dman
09-19-2005, 02:07 PM
What is the reasoning for having a bow that comes straight down to the water besides getting more waterline.I do not know the technical term but this doesn`t seem like a good thing to me.Comments
View Full Version : sailboat bows
Skippy
09-19-2005, 02:18 PM
It's easier for water to split off to either side of the boat than to go under it. Any water flowing underneath the hull must displace the water already there, wasting energy on sideways motion (athwartship). What you really want to do is slice the water efficiently, which is what the plumb bow does. An angled bow will tend to push the water downward, and has more to do with getting up waves or planing.
dougfrolich
09-19-2005, 03:30 PM
Plumb Bows are a way of Maximizing waterline length (for a given overall length). Thats why you see plumb bows on boats designed to a rule that restrict LOA. Plumb bows also tend to allow a narrow entry, and added volume, compared to a more "traditional" shape.
SailDesign
09-19-2005, 05:54 PM
dman,
What the others have failed to mention, and which will make much of it clearer, is that a longer waterline length, in general, makes for a faster boat. This may sound strange, but it is true. (long story - see other threads)
Thus, if your length is limited, then you want a plumb (upright) bow to make the most of it.
Steve
What the others have failed to mention, and which will make much of it clearer, is that a longer waterline length, in general, makes for a faster boat. This may sound strange, but it is true. (long story - see other threads)
Thus, if your length is limited, then you want a plumb (upright) bow to make the most of it.
Steve
dman
09-19-2005, 06:06 PM
Thanks for the replys,I understand the extra waterline for more speed but what about the effects on a cruising design.Why do you not see ships with that design?
Skippy
09-19-2005, 06:10 PM
Read the original post SD, he understands the waterline/speed issue. My understanding is that a square forefoot tends to trip the boat up when running before a gale. That's a big problem, since if you get caught in a blow, running may be your only option.
water addict
09-20-2005, 06:34 AM
Thanks for the replys,I understand the extra waterline for more speed but what about the effects on a cruising design.Why do you not see ships with that design?
You rarely see ships with plumb bows, but it has been done. A conventional bow, with flare, keeps green seas off the deck until you get in the extreme rough stuff. Hence it protects the deck gear and any cargo that may be stowed above deck, like containers, from getting smashed by the seas.
You rarely see ships with plumb bows, but it has been done. A conventional bow, with flare, keeps green seas off the deck until you get in the extreme rough stuff. Hence it protects the deck gear and any cargo that may be stowed above deck, like containers, from getting smashed by the seas.
Raggi_Thor
09-20-2005, 07:02 AM
Ships vith vertical bow?
Take a look at this :-)
http://www.marinelog.com/DOCS/NEWSMMV/2005apr043.html
Take a look at this :-)
http://www.marinelog.com/DOCS/NEWSMMV/2005apr043.html
Milan
09-20-2005, 09:27 AM
Plumb bows are nothing new, many traditional working boats had them. British pilot cutters for example. As for ships, there was a period when they were not only popular, but even dominant, (Titanic for example).
Aside from advantages in racing classes measured by the over all length, they are also simply most efficient, in terms of material usage. (The reason they were used by working boats and why they could be interesting for modern cruising boats).
Milan
Aside from advantages in racing classes measured by the over all length, they are also simply most efficient, in terms of material usage. (The reason they were used by working boats and why they could be interesting for modern cruising boats).
Milan
lewisboats
09-20-2005, 09:55 AM
Ships vith vertical bow?
Take a look at this :-)
http://www.marinelog.com/DOCS/NEWSMMV/2005apr043.html
A new meaning to the term "Bluff Bowed" ;) .
Steve
Take a look at this :-)
http://www.marinelog.com/DOCS/NEWSMMV/2005apr043.html
A new meaning to the term "Bluff Bowed" ;) .
Steve
usa2
09-20-2005, 03:19 PM
Ocean Cruisers and/or racers dont tend to use them because the waterline issue and the fact that in a seaway having overhangs of any sort becomes very uncomfortable and can knock the boat off course.
SuperPiper
09-20-2005, 08:02 PM
A plumb bow can have a finer entry.
I have always wondered why bows are not razer sharp from waterline to deck. Even modern racing boats will have a fine entry but will have a large radius at the deck level. Is this something to do with increasing the volume (and bouyancy) as a bow dips under a wave? Is it part of the rating game? Does it have to do with angle of attack as a hull heels or as the bow is submerged?
I am convinced that it is not a structural consideration.
I have always wondered why bows are not razer sharp from waterline to deck. Even modern racing boats will have a fine entry but will have a large radius at the deck level. Is this something to do with increasing the volume (and bouyancy) as a bow dips under a wave? Is it part of the rating game? Does it have to do with angle of attack as a hull heels or as the bow is submerged?
I am convinced that it is not a structural consideration.
PAR
09-21-2005, 12:37 AM
A bow profile is one of the most distinctive features the eye is drawn to when looking at a yacht. The style a vessel carries in these lines is more then their function (which has only been lightly touched on here). Racers and commercial vessels are duty bound with the tasks asked and their bow profiles typically reflect this. A cruiser isn't selected because it takes most advantage of available LWL, but many other, usually considerably more important constraints (to them), such as reserve buoyancy in a plunging sea, ample rode and chain locker stowage, a pretty place to hang trail boards, etc.
Bows come in all shapes and types. Reversed, submerged, bulbed, clipper, spoon, plumb, Indian head, etc. Some are pure styling exercises, others an attempt to beat racing rules or increase efficiency or other element, in this area of the design. The same is true of sectional and plan shapes used in the bow. A great deal of thought goes into a boat's entry, which covers several issues of concern in this location. Some will sacrifice a fraction of a knot in hull speed or cargo capacity, to make this area look nice, others can't afford this.
Bows come in all shapes and types. Reversed, submerged, bulbed, clipper, spoon, plumb, Indian head, etc. Some are pure styling exercises, others an attempt to beat racing rules or increase efficiency or other element, in this area of the design. The same is true of sectional and plan shapes used in the bow. A great deal of thought goes into a boat's entry, which covers several issues of concern in this location. Some will sacrifice a fraction of a knot in hull speed or cargo capacity, to make this area look nice, others can't afford this.
jtsailingaway
09-21-2005, 01:22 AM
I'm not an architect (as I'm sure will be all to obvious), but it seems to me that a plumb bow or even some of the more excessive examples here are requisites of "submarines"! IE: vessels designed to submerge. It makes sense to me that it is more efficient to a point to slice through the water than push it down, but at sea isn't it more important to keep the deck above water! Most racing (which I'm also no final word on) seems to be done in controlled environments or at least many times dependent on weather and conditions. When cruising, out at sea, and things get rough, you really can't just postpone the event. Isn't one of the main ideas to keep the water off of, and especially out of the boat?
dman
09-21-2005, 08:29 AM
When cruising, out at sea, and things get rough, you really can't just postpone the event. Isn't one of the main ideas to keep the water off of, and especially out of the boat? end quote This is what I am trying to find out.Which type is more seaworthy?I know it all has to work together(hull shape) but has anyone come out with any data to which is better suited to extreme conditions.
Alixander Beck
09-21-2005, 09:17 AM
I'm not an architect (as I'm sure will be all to obvious), but it seems to me that a plumb bow or even some of the more excessive examples here are requisites of "submarines"! IE: vessels designed to submerge. It makes sense to me that it is more efficient to a point to slice through the water than push it down, but at sea isn't it more important to keep the deck above water! Most racing (which I'm also no final word on) seems to be done in controlled environments or at least many times dependent on weather and conditions. When cruising, out at sea, and things get rough, you really can't just postpone the event. Isn't one of the main ideas to keep the water off of, and especially out of the boat?
Now you bring into play the height of freeboard (or whatever the correct name is for the distance from LWL to deck) having a longer freeboard with a plumb bow may not plunge the bow under the waves as by the time the freeboard is submerged the wave is sufficiently far enough beneath the hull for it to displace the water and not cut through it. I think it would enable the boat to track better in this instance.
Although having a short freeboard without a plumb bow may look as if it will ride over the waves better - but that may be only for a given wave length in relation to the freeboard. Anything more might be able to swamp the bow.
Personally I find it easier to visualize this design feature on a canoe as the movements and entries are so responsive it is easy to achieve an idea of how the design affects the boat.
Now you bring into play the height of freeboard (or whatever the correct name is for the distance from LWL to deck) having a longer freeboard with a plumb bow may not plunge the bow under the waves as by the time the freeboard is submerged the wave is sufficiently far enough beneath the hull for it to displace the water and not cut through it. I think it would enable the boat to track better in this instance.
Although having a short freeboard without a plumb bow may look as if it will ride over the waves better - but that may be only for a given wave length in relation to the freeboard. Anything more might be able to swamp the bow.
Personally I find it easier to visualize this design feature on a canoe as the movements and entries are so responsive it is easy to achieve an idea of how the design affects the boat.
jonsailor
09-21-2005, 05:15 PM
Most od my designs have a straight stem bow for the obvious reasons of speed but it does detract from cruising boats for silly reasons like banging your anchor on the hull when hauling it back aboard. Generally, the straight bow slams a bit more in a sea way and the long over hang bow can be a bit softer motion in a seaway because the entry is softer and the reserve bouyancy is more gracefull.
Saying this, I am sticking with the straight bow as with most of my designs
www.sayerdesign.com
Saying this, I am sticking with the straight bow as with most of my designs
www.sayerdesign.com
FAST FRED
09-22-2005, 05:46 AM
"Thanks for the replys,I understand the extra waterline for more speed but what about the effects on a cruising design.Why do you not see ships with that design?"
Ships are designed for a particular cruising speed ., not top speed.
Large stuff , oil tankers ect MUST travel with a midship wave , they would snap in two at "hull speed" .
Its cheaper to just build bigger and go at a moderate speed than accept the weight of a stronger hull and the attendant fuel bill of fast travel.
Different for the Navys of the world , they have no fuel bills to worry about.
FAST FRED
Ships are designed for a particular cruising speed ., not top speed.
Large stuff , oil tankers ect MUST travel with a midship wave , they would snap in two at "hull speed" .
Its cheaper to just build bigger and go at a moderate speed than accept the weight of a stronger hull and the attendant fuel bill of fast travel.
Different for the Navys of the world , they have no fuel bills to worry about.
FAST FRED
jam007
09-22-2005, 11:37 AM
One advantage of the long overhang bow is when mooring the boat in the natural harbours of archipelagos.
