ive built a few solo ocean race boats in my time. the current thinking is that every extra kilo is worth about 4 hours on a rtw race.

There is a very good statistical analysis on the web:
http://www.geocities.com/f16hpclass/F16HP_optimal_crew_weight_analysis.html
I recommend to completly read it, because the author actually made two analyses. One simple normalised time to finish over weight (light boats are better even in strong winds). In a second attempt he realised, that the good sailors have in general lighter boats. He compared than the relative performance of each boat in different wind conditions and found that light crews/boats perform better in light wind and heavy crews/boats better in strong winds.

Another proof is, that top sailors are in general not lighter than average and that female crews (which are lighter in average) are not the faster sailor in average.

If you can't use the benefit of a heavy crew in strong wind, than maybe because you don't have the right heavy weight trim for your boat.

Cheers,

Klaus

Basic marketing: If you want to sell a boat, you have to satisfy the wishes of the customers. There are also golf clubs out of CFRP and titanium and cars with four wheel drive which will never be driven outside of big cities, and so on. What counts is that they sell.

Every kilogram of resin, fibres or whatever is your boat from costs the builder something. Hence there is no interest in building heavy boats. BTW: manufacture costs and selling price are not the same.

Of course if somebody is convinced by the weight issue, his mind will be blocked until he get rid of the last gramm. As a marketing guy I would put even more fuel in this fire and offer extra sets of CFRP rudders and boards, dyneema sheets and so on.

Don't understand me wrong, I am very happy, that there are lightweight boats, because you can handle them so easy on the beach. But I concentrate on sailing and not on material.

Cheers,

Klaus

A heavier boat may in some conditions generate a higher righting moment however it is the ratio of righting moment to weight that drives performance. If Klaus is right I should be adding weight to my boat on heavy air days. I've never seen anyone do that.

A heavier boat only adds half of the extra weight to the righting moment, and multiplied only by the width of the boat: say 10 kgs of extra boat weight give 5kgs*2.5m=12.5 Kgm of righting moment; 10 kg of extra crew weight add 10kg*3.4m=34 kgm, practically the double of righting moment; boat of 2,5m width and crew of 1,8m assumed. This is why extra boat weigth is much more important than extra crew weight. Downwind it gives more or less the same disadvantage, at least for cats that go on two hulls downwind.

From my personal experience I we have found that older sails don't pay on a older boats in all but very light wind conditions. We gained a lot when we got new sails on our 1991 H16.

F=m*a...

This has been experienced over many different crews, all very good sailors.

With my crew I sailed with for 7 years, we steped onto the Capricorn at 186 kg, and by the time the AUS Worlds came about, we were 164kg. We could feel the difference in the boat as we became lighter. Just after the Worlds, I had several different crews jump on ranging from 85kg to 65kg. VMG was better as the crews got lighter.

Exactly. It is quite obvious that the weight should be added to the crew and not the hull.
Also, bigger boats should increase the water ballast in the back of the windward hull.

Thanks for the reply, it certaily makes sense to me. 18 kgs seems significant.

One more question.... let's use 10 kgs wieght difference in this example. What order would you place the following (from most important to least important - obvioulsy all would help)?

1. New set of sails
2. Completely faired hulls, rudders, boards
3. Get boat/crew to minimum weights (10kgs)
4. Extra 5 hours practice each month

What else should be added to the list?

Thanks for the input.

4
1
2
3

Time on the boat is always the key. 5 hours extra is not a lot but it helps. I would rather spend more time on the water than working on the boat to get it completely fair, to min. weight etc. etc.

Actually we do this on landyachts and several larger racing Cats and Tris have waterballast in this way.

It is being done; you were just never around to see it. <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Wouter

"the only place where weight improves performance is in a steam roller" ... Uffa Fox <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

water ballast is very different from static weight.

5. get the sail and rig trimmed
6. having a positive attitude
and I would split 2) in
2a. faired rudders, boards
2b. faired hulls *)

My ranking is:
6
4
5
nothing
1
nothing
nothing
2a
nothing
2b

*) long bodies are less sensitive to roughness than short bodies (i.e. rudders and boards) due to Reynolds number effects.

Cheers,

Klaus

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Water ballast in the transom.... Or what the big Multi sailors like to call them, the 'Oh [censored] Tanks'.

If they had a choice, they would prefer to run without them but are necessary for saftey

Apparently Uffa Fox (designer of the laser dinghy) didn't look around too much.

Many racing mono's have waterballast (Volvo ocean, Classe Mini (the open fleet), large cats and tri like Orange). Many competition landyachters put (bags of) sand in their **** during days with strong winds and competition glider planes use a significant amount of waterballast to improve both airspeed and distance covered before having to find another thermal to regain altitude for the next leg.

