which cat for me?

[Grizz]

HooBoy, this one could stir some sand off the bottom...

I had a sudden explosion of synapses that reversed my heavy displacement syndrome. I went through a phase of developing a sharpie for the final frontier when I was hit with the benefits and advantages of catamarans. Specifically, the wharram tikis suddenly dispelled all my prior biases toward multihulls when I was trying to make a sharpie do everything the cats can do, and failed.

The design goal was to produce a boat I could sail anywhere, thin or thick water, beach most anywhere, and be reasonably comfortable in most anything.

My last boat was a steel commercial fishing boat displacing over 50 tons. I always said that if I ever got a smaller boat it would have to be a lot faster. Now I'm into the sunset phase of life and need more exposure to those elements the seaman can't stay away from.

If I had a tiki 26 right now I could fulfill about 93 percent of my needs and desires. I can sail back to SE Alaska and gunkhole the spots I missed in a half-life of beachcombing. I can sail across to HI, and north to Dutch, and West to here again if I get that much time.

I like lots of stuff about the tikis. I love the lashup of the crossbeams. I always said that next to welding, lashings are the strongest way to attach stuff to boats. I have over thirty years experience doing that and can rely on line that way.

Tikis aren't the only possible solution, but they may be the cheapest, and may also be the quickest.

So what's the problem?

I do not like plywood/cloth/epoxy materials. Don't want to build one, can't endure too much exposure. And don't trust them against the stuff that goes BUMP in the night.

I would want the "pod" for on-deck watches out of the weather, for sleeping when solo, for their luxury. For a heat envelope in high latitudes, and shade in low ones...

So then I start seeing the other competing designs and see that you can get a lot more enclosed space, and start to wonder if that displaces, get it?, the tikis. But I want the convenience of regularly taking the beach as well as the passage making options.

But the final kicker is this: I want an aluminum cat. I know what I want and why. I want to cross the deep in a metal boat. And I eliminated steel as my material of choice by natural selection.

The tikis look susceptible to the origami method of hull production. Some other cats with "dory" bottoms, or squared bottom sections even more so because I could use an aluminum channel for the bottom and have enormous strength.

I realize the metal boat is heavier in comparison to the composite models, to a point. What point is that?

So maybe the Question is: what is the best small aluminum sailing cat design to equal the medium size wharram cats?

I hope I've ignited a long and good and beneficial discussion. Let's enjoy it.

Regards,

Grizz

[sandy daugherty]

The short answer is "there isn't one. build it your self."
And I predict the discussion will tend towards objections to your criteria rather than "OK if thats what you want". They will fall into conventient categories, tentatively described as:
"26 feet to Hawaii and back?"
"What cat can't be beached?"
"Durability; aluminum vs figerglass"
"Alergic to Epoxy, so what"
and finally
"Sailing to windward in a keel-less boat"

I recall an aluminum fiasco with lots of confident self-agrandizement that broke up on the first day, I think from the San Francisco area. It didn't fail because it was aluminum, but it may raise a few points for discussion here. I suspect that the problems traced back to some arbitrary decisions made in the dreaming stage.

[Grizz]

Thanks for the reply Sandy. This being a design forum, I thought we could discuss designs. I intend to build it myself. I can fit, frame, and weld metal boats. That's not an issue.

I invited discussion, and we can't keep out those with little or no experience. I'm hoping to gain the perspective of those with equal or greater experience.

BTW, a raft made of trash just crossed, a tiki 21 circumnavigated, can anyone question in good faith the sea keeping qualities of catamarans?

Thanks again for the response. I am interested in everyone's point of view, and good at spitting out the watermelon seeds...

Regards..,

[Richard Woods]

A Tiki 26, like most small plywood multihulls, uses 6mm, 1/4in plywood. The boat is designed round that skin weight. Very roughly a sheet of 6mm ply weighs 20lbs, or 2/3rds lb per sqft. Allowing for the paint and glass sheathing that you won't need on an aluminium boat maybe you could have a skin that weighs 1lb/sqft

As a metal worker you know how thin a 1lb/sqft aluminium sheet will be. You will also know that it isn't really possible to build aluminium boats using less than 3mm (1/8) plate

In other words, you cannot sensibly build a multihull in aluminium unless it is over 40ft long

Hope this helps

Richard Woods of Woods Designs

www.sailingcatamarans.com

[northerncat]

In other words, you cannot sensibly build a "sailing"multihull in aluminium unless it is over 40ft long
sean

[Grizz]

OK, that's a start, 40 feet.

