Multihull Structure Thoughts

Peter Dale. On page 1 of this thread is an index. The index is based on length in feet. the next number bis the page the boat is on. You will find EG Shilo on page 52. An easy way to get to that page is to look at the address bar above and you will see a page number at the end, change that page number to EG 52 then press return. Or if you want an easier way, bring up google and type in Multihull structure thoughts Shilo catamaran and often it will bring up the design in the thread. I agree it maybe a lengthened Shilo.

 

This design is from a design group I know little about but appear to produce some interesting multihulls (and mono’s). The architect and designer is Emilien FAURENS. The design I will focus on is the Semigun 8.5 cruising catamaran. It appears to be a plywood design that could be a good coastal cruiser.

The Semigun 8.5 is 27.9 x 14.8 foot with a displacement of 5,600 lbs. The sail area is unknown (guess about 400 square foot) but the mast appears to be about 29.5 foot high. The hulls appear to be about 8 to 1 length to beam. The draft is 1.6 foot to 5 foot over the dagger boards and rudders. There is a fixed keel option. It is listed as a Category C design. Category C means Inshore. This rating is for boats operating in coastal waters and large bays and lakes with winds to Force 6, up to 27 knots, and significant seas.

The accommodation appears to be 2 wide single berths in the stern of the hulls beside the cockpit another single berth forward in one hull. In the other hull there is a standing headroom galley probably with a toilet forward. The main saloon has a sitting headroom seat/table are that could be converted to a double berth. The cockpit is large and comfortable.

The design is flat panel multichine hulls and judging by other designs done by this designer, the build would be plywood and timber. Think 6 mm ply and stringers sides with maybe a 9 mm ply underwing, hull bottoms and maybe decks.

From an estimate from my simple performance calculator, I would suggest 7 to 8 knot averages in good conditions with peaks of 14 to 15 knots.

So about the limited jpegs.

 

...& where is the "next generation" of amateur boatbuilders needing plans? Was there more than 1 self-built boat in the 70+ boats anchoring fleet in Taiohae, Nuku Hiva in 2019? I don't think so...did all the cheap second hand Bavarias et al kill this market?

 

Hi Old Multi
Thank you for your direction to the Shilo.
If you have any info on Malcolm Tennant's Northern 11, this is the open deck Tennant design that Eric Knight was going to market..I believe an Australian company bought the design from Eric Knight..would like any info you have on the Northern 11 ..looking for specs/photos etc or anything on Northern 11 (meter)
I believe a guy named John Macfarlane wrote an article on Eric Knight (who has since passed) in New Zealand Boating magazine.. Seems Eric Knight spent much money on arranging for moulds to be built and then 2008 happened. Seems www.Tennantdesigns.co.nz is not working any more too.
Any info on this design would be of interest to me..thanks again.

 

Peter Dale. The closest Simpson I can find is a 10.2 which was 10.2 x 5.9 but was a full bridgedeck but was a cedar strip planking hull and a plywood build (page 42 this thread). The 10.3 x 6.1 was cold molded ply over stringers and frames and an open bridge deck design, I will do a small item on that cat tomorrow.
The next is an add for a Simpson design 11 x 5.5 mtr but built in fiberglass.
Used Simpson Inspiration 11 Simpson Inspiration for Sale | Yachts For Sale | Yachthub https://yachthub.com/list/yachts-for-sale/used/sail-catamarans/simpson-inspiration-11-simpson-inspiration/315671

Finally the Tennant Northern 11 did exist and there was a magazine review of it, but it was a production fiberglass boat. I hope the NZ guys may help.

 

Peter from page 40 of this thread, the Simpson 10.3 catamaran which is a plywood multichine boat. The cat is 33.75 x 20 foot open bridge deck boat that displaces 10,750 lbs carrying a 227 square foot main and 308 square foot genoa. The waterline beam is 3.7 foot with a length to beam on the hulls is 8.5:1. This boat was relatively popular as it was a realistic size that you could build in the back yard and cheaply transport to the sea for final assembly. The maximum hull width with the mini wing deck edge is 7.5 foot. This cats hull width does not match your information and also it is sheet plywood but Simpson often provided offsets for round bilge hulls. The boat has some real accommodation for 2 people to cruise in.

The hulls are 9 mm ply with a 12 mm ply flat panel bottom. The chine logs are 60 x 19 mm with stringers 42 x 19 mm. Internal keel is 2 layers of 90 x 19 mm. Bulkheads are 9 mm and some 12 mm at bulkhead points. The wood main cross beam is plywood and timber. There are 3 x 12 mm plywood webs with a 350 mm x 35 mm top and bottom timber flanges. The jpegs give some idea of the boat structure. If the structure does not match the above then I suspect Simpson designs are unlikely. Good luck with your search.

 

I always said 50 foot multis can fly, I never thought they flew this high thought (look at the jpegs). It was a far from simple operation: 50 x 50 foot, and 5,500 lbs had to be transported from Nembro, (Italy) to Marina di Carrara, south-east of La Spezia. 93 mi (150 km) and one mountain range to cross. The flight time was around three hours. A long flight time* which, when added to the need to climb to altitude, required Heliswiss International to refuel their AS 332 Super Puma helicopter during the trip.

The tri is a pure racing machine for the Ocean 50 class which has a series of fairly strict rules to reduce costs. The rules include glass fibre is required for the build, except for the crossbeams, mast, rudders and foils, which can be made of carbon fibre. The class implements other measures, EG you are only allowed to change sails every two seasons and the foils are one-design.

