55' boat with a 92' mast. Is there a better way

[Foolish Muse]

At the dock the other day and a 55' boat pulled up. It was an older style with narrow hull. The mast is 92' high. The skipper said that the mast is so high because he races it. He also mentioned that he had broken the original mast and the new one was heavier than it should be.

It got me to pondering about the trade offs of such a tall mast. Given that the square footage of the triangle sail will be really small for the top 20' of that mast, and all that weight up so high will significantly impact the the amount the boat leans over in a breeze so you'd need more crew with all the associated costs, and the added cost of the sails. I'm really wondering if he would be better to cut the top 20' off the mast. He'd have a boat that was almost as fast but with much lower trade offs.

Your thoughts on this? I'm a racer so I understand wanting to get every 10th out of the boat, but is it worth the trade offs? How much would his handicap rating change if he cut 20' off the mast?

 

[lw395]

You don't just lose the little triangle of area at the top, unless you put some sort of 'square top' sail with massive battens on it.
What was the mast made of? With carbon being mainstream now, masts ought to be getting taller for the same weight....

 

[lpdsn]

You don't just lose the little triangle of area at the top, unless you put some sort of 'square top' sail with massive battens on it.

And IRC just loves those.

 

[Foolish Muse]

Here is a very rough drawing showing the difference in sail plan between a 92' mast and 72' mast on a 55' boat. The red area shows the added sail size of the 92' mast.

Given the various costs (in money, crew size, sail handling, righting moment) compared to the increase in speed, I really wonder if it's worth it. Sure, if you are racing in a one design class, like an IMOCA 60, then every 100th of a knot is worth it. But if a guy has a 20 year old boat doing handicap racing, then I'm left to wonder where the costs outweigh the benefits. How much extra speed does he get for the extra 20' of mast? I'm not criticizing, just starting an interesting discussion. Do we have a handicapper here who can tell us the speed difference? A 72' mast is still bloody tall by most standards.

 

[flaming]

All sail area is not equal.

By having a tall mast you get a high aspect ratio sailplan, which is a lot more efficient than a low aspect ratio Sailplan.

All things being equal to get the best windward performance you want the tallest mast possible, fairly short boom, non overlapping jib. You also then get the advantage of being able to hoist a mahoosive kite when you turn around and go downwind as well.

 

[Foolish Muse]

By having a tall mast you get a high aspect ratio sailplan, which is a lot more efficient than a low aspect ratio Sailplan

That's interesting. Here is a link I found: http://forum.trailersailor.com/post.php?id=854970
The key line being "When working to windward, it's the vertical height of the foil that does the work, and not the length of the sail. "

 

[DFL1010]

AIUI, the longer the leading edge, and nearer to perpendicular to the airflow, the better (at least at the speeds we're talking about for sailing). So, tall mast means longer mainsail leading edge (obviously), and it also makes the headsail's leading edge more vertical and high-aspect for a given sail area.

 

[lw395]

All sail area is not equal.

By having a tall mast you get a high aspect ratio sailplan, which is a lot more efficient than a low aspect ratio Sailplan.

All things being equal to get the best windward performance you want the tallest mast possible, fairly short boom, non overlapping jib. You also then get the advantage of being able to hoist a mahoosive kite when you turn around and go downwind as well.

All that, and the top bit is in more wind and clear air.

Some people don't care about yardsticks or ratings, a fast boat, line honours can be more fun.

If the boat was built to some rating scheme before CHS, some of the formalas were public. You could work out what the compromises would be.
Might the boat be a 12 metre? In which case, the name of the game is level rating, so pile on whatever sail area goes with the hull design to give the answer '12'.
Not much call for 11.5 metre boats in a fleet of 12s....

 

[Bosun Higgs]

But what you guys are ignoring is increased weight and increased tenderness. I would have thought there was a sweetspot or sailors would simply install ever taller masts. 120ft anyone?

we have had trends carried to unworkable extremes in the past, for example with the very narrow beams

 

[flaming]

But what you guys are ignoring is increased weight and increased tenderness. I would have thought there was a sweetspot or sailors would simply install ever taller masts. 120ft anyone?

we have had trends carried to unworkable extremes in the past, for example with the very narrow beams

Of course, but carbon masts allow taller masts with the same weight. So the trend is upwards!

If you want to see real proof, look up the redwings. The only rule (at least originally, I'm not sure if they've tightened it over time) in that class is a restriction on total sail area.

 

[Keen_Ed]

Forestay has to be on the centreline, and they have to have a single masthead backstay. And the sails must be red.

200sq ft of sail

 

[lw395]

But what you guys are ignoring is increased weight and increased tenderness. I would have thought there was a sweetspot or sailors would simply install ever taller masts. 120ft anyone?

we have had trends carried to unworkable extremes in the past, for example with the very narrow beams

Yes weight aloft is a bad thing, from the heeling point of view it can be countered by more lead in the keel.
It's easy to dismiss this old skool type of design, until one knifes past you upwind.

More subtly, weight aloft increases the pitching moment, making the boat hit waves harder and slow down more.
Most extremes are products of rating rules. The rule then gets changed or superceded, leaving the extremes obsolete.

But some people enjoy having something that's not an AWB and good luck to them.

 

[Birdseye]

Not sure what it's got to do with AWB yachts. You can put an extra 20 ft of mast on one of those just as easily and the fact that designers of the likes of Benny Firsts don't go wild on mast height rather does suggest that in performance terms there is a sweet spot

 

[lw395]

Not sure what it's got to do with AWB yachts. You can put an extra 20 ft of mast on one of those just as easily and the fact that designers of the likes of Benny Firsts don't go wild on mast height rather does suggest that in performance terms there is a sweet spot

Performance/cost/rating.
AWB variety of yacht is generally not too much draught and not huge ballast ratio. So not massively endowed with righting moment. So the optimum mast height for an AWB is likely less than with a deep heavily ballasted boat.
The optimum for an open 60 seems to be 'as much as the rule allows' which is coincidentally not far off 92ft. With a nice square top main for area high up....

 

[Keen_Ed]

Open 60s now have a choice of two mast designs. One rotating, one fixed.