Multihull Structure Thoughts

[skaraborgcraft]

NICE! I have spotted a few laid up in yards in the UK in various states. Only ever met one cruising while in Majorca, owned by a couple of Dutch fellows. It has space for a small footprint. Its far more livable than a 24ft mono of the same era, and even a few today. Anything 6mm ply gives me sleepless nights, but I am well aware of some of the first posts to this thread and 4mm skinned inside and out with no issues, it just creeps me out.

 

[skaraborgcraft]

What about the plywood 8M Bobcat? I cant even find a photo online of one!

 

[bajansailor]

What about the plywood 8M Bobcat? I cant even find a photo online of one!

In the late 60's & 70's there was a Bobcat called Kareena owned by a hotel here - they took their hotel guests out for day sails on her. I don't know what happened to her, but in the late 70's the hotel bought a 9 metre Catalac (called Anna Kareena) to replace her, and she was in service up until a few years ago.

The Bobcats were built by a gentleman called Bill O'Brien (hence the Bob before the cat) - here is some more info and photos of them -

Bill O'Brien

www.trilogy-sailing.co.uk

There is a Facebook group, but I don't think they are very active

Facebook

www.facebook.com

I think that the Amazon might have been the forerunner of the Bobcat?

Amazon MK1 Catamaran with 2x diesel inboards - Morgan Marine

Ideal large family Catamaran / or first time sailor. Designed by the well known Bill O'Brien around 1974 known as a Bobcat.

morganmarine.com

The Bobcats were the predecessors of the Catalacs

Catalac Catamaran History – YachtSite

Following the successful development with Bill O’Brien of the Bobcat Catamaran in the 1960s, Tom Lack Catamarans LTD specialized in building these...

www.yachtsite.com

 

[skaraborgcraft]

The same Bill O Brian who designed the Swales boat that rounded Cape Horn!? An "Oceanic" ? (GRP)

 

[bajansailor]

The same Bill O Brian who designed the Swales boat that rounded Cape Horn!? An "Oceanic" ? (GRP)

Yes, that is him.

 

[Karstan]

The Diamond 24 catamaran...

THAT is a surprisingly pretty boat for a plywood, chined, home-built catamaran. Does anybody know if plans are still available? Or of similar designs?

 

[oldmulti]

Karstan. It depends on what you want. The Jarcat 6 plans are still available for a 20 x 8 foot cat that is really trailable and is designed very well for plywood construction. It sails well but is not an "offshore" type of cat. The Diamond 24 is offshore capable if sailed by good crew but cannot be trailed. Richard Woods designs some cats (EG Sango) that can be offshore and trailable but has limited accommodation that can be built in ply and other materials. There is also Spirit design that has a more modern design called Seascape, 20 x 8 foot which is foam glass. Attached is the study plan for the Diamond 24, also Bill Obrien BOB cat 30 ft that went global.

Next suggestion is for people with really good cyber security software. Look at some Russian sailing web sites EG Проекты яхт, лодок и катеров для самостоятельной постройки. Чертежи яхт, лодок и катеров. Yacht design http://amariner.net/design.html as they occasionally have pretty full plans of some of the older concept's plywood and some modern material cat designs.

 

[skaraborgcraft]

I do like a mizzen staysail! That Bobcat has more "funk" than many modern designs, or am I just old?

The amateur boatbuilding in Russia is quite impressive. I made the mistake of disclosing on another forum that I had spent some time there, which ended up with me being consistently harassed. There are some real nuggets on that site, some blatant copies, I have the drawings for their iteration of Herbulots "Corsaire" in plywood, and some "micro cruiser prams".

 

[oldmulti]

For those who have not seen a Bobcat 8 mtr the following may be of value.

 

[jamez]

Although different aesthetically the Pelin White Wings 7.4 is similar in size and spec to the Diamond. I've seen the 8.4m version it was based on - nice looking boat. There are plans for a couple of Roger Simpson small BD cats available from Boat craft Pacific. Bernd Kohler has a bunch of 'no frills' designs of all sizes and configurations. Woods Gypsy is also a well thought out relatively simple build that seems a lot bigger than it is. The problem is even a 'simple' design requires decent materials, fittings, rig etc. and nowdays they cost. Yes you can go a ways with second hand equipment, rig and sails, but sometimes that can be a false economy when something proves unsuitable.

 

[Eurosnob]

@oldmulti - do you know about this one?

