Multihull Structure Thoughts

This was to start out as an update on Tiki 21 information but expanded to an interesting variation on Tiki 21 cross beams. The Tiki 21 is 21 x 12 foot with a weight of 800 lbs and a displacement of 1800 lbs. The 20 foot 104 x 3 mm aluminium tube mast carries a 207 square foot rig. The draft is 1.15 foot.

I have found many parts of plans etc on the web which is shown in the jpegs, then I found a guy who had a Tiki 21 with aluminium cross beams to reduce maintenance. Initially, I thought it would be round beams then I saw he had an aluminium replica substitute for Wharram designed beams. Simple, effective and if welded up from parts you cut out, probably cheaper than tube beams.

The beams look as thought they were cut from 4 mm (6061 T or equivalent) aluminium top and bottom flanges with (guess) 4 mm web and bulkheads. The width of the flanges and depth of the web appear to be the same as the standard wooden beam (cross section of beam is in 1 of the jpeg). This would be a LOT less work to construct and maintain than the standard wooden beams. The “strength” of the aluminium sections at 4 mm is greater than the timber. No maintenance of the beam structure is required after a decade and 7000 miles of sailing.

The beams are “lashed” onto the hulls by fabric rope wraps as per the standard Tiki 21 design. The aluminium beams have rounded edges where the rope wraps go around the beam. To quote the owner “The plans specify 5 full turns of 3/16 low-stretch. I tried 3/16 dyneema but it was too bulky, and the 1/8 fitted well. The breaking strength of the 3/16 Robline low-stretch that I use all over the boat is 1,230 lbs, whereas the breaking strength of the 1/8 amsteel dyneema is 2,300 lbs. Another advantage of the dyneema is that it is very abrasion resistant.”

The mast step was upgraded later to allow the mast to be raised and lowered with less effort. Again, a simple solution from parts he made. The step components are made from 12 mm aluminium with 8 mm bolts to the beam and a 12 mm pivot pin through the mast. The mast has 3 mm plates on the outside and a 3 mm inner reinforcement tube in the base providing 9 mm of aluminium on either wall of the mast for the 12 mm pivot in to rest on.

And to give an idea of the performance of his near standard Tiki 21. “On this day, Little Cat was tacking through from a best of 96 degrees to a worst of 116 degrees, and maintaining an average 3 - 4 knots progress directly to windward. Working in our favour was a breeze in the golden range of 10-15 knots true, and Little Cat had a freshly painted (smooth) bottom.” His Tiki 21 has peaked at over 15 knots on reaches and can average 7 to 8 knots under favourable conditions without pushing too hard. He found good sails help enormously.

Jpegs give the idea.

 

You could make beams from 2 [] sections. Move one up and across so they interlock. Mostly uni top and bottom with 45/45 interleaved to get resin flow. Sides are just the 45/45. Make them on a mold and glue them together. Lighter than aluminium no rot no electrolysis. As light or better than ply or aluminium.

As I've mentioned before I owned tiki 30 and tanenui plans and I've seen the full T21 plans. You could build a woods Janus or acorn for similar money and if anything less time and have a massively better boat in every way. I know I go on about it, but it bugs me immensly.

"It also spoils the bunk front centrecase ergonomic."

I don't understand this ?

 

The Ray Kendrick (and others) centreboards use the bunk front or seat front if you like as the centreboard case so they are discreet and open up the interior.
The “L” shape centrecase would spoil this.

 

Guzzis3 and Redrueben. Another way of thinking about using an L shaped board is to have the L component attached to the centre b0ard with a one way hinge. As the board is raised the hinged part folds next to the board in the case. When the board is down the L filler piece fills the slot and is held in position by EG a spring. I will draw something in a day or so to show the function and work the logic a bit more. This means yo can fill the slot when the board is down and still have a low bunk/seat front when raised.

 

Burger. The following series of jpegs are of a moored Tiki 21 in San Francisco bay in 25 to 30 knots of wind and 4-5 foot seas. Notice the rudder kicking out in the last jpeg. Pitching can be a problem with Wharrams.

 

More possibilities
-You don't need an "L" shape to move that pivot forward -if you use two bars or a bar and slide you can make a virtual pivot about anywhere. Pivots are less foulable than slides.
-Sliding dagger boards must be constant profile. A more efficient profile would be more elliptical -which can be approximated by a vertical leading edge and a broad arc trailing. The point is you could get the same efficiency with less aspect ratio.