But for the sake of erasing my ignorance, how much volume would have to be added below the waterline of say, a given length tiki, to provide the necessary displacement to float the heavier hull?

And that hull weight isn't more performance squashing than, say, a large crew with tons of personal property and huge electrical appliances, is it?

But if 40 feet is it, so be it. Lots of trampoline space for snoozing.

Any pictures or drawings of the smallest aluminum cats around?

Thanks for responding. I should have mentioned the notice in my wheelhouse: No Task Will Be Evaded Merely Because it's Impossible.

Even if the impossible takes longer...

Grizz

[Gary Baigent]

Pajot's first Elf Aquitaine (67 feet) and the Peyron brothers alloy cat, theirs' was around 65 I think - plus the first 54 foot Paul Ricard foil tri and a few other French multihulls, were all big boats and none of them were particularly light, and they dented too. You need many, many stringers and frames with light skinned alloy construction, a huge amount of fiddly work. I think you should reconsider wood or foam sandwich construction and build a 35 or above cat - there are literally hundreds of good designs out there.

[Grizz]

http://www.planet.fi/~kcad/boxcat26a.jpg

Here's a 28 foot cat that would adapt well to aluminum build. Right shapes, plus extra displacement to handle the weight difference.

If the weight difference is only .3 pounds per square foot, then this design should be buildable in aluminum; it's a tiki with extra volume to support the extra plate weight. Or not?

Grizz

[Howaya]

Probably an inconvenient location for you and I'm uncertain it is still available, but not long ago there was an aluminum cat in FL for sale. It was about 33 feet LOA. Even if the cat isn't right for you, the engineer who built it may have some insights for you. Just a thought.

Mike

[Grizz]

Here is a tiki30 in aluminum. I think this boat sold in Nz. Obvious she doesn't sit light on her lines, but the boxcat's greater width should make the boat much more burdensome.

http://www.themultihull.com/wharram3/images/rh_alum30.jpg

Grizz

[Grizz]

Howaya,

Do you have a link to that boat? Thanks..,

[dsuursoo]

remember that aluminum's a real bastard to work. yeah, the tools are pretty easy to use, not as noisy, but your welds have to be PERFECT. glass/carbon would be a lot easier, given that. you'll need special gas, a covered work area, unless you're not building it yourself...

and unless you're using some of the aerospace aluminum, it's not going to be very much more durable than composite, perhaps even less. the ductility could be your downfall.

but hey, if you can do it, balls to you man.

[kengrome]

In other words, you cannot sensibly build a multihull in aluminium unless it is over 40ft long.Yeah, right.

Catamaran hulls do not have to be 'tall and slim' regardless of the fact that this is the way most have been built over the years. There is nothing wrong with building them 'wide and shallow' if you're willing to lose some benefits while gaining others -- such as shallower draft for example -- and in this case it would be perfectly acceptable to build a short multihull in aluminum.

[bill broome]

there's noise, and condensation, and weight, and some serious welding..

and because you're the nervous type, wants to live forever.

ok:

1: how bout a composite, aluminum bottom, lighter plywood above. doesn't have to glassed, plywood is quite strong by itself.

2: if you don't demand min draft, put a plank keel under your wood/glas boat. you can still get out and walk ashore, but are unlikely to puncture a narrow hull above the fin. add a couple of extra layers of cloth underwater if it will unclench your knees.

[the1much]

which cat for me?
i would get a tabby,, they are great mousers,, and very independent hehe :D;)

[sandy daugherty]

Griz!
I sense your preference for aluminum over fiberglass is more visceral than objective. Let me relate a few of my experiences.
A certain naval vessel carrying a Captain's Gig was sprayed by gunfire. Small calibre rounds penetrated the aluminum superstructure injuring two sailors. Identical rounds hit but did not penetrate the old Gig, built twenty years before out of fiberglass. One sailor repaired the Gig in one afternoon. The holes in the superstructure were covered with patches and were not repaired until the next yard period.
In a recent Huricane, a sturdy fiberglass cruiser was blown over a concrete seawall, breaking the capstones and scratching the hull. A well respected aluminum power cruiser close by was torn open at the wagterline on the same wall. The fiberglass boat is still sailing. The aluminum boat is now beer cans.

[Grizz]

Hi Sandy, thanks for the thought.

