Multihull Structure Thoughts

Does anyone have anything to say about Dory hulls or flat bottoms ?
Most of my offshore experience is in monos with that flat run aft and I will never forget the pounding those things handed out, and the Farrier tris in a short chop, bang bang bang.
I look at hulls like Fish and Chips and the Woods Eagle and just think NO.
The Selway Fisher Cat 254 I think is about the most I would like.
Comments. ?
PS I think I really like the rounded V shape which is why I have a fascination for tortured ply, but they lack volume. Sad face.

 

David Wilkins of WILKINS YACHT DESIGN did this design in 2015 as part of his graduation requirements for Westlawn. The 58.9 x 33.3 foot with a displacement of about 28,000 lbs. The 76 foot rotating wing mast carries a mainsail area is 1077 square foot, self tacking Solent jib is 518 square foot and a 1000 square foot genoa. The length to beam on the main hull is 10.4 to 1. The float length to beam varies between 16 to 1 and 12.5 to 1 depending on the heel. The hull draft is 3.4 foot. There is no indication of a centreboard/daggerboard.

My only comment about the hull design is the float shape, which pushes the float centre of buoyancy very far forward of the main hull centre of buoyancy. Other designers slightly shift float centre of buoyancy forward to help in power reaching and minimise pitching. But other designers float shapes are longer and fuller in the stern. Tris can be pushed backward in big waves and a least 2 have “reverse” capsized due to a lack of rear float buoyancy, its rare but it has happened. Larger tris generally have less trouble but this design was done about 2015 when the OMRA 60 footers had become very refined in hull shape.

The aim of the tri is to be a fast global cruiser. The speed prediction program predicts 20 knot top speeds. My calculator says 10 to 12 knot for 24 hours is possible. I think that will be enough performance. The accommodation is practical with 2 double cabins with attached toilets and a single berth cabin. The main cabin has a galley, seating and dinette. The steering position is well protected in a covered cockpit.

The structure is primarily 25 mm Corecell M130 with e-glass in epoxy. The layups suggest 3 layers of 3300 gsm triaxial (plus extra’s) on the outside of the core and 2 layers of 3300 gsm triaxial on the inside depending the location. If that is the case this tri main hull structure is strong, which would explain it meeting the ABYC classifications requirements.

An interesting design study. Sorry about the limited jpegs but please study the hull deck structure design detail jpeg.

 

Redreuben. I agree that flat stern section can bang a little in short chop, but I will accept the noise and bangs for the improved sailing performance especially upwind in a seaway. I have sailed on a Spindrift 37 and a Spindrift 45 cat in there original fine end hull forms. They were both modified to have bulb bows and fuller flatter sterns (up to 200 mm additional foam, some ply and glassed over) . Both these cats pitched less and were faster especially up wind after the modifications. Yes, they had a slightly rougher ride. Flat sterns or dory shapes in narrow hulls has less impact than in wider hull shapes. Translation I personally will put up with the discomfort for the performance gain in a well shaped hull. PS I sailed on a 42 cat that had a very flat stern for about 3 foot, but with rounded edges leading to a round bilge hull shape. This hull shape really worked on this fast cat with its 13 to 1 length to beam hulls.

 

I understand fatter sections for pitch control I really do, it’s what I don’t like about Wharrams but a Dory hull at 8.1 is a much different boat than a Dory hull at 13.1
I think it’s an easy way to get volume in a simple build shape.
I really like Fish & Chips but at 7 panels per hull it still has a wide flat bottom panel, the Eagle at least is simple.
I like the basic hull shape of Evergreen the Laurie McGowan Michael Schacht cat.

 

FWIW, and given it's my opinion it's not worth much...

The cat dory hulls are narrow so should be less of a problem, but RW has a whole range of chined hulls which have a narrow center panel and 2 sloped side panels before a big side panel. See Romany, Vardo, Saturn and probably others. These are only slightly more work, better approximate a rounded hull, IMO are prettier than a dory and shouldn't slam appreciably.

I have the Saturn plans and hope to build one when things settle a bit for me. I know it's been a while but I'm still sorting my life post stroke.