MikeJohns
09-23-2005, 08:06 AM
When cruising, out at sea, and things get rough, you really can't just postpone the event. Isn't one of the main ideas to keep the water off of, and especially out of the boat? end quote This is what I am trying to find out.Which type is more seaworthy?I know it all has to work together(hull shape) but has anyone come out with any data to which is better suited to extreme conditions.
overhangs give more reserve bouyancy and a softer ride at sea for a given WL length but there are many factors to consider here , suffice to say it is a complex issue and depends on the rest of the hullform.
overhangs give more reserve bouyancy and a softer ride at sea for a given WL length but there are many factors to consider here , suffice to say it is a complex issue and depends on the rest of the hullform.
SailDesign
09-23-2005, 10:24 AM
overhangs give more reserve bouyancy and a softer ride at sea for a given WL length
But the marina charges by LOA, and the plumb bow gives more reserve buoyancy per foot of LOA. Your call :)
Steve "just another sample of the complexity of the whole argument"
But the marina charges by LOA, and the plumb bow gives more reserve buoyancy per foot of LOA. Your call :)
Steve "just another sample of the complexity of the whole argument"
LP
09-23-2005, 10:29 AM
Another consideration in design the bow of the craft is in the shape of the forward sections. Are they exhibiting "flare" or "flam"? See the attached JPEG. Flam sections have an initial rapid increase in reserve bouyancy with a reduction in the rate of increase with increased submersion. i.e. They respond to wave entry sooner and the the response remains fairly constant with increased submersion. A flared has a slow increase in reserve bouyancy so it takes longer to respond to wave penetration. Also, there is a rapid increase in reserve bouyancy as submersion approaches the sheer which accentuates the upwards accelations of the bow as it responds to the wave. Flammed sections start their response sooner and at a more stable rate than flared. Flared forward sections will be less comfortable in heavy conditions when compared to flamed sections. As to whether a flammed section is less likely to submerge than a flared section, I'll leave that response to the experts.
I'm going to go out on a limb here. Flared are generally associated with larger deck areas forward. I which case, flared forward sections may have more difficulty in responding to submersion than flammed sections. For the same deck area, flammed forward sections will carry more bouyance (and more interior volume) than flared sections.
I hope this wasn't too much of a tangent for you, but the boat as a whole has to be considered. I like plumb stems and many a classic design carries them. Overhanging stems can be overated. Herreshoff took them to the extreme. They are beautiful to look at, but they are a rules beating design and I don't mean to imply anything bad by saying it. It was quite the design coup. As the craft heeled, his craft would submerge a bit and actually increase the effective waterline.
I'm going to go out on a limb here. Flared are generally associated with larger deck areas forward. I which case, flared forward sections may have more difficulty in responding to submersion than flammed sections. For the same deck area, flammed forward sections will carry more bouyance (and more interior volume) than flared sections.
I hope this wasn't too much of a tangent for you, but the boat as a whole has to be considered. I like plumb stems and many a classic design carries them. Overhanging stems can be overated. Herreshoff took them to the extreme. They are beautiful to look at, but they are a rules beating design and I don't mean to imply anything bad by saying it. It was quite the design coup. As the craft heeled, his craft would submerge a bit and actually increase the effective waterline.
marshmat
09-23-2005, 05:04 PM
There's been a bit of mention of the desirability of keeping the deck above water. I won't argue that every sailor wants the deck to stay dry. But in the ocean, there will be waves that will come over the bow. When this happens you want that water to get off your deck quickly and have your bow rise back up quickly. A sharply swept bow with a lot of flare is not exactly conducive to this. Personally I prefer a narrow bow, either swept or plumb, with a cambered deck and a deckhose shaped to allow the boat to "submarine" without harm when things go bad. If the bow stuffs into a wave and can't easily get back out you are in serious trouble. So my vote goes to fine bows with a lot of reserve buoyancy.....
yokebutt
09-23-2005, 08:47 PM
Marshmat is on the right track, just leave the transom open so the wet stuff can get off the boat.
Yoke.
Yoke.
usa2
09-23-2005, 08:59 PM
keeping the boat above water is always a good idea...
PAR
09-24-2005, 01:30 AM
Flare in the bow sections permits the stem to drop quickly in a wave and then suddenly gain a lot of reserve. In rough weather this can cause damage, so excessive flare should be avoided. Flam on the other hand brings on reserve quicker as the bow plunges and increases the amount of buoyancy gently, with much less risk of "canning" or stoving in the forward section in a rough sloshing. Flare can have a dramatic effect on usable deck space in the eyes of the boat and can be easily taken to extremes, with the boat having to tolerate server slamming loads in some conditions. Flare is a fair weather shape, in my opinion, good at slapping down chop and spray, but easily over matched in harsher seas. Neither of these (flam and flare) has much to do with the bow profile.
It is particularly true that the underbody profile of the hull will have considerable influence on the sectional shapes in the ends of the yacht. Racing rules force decisions in some of the shapes used, but aside from this, client needs in concert with designer's ideas, generally generate the wide array of bow profiles used currently, as it has since the first boat was designed for a customer.
The clipper bow was once the most scientific available and many words bestowing it's virtues were written. In fact, each profile will have it's fans and opponents, both equally convinced their ideas and rational are correct. Bow profiles, just like the vast number of other compromises made in the design process, try to meet the requirements of it's intent. An ice breaking research vessel's bow will be decidedly different then what may be asked of a ocean cruising passage maker's. These two bows, may have boats of similar shapes, displacements and other important comparisons, but the passage maker is relieved of the ice breaking burdens, which may have limited the research vessel's bow shape.
So in answer to your questions Dman, there is no truly supreme bow profile that will be the best thing to have at sea. Shedding water off a recently dunked deck is a function of many things, bow shape being one, entry, hull form, freeboard, deck crown and rail height are a few of the other considerations also.
For what it's worth, a 400' LWL vessel steaming along at 27 knots is doing hull speed, and it is regularly done. I personally clocked the USS Nimitz doing over 50.
It is particularly true that the underbody profile of the hull will have considerable influence on the sectional shapes in the ends of the yacht. Racing rules force decisions in some of the shapes used, but aside from this, client needs in concert with designer's ideas, generally generate the wide array of bow profiles used currently, as it has since the first boat was designed for a customer.
The clipper bow was once the most scientific available and many words bestowing it's virtues were written. In fact, each profile will have it's fans and opponents, both equally convinced their ideas and rational are correct. Bow profiles, just like the vast number of other compromises made in the design process, try to meet the requirements of it's intent. An ice breaking research vessel's bow will be decidedly different then what may be asked of a ocean cruising passage maker's. These two bows, may have boats of similar shapes, displacements and other important comparisons, but the passage maker is relieved of the ice breaking burdens, which may have limited the research vessel's bow shape.
So in answer to your questions Dman, there is no truly supreme bow profile that will be the best thing to have at sea. Shedding water off a recently dunked deck is a function of many things, bow shape being one, entry, hull form, freeboard, deck crown and rail height are a few of the other considerations also.
For what it's worth, a 400' LWL vessel steaming along at 27 knots is doing hull speed, and it is regularly done. I personally clocked the USS Nimitz doing over 50.
usa2
09-24-2005, 08:16 AM
i dont mean to dispute you, but from what i have read and seen the top speed for a Nimitz class carrier is around 36 knots. Where did you see this?
Skippy
09-24-2005, 01:20 PM
Setting aside generalities about different solutions for different problems, this is a good discussion and an interesting topic. My personal interest is mostly dinghies and cruisers, but it's also nice to have a feel for what the variables are over a wider range of applications.
One relationship between bow width and vertical fullness is how the ratio between them affects helm balance when heeled. Back in the 1960s, Francis Chichester's Gipsy Moth IV had a fine, plumb bow with a deep, square forefoot. Any time the boat got pushed over more than 30 degrees, the bow lost lateral surface area and developed a wicked lee helm at the worst time possible. Newer designs seem to keep the two dimensions more evenly matched.
One relationship between bow width and vertical fullness is how the ratio between them affects helm balance when heeled. Back in the 1960s, Francis Chichester's Gipsy Moth IV had a fine, plumb bow with a deep, square forefoot. Any time the boat got pushed over more than 30 degrees, the bow lost lateral surface area and developed a wicked lee helm at the worst time possible. Newer designs seem to keep the two dimensions more evenly matched.
marshmat
09-24-2005, 04:11 PM
A note on the big-ship side of things... with nuclear power there can be quite a big difference between "full speed" and "flank speed", the latter being absolute maximum possible engine output, no holds barred. As for the tankers/freighters- there's a big difference between a 115,000 tonne aircraft carrier and a 475,000 tonne supertanker. Such tankers, if taken to hull speed, would actually crumple in half in the middle for lack of support due to the bow wake. So they travel slow with a midship wave or two. Carriers are strong enough to reach hull speed, but never do because none of the surrounding battle group can keep up.
gggGuest
09-24-2005, 08:11 PM
The actual section shape further aft, combined with the waterlines has a significant affect on the bow profile. If you are planning to draw the waterlines parallell you tend to end up with a raked spoon bow. With a vertical bow the waterlines tend to finer at the bottom than the top. If you have flared sections you tend to end up with a clipper bow and so on...
Bergalia
09-25-2005, 07:39 AM
Sharp straight bows have long been favoured by the Scots for fishing the North Sea and beyond (rough, rough waters). In 1879 the Zulu appeared off Fraserburgh (North East coast above Aberdeen). She had the sharp straight bow of a Fifie and the 45 degree raked stern of a Scarfie, which the designers considered the best of both worlds for North Sea, Atlantic conditions. Up to 80 feet long, double masted, double ended (are you listening Fast fred) they were among the fastest, safest sailing work boats of their day. Fifty years ago I was lucky enough to crew one for a season around Iceland. Sure I was cold - but fully confident of her capabilities (after all she was a century old then). :rolleyes:
Seafarer24
09-27-2005, 09:14 AM
All this talk of "reserve bouyancy" for keeping your bow about a wave is rather BS. If you wanted to keep the bow up, you'd have AS MUCH BOUYANCY AS POSSIBLE, as low as possible, to keep the bow from diving in the first place.
So where do we end up with swept bows? Racing boats, of course. When the rules measured the LWL, those long overhangs could beat the rule by only coming into effect when the boat was heeled. Also, in light air where nothing will reach its hull-speed, less wetted-surface rules the day.
Where does the anchor rode get stored? In the bow, of course. Where is the worst place to concentrate the weight of all that chain? In the bow, of course. Now, take all that weight, keep it placed up high, and give it two feet of leverage. That is what a swept bow does for you.
