Sheer?

[ted655]

I'd like to know more about sheer.
It's purpose? I understand it adds to the beauty of the boat & helps ease the turning effort?
Is there a rule of thumb for designing it in? So many inches per length of hull?
What is the correct way to talk about it? If I say, "2' of sheer in 62', is that understood as the center of the hull is 2' lower than the bow or stern? Is there a better way to describe the amount of "dip"?
Is sheer equal, between bow & stern?
I hear of banana shaped hulls & how they are driven more efficiently. Is this a referral to the sheer?
Is there a difference between sheer in a power boat as compared to a sail boat?
Are there drawbacks to having sheer?
.
Inquiring mind wants to know. Thanks.

[alan white]

Sheer has nothing to do with how a boat performs except where high ends or low freeboard factor in. Of course, with angled sides, beam is effected, so it is wider if the sheer is higher at the midsection.
In general, designing the sheer is an aesthetic problem. There are many different types of sheers; classic downward curving, reverse (humped), straight, s-curve, stepped, and so on.
Each designer has developed his own carefully nuanced sheerline.
There are some "formulas" as well, based on what has made certain classic designs shine.
I personally like to draw the lowest point of the sheer about two-thirds aft, with the bow maybe 4/3 higher than the stern, except on canoes and dories, which I prefer only slightly higher at the bow, and which have more symmetrical fore and aft profiles.
Practice drawing what looks just right without formulae, and then measure the results of the ones you really like, to get some kind of formulae that will speed the design process.

Alan

[BOATMIK]

There are many great looking boats with concave sheerlines, convex sheerlines, dead straight sheerlines. Even ones with "S" shaped ones (I am thinking of some traditional craft here).

There is no rule. However the sheerline can be used to make a boat look much bigger or smaller in terms of volume.

"Nice" sheerlines are a purely cultural artifact - so it depends what boats you have been surrounded by during your life.

Best wishes.

Michael Storer

[ted655]

Glad I asked. Basically, beauty is in the eye of the beholder, (or in this case, the designer).
I am surprised though. As i learn more about boat design, I learn that there is usually a sound, practicle reason for each element of design, a form follows function rule.
To think, the looks of a boat are given that much time & effort.
Go figure! Old Salts are "arteests" at heart. :D
Thanks.

[amolitor]

There WERE lots of reasons for sheers to be the way they were. Working boats of various sorts typically have a need for low topsides, somewhere. Where, exactly, depends on the type of work. Classic also come from the natural shapes planks fall in to when you bend them to form the hull. Modern sheerlines are frequently about making more internal space without making the boat seem too tall.

[BOATMIK]

Howdy,

Form following function is a load of rubbish.

People are continually confuse function with "conventional". And so we get into discussions about culture again.

Why did all cruising boats have masthead genoas in the 60s, 70s, 80s and 90s?

We know those sails are expensive (because you need several different headsails) labourious (requiring extra people and expensive gear - big winches). But it looked "Right" at the time.

Or the shock and horror when Illingworth sailed the flat sheered and short ended and high freeboarded (not to mention light displacement) "Myth of Malham" into the record books and revolutionised ocean racing.

Or John Spencer or Vandestadt with their light, cheap and possible to amateur build sheet plywood racing yachts which were banned by most ocean racing clubs when they could show they were much better boats. They looked completely wrong and both Spencer and V. decided the battle was too hard and headed off in different directions.

Or the upset from the yacht sailors when Farr and Whiting broke into that scene. Us dinghy sailors thought that they looked "just right" - the yachties were horrified at the appearance of the boats. They "look completely wrong" are "dangerous".

Or the non acceptance of multihulls in mainstream yachting from 1890 through to now. They just ended up creating their own sailing scene. "You can't have THAT going offshore".

Or the failure of the IYRU to accept the 10sq metre canoe as its single handed class when it won every race in the sail off selection trials. So now it is managed by the International Canoe Union (or whatever they call themselves).

Or when the British sailing canoists got burned to pieces by the Americans when they visited it in the late 1800s. They though it "unseamanlike" to sit on the sidedecks!!!! The Americans had no such qualms so whipped their sorry ...

