Multihull Structure Thoughts

Small tri was built to satisfy a man’s desire to sail. He saw Kolher’s Little Tri and was inspired. So, he found an 8 ft dingy, some bamboo for mast and yards. He cut down a polytarp for a sail. The tri is 8 x 8 foot.

The crossarms are aluminium tubes and the floats are 150 mm PVC piping with the forward ends cut at an angle. The ends have plywood plugs with resin and fiberglass to seal them. The cross arms are attached with plywood struts, bolts and fiberglassed as required. The bamboo mast is free standing in a PVC tube glassed to the deck and keel.

There are 100 mm deep wooden keels glassed onto the bottom of the floats and a daggerboard in the main hull. The entire tri took 1 week to “build” after they found the 8 foot dingy. This boat sails well for what it is and would be a great training toy for kids or a lazy afternoon cruiser for us older folks. The jpegs give an idea of what $300 and 7 days effort can do.

 

For US buildings, allowable design stress for common lumber has been lowered to account for the reduction of common lumber quality.

Any thoughts on using LVL? I almost asked in response to the post the other day about grain orientation of plywood when used for beams. LVL fixes that, and it comes with published design values. Part of its qualification process includes creep testing.

 

Srimes. LVL can be a good substitute for "normal" timber beams. If you can get really good quality knot free clear grain timber, then use that, but in most parts of the world LVL has better characteristics due to the laminations of timber. Any imperfections in a lamination only has a marginal effect on overall strength. The only problem of LVL is the quality/rot resistance of the timber used in the laminations as often a lower quality of timber is used in LVL. I would use it when needed.

 

An interesting production cruising tri of 1982 is the T11 produced by Mattia and Cecco. The designer was E. Contreas who has designed the ICE 62 catamaran a couple of years ago and many high performance mono’s. The tri is 37 x 26 foot and can fold to 12.8 foot. The weight of the design is 6,800 lbs and the displacement about 10,000 lbs. The 40 foot mast 9is a masthead rig that carries a 350 square foot mainsail and a 260 square foot foretriangle. The genoa looks about 400 square foot. The length to beam on the main hull is 10 to 1. The mainhull has a centreboard that draws 6.5 foot and an outboard rudder.

The real fun of this design is the folding system (jpegs show the shape). As the design is built in balsa/foam fiberglass I am assuming the folding crossbeams are a fiberglass lattice. The design of the crossarms geometry is good. As the float is folded in, the float is pushed deeper into the water to add stability when moored in EG a marina. The floats have full ends for the time which I suspect is because of the relatively low freeboard to allow the floats to fold under the tri’s wings. The mainhull shape has more rocker than modern designs also the buoyancy is further forward to provide additional buoyancy for the classic bow shape and the rig being relatively far forward. The mast is at 33% of the waterline from the bow. Most modern designs masts are 40 to 50% of the waterline from the bow. There are at least 4 of the T11 that I know off and their second hand price for a 1982 boat indicates they are reasonable tri’s.

The finish quality on the interior is 1982 standard not current interior molding standard. This is the major difference between older boats and home built boats versus modern production boats. The interior finish of modern production boats is almost house like quality. The reason you make a choice early about the intended use of your boat is that a quality interior build will take longer and cost more but the rewards will come in a higher second hand price. But if you want to cheaply cruise the world build a serviceable boat that you can easily maintain and don’t make it so smooth you can see your reflection in it. Wharfs, rocky sandy bottoms, dinghies and humans being thrown around on the interior of multi’s all have bad habits of scratching up your perfect finish.

The only comment about performance I have read indicates the T11 sails OK and goes upwind well due to its beam and stability but it is not a really high performance boat. I think this is a 7 to 8 knot average sort of tri. This is a great design concept for those who have to live at a marina but still like to have a real sailing vessel that doesn’t heel to much. The jpegs give the idea.