With a plumb bow the weight of that chain can be placed much lower, and there is bouyancy directly underneath it to support it. If you want to keep your anchor from banging the topsides of the boat, you'll have to use a short sprit with a roller to launch and retrieve. Your boat will also have a higher hull speed, you can always reef if this bothers you.
Taking this to the "extreme" are the new racing catamarans. Their (ever-so-slightly reverse-swept) bows are wider at the bottom than the top! The bouyancy comes on even quicker this way. The shape allows the bow to punch through waves at high speeds very well, and rise up quickly when the bow is submerged. Sure, they are a wet ride, but so are the more conventionally shaped catamarans when going over 20 knots.
So where do we end up with swept bows? Racing boats, of course. When the rules measured the LWL, those long overhangs could beat the rule by only coming into effect when the boat was heeled. Also, in light air where nothing will reach its hull-speed, less wetted-surface rules the day.
Where does the anchor rode get stored? In the bow, of course. Where is the worst place to concentrate the weight of all that chain? In the bow, of course. Now, take all that weight, keep it placed up high, and give it two feet of leverage. That is what a swept bow does for you.
With a plumb bow the weight of that chain can be placed much lower, and there is bouyancy directly underneath it to support it. If you want to keep your anchor from banging the topsides of the boat, you'll have to use a short sprit with a roller to launch and retrieve. Your boat will also have a higher hull speed, you can always reef if this bothers you.
Taking this to the "extreme" are the new racing catamarans. Their (ever-so-slightly reverse-swept) bows are wider at the bottom than the top! The bouyancy comes on even quicker this way. The shape allows the bow to punch through waves at high speeds very well, and rise up quickly when the bow is submerged. Sure, they are a wet ride, but so are the more conventionally shaped catamarans when going over 20 knots.
LP
09-27-2005, 07:53 PM
En boca cerada, no entran moscas.
MikeJohns
09-27-2005, 09:11 PM
Things really are not that simple Seafarer , the red comments are mine.
All this talk of "reserve bouyancy" for keeping your bow about [above ?] a wave is rather BS. If you wanted to keep the bow up, you'd have AS MUCH BOUYANCY AS POSSIBLE, as low as possible, to keep the bow from diving in the first place.
There is more to longitudinal stability/matacentric height than the amount of bouyancy in stem area. Consider also the longitudinal mass distribution of the vessel and the inertial component , it is a dynamic event.
You must also consider a sea going vessel will usually be in continuos wave trains, higher reserve bouyancy lower down can give high accelerations in the pitching characteristic and lead to a vessel that is prone to hobby-horsing. This can be a problem with short ended vessels unless they have a high inertia ie are extremely heavy such as Bergalia's work boats.
long overhangs coming into effect when the boat was heeled. Also, in light air where nothing will reach its hull-speed, less wetted-surface rules the day.
Sounds like a plus
Where does the anchor rode get stored? In the bow, of course. Where is the worst place to concentrate the weight of all that chain? In the bow, of course. Now, take all that weight, keep it placed up high, and give it two feet of leverage. That is what a swept bow does for you.With a plumb bow the weight of that chain can be placed much lower, and there is bouyancy directly underneath it to support it.
With a plumb stem you want to get the weight well back too.
You can store the chain low with any bow shape . just a matter of where you put the winch & chain locker.
If you want to keep your anchor from banging the topsides of the boat, you'll have to use a short sprit with a roller to launch and retrieve. Your boat will also have a higher hull speed
A higher hull speed than what?
In a cruising design with a large sail area the angled stem gives a good start to providing a distant forestay attachment and enough of a sail plan fwd so you can get enough forefoot to give her reasonable directional stability.
Taking this to the "extreme" are the new racing catamarans. Their (ever-so-slightly reverse-swept) bows are wider at the bottom than the top! The bouyancy comes on even quicker this way.
They are actually wave cutting shapes with lower reserve bouyancy , if you can reduce the pitching then you can go faster.
You also need to consider the damping characteristics overall of the hull form, what are the stern sections like?
The shape allows the bow to punch through waves at high speeds very well, and rise up quickly when the bow is submerged. Sure, they are a wet ride, but so are the more conventionally shaped catamarans when going over 20 knots.
There is a big difference between ships catermarans and sailing mono-hulls the requirements are not comparable.
Overall their seems to be some confusion on the reserve bouyancy issue. The longitudinal restoring moment increases more gently and with far more reserve volume in the raked stem than the plumb bow for a given WL length. Lightweight boats benefit form a plumb stem as it keeps the VCG lower with less deck and topsides fwd. Marina requirements also favour a shorter overall boat so for a given LWL the plumb stem wins.
Also consider the freeboard and total required reserve bouyancy, a low windage hull will need to make up the reserve bouyance with overhanges, overhangs also add to the usable interior voume. Overhangs cost very little in terms of materials in the construction , they give a much more usable deck area fwd for a fine bowed craft, and offer a much more sensible collision zone for many floating hazards.
Also consideration needs to be given to construction material and method.
All this talk of "reserve bouyancy" for keeping your bow about [above ?] a wave is rather BS. If you wanted to keep the bow up, you'd have AS MUCH BOUYANCY AS POSSIBLE, as low as possible, to keep the bow from diving in the first place.
There is more to longitudinal stability/matacentric height than the amount of bouyancy in stem area. Consider also the longitudinal mass distribution of the vessel and the inertial component , it is a dynamic event.
You must also consider a sea going vessel will usually be in continuos wave trains, higher reserve bouyancy lower down can give high accelerations in the pitching characteristic and lead to a vessel that is prone to hobby-horsing. This can be a problem with short ended vessels unless they have a high inertia ie are extremely heavy such as Bergalia's work boats.
long overhangs coming into effect when the boat was heeled. Also, in light air where nothing will reach its hull-speed, less wetted-surface rules the day.
Sounds like a plus
Where does the anchor rode get stored? In the bow, of course. Where is the worst place to concentrate the weight of all that chain? In the bow, of course. Now, take all that weight, keep it placed up high, and give it two feet of leverage. That is what a swept bow does for you.With a plumb bow the weight of that chain can be placed much lower, and there is bouyancy directly underneath it to support it.
With a plumb stem you want to get the weight well back too.
You can store the chain low with any bow shape . just a matter of where you put the winch & chain locker.
If you want to keep your anchor from banging the topsides of the boat, you'll have to use a short sprit with a roller to launch and retrieve. Your boat will also have a higher hull speed
A higher hull speed than what?
In a cruising design with a large sail area the angled stem gives a good start to providing a distant forestay attachment and enough of a sail plan fwd so you can get enough forefoot to give her reasonable directional stability.
Taking this to the "extreme" are the new racing catamarans. Their (ever-so-slightly reverse-swept) bows are wider at the bottom than the top! The bouyancy comes on even quicker this way.
They are actually wave cutting shapes with lower reserve bouyancy , if you can reduce the pitching then you can go faster.
You also need to consider the damping characteristics overall of the hull form, what are the stern sections like?
The shape allows the bow to punch through waves at high speeds very well, and rise up quickly when the bow is submerged. Sure, they are a wet ride, but so are the more conventionally shaped catamarans when going over 20 knots.
There is a big difference between ships catermarans and sailing mono-hulls the requirements are not comparable.
Overall their seems to be some confusion on the reserve bouyancy issue. The longitudinal restoring moment increases more gently and with far more reserve volume in the raked stem than the plumb bow for a given WL length. Lightweight boats benefit form a plumb stem as it keeps the VCG lower with less deck and topsides fwd. Marina requirements also favour a shorter overall boat so for a given LWL the plumb stem wins.
Also consider the freeboard and total required reserve bouyancy, a low windage hull will need to make up the reserve bouyance with overhanges, overhangs also add to the usable interior voume. Overhangs cost very little in terms of materials in the construction , they give a much more usable deck area fwd for a fine bowed craft, and offer a much more sensible collision zone for many floating hazards.
Also consideration needs to be given to construction material and method.
Bergalia
09-27-2005, 10:41 PM
En boca cerada, no entran moscas.
So, Learpilot - ningunnas moscas en usted.... ;)
So, Learpilot - ningunnas moscas en usted.... ;)
LP
09-28-2005, 12:08 AM
No se. Como se dice? Yo no hablo espanol. :p
Bergalia
09-28-2005, 04:06 AM
No se. Como se dice? Yo no hablo espanol. :p
Then we're both faking it my friend Learpilot :D :D :D
Then we're both faking it my friend Learpilot :D :D :D
SailDesign
09-28-2005, 06:45 AM
if you can reduce the pitching then you can go faster.
That's what I've always said, but I have usually said it during an argument over weight in the ends (more weight in the ends = less pitching) and no-one believes me :)
Steve
That's what I've always said, but I have usually said it during an argument over weight in the ends (more weight in the ends = less pitching) and no-one believes me :)
Steve
LP
09-28-2005, 08:36 AM
Then we're both faking it my friend Learpilot :D :D :D
LWL ... no penso es LOA ... no ... oh yeah, it's .......
LOL :p :p :p
LWL ... no penso es LOA ... no ... oh yeah, it's .......
LOL :p :p :p
skinny boy
09-28-2005, 10:48 AM
Weight in the ends doesn't reduce pitching. It does resist pitching at the start more than light ends but continues to pitch more after it starts. In smooth water weight in the ends is not bad in a seaway that weight will make the boat want to hobby.
SailDesign
09-28-2005, 12:14 PM
Skinny boy,
Weight inthe ends increases pitch inertia, making the boat slower to start the pitch. In reality, it means that the boat is already out of the wave (in most cases) at a lower pitch angle than it would have been with light ends. At this point, the pitch acceleration flips to the other direction, thereby reducing pitch. The added advantage is that the rig can continue to work efficiently in air that is not greatly perturbed. The downside , of course, is that the hull will have added resistance as it goes through the wave rather than bobbing gayly over it :)
Steve "compromises, baby, compromises......"
Weight inthe ends increases pitch inertia, making the boat slower to start the pitch. In reality, it means that the boat is already out of the wave (in most cases) at a lower pitch angle than it would have been with light ends. At this point, the pitch acceleration flips to the other direction, thereby reducing pitch. The added advantage is that the rig can continue to work efficiently in air that is not greatly perturbed. The downside , of course, is that the hull will have added resistance as it goes through the wave rather than bobbing gayly over it :)
Steve "compromises, baby, compromises......"
LP
09-28-2005, 12:32 PM
It's interesting to see how this thread has morphed. It's all been good stuff, more the most part.
