If you want a light boat, make it simple and clean!
* Glue the boat together, no screws or heavy fittings to transfer the load from the beam to the hull.
* Remove the jib, and make lighter hulls since the compression of the hull is reduced.
* Without the jib you can use twin forestays and get a stiff boat.
* Use lashings for the stays and use something else than stainless wire for the stays.
* Use light sails, different materials in the sails can differ several kg! For example the MAXX sails are quite heavy since they are strong in all directions compared to "normal" cloth.
* Remove fittings and trim lines. Check the latest A-class boats from geltec, they are clean!!

If you want to go the other way you can see how the M20 was downgraded by some owners by adding a jib with bridle, stainless wires, external halyard for the spi and a big fat block system for the main sheet instead of a light caskading system, no wonder it weighed 120 kg. But which version of M20 won the texel, the original M20 of course!

/håkan

There are really no issues with sailing light boats in strong winds compared to sailing heavy boats in strong winds, in fact as with everything the lighter the kit the easier it is to use.

A hobie 17 is often reckoned to be an easy boat to sail in a strong wind compared to an A cat, but is that because it is twice the weight or because it is very undercanvassed compared to the A.

To make an A go as slow as a Hobie 17 you would have to reduce the mast height by 6 feet AND the sail area by 1/3, now which boat do you think would be the easiest to sail.

Conversly to make the Hobie 17 as quick as the A class you would have to add8 feet to the mast and a whopping 42% extra sail area, whose going to hold that down in 25 knots.

My point is that it isn't the weight (or lack of it) that makes a boat hard to sail more the size of the sails compared to that weight. So in order to compare how easy one boat is to sail against another you must pick boats of similar width and speed.

A Hobie wave weighs in a lot less than a Formula 18 so does that make it harder to sail when the wind gets up.

Back to the original question (how light could a 20’ cat be built) and disregarding all the other considerations/arguments IE water, wave, wind, handling characteristics on and off the water, etc, given the available manufacturing equipment, (high pressure die moulding) the availability of the high grades of aramids and aerospace carbons, the latest high modulus high temperature resins, and an unlimited budget (wouldn’t it be nice if it wasn’t just a dream), there is no reason why a “bullet proof” 20’ cat couldn’t be built at a weight of less than 50kgs all up.

I'm calling BS on this one.

One of the very first problems, of many, you'll run into will be the lack of stiffness. Additionally nearly every component will be in constant danger of buckling.

We are talking about a 20x10 foot racing beach catamaran here. It has to go out through a surf, carry two people and carry enough sailarea and a spi to even have a remote chance of winning a race.

Sorry guys, 50 kg all up ?, we are getting into the realm of BS now.

Wouter

I am sure that was a typo Wouter........ Missed the 1 at the front <img src="http://www.catsailor.com/forums/images/graemlins/wink.gif" alt="" />

I like what John P says. It is more about the sail area you can carry in the given wind strength. I have wondered why beach cats don't have different rigs for different wind speeds, just like the 18' skiffs and windsurfers use. That way, you could build a very light platform, use the small rig for big wind and the big rig for light air. Of course you would also need a medium rig for those medium days! <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" />

But it would cost 3X $ for 3 different sail packages, if you used the same mast. And you would have to make such a boat practical as Matt has said above, or nobody will buy it.

I wonder if the surviving Inter 20 boys from last weekend's Steeple Chase could add their thoughts to this? I'm thinking if they had put Hobie 16 sails and a smaller F18 spinnaker on the Inter 20 platform, they might not have been flipping so much and been "faster" to the finish line. Also, if you could put 10' beams on the Inter 20, it would be more stable. Too bad there were no Tornados to compare with this year.

You guys want lighter and lighter boats, that always turn out to be wider and wider! <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

How about developing the rig more? There is an archaic rig, called a sliding gunter, that is still used on light canoes. It might offer the kind of versatility Timbo suggested.

It would require A LOT of redesign, but for engineers who are looking for a challenge. . . ! <img src="http://www.catsailor.com/forums/images/graemlins/shocked.gif" alt="" />

If you were prepared to be really radical <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

I could easily make a 20ft version of my 4 hulled boat down to 75kg, just substitute the Al beams and submasts for carbon and glue the beams to the hulls.

The biplane windsurfing rigs allow you to easily get different rig sizes just like on a windsurfer. 3 rigs 12m, 9m and 6m would give you 3 rig sizes 15m 18m and 21m, which is still quite inexpensive and lightweight. Total rig weight, mast, boom, sails, blocks, stays etc is 25kg for a 16sqm rig. How does that compare to a conventional rig?

Also you can carry a much higher sail area for a given wind strength on a biplane rig.

I could probably make a cat by having a soft central "hull" bridging the front and rear hulls and not increase the weight by much.

Gareth
www.fourhulls.com

Start with the data points that are out there

A class catamarans. Newer Australian a cats are coming in at as low as 150 lbs (68 kg). These boats have gel coat finishes and foam cores and are made using resin infusion. They are rugged and don’t break under normal racing. In Bristol, RI which is a moderately windy venue there has not been a mast break in 2 years, this translates to ~ 25 boat years sailing without a mast break. Current A cats cost 17-23K new.

