Cruising Cat Width

I am interested in designing a family oriented cruising catamaran of approximately 40 feet in length. I am familiar with the technical issues associated in structurally designing the width. Most performance enhancements suggest that more width is desirable. Obviously, more width also provides more interior space in the bridge deck. A cursory Internet survey of current production and plan designs indicates a width usually between 50% and 75% of the length with most around 60%. What I would like to know are some of the more real-world/practical issues. For instance… Are there harbors in the world that restrict on width of a cruiser? If I were one foot wider would I have harbor fees twice as expensive? Although greater width theoretically reduces capsizing, does it degrade some other safety or handling aspect? Any light in this area would be appreciated.

 

Inland waterways and canals may have width restrictions. Certainly the case for Europe. Wider may be better for other reasons. Less wave interference between hulls.

 

Hi there,

It is true that there are many performance enhancement that will come from a wider beam but it does not automatically results in an improved performance.

Increasing the width will improve the capacity to carry sail in stronger winds and increase the power of the boat.

However, there are other factors that are very important for the performance of a catamaran: Weight and Windage

About the increase width of a catamaran, there are many yacht clubs that will charge double rate for a sailing catamaran. In my region, all of the harbour are designed with a 36' keel boat in mind and anything above that, especially a catamaran will be charged extra. Some times, catamaran will go to the fishing harbour where there are treated more failry

Another point is tacking ability. When you increase the beam of a catamaran, you decrease the tacking ability especially if the boat is light and has a good windage.

In terms of stability, there are many opinions on the safety of a catamaran in open seas. I am a major supporter of multihulls but I agree that any boat can capsize! And if a boat is wide, it might not right. I have noticed that John Shuttelworth has very nie designs that have some side overhangs on the hulls to improve the capside resistance. Other designers have also includes the side overhangs and I believe that this is a major improvement.

If you make the catamaran wider and if you increase the power of the rig, you will have to incease the strength of the bridgedeck and add alot of weight and since the weight is very important for the performance of a multihull, your performance gain might not be as strong as expected unless we are looking at an open deck catamaran.

Finally, I come from the commercial side of boat design and there is a more direct price to pay for the increase in weight: price itself! If a boat is twice as heavy as another boat, building material will cost twice as much, the more powerfull rig will also be more expensive.

If we take the an example from Richard Woods, I was looking at some of his designs and comparing a larger open deck design with a smaller bridgedeck design and I think that the open deck would have been slightly faster to build and cheaper than the smaller bridgedeck. This was my impression but I did not purchase the building plans so I was not able to make a good estimate of the building price.

Keep us posted on your design

Charles Leblanc

 

At some point the width is no longer the controlling factor in stability. Pitchpoling becomes the worry. The ratio is somewhere around a beam to length of 50% depending on the hull design.

 

Charles Kanter has a good discussion of cruising cat beam in "Cruising on More Than One Hull". He lists several disadvantages for beam > 50%:
- ratio of fore-aft to side-to-side stability changes, increasing the probability of burying the lee bow
- greater bridgedeck clearance is required
- increased bridgedeck height increases windage
- more structure (and more sophisticated structure) is required
- turning radius is increased
- haulouts are more difficult (hard to find travel lift able to handle > 16 ft beam; > 20 ft beam requires commerical shipyard or crane)
- dockage is harder to find as most marinas are built around 16 ft beam

 

Thank you all. All these replies will fuel further research. The harbor restrictions / ”discouragements” (in your area) are the ones of particular interest since I can’t get those things out of my engineering books.

Also… I’d like to thank the keepers of this forum. I was using the forum of a boat architect whose plans I purchased. The responses were slow in coming… After a month, none of my questions have 4 replies. I also like getting the more generalized (even monohull crowd) biases.

 

Sorry I'm one of the monohull crowd Inquisitor, but I do have a mate who bought a cruising cat. His main criteria if I remember was beam. He wanted to cruise with wife + 2 kids but mainly on waterways and through locks, lots of locks. He had the cat for about 4 years and did most of the inland waterways in Europe into the Med then crossed the Atlantic to your east coast and again got into the waterway system. If you think that may be relevant to your needs let me know. I'll try to track him down. He lives in Canada? now.
Regards, Rob.

 

Rob,

For ship design, I've learned more in the past month than my sum knowledge before hand. Both this site and POYD have been instrumental. So far, I favor the multihull, but the jury is still out. It’s a hard decision since the camps seem to be so vehemently opposed. It’s hard to sift through the personal bias to the real objectivity. The fundamental safety issue argument… cats flip versus mono’s sink. In either case I’m more likely to die in a car accident here in Atlanta. So in either case the risk is down in the noise level.