 

Produced by Cantieri Magazzu the Magazzu Tris 10 (Surfing tris 10) is an Italian design of 32.5 x 30.8 foot that can fold to 13.1 foot. The weight is about 7,000 lbs and a displacement of about 10,000 lbs. The masthead rig has a Nemo 43 foot aluminum mast and boom with a mainsail of 441 square foot, jib is 120 square foot and a 450 square foot genoa. Gennaker 807 square foot. The rigging in later versions is textile rigging in Dyneema. The mainhull has a length to beam ratio of 9.9 to 1. Some tri’s of this design has angled foils on their floats, other versions have a centreboard with a spade rudder on the “hull extension” in the mainhull. The sailing performance is claimed to be very good with a top speed of 20 knots possible. The performance is possible if the weight is realistic and you don’t add large outboards etc.

I am a little confused over the cross beam structure. Yes, its folding but there are 2 different versions on 2 different tris in the jpegs. Version 1 as in the plan jpeg with a 2 part folding cross arm with a 2 part waterstay support structure. The next version is a 1 part beam with a waterstay going to the mid beam. I would suspect the 2 part folding crossbeam were first and the single unit cross beam was second. PS the beams are very slim for the task they are asked to do. Judging by the jpegs the folding beams are aluminium structures with I assume stainless steel waterstays. The pivot pins in the floats and on the main hull are large in diameter. The cross beam folding and unfolding is done by electrics and hydraulics.

Next confusion is the dual outboards. There appears to be “additions” to carry the dual outboards and an addon extra “buoyancy block” added to the back to help support the weight. Two 15 hp outboards will drive the tri at 12 knots and if you have two 50 hp outboards it can be driven at 18 knots under power. The tri has CE certification, Ocean A design category. The central hull has compartments with double bottoms and the sealed buoyancy components in floats which “guarantees” the unsinkability of the tri.

The construction of the tri looks like solid fiberglass with stringer support in the main hull and floats. Unusual in 2006 when these tris were still being produced. The cross arms are aluminium. The interior is lined and finished with light “timber” panelling. The tri can sleep 5, has a decent galley and dinette with a loo. But like all smaller tris I would not go long term cruising with any more than 3 people, there just is not a lot of real room for people to move around each other etc.

The jpegs are broken into 2 parts. First set of jpegs the 2 part cross beam model with a 2 part waterstays. The next set is the single folding cross beam with single waterstay. The final jpegs are the sail plan and interior. Interesting and if anyone knows any more could they please advise.

 

Anchoring is a topic that is often overlooked by many who are used to either trailering or are used to parking at marinas. But it is a very real topic, I have sat on a 38 foot cat anchored in the lee of an island and was “securely” anchored with a 35 lbs CQR for 4 hours with a consistent wind, then the anchor lets go. We had to pull up the anchor and reset the anchor with a longer rode and set a second anchor for security. The cat held its position after this. So where does this leave us. The conflict is the ideal anchoring set up is a heavy anchor, a lot of chain and a long rode to minimise up lifting loads on the anchor. This weighs a lot and is not good for performance. The trade off is you will still have a non damaged boat in exchange for the slightly reduced performance.

There are many views on types of anchors and each type has its strengths or weakness depending on the type of bottom you are anchoring in. There is no ‘universal’ anchor that suits all circumstances and all bottom types. You pay your money take your choice. I personally have found a 35 lbs CQR and 22 lbs Danforth with 60 feet of 10 mm chain on each and 200 foot of nylon rode on each a reasonable setup for my environment. The problem is that weighs about 270 lbs with shackles etc. When I went serious cruising this was upgraded with an additional 35 lbs CQR and another 60 foot of chain. The purpose was in difficult conditions with waves and/or variable wind conditions was to join the 2 CQR in a line. CQR 60 foot chain, CQR 60 foot chain, swivel then 200 foot of nylon rode. The cat did not move with that setup, but it required an anchor winch to haul it in. This total 3 anchor set up including the anchor winch and batteries came in at about 530 lbs. This is cutting into your available payload.

When buying anchors, chain, rope, swivels and shackles buy quality stuff. Especially check the quality of shackles and swivels which should be “proof tested” products. I know a guy who lost his anchor and chain because the shackle either broke or undid between the anchor chain and the nylon rope. Tie shackles etc closed with wire to ensure it they don’t accidently undo. Also please understand some of the loads on an anchor chain etc. A 50 mph wind puts 10 lbs per square foot on the front of eg a 40 foot cruising cat 200 square foot. That’s a 2000 lbs load without any wave induced shock loads etc.

