# Narrowing the beam

Discussion in 'Multihulls' started by Dr. Peter, Apr 1, 2010.

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### spenanceJunior Member

Use a tilting trailer and use the size beam you want and lift it to 2.5 meters.
Drop trailer and lift mast, no beam assembly.

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### Dr. PeterJunior Member

Pythagras' Theorum and lifting one cat hull on the trailer

Spenance,

I used Pythagoras' Theorum a^2 + b^2 = c^2 to work out how high I might have to lift the catamarans in question. Please forgive me if I work in metric but most of the world does.

Model Beam Beam squared
Tiki21 3.66m 13.40m
Tiki26 4.60m 21.16m
Windrush 600 (wide) 3.45m 11.90m

The legal width for a standard trailerable load in Australia is 2.50m. 2.50m squared is 6.25m.

Picture a right-angled triangle. The base represents our trailerable width squared (6.25m). This can be a^2. The sloping side is our catamaran and its length depends on the boat - once again we have to square this measurement (see list above). This will be b^2.

We add a^2 and b^2 together to get c^2, and to find c we have find the square root of c^2. Relax its a button on most calculators.

The purpose of all this is to find out how far we have to lift up one hull on a trailer to make it faill within the legal width requirement.

Model c^2 square root of c
Tiki21 19.65m 4.430m
Tiki26 27.41m 5.23m
Windrush 600 (wide) 18.15m 4.26m

The legal height for a load in Australia is 4.6m - I think only the Windrush has a very small chance of fitting within this dimension. I have not accounted for the height the trailer lifts the boat off the road, or the depth of the hulls.

I think this approach might have some merit for a super-wide OTB catamaran with very light hulls. Anything heavier like the boats we have been discussing presents some very interesting engineering challenges.

In any event I think it gets away from the simple straightforward approach being sought.

Peter

Last edited: Dec 27, 2010
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### spenanceJunior Member

Dr. Peter,
You are right.
I was thinking of the hydros tipped up.
Spoke too soon.
I too have been pondering the Tri / folding / trailering difficulties.
Have decided to think outside the box and throw out these guidelines and see what develops.
spenance

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### Steve WSenior Member

This is an interesting idea, several beachcats do it of course but i dont know of any bigger cats. Dont forget that you can still narrow the beam of a net and tube cat such as the Windrush to get it under height realativly easily but it may not have to be much. If you have to take say, 6" off the beam of a 12ft beam cat to get it under the legal height it would be a lot easier than trying to get it to legal width.
Steve.

5. ### outside the boxPrevious Member

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### spenanceJunior Member

I have seen this site. Would love to try all the designs.
In a perfect world we would not have to compromise proformance for locks, bridges, trailers, storage, slips.
Thinking outside the box is I'm sure not going to produce a favorable design but will make me feel better. Who knows, we all have to try new avenues. Maybe it will be a home run!

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### Paul ScottSenior Member

1) Something to ponder- launches fast, solid deck makes camping easy, and trailer is way cool....

http://sharkcatamaranclass.org/WHAT.HTML

2) It sounds as if you've had a bit of performance experience, so how about the following- just a 'what if' to mull over, say, 1 finger of Edradour, for example-

Find some hulls for something that already exists, say a Tornado, or some other beachish open net cat up to say 27 feet or so, get some aluminum extrusions (or I suppose you could cut down the existing beams) that fit the hull attachment, and use them to make the beam width you want. Then figure out how to make some wings that you could sit out on, and hinge them to fold in, either on top of the trampoline, or better yet, to make an A frame, which could double as a tent, a cradle for your mast/boom on the trailer, and which might help raise/lower the mast. If you don't want to go with wings long enough for an A frame, swing shorter wings up to vertical, and use them as the sides of a tent, with the boom (which might be pulled up the mast a bit) as the tent's ridgepole. Porta Potti and sink in one hull, if they're big enough, and galley in the other.

The Dashews did a class D cat with a tentish pod on it that apparently worked pretty well for coastal work.

No jib, una rig with an assym for the lighter stuff- kind of like what Marstrom and Hobie are doing with some of their models. Make sure you can reef the main, so you can sail it yourself.

You might have to fiddle with daggerboard/rudder sizes for balancing CE, maybe not (?)

This way you can get easy launching, leverage, some performance and an overnight tent that is easy to set up, and possibly minimalist standing and running rigging. If you can find existing hulls already manufactured or second hand, with some thought and looking around, it might be more a matter of assembly rather than building. You might need a few hours of an NA's time to make sure the loads you are expecting are met structurally. (And you might find someone with molds of hulls you like that could be manufactured for you.)

Boats are so easy when they only dance in the firings of the frontal lobes......

Paul

another edit- and if you consider that the owner of the Bieker Trinado had Irens design new amas to replace the Tornado hulls, which they then attached to the existing beams, the use of existing hulls idea (or finding someone with molds, etc.) above might not be that outlandish. (?)

Last edited: Dec 28, 2010
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### Dr. PeterJunior Member

Narrowing the beam - Summary of ideas

It seems to me, as the original poster, that this thread may have run its course. So at this point, the researcher in me says, it would be useful to interested forum members to summarise the main ideas of the thread in one place. These ideas relate to the boat and / or the trailer:

1. Just buy a road legal width cat (and go long?), or
2. Make the trailering width legal by:
Folding beams
Scissoring beams
Telescoping beams
Replacing the 'sailing-width' beams with 'trailering-width' beams
Raising one hull on the trailer high enough for it to be road legal, alternatively
3. Go slightly over-dimensional and use a 'wide-load' trailering approach

I think all the methods have their applications. To decide which is the better approach for you means you have decide what use you want to put the boat to, how big the boat is, how much complication you want in your boat, in your trailer, and/or in your travelling arrangements.