Talking about weight in the ends is delving into the subject on moments of inertia. A greater influence on pitching, than anchors in the bow, is the distribution of ballast.
A vessel with ballast distributed along the lenght of the keel will have a greater MOI (Moment Of Inertia) than a vessel with the ballast concentrated at midships/CG (and/or heavily ballasted). In real world terms, this means that the high MOI vessel will tend to plow though waves more than the other. In the extreme, the bow will bury itself before the righting moment can take effect to raise the bow to the oncoming wave. And yes, once the pitching starts, it takes more energy to stop it. Generally, the hind quarters offer more bearing than the bow and contribute (a great deal) to stopping the pitching once it has started. At any rate, a craft like this may actually be too stable along it's longitudinal axis. The worst case scenario, I think, would be to get into a wave train that was harmonic the the vessel's pitching. A situation that is easily alleviated though.
On the other hand, a vessel with a low MOI, ballast concentrated at it's CG (and/or lightly ballasted), but not as with a deep fin keel, will pitch easily. The bow will respond easily and quickly to wave action, possibly creating vessel that is irratic and uncomfortable to sail on. Not to mention the additional stresses put on rigging and equipment.
Ballast on a fin keel also serves to increase the longitudinal MOI though it is technically located about the CG. (The lawyer clause.)
Once again, it's all about trade-offs and compromises.
Talking about weight in the ends is delving into the subject on moments of inertia. A greater influence on pitching, than anchors in the bow, is the distribution of ballast.
A vessel with ballast distributed along the lenght of the keel will have a greater MOI (Moment Of Inertia) than a vessel with the ballast concentrated at midships/CG (and/or heavily ballasted). In real world terms, this means that the high MOI vessel will tend to plow though waves more than the other. In the extreme, the bow will bury itself before the righting moment can take effect to raise the bow to the oncoming wave. And yes, once the pitching starts, it takes more energy to stop it. Generally, the hind quarters offer more bearing than the bow and contribute (a great deal) to stopping the pitching once it has started. At any rate, a craft like this may actually be too stable along it's longitudinal axis. The worst case scenario, I think, would be to get into a wave train that was harmonic the the vessel's pitching. A situation that is easily alleviated though.
On the other hand, a vessel with a low MOI, ballast concentrated at it's CG (and/or lightly ballasted), but not as with a deep fin keel, will pitch easily. The bow will respond easily and quickly to wave action, possibly creating vessel that is irratic and uncomfortable to sail on. Not to mention the additional stresses put on rigging and equipment.
Ballast on a fin keel also serves to increase the longitudinal MOI though it is technically located about the CG. (The lawyer clause.)
Once again, it's all about trade-offs and compromises.
LP
09-28-2005, 12:35 PM
SailDesign,
Funny, you posted while I was writing. Hmmmmmmmmmm. :idea:
Funny, you posted while I was writing. Hmmmmmmmmmm. :idea:
Bergalia
09-28-2005, 11:38 PM
LWL ... no penso es LOA ... no ... oh yeah, it's .......
LOL :p :p :p
Hable más despacio, por favor. No hablo espanol. Habla usted inglés ? ;)
LOL :p :p :p
Hable más despacio, por favor. No hablo espanol. Habla usted inglés ? ;)
Raggi_Thor
09-29-2005, 04:26 AM
If you are unlucky (and you sometimes will be!) the boat with distributed weight (= slow period of pitch) will have a natural frequency that happens to be the same as the waves, so the pitch amplitude will grow and grow and grow....
On the other hand, traditionalists say you should have a heavy mast and the ballast in the bilges (as far out as possible) to make the boat roll slowly...
On the other hand, traditionalists say you should have a heavy mast and the ballast in the bilges (as far out as possible) to make the boat roll slowly...
Hans Friedel
09-29-2005, 01:56 PM
Do anyone know the story behind the shape of the AC bows
http://www.victorychallenge.com/show_pic.phtml?pic=gallery_big__582.jpg
http://www.victorychallenge.com/show_pic.phtml?pic=gallery_big__582.jpg
gggGuest
09-29-2005, 04:19 PM
Rules.
Hans Friedel
09-29-2005, 04:30 PM
Yes but anyhow they seems woork pretty OK. Even not being to sharp in shape.
Seafarer24
09-30-2005, 09:08 AM
It looks to me like it's designed to promote planing. I'd imagine that with all the sail these boats are carrying they'd need a very bouyant bow like that to keep from stuffing it under too often
usa2
09-30-2005, 03:04 PM
Alinghi won the last America's cup supposedly because their bow had more volume in it than TNZ. (TNZ falling apart also helped).
Robert Miller
10-01-2005, 10:33 AM
I've come late to this thread, but would like to contibute my thoughts and receive comment from others as they may...
Two quotes given above:
That's what I've always said, but I have usually said it during an argument over weight in the ends (more weight in the ends = less pitching) and no-one believes me
Steve
I believe you, absolutely. Weight in the ends increases moment of inertia because of increasing distance from the transverse axis of rotation.... and this decreases pitching by increasing force necessary to create the pitching motion. The transverse axis of rotation usually corresponds closely, but not exactly, to CG; (not exactly CG in a boat because of additional contribution to the axis of rotation due to CF and CB).
And ...
Weight in the ends increases pitch inertia, making the boat slower to start the pitch. In reality, it means that the boat is already out of the wave (in most cases) at a lower pitch angle than it would have been with light ends. At this point, the pitch acceleration flips to the other direction, thereby reducing pitch. The added advantage is that the rig can continue to work efficiently in air that is not greatly perturbed. The downside, of course, is that the hull will have added resistance as it goes through the wave rather than bobbing gayly over it
Steve "compromises, baby, compromises......"
I agree with most of this as well (and said almost the same stuff above). Comfort and continued forward drive absolutely result. The only point I would add is that "bobbing gayly over it" (increased pitching amplitude, beginning earlier, in boats with less weight in the ends) must ALSO (and does) decrease forward drive as would the drag of "added resistance as it goes through the wave" ... while providing a far less comfortable - more fatiguing - motion for the crew. "Bobbing gaily" does require that the hull travel uphill on the wave ahead, decreasing forward speed. (I guess the size of the wave, shape of the bow, forward underbody, and beam must all come into early play here.)
On balance, however, I should think that in most conditions ... the forward motion retarded by drag going through the wave, is less detrimental to foward speed than the quickly rising bow of a sailboat that must sail uphill over each wave.
Exceptions to my argument above are easy to imagine. But for most conditions ....... well, like Steve said, "Compromises, compromises..."
Robert
Two quotes given above:
That's what I've always said, but I have usually said it during an argument over weight in the ends (more weight in the ends = less pitching) and no-one believes me
Steve
I believe you, absolutely. Weight in the ends increases moment of inertia because of increasing distance from the transverse axis of rotation.... and this decreases pitching by increasing force necessary to create the pitching motion. The transverse axis of rotation usually corresponds closely, but not exactly, to CG; (not exactly CG in a boat because of additional contribution to the axis of rotation due to CF and CB).
And ...
Weight in the ends increases pitch inertia, making the boat slower to start the pitch. In reality, it means that the boat is already out of the wave (in most cases) at a lower pitch angle than it would have been with light ends. At this point, the pitch acceleration flips to the other direction, thereby reducing pitch. The added advantage is that the rig can continue to work efficiently in air that is not greatly perturbed. The downside, of course, is that the hull will have added resistance as it goes through the wave rather than bobbing gayly over it
Steve "compromises, baby, compromises......"
I agree with most of this as well (and said almost the same stuff above). Comfort and continued forward drive absolutely result. The only point I would add is that "bobbing gayly over it" (increased pitching amplitude, beginning earlier, in boats with less weight in the ends) must ALSO (and does) decrease forward drive as would the drag of "added resistance as it goes through the wave" ... while providing a far less comfortable - more fatiguing - motion for the crew. "Bobbing gaily" does require that the hull travel uphill on the wave ahead, decreasing forward speed. (I guess the size of the wave, shape of the bow, forward underbody, and beam must all come into early play here.)
On balance, however, I should think that in most conditions ... the forward motion retarded by drag going through the wave, is less detrimental to foward speed than the quickly rising bow of a sailboat that must sail uphill over each wave.
Exceptions to my argument above are easy to imagine. But for most conditions ....... well, like Steve said, "Compromises, compromises..."
Robert
Chickadee
10-01-2005, 06:30 PM
Hard to add anything to this thread, and calculations are quite useless, when you see the variety of waves. But I believe the idea of going through waves is valid for small seas and maxi boats mainly. More weight near the ends is not a good idea to increase seaworthyness. Then there is something about comparing load to curve areas (volumes), with less weight in the ends you can afford sharper lines so better performances.
So back to banging anchors and plumb bows. MY question is, what's better, adding a prominent structure (increased weight and LOA) or keeping cans of paint onboard ?
So back to banging anchors and plumb bows. MY question is, what's better, adding a prominent structure (increased weight and LOA) or keeping cans of paint onboard ?
Skippy
10-01-2005, 09:34 PM
"On balance, however, I should think that in most conditions ... the forward motion retarded by drag going through the wave, is less detrimental to foward speed than the quickly rising bow of a sailboat that must sail uphill over each wave."
I would find that very hard to believe. What goes up must come down -- the emphasis on going up the wave ignores the energy returned to the boat on the way down the other face. Plowing a hole in the wave, on the other hand, will generate lots of wave energy that does not return. Ignoring comfort for the moment, the only advantage I can see of not pitching is that the sails may flow more smoothly through the air.
Variety of waves is right. A small boat in big seas also doesn't have to worry much about pitching, as long the swells aren't breaking a lot. Going through a huge wave is out of the question, the little boat will have to "bob gayly". The most important situation is where the wavelength and boatlength are comparable.
I would find that very hard to believe. What goes up must come down -- the emphasis on going up the wave ignores the energy returned to the boat on the way down the other face. Plowing a hole in the wave, on the other hand, will generate lots of wave energy that does not return. Ignoring comfort for the moment, the only advantage I can see of not pitching is that the sails may flow more smoothly through the air.
Variety of waves is right. A small boat in big seas also doesn't have to worry much about pitching, as long the swells aren't breaking a lot. Going through a huge wave is out of the question, the little boat will have to "bob gayly". The most important situation is where the wavelength and boatlength are comparable.
JPC
10-02-2005, 02:01 AM
I should think it's a threshold question with both matters (and that's my seat of the pants sense, but let me know what I'm missing):
(this ignores a lot of other factors like the particulars of the hull shape, etc.)