The next problem of anchoring is not with the anchors etc, it is what you attach your anchor nylon rodes to on your boat. You not only need a strong point to tie off to, but a clear non chafing path for the rope from the strong point to the front or rear of the boat. Yes, you need strong points at both ends of the boat. You may need to anchor fore and aft or have a bow attached to a pier and need a rear anchor to hold off the pier.

The strong points are NOT aluminum cleats with 6 mm bolts to a 9 mm ply deck. They need to be EG a 75 x 75 solid hardwood timber post glued and screwed to a strong internal bulkhead. An alternatively would be a stainless steel cleat with 9 mm bolts though a 9 mm solid deck with large aluminum or stainless backing plates. If you tie of your anchor line to an anchor winch again make sure again it is solidly mounted.

To minimize hunting movements while you anchored you can use a bridle off eg each bow of a cat. This is useful but make sure it does not interfere with the letting out more rope or when recovering your anchor. Again make sure nothing chafes.

The attached jpegs show “normal” anchoring setups, then some severe weather anchoring setups with some indication of the loads that happen when you use sort rode or step angle rode set ups. Long rodes, chain and heavy anchors is the best solution. The PDF is by John Marples on anchoring.

 

The following is a very nice small folding tri designed and built by a home builder. The tri is 16 x 12 foot, that can be folded to 8 foot, of unknown weight, with a 420 dingy rig with a 20.5 foot mast 80 square foot mainsail, 30 square foot jib and 95 square foot spinnaker. The guy who designed and built the tri did a good job and most of the work is documented at the following half Greek, half English web site: ONYX 16 trimaran : 04/17/13 http://onyx16.blogspot.com/2013_04_17_archive.html

I will only focus on a few aspects of the tri. The basic tri is a plywood hard chine main hull with tortured ply floats. The cross arms are solid timber with metal plate folding hinges like the Cross 18 trimaran. The cross beams are 100 x 45 mm but the weight was heavy, so he cut them to the desired dimensions and shapes then drilled 40 mm holes separated by 60 mm and reduced the weight by 30 to 40%. The holes were filled with polyurethane foam. The hinge plates are 3mm stainless steel and cut with laser, (Cross 18 uses 4.5 mm stainless steel hinges plates of a very similar shape). The bolts used for opening - closing are 10 mm while the bolts attaching the plates to the beams are 8 mm. The daggerboard was a 0012 naca foil shape in a 15 mm marine ply (used as core), and then laminated with two layers of UD 520 gsm fiberglass in epoxy then covered with a layer of carbon fibre.

After initial sailing trials it was found the tri lacked buoyancy in its stern. The stern had an addition 100 mm thick foam added to the sides of the stern which was faired and glass covered. The additional stern buoyancy added to the boat’s performance. The floats had additional buoyancy added as well. The cross arms were strengthening by adding carbon fibre. The mast has been lengthened to add sail area.

The performance of the tri is quite good. In initial trials with just a light breeze of 5-6 knots and some 8 knot gusts the tri achieved an average of 6 knots with 7.5 knots maximum. There are several video’s of the tris sailing ability and usability on the web site.

Please view the web site and the attached jpegs for the best idea of a nice small tri.

 

The pH 850 is an open bridgedeck performance cruising catamaran that measures 28 x 17 foot. The pH850 weighs 1200 lbs. The 44 foot carbon fibre wing mast carries a 302 square foot mainsail and 128 square foot solent for an upwind sail area of 430 square foot. The length to beam ratio at the waterline is 12 to 1. The hull beam at the gunnel is 3.25 foot. The design has curved daggerboards that draw 5 foot when down. The curved daggerboards in each hull generate upward and windward lifting force to increase the righting moment which helps the cat point well upwind. The wave piercing bows and wide underwater transom section helps the hull ride smoothly though choppy seas. There are outboard rudders that can be raised for shallow water or trailing.