 

The following is about a light tender required for a catamaran. Spirit designs do a range of catamaran tenders called the Ripple. They range from 2.8 meters to 4.2 meters. We will focus on the 3.6 meter model. The Ripple 3.6 meter is 11.75 x 4.75 foot that weighs 120 lbs and can carry 715 lbs for a total displacement of 835 lbs. The underwing clearance is 150 mm and the draft is 100 mm. The tender can be powered by a 15 HP. A 6 HP test engine drove this build at 5 to 7 knots when overloaded to 1000 lbs. The 15 HP drove the tender onto the plane. This build had a few modifications as per usual. The actual length is 13 foot due to a “step” stern extension.

The builder ordered the standard build kit for the Ripple 3.6 then asked for a lighter construction that the Ripple options listed in the jpeg guide. PS the beam listed in the guide for the 3.6 is questionable.

The structure suggested by Craig Schoinning and ATL was “10mm 80kg foam (Divinycell H80) with 300gm carbon plain weave as main laminate each side of the foam with additional 450gm double bias tapes or drops where required. This can be e-glass and applied anywhere where impact can be expected. These areas are: Hull bottoms, top of bridge deck, foredeck, floor area in hulls. The hull bottoms and internal floor area is covered when the tapes are applied so this adequate as standard. The bridge and foredeck will need additional laminate however an extra 300gm may suffice. Remember that the tapes for the joins are additional to the main laminate and should be applied as specified in the plans.” The final build was 300 gsm carbon fibre with 200 gsm e-glass cloth over on panels for additional “knock” resistance.

There were calculations that suggested the carbon fibre build would be 20 to 30 lbs lighter than the standard build depending on the builder’s skill and how much reinforcing glass is used in impact areas. The builder ordered his carbon fibre cloth directly from China and found it cheaper than e-glass from an Australian source.

The build had fabric vacuum bagged on one side of hull panels and fully glassed on both sides of bulkheads. The MDF male mold provides a solid shape base. The hull panels are attached to the mold with the glass face attached to the mold. Then the unglassed external foam is faired, glassed and vacuumed bagged. The shell is then taken off the MDF mold and the interior is taped and premade bulkheads, decks etc added. Finally finishing and painting. The build is meant to take 85 hours but I suspect this is an underestimate judging by 2 build commentaries I have seen.

The jpegs tell some of the story. The actual build weight was about 75 lbs for the shell and under 120 lbs for the finished tender. The owner has found the tender to be lighter, easier to handle and more capable of load carrying while providing more space than his previous rigid bottom inflatable.

 

Oh ok. I was thinking it'd be angled against the hull side so it'd only intrude by the width of the board plus case side plus hull side curve. Makes the walkway a tad narrower and would interfere with any cupboards but shouldn't be too bad. Upside is you lose no window area..

Skyak
"More possibilities
-You don't need an "L" shape to move that pivot forward -if you use two bars or a bar and slide you can make a virtual pivot about anywhere. Pivots are less foulable than slides.
-Sliding dagger boards must be constant profile. A more efficient profile would be more elliptical -which can be approximated by a vertical leading edge and a broad arc trailing. The point is you could get the same efficiency with less aspect ratio."

I have no idea what you are saying here ? The L shape has nothing to do with pivot location. My post had nothing to do with daggerboards. You design and build as per normal swing centerboard but make the case higher, possible quarter circle shape. Make the board as per normal except you add an equal length arm at 90 degrees to the fin. Leave this arm rectangular not aerofoil shape. When the centerboard is swung vertical this second "leg" swings horizontal and blocks up the slot in the centerboard case. Just dampens turbulence, that's all.

 

Quick question, does the hdpe stuff that gets used for bearings and that sort of thing attract fouling ?

 

I have no direct experience of it on boats but have made stuff from it a lot over the years. I would be very surprised if it DIDN'T attract marine growth.

 

This is about Neel trimarans and how they design their trimarans. I amusing the Neel 43 as an example but it applies across the range. The Neel 43 is 43 x 24.6 foot with a weight of 20,000 lbs and a displacement of about 27,000 lbs. The 56 foot aluminium fixed mast carries a 630 square foot mainsail and a 466 square foot headsail. The main hull has a length to beam of about 8 to 1. The draft is 4.5 foot over the low aspect ratio keel on the main hull. This limits the beaching capability of the tri unlike cats who have 2 keels to sit on.

The primary designer of the Neel 43 is Marc Lombard who has designed many quality racing and cruising multihulls. He designed the general design then with the builder collaborated with TENSYL with whom we have previously worked on the structure of the racing trimaran TRILOGIC. TENSYL has made a specialty of the structural design of multi hull racing and cruising composites. Sampling is determined from the most critical cases of offshore loading on the structure, for example catching a wave at high-speed or sailing with the wind on the beam. The analysis programs transmit relevant information which are compared to nominal values in the specs. Color displays are particularly instructive in sample determination. The overall research programme aims to define type and quantity of construction materials best suited to each zone in order to eliminate unnecessary weight and apply suitable safety margins to load bearing elements. The first 2 jpegs give the idea of the FEA stress models used by TENSYL to determine the high load area (red is high stress blue is lower stress). There are many models done to determine the load paths for different sea states, wind angles and load states.

