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Old 21-03-2007, 15:44   #16
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Originally Posted by FrankZ
In a similar vein. My bow is not a straight line (profile viewed from the side) but curved. I would suspect there is a name for this (and probably more math to do). Anyone know what this would be called?

Clipper Bow.
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Old 21-03-2007, 18:58   #17
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To Sum Up

plumb bow: straight vertical line from deck to water.
spoon bow: as its name suggests, a convex curve: vertical near the deck, then sweeps back to an angled entry point at the waterline.
raked bow: a straight line, down & back to an entry point abaft of the stem.
clipper bow: a rather sharp concave curve, leading back and down from the stem, either establishing a raked front edge or quickly breaking into a rather gentle convex curve (spoon) that flows to the waterline.

Within each type, there is infinite variation: gentle spoon bows, near-plumb bows (technically a slight rake), sharply raked bows, radical clipper bows, etc.

Now, lemme know if something here isn't right.
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Old 21-03-2007, 21:04   #18
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The definition of sheer given above is certainly accurate. To bring it down to layman's terms...when people talk about sheer they are referring to the line of the hull and deck joint when the boat is viewed in profile.
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Old 22-03-2007, 01:07   #19
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The plumb bow is somtimes known as a "Sharpie bow"
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Old 22-03-2007, 01:28   #20
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This is a "Cutaway bow" Found on only a few aircraft carriers.Not good at speed but,It scares the hell out of destroyer captains.Mudnut.
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Old 22-03-2007, 02:19   #21
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Just to keep things straight, here's a picture from an old sailing encyclopedia "One-Design & Offshore Yachtsman"
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Old 22-03-2007, 07:01   #22
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As the owner of a plumb bow cruiser, have to say I much prefer not just the look, but also the added volume down below this stem design allows.

The plumb bow retro look of say The Oyster 42 Power Yacht - or the sailing designs of say Greg Elliot - are to my mind synonymous with faster designs.

Also as one who has owned yachts with various angles of bow rake - can say the notion they might create more spray is a nonsense - however I do accept the amount of 'reserve boyancy' is reduced.

But remember the static boyancy is invariably greater all the time if one has a fuller bow section afforded by such a design.

At the end of the day its what you like and what you think looks good.....and its great to have the variation around.

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Old 22-03-2007, 07:37   #23
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Wouldn’t the reserve buoyancy only be reduced if one used the extra interior space (afforded by the plumb bow) for storage?
If loading restraint is exercised, the total buoyancy would actually be greater than the various raked bows offer.
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Old 22-03-2007, 08:36   #24
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John - I defer to your experience on the spray issue. On static buoyancy though, I don't know how you figure that; the displaced volume is the same for boats of equal displacement regardless of the bow shape. A fuller bow (having greater displaced volume forward) may reduce the tendency to pitch, or at least require a greater moment to pitch, but in no way changes the amount of buoyancy.

Gord - I see "reserve buoyancy" as the total watertight volume above the waterline. So raked bows, greater sheer and hull flare all add to reserve buoyancy. IIRC, timber carriers also include the volume of wood as deck cargo into "reserve buoyancy"; it seems counter-intuitive until you give it some thought. As with loading up your storage space - the weight of the stores will be seen as increased displacement equal to the loss of reserve buoyancy.

Mudnut - what's the story behind the pic? Carrier/destroyer interractions are pretty commonplace; most destroyer guys don't realize how fast and manoeuvrable the carriers are, until they have a close call.


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Old 22-03-2007, 08:43   #25
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Quote:
Originally Posted by FrankZ
Boats are like women, they should have curves and be well proportioned.
Boats are also like men... the longer the better....


Just had to represent the "Why do folks buy large" crowd.....
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Old 22-03-2007, 09:27   #26
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Sharpies

Quote:
Originally Posted by cooper
The plumb bow is somtimes known as a "Sharpie bow"
....because the Sharpie - which is a two / three man racing dinghy still popular in Australia - has a plumb bow.
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Old 22-03-2007, 09:33   #27
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Hi Lodesman, you said.....