Or the danger that was posed by having the rudder separately hung from the keel. "Dangerous", "structurally weak", "vulnerable". They neglected to mention it also resolved the wild steering problems of some short keelers.

Or Bolger's mucking around with canard rudders - or the follow up of Blackaller's canard 12-metre or the winged keel of Lexcen.

Or that wide flat "planing surfaces" aft and a long clean run were necessary for speed downwind and up. The Australian Skiff classes blew that out of the water a couple of decades ago (thanks to Julian Bethwaite and also the Moth designer/builders)

What "looks right" is purely 100%, completely .... what you are used to.

The things that make a boat go are a subtle mix of relationships and ratios that are not available to the casual viewer at all.

When a designer finally starts to see those relationships and ratios in a clear way (and it doesn't necessarily require that you pull out the calculator at all - often experience is enough - of both sailing and designing) then the real design starts to happen.

It is exactly that sense of "what looks good" that is restrictive and prevents progress in a real understanding of any type of design.

In general we are pretty flexible - when something comes along that does the job better we are usually a little shocked that it works so well but looks (ahem) a little odd.

However we quickly accept it and that in turn becomes the new restriction.

Just take a look at all the production yachts for general use that are reflecting Open 60 design themes. They look cool on the dockside, but a more miserable seaboat is hard to find. Hard to sail, the hull volume makes them bounce around. Because of the greater wetted surface they require bigger sails - which are expensive and harder to handle. Which requires a deeper keel which restricts the boats the water can sail in - or requires a really heavy bulb which increases the displacement which reduces the performance.

There is no form following function in such boats - they are a mere repetition of accepted norms - a verisimilitude of "performance" design - not an iota of original thinking in those themes. But geez they will look good at boat shows with the "take your shoes off before coming aboard signs" on the sidedecks and the vase of cut flowers on the saloon table (if it is a marina exhibition see if you can remove the blutack from the vase base while the salesman is not looking). "Look - daaaaahling - all that space!!!."

Best wishes
Michael Storer

[BOATMIK]

Oh ... as far as sheer ...

These are my rules for a nice sheer

If you are designing in 3d look at it from different angles with the boat heeled in different directions to make sure it doesn't look uncool from any angle. Don't forget about sheerline on the far side of the boat either.

When designing 2D - put a bit more sheer in the ends than you think and when building the boat leave some excess on the top edge of the hull so you can stand back and walk round when the boat is upright (don't forget that most people will not be standing in neck deep water when looking at your boat) and set up a batten that looks nice - add corrections to the drawing later. If you have done a good job the sheer on the drawing will require very little adjustment.

Amolitor is exactly right about there being traditional reasons. Usually to do with getting loads aboard or providing suitable perches for archers or cannons or reducing cost and resources by reducing hull surface area without affecting seakeeping too much. Most of these reasons are irrelevant now but persist as cultural artifacts.

Best wishes
Michael Storer

[PAR]

Easy Michael, switch to decaf for a couple of days man . . .

Sheer has become a generic term, that is applied to anything that has a sweep or curve to it, in the horizontal plane.

An example would be a cabin roof line that sort of follows the deck line. This line would be described as having a "complementary" sheer, meaning the roof line sort of mimics the deck line in a pleasing fashion.

There are practical reasons to sheering the lines on a boat. An upward sheer in the deck line produces a dryer boat underway, while at the same time reduces freeboard midship, making boarding easier. An upward swept stern, can keep a following sea from climbing aboard.

Conversely, too much sheer in the stern can cause a boat to march around it's hook in an anchorage or be difficult to handle in a stiff blow on a sail boat. Too much bow sheer can keep a boat from pointing too high, letting competition whip it's butt to windward.

There are many very general guides you can incorporate into a sheered line. The amount of rise, it's relation to the rest of the line or boat, location of the lowest point, quickness of the curve, etc. The list is quite long and frankly useless, in little more then a reference for classic shapes.