Yup, I prefer aluminum for personal reasons, that's just how it is.

My experience is from half a life time in various boats in Alaska. I've seen lots of different variations on that theme. And I still believe that I can build a very good one for my needs from aluminum.

I like the illustration of the BoxCat I posted above. That looks like it's made for metal doesn't it?

[kengrome]

I like the illustration of the BoxCat I posted above. That looks like it's made for metal doesn't it?

I might have an opinion if I could see it, but it's so dark I cannot distinguish the shape. Can you re-post it using colors that are clearer and easier to see?

[Grizz]

http://www.planet.fi/~kcad/boxcat26.htm

Here's the designer's website. I should have posted the link earlier. I like the looks of the boat because it's got perfect shapes for metal.

but there aren't any experts who like aluminum in this size range.

very interesting

[terhohalme]

kenneth and grizz, loot at here:

http://picasaweb.google.fi/terhohalme/Catharsis27#

The old Boxcat 26 never built and I have no access into that site anymore. Now there are two Catharsis 27 under construction. This one is also "a plate" construction. Plywood, sandwich or aluminium (just can't see why), what ever. And much better from hydrodynamic point of view.

Terho Halme

[Grizz]

Catharsis is a good looking boat. Are you the designer? Or the builder? Are there pictures of finished boats?

What is the displacement?

The rudders appear vulnerable. Can they damage the hulls if they hit something, say a submerged container or rock?

Thanks

Grizz

[terhohalme]

Yes, I am the designer of Catharsis catamarans. The two first Catharsis 27 are under constuction in Omnia vocational college in Finland, Kirkkonummi. I'll send more pictures to web when there is some progress.

Estimated displacement of the empty boat is about 1500 kg (nidacore sandwich) and about 1800 kg (plywood). Full loaded mass is 2600 kg.

In every catamaran rudders can be damaged if they are hitting something hard and heavy. The skeg doesn't help much.

The rudders for the mini keel version are normal spade rudders with a shaft. They have some shelter from mini keels as they are on the same draft.
In the centerboard version, the rudders are pivoting up like in dighnies.

[Grizz]

Thanks for the reply.

I am interested in the swing up rudders for several reasons. I want a boat I can feel free to beach. And I want a rudder that I can make at-sea repairs to if necessary. And I want a rudder shaft that is not in the water-tight area so it can not sink the boat if damaged.

I am interested in aluminum because I want to be able to travel in high latitudes with less worry. I spent half my life fishing commercially in Alaska. Most new boats built for that area are either steel or aluminum.

Did you design BoxCat? I like the shapes for building. Easy to plate and weld, or easy plywood shapes. I like the additional displacement down low compared to the Vee shape of the Wharrams.

Regards,

Grizz

[terhohalme]

Yes, I designed BoxCat, she was just a proposal. Catharsis 27 is as easy to build as BoxCat. Can't see why she couldn't be beached. The mini keels are strong enough.

[boat fan]

...Estimated displacement of the empty boat is about 1500 kg (nidacore sandwich) and about 1800 kg (plywood). Full loaded mass is 2600 kg.....



Nice boat with very nice lines !

Interesting weight estimates . Seems the plywood is still quite light in comparison to the Nidacore.Are the weight estimates for 9 mm Ply ?

Do you need to add stringers or additional ring frames if you build in plywood , or is the build the same as Nidacore ?

I assume the Nidacore hull is taped then glassed over inside and out ?

[terhohalme]

Yes, 9 mm plywood. The stucture is very similar for both material.
Nidacore is fist infused with glass, then nc-machined and then taped together. Nidaplast as is was too flexible into jig frames.

[boat fan]

Yes, 9 mm plywood. The stucture is very similar for both material.
Nidacore is fist infused with glass, then nc-machined and then taped together. Nidaplast as is was too flexible into jig frames.

Thank you terhohalme.

Your boat will have a lovely clean interior .Those lines are really nice .
You have a good eye.

[Ilan Voyager]

terhohalme, my best compliments, it's a very neat design. You have worked hard the design for a simple construction. I'm impatient to see the pics when finished and to read the memo of the sea trials.

The panels glass-nidacore are beautiful. Where have you bought the Nidacore? It's produced in France by Nidaplast, and sold in the States by Baltek, I believe, under the name Nidacore. The interior is very clean without stringers and this composite has plenty of insulation by itself.


