Multihull Structure Thoughts

Peter Dale. If a hull is stretched or extended and no other parameters are changed (eg width or draft or shape) the displacement is simply a multiplication. A 30 foot hull "stretched" to 36 foot = 6791 lbs x 1.2 = 8,365 lbs. But in Tennant's boats the "displacement" is more likely to be the weight. Shilo payload was 2,700 lbs. Result a real displacement of 9491 lbs x 1.2 =11,389 lbs. The structure add on weight of 1,500 lbs is a guess based on some past experience of "modified" boats. So my estimate is about 3000 lbs payload is possible. As for pitching or sailing characteristics most of Tennant's boat sailed well. A small lengthening of a boat (realistic max is about 10 to 15% but some still work at 20% extra) generally does not alter the sailing characteriscs to much if the build does not add to much weight overall or in the ends. Good work on tracking down Windzang. I suggest writing to the owners/charter company of Samoa Shilo they may know the weight of the boat. Good Luck.

 

Hi again..
With the corresponding weight increase, would it be feasible to increase sail size to some 8oo sq ft, in line with other yachts that size? Need some increase in power..
I have run some numbers with 8oo sq ft on multihull dynamics with these specs, seems about correct size sails to me.

 

Peter Dale. You have reached a point that is a little difficult to deal with. Agreed More sail area may help BUT a 20% increase in displacement also means in very simple terms a 20% increase in "righting moment" which means the cat can carry maybe 15% more sail area for the same wind strength. A bigger rig also implies a taller mast and a higher centre of effort on the sails which means you cannot expand the sail area by 20 plus % without either having to reduce sail earlier or have more weight or a wider beam.

Also you have reached a point where you really have to understand the structure supporting the mast and rigging. Designers "over design" a structure for a home design but there are limits. When you put a bigger rig on there may be problems EG the bolts on the chain plates may need to be 9 mm not 8 mm, the chain plate may need to be 10 mm thick not 8 mm, the backing plates for the chain plates may need to strengthened etc. The main cross beam supporting the mast may need wider and have thicker top and bottom flanges etc. This is where you need a serious Naval Architect or designer. In short putting an 800 square rig on a cat that has been designed for a 610 square foot rig needs some serious thought. Good luck.

 

This is a small day trimaran to meet the needs of people who wanted a good small tri that could be trailed without having to assemble it in any way. Just load it on or off the trailer. The Treasy 4.0 was designed by Emilien FAURENS for 2 people to sail and is a smaller sister of the Treasy 5 daysailer which requires assembly before sailing.

The Treasy 4.0 is 13.1 x 8.35 foot and weighs 213 lbs. The crossarms are bolted on and can be disassembled if required. The 19 foot rotating mast carries a 60 square foot mainsail, a 20 square foot jib and an optional 76 square foot gennaker. There is a daggerboard of unknown draft. The motor can be an electric trolling motor.

The build is interesting it is listed as “all polyester/glass composite”. In boat this small it can be solid glass or have a thin core. At this size pure foam glass can have very thin skins that can be punctured easily, solid glass is often better.

Performance is described by the designer. Emilien tells us: " On board, I rediscover the sensations of a Laser. But with comfort and no risk of desalination! ". The rigid benches attached to the central hull contribute to this sense of security, "J i deliberately don't want to use trampolines to reassure my users "adds the designer.

The jpegs give the idea of a fun daysailor.

 

Thanks again for all your help, your reservations about a larger rig is well heeded. Speed is not critical to me, just want to do the mast build once, correctly. Looks like 610 is the safe route to follow..Go well and your help has been much appreciated.

 

Seawind has been building boats for 42 years and understands its user base well. Seawind knows a lot of its user base wants an offshore-capable catamaran in the 40-foot range – like the new 39-foot (11.9m) 1170. This is the first tests that I have found for the Seawind 1170 cruising catamaran. Seawind focus on practical performance cruisers with an emphasis on a few comfortable cabins, not a floating hotel. The Seawind 1170 shares the best proven design features of the Seawind 1160 & 1260, and developed into a new set of modern lines with a 100% new tooling, underwater shape, interior moulding, styling, and finishes. The designer Richard Ward (CEO of Seawind) has improved the ergonomics, layout, and functionality of then Seawind 1170.

