Multihull Structure Thoughts

Wow. Thank you. My husband will be happy to hear she still sails.

 

The following South African designed and built trimaran is described as an 18-foot Exploration Eco Trimaran. South African Guy Joubert is an adventurous person who has hiked, climbed, swam and camped in a lot of Africa. He wanted a practical boat he could trail and camp cruise the many coastal and lake areas. Result in 2007 he designed the Crusoe Modular 18 foot Adventure Trimaran.

The trimaran is 18 x 13 foot (can be folded to 6.6 foot for trailing). The weight is 700 lbs with a displacement is 1,500 lbs. The floats are 10.1 foot long. The 22.7 foot mast carries about 120 square foot mainsail and an 80 square foot jib. Draft from 1 foot to 3.3 foot over the lee board and rudder. Length to beam main hull 4.4 to 1. The float length to beam is 9.2 to 1 at the gunnels. The engine options are vast ranging from a 4 HP 4 stroke petrol outboard (9.9 HP is preferred), an electric outboard or a hybrid diesel electric combination.

This tri is not a performance sailor. Under power he Torqeedo Diesel electric configuration promises to push the tri at between 6-8 knots depending on conditions and loading. Under sail my guess is a peak speed of 10 knots with 6 to 8 knot averages. This tri will sail on all points but its fat main hull will limit its peak speed. It will be a good small motor sailor.

The open cockpit can store the float hulls or act as a sleeping area. The hulls have 21 separate storage areas for camping gear etc. There is a tent that covers the full width of the trimaran so you get in effect a 13 x 10 foot standing headroom “cabin”.

The design is built in fibreglass and has aluminium cross beam components. Simple structure that is built from several moulds. The skill here is the design. Each mould has all components (eg locker shapes) molded in from the start to increase strength and reduce production costs.

The Crusoe Modular 18 foot Adventure Trimaran was an interesting development. The jpegs give the idea.

 

Gary Baigent a New Zealander, was a prolific builder experimenter of very lightweight trimarans and foilers. He built several out of tortured 3 mm plywood with minimal fiberglass and or carbon fibre external glass. His original Sid float foiler was 25 foot and weighed less than 900 lbs all up sailing (first 3 jpegs). He designed tris up to 36 foot long that were to be built in 3 mm tortured ply including one for the Round Britain race. The largest he built was about 33 foot and yes it was very light for its size.

The tri we will focus on is a design that was not built but based on the Sid model called the “Scissoring Sid”, a 25 x 26 foot wide tri that weighed 900 lbs that had a main beam that pivoted on large bearing for trailering, then locked with solid water stays and large pins. The 36 foot high by 3.25 foot cord wing mast had a mainsail attached that provided the main power with a small jib to help the wind flow over the main. The J foils on the floats were intended to provide the majority of the stability allowing very small floats for light weather and folding. The intention was to have the entire boat foiling on the J foils and an aft rudder mounted T foil.

The accommodation was to be very limited but there was a bunk allowed for.

The construction was around Gary’s basic approach. Build light and only strengthen if it breaks. His experience had taught him that most boats are overbuilt and if you build a light hull then you can build a light cross beam which means a smaller lighter rig etc. If you apply this approach well you also end up with a cheaper boat that will surprise some who pay more for there mainsail than Gary spent on an entire tri. Result Gary builds 3 mm tortured ply tri’s that can withstand and sail in some very strong winds in his area.

The jpegs give the idea of “Scissoring Sid”.

 

Hello,
I followed Gary through the build of "Sid" and his latest finished creation "Frog". It was also built with 3mm ply and I liked it very much, because of it's small dimensions (6.5m), radical design and interesting rig. But I don't believe that a tri with a 3mm ply skin and a little glas is robust enough for "strong wind with waves" conditions or with a hard touch at the dock. Ok, both situations were not important for Gary because he was sailing mainly in calm conditiones (according to his posted photos) and he has bstored his boats at a mooring.

Very interesting was the rig used for Frog. It was a rotating D-Section mast with a double layer mainsail. Gary's favorite was the cat rig and "frog" .



Does anybody know what happened to Gary? I have no information why he does'nt post anymore.

