Multihull Structure Thoughts

To be clear,
1) the comparison was with the same skin thickness (9-10mm). If thicker foam was used, most of the stringers and some of the frames could be eliminated, along with the work of setting them up and planing them to shape. With the current cost of foam and decent timber, this would be cheaper as well as quicker and lighter.
2) Foam compounds a lot more than ply. Glassed foam a lot less. Infusing flat panels is much less effort than scarfing, glassing and finishing ply, but may not work on heavily compounded ply hulls. Infused panels also provide a lot more options in terms of core thickness and weight, skin weight and type and the ability to include numerous items to speed up and simplify the fitout.
3) Kevlar is a good option for inner skins, it takes a lot more impact and wear damage than fibreglass. eg, if the hull is siting on rocks and the outer skin and core are worn away, the kevlar will remain and be mostly watertight. But it is hard to work with. Get decent scissors to cut it and use peel ply for surface prep. Take care finishing edges so they don't need to be cut. Sanding kevlar results in a fuzzy surface which is difficult to do anything with.

This is nonsense. "Guesses" of speed are rarely accurate; "going to windward" is anything from a tight reach to pinching upwind. 17 knots is more likely to be 4 knots, assuming hard on the wind, the poor shape of rolled jibs and the added windage of the top mast when reefed.

 

Sailaday 60 is a NG Design (Tahiti based) for day charter that is built in foam/fiberglass sandwich infusion. This cat caught my interest because the hull sections are symmetrical both horizontally and vertically. This permits one half hull mold to make the four parts required for the cat. That’s smart. The Sailaday is 60 x 29.9 foot that weighs 28,000 lbs. It can carry from 12 to 50 passengers which means a payload capability of around 10,000 lbs. The Sailaday carries a 73 foot mast with 1870 square foot of sail area in the main and self tacking genoa. The length to beam on the hulls is 10.5 to 1. The draft is 4.1 foot over the keels or you can have daggerboards. There are 2 x 75 HP inboard engines.

The cat is a charter machine but if done correctly could be converted into a light fast cruiser. The base design has 2 double berth cabins and a toilet in each hull. There is a small galley bar on the open bridge deck near the helmsman.

The construction is foam/fiberglass sandwich infusion in the one half mould that can do all 4 half hull moulds required for 2 hulls. The hull shape is good and using resin infusion it will be a very fast build approach. The “only” other requirements are flat panel bulkheads, box cross beams, underwing and roof over the cockpit. This cat could be built in the time of a 40 foot full bridge deck cruiser. Unfortunately, the material and rig cost would probably be twice the 40 footer.

The jpegs give the idea of a nice well designed functional cat.

 

I was asked a while ago for any Gougeon Brothers Stressform wooden wing mast instructions I had. Again, it took time to find them. They are old, photocopied some are faded and not photocopied well but I present them as I have them. It will take 2 days to give the 3 PDF’s as each PDF is about 4 megs. The first PDF is an overview, the second PDF gives more detail on how to build the mast. The final PDF tomorrow gives a general overview of stressform construction of hulls and wing masts. The actual “A” Stressform wing mast plans are on page 5 of this thread. They are for a 25 foot tri that has a righting moment of about 20,000 foot lbs and uses thinner ply on the walls. The “A” plans were designed for multihulls up to 35,000 foot lbs righting moment (if you use high quality materials throughout).

I have added a few jpegs of the mast builds to help. Gary Diekering built two 60' Stressform wing masts. 4mm birch ply sides, spruce web spars with carbon uni, strapped together with plastic banding for curing before finishing. The base has timber inserts to support the rotating mast base.

 

This is the next part of Stressform wing mast instructions. This gives a general overview of stressform construction of hulls and wing masts. I have added Gary Baigent’s quick overview of building a plywood skin wing mast (he has done several). “The other way for the non professional unable to pay a fortune to boat builders is to use tension ply. And this is a quicker method - and the results can be excellent IMO. Get the Gougeons' book. Explaining it all here is a very boring read. In short: Mast length I beam glassed both sides - cut frames in 4mm ply or glassed foam, cut out areas for halyards to run, also cuts weight, now cut frames at thickest section, glue these to I beam, there's your skeleton. Glue two lengths of thin wood to trailing and leading edges of skeleton, that's the bases for 3 mm ply attachment (leading edge) and alloy bolt rope tube for sail (trailing edge). Skin with 3 mm ply, or lighter aircraft ply if you can afford it. You can do this in the 2.4m ply length sections by carefully lining up the scarphs, glue and staple. Staple gun and lots of clamps are essential. Was that a bloody boring description or not?”

