which design criteria for MAST HEIGHT

[TheThunderbird]

As to many naval architecture issues, i feel like much is left to handy practice, tradition, imitation (replica).

Sure, we know that the more speed-prone a boat, the higher the mast. Then you calculate for the RM, possibly decide to add another pair of shrouds... etc.

In reviewing Whitehack, now Whitefin (1979, Camden, Ml) l see a 93' sloop with a mast height of 147', or 159% of LOA.

IT IS a dearingly high ratio! A modern Vismara 60' has a 90' mast (150% - carbon fibre).

Thus, nothing anew under the sun. In spite of new materials, and Whitehack being not a racing machine..
Puzzling, isn't it?

Nauta 54 (1989), a sporty ocean racer by design, has a mast of 74' (keel stepped, mast height say 2' less..) and a ratio of 133% approx.

Yet, many lazy cruisers seem to sport a similar ratio ... and actually marinas show an even skyline, with few exceptions... The even Dullest boat has a mast way longer than its LOA, bar the motor-yachts with some rigging.

At a look, sporty masts are eventually THINNER/LIGHTER, not longer..

Conclusions (tentatively) :

The rule of thumb seems to call for a 130% ratio, no matter what (bar the extremes)

No major development in 40 years? (Though old profiles are decommissioned by mast mfrs)

No major changes in overall design, as to mast height, despite carbon

Dull design (?) with little variety among NAs, or the forceful truth holds that the RM is the only final/ commanding criteria? But even so, do NAs calculate the RM just to equalize the height mast to LOA ratio???

[TeddyDiver]

Originally Posted by TheThunderbird

As to many naval architecture issues, i feel like much is left to handy practice, tradition, imitation (replica).

Sure, we know that the more speed-prone a boat, the higher the mast. Then you calculate for the RM, possibly decide to add another pair of shrouds... etc.

In reviewing Whitehack, now Whitefin (1979, Camden, Ml) l see a 93' sloop with a mast height of 147', or 159% of LOA.

IT IS a dearingly high ratio! A modern Vismara 60' has a 90' mast (150% - carbon fibre).

Thus, nothing anew under the sun. In spite of new materials, and Whitehack being not a racing machine..
Puzzling, isn't it?

Nauta 54 (1989), a sporty ocean racer by design, has a mast of 74' (keel stepped, mast height say 2' less..) and a ratio of 133% approx.

Yet, many lazy cruisers seem to sport a similar ratio ... and actually marinas show an even skyline, with few exceptions... The even Dullest boat has a mast way longer than its LOA, bar the motor-yachts with some rigging.

At a look, sporty masts are eventually THINNER/LIGHTER, not longer..

Conclusions (tentatively) :

The rule of thumb seems to call for a 130% ratio, no matter what (bar the extremes)

No major development in 40 years? (Though old profiles are decommissioned by mast mfrs)

No major changes in overall design, as to mast height, despite carbon

Dull design (?) with little variety among NAs, or the forceful truth holds that the RM is the only final/ commanding criteria? But even so, do NAs calculate the RM just to equalize the height mast to LOA ratio???

Mast height is just one thing to consider. What matters more is the height of center of effort of the rig (CE), aspect ratio of the individual sail and how they match to the hydrodynamic properties of the boat. There are books written about the subject so a bit complicated matter.
What comes to masts thinner ones need more support ie multiple spreaders and shrouds to prevent buckling of the mast with the cost of bit additional windage of more complicated standing rigging. That's the negative. The positive side of a thinner mast profile is less weight a loft and thus more weight in the keel, hence greater RM and more force to be taken from the sails.. Hope that helps.

BR Teddy

[Benz]

A lot of design, through the ages, is driven by fads and marketing. When racing boats started sporting ridiculous, unseamanlike overhangs fore and aft due to an imbecile racing rule (for the record, any time design is compromised for the sake of a racing rule, idiocy has happened), a whole bunch of designers drew in overhangs, though they serve no real purpose outside of a waterline rule. When racers decided that jib-headed mains were better, all the designers, even of non-racers, went jib-headed. Why? "Your boat can be like a racer too!" It was herd mentality, the same herd mentality that briefly embraced hull chines, that now loves extra-wide transoms, double helm stations, and twin rudders. It was that sort of marketing that brought about the ultimate oxymoron in the sailing world: the racer-cruiser. Hmmm, lets see: in order to race well, everything--weight, comfort, space--must be sacrificed to speed (look at those silly, wet, crew-intensive Imoca 60s). In order to cruise well, there must be carrying capacity and dryness and comfort. Mutually exclusive, but designers had to put food on the table: that's what the marketing department wanted, that's what they got.
I've probably drifted a little here, but the point is: modern cruising boat design has nothing to do with good sense, or good taste, or with designing a boat for a specific purpose--it has everything to do with trying to keep up with whomever the marketers tell you is cool. They go for taller masts? so will we! square-top mains? us too! (this from the crown that sneers in their ignorance at gaffers) two helms next to each other? we're in!
So to answer your question: most designers will mimic whatever mast height is currently in fashion, and sadly, they almost always have, to the destruction of much good that might have been.
Ben
zartmancruising.com