This design is a transportable cat more than a trailer sailor and can be broken down to 8.5 foot wide package for trailing. The central beams/hard cockpit section with integrated engine pod can be unbolted from the hulls allowing the hulls to be pushed together for trailing. The 8.5 foot central beams have end flanges that bolt onto the hull wing shelf sides. This approach is OK but requires really good design of the bolt connection holes as there are very high point loadings in this area. It is much easier to put a long crossbeam on either gunnel to spread the loads across a hull.

The entire structure is built is pre-preg carbon fiber foam construction in epoxy. The hull deck units, mast, prodder and cross beam structure are molded and “cooked” to obtain good strength to weight ratio’s. The designer and builder of this boat also charters a Stiletto 30 as another side hustle, so I suspect he was inspired a little by this design.

The pH 850 has just enough interior space for 3.1 foot “twin berths”, a head and a galley. The twin berths would be good singles and “honeymoon” doubles. To quote the builder “While the interior is sparse in order to reduce weight, it is useful for light cruising and camping adventure, featuring twin births in each hull with head and galley options”. Notice the words “head and galley option”.

The components of this design indicate its performance will be very good and with the right rig accessories this cat will travel at wind speed or better up to about 12 knots. This cat’s top speed will probably be 20 knots or better.

The jpegs give the idea. A modern interpretation of a Stiletto.

 

Due to the fact I will be having an internet “upgrade” in 12 hours I am doing tomorrows info today. These internet upgrades have “failed” with some of my neighbors and they have not been able to get full internet access for a week. Hopefully all will go well but if you don’t hear from me for a few days be sure I will return, that’s if you care. Michael Kasten is a long term designer (1987 onwards) who has done power and sail monohulls mainly in steel aluminium, wood and some glass composites. He has designed and had built solid wholesome mainly heavier displacement cruising monohull boats from 23 foot to 160 foot. He did a preliminary power tri design a decade ago. But now he is meeting the market demand for multihulls.

The first cat we will discuss is Radian a 58 x 27.5 foot full bridgedeck cruising cat that weighs 42,000 lbs. There is no rig specified beyond a fractional or ketch rig, this cat could handle a cloud of sail either way with its beam and stability. Ideally the sails will be battened in order have a generous roach and somewhat elliptical profile. The hulls have a length to beam of 10.3 to 1 at the waterline. The hull prismatic coefficient is 0.7 which is high for a cruising cat hull but it provides full ends and high prismatic hulls generally have less drag at higher speeds but have more wetted surface at lower speeds. The hulls have low aspect ratio keels and skeg rudders.

The general concept of Radian according to Michael “is a composite or aluminum fast sailing cat intended for ocean sailing. The overall notion is that this would be an ideal hull form for two couples, each having identical accommodation spaces below, plus comfortable shared spaces in the wheel house and on deck. The idea here is to have generous spaces, rather than to crowd a larger number of people into a lot of little spaces.” Michael and his team are very experienced in aluminium design and construction so I would have no doubts about the structure of this design.

The accommodation includes a dedicated inside steering station in the bridgedeck cabin located centre forward. The house will also contain a large galley to port aft and wrap-around settee. A companionway on centre will lead up and aft to the cockpit. The large aft cockpit area is planned for fair weather "hanging out" and dining, as well as being the primary helm while sailing.

Two companionways lead below to each hull where there will be access to sleeping cabins with a king size berth, located within the bridge between the hulls, rather than down in the hulls. This is intended to keep the sleepers comfortable in a location where there is the least motion, and to also allow a view from each stateroom. Within each hull will be built in cabinets and a walkway leading forward to a "walk through" closet / bureau / dressing area, then forward to a private head. The engines will be located aft of amidships in each hull, and will make use of V-drive gears.

The jpegs on web page 60' Fast Catamaran RADIAN http://www.kastenmarine.com/fastcat60.htm are of initial CAD models give an indication of the vessel.

 

No worries mate, we all do care, and very much enjoy your posts and encyclopedic knowledge of multihulls.
Thank you for this amazing thread - almost 1,500 posts, most by you, and no signs of abating, excellent!