Have Fun, Michel

 

Here you can see the double layer mainsail behind the rotating D-Section Mast. Look at the sailbattens, there you can see the the airfoil section formed. By the way, the two layers are flat plain sails without built in profile.

 

these floats have no buoancy at all forward? How is the diagonal stability then? Would the boats not be extremely susceptible to pitchpoling?

 

It's a foiler. And the sail area is aft, like a ice boat the long bow picks up the forward buoyancy.

 

I was going to do a small item covering some of Gary Baigent’s various tri’s and a cat. I searched and then found more than I expected. So lets start at the beginning. Gary a New Zealander was interested in boats. He built a few then decided he liked Malcom Tennants radical (for its time) Bamboo Bomber a 32 x 18 foot tube cat with a wing mast and very light 4 mm tortured plywood hulls. Gary built the wing mast version which was again advanced for its time. It sailed well but was not good on a mooring as the wing mast took control in high winds. Result a damaged cat after a partial capsize.

So we get to Gary’s first home design tri. Gary is an excellent scrounger. He cut down one hull from Bamboo Bomber and used it for the main hull, he got a wing mast and mainsail from a B class cat, used some aluminium tubes for cross beams and added some boards that turned into foils on some small floats made from 3 mm plywood covered with light glass. The name of this tri was Flash Harry built in about 1980.

Flash Harry was 20 x 20 foot, weighed 320 lbs and had a 30 foot wing mast carrying about 200 square foot of mainsail area. The B Class wing mast was changed to a new “Flash Harry” wing mast that is 450 mm x 140mm in section and has carbon reinforcing running up the thickest area of the mast and directly under that is the 4mm ply I beam. There are hollowed ring frames at 3.25 foot spacings plus leading and trailing edge stringers - for the 3mm skin attachment areas and also the 6mm mainsheet track (which you can just see). The hounds fitting is a wooden beak, reinforced with uni- carbon wrapped round the leading area of the mast, with a shackle taking the three shrouds; the female bearing is wood and glass, as is the male bearing; the halyards have to finish on the mast to allow rotation.

The jpegs give an idea of a faster than wind speed up to about 12 knots of wind speed day sailing semi foiling tri. This tri inspired Gary to build a bigger tri which we will get into tomorrow.

The first 3 jpegs are of Supplejack 32 foot cat, the next are of Flash Harry 20 foot tri.

 

Groucho Marx is over 40 years old and has been rebuilt several times due to several design changes and misadventures (Gary’s mooring area is not kind in strong winds), so I will give you the numbers I know. Groucho Marx is 36 x 36 foot with a weight of 1460 lbs. The 50.5 foot ply wing mast has a 520mm section with a straight luff and carries about 500 square foot of sail area. The main hull length to beam is about 15 to 1. The draft over the retractable rudder and foils ranges from 1 foot to about 5 foot. Groucho foils have changed and developed over time from J foils to inverted Y the L foils and T foils.

The accommodation is limited to 2 small berths and some storage areas. This is basically a very fast experimental daysailor more than a cruiser.

Groucho Marx can sail faster than the wind and is very stable with small floats supporting a good foiling system. To quote Gary: “After a new mainsail was installed, in light 5-7 knots wind, Groucho 9 knots to windward, 10.2 knots downwind, fastest with me not on helm - but top battens need work, halyard stretches loosening luff, so-so for first time - but will improve.”

The construction is a 4 mm tortured plywood main hull, 3 mm tortured plywood float hulls (all covered by light glass). The wing beam (cross beam) on Groucho is in strip planked paulownia, in four shells off the simple female moulds, reversed them for the other sides, sheathed inside and out with 200gsm but later, when shells glued and taped and attached to main hull and floats, wrapped the beam in carbon strips, some at 45 degrees - has lasting well. The main asymmetric foils when rebuilt and altered for Groucho had new vertical paulownia sections and there are 10 layers of uni directional carbon each side around the L junction curve and up past the float/foil hard point area - so it is almost solid carbon there. The tips have been altered and the L lifting area is now level - whereas before they angled down at a slight angle - and touched bottom early in shallow water.

There are several jpegs of the “rebuilt” versions of Groucho Marx. I am amazed that Gary has done Groucho Marx rebuilds along with at least 3 other “new build” tris over the same time. The jpegs give the idea.