In Canada aluminium is used because it's "dirt" cheap as the Canadian are one of the major producers of this metal. In Mexico marine aluminium is close to 7 dollars a kilo, more expensive than polyester and glass...

Fishing boats have no great concerns about weight savings as a heavy displacement boat has softer reactions to sea (greater inertia) so making the work of the fishermen more confortable. But in multihulls YES weight is a concern, because of the great surfaces involved. And 1/8 inch aluminium (the minimum for welding) is simply too heavy, not enough rigid, and will need miles of stringers and weldings, plus a complete insulation...very expensive.

It's seems after the bad experiences of multihulls made in aluminium in the years 1978-1982 in France, that this metal have acute problems of fatigue and corrosion for this use.

All these multihulls had big structural problems: Elf Aquitaine almost broke in two, Roger et Gallet became a piece of junk, Paul Ricard same thing, PenDuick IV (Manureva) sank probably of a structural problem. And all were too heavy, truly very heavy. None has been a good boat.

Even for cruising sailing multihulls of less than 20 meters, metal is disregarded for the reasons exposed supra.

[surf boat man]

for what its worth I had a 42 Warrem cat for about a month before i lost it in a massive storm.
She was absolutely brilliant. The guy I bought her from built her in airex foam. An inch think core that was sheathed in glass. He also built a bridge deck that straddled the hulls.

Though we lost her in this massive storm she stood up to it brilliantly- it was only when we got rammed by one of the rescue boats9 a large container ship) that she broke up- well the first 6 feet of the bow. The amazing thing is even after that she didn’t completely sink- which gave us a huge platform to hang onto while the rescuers sorted themselves out.

Warram cats are great – airex foam is also an amazing product to build one out of. I would hate to think what would have happened to us if she was made of anything else.

[terhohalme]

Thanks guys for you nice words...

Would be fun to build a Wharram from Nidaplast and glass... Need some calculations though...

Nidaplast has a Finnish distributor, Muovikemia Oy. Can't tell a Mexican one.

Try: http://nida-core.com/

Terho

[Grizz]

so if aluminum can't make a good catamaran, are there any successful trimarans built of aluminum?

curiously,

Grizz

[jaydh]

Hey guys,

Grizz...got your pm, apologies for the delay. Look at www.far-away.net and check out Chameleon and Mozart. Both alloy cats same shell I believe with different layouts. Once again, larger then what it seems you were thinking of, but hell, fun for a looksey.

I see a few digs at aluminum for cats in this thread. I'm about as far away from an expert on this, but a wise man once told me to beware the experts! Thought I'd throw this in the mix to play cheerleader for aluminum.

My lovely wife and I are building a 14m alloy sailing cat and we too were wary up front. Heard all the horror stories....was it Alco in the States that had a bad batch that screwed up some larger power cats in the NW area? Rampant corrosion, too heavy, PHD needed to weld/design aluminum, etc, etc.

Alum is fairly popular in Australia. They love the stuff here and a few guys have been turning out alloy sailing cats for years. 40some foot range is the average size I've come across. 4mm hulls and 3 or 4mm deck for the sheets. We routinely weld 3mm and that's less then 1/8" yeah? 2mm easy also....welding straight forward...keeping it from distorting...now that separates the men from the boys! Years of cruising noticed the experienced cruising Euros preferred alum monos....hey!...if the French like it can't be that bad. ;-)

We have four mates that have the same cat as we're doing and know of 10 or so more out there. They all go fast, are pushed hard and have even hit steel things at 10 knots. No dramas. Corrosion not the boogey-man as rumored (though one can't be stupid and ignore it). It's easy as hell to work with and the end result only limited by your own patience and skill. Quick to build....no curing times/windows, etc....and ya don't even have to paint above the waterline if one chooses.

Anyone out there thinking of building a cat in the 40-50 foot range do take some time to check out alloy. It'll either be for you or not, but at least worth the effort to research. Alloy is fun to work with and decent results obtainable by amateurs like us. Below a few pics - the one without the cabin is ours...the other two a mate built in the same shed last launched a year ago.

best - Jason

[jaydh]

crap...pics didn't upload...will try again later in case anyone interested...

- J

[jaydh]

trying again...

[Grizz]

Wow Jason that looks good. 3mm is right at 1/8" and I've welded that no problem. 2mm seems thin, but engineering and good welding technique takes care of that. What type of internal framing? What size and spacing? Are you MIG or TIG welding the 2mm sheets? Are you using ply for interiors? Are you using foam for insulation?