1) Pitching: if the wave is small enough that the applicable inertia is still retarding the rise of the bow by the time the crest is reached (that is, the bow is still burying and hasn't 'caught up' with the rising wave yet), then the higher inertia produces the advantage and has reduced the total pitching;
however, if the wave is large enough that the bow has been accelerated, then the high inertia boat contributes to more pitching because the bow will keep rising after passing the crest.
(and I do mean acceleration, and not just that the boat as a whole has reached the angle of the wave face; in the latter case, it's a question of the balance point of the boat, not that it has developed rotational inertia)
2) Punching: hullform matter, which in conjuction with the pitching issue might dictate a 'sweet spot' for how much any boat should punch versus pitch for maximum efficiency in a given wave size. My experience has been that the fine bow'ed boats profit from punching (and they rise out of a buried bow situation more readily as well; as a general matter, the bow is not vertically yanked around as much by waves, and there's a bit of a wave-piercing value). But this obviously has a limit depending on hull/topsides shape (wet spreaders are too much ;) )
Kind of a lousy comment, I suppose, since what I'm saying is 'it depends' - but I think that's the case -depends on the wave amplitude and wavelength, along with the speed of the boat through x-degrees of the given waveform.
Sharp, light bows with a high knuckle take more driving attention in bigger waves, but the driving is very easy.
-JPC
(this ignores a lot of other factors like the particulars of the hull shape, etc.)
1) Pitching: if the wave is small enough that the applicable inertia is still retarding the rise of the bow by the time the crest is reached (that is, the bow is still burying and hasn't 'caught up' with the rising wave yet), then the higher inertia produces the advantage and has reduced the total pitching;
however, if the wave is large enough that the bow has been accelerated, then the high inertia boat contributes to more pitching because the bow will keep rising after passing the crest.
(and I do mean acceleration, and not just that the boat as a whole has reached the angle of the wave face; in the latter case, it's a question of the balance point of the boat, not that it has developed rotational inertia)
2) Punching: hullform matter, which in conjuction with the pitching issue might dictate a 'sweet spot' for how much any boat should punch versus pitch for maximum efficiency in a given wave size. My experience has been that the fine bow'ed boats profit from punching (and they rise out of a buried bow situation more readily as well; as a general matter, the bow is not vertically yanked around as much by waves, and there's a bit of a wave-piercing value). But this obviously has a limit depending on hull/topsides shape (wet spreaders are too much ;) )
Kind of a lousy comment, I suppose, since what I'm saying is 'it depends' - but I think that's the case -depends on the wave amplitude and wavelength, along with the speed of the boat through x-degrees of the given waveform.
Sharp, light bows with a high knuckle take more driving attention in bigger waves, but the driving is very easy.
-JPC
Tim B
10-02-2005, 08:34 AM
It is worth noting, that Adrian Thompson's work with wave-piercing hulls was highly sucessful on racing catamarans (especially on Team Phillips (until it broke)). On racing monohulls, the plum bow has the advantage that no matter how much wetted surface area is added going into a wave, it's nothing in comparison to the load (both slamming and wave drag) of a swept bow. If anybody wants a good example of this, race a LARK and a 420 in waves in a decent breeze.
Also, did someone mention plum bows giving wet boats? That's not a theory I agree with I'm afraid. Dryness has a lot more to do with the shape of the section near the deck-joint, and how the deck joint itself is put together. It is also dependant on the freeboard, heel angle and 101 other variables.
Tim B.
Also, did someone mention plum bows giving wet boats? That's not a theory I agree with I'm afraid. Dryness has a lot more to do with the shape of the section near the deck-joint, and how the deck joint itself is put together. It is also dependant on the freeboard, heel angle and 101 other variables.
Tim B.
FAST FRED
10-10-2005, 05:44 AM
Has anyone used the bulbous bow to change the pitch motions?
Seems there would be a big difference if it was dry or intentionally flooded.
Pumps are cheap too.
FAST FRED
Seems there would be a big difference if it was dry or intentionally flooded.
Pumps are cheap too.
FAST FRED
Tim B
10-10-2005, 08:18 AM
bulbous bow??? ouch, only works at one speed and think of the wetted surface area! hardly likely to be a gain there!!!
Tim B
Tim B
cyclops
10-10-2005, 11:11 AM
Can I give some first hand sightings in North Atlantic storms? Clear, sunny, smooth sailing day for all the USN destroyers in our unit. The aircraft carrier was getting the crap pounded out of her at the same time. Reason, at 900' she was on course in 1/4 to 1/2 mile long swells that would slowly lift her bow clear for 1/4 of her length then drop it into the base of the next wave. It would roll and cover 1/3 of her deck for about 30 seconds. the stern, screws and rudders were all visable and spinning. That long, wide, flaring bow and deck were a handicap.
cyclops
10-10-2005, 03:31 PM
I just realized that is one of the reasons why Super Tankers have vertical bows.
Omer
10-17-2005, 09:29 AM
Yes definately longer water lines make faster boats when approaching hull speeds. But faster boats are also penalised by the rating rules to give all boats an equal chance on the race cource. New rating rules like IRC are kept confidential in order not to produce rule optimised boats. Therefore are we any longer convinced and certain that for the same overall length a boat with a plumb bow maximising its waterline length is more advantageous than one which has an overhang and therefore a shorter waterline.
We simply do not know how the rule makers treat these parameters and favour one type over the other.
Probably the only way to find this out would be to create identical boats in every measurement and ratios except the bow profile and waterline length and race side by side enough number of times, switching crew as well and see whether one has a distinct advantage after rating corrections.
My point therefore is, it is probably no longer true to say that a longer waterline length is a sure recipe for success in race course any longer.
if there are any wiews to the contrary, i would be very interested to know.
We simply do not know how the rule makers treat these parameters and favour one type over the other.
Probably the only way to find this out would be to create identical boats in every measurement and ratios except the bow profile and waterline length and race side by side enough number of times, switching crew as well and see whether one has a distinct advantage after rating corrections.
My point therefore is, it is probably no longer true to say that a longer waterline length is a sure recipe for success in race course any longer.
if there are any wiews to the contrary, i would be very interested to know.
Stephen Ditmore
10-20-2005, 01:28 PM
I wrote an article on this question for Professional BoatBuilder a decade or more ago, advocating plum bows on "performance cruisers". Some have traditionally argued for raked bows in terms of "reserve bouyancy", but I believe that analysis to be flawed. It depends very much on what you assume is fixed, and what is varied, so it's a difficult issue to frame properly (and I'm not sure my article was altogether successful at explaining it).
The America's Cup question is related. Like the 12 meter (or "universal") rule before it, the IACC class essencially limits waterline length. This is taken a little above where the boat floats (half a meter above if I remember correctly). No hollows are allowed, so you can't just have a dimple there (Though New Zealand tried to get around this in the stern). You can, however, have a flat spot. Early in IACC class development there was "spoon bow" vs. "destroyer bow" competition. That was settled by the success of Laurie Davidson's solution in 2000, which was a compromise -- two knuckles with a flat spot between.
If you left displacement and sail area alone and, using the same deck, dropped a plum bow, it would be both faster AND have more reserve bouyancy (though the boat's center of gravity would be a little aft of optimum if you didn't move weight forward, which would cut the gain in reserve bouyancy down some). But the modified boat would measure too big to be a legal America's Cup boat.
Ted Brewer's objection to a plumb bow on a cruiser (in a letter to the editor taking exception to my article) was that bow overhang makes it easier to recover the anchor without damaging the hull!
The America's Cup question is related. Like the 12 meter (or "universal") rule before it, the IACC class essencially limits waterline length. This is taken a little above where the boat floats (half a meter above if I remember correctly). No hollows are allowed, so you can't just have a dimple there (Though New Zealand tried to get around this in the stern). You can, however, have a flat spot. Early in IACC class development there was "spoon bow" vs. "destroyer bow" competition. That was settled by the success of Laurie Davidson's solution in 2000, which was a compromise -- two knuckles with a flat spot between.
If you left displacement and sail area alone and, using the same deck, dropped a plum bow, it would be both faster AND have more reserve bouyancy (though the boat's center of gravity would be a little aft of optimum if you didn't move weight forward, which would cut the gain in reserve bouyancy down some). But the modified boat would measure too big to be a legal America's Cup boat.
Ted Brewer's objection to a plumb bow on a cruiser (in a letter to the editor taking exception to my article) was that bow overhang makes it easier to recover the anchor without damaging the hull!
Skippy
10-20-2005, 03:03 PM
Stephen Ditmore: Some have traditionally argued for raked bows in terms of "reserve bouyancy", but I believe that analysis to be flawed. It depends very much on what you assume is fixed, and what is varied, so it's a difficult issue to frame properly
That problem seems to be very common. Obviously you cannot add extra buoyancy by cutting away flotation! The raked bow would have to be longer to compare more equally on the basis of overall size. In that case, speed, interaction with waves, and lateral resistance when heeled or yawed become more important differences.
That problem seems to be very common. Obviously you cannot add extra buoyancy by cutting away flotation! The raked bow would have to be longer to compare more equally on the basis of overall size. In that case, speed, interaction with waves, and lateral resistance when heeled or yawed become more important differences.
Stephen Ditmore
10-20-2005, 04:58 PM
True, but there are ways to begin to quantify reserve bouyancy that make sense. I see it as a ratio between longitudinal gyradius and height of the center of effort in the numerator, and in the denominator the longitudinal moments of inertia of the waterplanes forward of the center of gravity about an axis taken at the center of gravity.
What that means in practice is something Bruce Farr observed years ago (and it's helped him design winning boats): boats with low displacement/length ratios need less reserve bouyancy forward than boats that are short relative to their weight.
What that means in practice is something Bruce Farr observed years ago (and it's helped him design winning boats): boats with low displacement/length ratios need less reserve bouyancy forward than boats that are short relative to their weight.
dman
10-20-2005, 06:08 PM
What we have here in many cases is the guy who drives a sport bike comparing his bike to the guy who rides a Harley.
Tactic
10-21-2005, 02:14 AM
I have just completed major bow surgery on my circa 1967 20foot trailer yacht.