 

Im not sure where you got your info from Luckystrike but the twin-skin sails on this rig are definitely not flat as you claim, they were shaped and designed using Pro-Sail - I made them. I also designed a system which linked the separate outhaul of each of the twin skins to the rotation of the mast which automatically tightened the windward side while easing the leeward one but this was not built into Gary's rig.

 

For today we will discuss Gary Baigent’s Sid again but provide some build jpegs to give an idea of how to build a very light tri. Sid had a variety of “Sid” names depending on the point of development. It started as a 25 x 26 foot tri but was extended to 27.9 foot. The boat weighed about 450 lbs in most configurations. The 36 foot high wing mast carries 355 square foot upwind and 538 square foot downwind. The length to beam is 21 to 1 on the main hull. The draft over the rudder is 3 foot and over the float based foils is 4 foot.

Gary indicated a few design measurements: ”7.62 LOA x 7.9m BOA, main hull WLB 0.350m, Block coefficient 0.32, Prismatic coefficient 0.44, Vert. prismatic coefficient 0.54, foil measurements 185 x 1500mm OA, 400mm bury, rudder 185mm x 1200mm, IT area 185mm x 1m approx, SA upwind approx - 33sq.m, displacement approx 200kgs, Bruce No. upwind 2.5, rig height 11m, wing mast chord 1m (perhaps), SA downwind 50m2”

Now a little history Sid originally was to have a tilting wing sail that pivoted on a short mast (see jpegs). The wing sail had an asymmetric profile. The tilt wing destroyed itself in a strong wind breaking in the middle. The wing sail leading edge was maintained and “symmetrical” backend was added prior to adding the mainsail.

Sid hulls are 3mm gaboon, with mostly 6oz box weave glass sheathing and uni directional carbon in high load areas. The build jpegs below are of Sid’s main hull and foils in one version. The cross beam section gives an idea of the structure and again features EG 3 MM plywood web panels and fairing. Yes, you can build very light and cheap if you want and it will absorb punishment.

Gary described his build technique as follows: “I make a simple strongback for building upside down - and for a narrow multihull that can be just one long plank with some crosspieces in the hull's widest mid section areas) then fit the three or four main bulkheads/ringframes, plus the stem and transom to the strongback, then run the keelson, gunwhales and stringers (plantation white cedar in NZ) over and around the heads/frames, these set in and glued into slots cut into the frames. So there is quickly the skeletal shape of your hull. Working on your own makes it difficult to handle the full length, scarfed 3mm klinki hull sides - so I just work a couple of opposing lengths/sheets/sides at a time, that is, glue and staple to the keelson and when it is cured, bend each length round the bulkheads/frames and glue/staple to the gunwhales. I coat the inside ply with epoxy just before I start bending it, then cove the joints with thickened glue. Working with two or three people you can do the two complete hull length sides at one time ... but you have to work fast and accurately. But on your own, just a couple at a time, works okay. Each ply length is already scarfed both ends of course, so for the next length scarf connection, I do a dry run just stapling, no glue, and pencil mark the correct positions- then glue/staple to keelson etc. coat the interior and move on. After all this is completed and cured, cut the excess ply from the roughly shaped panel sides to the gunwhales. Although this method is not as magical as true tensioned ply building, like the Tornadoes were/still are done, it is sort of halfway between and more suited to one person working on his own. Of course it is a lot easier with two or more people.”

The jpegs will give the idea and yes Sid sails very well again in excess of wind speed in light to moderate airs.

 

Sid part 2 after build of shell now tilt rig then conventional wing mast.

 

Hello Luff Tension,
I have this information from Gary hinself. He posted it in his building thread about "Frog" post No 384 and 385
6.5 to 7.5 metre performance/cruise multihulls https://www.boatdesign.net/threads/6-5-to-7-5-metre-performance-cruise-multihulls.52655/page-26

Iam glad that you corrected this information. Iam fascinated by this rig and see it as a option for one of my next projects.

Have Fun, Michel

 

luckystrike. Gary is still around having a beer or two but has "retired" from talking much about boats. He has many other interests such as photography etc to keep him amused as well as sailing.

 

Cheers Gary!