 

Yesterday we spoke of Michael Kasten’s Radian 58 aluminum catamaran, now we will speak of the “developments” of this catamaran. The Greyhawk 60 aluminum catamaran series shows how cats evolve due to both client and designer inputs. The basic Greyhawk series is 60 x 31 foot and weights 48,000 lbs with There is no rig specified beyond a fractional or ketch rig with the main and mizzen sails should be battened in order have a generous roach and somewhat elliptical profile. The hulls have a length to beam of 9.7 to 1 at the waterline. The hull prismatic coefficient is 0.57 which is in the “normal” range for cruising catamarans, this is a balance between a fuller ended lower resistance hull shape at higher speed and lower wetted surface shape for lower wind speeds. The hulls have low aspect ratio keels and skeg rudders. The keel can be varied, or eliminated in favor of centerboards or dagger boards. Low aspect ratio keels in the Greyhawk 60 track well and protect the hull itself when drying out at low tide.

According to Michael if he was doing a pure long distance cruising version of the Greyhawk 60 the displacement would be increased for to carry a greater load of fuel, water, stores and 'stuff'. The hulls would be deeper and wider having a waterline beam of around 7.25 feet giving a length to beam of 8 to 1. The displacement would be around 60,000 lbs and the overall beam would be around 32.5 feet.

The Greyhawk 60 has evolved over 3 variants. The jpegs are on the following web page. 60' Cruising Catamaran GREYHAWK http://www.kastenmarine.com/cruising_cat_60.htm The GREYHAWK-I model has the house located fairly far aft. This version will benefit from having the engine room and house batteries located forward of amidships, primarily in order to offset the weight of the aft house without requiring trimming ballast.

The GREYHAWK-II and GREYHAWK-III models have the house located much farther forward, and would likely be able to avoid trimming ballast if long term provisions and the house batteries are placed forward of the sleeping cabins.

The accommodation plan is intended to be similar in all three versions, with the exception being the GREYHAWK-I model would have the engine room forward, and a long shaft to the propeller. The GREYHAWK-I also has a more upright transom and short stairway to the swim platform. An inside helm and chart / electronics area is planned on center forward in the house. The house will contain a large galley to port aft and wrap-around settee to starboard aft. Sliding doors on center will lead out to the covered aft deck. Forward of the galley / settee will be two companionways on each side leading below into each hull where there will be two sleeping cabins in each hull, one forward and one aft. Each of the sleeping cabins will each have a head, walk-through closet / dressing area, and a double berth at the end.

The construction of the cats again will be aluminum. Most of the panels are slightly compounded on frames and stringers, this does not require any formal shaping. The design has rounded chines sections (which require some shaping) which gives the impression of a round bilge while still using flat plat for the majority of the hull. The real advantage of aluminum is the rig can be also aluminum at a low cost.

The jpegs are broken into 3 groups of the 3 variations of the Greyhawk series. This is an interesting exploration of a designer’s evolution of a catamaran series from the Radian 58 to the Greyhawk 111. Good stuff.

 

My apologies about the disappearing jpegs yesterday, issues. Today we will be about a 62 foot David DeVillier’s aluminium cruising cat. The cat is 62.33 x 30.33 foot with a “displacement” of 43,000 lbs. The ketch rig has 2067 square foot of sail area. The length to beam ratio of the hulls is 11 to 1. The numbers indicate the cat will have good performance especially for a cruising cat. The cat was launched in 2009 and has sailed over 100,000 nautical miles including a circumnavigation.

This will be a 2 stage presentation spread over 2 days. Today we will focus on the construction of the cat and associated jpegs. Tomorrow we will show jpegs of the cat sailing, interior, sail plan and other items.

The structure of the 62 foot cat is in aluminium. The plan sets are detailed and together with the comprehensive build kit information (assembly drawings and nested CNC cutting files) allow a build yard to precut and assemble the cat. As you can see from the jpegs, the frames are CNC cut with reinforcing flat bar sections welded to any opening. Next are flat bar keels and inverted T section stringers positioned to form the hulls shape. A flat bar keel panel is placed on top of the vertical keel. Pre curved aluminium lower hull panels are welded in next, followed by flat topsides panels and underwing panels. You are now about 15% of the way there. Next is the turn over the completed hull and the deck framing is commenced along with any internal framing for engines, tankage, steering gear, centre board cases etc. After this the main deck cabin is commenced etc.