Home - QE IV Ferry

Convenient and Scenic QE IV Ferry Service Travel from St. Croix to St. Thomas with Ease BOOK NOW Our services STX Gallows Bay to STT Blyden terminal This two hour ferry ride will take you from the port in Gallows Bay to the port in STT Waterfront. $85 BOOK NOW STT Blyden terminal to STX […]

qe4ferry.com

 

[oldmulti]

While we are on the Bill Obrien theme the following design was done in 1960 and was the first production design done by Bill whilst he was a naval architect Hawker Siddley in Britian. The “Shamrock” was described as aa twin hull motor sailer. Several were produced before demand for larger designs were requested. Bill produced 5 main sizes from 22 foot to near 40 foot with the 30 foot Oceanic being the most popular.

The Shamrock was 22 x 12.66 foot with a “displacement” of about 3,000 lbs (may be weight as these boats were heavily built). The aluminium fixed mast of 27 foot carried a 144 square foot mainsail and a 97 square foot genoa. The draft over the deep V chine hulls was 1.33 foot. There were no keels in this design and it depended on its deep V hulls for lateral resistance.

The accommodation was a big double berth forward (they claimed 2 doubles but each one was only about 3 foot wide). The saloon had seating for 4 at a maximum with a 7 foot galley in one hull and a toilet in the other. There was standing headroom in the hulls with 4.5 foot headroom in the saloon.

The build was timber frames and stringers covered with early plywood and a thick layer of csm polyester glass. The glues in 1960 were mainly Aerolite. The fact that a couple of Shamrocks built in 1960 are still used for charter work shows that with a little care these can be long lasting boats inspite of the glues etc.

The performance was “10 to 12 knots in Force 6 winds”. Read that as running or broad reaching. Due to the heavy rocker deep V hulls the cat could tack well but was not a real upwind cat. An 18 HP outboard provided 8 to 10 knots when required. Remember the design was described as a twin hull motor sailer.

The jpegs give an idea of an interesting design for 1960. The blue hull is available for charter.

 

[oldmulti]

To all who are interested in smaller plywood cabin cruising cats that can really sail, Bernard Kohler at the following web site: Design https://ikarus342000.org/DESIGN.html will satisfy most home builders. His Duo 480 cruiser is a very impressive minimal cruiser for 2 that can do limited coastal cruising. His Eco 520 has more room and capability and still is a simple build. The ECO 550 sail and ECO 600 sail are bigger builds, but the internal room is larger, and you are moving into cats that have more coastal sailing capability. Bernard has larger options and a variety of rig options as well. Bernard still runs a very active user group for assistance. Richard Woods 18 foot Chat is also an excellent sailing design for weekend cruising but has more limited accommodation. All off these designs are plywood/timber simple to build designs.

 

[oldmulti]

Back in 2019 we published a small catamaran design by Mark Grumpecht. Mark built the design in a year himself but I could not find any plans for the design. The cat was later sold and no further details came forth. A small request and hopefully someone can lead us to the plans of this cat. I do not know if Mark is still active or someone has a copy of the plans. If they do, could they please advise us as the design looked good.

Mark Grumpecht small cruising catamaran is 22 x 8.5 foot weighing 1900 lbs with 24 foot wing mast as used on his Drifter 17 trimaran design. The cat has a lifting centreboard and central rudder. Mark designed and built the cat in one year. It is plywood with light e-glass cloth outside. It uses mahogany wood on the interior and for some framing etc. I do not know any structural dimensions. The cat has aft sugar scoops with steps.

The cat is trailable on a 3500 lbs capable trailer (the trailer weighs 700 lbs). The engine is a 6 HP long shaft outboard. The custom mast raising rig, uses trailer winch. The cat has two single speed winches mounted on the cabin top. The cockpit is 5.5 x 6.5 foot and the cat has a micro galley with a 2 burner propane cook top and small sink. The cat has a custom private head with door on port side and a thetford porcelain marine head. The cat has a double berth with 2 child single berths. The front mini tramp can have 1 adult or 2 children on it is very comfy and cool to be on while sailing or at anchor. The cat is a coastal cruiser that is claimed to perform well.

The jpegs give the idea but we need more detail please.

 

[skaraborgcraft]

^ That reminds me of the old Hirondelle, which is slightly larger.

Hirondelle (catamaran) - Wikipedia

en.wikipedia.org

I am pretty certain that i have seen a brochure at some point in the past for a 20ft open backed cabin version.