More dinghy speculation...

[dancrane]

I looked at a site that details the dimensions/displacement/race rating figures of over a hundred dinghies, in order to pin down why certain designs are so much more appealing/successful than others.

To be honest, I'm not much wiser than before!

I think I was most surprised by how similar most 'average-sized' dinghies' mast heights are. It could also be that the figures quoted were inaccurate - I've seen some lousily approximate conversions from imperial to metric, and inconsistent details even in official class association documents.

But almost every design measuring more than about 14 foot long, regardless of racing/cruising/training use, seems to employ a 6 to 7 metre mast, or thereabouts. Isn't that weird?

GP14? 22 foot mast. Flying fifteen, (six foot longer, with an iron keel for stability)? 22 foot mast. Contender? 5-0-5? Wayfarer? All the same within a foot or so.

I know there are exceptions to this, but I'm surprised there's any common measurement, amongst designs that are otherwise so varied in their dimensions and form. Is it a magic point seven yards or so above the deck, higher than which sail area just can't be controlled?

Or was the document littered with mistakes? Here it is...

http://www.yosc.org.uk/pys.pdf

 

[William_H]

Mast height

Just from memory I did not think a GP14 had a 22ft mast. And I would feel sure a Flying Fifteen has a lot more than 22ft mast. The hull being near that long. So info may be duff.
However Al mast lengths tend to be dictated by the other dimensions of the mast. So 22ft might be about the length of a typical piece of Al section that might be appropriate to a dinghy. olewill

 

[westernman]

Also watch out for deck stepped vs keel stepped, height above waterline etc etc.

 

[Stu Jackson]

For boats that size, the hull shape has a lot to do with the mast height and sail area.

Come to think about it, almost ALL sailboats do.

 

[Seajet]

I agree with William H, the figures sound a bit dubious.

However, length of alloy extrusion seems reasonable ( though boats used to be built in much more expensive ways than today, sadly, and some started with wooden spars ) - another factor and I'd think the major one leading to a fairly common rig size is, 'what can 2 average people hold up when hiking on the side ?'.

 

[shaxi]

another factor and I'd think the major one leading to a fairly common rig size is, 'what can 2 average people hold up when hiking on the side ?'

i'd want to know too !

 

[nickd]

I think there is also;
A limit to the length that can easily be stepped, dont forget these are dinghies that are trailered around often
and
A limit to how long a mast one can practically have on the towed dinghy before it either bows too much or sticks out too far

 

[Iain C]

What you need to bear in mind is that a racing dinghy will be designed to operate in "average" windstrengths, and generally won't be reefable. Some dinghies are designed for certain conditions...eg Thames A-Rater has a very tall rig to get uninterrupted airflow up high above the trees on the river bank, but will be a handful in a blow. Obviously the more righting moment you have (by adding crew weight/crew numbers/trapezes/beam) the bigger rig you can carry, and the faster you go (see "sail carrying power" in Bethwaite)

An intersting boat on your list is the Cherub, a development class. I was on the class committee when the rules were changed in 2005 to a bigger rig and twin wires, beforehand the mast height was unrestricted. There were some boats with very tall rigs which did very well in light breeze, and boats with short dumpy rigs that were unstoppable in a blow. We brought in maximum and minimum mast heights to make it a bit more even.

Some dinghies have multiple rigs...the RS600 is reefable, with a stump you can add to the mast, 18 foot skiffs have two complete rigs, and 12 foot skiffs have four! However go out on the wrong rig and you will get a kicking, either on the results page or at the hands of mother nature!

 

[Sailfree]

A factors may be economy so they choose a "standard" mast from Selden etc. The other is total length for convenient towing.

 

[dancrane]

Those sound like sense, and may well be among the reasons.

But I'd expect the ambitious designers of dinghies to circumnavigate the problem of towing length and fixed standard-length products, by using segmented masts - surely it wouldn't be difficult to wedge an extra couple of yards of pole up the mast's base, to give the rig an extra fifty square foot on force-one days.

 

[EBoat126]

Some dinghy masts are deck stepped and some on the keel band on the floor of the boat so you can gain or lose a couple of feet there.

The mast on our F18 is 9m and is a pretty common section used by most beach catamarans to keep cost down (not that you'd think so having just bought one)

 

[dancrane]

I was thinking, if a dinghy designer wanted a taller rig, he could easily specify a mast from a larger vessel and lop off what isn't needed.

Hard to believe that any new boat's ground-breaking thrilling performance, would be written off in the constructor's shed, by a lack of suitable standard masts.

Must admit, I've regularly been overpowered by the standard rig aboard much smaller dinghies with much lower rigs than the popular 6.5 metre mast height. I can predict, in a force 4 next year (whatever dinghy I choose), I'll wish I'd never suggested the sailplan was undersized.

Then again, I've often been intensely frustrated in a drifter, by the designer's assumption (or commercial obligation to assume) that one, not too-big, not too small size will suit all occasions.

