The micromultihull rule

Micro multis

Gday all

As someone who has designed and built one finished and one partially finished small cats I think I can give some idea of their strengths and weaknesses.

I think a micromultihull rule will not work as long as it is made for fast boats. That is not a typo. I have a big thing about the best race boats being re-usable. Take a Laser, Hobie 16,J24 Etchell or back in the old days a Windsurfer. You could use any of these boats for
-racing the best sailors in the world with a fab new boat.
-racing good sailors in your area
Then when the boat got older
-you could race in the middle of the fleet with your club
-use the boat as an afternoon racer
-cruise the boat
-use it to teach sailing
-hire it out (Laser, Hobie, windsurfer)

So my take on the micro multi rule is to make the boat the very best CRUISER it can be. It has to be able to take people away for a night or two, take newbys out sailing, fit into many different niches and survive well. It has to be tough and long lived and not really very fast. In fact racers actually do not need to be fast as they usually come back to the same spot where they started. Cruisers need to be faster as they actually have to get somewhere.

This is all a bit upside down but I am an ex racer who qualified for the worlds in a Laser - Racing was ALL I did and it was the racing that got me - not the speed. I got heaps more adrenalin from a start of 160 slow Lasers than racing 8 other superfast Tornados.

cheers

Phil

 

thx for those two links, rzj. the 'folding cat' is just my ideal size and shape, but the machinery too complex for my taste. "add lightness, and simplicate" as some motorcycle designer put it.

 

After all you are down under

 

I quite agree with Catsketcher.

When I developed the micromultihull rule I wanted to ensure that boats had a dual purpose and could be used for cruising. In a way it is more important to do that with small boats as they are often bought on a budget and owners cannot afford to have a boat sitting idle or losing money on a boat with a low resale value.

In fact in the original rules I suggested that major regattas had a long race which finished in a different port than it started. That was to force all crews to live on board. At the time it didn't occur to me that crews would stay in hotels. But at least I tried.

I also didn't want the boats to get too extreme, in part because I know that many people aren't as good sailors as they think they are.

So the F28, the racing offshoot from the micro class only lasted a couple of years, as did the F40. Whereas the micros are still being cruised and raced.

My version of the folding cat problem is solved with my 22ft Wizard and 25ft Sango designs, both of which you can see on my website.

And on the Articles pages you can read a history of the Micromultihull rule and some newer thoughts on performance boats.

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Right. This is why I found the micromultihull rule so attractive-- the boats were required to have some degree of accomodation, so they could be used for something other than racing.

 

Its really hard

As someone who has designed two small cats - 6 and 7 metres I think one of the reasons that small multis aren't designed much is that they are really hard to do well.

Any idiot can get two hulls and bang em together but if you really try to fit people in a small boat basic problems emerge. People need 3ft above berths that are 6 ft long no matter what the boat length. Also water and stores weigh almost the same no matter what boat you are on. The chance for error is so great on a small cat.

If a designer gets the weights of his large cat wrong it will usually be because the builder added stuff or people added extra comforts. Maybe an extra 15% is added and the boat floats down just a bit, usually at the bum.

Half of those extra comforts on a 800kg cat are catastrophic as they are so much of the total weight of the boat. When the four of us go away in Cats-paw we add almost 400kg to the displacement of the boat and it doesn't weight anything near 800kg. Our 38 footer gets almost the same load and the proportion is not half but 10%. The boat barely notices. If the designer gets it a wrong with a big boat - big deal add a transom extension. If a small one goes wrong the boat needs to be cut in half and rebuilt.

Look at the video of the Shuttleworth cat. If you look at the flare you will see that with the load on it the flare is in the water - light ship. Add water and stores and you have very fat hulls. This wouldn't happen with higher immersion rate large hulls. I would be very unhappy to sail this boat - the lee hull will be high drag in all weather but especially in chop and without major modification (cutting the thing in half and widening) you can't fix it. Lee hulls go down in cats. The Shuttleworth flare type hull is great in large cats but in small cats it is disastrous if the weight is over the designed limit. I use this shape myself and am very aware of its problems.

As to Bill's point about simplicity - this is a hard one. Folding adds complexity straight away. Add floors, keeping the rig up, keeping hulls aligned, stopping hulls rotating, keeping fingers safe and more and you have many very necessary conditions needing fulfilling. There are many complex and reliable machines - cars, computers, clocks, a roller door, kitchen rollers etc. They can be made to work but a small cat has very very little room for error. I like the idea of small cats which is why I am refitting the 38 footer for sale but the amount of design restrictions you get is amazing - especially if you want to trail it.

cheers

Phil

 

I have to agree with just about everything Phil says. With small cruising cats the difficulty is not in making them sail well-- it's in making them comfortable.

As an example of the severe constraints you encounter in drawing tiny cats, my 16' open cruising cat, Slider, presented me with a difficult choice very early in the process. No matter how I squirmed, I couldn't figure out a way to have both cabins and comfortable seating in a boat that small. This dilemma turned out to be a godsend, because it led to a breakthrough in my thinking that resulted in a boat that as far as I know is unique. And though I don't have cabins, I do have the most comfortable-to-sail boat I've ever been aboard.

Here's a construction pic that shows the perfect ergonomics of Slider's seating.



It's like sitting in an armchair, because the steering lines run around the outside of the cockpits, so you steer with your outside arm lying along the deck at the same height as an armchair's arm rest.

What Phil says about weight is absolutely true. Slider is designed to carry two people and their camping gear. Last summer I took my two teenaged sons cruising, and for the first time ever we got a little spray in the face while crossing a choppy bay. They're both skinny kids, but their weight and the weight of their food, water, and big tent was enough to make Slider a less dry boat.

I think the failure to consider ergonomics is one of the most common reasons that small cat designs can fail. I remember years ago a novice designer showed me drawings of a small trailerable cat. To me, it looked as if his single berths were only about 16 inches wide.

I'm currently struggling with these ergonomic issues on a 23.5 foot cat I'm doodling. To my eye, the cabin looks too high for the hull, but unfortunately, a bunk needs 40 inches above the bunk board if you're using 4 inch foam as a cushion. Unless you have this much headroom, you can't sit up in the bunk, and if you can't sit up, claustrophobia may result, as well as bruises on the head.



You can giggle at the rig; I don't mind. I've really enjoyed Slider's sprit rig, and I was curious about what a split rig might look like on the new boat, so I drew one. To use a single stick conventional rig, I'd need a mast slightly over 30 feet. I actually own such a mast, and a good mainsail to go with it, but I'm scratching my head over the problem of getting it stepped at the ramp. I know it could be done with gin poles, but the masts for the divided rig would be a lot easier to handle. I might be willing to lose some windward efficiency to get added convenience; besides, Slider's sprit-sloop rig has proven to be surprisingly weatherly.

 

Okay, that was just silly.

But here's another idea:



This is sort of a hybrid sprit rig, with the sprit hung from a snotter that is suspended from the main halyard by a Dyneema line, so that it moves up and down the mast with the throat of the sail. The advantage is to lower the CoE of the rig and approximate an elliptical plan form, but without the expense and hassle of a fully battened sail.

 

I always thought (and experienced) that battens in mainsail were to avoid hassle. Expensive though.

 

Terho, I guess it depends on which hassle you're talking about.

For a conventional main with a lot of roach that must be supported by battens, there are some hassles involved: chafe, weight aloft, difficulty of reefing or lowering sail off the wind in strong conditions.

Folks differ on whether these are outweighed by the many advantages of battened sails.