The first PDF is Stressform part 3. The second PDF is Kurt Hughes general description of wing mast builds. The final 3 jpegs are of large French cats foam glass wing mast builds. It is written in French, sorry. Gary Baigent found it.

 

Foam is dear, glass and resin is cheap. Personally I'm fond of solid glass to the waterline for ruggedness and foam above for weight, but all the common options work well. Solid bottoms are probably more logical in round bilge multi chine would be a weird choice there I think. And you might need extra stiffening between bulkheads.

 

If you want to go solid below the waterline then consider Coremat to bulk out the laminate.
Lantor Coremat®; The original laminatebulker https://www.lantorcomposites.com/textile-foam-cores/coremat/

 

Gypsy and its later Saturn iteration is a clever concept, with a modular build and a number of material options, adequate space for small family cruising etc etc. The Saturn for the same weight/disp is a tad longer, a little wider, has a little more sail and I suspect skinnier hulls. What I can't understand is why the head room has been dropped from 6' in the Gypsy to just over 5 foot in the Saturn, unless it was to save some structure and keep the weight the same as Gypsy. If that is so, then fair enough, but at 6'2" I would hardly describe a substantial decrease in head room on a cruising cat of this size as an improvement.

 

Thank you very much oldmulti ,for the stressform info much appreciated

 

Albert Sedlmayer of Sedlmayer Associates Pty Ltd has gone into semi retirement and now focuses on conceptual designs and consulting on specific projects. In mid 2019 he was negotiating a potential design contract for a near 100 metre sailing catamaran megayacht. The concept was drawn but the client lacked funding. But we will show what Albert drew which is an extension of other large cats and commercial vessels he has designed and had built.

The SPECTRUM 98 is 322 x about 110 foot. The displacement is unknown. A 2-mast Dynarig was chosen for ease of handling and clear sail deck, and with the bridge forward of the main mast. The free standing masts are 200 foot high with a total sail area of about 45,000 square foot in the schooner Dynarig. The draft is about 8 foot. The power is currently Diesel-electric, with several generator modules that can easily be removed through large hatches. When hydrogen cell technology has come of age, generators can ultimately be replaced with this technology.

Now we get to the 5 accommodation decks with 5 lifts to get between decks. The outline arrangements of all the decks are tank deck, crew deck, accommodation deck (10 identical family suits plus a VIP suite on the bridge deck), main deck, bridge deck and sail deck (with D12 helipad). Security has been thought of with beach club panels are all fold-down sea doors that lock up tight. All open side decks on the accommodation deck have garage-door-type pull-up armour glass doors, so that the hull sides from waterline to bulwark top (about 8m above sea level) can be completely closed with no hand or footholds. Piracy opportunities are reduced. Ship to shore options include several power boats, a helicopter or a seaplane. there is also a submarine if required.

This is another several hundred of million dollar yacht that will be sensational if its ever built. The performance of a cat this large with the size of rig with be good with 20 knots possible. Windward may not be that good though. I sure the engine will help. The jpegs give the idea. Again, sanity will resume tomorrow.

 

Hey Rob,
I’ve always wondered about, bagging the foam onto the outside skin and folding that up to shape and then apply the inside skin ? Sort of having a bet each way ?

Kevlar, you can fix the fluff by wet sanding it with a coarse wet and dry paper, of course you then have to heat gun it to dry it out but it gets the job done.

 

We are going to talk about 2 cats that are really 1 cat and another with 3.6 extra feet added. The architect Phil Southwell designed the Mavericks which are built in South Africa. The Maverick 400 is 40 x 24.5 foot displacing 21,000 lbs and carrying a 56 foot mast with 639 square foot of mainsail and 351 square foot genoa. The draft is 3 foot over the fixed keels. The Maverick 440 is 43.6 x 24.5 foot displacing 22,000 lbs and has a 60 mast with a 732 square foot mainsail and a 462 square foot genoa. The draft is 3.2 foot over the fixed keels. The engines in both cases can be 2 x 30 HP inboards. The reason for saying they are the same cat is the same basic layout/structure is used on both models with the rig size and the aft extensions the only major changes.

The Maverick 400 was originally designed to be a high volume cruising catamaran that had good sailing qualities. Phil Southwell widened the hulls and made the boat wider overall, which gave owners bigger, more spacious cabins and a very roomy saloon. The accommodation in the hulls has a large toilet and either 2 double berths cabins or one master owner’s cabin. The bridge deck cabin contains a galley, navigation area, entertainment area and a dinette double berth area. This is a large main cabin for the size of cat. The Maverick 440 is basically the same.