After the design phase the builder then attempts to build the design to the structural specifications given. Please understand the optimum structure is not always able to be built due to EG unavailable materials, excessive labour required to taper materials etc. In the case of the Neel the hull, floats, bridges and roof are made in vacuum bonded PVC/foam and glass fibre/ isophthalic polyester resin sandwich structural material. The boards are fabricated from honeycomb PVC vacuum bonded with glass fibre/isophthalic polyester resin structural material.

Resin is infused through the fibreglass according to a sampling plan determined by finite element structural analysis. Depending on their role in the structure of the trimaran, the type and number of glass fibers are either unidirectional, bidirectional, 0 ° / 90 ° or bi-directional 45 ° / 45 °, Quadri-directional, carbon fibre roving or twill. Phonic and thermal insulation, along with floatation (unsinkability) are provided by the interior of PVC foam sandwich laminates.

Result of this is a trimaran with good accommodation 3 double cabins and 2 singles. The main saloon area has a good galley and seating. The performance of a Neel 43 can be summed up by one tester “After hoisting the mainsail we cut the engine and bore away, unfurling the headsail with the wind on the beam. In only 14 knots of true wind we quickly accelerated to a consistent 10 knots of boat speed. Sheeting in and squeezing up to a true wind angle of 65° – and 40° apparent wind angle – only saw speed drop by one knot. When the breeze picked up a little to 15-16 knots true, we sheeted in and luffed up to 115° off the true wind, accelerating to an easy 10.5-11 knots of boat speed.”

A more general long distance indicator was an ARC, where a Neel 45 left the first cat, an Outremer 51, 6 hours behind, making an average speed of 10kts with top speeds of around 20kts. An Outremer 51 is a fast cruising cat

Interest design concept and tri. They have a different sailing feel to cats but for some people they prefer it. The design range has improved with each model and with 130 boats built the Neels are becoming popular. The jpegs give the idea.

 

The T77 42 foot trimaran is a Tony Grainger design study for a European client who wishes to have a fast 42 x 33 feet all carbon trimaran that is a daysailer with weekend/week possibility that can be ocean going, safe and fast. The tri may sail 48 hour trips (2 overnights) to cross the Mediterranean. The tri has to look good (slim main hull! All lines to the cockpit under deck.) Amas are not to have C-foils.

Low maintenance, fast off the dock (no big preparations before going for a sail) made for singlehanded sailing in all conditions, singlehanded docking stern to in a tight marina and singlehanded anchoring. All manoeuvres without leaving the cockpit.

The tri is 42 x33 foot with a weight of 7,200 lbs and a maximum displacement of 10,000 lbs. The 63 foot rotating wing mast (assume carbon fibre) carries a 750 square foot mainsail and a 430 square foot fore triangle and a 800 square foot code 0 with a 1500 square foot asymmetric spinnaker. The main hull has a length to beam of 11.6 to 1 and the floats are 16.5 to 1 length to beam. The central dagger board draws 6.4 foot, the rudders draws 4 foot.

The rig is in the middle of the boat and the centre of buoyancy in the main hull is 57% back from the bow which helps the tri to reduce pitching and reduce pitching forward in hard conditions. The numbers would indicate a very high performance design if the actual design comes close to the above numbers. We are talking over 25 knot peak speeds and 15 knot plus averages in the right conditions. The systems and gear on this tri will have to be first class for it to be able to be sailed at near its peak performance for a singlehanded by a non professional sailor.

The tri is intended to be all carbon fibre foam construction, which will be required to meet the weight requirements of such a powerful boat. Assume carbon fibre foils, mast, boom etc to allow for things like bow thrusters, anchoring gear and some accommodation with EG showers, associated water tankage and a 15 HP Yanmar sail drive. An X beam configuration appeared to be the logical approach for the cross beam structures given that it will provide the optimum resistance to twisting in the structure.

The accommodation is aimed at 6 people for a daysail, sleep 2 comfortably (shoulder width of double bunk >= 1,7m), electric toilet with holding tank, inside shower, lithium batteries, Wallas Diesel cooktop (or gas?), fridge and a gas grill in cockpit.

The jpegs give the idea of the design study. The specifications may alter if the client gives approval for the final design. A very interesting design.