Most of the "conventions" regarding sheers are no longer used. As has been pointed out, each designer develops their own idea of the ideal sheer. Personally, I can recognize different designers work a half mile away, by the sheer and the visual clues, like bow profile, etc. I hope I'm not as predictable, but giving it some thought just now, I tend toward Indian head or plumb bows, similar foil shapes and rigging choices and I labor over sheer sweeps a great deal. Maybe 50 years from now some one will pass a puddle and say, "hay, look a PAR design." . . . "I can tell by the ugly bow and funky sheer" . . .

As far as accepted norms and form following function, I see two avenues. One peruses sales, in which anything goes. Form follows marketing trends in these cases. In the other is clever engineering and invention. From the crab boat that develops a special winch to haul its pots to a racer that reduces windage by placing it's turnbuckles below decks, all functional elements, which will be followed by the folks that hadn't thought of it yet. It may not be necessarily correct for each application, but how do you know unless you stub you toe on the thing in the middle of the night.

[BOATMIK]

:-) PAR,

I am inclined to be more one eyed on this!

Focus on function and let the form take care of itself.

People might not like the result .. but they will grow to like it if the function is noticeably superior.

If Spencer and Vanderstadt had been accepted by the mainstream clubs and the general Yachting establishment the history of boat design would have been much different.

There would have been an era of cheaper, faster, easier to build ocean racers and cruisers with good righting moments and easy to handle fractional rigs.

http://www.storerboatplans.com/Orangeboat/Blacksoo.jpg

And everyone would have the "chine" as the universal standard of beauty.

(I would probably be spending my time designing round bilged boats just to show em!!!).

"C'mon guys ... these things have real advantages"

"But MIK, they are sooooooo 1870's"

Best wishes
Michael Storer

(PAR knows I am really too lazy as a boatbuilder to be bothered with round bilges - and as a designer I wouldn't force something on other people that I am not prepared to do myself)

[ancient kayaker]

OK, I got it, the purpose of sheer is to stop the gunwales from fraying at the edge. It's just easier to make it a smooth curve instead of a saw-edge. Right?

[ted655]

:confused: I think you misread me.
.
====="Focus on function and let the form take care of itself."=========
. I said the same thing. Form "follows", (as in comes last, behind, after), function, (as in, IT is more important).
Anyway, I'd much rather something work well, last longer, than look good. A rare event here in the USA. As a culture, we want it fast, cheap, & COOL looking first. Even better if it is short lived or can be made obsolete in a month. :D
.
Anyway, I'm getting an ear full about "sheer", thay's the best part.

[BOATMIK]

Howdy Ted,

I guess my main point is that there are no rules or guidelines.

And maybe I am saying that function follows function. Appreciation of form is something that happens after the fact and that appreciation is a malleable thing. Function you can trust - form is fashion or culture.

There was also a bit of a feeling that you were allowing an aesthetic form be a guide to correct function.

I don't agree - but I might be wrong about what you meant - and I might be wrong too!

I think that what you said cut to lots of important issues about design in general.

And perhaps I am a little bit (ahem) enthusiastic about them.

Best wishes
Michael Storer

[PAR]

I think all the truly gifted designers have employed aesthetically wonderful lines and shapes, which proved to be cleverly engineered structures, fitting the function element of the formula.

I do take exception to function for function sake and letting things fall where they may visually. If this were not the case, we all would be building Bolger Bricks (or PD Racers Michael, which to me look like home made concrete mixing tubs) and couldn't care a lick about a Matincus Pea Pod or Rangeley boat as it glides past our view.

I'm an admirer of many Bolger designs, including some of the box boats that seem to be children only a mother could love visually. The brilliant design skills that make most of these boats perform so well (they'd better considering their looks) are noticed in me, but they could have been pretty also.

I work hard to get a sheer just right for the type I'm working on, though it may bear little in the performance envelope of the craft, I have to be proud it looks fine sitting on her marks come launch day. Maybe this is vanity, but I think you can have both and the better among us seem to do this much more often, compared to hacks like me, who might get lucky every once and a while a wiggle into a pretty bow profile by accident.