[Stumble]

As teddy mentioned mast height is only one of a number of factors that determine performance and not even close to the most important. Because almost all sailboats operate in displacement mode all of the time let's just look at those and exclude planing completely for a moment.

For a given LWL the hull speed of the boat is pretty much fixed, so the only thing you can do to effect speed around a race course is 1) maximize the percentage of time the boat operates at hull speed and to 2) increase its pointing angle while 3) decreasing its jibe angles.

Sadly each of those desirable elements are contra-indicated. Meaning as you increase the boats performance in one you decrease its performance in others and even within a catagory there are tradeoffs.

As an example: For maximum light air upwind performance you want a very 1) tall 2)thin 3) light rig. Each of these desirable traits however forces you to make other compromises. Making a rig taller in isolation does a lot of good, it increases aspect ratio, allows bigger sails, and allow some access to higher wings that tend to be more steady and stronger. On the downside however they reduce the RM of the boat, add wind resistance, and complicate the standing rigging.

So to offset the RM lost you need to increase the ballast, increasing the wetted surface, and therefore the drag of the boat even more. So yes you have added more sail area, but have added substantial amounts of drag (air and water) to the boat. Wether it is a net gain or not depends on the wind speed the boat operates in, in lower wind the drag (which goes up exponentially with speed) isn't a big issue, but as wind speed and boat speed increases the drag players a larger part. At some wind/boat speed the extra drag hurts more than the extra sail area helps.

It's even more complicated though. Air and water drag also reduces pointing angle because it reduces the efficiency of the foils. So you also have to account for the fact that a single the wind speeds up the boat can't point quite as well as the boat with the shorter rig. Where the crossover point is depends heavily on the specific design, but there will be one.

There is also the follow up problem that assuming all else is kept even a tall mast will need more substantial standing rigging. Either a whole new stay, or to increase the size of the stays. This also adds wind drag, and weight aloft (reducing RM, requiring more ballast). The added stays and rig tension also increase the loads on the hull, so you may need more structural strength in the hull to keep it from flexing, adding weight, and thus drag.

Now keep in mind all we have done so far is increase mast height, same sectional area, same size extrusion, etc. the more money you want to throw at it the more complicated it can get. As an example, by switching to a carbon rig instead of aluminium you have a few options...

1) you can reduce the weight aloft regaining RM
2) you can use a thinner tube reducing drag
3) You can use a stiffer tube reducing standing rigging requirement
4) You can keep the weight and size the same and add strength
5) Taper the mast to reduce tip weight, and drag
6) mix and match the above to design an all round better mast

A taller mast can only help in wind speeds low enough that you are still looking for more power (below hull speed in non-reefing conditions) and the extra drag makes it harder to reach that point. But you carry the penalties with them all the time.

When you make simple ratios you need to be very careful to only use boat so designed for the same conditions. A vessel intended to be used in the North Sea will have a much smaller mast than one intended for a low wind area. A heavy cruising boat may have a larger rig than a race boat to overcome its weigh penalty. And a carbon rig for one boat may have completely different design requirements than another.

[newhaul]

OK here is what I learned when I was in school to become a naval architect and shipwright .
General rule of thumb is to use the lOD plus the beam as a starting point . Then adjust as needed for best appearance and performance. Fwiw

[TheThunderbird]

Dear all, with all due respect, it's all well established plain vanilla.

Again, my point was that, in spite of 40+ years in design development, new materials, relatively beamier boats,... some boats designed 40+ years ago seem to equate, not to say surpass some current racing criteria.

Whitehawk and nauta54 are no lake-toys, nor were they intended for extreme performance.

In 40 years, top Lamborghini model has say +24% engine capacity and +40% power. But the linear speed of a Spitfire engine is still equal to that of a F1 engine!!