The 1170 is 39.25 x 21.3 foot with a displacement of 20,200 lbs. The 55 foot aluminium fixed mast has 10 mm dieform rigging and 6 mm dieform diamonds carries a 614 square foot mainsail, a 296 square foot self tacking jib, an optional 548 sqaure foot screecher and a 1,194 square foot spinnaker. The draft is 4 foot over fixed fin keels. The underwing clearance is 2.3 foot. The twin Yanmar 29hp Sail Drives at wide open throttle and 2,900 rpm, motored at 8.9 knots, but at a more economical cruising speed did 2,400 rpm and 6.5 knots.

The electrics are twin 200-amp gel batteries which can be upgraded to lithium batteries. A review boat had a bank of three 400-amp lithium house batteries in the nacelle, along with a large inverter; able to run white goods should you want to avoid installing a generator. Fast and wide-spectrum charging are what you pay the big bucks for with lithium batteries. This number of batteries with 960 watts of solar panels integrated into the hardtop, which will keep the batteries topped up even with most systems working. Outfitting options include air conditioning (a 32000BTU/24V system was fitted), a watermaker, a washing machine, and oversized alternators combined with a lithium battery bank to eliminate the need for a generator.

The accommodation has forward double berth cabins with attached toilet shower areas. One hull is devoted to the owner. The other hull has a forward double berth cabin, a gelley and an aft double berth cabin. The main saloon is devoted to seating and a navigation area. Seawind started the sliding folding door concept to allow integration of the main saloon to the cockpit. The practicality of the concept has been proven on many of the previous Seawind boats.

The build of the Seawind 1170 has the entire hull structure done in infused vinylester resin triaxial cloths foam core. The rest of the deck bulkhead is infused polyester resin foam core construction. The vacuum-infused construction is a mix of vinylester resin with carbon fiber reinforcement in key structural areas. These strong but lightweight composites are the work of New-Zealand based Gurit, which is also responsible for other models in the Seawind line.

The performance of the Seawind 1170 is interesting. A test sail with18 people aboard “The heavy load did not phase this cat as this 39-footer performed remarkably well in the flat water of the South River, slipping along at 6.8 knots in just 10-12 knots of true breeze on a beam reach with a full-hoist mainsail and the screecher on a continuous furler.” And also this comment “we turned and headed upwind, rolling out the self-tacking jib. I pinched up to 38 degrees apparent wind angle (AWA), and not only did we continue to move nicely, we tacked through the wind easily. This was impressive, especially for a boat with only mini keels rather than daggerboards.”

The second test was in 24 knots of wind. “Kite hoists are done from the mast winch, which went smoothly using a snuffer sock. The 9.2-tonne Seawind 1170 felt lively with good feedback from the composite steering wheels. Before the kite run, we’d beaten upwind (doing 7.5 knots at 35º apparent in the 22-knot breeze) and tacking nimbly through 95º without touching any sheets, thanks to the effective self-tacking jib and my steering efforts sitting out on the coaming race-style.

Unfurling the screecher was also without drama, allowing us to go 60 degrees upwind, as well as broad reach (managing 9.0 knots with wind on the beam). Most surprising of all was the windward pointing ability of the 1170, which relies on mini keels only, integrated into the composite hull.” In short a cat capable of sailing well on all points of sail.

An interesting design, the jpegs give some of the idea.

 

Awesome boat.., best of Aus design and Seawind have really made a classic since they hit the market sweet spot with the 1160/1170, (however I think the beam is 21ft 4", not 41.3ft as above)..

 

Peter, thanks for the correction.

 

This is a question of form follows function or are good shapes more important than function. The following tri (of which only 1 was built) is a very practical 24 footer but may not suit everyone’s aesthetic tastes. The designer Emilien FAURENS created this as a European Category D – Inland or sheltered coastal waters up to Force 4 winds.

The Treasy 24 is 22.9 x 17 foot (can be disassembled 7.2 foot by undoing the bolted on cross beams) with a displacement of 2,464 lbs. The mast height and sail area is unknown but it scales at about 31 foot which implies a sail area of about 300 square foot. The draft is 1 foot to 4.3 foot over the centre board. It has outboard power. The hulls are basically flat bottomed dory shaped due to the construction method.