If L. Francis's "Ticonderoga" had a ugly reversed sheer, but still the enviable racing career she piled up, would she still be intact? I think she would have been left to die or broken up. I suspect all yachts would be broken up for their equipment, metals, etc. in favor of the latest butt ugly, though especially functional creation.

I for one, am quite glad it's difficult to design beautiful and functional craft. I think separating the gilded and functional, from the mundane and exceptionally functional is a worth while goal. I hope to live long enough to draw up something as spectacular a sight as "Big Ti" on a reach, rail washed and crew drinking wine.

[BOATMIK]

Howdy PAR,

I think you would know with more certainty than me, but I seem to remember that everyone thought of the big T as a "bit of old hat" and "too old fashioned" by the racing crowd in the era in which she was launched.

By then everyone was considering S&S, Finisterre etc as the way to go. So because they did not realise that their aesthetic sense was a cultural adaptation they were never able to see the real function of the boat.

(actually they thought Finisterre wouldn't go either - "a fat centreboarder, had Olin been listening to Rod playing the Accordion for too long)

They didn't understand Ti's Ketch rig at all either. "they don't go windward".

So she is a great example of how the ratios and relationships are the things that give you function and everyone makes mistakes when they think they understand something from the appearance of the boat.

Also L. Francis is a good choice. One of my favourite boats - his 1929 "Live Yankee" in the R-class drove a 18 wheeled truck through the rating rules of that time (that had been thought up by his dad!). Flat sheer, heavily radiussed deck edge, aircraft construction horrified those who were used to conventional counter sterns and graceful sheers.

But Live Yankee now looks as modern as a 1928 Marcel Breuer chair.

http://www.classicdesign.it/images/breuer-chair.jpg

Looks like it was designed yesterday

So I think your example of Ti and its designer supports my point.

Just because it does or doesn't "look right" doesn't mean that it works well.

And thanks for bringing up my version of the PDRacer. The fastest sailing concrete mixing tubs in the universe!!!! You should have seen all the guys tweaking ropes in their lovely Oughtred designed dinghies and yachts when I (and Ted in his boat) sailed round them in light winds and flat water at the Stansbury Wooden Boat Festival last weekend.

(The oughtred boats are very good sailers - but the PDR just hit the right bunch of conditions to be a lot better - on average the PDR would be a lot slower because it is shorter).

PAR, You know I have a good aesthetic eye - and also know I am restricted from doing anything particularly pretty by the PDRacer class rules.

Because they are a box people think they cannot sail. But because the ratios and relationships are right in my version their performance is very good in spite of the rule restrictions.

Don't get me wrong - I love Ticonderoga, I love Oughtred boats (I like PAR's boats too). But I evaluate the aesthetics quite separately from the function.

Now if the designer gets the two non related factors of correct function and appropriate aesthetics then that is the very best thing of all.

Luckily because they are independent they are also non exclusive - so it is possible to have both together.

However if I did have to choose ... I am very clear which way I would go ... and I know that everyone reading this would be forced to make the same decision.

Best wishes
Michael Storer

[PAR]

Michael, I think we're saying the same things, just going about it differently.

My contention is though she didn't fit conventions, Big Ti kicked serious butt, for many years on the course. All of the would be "experts" predicted her quick conversion to fractional sloop and dramatically increased area, but she just slide by, crossing line after line with the honors.

Finisterre and Live Yankee are also good examples for this debate. All of the above mentioned where fine looking yachts, who's form exceeded expected function. These are the hallmarks of great designers, making a beautiful thing do beautiful things.

Did they need to be lovely, nope, but I'm damn glad they were. You're correct in that if it doesn't look right it doesn't mean it can't perform well. I do wish that PD Racer was a more stylish concrete mixing tub, but it does offer modest performance for what it is.

Given the choice I want both the aesthetic and good functionality. Depending on how much penalty I must pay for these looks issues, I suspect most will error toward the pretty slug, then the ugly butterfly. If you have to be seen, in something that's getting it's butt kicked, they you should look good doing so I guess. So, this is where we differ. Maybe it's because I had a good looking sister and defended her honor, much to the regret of a few boyfriends, that would have likely preferred she was a bit faster.