 

It is interesting how far the design of charter catamarans has come. Ocean Voyager employed Naval Architect Pierre Delion and designer Franck Darnet to design a new version of a new 40-foot multihull charter cat the Optimo 40. The Optimo 40 is 39.3 x 22.5 foot with a weight of 20,950 lbs and a displacement of about 32,000 lbs with a 35 passenger load. The fixed aluminium mast carries a 670 square foot mainsail and a 335 square foot self tacking jib. The hull length to beam of the hulls is about 7.5 to 1. The draft is 4 foot over the low aspect ratio keels and rudders. Engines are 2 x 30 or 2 x 50 hp diesels.

There is limited accommodation in the hulls. Both hulls contain a forward double berth, living space and stowage. One hull contains the public toilet and a minimal galley. The main bar and food service area is aft on the passenger cockpit/deck. The passenger seating can be in several configurations with up to 35 passenger seats. The deck is covered by a large Bimini which also by default acts as a nice end plate for the mainsail. The skipper has an excellent view of all sails and guests whilst sailing. The only downside is the forward self tacking jib which is lead to a mast base control centre at the base of the mast. Flaying ropes during an uncontrolled manoeuvre and people watching the view can lead to problems.

The Optimo 40 is a composite construction structure in the hulls above the waterline, beams and main deck. I think the hulls below the waterline are solid glass. The mast base comes down to a “pod” on deck with supporting beams laterally and fore and aft under the wing deck to carry the loads. The hulls have 4 watertight compartments and 2 serious engine rooms allowing room for maintenance.

This is a very thought out design that is suitable for day charter work. Ocean Voyager claims that this cat could earn 6000 Euro’s per day in the right day charter locations. PS please be careful in offshore locations with this cat as the full bridge deck all the way forward could catch a wave in the wrong conditions. The design is very good and it is a lot safer than most, with high freeboard and relatively full bows as indicated by the double forward bunks. The jpegs give the idea.

 

I'm wondering if anyone knows who owns this photo, where it came from, and if there are more?
I can't fault the Gougeon brothers for anything except their photography skills.

 

Samin who did the attached jpeg was a regular poster on Multihull Anarchy. The comment associated with the jpeg is “ Here is a photo from sept last year of my new 8.5 Tri. you can see on the right is the pre folded float, and on the left the folded float upside down nearly ready to glass with the deck jig on it. Its quite a good photo for people who havent seen the way you build a tortured ply hull. The left hull has to be bogged and glass taped down the centre. Once that is done you steam it and bend the gunnel in with ratchets and pop the deck jig on. The whole 8.5 hull takes three days to build if your organised. It then takes about three months to put the bulkheads in, build the deck, glass and fair it!”

Hi Samnz. "Hows your new tri coming on ? And who did you sell the "Green Terror" to ?? Oldsailor. December 19, 2010"

His claimed birthday is 04/01/1981. Samnz was on boat design net. Based in Auckland NZ up to 2014.

Attached are jpegs of B24 and the 8.5 tri sailing (the floats are the ones in the jpeg you posted). The sail number of the tri is M 7153 which may lead to an owner. Web address of the jpeg and Samin comments is: Buccaneer 24 Trimaran https://www.boatdesign.net/threads/buccaneer-24-trimaran.25159/page-9 Read a few pages before and after in that thread for more of his comments including about the modified cross beams. The current owner of 7153 (which is a Buccaneer 24 called Capricorn) is an Andrew Barney. Confusing but it may help lead to original person.

The jpegs are of the original green Buc 24 with modified cross beams. The 8.5 tri which may be the Buc 24 with the 8.5 mtr floats and the cross beam build. The broken float jpeg was cosmetic damage after hitting another boat. There is more details elsewhere but it is early AM and I need sleep. Hope it helps. NZ folk can we find Samin?

 

This about a 3D printed dingy but it could be applicable to a larger multihull. This is not about the dingy itself, it’s about the build process. “Beluga” a dingy with a 3D printed hull as produced by a partnership between Caracol and NextChem. Caracol is a 3D print service and a 3D printer manufacturer and they also produce their own software systems to manufacture almost any desired object. It’s a robotic extrusion system, with a six-axis reach that allows the machine to 3D print any required geometry. They partnered with NextChem, a business focused on the production of “green” plastic material for industry. For this project, they provided their MyPlast recycled material.

Normal 3D printing has size limitations due to the technology used and associated heating required. Caracol due to the robotic 6 axis extrusion system allows a 3D printed boat production facility that can produce hulls of any size and dimensions on request, one after another. Each boat can be produced as a unique one off or a series run can be done. As you will see in the jpegs the multi axis robotic 3D printer you can produced integrated multi-dimensional shapes including hull, deck and framing all in the same continuous run.