Attached is before and after drawings from an older thread
http://www.boatdesign.net/forums/showthread.php?t=7997
Also a link to a Delft paper on bow shapes.
http://www.rina.org.uk/rfiles/HISWA/2000/16th%20-6-%20The%20influence%20of%20the%20bowshape%20on%20the%20performance%20of.pdf
Attached is before and after drawings from an older thread
http://www.boatdesign.net/forums/showthread.php?t=7997
Also a link to a Delft paper on bow shapes.
http://www.rina.org.uk/rfiles/HISWA/2000/16th%20-6-%20The%20influence%20of%20the%20bowshape%20on%20the%20performance%20of.pdf
cyclops
10-21-2005, 11:10 AM
It looks better with a vertical bow. Enjoy
hateka
10-22-2005, 12:55 PM
A sharp, vertical bow does not give yoy much reserve buoyancy, and will allow more pitching. Off the wind, at high speed, it cuts more, maybe ending on a broach. The waterline is longer, and will provide a lower friction coefficient, but it also adds wet surface. It all depends of the water you will sail in, heavy waves, you are better off with a falling bow.
SailDesign
10-22-2005, 04:08 PM
hateka, you have not been listening... :)
A vertical bow has MORE reserve buoyancy (for its length on deck)
Steve
A vertical bow has MORE reserve buoyancy (for its length on deck)
Steve
Tactic
10-22-2005, 04:31 PM
hateka,maybe if you read the paper in my link above.....
chandler
10-23-2005, 01:03 PM
How about the freeboard of the bow? Would 5' seem outrageously high for a nearly pumb bowed 33 footer?? Would it be too much windage?
hateka
10-25-2005, 01:44 PM
A sharp, vertical bow does not give yoy much reserve buoyancy, and will allow more pitching. Off the wind, at high speed, it cuts more, maybe ending on a broach. The waterline is longer, and will provide a lower friction coefficient, but it also adds wet surface. It all depends of the water you will sail in, heavy waves, you are better off with a falling bow.
My reference is the waterlinelength. If you take the decklength as a reference, you are subtracting reserve bouyancy with a raked bow. With the waterline as reference (What I am tought as common practice, i.e. length between perpendiculars), a raked bow adds buoyancy. The decklength is a strange criterium, the hydrostatic values, friction etc, are all based on waterline length.
My reference is the waterlinelength. If you take the decklength as a reference, you are subtracting reserve bouyancy with a raked bow. With the waterline as reference (What I am tought as common practice, i.e. length between perpendiculars), a raked bow adds buoyancy. The decklength is a strange criterium, the hydrostatic values, friction etc, are all based on waterline length.
Stephen Ditmore
10-25-2005, 03:00 PM
I agree that Hateka's way of looking at this is the conventional way. It's also the way my article in Professional BoatBuilder argued is flawed. Deck weight raises the boat's center of gravity, requiring more ballast be added to offset it. If you were to start with a sail area and work backwards, deck weight would drive displacement more than waterline length would.
The thing one has to wrap ones mind around that what we're talking about is longitudinal stability relative to pitching inertia, which generally translates: volume in the ends relative to displacement.
The thing one has to wrap ones mind around that what we're talking about is longitudinal stability relative to pitching inertia, which generally translates: volume in the ends relative to displacement.
hateka
10-25-2005, 03:12 PM
I see your point. Maybe I am too old. Back to the bowsprit. Shorten the mast at the 7/8 point and go for a carbon gaff. Hateka
hateka
10-26-2005, 02:13 AM
Sorry for making a joke, last night. I have indeed always been thinking starting from a given hull, and not from the sail area or the rigging. This makes me agreeing to the vertical bow and the negative transom, only from the weights in the ends. Not from the lookings. Hateka.
Skippy
10-26-2005, 09:57 AM
Many important things are based on or related negatively to decklength, including dock fees, and the weight and price of the boat. A heavier boat can be harder to trailer (small) or singlehand (large), and hydrodynamic advantages won't be enough if the person can't afford the boat or store it in their yard.
yokebutt
10-28-2005, 10:07 PM
The way I see it, since you're paying rent for the whole length, you should optimize your rent/speed ratio.
Yoke.
Yoke.
cyclops
10-28-2005, 10:12 PM
Thanks for the chuckle, Yokebutt.
Doug Lord
10-29-2005, 09:50 AM
Good one, Yoke!
hateka
10-29-2005, 10:59 AM
Agree. Hateka.
LP
10-29-2005, 10:51 PM
If you'll look at more traditional designs, I think you'll find that a plumb stem was standard fare. Before the days of lightweight powerful engines, lightweight hulls and 6-1 A/R's, designers had to maximize hulls to get the maximum performance that was available to an LOA.
If I were designing/building a 60'+ yacht, I could probably also hire a hydrodynamnasist(sic) to to check the lines and create the slipperyist hull possible. But, as it is, I have no hydrodynamic expert, so I'll have to rely on my own judgement in regard to hull shape AND put as much waterline on the sun-of-a-gun as LOA, form and esthetics will allow.
Losing 5' of WL on a 60'er equates to roughly a 5% loss in hull speed where the same loss ao a 25'er is about a 10% loss of hull speed. Even the long overhangs of Herreshoff designs were not put there for reserve bouyancy, but were a means of beating the ratings rules. When the hulls were heeled, they would "sink" and thus, present more waterline. So, in this case, the overhangs, while adding to reserve bouyancy, are intended to create more waterline and the hull shape presented to the water depends more on section shape than on overhangs for it's reserve bouyance in many of it's missions.
So then a question arises. Two boats of equal LOA. One, for the sake of arguement, has a waterline equal to the LOA and the other has a waterline at 75% LOA. Can we draw any conclusions in regard to performance, comfort, seakeeping, accomodation, etc. from just this bit of information? Probably not.
If I were designing/building a 60'+ yacht, I could probably also hire a hydrodynamnasist(sic) to to check the lines and create the slipperyist hull possible. But, as it is, I have no hydrodynamic expert, so I'll have to rely on my own judgement in regard to hull shape AND put as much waterline on the sun-of-a-gun as LOA, form and esthetics will allow.
Losing 5' of WL on a 60'er equates to roughly a 5% loss in hull speed where the same loss ao a 25'er is about a 10% loss of hull speed. Even the long overhangs of Herreshoff designs were not put there for reserve bouyancy, but were a means of beating the ratings rules. When the hulls were heeled, they would "sink" and thus, present more waterline. So, in this case, the overhangs, while adding to reserve bouyancy, are intended to create more waterline and the hull shape presented to the water depends more on section shape than on overhangs for it's reserve bouyance in many of it's missions.
So then a question arises. Two boats of equal LOA. One, for the sake of arguement, has a waterline equal to the LOA and the other has a waterline at 75% LOA. Can we draw any conclusions in regard to performance, comfort, seakeeping, accomodation, etc. from just this bit of information? Probably not.
hateka
10-30-2005, 03:00 AM
When I wrote bowsprit and a gaff rig a few days ago, it was not only a joke. I just got a poster of the Volvo-Open 70 competitor ABN-AMRO-2, which has both. I assume the bowsprit to reduce weight at the forward end, and the 'gaff' to reduce mastheight. Hateka.
Vega
10-30-2005, 06:34 AM
So then a question arises. Two boats of equal LOA. One, for the sake of arguement, has a waterline equal to the LOA and the other has a waterline at 75% LOA. Can we draw any conclusions in regard to performance, comfort, seakeeping, accomodation, etc. from just this bit of information? Probably not.
This is the QUESTION that matters, at least for me, or from a cruising point of view. (Of course there are always the rent problems referred by Yokebutt:) )
Please give some answers!
This is the QUESTION that matters, at least for me, or from a cruising point of view. (Of course there are always the rent problems referred by Yokebutt:) )
Please give some answers!
chandler
10-30-2005, 12:39 PM
Ok, so anyone have any comment on 5' of freeboard at the bow of a 33' sailboat. The rig would be lug yawl with the main stepped similarly to a cat boat in the fore and aft position..
LP
10-30-2005, 10:22 PM
No easy answers Vega. Too many variables. I would venture to say that long overhangs will also be associated with a leaner hull form. Meaning less interior volume (accomodation) for similar LOAs.
From a cruising standpoint, I would think think interior volume jumps to the top of the list as long as it doesn't detract from an efficient hullform.
An easily driven hullform, one that reaches hull speed easily, is important also. A lean entry with a gentle exit are going to be easier create with a longer lwl.
How do you plan to generate sail carrying power? Lots of ballast down low or a combination of ballast and hull form? Hullform stability will call for greater beam and firmer bilges than low slung ballast. A wider beam will dictate a longer waterline to avoid a bluff hull.
But, a hull that derives sail carrying power from form and not ballast is going to have a lower lower ballast ratio. This equates to a hull that is subject to quick accelerations, corky.
And so on, and so on....
From a cruising standpoint, I would think think interior volume jumps to the top of the list as long as it doesn't detract from an efficient hullform.
An easily driven hullform, one that reaches hull speed easily, is important also. A lean entry with a gentle exit are going to be easier create with a longer lwl.
How do you plan to generate sail carrying power? Lots of ballast down low or a combination of ballast and hull form? Hullform stability will call for greater beam and firmer bilges than low slung ballast. A wider beam will dictate a longer waterline to avoid a bluff hull.
But, a hull that derives sail carrying power from form and not ballast is going to have a lower lower ballast ratio. This equates to a hull that is subject to quick accelerations, corky.
And so on, and so on....
kenwstr
11-01-2005, 09:35 PM
Hi
I haven't read all the posts here but would like to comment on some I have.
If for displacement hulls, we assume a simple bow shape so we are discounting things like bulbs, then we consider only simple vertical, raked or rounded shapes.
I think it is a mistake to consider a shallow raked bow as pushing the water under it. Water has a lot of mass, 1000 kg per cubic metre, more if it's salty.
So in order for the hull to push water down or sideways, that water has to push the water next to it and so on. Water is incompressible so this means a very large mass would have to be moved, many thousands of times the hulls weight. So that can't be what happens. The only place the displaced water can most easily go is up to the surface where it becomes part of the bow wave. So the water is moveing not along the hull but up from the keel to the surface at right angles to the boats movement. At least I believe that is the case wherever the hulls X section is increasing along it's length. Now we could design the hull so the lengthwise displacement distribution displaces a single outward sin wave between the bow and quater waves at max displacement speed. This gives a very long shallow (min height) displacement wave. Considering this sin wave form, the steepest part of the wave represents the maximum rate of displacement at the bow entry and the crest shows no increase or decrease in displacement which, depending on keel shape is at or near the beem. We can see from this that the water flow at the bow is the shortest distance from keel to surface at 90 degrees to the direction travelled. The least acceleration of this displaced water is the shortest distance from keel to water line, a straight line across the hull.