With frames are every 900 mm and stringers every 300 mm there is about 2500 foot of stringers which have a tack weld every 100 mm or so. 10,000 welds on hull stringers alone. The underwing has stringers every 300 mm, 16 of them. Add another 1600 tack welds and we have done less than 25% of the welds on this cat. The majority of the remaining welds are long runs joining sheets together which require real skills when you are welding 4 or 5 mm aluminium together. We are talking over 3000 foot of long weld runs. Now, aluminium is a fast way to build a boat, its slightly faster than building in ply/timber and a lot faster than a foam glass cat built in a conventional way. A flat panel or moulded glass cat may be shorter as long as you don’t have to build the moulds first. But please remember this is only the shell structure.

The internal fitout and establishing deck gear etc will take roughly the same time to build and install irrespective of the shell construction method. EG an aluminum structure will require insulation before liners go on for an internal fitout. A foam glass hull structure will need to be sanded and finished prior to painting and fitout. A ply timber structure will require a west type epoxy finish prior to fitout etc. The engine, electrics and plumbing are addons. Deck gear needs the same number of bolt holes etc irrespective of the underlying material.

Translation, please look at the jpegs from Facebook and understand the amount of work that’s involved in a 62 foot cat. This cat had the owner and designer in the design and organization process for a year before construction started. Big boats require a very good design and a well organized group to bring them to an ocean crossing sailing cruiser.

 

The second part of our look at the 62 foot David DeVillier’s aluminum cruising cat “Elcie”. The cat is 62.33 x 30.33 foot with a “displacement” of 43,000 lbs. The ketch rig has 2067 square foot of sail area on a 65 foot fixed aluminum masthead fore mast and a 53 foot fixed aluminum mizzen mast. The low rig height helps stability whilst breaking down the sail area into smaller units for easier handling. The length to beam ratio of the hulls is 11 to 1. The numbers indicate the cat will have good performance especially for a cruising cat. The cat was launched in 2009 and has sailed over 100,000 nautical miles including a circumnavigation.

The original owner was from the US and communicated with David DeVillers (south African by birth living in NZ) by emails and preliminary paper drawings the boat he envisioned. Phone calls helped hash out details and discussed changes. Several days later revisions would appear as email attachments; boat design in the Internet age. Since the design process with David began over a year before the keels were laid, the owner had time to research systems, deck equipment, rigging and lightweight building materials.

The major items wanted by the original owner were a shallow draft of 3 foot with boards retracted. A low Centre of effort and easily handled Ketch Rig. Robust aluminum hull construction, compliant with ISO and Lloyd’s SSC.

The total concept was for a fast, capable and comfortable passage-making catamaran with efficient sailing performance and accommodation for 10 people in 4 cabins. The unmatched all-round visibility from the deck saloon and safe comfortable sail handling from the forward cockpit was a bonus. The forward cockpit is protected by oversize scuppers designed to drain the cockpit in under 2 minutes. Elcie changed ownership in late 2019 after 10 years operating as a blue-water adventure cruiser under her original owners.

Now one of the HUGE advantages of an aluminum boat build is that if the builders are competent and good at welding you do not have to finish, fair or paint the external of the boat. This will save on a boat of this size about $100,000 and a lot of maintenance. The downside of an aluminium boat is you need to understand electrolysis. As Redruben said he used to sail on a aluminum monohull they nick named “Asprin” (a headache pill) as it was dissolving in water.

The jpegs give the idea.

 

The ACCWing project is an Automatic Camber Control Wing that is being tested on an all-carbon catamaran, 33 x 29.5 foot (beam including its hiking wings). It weighs less than 2250 lbs. On October 29, 2020 the partners tested the first prototype of their flexible wing on the catamaran built by the Crazy Lobster yard.

The rig is composed of a carbon mast, hairpin battens and a light sail cloth, this thick sail can be lowered and stowed for reefing purposes. "It is a 645 square foot wing with a lot of power and finesse. There is a real ease of trim and also of tacking. There is no need for a forward triangle," says Philippe Marcovich, financier of the ACCWing project.