The performance of the Maverick, in cruising mode, is about 50% of true wind speed (up to20 knots TWS) and surfing down swells may do a little better. This is a cruiser not an outright racer. It tacks and handles well. The Maverick 440 with additional sail area is claimed to be on average about 1 knot faster than the Maverick 400.

The hulls and bridge deck of the catamaran are laid up together in one process. All Mavericks are cured in the molds for a minimum of 24 days. The combination of the single layup and curing times ensures maximum strength and durability of the hull over the lifetime of the yacht. The hulls are laid up in composite sandwich construction using a vacuum bagging technique. Hand laid stitched fabrics form the outer layer of the PVC Foam Core. The resins used in the original build were polyester, I do not know if they are using vinylester currently. The central spine of each hull is solid fiberglass for additional strength and durability. All cross member bulkheads are made of marine plywood. The ply bulkheads provide torsional and lateral strength qualities and ability to withstand harsh conditions. The hulls under the waterline are double coated with International Gel Shield Epoxy and then further protected with two coats of International anti-fouling as standard. The standard yacht includes wood finishes for the furniture. The interior modules have marine honeycomb or PVC foam core for weight saving and use real wood veneers for a high-end finish.

Keels are sacrificial and are glued in place with no fixed bolts so they can be easily replaced. The central spine of the yacht is solid glass with additional rows of bulkheads to house the keels. The keels are long and shallow that provide protection to the sail drives and allow the yacht to be beached. There are two front collision bulkheads in each hull, one below the waterline & one above the water line.

The build is interesting and appears to be a mix of old concepts and new approaches. If you are interested in this design do a deep web search about the vessel. The jpegs give an idea of the cat.

 

Tevake is a 30 foot pacific proa designed by W.Heinczel and constructed by E.Zemann in Germany. This is a good “home” design that was designed to test such things as a crab claw rig. Tevake is 32.5 x 16.4 foot, weighs 1100 lbs and displaces 1800 lbs. The sail area in the rig is 270 square foot on a 14 foot stub mast and 29 foot yards. The draft is 1.1 foot or 4 foot with daggerboards down. The length to beam on the main hull is 16 to 1. The 1,000 lbs buoyancy float has a length to beam of 20 to 1. The engine is a 5 HP outboard. The proa is able to be disassembled and trailable.

The accommodation is for 2 or 3 people in a simple layout. The interior has 2 access hatches; 2 seats facing each other, folding table. space for chem. toilet, battery, small water tank etc. Storage spaces/swallow nests in the leeward platform. 2 bunks each 6.5 x 2 foot tapering to 1.5 foot, storage space underneath. Between berths and bow a storage space with a hatch.

Main Hull construction is a combination of solid glass epoxy below the waterline and ply above the waterline. The solid glass epoxy thickness is 5 mm with an additional layer of TWARON (aramid fiber) below the waterline. The rest of the hull structure is made of 8.0mm Okume plywood with 165gsm glass fiber as the outer skin. All sealed and glued with WEST epoxy. Paint 2-component PU paint. The main hull is unsinkable due to 0.6m3 polyurethane foam in each fuselage end and 4 collision bulkheads. The float is made of epoxy/glass solid laminate, approx. 4.0mm wall thickness with 2 stowage spaces with watertight bulkheads and hatch covers. The are 2 box beams connecting the floats to the main hull.

The limited jpegs give the idea. If anyone knows the performance of the proa it would be appreciated.

 

Well I don't know what follows for certain, I've not asked the specific question, but I THINK:

Saturn was drawn for a client who had specific use in mind. Mr Woods I think specifically mentions somewhere it's a development/replacement for Skua. Construction is potentially simplified by the chines over Skua's round bottom possibly drawn with double diagonal ply in mind as other early Woods boats were designed for that. The cuddy is of course optional, it just needs the mast stepped a bit further forward.

Thus I think it's wrong to think of it as a fast Gypsy, but rather a more versatile and easier to build Skua, with more carrying capacity. The main reason I compared it to Gypsy is Gypsy doesn't offer a multi chine hull like Romany for example. If you don't want the hassle of casting a round bottom but don't like the dory it's a middle option. Might be a stretch to get 6' (or more) headroom out of it, so... a compromise. Mr Woods MIGHT be willing to do a multi chine gypsy, or as I mentioned previously if you don't want strip for whatever reason (cost!) building a mold to the step and casting the bottoms of the hulls in either solid glass or foam is doable and not too bad.