This tri was built in 2020 and was named Planet Warriors then Ciela Village then Koesio and has sailed in many races including winning the 2022 Route du Rhum in the livery of Koesio. The length and beam of 50 x 50 foot with a weight of 7200 lbs. The draft of both over the central daggerboard and float based C foils is 11.5 foot. The 2020 design has a 67 foot rotating carbon wing mast with an upwind sail area of 1,904 square foot and a downwind sail are of 2,850 square foot. The power to weight of these single-handed racing tris is amazing. And before you ask these tris can average 20 knots and peak at over 30 knots.

VPLP studied many configurations with the aim of optimizing weight. Weight-saving efforts also included the static parts of the boat, such as the fittings, the engine, the lines, the pipework and the wiring. As a result, Ciela Village is the lightest boat in the Ocean Fifty fleet. Next came the hull shapes, VPLP drew on feedback relating to foiling behaviour from the two previous Ocean Fifties designed by the firm (Solidaires en Peloton-ARSEP and Ciela Village, now Leyton), thus turning the research significantly towards enhancing performance. In practical terms, a lot of work was done on the longitudinal centres of volume, moving them aft to stop the boat from porpoising too much because of the lack of foiling surfaces in the stern.

Another innovation involved the K-shaped set-up of the beams, with the after beam extending to the foot of the mast. This freed up space so the cockpit could be twice as long and entirely shielded with plenty of room under the canopy. This has been a huge improvement for the skipper’s protection out on the ocean, but also for the Grands Prix because weight could be centred, the winches and other gear having been moved forward. “As a result, the crew are further forward, giving the boat a better trim overall,” said VPLP.

A comment from the Route Du Rum Ocean 50 skippers “The skippers talked about it at the finishing line. It’s obvious that, given the level of commitment and the intense pace, particularly in the first week, those who were better protected from the elements were able to maintain higher average speeds.”

A lot of work was also done on her aerodynamics with a view to reducing as much as possible air resistance, a factor that is becoming increasingly problematic for these boats which are sailing faster than ever.

The jpegs give the idea of an interesting trimaran.

 

Holy smokes, the transport probably cost as much as the boat !

 

Hi Old Multi

Again, thanks for all your info. definitely not the Northern..

After much comparison of the layout of the Shilo, I think the original design may be a Shilo. It seems there is a Shilo 11 in Samoa doing charters (it looks to me without extensions)

The aft transom bulkhead of my boat looks very similar to the aft bulkheads on the attached photos, especially the height where I know you cannot stand upright at 5 ft 10" in my boat your head and shoulders will be well out of the hatch in the rear of the transoms. (attached a photo of the rear transoms of this charter boat, which they advertise as a Shilo 11 (ie. not 10 meters) and it looks like there are no extensions added too. So I am thinking that the Shilo may have been built differently, eg Windzang seems to be under 5m beam(due to mooring constraints) and is the shorter version of the Shilo too (specs are on the evecom.com site). The fore cabin sizes and saloons and general layout seem to be same as my boat as per the Tennent archived design layout.

If I do a calculation off the Shilo design layout from Tenant design, I also get dimensions of 11mx6m, and there is a scale on the design layout..(different to his stated lengths of 30ftx18,3ft) on his old site which I managed to get to through archives on the internet.

Also, the hulls at the rear of my boat towards the transom seems to have been added/constructed differently to the rest of the hull. Hence maybe this was an extension, which has been added to by the extensions which show in the photo. I am still working through exactly what has been done aft.

If my suppositions all are correct, my boat is a Shilo design, with rounded moulded hulls at the base for most of the hull, with a Simpson 10.3 interior, with the 9 stringers running longitudinally, so maybe the constructor just took the easiest construction method he knew and applied it. The bouyant convex hull shape definitely points to the Shilo/ Tennant design.

So, pretty confirmed it is an extended Shilo, but just wondering why the builder did his own thing on the sides of the hulls.

Interior layouts of Shilos (I have Windzang interiors already) will help as well as interiors of the 10.3. To me the 9 stringer hull looks same as most 10.3's were constructed.

 

Hi Old Multi

Apologies for the replication of photos, need to get used to the forum tools (but they are nice photos anyhow)
This is a copy from the advertising of the Samoan Shilo:
"Shilo II is a 35 ft sailing catamaran, I think the only one based in Samoa"..

Going to try to upload the tennant published layout now..

 

Peter Dale. If you are correct about the cat being a Tennant Shilo extended to 11 mtrs then the displacement would be about 11,400 lbs. Even allowing for the extra "add on" structure and a little weight added to make it "stronger" the weight maybe an extra 1500 lbs. Pure calculated guess here, but you may end up with a payload availability of 3,000 lbs. The red Shilo on page 52 of this thread "Windzang" was a Dutch build if I remember and was constructed to fit through the canals of Europe, translation only a 5 mtr beam. Are there any Shilo builders or plan owners out there that can confirm the Shilo structure is similar to what Peter is describing.

 

Hi Old Multi
These are the exact specs for Windzang as per Evecom.nl site
9,3x4,5m LOA to beam
displ 31kgs
height of mast 12,7m
57m sq sails.
I measured to the best of ability my boat to be:
11,6mx5,6m.. which more or less ties in with Shilo11 in Samoa. (11m without ext which are around o.6m)
Would you still guess off these figures some 3ooolb payload, displacement 11400lbs?
I would love to know weight of that Samoa Shilo..

 

herewith original writeup on Tennant website..