At the beem, there is no displacement change so the flow is along the hull there. At the stern, folw is across the hull from WL the keel in the trough of the displacement wave. The quater wave crest will then be around a 1/2 wave aft of the stern.
Now I must point out that such a hull shape while dynamically good offers a lot of surface for its displacement so a compromise between skin and dynamic drag is much more the norm but this may serve to point out the water flow pattern is much the same regardless of the bow elevation shape.
I must also say there is another flow dynamic that becomes stronger below the surface and that is where the mass of water above a moveing object is high, the water can only flow around the object by speeding up, much like through a constriction in a hose. The deeper we go, the stronger this flow pattern becomes.
Consideration of bow elevation must then ballance max displacement speed for length restriction (vertical bow) against reduced surface area for minimum skin friction at lower speeds. Then there are sea keeping and manouverability issues to consider as well. It's all compromise.
OK so here I admit, this is all what I have personally figured out, what do I know. Some you may well like to correct me, please feel free to do so.
Regards,
Ken
I haven't read all the posts here but would like to comment on some I have.
If for displacement hulls, we assume a simple bow shape so we are discounting things like bulbs, then we consider only simple vertical, raked or rounded shapes.
I think it is a mistake to consider a shallow raked bow as pushing the water under it. Water has a lot of mass, 1000 kg per cubic metre, more if it's salty.
So in order for the hull to push water down or sideways, that water has to push the water next to it and so on. Water is incompressible so this means a very large mass would have to be moved, many thousands of times the hulls weight. So that can't be what happens. The only place the displaced water can most easily go is up to the surface where it becomes part of the bow wave. So the water is moveing not along the hull but up from the keel to the surface at right angles to the boats movement. At least I believe that is the case wherever the hulls X section is increasing along it's length. Now we could design the hull so the lengthwise displacement distribution displaces a single outward sin wave between the bow and quater waves at max displacement speed. This gives a very long shallow (min height) displacement wave. Considering this sin wave form, the steepest part of the wave represents the maximum rate of displacement at the bow entry and the crest shows no increase or decrease in displacement which, depending on keel shape is at or near the beem. We can see from this that the water flow at the bow is the shortest distance from keel to surface at 90 degrees to the direction travelled. The least acceleration of this displaced water is the shortest distance from keel to water line, a straight line across the hull.
At the beem, there is no displacement change so the flow is along the hull there. At the stern, folw is across the hull from WL the keel in the trough of the displacement wave. The quater wave crest will then be around a 1/2 wave aft of the stern.
Now I must point out that such a hull shape while dynamically good offers a lot of surface for its displacement so a compromise between skin and dynamic drag is much more the norm but this may serve to point out the water flow pattern is much the same regardless of the bow elevation shape.
I must also say there is another flow dynamic that becomes stronger below the surface and that is where the mass of water above a moveing object is high, the water can only flow around the object by speeding up, much like through a constriction in a hose. The deeper we go, the stronger this flow pattern becomes.
Consideration of bow elevation must then ballance max displacement speed for length restriction (vertical bow) against reduced surface area for minimum skin friction at lower speeds. Then there are sea keeping and manouverability issues to consider as well. It's all compromise.
OK so here I admit, this is all what I have personally figured out, what do I know. Some you may well like to correct me, please feel free to do so.
Regards,
Ken
hateka
11-02-2005, 02:06 AM
You figured it. It is all compromise. Hateka
brian eiland
11-02-2005, 09:06 AM
I've not seen much discussion of the aesthetics of the situation so here I offer some.
A bow profile is one of the most distinctive features the eye is drawn to when looking at a yacht. The style a vessel carries in these lines is more then their function (which has only been lightly touched on here). Racers and commercial vessels are duty bound with the tasks asked and their bow profiles typically reflect this. A cruiser isn't selected because it takes most advantage of available LWL, but many other, usually considerably more important constraints (to them), such as reserve buoyancy in a plunging sea, ample rode and chain locker stowage, a pretty place to hang trail boards, etc.
Bows come in all shapes and types. Reversed, submerged, bulbed, clipper, spoon, plumb, Indian head, etc. Some are pure styling exercises, others an attempt to beat racing rules or increase efficiency or other element, in this area of the design. The same is true of sectional and plan shapes used in the bow. A great deal of thought goes into a boat's entry, which covers several issues of concern in this location. Some will sacrifice a fraction of a knot in hull speed or cargo capacity, to make this area look nice, others can't afford this.
So in answer to your questions D-man, there is no truly supreme bow profile that will be the best thing to have at sea. Shedding water off a recently dunked deck is a function of many things, bow shape being one, entry, hull form, freeboard, deck crown and rail height are a few of the other considerations also.
Also consider the freeboard and total required reserve buoyancy, a low windage hull will need to make up the reserve buoyancy with overhangs, overhangs also add to the usable interior volume. Overhangs cost very little in terms of materials in the construction, they give a much more usable deck area fwd for a fine bowed craft, and offer a much more sensible collision zone for many floating hazards
PAR, I agree with you. The two most distinctive lines on a boat are the sheer line and the bow line/profile. A year or so ago I saw an article in Soundings magazine by Ted Danforth speaking of Ray Hunt designs. I wrote him in response to his article, “And most importantly, you included the oft forgotten element, the sheer line. What a terribly important factor! Romantically stated, but oh so true, it is simply her sheer… sheer beauty that is. She enters the harbor like a beautiful woman entering a room. Her sheer is the line we try to get right when we doodle boats.”
I consider both the sheer and the bow line/profiles as the two most important lines on a vessel. And I am convinced that a computer cannot match the human, hand-drawn line for these two. The computer renderings can be useful for viewing the design from many various perspectives, but don’ t ask it to draw the original line.
When I first became interested in sailboat design there were still quit a number of wooden boats, and many of these had long graceful overhangs that contributed to longer waterlines upon heeling. Not only were they practical, but they were beautiful. From my letter to Danforth , “Your article brought some of that feeling back to me…some of that feeling that first inspired me to want to learn of sailing yachts and their design ….that had me (virtually a non-sailor at the time) putting together a scrapbook of designs, both good and poor, for future reference. You captured not only the factual history, but more importantly, some of the essence of being involved with yachts and yacht design itself….. ‘the measure of total understanding of the nature of a boat’.”All thru the late 60’s and 70’s I experienced the dawn of the fiberglass boat, and the need for the manufacturers to cram ever-more accommodations into a certain length vessel. I saw the disappearance of overhangs. I saw the boats become more and more like just so like many “floating Clorox bottles”, I termed it. No distinctive bow shapes and straight, non-descript sheers.
Now it so happens that I got quite heavily involved with multihull craft because here is where free thought and innovation abounded, and here it is even tougher to create a pretty sheer line. Look at the number of vessels on the market that look like their sheer lines were drawn with a straight-edge ruler. And this current fad of plum bows just doesn’t do anything but add to the already boxy look of multihulls. One of our major problems in the early days of selling multihulls was not only overcoming the ‘capsize issue’, but also the boxy looks of our craft. Lots of folks aren’t interested in being associated with a ‘floating box’. Boats need to be practical, but they also need style.
Now I know I will take some heat for this next remark, but here it is anyway. I was once looking for some aero kits for a Mercedes auto to jazz it up a little. I was so disappointed in what I found in Germany designed by the Germans. My thought was they can let the Germans build it, but let the Italians design it. The Germans are all practicality, but the Italians add some flair. What’s sexier looking a Ferrari or a Mercedes?
I look thru the production multihull market right now and see some practicality, some innovation, some experimentation, but I don’t see very many pretty designs. I’m going to attach a number of illustrations to this posting, both good and poor (in my opinion). Feel free add your own illustrations and/or comments to those I presented. Oh, and I’ve just included sailboats here. The power cats are a further disaster, most are out and out ugly.
I will also address plum bows in a separate posting, as well as bulbous bows.
How about this Lock Crowther design “Investigator II”. She is a beautiful proportioned 55’ vessel with a handsome and proud bow. Or Peter Wormwood’s “Indigo” 60’ design, unique in how it disguises its freeboard into a much slicker sheer line. How about this variation on a plum/bulbous bow by Lock on the vessel “Wahoo”, pretty good. I don’t think Lock ever drew his lines with a computer. His son Brett does, and I’m not impressed with his designs aesthetically. Nor am I impressed with Tennant’s or Hughe’s, too many ruler-straight lines. I’m not even happy with mine. My 65’ is OK, but that 42’ looks like a stacked wedding cake because I tried to cram too much into its length, and add a plum bow. (Some profile illustrations (http://www.runningtideyachts.com/motorsailing/) of mine can be found on this page)
Like I said, the multihull vessel form is even tougher to make look good.
A bow profile is one of the most distinctive features the eye is drawn to when looking at a yacht. The style a vessel carries in these lines is more then their function (which has only been lightly touched on here). Racers and commercial vessels are duty bound with the tasks asked and their bow profiles typically reflect this. A cruiser isn't selected because it takes most advantage of available LWL, but many other, usually considerably more important constraints (to them), such as reserve buoyancy in a plunging sea, ample rode and chain locker stowage, a pretty place to hang trail boards, etc.
Bows come in all shapes and types. Reversed, submerged, bulbed, clipper, spoon, plumb, Indian head, etc. Some are pure styling exercises, others an attempt to beat racing rules or increase efficiency or other element, in this area of the design. The same is true of sectional and plan shapes used in the bow. A great deal of thought goes into a boat's entry, which covers several issues of concern in this location. Some will sacrifice a fraction of a knot in hull speed or cargo capacity, to make this area look nice, others can't afford this.
So in answer to your questions D-man, there is no truly supreme bow profile that will be the best thing to have at sea. Shedding water off a recently dunked deck is a function of many things, bow shape being one, entry, hull form, freeboard, deck crown and rail height are a few of the other considerations also.
Also consider the freeboard and total required reserve buoyancy, a low windage hull will need to make up the reserve buoyancy with overhangs, overhangs also add to the usable interior volume. Overhangs cost very little in terms of materials in the construction, they give a much more usable deck area fwd for a fine bowed craft, and offer a much more sensible collision zone for many floating hazards
PAR, I agree with you. The two most distinctive lines on a boat are the sheer line and the bow line/profile. A year or so ago I saw an article in Soundings magazine by Ted Danforth speaking of Ray Hunt designs. I wrote him in response to his article, “And most importantly, you included the oft forgotten element, the sheer line. What a terribly important factor! Romantically stated, but oh so true, it is simply her sheer… sheer beauty that is. She enters the harbor like a beautiful woman entering a room. Her sheer is the line we try to get right when we doodle boats.”
