losing precious degrees from your desired heading.

Prop walk. This occurs for two reasons. The water arrow surrounding the lower half circle of the prop is slightly denser due to the increased weight of water the deeper you go, plus there is less boat structure interfering with the flow of water in this lower portion. Hence the lower section bites the water more effectively, causing the side ways 'walking' effect.

This is more pronounced astern where the water washing off the prop impinges directly onto the structure from the upper part circle.

 

[nigelmercier]

Lee-bowing. I suspect that it's actually something bloody obvious, but every attempted explanation I have seen has just confused me.

I searched online, and was surprised to find many pages saying it is a myth; this is not my experience. This explanation makes sense to me:

Lee-Bow Effect: This brings up the famous lee-bow effect. If the current is coming at you at an angle that is very close to the course you are sailing and if, by pinching just a little bit, you can get your lee bow into the flow of the current, the movement of the water is going to push against the hull, the keel, and the rudder, and it is going to drive you up to windward even though you are going slower over the bottom. If you are on the other tack the current is going to be hitting you broadside and pushing you down. If you can get the lee-bow effect to push you to windward, I feel you also increase the wind pressure on the sails. If I am on the tack that goes across the current I feel I am losing speed and distance to the mark. That is why, unless there is an obvious way to get out of the current entirely, or at least to a slower flow, I think you should always make your longest tack to the next mark sailing in the lee-bow position. And I would do this even if it meant pinching a bit to do so.

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

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.

 

[cryan]

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.

Does the thermostat not just direct the water either through the head and block or straight out through the exhaust manifold depending on the temperature? Or am I missing the point of the question? I presume the thermostat is operated by wax plug?

 

[nigelmercier]

I can never quite get my head around prop-walk when in reverse.

Next time you are on your boat, still tied up, put the engine in reverse at mid-range revs. Now walk forward and look over each beam: on one side you will see a rush of water. This is what causes prop-walk.

Another question: don't people realise that posting large images really messes up the forum. Crop them to 800 pixels or less. Please.

 

[reeac]

Does the thermostat not just direct the water either through the head and block or straight out through the exhaust manifold depending on the temperature? Or am I missing the point of the question? I presume the thermostat is operated by wax plug?

More or less. You need a flow of water through the exhaust whenever the engine is running in order to stop the system melting. Once the engine is up to temp. the thermostat opens and water flows through the cylinder head as well. Certainly on my VP2002 I ran for some time with a thermostat that was jammed closed and up to 2000rpm. there was no problem but at higher revs. it overheated. At lowish power the cylinder head is cooled sufficiently by conduction into the exhaust manifold.

 

[dancrane]

A bolt has a threaded portion and a smooth section.

A machine screw, often called a screw, is threaded all the way from the tip to the head

A wood screw, also often called a screw, has a much coarser thread and is tapered from tip to head.

Got it. I think...

 

[findus]

The illustration of this that I like is a steam train standing still with the wind blowing at 90 degrees across it. The steam/smoke from it blows away at 90 degrees - this is the true wind. The train begins to move forward, the steam/smoke trail moves back. The faster the train moves, the further aft the trail moves. That is the apparent wind.

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

 

[Tranona]

Got it. I think...

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.