[lacage]

If you have a look at my blobspot, you will see how easy it is for me to instantly adjust the sheer line using my method of construction. Then for me it is just an asthetic choice. bourneboats.blogspot.com/
Cheers from down under Peter
bourneboats

[ancient kayaker]

I'm not sure Ted455 has got the answers he was hoping for. As a relative newbie to boat design I would like to learn more, too.

The factors going into sheer design identified so far include workboat needs, natural bend of planks, internal space, seakeeping, behavior at anchor and performance, the desire for a dry boat, and of course the cultural and esthetic considerations that seem to have hogged the limelight so far.

He asked for information on how to measure sheer, plus sheer variations due to propulsion - power/sail, I would add manual and towing. Then there's the environmental influence such as type of waves encountered - short-choppy-breaking waves and power boat wakes, open vs decked craft ...

Could you take some of the more extreme styles of boat sheerlines and explain why? Ti was mentioned, presumably the reverse sheer curve keeps the bow and stern profiles low and the higher sheer midships keeps water off the deck for safety and drag reduction when heeled. Is that correct? Some boats have long, gentle sheer curves whereas others curve up sharply at bow and/or stern; Why? Perhaps an initial discussion could start with open boats to keep the number of variables down.

[BOATMIK]

One of my posts at the top explains my method of developing a nice looking sheerline.

The biggest consideration is that it is hard to work out how a three dimensional curve will present in real life when it has been designed by 2 dimensional methods - on a computer screen or on paper.

The methods of trying to make that happen are mentioned in one of my posts near the top.

If you are looking for some guidance as to the "correct" sheer - then there are none.

Alan White in his post near the top does give a rough formula for drawing a classical sheer - but he knows it is only a rough guideline but he trusts his eyes (and knowing the required interior volume of the boat) to get it right.

On most modern designs the displacement is so low and the hull volume so high that any sheer is practical without changing the performance or behaviour of the boat much at all.

With a big heavy boat - long graceful ends and plenty of sheer help it get up and over waves. But a light boat will get up over waves whatever you do with the sheer. In that case you need reserve buoyancy in the ends and sheer is one of the ways to get it - as are overhangs. But if the boat is not likely to see rough water it is a moot point.

There are some other repercussions mentioned too as far as blowing around anchor, but you cannot be definitive about it because it depends on what is happening under the water too.

With most modern designs (even the ones that look like older boats) it probably makes very little functional difference to the boat (except in terms of interior volume - though there is no rule that the sheer has to be equal with the deck level) so just draw something that seems to match the style of the boat you are designing.

Best wishes
Michael Storer

[PAR]

Sorry Ted, we have driven the cart of the trail a fair way.

Other then some very general guide lines, typically surrounding classic yacht sheer, there aren't any real set rules.

Styling and racing trends seem to dominate more then anything else in the last 50 years of design.

There are so practical considerations, such as internal volume, standing headroom, decreasing weight in the ends, windage, etc., but these are usually judgment calls on the designer's part. The ideal sailboat sheer would be flat and right on the LWL, but practical issues such as boarding waves, stowage and accommodations would tend to get nixed in the deal.

Sheer types vary with the times, much like sail plans or the currently popular amount of transom deadrise to use. They swing back and forth through the decades, not being ideal for any given design.

This said, most boats will look terrible with the wrong sheer on it and it's quite difficult to anticipate the actual 3D shape as Michael mentioned. Experience teaches one how much to "cheat" here or there and some hull types require more cheating then others.

A fat, well burdened hull will need a healthy sweep to it's sheer or it will appear to droop at the ends. This is why working craft usually have a pronounced sheer. A lean racer would be carrying excess weight if the sheer was "springy" and it would probably have a weird reverse near the bow at some angles. These examples are a result of the hull shapes affecting the 3D shape of the boat.