The second most important aspect is the materials being used in the production of a hull. The current print material is from recycled plastic and is a consistent density. Translation “no foam core” separating skins. This means either a thicker heavier hull skin or plastic materials that are composed to produce a lighter density whilst maintaining similar strength. The final approach may be producing a 3D inner and outer shell and pumping foam between the 2 shells. There is a lot of development happening in the material field. HDPE sheet boats are growing in popularity which shows certain types of plastic can be used to produce large boats (up to 45 foot and 33,000 lbs displacements).

The jpegs give the idea of a future. The web address of a news item on this is: World's First 3D Printed Sailboat Made From Recycled Material « Fabbaloo https://www.fabbaloo.com/news/worlds-first-3d-printed-sailboat-made-from-recycled-material

 

The original Buc 24 Capricorn post was at Multihull Structure Thoughts https://www.boatdesign.net/threads/multihull-structure-thoughts.62361/page-39

Jamez may know the guy who built the floats. Jpegs are of Capricorn over time.

 

Those Buccaneer 24 photos make me nostalgic for the "good old days", where people built their own boats and goofed around with them more. I really miss that. Around here we don't have enough natural harbors or young people who want to build stuff. So glad I missed having a smartphone as a kid.
I'll try to contact Jamez on SA. Hoping for more photos and permission to use them. Didn't see those hulls on the green Buccaneer, but it looked like it needed them.
Looks like two Australian teams signed up for this year's R2AK race.
Thanks so much for all your help, Oldmulti. You have funneled a lot of information my way and it's appreciated.

 

Russell

I have messaged "Jamez" about your query re Capricorn. He knows Samin. Capricorn is now owned by a guy called Eric, or was before all the lockdowns that were going on here. (It is easy to get out of touch when one is forced to treat his fellow man like a leper) . I went to a get together at Jamez's with Eric and Gary Baigent several years ago that was for the sole purpose of chewing the fat over multihull design (I was completely out of my depth but loved it). Gary has had a bit to do with making B24s go faster, over the years. Not to mention his own wonderful creations. Anyway, as a mostly lurker on these pages, I really enjoy what the experts have to say. Hopefully James will answer back here shortly

cheers all

 

This about an experienced German sailor who designed a cat for himself which he called “Waveschapel”. The idea of the cat was first conceived in 2003 as a 46 foot aluminum cruising catamaran, then over time the design grew to 52 foot and finally after several iterations grew to 17.6 meters (58 foot). The weight of aluminum in the design is 23,000 lbs, implying a base weight of about 30,000 lbs with equipment and engines etc aboard. The mast is 62 foot high. The mast is constructed from 3 vertical tubes in a triangle shape with short tubes connecting the 3 vertical tubes. The mast weighs 1,800 lbs with spreaders. The daggerboard draw a guess of 7 foot. The cat was initially conceived as a good cruiser then developed into a charter cruiser which was part of the reason for the size growth.

There are several aspects to the design and build that are interesting. Being a home design is not a problem if you have the skills to design a structure and understand the build process. But one thing that often separates a home design from a professional design, a sense of proportion between various shapes in a design. What looks OK on paper does not always translate into a visually acceptable when its actually built. In car design the size of windows needs to be smaller on a paper design because in the real car the windows “look” larger. In this design the cabin top looks OK on the initial CAD designs but is visually jarring in the actual build. The hull bottoms are round and smooth, the cabin top looks like a block of flats. A few curves in the cabin top would give a better looking cat.

Next the construction of the cat was done in Crete and the owner designer lives in Germany. The owner purchased 33,000 lbs of aluminum in Europe then shipped it to the builder in Crete. The owner designer then had to spend extended time in Crete to ensure all was going well. In both cases when you are building a cat this big, a professional designer can achieve good outcomes with minimal stress on the person paying the bills.

The cat was finished in 2015 and has been cruising since. The owner is happy with the results and the cat can cruise at 10 knots under the right conditions. The jpegs give the idea.

 

Part 2 of Waveschapel. The on or near water jpegs.

 

Hi Russell, got your message on SA Can you please PM me an email to pass on to Sam?
Pic of the finished floats and boat.