Of course keel boats need weight on the end of their "fin" to even be able to make forward progress and sailing ships or a past era (galjons and clippers) used massive rock or brick ballast placed inside the hull on the keelline to stablize the boat, they would capize otherwise. Actually these bricks would be transported in the otherwise empty ship to the colonies where part of it was unloaded and used to build the settler towns. This was possible as the return cargo of species and other goods would make up for the reduction in this ballast.

I guess the designers of all these championship craft are just misguided.




But they don't have that choice as the alternative is to cut down on the saildrive and that loses more performance. Therefor it is not only a matter of safety, it is a matter of performance where they are unwilling to solve the issue by powering down the rig (loose performance)

Wouter

Well put Jimmi.
<img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />

C'mon Wout, that's not fair! The man was brilliant.

http://www.uffafox.com/uffabiog.htm

btw- I can't find any mention of his having designed the Laser. I'm not saying he didn't! Just can't find a citation.

There are alot of misconceptions associated with boat weight, some falsehoods even.





First of all, the same water that is pushed out of the water pushes back against the hull on the rear part of the hull and thus negates a very large portion of the "push-away" drag on the front part. The form drag is actually ONLY the net difference between the "push-away" and "push-back" phenomenon and in a frictionless fluid this net difference would be zero, resulting in zero drag. In real life fluids like water are not frictionless and the amount of internal friction forces for a given fluid determines the amount of form drag. That is why the same hull in water has less form drag then say in oil.

Therefor the popular representation ;"each extra lb. of weight in the boat/crew is another lb. of water that water that has to be moved out of the way for each boat length travelled" is misleading as it omits the part where the same additional lbs pushed back later and gives back some of the energy lost on the front part of the hull.

Secondly for some factor to be very important for the overall performance of a sailcraft it needs to constitude a significant part over the overall drag. If a given component only makes up 10% of the total drag then a 25% reduction of that factor only amounts to 2.5% drag reduction of the total with an even less performance gain (= for floating objects typically (1-1.5%)

The team for the C-class catamara Miss Nylex publized some of their research data and I give some of their conclusions regarding drag factors.


Hull drag (subtotal = 35%)

-1- wave/form drag = 15%
-2- skin friction drag = 20%

Sail drag (subtotal = 25%)

-1- form drag = 9%
-2- induced drag= 16 %

Centreboards = 20%

parasitic drag (group of 7 subcomponents like rigging and crew each less the 4%) = 20%


Note that even form and skin drag combined only make up for 35% of the total drag on a C-class catamaran with a highly efficient wingsail. On our catamarans the rig is less efficient and the sail associated drags will increase reducing the relative magnitudes of the hull form and skin drag factors.

35% may sound like a large portion but we still haven't completed the analysis yet. 1% additional weight doesn't increase the hull related drag by 1% of 35% = 0.35%, it is less. This is because of the non-linear dependence of volume (weight) and surface area upon size. We all know this to be true as a bottle that is twice as large will have 4 times the surface area and 8 time the enclosed volume (weight).

Assuming the hull can be optimized for a given boatweight and crewweight then for each 1% of additional weight you only have to entlarge the hull by 0.33% resulting in similar fractions (0.66%) of increased hull area and crossectional area. Also the fractions became smaller within increased additional weights, again due to the non-linear behaviour.

Basically (a simple example) an additional kg on a 100 kg boat + 75 kg crew (0.57% weight increase) results in a hull drag reduction from 35.00% to 34.86%. Which on the total drag of a sailcraft like Miss Nylex results in a less then 0.140% reduction => ... => on average 0.1% performance increase for a waterborne craft (= about 3 second per hour racing). Of course this is for lightweight boat with a singlehanding crew with everything else like sailcut and windconditions being perfectly equal. When looking at doublehanded crews on heavy boats the difference becomes MUCH smaller as 1 kg difference here will be a much smaller fraction of the total. In effect the solo sailor on a lightweight singlehander is the worst case scenario. However, allowing different sailcuts (formula classes instead of One-design) is so potent that it is able to complete ofset this weight dependancy, as proven over and over again in the A-cat class where 85kg skippers are competitive with 65 kg skippers on a world championship level. That is how small the dependence of weight in the larger picture can be and why OD garanteed equality in performance is such a myth. In several cases the OD character of a class makes the differences in performance worse !

We should now do the analyis on 1% difference in sailarea and see the difference between that and the dependency on weight. That tells an interesting story as well and why water or sand ballast can be an advantage on sailboats and landyachts.

Wouter