Narrow boats require less sweep, beamy more as a rule. The actual sweep of the sheer is a pretty complex curve and requires some practice to get a sweet looking one.

As has been pointed out, with practical issues addressed, you can have pretty much any shape you want; classic, flat, reversed, S or reversed S are most of them.

If you're looking to strike a new sheer line then get a long batten, one at least 10% longer then the boat and tack it in place, roughly where you think it should be. Then stand well back (50' or more) and look her over, from every angle, sighting down the sweep to insure it's fair and the curve sweep is what you desire. This sounds easier then it is. I've cut new sheers into boats and it's difficult, requiring many adjustments and subtle batten moves to get it just right from every angle. Once you're satisfied, then call a trusted friend and have them look at the line you've created and have them look from every angle.

One tip is to insure the batten continues past the ends of the boat in a fair line. This is a common mistake. By not doing this you can have a hump or flat spot in the ends of the curve, but you'll not be able to see it because there's no reference to eyeball. On paper we design the sheer the same way, well past the ends of the boat so it's really fair.

So 'ya thinking about cutting a new sheer into something?

[yipster]

almost sketched a dozen different sheer lines as i think
the sheer line of a boat is the most eye catching
but its a whole lot more and can have many forms
sheer in wiki gives lingery, form follows function ;-)

http://www.vaartips.nl/images/bakdek.jpg
here a "bakdek" (what is it called, just S sheer?)
from witch i direved the ladybird sheer (see my galery)

[Knut Sand]

almost sketched a dozen different sheer lines as i think
http://www.vaartips.nl/images/bakdek.jpg
here a "bakdek" (what is it called, just S sheer?)
from witch i direved the ladybird sheer (see my galery)

Here in Norway, I have heard the name "Serpent line" for that "S" shaped line, but then again, I may be wrong... :D

[Brent Swain]

If you are one of those people who don't have an eye for what looks good , hiring a marine artist to help you get it right is a worthwhile investment.
The classic sheer, the fife sheer was a section of an elipse. To draw an elipse is easy. Pick out two focal points on a board , then put a nail thru each end of a string into the board . Then put your pencil in the loop between them, and draw the elipse, using the string as a compass with two focal points. Changing the length of the string or the spacing of the two focal points , changes the shape of the elipse from narrow to wide. The classic sheer is a section of this elipse, from the middle to one end, the middle being the bow and the end being the stern. How deep and how far back takes an artists eye, but using an elipse in this way gets you closer to home base easily, and eliminates screwups in the middle.
Brent

[BOATMIK]

Yipster,

A raised (fore)deck with a broken sheer would be a/the normal description.

the common trick is to put a secondary strake along the side of the boat to provide a continuous visual sheer below the deck edge - exactly as in your example.

Their secondary strake looks a bit straight to me and don't like the steady rise from stern to bow - I would tend to make it more parallel with the actua sheer right near the transom then gradually accelerate the curve up - but that is personal :-)

Not going to argue - everyone can be right with sheerlines as they are non functional for most boats!

MIK

[ancient kayaker]

I design mostly canoes at present and since the boat ends at the sheer it's functional all right! I get nice sheers with a straight sheer plank angled out slightly so the plan curves create the profile; not much sheer rise to the stems but OK for river use. A circular arc for the sheer plank in development tips the ends up nicely for more choppy conditions. With short decks at the stems in the classical Peterborough canoe style, a sheer plank with a hyperbolic top edge blended into straight ends with a constant sheer plank angle has the benefit that the decks peak at a straight king plank so the planks can be wide; it looks good too.

The conic family of curves are easy to generate on drawings and planks developments and seem to produce a good appearance every time. Not sure if that method would translate to boats with full decks and topsides. Interestingly, some classic designs I have investigated also seem to use conics.

[brian eiland]

...from a reply letter I sent to Soundings a few years ago

Just finished reading your article about Ray Hunt in the June issue of Soundings, I wanted to write and let you know how much I truly enjoyed the article.

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.”

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.” So many of today’s boats lack this beauty, and correspondingly, some of the essence of yesteryear’s yachting.