You can definitely build these boats lighter if you are willing to pay for it. Change to prepreg carbon with a nomex core autoclave cured hulls, cuben fiber mainsail, use of boron fiber in the mast, all composite rigging, lighter trampoline. The problem is that you now have a very expensive boat. What would it weigh? You could reduce the weight by at least 10% if you were willing to increase the boat cost to say 30-40K$. You are in the range of diminishing returns for a 60 kg boat.

On the other end of the spectrum is a modern C class catamaran. 25 ft long 16 ft wide, double trapeze, wing sail ~ 365 lbs (new Canadian boat) 165 kg. It is a very expensive toy. I don’t even want to guess at costs.

It seems to me if you want a light 2 person 20 footer that did not cost a huge sum, what I would go for is 8’6” beam (not 10) Resin infused, foam core hulls, carbon mast and glued carbon beams. It would be a unirig with a 33 ft wing (not pear) mast and a flat 240 ft^2 spinnaker. It would weigh about 250-275 lbs. Rigging would be dyform, attached with lashings and have aramid trap lines. More importantly, it would be easy to handle on the beach and awesome to sail.
It would not be all that much faster then an inter 20 in most conditions. It would cost around 30% more then an inter 20 and very few people would buy them. Those people that did buy them can’t understand why everyone else in the world does not send their I-20’s to the dumpster and get with the program. Soon Bob Curry pronounces that this new lightweight boat is just a fad.
The builder, in order to stay in business, cuts 2 feet of the bows of the boat, adds a jib, pours in an 80 lb bag of Portland cement in each hull, paints the masts silver and calls his boat an F-18. Soon he is outselling all the 20 footers in the world and making millions of dollars.
When the price of Portland cement increase to 90$ per barrel, he sells his boatbuilding business to an Arab named Vinny Marawck Al Saud and retires to Costa Rica where he buys a 3rd rate brothel and dies of a previously undiscovered and incurable venereal disease.

This is why light weight double handers will ultimately fail, and condoms are very important.

Eric Anderson

You got it absolutely right, thanks for the laugh <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />
If catsailor.com had a "post of the month" or even "post of the year", this would be the winner.


Why lashing dyform rigging instead of synthetic shrouds when you alread have gone for aramid trap lines, and what would you lash it to?

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

Interesting concept... will talk to my investors and present this as my business plan!!!

Clayton

Nice one.. you got me interested right at the end.

I think you should use carbon nanotubes. forget about carbin fibre and kevlar..that is old school.

...and Sinclair Molecule Chain for shrouds!

Eric actually point out a rather important issue. Who wants lightweight 20 footers with 10 foot beam? Why would sailors buy/build them and not I-20s or similar boats. What would the selling point be?

I think this may have been discussed a couple of times before <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

Actually, F18 would be nice if they could get rid of the 80lb Portland cement...

S

Håkan,

I'm truly sorry to notify you about the following :





It was actually the original 2003 PRODUCTION version of the M20 that was finally and officially measured at 120 kg, not the modified sloop rigged M20's that can be found in NL now, those are around 137 kg ! I seem to remember that in 2003 we measure 3 or 4 M20's and took the average of the weight measurements.

I know as I was actually the round Texel 2003 rating official who personally cleared the 2003 M20 measurement right there in the Race Committee office.

However, even since then the weight of the M20 has been on the rise. Currently the Texel measurement system quotes 127 kg for what you call the original M20. Look for yourself : http://www.watersportverbond.nl/data/5Z2_numdet1_3-7-2006.pdf

Interestingly enough the 2006 Round Texel M20's were all sailing of the Texel handicap rating number for the 127 kg boat. If the Swedish boats were much lighter then that then that is cause to protest their final results on the grounds of using incorrect (too slow) handicap numbers.


Wouter

Rolf,
there is always a tradeoff between Higher tech and light weight vs cost. I don't think synthetic rigging is worth the cost and hassle vs weight savings.

You can build a moderately high tech boat (A cat like levals of technology) without going up wildly in price.

On the other hand Jim Boyer tried to import taipan 5.7's into the US and no one bought them. They were a sweet sailing, well built boat that was 170 lbs lighter then the nacra 6.0 it competed against. The problem was it was 3-4000$ more then the nacra and not that much faster. It sure was alot nicer to sail though. All that means nothing if people don't buy them.

Wouter,
are you really sorry about the M20 weight!?

I think we have the answer to the question here. If you want a 20x10 uni rigged boat with spi it is hard to get below 100kg. Marstrom started at 108 kg but 15 boats later the boat weights 120 kg. Why? The parts that have been reinforced on the M20 are rudders and centerboards.
The rest of the weight increase is a mystery to me!

/håkan

I have a true story on the concrete thingy!!!

Booth made an F18HT of an A-cat (M18) and had to add loads of weight on the boat to get it up from 75kg to 130kg of boat weight. He didn't use concrete, he used lead in the main beam. Some of the weight came from a taller mast, bigger centerboards, bigger sail and spi kit but the rest was lead.

/håkan