The one aspect that has not been covered (to my satisfaction) is how I will be restricted. Mono’s will depth limit me, Multi’s will width limit me. I want to do Bahamas, Caribbean, Florida Key and US Inland waterway. I might get to Europe. Who knows, I might get to your area of the world. Multi’s obviously get me in shallower, but will my 40’ cat be charged like an 80’ mono? Will I be sent away?

Anyway the info your mate has would be vitally useful.

Thanks,
Dennis

 

Many marinas will charge by square footage; they take the product Length*Beam of your boat and charge based on that. Others charge a flat rate for a given slip size. (Both are highly anti-cat discriminatory.) If you are faced with this situation, simply drop anchor (or catch a mooring) and tender in to shore. (The wide beam allows you to carry a much nicer tender than a similar sized mono, too.) Cats are said to be wonderfully stable at anchor.
In terms of other restrictions for the beam: The waterways you mention should be passable by a 40' cat. On many Canadian waterways (I don't know about the States) they charge a flat rate per boat, or per boat/day regardless of size. But be aware that a beam over six metres greatly restricts your ability to use a lot of nice inland canals, as does a draft of more than about 1.4 m. The only places your multi will be refused are places where its mast height and/or beam are more than the dimensions of a canal lock. In general they are attractive boats and are welcome anywhere, so long as you're willing to tender in to shore if there's no space on the pier.

 

Hi Rob,

I would appreciate the benefit of your friend's experience as I am planning to do a few years on those same European waterways in my solar electric liveaboard catamaran.

 

I have lived in the caribbean for last 6 years and have sailed up and down the chain in a 65x35 foot tri. most marinas charged extra rate for multis. somewhere between 1.3 and 1.6 times the rate for monohulls. rates are the same on T dock ends but they are always dearer than other slips anyway. being haulled up to about 32 foot beam is not a problem in the caribean, multihulls are definately taking over the charter market.

 

Inquisitor, Jonathan. I'll start tracking him down, but I know he works at sea 3 weeks on /off so it may be a while.
Inquisitor, Over here if you are lucky you will be charged per length... but it is always LOA and in a marina that means every overhang that the marina manager can hang his tape measure..Oh! and it is usually rounded up to the next metre. You may be charged double as most pens up to about 40' are doubles, the cat takes both.!
But the good news is we have so many bays that when cruising most of my time is spent in secluded anchorages. All can be free if I anchor off the town jetty. In many ways I lament the festering spread of marinas, They monopolise the best spots often and allow "yachties" to cruise with inadequate ground tackle and no knowledge on how to use what they have.
As to the mono/cat debate I have always been nervious about going to stable position #2. My only real experience with cruising cats was the beautiful cruising cat (about 38') that we ploughed past on our return trip across the Gulf (33NM) a few years back. The wind about 25 knots gusting to 35 and as always.. on the nose with a short 2m chop to punch through. The moderate displacement, (nowdays called heavy), cruising yacht relishes these conditions. But then he can drive up onto the beach, I can't. He can hold dinner parties in the cockpit, still... there is room for two to tango on mine. We should start another thread on what makes a good cruising yacht.. probably been done to death though. One of the biggest issues when long term cruising is the quantity of gear you will take and must have capacity (volume and weight) for. And don't forget all the extras that disappear into the hull as the boot topping disappears never to seen again until the boat is sold. A friend who cruised for a few years and decided he needed a house instead cleaned the boat out for the new owner after he signed a contract subject to a test sail... He told me the boat was so high out of the water and sailed so well he wished he'd never sold it. Regards,

 

You bum you!

You tell me something like that and don't send pictures! Show me the boat in a tucked away cove with young nymphs frolicking on the deck!

But thanks for the info… I was getting the sense that cats were starting to be appreciated and treated as a market to be catered to… not exploited.

 

That last one was for Bazza... the bum! That'll keep me up all night thinking about it!

 

I made it once from Berlin, Germany to Sete in France.
Record mileage 50 a day, record # of locks 25 a day. Total # of locks Berlin-Sete ~ 240.
I guess, the most frequent used canal is the Canal du Midi.
Check the max. width here:
http://www.midicanal.fr/bateauGB.html
Jonathan, some of the larger rivers in Europe have quite some current, particular where the river narrows at bridges expect 5 knots of current. I don't know how much power your solar powered cat has, but loosing it while under a shady bridge will get you in the middle of commercial traffic and in deep trouble.
Otherwise, look forward to your trip.
http://www.rollintl.com/roll/rhine.htm
Enjoy the whine and don't hurry. Particular in France and small canals, locks are manually operated. It is somewhat expected to buy some of the lock keepers vegatables and taste a heavy red whine. Dependent on how much you can drink, you possibly make it only to the third lock...