Please post more pictures if you feel inclined, I appreciate the ones you've posted.

I love the tikis but they seem like throw-aways. Your boat looks very comfortable and long lived...

Regards,
Grizz

[masalai]

Arrr Jim, little terriers are better rat/mouse catchers pussy cats need to be "altered" as cats are boats and pussy is part of something else again....

Now a little bit more serious, 40ft is a nice comfortable size range for a cruising cat - I like a beamy 20 to 24 ft on fairly slim hulls - look at Bob Oram Designs 44C (my choice is the 39C with forward cockpit) http://www.boboramdesign.com.au/39-c/ or the Fusion 40 which is available as a kit or built in USA http://www.fusioncats.com.au/

I suggest, buy for resale, as big as you can afford and most importantly TRAVEL LIGHT for weight kills any advantage of a cat - - If you like to add this, that and many other things too then DO NOT GET A CAT....

[jaydh]

Hey Grizz,

The 2mm is not in the boat...we just welded some scrap to see if we could do it. Have some 2mm diamond plate for fun cosmetic stuff....that was just a welding comment.

The full deck has stringers running fore and aft roughly 300mm apart with gussets installed between everything at 300mm again. The side sheets and bottom plates follow the same 300mm spaced stringers more or less without the gussets. Here you have 13 bulkheads per hull (two of which are watertight #4 & #11). without checking the exact measurements of each you can pretty much say they are equally spread out fore and aft more or less. this is of course a very simplified explanation. I'll have to put some shots up before the bottom plates went on and the deck inside.

We are using MIG. Got a sweet Fronius 2700 and love it. 5183 wire. 1.2mm. Plain old argon. A few sconds and you're welding steel then TIG. Easy set-up, whole thing WITH a 6kg roll in it weighs just 20-30kg or so. Simply love the pretty red-orange thing!

insulation we're going to try Armacell/Armaflex as opposed to the 2-part spray in others have been using. No ply...all plastic for the finish...probably rigid pvc foam or something like Multiboard. Deck will be a product called Aquadeck from Comcork Australia...made from recycled tires and cork.

The other guys have been getting their fitouts done in the Philippines and it does look great....full on glass and custom/local wood floors. Will post a pic of that too...we just don't have the time to do that. I heard the full fitout in the PI is 15,000 and takes 7-9 months.

Thanks for your interest....I too just like to look around and see what others are up to. Pics up sooner or later....

best - J

[northerncat]

how much did the fronius set you back?
sean

[jaydh]

Hey Sean,

Long time no hello...last time was when we were in Las Vegas, I think??

The welder was between 10 & 10.5k. Got it new from Queensland welding supply on Lytton Rd Brisbane outer suburb. Was much more then we wanted to spend, but haven't regretted it for a moment. QWS has been great to deal with, btw.

Looked at several used MIG and they were trash and still half + of the new Fronius. No decent deals were available and we were pressed for time to get rolling. Still happy we bit the bullet on this machine. Not one drama with the fronius push/pull gun and we use it nearly every day since February. One LED light on the interface wants to go out now and then, but it doesn't affect anything else. Will just fix that when it's convenient. Otherwise, not one hiccup.


best,
J

[Grizz]

I have a 300w thermalarc inverter running a miller 1# spool gun. I ran it 3 phase off of my boat generator. Works for me. I'd like to try TIG some day... never have but it looks like fun, and I do fairly well acetylene welding steel so I think I can do it. Unless my motor skills have deteriorated too much!

[northerncat]

yes great to see the progress of your boat, mines now floating but it's just a motorcat at present, i am thinking fairly seriously of building an aluminium boat next so i may know where to get a cheap fronius in 6 mths judging by your progress 8-)
have you managed to stay in the figures that you were talking earlier?
sean

[jaydh]

sean...sent you an email. sean, grizz here's two finished, same model.....
J

[TomT]

Haven't been there or done that, but I have cruised the net for years. Two places to see alloy cats-www.bodenboatplans.com heavy displacement but designed in steel or alloy. Also an older site home designed home built by a self taught welder Tony Bigras-www.ideaintegrator.com/boats/ Osram VI Historical site no longer active but shows what can be done in alloy lots of
info but states plans are not made available. The idea of two alloy huls joind by lashings ala Wharram seem to be a great solution to the cycling problems that can bee associated with alloy hulls.