The composite components for the 55 foot high wing were built by Tual Le Guillerm at the Crazy Lobster ship yard. The 55 foot carbon mast is tapered. Philippe Marcovich reports that the rig provided ample power in light airs that prevailed on the day. Philippe was impressed that the rig sails very close to the wind and tacks quickly and effortlessly. Philippe is keen to carry out further trials in open waters after a few fine adjustments have been made to the rig.

One of the major advantages of the ACC Wing is that it is perfectly compatible with Gennakers, Code Zéros, and spinnakers. Philippe says the rig is adaptable to yachts of any size from about 10m up and he's keen to see it fitted to a vessel suited to long range ocean sailing.

The technology that makes the wing so unique is still under wraps (a patent is in the works) but the builders have fitted an example of the rig to a model of Grainger’s 20m Mauritius trimaran. Forth jpeg.

Hopefully this is an advance on several other wingsail systems that are reefable flexible soft wings. In each wingsail system reports improved performance in most conditions. The only real problem is they need to be trimmed consistently to get that improved performance. Wingsails have better lift drag ratio’s when they are at the near perfect angle to the wind. Unfortunately, if the angle to the wind is poor, wingsails stall faster than a conventional soft sail. Conventional soft sails have flexible fabric and can do slight adjustments to wind strengths and angles. You pay your money and take your choice.

The first 4 jpegs relate to the ACCWing, the remaining jpegs are other soft reefable wing sails.

 

Kurt Hughes 45 bridge deck cat has evolved again and is one of his more popular designs. On page 55 of this thread we featured a slightly older 45 version, but now the 45 cat is 45.9 x 26 foot that weighs 13,900 lbs and displaces 18,300 lbs. The aluminium or the composite mast carries an 884 square foot main, 202 square foot blade, 368 square foot genoa and a 1120 square foot spinnaker. The changes from previous versions are slightly more beam, a bit more weight and larger sail area. The hull length to beam is about 12 to 1.

The above numbers indicate good performance across a wind range but I have only spoken to one 45 owner of the older 45 with a non flared hull model. He was very happy with his boat saying it was a great cruiser with reasonable speed and a simple rig. He could get 8 knot averages (200 mile days) which is all he wanted. Top speed was irrelevant to him.

The previous versions had a cylinder moulded ply or fiberglass composites hulls with ply or composite beams decks etc. The mast can be aluminium or carbon etc. Request the build option you like and Kurt Hughes will probably be able to provide it.

Earlier versions of the 45 had a simple U hull shape without steps or flares and an old “normal” bow. Now the hulls have reverse bows to dampen pitch in waves, and a spray deflector that slides back into hull flare. The hull flare is the best way to get good room inside the hulls and still have a skinny waterplane so it can be fast. The diagrams of the hull shapes are one builder’s 3D interpretation of the hull shape to help him understand what he was about to build. Do not take them as the designer’s actual shape, a close guess more than the actuality.

The structure diagram tells the real truth. This is a “simple” complex build. Hulls are 19 mm PVC foam with biaxial/uni outside and triaxial glass inside with vinylester or epoxy. The interesting part is the flat or near flat deck or underwing surfaces which have 4, 5 or 6 mm plywood either side of 12, 18 or 25 mm balsa. The plywood is covered with 200 gsm cloth all in epoxy. Why did I say “simple” complex, because the ply balsa sandwich does 4 things. It provides a “solid walking” surface without the need for excessive glass, it is very easy to fair as an epoxy paint primer can act as the fairing compound if you have done the 200 gsm surface glassing well, it is not as sensitive to heat build up on deck as a foam glass deck would be and finally your interior is already a plywood surface that can be painted without much further preparation.

Kurt has many years of experience in all sorts of multi’s and a lot his experience is not always obvious. What appears to be a lot of varied materials for one boat simplifies the hardest part of boat building. Fairing, finishing and painting. Study the jpegs, there is a lot of knowledge in them. The final jpeg is the plan for the foam core, orange is 100 kgs/meter and blue is 80 kgs/meter PVC. The 100 kgs/meter is at the high load area fore and aft and at the points of the main crossbeams.