Sails developed, as well as hull lines, foils, appendixes... did.

On the mast side, no real breakthrough, and the old wooden masts made up of different sections still go up (higher) more daringly than any current commercial design..

This is not to say that taller is better, nor necessary. Just, it didn't happen, or couldn't it happen!?

A boat due to sail the Adriatic sea has a taller mast than a 'Mediterranean ' one, in turn taller then any one operating in the Solent/ Northern sea.

In refitting the fastest trimaran ever (missing the name), the mast was shortened as it was forced before to reef the main way too early....

That said, it seems that the Thumb rules out :-)

Furthermore, i believe that a mast/LOA ratio would make some sense, mainly if considered together with ballast/D ratio, and SA/D.
SA is related to madt length, but it can be accomplished in many different ways/tricks....

Finally, a taller mast (to some extent...dpare derogative comments, pkease) makes the boat more elegant...usually..

[Benz]

Dear OP,

If it's all "Established Plain Vanilla," Why did you ask a question? It seems you have already decided what you think about this, so to ask us and then scorn our erudition (well, Stumble's, really) seems pointless.
Ben

[TheThunderbird]

Benz, I asked about any established design criteria (not how.l/you would do it), and apart a %ratio to LOA (ex-post!?) none seems to exist.

We are all aware of the pros/cons of different solutions.. and saying that stronger is heavier, or bends more if longer, is way too obvious (momentum being the same).
Indeed, i hinted at serial iteration of calculus to sub-optimize design
My sentiment is, young designers just use software, with little solid background behind...

I am mech.engineer. Saint-Venant theory is at the foundation of structural engineering, yet i'm aware that many (N) Architects got a degree while skipping that tough examination.
(It is like teaching Italian without knowing Latin. Simply shallow.)
I hope Kaufman wasn't among those NA :-)

[TheThunderbird]

I provided for 4 precise Qs in my post, for sake of clarity. Feel free to add more, eventually.
I expect gents to provide quantitative information, as i did, or their own design experience.
Many thanks.

[UNCIVILIZED]

On average, I think that you'll find that current rigs are a bit taller than those of a few decades ago. On perfomance boats especially. Though we're only talking about a few percent, or 10%, not 40%. For many of the reasons Stumble sites, plus some others. Such as that the more weight that's aloft, & the higher up it is, the more it's movement will affect the boat, her foils, & sails. And this motion disrupts the flow over the sails & foils, which causes her to loose pointing & speed. Which makes her slower. So then a shorter rig past a certain point is faster.

Another item not mentioned is that boats more current in terms of design & construction are hugely lighter than their predecessors. It's not at all uncommon to find 40'ers weighing all of 10,000lbs. But if you go back 40yrs, 10,000lbs was a weight common mostly in performance oriented 30'ers. And 40'ers of that era trended towards double that. So it's a lot easier to drive a more svelte boat, & that can be done with a smaller sail plan. One with less drag.

Also, consider that on older boats it's the norm to need a big overlapping genoa in order to get a boat up to hull speed in winds of under 15kts or so. Where now, on performance designs at least, overlapping jibs are long gone. Yet even with these "reduced" sized rigs, the boats have SADR numbers that one could only dream of a few decades ago. So the designers draw the boats pretty much up to the point of diminishing returns again. As beyond it, you then need to add more keel, which means adding more hull to support said keel & bigger rig...

You might also consider that even with modern materials, there are practical limits to things. Especially when you consider that many of the loads on rigging & spars vary in proportion to anywhere from the square of spans, to the 4th power of those spans. So both the costs, & the loads go up geometrically. And as this goes in the rigs & rigging, so does it in the rest of the boat. For everything.

And in the end, the biggest player, as usual, is money. The designs have to sell, so the designer draws what's in demand. This while trying to add his personal signature to each boat. Oh, & the rigs still have to be short enough to be practical. So that they can do things like pass under bridges. Where the limit is 65' +/- thanks to the ICW. Get above that, & a lot of folks will shy away from such purchases, even if they rarely (or never) travel near such bridges.

Them what design, build, & work on boats do have to eat


Edit: You ever try & ship a mast that's 1.5-2x the length of the boat? Since, for example, the mast on my 2-tonner. A 41' long boat. Was 64' long, due to being keel stepped, & having an I measurement of 56'. So, yeah, long tubes can be a pain. As you can realistically motor around much with 12' of spar hanging off of each end of the boat. Docking's a bitch.