The construction is listed as “plywood/fiberglass/polyester”. This is a very simple box shape that would be good for ply but the framing appears to be light. I suspect if it is ply the hull skin is probably EG 9 mm ply that would require less framing support in this size.

The accommodation appears to be a double berth forward and in the main cabin seating one side and a reasonable galley area opposite. The headroom is 5.6 foot.

No mention of performance but it appears to sail OK in the jpegs. Interesting design.

 

Thats a big little boat a veritable Tardis, its not sleek though.

 

A short one. This is another of Emilien FAURENS designs from France. This tri is a fast cruiser that has some serious accommodation available. Think of this as part Piver, part Norm Cross with a modern hull shapes but still retaining simple construction techniques. The design is rated as Category B that is, boats operating offshore with winds to 40 knots and significant seas to 13 feet.

The SKIREL 9 is 29.5 x 19.6 foot with a displacement of 5,600 lbs. From here on you will need to speak to the designer as there is little detail on the web page: PLANS BATEAU 3D | FAURSAIL https://www.faursail.com/plans-bateau-3d

Assumptions from here on. The tri looks as though it has a fractional sloop rig on a fixed mast, probably about 400 to 500 square foot. I assume the tri has a centreboard or a fixed keel as the designer likes some form of foils on his other designs.

The accommodation is comfortable for a 30 foot tri. There are 2 seating table areas forward in the main saloon with a stand up galley port aft of the saloon. On the wings are 2 doulbe berths. Forward of the main beam is a toilet shower area. The cockpit is large.

The construction is unknown but the designers earlier work was plywood, glass, polyester. His later designs are polyester, glass and some foam. Again please contact the designer if you are interested.

An interesting design of which I can only find 3 “study print” jpegs.

 

I’d say half Piver half/Neel. More Euro designs please.

 

Redrueben, yes I will search for more European designs. The final Treasy for a while. The Treasy 26 is an upgrade on the Treasy 24 but designed for home or professional building. It again is designed by Emilien FAURENS who again has gone for a simple build shape but this design has more style about it. This is a category C which means the tri is capable of operating in coastal waters and large bays and lakes with winds to Force 6, up to 27 knots, and significant seas 7 feet high.

The Treasy 26 is 26.25 x 19.5 foot with a displacement of 3,360 lbs. Again, not much further detail but an estimated sail area of 400 square foot on a about 33 foot mast. It has a centre hull based daggerboard. The hull shapes are flat bottomed dory shape with a small V section near the bows of the main hull and floats. The cross beams look as though they can be unbolted for trailing.

Accommodation has a double berth forward in the bow and another double berth under the aft cockpit. The main saloon has a galley to starboard and a dinette port. The enclosed toilet area is between the saloon and forward double berth. This tri would be a very practical cruiser for a couple for a month at a time.

The construction is unknown but the designers earlier work was plywood, glass, polyester. His later designs are polyester, glass and some foam. Please contact the designer if you are interested.

This tri will be a very capable sailor on all points but is unlikely to beat a Farrier F25 around a race course. As I said, a good reasonably fast cruiser. The limited jpegs give the idea.

 

Hello Oldmulti,

do you have information about the Newick / Marples / Brown / Weld " SIB" (small / simple is beautyful) workboat, "Sailing Pick Up Truck" for the Caribbean. It was the prototype along the Constant Camber building method, all develloped for third world water people. The SIB was featured in Multihull Magazine Nov/Dec 1978.

I don't know the length of SIB, so browsing the index is difficult.

There is a threadabout this topic in the Sailinganarchy Forum, but nobody has the dircription of the boat or any drawings / photos

Perhaps you have some? Or anybody else reading this.

Have Fun, Michel

 

Michel. Page 39 has the 32 foot cabin SIB which is a slightly larger version of the original 30 foot version. The original 30 version was an open deck version with the following specs according to my records. 30 x 20 foot with a displacement of 3500 lbs and 350 square foot of sail.

The structure is constant camber panels of 3 layers of 3 mm WRC or ply with 9 m plywood bulkheads and 9 mm ply decks. The wood box beams are 300 x 150 mm box beam. Where crossbeam go through the main hull there are doublers that build the hull thickness up to 27 mm. The beams are attached initially by lashings but later by 12 mm galvanized bolts. This would be a relatively fast boat to build.

I have more information else where which I will find and probably do an item tomorrow.