As was said, provision of a tough, really big rig that can yet be effectively and efficiently reefed in hard weather, would be ideal.

Another case of DIY-only, I guess.

 

[ff_nick]

Inaccurate figures I think. The luff of a Flying fifteen main is 6.25m (20'6"), the mast about 7.5m (say 24'). Apparently the whole rig is a straight copy of one from Uffa's contemporary I14s. 505 rig is almost the same. I guess a GP's mast is quite a bit shorter.

Edit: just checked the class rules. 22' is correct for the GP14 mast.

 

[dancrane]

The Flying Fifteen certainly appears in diagrams, to have its masthead 23'6" above the waterline...which I regard as the mast's height, as opposed to its length. Information from a former GP14 owner, here...
http://www.shorebase.co.uk/boating/sailing/gp14/gp14.asp
...describes the GP's mast being 23' long.

Not sure about his accuracy; nice article though. And that measurement does bear out the figures in the YOSC list.

Not much in it, then...which is my point. I too would have thought the bigger boat would carry a much taller rig.

What really surprises me, is that it isn't possible to find the mast-height figures at once, on the same association sites where dinghies' LOA, beam, displacement and sail area are listed. I know some classes deliberately don't have a standard mast length - but most classes' racing rigs are broadly alike, yet the small matter of actual dimensions isn't mentioned.

Not even by the mast-makers! I've been through Selden and Proctor sites, and they're happy to be very specific about tensile strengths, weights, shapes, etc...but no mention of the pole's length!

 

[Seajet]

Not much in it, then...which is my point. I too would have thought the bigger boat would carry a much taller rig.

Me too, not least as the Flying Fifteen had a ballast keel; however I suppose that was the time of slim, elegant designs like the Flying Fifteen, Dragon, the earlier Sharpie and even the 1970's Aphrodite 101, all 'sailor's boats' which didn't require a big rig to push them.

 

[Stork_III]

The Flying Fifteen certainly appears in diagrams, to have its masthead 23'6" above the waterline...which I regard as the mast's height, as opposed to its length. Information from a former GP14 owner, here...
http://www.shorebase.co.uk/boating/sailing/gp14/gp14.asp
...describes the GP's mast being 23' long.

Not sure about his accuracy; nice article though. And that measurement does bear out the figures in the YOSC list.

Not much in it, then...which is my point. I too would have thought the bigger boat would carry a much taller rig.

What really surprises me, is that it isn't possible to find the mast-height figures at once, on the same association sites where dinghies' LOA, beam, displacement and sail area are listed. I know some classes deliberately don't have a standard mast length - but most classes' racing rigs are broadly alike, yet the small matter of actual dimensions isn't mentioned.

Not even by the mast-makers! I've been through Selden and Proctor sites, and they're happy to be very specific about tensile strengths, weights, shapes, etc...but no mention of the pole's length!

The actual mast length is incidental. Most dinghy classes will specify the limits for the mast bands which controls where and how bid the sails can be. The FF has 4 mast band positions specified.

 

[dancrane]

Hmm. Good points, thank you. The subject I'm working painfully slowly round to, is whether a FF mast and sails would be a suitable rig to put aboard a much smaller dinghy, with a view to increasing its sail area and power in light airs.

I see what Seajet means, and the FF certainly has that old-school lean-ness that didn't need much driving. The sad point being, that as the FF's rig isn't very big, its use as a dinghy-booster is probably doubtful! Pity - lots of cheap old FF kit out there...

 

[ff_nick]

I see what Seajet means, and the FF certainly has that old-school lean-ness that didn't need much driving. The sad point being, that as the FF's rig isn't very big, its use as a dinghy-booster is probably doubtful! Pity - lots of cheap old FF kit out there...

How big do you want? FF rig is the same size as an 1940s International 14 - about 150 sq feet. 505 is about the same (ignoring the kite). Of course there's always a lot of used 505 stuff around too.

 

[dancrane]

Thanks, I'm sorry to be so vague myself. I read that the 17'6" Javelin carries 170 square foot, upwind. A big rig, but they're pretty rare.

Any of these - 505, FF, I14 would likely give a fair jolt of extra power to an otherwise too-sober design like a Wayfarer, I suppose, while leaving the hull itself as practical as ever. Any big yet reefable rig would suit, after trials to adjust centre-of-effort, etc.

Wouldn't want the new rig weathercocking or leehelming uncontrollably, though I suppose any larger-than-standard rig stepped in the existing mast plug, is unlikely to cause lee-helm.

 

[Iain C]

Dan

If your whole post basically revolves around trying to turbo-charge a Wayfarer, the answer is very simple. Just put a trapeze on it. The speed difference in decent breeze will be a lot, however you can go and put a huge rig on it in light airs and it won't be that much faster.

However weight and hull shape are far more important...stick as much rag on it in light winds as you want but it will never go that fast!