I consider both the sheer and the bow line/profiles as the two most important lines on a vessel. And I am convinced that a computer cannot match the human, hand-drawn line for these two. The computer renderings can be useful for viewing the design from many various perspectives, but don’ t ask it to draw the original line.
When I first became interested in sailboat design there were still quit a number of wooden boats, and many of these had long graceful overhangs that contributed to longer waterlines upon heeling. Not only were they practical, but they were beautiful. From my letter to Danforth , “Your article brought some of that feeling back to me…some of that feeling that first inspired me to want to learn of sailing yachts and their design ….that had me (virtually a non-sailor at the time) putting together a scrapbook of designs, both good and poor, for future reference. You captured not only the factual history, but more importantly, some of the essence of being involved with yachts and yacht design itself….. ‘the measure of total understanding of the nature of a boat’.”All thru the late 60’s and 70’s I experienced the dawn of the fiberglass boat, and the need for the manufacturers to cram ever-more accommodations into a certain length vessel. I saw the disappearance of overhangs. I saw the boats become more and more like just so like many “floating Clorox bottles”, I termed it. No distinctive bow shapes and straight, non-descript sheers.
Now it so happens that I got quite heavily involved with multihull craft because here is where free thought and innovation abounded, and here it is even tougher to create a pretty sheer line. Look at the number of vessels on the market that look like their sheer lines were drawn with a straight-edge ruler. And this current fad of plum bows just doesn’t do anything but add to the already boxy look of multihulls. One of our major problems in the early days of selling multihulls was not only overcoming the ‘capsize issue’, but also the boxy looks of our craft. Lots of folks aren’t interested in being associated with a ‘floating box’. Boats need to be practical, but they also need style.
Now I know I will take some heat for this next remark, but here it is anyway. I was once looking for some aero kits for a Mercedes auto to jazz it up a little. I was so disappointed in what I found in Germany designed by the Germans. My thought was they can let the Germans build it, but let the Italians design it. The Germans are all practicality, but the Italians add some flair. What’s sexier looking a Ferrari or a Mercedes?
I look thru the production multihull market right now and see some practicality, some innovation, some experimentation, but I don’t see very many pretty designs. I’m going to attach a number of illustrations to this posting, both good and poor (in my opinion). Feel free add your own illustrations and/or comments to those I presented. Oh, and I’ve just included sailboats here. The power cats are a further disaster, most are out and out ugly.
I will also address plum bows in a separate posting, as well as bulbous bows.
How about this Lock Crowther design “Investigator II”. She is a beautiful proportioned 55’ vessel with a handsome and proud bow. Or Peter Wormwood’s “Indigo” 60’ design, unique in how it disguises its freeboard into a much slicker sheer line. How about this variation on a plum/bulbous bow by Lock on the vessel “Wahoo”, pretty good. I don’t think Lock ever drew his lines with a computer. His son Brett does, and I’m not impressed with his designs aesthetically. Nor am I impressed with Tennant’s or Hughe’s, too many ruler-straight lines. I’m not even happy with mine. My 65’ is OK, but that 42’ looks like a stacked wedding cake because I tried to cram too much into its length, and add a plum bow. (Some profile illustrations (http://www.runningtideyachts.com/motorsailing/) of mine can be found on this page)
Like I said, the multihull vessel form is even tougher to make look good.
brian eiland
11-02-2005, 09:38 AM
...couple of more bow examples...
Which of these examples would you choose??
Which of these examples would you choose??
aitchem
11-02-2005, 11:59 AM
I'm glad to find I am not alone in finding modern CAD designs uninspiring.
You guys need to retrace back to the beauty of the J's and Fifes.
You guys need to retrace back to the beauty of the J's and Fifes.
SailDesign
11-02-2005, 12:32 PM
Now, HM, if your definition of beauty finished with the J boats, you have been missing out. :)
That's like saying that the last beautiful woman was Mae West.
Steve
That's like saying that the last beautiful woman was Mae West.
Steve
aitchem
11-02-2005, 02:19 PM
Show me a recent sexy 14 Metre alu cruiser.!
hateka
11-02-2005, 03:10 PM
Think of the Morning Cloud. Hateka
chandler
11-02-2005, 04:31 PM
Aitchem
I agree wholeheartedly. Besides the js and fifes, all the traditional sail craft, friendship sloops, french fishing luggers, etc.
I see the modern cad renditions on this site and wonder?
Aesthetically, nobody's done anything in the last 40 years.
When I was a kid there was a TV series called the 21st century. It gave us a glance as to what the future would hold. We're probably 10 years behind,however the designs are similar to the cars we drive today, I don't think it works for the yachts of today. Just imagine why anyone would consider a supersonic boat, a popular thread in this forum.
I agree wholeheartedly. Besides the js and fifes, all the traditional sail craft, friendship sloops, french fishing luggers, etc.
I see the modern cad renditions on this site and wonder?
Aesthetically, nobody's done anything in the last 40 years.
When I was a kid there was a TV series called the 21st century. It gave us a glance as to what the future would hold. We're probably 10 years behind,however the designs are similar to the cars we drive today, I don't think it works for the yachts of today. Just imagine why anyone would consider a supersonic boat, a popular thread in this forum.
cyclops
11-02-2005, 05:12 PM
If you had a supersonic boat you could put Mighetto in a dingy 100' behind it during the cruising party. :)
SailDesign
11-02-2005, 05:32 PM
HM, you show me an aluminium J or an aluminium Fife, and I'll think about finding a sexy alu 14m cruiser for you. :)
aitchem
11-03-2005, 05:01 AM
hereyago
http://www.sy-ranger.com/
http://www.sy-ranger.com/
SailDesign
11-03-2005, 06:48 AM
No fair - I said Aluminium....
Ranger was steel.
Ranger was steel.
aitchem
11-03-2005, 07:45 AM
splitting hairs.?
aitchem
11-03-2005, 07:55 AM
sexy, want this, alu, for 2 +occasional2 cruising, round the globe
SailDesign
11-03-2005, 09:21 AM
splitting hairs.?
Heh heh! Probably... :)
I still think you are dissing all designers since the 30's. Speaking as one of those designers, I might occasionally take umbrage.
Steve
Heh heh! Probably... :)
I still think you are dissing all designers since the 30's. Speaking as one of those designers, I might occasionally take umbrage.
Steve
aitchem
11-03-2005, 10:29 AM
No offence intended, just get your pencils out
chandler
11-03-2005, 01:19 PM
SailDesign
You were designing boats in the 30's? Unless you started when you were 10 you must be 100.
So a question I can't seem to get a response to. What do you think of 5' of freeboard at the bow of a 33' french fishing lugger type cruiser? Is it way too much? I'd really appreciate any comment as I'm in the lofting process and running out of white paint and erasers!
You were designing boats in the 30's? Unless you started when you were 10 you must be 100.
So a question I can't seem to get a response to. What do you think of 5' of freeboard at the bow of a 33' french fishing lugger type cruiser? Is it way too much? I'd really appreciate any comment as I'm in the lofting process and running out of white paint and erasers!
SailDesign
11-03-2005, 03:29 PM
Chandler,
If I had said "dissing all designers since the Ark", I would still be OK, since my designing days have been "SINCE" the Ark..... :)
Steve (only about 50)
If I had said "dissing all designers since the Ark", I would still be OK, since my designing days have been "SINCE" the Ark..... :)
Steve (only about 50)
Cliff Pope
11-04-2005, 04:41 AM
I think fashion comes into it a lot, historically anyway, as the person who mentioned the Titanic suggested.
I think another factor affecting seaworthiness is the horizontal sheer and the fore-aft angle of the keel. Traditional working craft, fishing smacks, Victorian cruising yachts based on those styles, had long straight keels with maximum draught at the stern, and a pronounced slope of the deck from front to back. This would surely offset any "plunging" tendency from the sharp plumb stem.
I think another factor affecting seaworthiness is the horizontal sheer and the fore-aft angle of the keel. Traditional working craft, fishing smacks, Victorian cruising yachts based on those styles, had long straight keels with maximum draught at the stern, and a pronounced slope of the deck from front to back. This would surely offset any "plunging" tendency from the sharp plumb stem.
FAST FRED
11-05-2005, 06:28 AM
Ok, so anyone have any comment on 5' of freeboard at the bow of a 33' sailboat. The rig would be lug yawl with the main stepped similarly to a cat boat in the fore and aft position..
No problem , will make a drier boat , better offshore.
FAST FRED
No problem , will make a drier boat , better offshore.
FAST FRED
chandler
11-05-2005, 10:18 AM
Thanks Fast Fred, where abouts in Conn. I grew up there,currently in southern Maine
LP
11-05-2005, 04:51 PM
Just for grins. Here are a couple of 33'ers. Very basic, down and dirty stuff. They're actually quite slack bilged. One with 5' freeboard at the bow and one that is 4'.
The higher freeboard makes the vessel look shorter. More like something in the 20' range. I'd be concerned about windage on such a boat. I don't know that you would gain much in the dryness area either.
I'd go to the marina or go to some manufacturers websites and get some actual figures off of some boats of that size to see how close or how far you would be from some production boats.
Oh, these were done with FREE!ship.
Goodluck
The higher freeboard makes the vessel look shorter. More like something in the 20' range. I'd be concerned about windage on such a boat. I don't know that you would gain much in the dryness area either.
I'd go to the marina or go to some manufacturers websites and get some actual figures off of some boats of that size to see how close or how far you would be from some production boats.
Oh, these were done with FREE!ship.
Goodluck
chandler
11-05-2005, 05:27 PM
Thanks learpilot, my design has a more pronounced sheer than those, almost a Maine lobsterboat sheer, I live in Maine. I've been to the boat yards and the manufacturers websites, know something, they all look the same, guess I'll just trust my instincts.
LP
11-05-2005, 06:53 PM
Chandler,
New thread, "Lobster"
New thread, "Lobster"
FAST FRED
11-06-2005, 09:54 AM
When motorsailing , or punching into the waves , a 4 ft freeboard will take water over the bow at 4ft 1 inch of imersion.
A 5 ft bow will begin to have grean seas after 5ft 1 inch.
The difference is extreme as much more hull must be immersed to get the slopy seas sweaping aboard.
Its a foot extra of BOAT that must be immersed.
FAST FRED
A 5 ft bow will begin to have grean seas after 5ft 1 inch.
The difference is extreme as much more hull must be immersed to get the slopy seas sweaping aboard.
Its a foot extra of BOAT that must be immersed.
FAST FRED
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