I would like to thank everyone who has involved themselves in this thread. The point about narrowing the beams of a Wharram has become moot for me, as my wife, herself a keen trailer sailer, has her head and heart firmly set on a monomaran. And, in the interests of marital and maritime harmony (see my other threads), this idea of narrowing the beam of a cruising cat must be laid to rest for me.

However, the forum has suggested another concept, which I rather like, of a light-weight day-cat with a wider-stance; I could use this boat solo as a light application cruiser. I think a OTB cat with good positive buoyancy and some storage capacity (for tentage) would serve. I like the idea of wing-seats too as they get ballast out wide in a relatively pain-free way. I think a boat like the Hobie Getaway is getting there.

With a boat this light I would look keep the the boat wider than road legal - every little bit helps for leverage, and then modify the trailer to cope with the width by raising one hull higher than the other. This keeps the boat strong (no mechanisms) and stable (wider beam). To me this offers a relative simple solution with respect to setting up and trailering as the raised hull could be raised and lowered from, and to, one of the beach rollers.

Peter

Last edited: Jan 4, 2011
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### dstgeanSenior Member

I'm not sure about another topic for this one, but I'm thinking about what make a good beachcat based cruiser for me. After seeing the Pacific cat 19, it kind of melded some of what was already rolling through my brain. I already have two Gary Dierking Tamanu hulls, so I'll be basing my cat off of that although a more suitable dory form, stressed ply, stitck and glue, whatever would most likely be better since one could have better load carrying capacity at the stern.

I'd like to stick with:
*trailerable beam
*hard deck aft big enough to tent on
*front tramp
*foot wells for comfortable seating
*hiking wings for both leaning back against and sitting on
*centerline mounted outboard
*possibly use a reefable Una rig and an asymetrical to keep rigging time to a minimum
*Reuse a beachcat rig for keeping the whole thing cheap, but add shrouds at 90 degrees to make stepping the rig dead simple.
*doesn't need to be a speedburner, but should do double digit speeds easily
*should look a bit retro CSK or Pacific rather than racy
*rightable w/o outside assistance
*reasonably light for it's type without going exotic on materials

Essentially it's a Pacific cat 19 out of ply with a uni rig I guess. Beach cat meets open beachcruiser.

Dan

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### Paul ScottSenior Member

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### dstgeanSenior Member

pretty much what I'm thinking. Schacht's Old school, the PC 19, El Gato, and Munoz's malia are right in the mix for the aesthetic I'm looking for. I'd like to stay beachcat width for trailering, add wings for some hiking power and comfy seating, and make it a camp cruiser. Making it fast and easy to sail leads me to think of going Unirig with an Asym. spinnaker on a roller furler. I've stripped a few boats and built a few ply ones so either hull shape is fine, but draggy transoms aren't--even with the varying loads I might wish to haul. I saw a Getaway at the Sanibel Causeway on New Year's day and thought they got a lot right on that recreational cat. Adding a bit of load capacity and simplifying things a bit might be even better.

Dan

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### Paul ScottSenior Member

Been doodling the same thing for 15 years- wound up with a custom 40' uldb instead! But that's up for sale, so with any luck I'll have some \$\$ left over to mess with a cat.

For some reason I've been obsessed with making the thing inside the Class C cat rules, but with a bit more sail (una with an assym): legal trailering width for the hull beam with hinged wings out to Class C legal beam that would fold in to become at least part of a tent system/sofa/hiking wings, solid deck, central pod/blister just large enough to crawl into at night if too tired to put up the tent (make it out of smoked lexan?), maybe a net forward. Probably no porta potti or galley in the hulls, but that would be nice.... Wouldn't be near as fast as a real class C, but kind of cool. Power of limits, I guess.

Hope you get her built soon!

Paul

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### dstgeanSenior Member

That would be a real long lean cat. I suppose you could mix and match by buying C cat hulls if any were available for a reasonable price and with the narrow beam go with an A cat ish main sail. With the hiking racks you could probably have a bit more area though. Interesting concept. While I like the old Beowolf VI or whichever the Dachew's ended up with before they went to monos, that too spendy for my meager salary. A beachcat size should suffice for my tastes though.

Dan

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### Paul ScottSenior Member

Thanks. I think 24' would be a nice size, and assuming 8' wide trailering, thats only 3' on both sides for wings. You're right, an A catish rig, since there seem to be a lot of cats with around 29'-30' masts about, maybe go more of a NZ 8.5 main planform, in other words a bit more squatty AR, but still square headish, a lightish air flying headsail, and see if the main would be enough in above 8-10 K? But at what WS the una would light up without an assym is a guess, I guess

The main reason I'd go with the extra length would be to get some breathing room around going over the bows, better seakeeping, a bit more waterline speed, and enough deckspace for lounging/sleeping. WS might be a problem, though, although it seems it could be kind of light, so narrow hulls for smaller wave making at least. The Shark isn't that heavy, and it does thunder along, even with 3 or 4 on board.

It seems you are looking at B class size?

Paul.

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