How light is it possible to build a 20 feet platform that is tough enough to endure hard sailing and tough conditions(texel, worrel etc)? Some will say that the M20 at 120kgs is already pushing the limit, and might have pushed it too far as some M20s have proven to be a bit too fragile in rough conditions. Macca, who by the performance and sheer looks of his upgraded Taipan 5,7 obviously knows what he's doing, recently mentioned in the Super Taipan thread that he thought it was possible to push the weight of a 20 feet long,10 feet beam cat down to 105kgs. I know Wouter disagrees, but what about the rest of you?

5.7 meters = 18.70 feet

105 kg is very light. As soon as you go 10 foot beam, the loads increase quiet a bit and the boat needs to be beefed up.

Note the M20 is 9 foot wide also.

Not saying it can not be done, but it would be a serious accomplishment. Fun to give it a go.

Jimi,
A superlight boat would be nice if you are only going to sail it in superlight conditions and superflat water.

If a squall comes through with winds of 30-60 knots, how do you hold that boat down? It is going to go flying away like milkweed seeds on the wind.

How light is it possible to build a 20 feet platform that is tough enough to endure hard sailing and tough conditions(texel, worrel etc)? Some will say that the M20 at 120kgs is already pushing the limit, and might have pushed it too far as some M20s have proven to be a bit too fragile in rough conditions.




I don't really think it is a question of it can or it can't be done. There is a transition area (grey area) where it dependents on what is considered to be "hard sailing".

I'm sure a 20 ft x 10 ft wide platform with a sloop rig can be build at 105 kg. How it holds up under varying condition is a different matter. How it will hold up in the (grulling) Worrell 1000 is yet again a seperated issue alltogether.

All I was saying in the other post is that Marstrom for some reason decided to forget about the initial 108 kg M20 and replace it with a 120 kg one instead. Remember this boat also doesn't have a jib setup which does really load up the bows !

I think Stephen has is on the right track and I want to expand on that. Reducing the overall weight of a beach catamran gets harder which each additional kg. Say you take the 140 kg Taipan5.7 (incl 5 kg spi setup). The hulls are already pretty lightweight so not much to be gained there. You want the boat to be significantly wider, this means that the use of carbon in the beams will not result in much weightsavings relative to the 5.7 as you'll need all the material you can get to restore platform stiffness. What is left ? Carbon mast ? 5 kg gains. Lets say you win 10-15 kg by using kevlar in the hulls, carbon mast, carbon beams, boom, pole and some other things. That still leaves you at 125 kg. Cuben fibre sails. Another 3 to 4 kg. Lets say you are down at 120 kg. What is now left to win those additional 15 kg of weight ? ... Not much at all. That is why some builders have decided to loose the jib as then the bows can be build lighter again. However it is still a very long way to 105 kg. Remember that Taipan 5.7 isn't an overbuild boat like the F18's.

What we are saying here is that we want to make an additional weight savings of 35 kg when a professional builder like Boyer had to work hard to win the first 40 kg. You must come up with some very smart things to do that.

It will definately be engineering challenge.

Wouter

Take a good dump at the little boys rooom & leave all the beer on the bar the night before a regatta, take 1 paddle instead of 2, only wear a shorty wetsuite, take off all the extra gear , lines, bags, waterbottles etc and do some exercise a 2x a week.. [I do non of the above..]this all will save you easly 15~20 kg. That 15~20 kg I personally would love to have [and stay] in the structure of the boat [remember Texel 2005]

But you do want to make you boat as light as possible don't you, no matter what the conditions? Ideally, if you could have a "bulletproof" boat no matter what the weight of it, a lighter boat would be faster than a heavier boat in all conditions would it not?

Oh and Wouter, this is exactely why I'm studying to become an engineer in marine technology. Give me a few years and I will take that challenge <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

I just don't get it. If I am out on the water in a LOT of wind, I for sure do NOT want to be on a super lightweight boat. Nobody seems to address this issue about how you hold the boat down and keep it from flying away, literally.

Obviously not being an expert, I can only give you a short answer. This is also why I started the thread in the first place.
I have seen a few pictures of flying A-cats, where it really did seem as a problem that the platform was too light. However, a lighter platform will require less force to drive it through the water, decreasing the all up loads on the platform and rig and therefore making it easier to control even in a big breeze. Still, when you go windsurfing and the wind is picking up you go for the smaller boards. It would be natural to conclude in the same for a beach cat. Hoping for some good answers on this one.

As much as I hate to say the following thing it is true nevertheless. A boat design can be TOO light to perform to its full potential.

I won't go into detail at this time, but suffice to say that the ratio of wetted surface area to bouyance (=overall boat weight) does play a factor, as well the ability to hold some momentum when sailing through choppy seas.

Also the first thing a good engineer needs to learn is that it is very traiterous to extrapolate (approximated) behaviour into extreme points.