John - I defer to your experience on the spray issue. On static buoyancy though, I don't know how you figure that; the displaced volume is the same for boats of equal displacement regardless of the bow shape. A fuller bow (having greater displaced volume forward) may reduce the tendency to pitch, or at least require a greater moment to pitch, but in no way changes the amount of buoyancy.

Agreed 100%, and appreciate the way you've clarified what I was trying to get over.

Cheers
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Old 23-03-2007, 03:21   #28
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Quote:
Originally Posted by Lodesman
John - I defer to your experience on the spray issue. On static buoyancy though, I don't know how you figure that; the displaced volume is the same for boats of equal displacement regardless of the bow shape. A fuller bow (having greater displaced volume forward) may reduce the tendency to pitch, or at least require a greater moment to pitch, but in no way changes the amount of buoyancy.

Gord - I see "reserve buoyancy" as the total watertight volume above the waterline. So raked bows, greater sheer and hull flare all add to reserve buoyancy. IIRC, timber carriers also include the volume of wood as deck cargo into "reserve buoyancy"; it seems counter-intuitive until you give it some thought. As with loading up your storage space - the weight of the stores will be seen as increased displacement equal to the loss of reserve buoyancy.

Mudnut - what's the story behind the pic? Carrier/destroyer interractions are pretty commonplace; most destroyer guys don't realize how fast and manoeuvrable the carriers are, until they have a close call.


Kevin
Kevin,82 sailors out of a compliment of 293 died when Melbourne collided with HMAS Voyager on the 10th Feb 1964 during exercises,Voyager sank.Melbourne started life as HMS(English) Majestic 15-4-43.Launched on 25-2-45.Renamed HMAS Melbourne 28-10-55.She sank two destroyers in the course of her commision,the other being USS Frank E Evans in the china sea on the 3-6-69,with a loss of 74 lives.In both cases the Destroyers were at fault,cutting accross her bow while she was at flying stations at night.Melbourne was our flagship.Yep ya don't mess with the big ladies of the sea thats for sure.Mudnut.
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Old 23-03-2007, 06:31   #29
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Quote:
Originally Posted by Lodesman
Gord - I see "reserve buoyancy" as the total watertight volume above the waterline. So raked bows, greater sheer and hull flare all add to reserve buoyancy. Kevin
I don't see how rake can increase reserve boyancy.
Boats are compared on their length overall and not by the wl length, bowsprits excluded. If the stem is cut away or angled it is removing volume from the area imediately above the waterline. Take an extreme case. Imagine 2 profiles of equal length overall, one with a stem that slopes back to the mid point of the vessel and the other plumb. The plumb bow must have more boyancy foreward. It will also have a more foreward distribution of static displacement that will serve to further resist pitching.

Flare in the traditional sence is a concave surface of the hull sides in the for'd region. This serves to reduce reserve boyancy. A reverse flare where the sides rapidly widen with a convex curve to the sheer would increase reserves.

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Old 23-03-2007, 07:13   #30
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Whimsical,

You're comparing apples to oranges - static buoyancy and reserve buoyancy are two different kettles of fish. I agree that a plumb bow will have a more forward distribution of buoyancy that better serves to resist initial pitching moment. But reserve buoyancy is the watertight volume above the waterline - a raked bow of the same fineness as a plumb bow will have more volume above the WL, therefore more reserve buoyancy. Induce a forward pitching moment (ie. shove the bow down) with a given amount of force and the bow with less reserve will go down further.

Flare in the traditional sense is the increase in beam from waterline to the deck. The opposite is "tumblehome". I don't recall terms for convex and concave hullforms, other than what has been mentioned, though I think the term "fuller" is often applied to convex hulls. And yes, a convex hullform would have more reserve buoyancy than a concave one, where all other parameters were equal.


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