Be aware that various people have built Gypsy 10% longer which increases the length to beam ratio slightly increases displacement and may even affect pitching.

 

The following is the reason I have doubts about buying something second hand then “fixing’ it up to suit your needs. The cruising cat we are talking about started life in 2011 in Latvia as a new million dollar build and then was chartered in the Baltic and Caribbean under the name Wildcat. The cat was purchased in 2020, cruised a bit, then taken to NZ for a name change and refit. “Dulcinea” is an Erik Lerouge design and is 65 x 34.4 foot weighing 47,000 lbs and displacing 58,500 lbs. The 71 foot carbon wing mast carries 1528 square foot main, a 980 square foot jib, a 1820 square foot Code 0 and a 2980 square foot spinnaker. The basic draft is 5 foot.

The accommodation originally had 4 family cabins, each of which has three beds – two for adults and one for a child. Each cabin has a toilet and shower with hot and cold fresh water. Two separate cabins are provided for the vessel’s crew. In cold weather, a heating system provides heat to the vessel’s indoor spaces, whereas conditioners ensure that guests remain cool in the heat of the summer. The galley has a fridge, freezer, kitchen sink, oven, microwave oven, gas cooker, coffee machine, dishes for 20 guests and a water desalinator. There is a washing machine and 220 volt power grid and both hot and cold drinking water. For entertainment of guests, there is a wide screen television and modern sound and video system in the vessel’s saloon, which can be connected to any data carriers in all the most popular format, including DVD and Blu-Ray. This was all in the originally built Wildcat.

Now the new owners wanted to upgrade and modify the cat to suit their requirements. The new owners then in 2021 shipped the boat to New Zealand for a full refit, at Orams Marine Services in Auckland. 16 months later the job was complete at a cost of $4 million. The work involved anew rig and sails, reworking of interior furnishings and cabins as well as the forward part of the saloon was re-purposed to accommodate a huge battery bank, hidden under a (very) wide, hinged shelf. At the same time, this created an additional strengthening box construction under the mast. This space contains 12 x 200Ah lithium phosphate batteries, running a 24V system. There is a lot of solar panels to help charge the batteries which allows the cat to be completely autonomous from land for weeks at a time with minimum charging required.

The basic structure is foam glass with a lot of carbon fibre reinforcement in structural areas. The new furniture that was from light weight panelling etc.

This refit is a major undertaking and would have required a large crew to complete the task in 16 months. But at a cost of a $4 million refit plus the purchase price second hand of maybe $1 million makes me think hard. A new build of a cat about the same size can be had for under $3 million. Some late build second hand cats EG 2019 Balance (a 63 foot) can be had for $2 million.

Admittedly “DULCINEA” is virtually a new boat with all the upgrades but its an expensive way to get there. The jpegs give the idea.

 

Today we will talk about a VPLP designed 40 x 16.4 foot electric powered foiling catamaran. The draft of the cat is 7.5 foot over the foils. SDK in the US conceived the concept and approach VPLP to do the naval architecture, design, structure and foils. Other companies specializing in the fields of electronics, motorization and energy also contributed to the project. This catamaran benefits from innovations in ocean racing sailing cats and tris, in particular technologies related to flight and its control. The cat has a range of 90 nautical miles at a cruising speed of 22 knots with 8 passengers.

The cat is powered by two electric motors, equipped with a main lifting foil and two rudder power foils aft. A control system is installed on board, making it possible to stabilize the flight and to promote piloting by a person familiar with more conventional motor vessels. Antoine Jarry-Lacombe said the trials in the Bay of Concarneau: " We are very satisfied with the result, this catamaran is functional and easy to handle, it has very interesting energy efficiency when in flight, which allows it to overcome friction with the water and reduce the power necessary for its propulsion. Therefore, the boat consumes less energy for a same speed, that's the whole point of using foils on pleasure boats and more broadly for transport. "

After several months of construction in the King Marine workshops in Spain then in Concarneau, the two blue hulls of the new electric hydrofoil catamaran developed by François Gabart's teams hit the water for the first time on February 14, 2022. The cat is basically foam carbon epoxy (with some bio-sourced materials). The foils are carbon fibre with some foam in epoxy.

The jpegs give the idea. This is the direction of the future. Electric motor vehicles are advancing battery and electric motor technology quickly which will allow greater range in boating etc. Combine the technology advances with better foil design and control and we will have really interesting effective electric foilers.