But these are all topics for another time.

Wouter

"Also the first thing a good engineer needs to learn is that it is very traiterous to extrapolate (approximated) behaviour into extreme points."

Wouter, could you try to explain this in easier words for a simple, Norwegian student to understand? As I am studying to become an engineer, I will use all the advices I can get to become a good one!

Let's say you wanted to find out the relationship between the density of water and temperature. So, you measure the density of water at 10 C, 50 C and 90 C then fit a line through your data points. That's well and good, but you might run into problems using that line to predict the density of water at 101 C or -1 C.

If you stick with engineering you may hear about the concept of "inference space". Roughly speaking, that's the range of values for which we have experimental data. Using an empirical relationship outside of its inference space can lead to problems. In the example above, there are state changes just outside of the inference space which are not considered in the relationship. In other cases a variable may have a fairly constant value across the inference space (and therefore be ignored in the relationship) but not outside of that space.

I am with Mary... Heavy conditions, heavier boat. Lighter conditions, lighter boat. Obviously there is a very large overlap in the moderate conditions range but on the extreme fringes I like Mary's angle.

30 knots on the SC20 at 12' wide and well over 400 lbs was was at times a very tenuous situation, skipping on top of the water at one point then standing on the nose a second later. Without the weight and beam I am sure that we would have dmaged the boat in some fashion.

What about a hulls terminal speed?

I would hate to try and put this into a translator>>>

I believe what Wouter is trying to say is that every feature in a design has to be carefully ballanced to make a boat that can be considered good in more than 1 condition. The MacQuaire Innovation speed sailing boat is pretty fast and light but it only goes 1 way on flat water. Upwind performance must be ballanaced with downwind performance, abilty to sail in flat water has to be compromised for performance in waves or chop, no 1 design will do it all.

It is possible to build a boat significantly lighter than what is being typically made up there now. The loads on a boat during sailing are not the only consideration you need to make though. Hnadling a boat on land, on and off a trailer and through non-sailing gyrations such as righting after capsize etc. require quite a bit more structure to make something that will last. A min weight boat designed with consideration to the sailing loads only will most likely look like a golf ball after a few weeks due to heal and other body part contact, and you will probably have gone through a few masts and other rig parts as well.

From a practical consideration my opinion is that the current A cat is about as low as you would want to go design wise. Even here you only have a 1 up uni rig platform that you will only rarely see going out in winds over 20 knots, and when violently pitch poled stands a pretty good chance of requiring a new mast.

The other trade off I have not mentioned hits on the cost. Lighter is better, but below some already explored limits the advantage is questionable at best. If you realy want to save weight the biggest bang for your effort is still a diet.

<img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Matt

<img src="http://www.catsailor.com/forums/images/graemlins/shocked.gif" alt="" /> <img src="http://www.catsailor.com/forums/images/graemlins/laugh.gif" alt="" />

Had this conversation ages ago one night at the sailing club. I had a sailing mate who worked to Lola (race cars in case you did not know). His comments were that given a big budget you could get down to somewhere around 80 kg. It was really down to cost. Buy the best stuff, cook it properly and you get strong and light. BUT it will cost loads ! How much does a race car cost to build - Lots. Mucho expensive carbon !

He did a fag-packet spec, and he was saying that the problems would be the fittings. We got top the point where we were building custom carbon blocks, carbon eyes for the tramp etc. Got silly, but he suggested 80kg was possible, but expensive !

Wow, 80kg!!! That is a little lighter than my Nacra 5.2, I am sailing a battleship compared to some of the stuff out there.

Sailing a 140 kg Taipan 5.7 myself (with JIMI), I would say that Wouter's estimate of weight savings seems reasonable. Producing a reliable 20-foot cat lighter than 120 kg may not be worth the effort.

"I won't go into detail at this time, but suffice to say that the ratio of wetted surface area to bouyance (=overall boat weight) does play a factor, as well the ability to hold some momentum when sailing through choppy seas."

This I did not understand (it is not the extrapolation that is difficult). If high momentum was a priority, we would not see the light-weight building that we see in all development classes. And losing weight in the mast, bow and sterns is always desirable in order to cope with waves.

What did you mean by "ratio of wetted surface area to bouyance (=overall boat weight) does play a factor" ?
The distribution of volume/weight is of course important for the boat's behavior in different conditions. Did you mean that reducing overall weight is less important than which parts of the boat which is made lighter?

Stein

"If a squall comes through with winds of 30-60 knots, how do you hold that boat down? It is going to go flying away like milkweed seeds on the wind."

How heavy a boat do you need to be "safe"?

History of all development classes seems to show that initial problems of surviving in strong winds are overcome by improved boat-handling technique. E.g. the 49ers have moved their max-wind limits quite a bit since their debut.

As an amateur, I am more worried about breakage than being carried away (if you excuse the pun).