 

The Dragonfly 920 swing wing cruising tri was built by Quorning Boats and designed by Borge Quorning/Jens Quorning. There were 168 Dragonfly 920’s built between 1996 and 2008 in 3 different versions. Now we come to the hard part. The Dragonfly 920 is 30.2 x 22.3 foot and using its swing wings can be folded to 10.2 foot or disassembled to fit on a 8.2 foot wide trailer. The tri is claimed to be a trailer sailor but in many jpegs you see cranes being used to shift things around which leads to the second confusion. The weight is listed as 4,250 lbs or a standard tri weight is 4,800 lbs. The maximum total weight excluding crew is listed as 5,370 lbs and the maximum total displacement including crew is 5,950 lbs. Total weight of tri and 1,700 lbs trailer is 6,600 lbs. I suggest you can move the Dragonfly 920 around but as weekend trailer sailor you would have to be enthusiastic. Especially when you have to put up a 47.5 foot aluminium mast that carries a 355 square foot mainsail, 236 square foot genoa 807 square foot spinnaker. The draft varies between 5.1 foot and 1.5 foot. The Dragonfly 920 Extreme had a slightly larger rig with more sail and slightly reduced weight.

The result of the above is the following: “The Dragonfly 920 Extreme is fast, in fact it’s very fast. We took it out on Southampton Water with the wind up and down from 12 to 20 knots and got consistent speed readings in the high teens — sailing to windward, without trying. Offwind on a reach we clocked a best 23.3 knots (GPS approved) and there’s no reason to suppose the boat couldn’t make 25 knots with a little more knowledge” according to a Yachtsandyachting tester. The standard Dragonfly 920 is a very high performance tri as well according to other test reports.

The structure is foam glass with stainless steel pivot pin structurers. They pivoting structurers are very well designed and have been used on Dragonfly tris up to 40 foot. For those looking for centreboard ideas look at the shape of the Dragonfly board. A near full slot filling board shape whilst still maintaining a reasonable foil shape.

The accommodation is useful with 3 effective berths, reasonable seating, small galley, navigation and separate toilet.

The jpegs give part of the story. This is a practical very high performance tri that could be a good second hand buy.

 

This is about a cat that was meant to be displayed in mod 2020 but I can not find if it is built yet. The Dazcat 1895 is conceived as a very high performance cruising catamaran designed by Dazcat and Ben Rogerson Yacht Design. The Dazcat 1895 is 62 x 27.9 foot with a weight of 26,900 lbs and a displacement of 35,800 lbs. The 80 foot rotating carbon fibre wing mast carries a 1355 square foot mainsail, a 753 square foot self tacking jib and a 3766 square foot spinnaker. The hull length to beam 11.7 to 1. The underwing clearance is 3 foot. The draft over the daggerboards is about 9 foot (estimate). The rudders are spde T foils. The auxiliary two 50 to 75 HP inboard diesels.

On deck, the Dazcat 1895 is “optimised for shorthanded and fully crewed sailing. To maintain total control at high speeds, powered rewind winches for the main traveller, mainsheet, self-tacking jib give the helm fingertip control and the dagger boards are set up with on line drivers for easy deployment”. Good words, but setting and hauling in a 3800 square foot spinnaker by 2 crew in anything other than light winds is often an expensive trip to a sail maker. Power winches will be required to handle the weight of raising the fat head mainsail and haul in any genoa etc in anything over 15 knots of wind. When you have a double reefed mainsail that is 505 square foot you will be using your power winches to control it in 40 knot winds, as it will have 5000 lbs of sail force at a 30 foot centre of effort equalling a 150,000 foot lbs overturning loads to deal with. PS this cat has 400,000 foot lbs of stability.

The accommodation is what ever you want but the standard layout has 5 double cabins and 3 toilets in the hulls. The bridge deck cabin has a large galley, seating and navigation area’s with many mod cons. Even the crew cabin is comfortable.

The structure uses high-quality construction techniques, using the latest infusion technology with carbon/glass hybrid and foam core composite to create the best possible stiffness to weight ratio. Meaning, vastly improved power translation and high tolerances that are repeatable from boat to boat. The mouldings are produced by female CNC tooling to provide an accurate repeatable cat. An all carbon mast and boom, with hay racks and carbon sails are specified ensuring the rig is very light and very stiff. A top racing specification Antal mast track system and halyard locks are used to aid higher load sail handling. The spinnaker tack line is mounted to carbon spinnaker pole. All the foils are carbon fibre. To show how serious to light weight the company is, the steering cables are carbon fibre.

This will be a 25 knot peak speed type of boat with 400 mile days possible. It will capable of sailing very quickly on all points. It will also be comfortable. The only downside 3 million pounds (about $US 3 million) starting price. End of those dreams. The jpegs give the idea. The jpeg of the hull lift aft under sail is actually based on a Dazcat 1495 Apollo in a Fastnet race. Good image.