KHSD demountable 27 or 30 ft catamaran

Hi all!

I am considering building one of those, probably smaller 27.
I like the idea of flat table usage and "shiny side out" method proposed by Kurt.

I am very much tempted by light weight and possible trailerability of 27.
Do you think proposed slide out is feasible?

They did make cat2fold based on his design. I wonder would that work with smaller cat.
Comments welcome.

27 demountable
Kurt Hughes Multihull Design - Catamarans and Trimarans for Cruising and Charter - 27' Demountable Catamaran https://www.multihulldesigns.com/designs_stock/27cat.html
27 Catamaran Design | Multihullblog https://multihullblog.com/27-catamaran-design/
the New 27′ Demountable Cat Design | Multihullblog https://multihullblog.com/the-new-27-demountable-cat-design/
More 27 Cat | Multihullblog https://multihullblog.com/more-27-cat/

27 Cat Update | Multihullblog https://multihullblog.com/27-cat-update-3/

30 demountable
Kurt Hughes Multihull Design - Catamarans and Trimarans for Cruising and Charter - 30' Demountable Catamaran https://www.multihulldesigns.com/designs_stock/30tcat.html
Found only
30' cruising catamaran repair log https://www.boatdesign.net/threads/30-cruising-catamaran-repair-log.53898/
The James Dory Page https://www.dorydesign.com/boat.html

and
themultihull Forum • Information https://mail.themultihull.com/forums/viewtopic.php?f=74&t=756
but not accessible any more.

 

Hi @etoimene , Welcome to the forum.
I'm not entirely sure that such stylized crossbeams as those seen on these catamarans are capable of withstanding the global loads that such a boat, with such apparently heavy hulls, can experience.

 

Thanks for the warm welcome!

Hm, you can check Jim Dory site where 30 ft catamaran carries crabbing nets. Doesn't look light load to me.

27 ft one has declared total weight 500 kg. I wouldn't call that heavy. I am hoping that with light trailer I could be under 750 kg (EU light trailer rules). Less paperwork and my driving license would be compliant.

From what I have seen, Kurt Hughes designs have traveled oceans and withstand heavy commercial use.

 

Well, I'm sure I'm wrong. If so, the better for you.

 

I hope so.

I found a comment about the 30 ft plywood version.
Multihull Structure Thoughts https://www.boatdesign.net/threads/multihull-structure-thoughts.62361/page-235#post-951243
"the real consideration is the availability of the aluminium cross beam tubes."
"Reality is “simple builds” of EG aluminium cross beams need a lot of work in the installation points in hulls"
"This approach is just a “large Tornado”

Very informative.

 

Yes, the slide-out is feasible but don't expect to much from it. It's not something you can do on a regular basis without a crew. You will need some form of mechanical advantage, be it pulleys, jacks, etc.
I don't see any advantage to it when compared to standard bolt on beams like beachcats and other tube cats have, and those will be easier to make and install. The set up time will be similar and the screw on top beams allow for more versatility.
I wouldn't bother with the sliding system, but that's only my opinion.

The cat2fold system is more practical to operate alone, but a lot more complicated to make. The manufacturing has to be exactly right, there is no room for errors.

As a tube cat designed to be trailered with the hulls side by side, inside space is limited. To understand how limited, take some cardboard and make a box 1.20m wide at the top and 0.5m wide at the bottom, then go inside. Or go find a similar sized Wharram to visit. It's absolutely fine if all you want is a dry place to sleep at night without having to set up a tent. Just don't expect the accommodation to be anything more then they are.

As for the construction method, there are many "rapid systems" for moldless construction. They all promise to cut down sanding time, but ultimately it comes down to this: if you want a nice surface finish you have to sand the entire surface by hand several times. It's just that some methods promise (and sometimes even achieve) a thinner filler layer. You have to judge for yourself if some "system" appeals more.

 

Thanks!
Good point on sliding system. I would do it once or twice a year for a few weeks vacation. Don't intend to do it for the weekend.
I don't think it would be feasible to ask for the design change for screw-on-top. Probably better to look for different design.
Probably the same with asking for cat2fold system. I would have resources to build it but cat2fold is 9 ft longer ... Who knows how it would work with 27.

We use inside of the boat just to overnight, maybe take a nap and keep our stuff so ...

Also, good point about the finish - I am not very picky there.

 

Another no vote for a sliding system here.I have enough trouble keeping boat hooks and tiller extensions working !
Apart from sand and salt and other debris sun damage on the seals etc etc sliding systems rely on some pretty precise alignment which in real world application is extremely difficult

 

Thank you! I am not that much into sliding system as I am interested in trailerability (or more generally movability - I could hire a flat bad truck too).
That "demountable" part is important. I have still not bought study plans so I have no idea how that should work.

 

The reality that I've noticed is that even trailable mono's tend to get parked at the yacht club the trailer license expires and thats where they live until sold.
If you are keen to sail regattas or have an itinery in mind I'd be wary of the compromises demountable entails.
Demountable boats are most useful when you sell them and they have to go to a new home.

 

Ahahahahaha! Something to keep in mind, for sure. I have no experience with demountables.

 

Trailable and demountable are not the same thing, especially for catamarans. Trailable generally means expand the trailer make the connections and go sailing maybe 45 minutes to 2-3 hours max.
Demountable can mean jinkers for each hull a crane and 2 days assembly time.

 

I agree. Explained a few posts earlier.