Multihull Structure Thoughts

The Minimus 11 project mentioned in this thread page 21 number 303 has been developed further and has its masts and rig on. Details are at Untitled 1 https://www.omick.net/adventure/minimus_ii/building/building.html

This is one man’s dream based on a lot of sailing reality. He has sailed a 14’ monohull from Seattle to Alaska, a 23’ Wharram designed catamaran from Mexico to Hawaii, a 20’ monohull from Seattle to southern Mexico and most recently, a 25’ monohull (Minimus) from California to Tahiti. The catamaran was the best sea boat in his opinion. It was, a somewhat faster boat than any of the others, but of the various attributes of multihulls, he values speed the least. Based on his experience, the most notable features are their safety and comfort at sea. He wanted the next boat to be offshore capable, as small as possible for two crew and their provisions for 4-6 weeks at sea, unsinkable, be quick and economical to build of plywood and epoxy using "instant boat" techniques and junk rigged.

She's an open deck design, 23.75 x 13.3 foot which is about as small as one can go in an ocean-crossing multihull with enough weight-carrying capacity for a crew of two, around 1200 pounds, which is what we figure for ourselves, gear and provisions for 4 to 6 weeks at sea.

Her hulls are dory style with narrow flat bottoms and V-shaped sides. The rig will be unusual, with 4 masts, two mounted in each hull. The construction has 12 mm ply side panels bent around bulkheads to form the basic shape of each hull. The bottom is then attached, bottom paint applied and the hull is turned right-side up to finish the decks and cabin. Just over two weeks into the build, the first hull is almost ready for bottom paint. Minimus II is being constructed of 12 mm plywood, which is thicker than usual for this size multihull. Somewhat offsetting the additional weight will be a lack of stringers. Most plywood multihulls are built using a framework of bulkheads and stringers over which the plywood sides are then fastened. He built the Wharram catamaran that way and found it to be a slow, tedious process in which a building base has to be constructed and the various frames and stringers carefully aligned.

An interesting design. Size is OK, I think it can have fewer masts, but the rest is good I wish him well. The web site gives a lot more detail.

 

Catharsis 26 (27) is 26.3 x 16.3 foot weighing 2000 lbs and displacing 3600 lbs. The hull length to beam is 8.2:1. The designer is expecting peak speeds above 14 knots. The structure is infused glass and polyester over nidacore honeycomb, that is Resin infused. Catharsis hulls etc are Nidaplast is 10 mm thick with one layer of 850 g/m2 multiaxial 0/90 glass on both side. The laminate is quite dry and nice, panel weight is 4.3 kg/m2.

Infusion was quite easy, though building the panels is time consuming. A simple vacuum pump made a descent vacuum (75-80%) and we made resin trap from the 5 liter tank of pressure paint gun. Resin is Reichhold Polylite 506-677 for resin infusion, 1% MEKP gives more than two hour infusion time. Wetting time over the sheet (1.2 m) is about one hour. We use flowing net and peel ply. All the hull sheets will be infused to full length on the long table. The long nida sheets are NC polyester. Then we will glue all the bulkheads. The places of bulkheads are marked by small NC holes inside the hull machined before infusion. Normal sheets (bulkheads and so) are NC machined after infusion, so far the quality is superb. Then the long sheets are taped together in jig with -/+45 biaxial and sheets. The outside seams will be filled with vinylester bulkhead glue (similar to microspheres+resin) and then taped. This design was originally for plywood and we just replaced ply with nida (cheaper and lighter).

Who designed this boat? Terho Halme who is a university lecturer on boat design in Finland. He has done several boat designs and builds. He did not complete this boat as he was made an offer part of the way through the build he could not refuse. Interesting boat. Tomorrow we will look at another one of his designs and builds which is completely different.

 

Just being picky but you're better off using inhibitors rather than low mekp levels, 1% is risking undercure at least with the resins I have used. Interox make a slow cure catalyst call SR for obvious reasons.
All resin systems are a bit different though.

 

Ping Pong is a proa with a junk rig mast. Terho Halme designed and built it in 2003. The Proa named initially EQL 7 was finally named Ping-Pong and is 24 x 10.8 foot weighing about 700 lbs. The single mast junk rig carries a 245 square foot sail with a 6% chamber with maximum depth at 45% aft of leading edge. There are 15 x 50 mm batterns sewn into the sail. Ping-pong hulls have a Cp of over 0.6, and a length to beam near 15:1.

The structure is 6.5 mm pine plywood, stich & glue, taped with 446g/mm2 +/-45 glass and epoxy. Coated simple with white acrylic house paint. The plywood sheets are already waiting for cutting and lengthening at the workshop. The bottom of the hull is v-shaped, the shape is modified to maximise lateral force and a high prismatic coefficent. There will be no leeboards (before sailing test anyway). The sleeve pipes of rudders are connected by bar which changes and locks the rudder positions. The rudders are wired to a wheel in cockpit. Junk rig is used to minimise building costs. It should work well, because the sheeting system is easy to build for a wide boat like proa. Junk rig is easy to reef and it also eliminates caught a back allowing the sail turn in freely. The final costs were about $3500 after 10 weeks and 450 hours of build time. The last two weeks were spent with the rudders.

The performance evolved with initial trials in 10 to 12 knots winds and 2 foot waves. Three panels of junk sail up and go. Junk sail worked well, it is quite balanced so the sheeting force was low. Speed about 5 knots. With the whole sail up, 6 to 7 knots. After few legs we sailed downwind and get our maximum 8.6 knots. The best feeling was with shunting angle about 100 degrees. The Junk rig is cheap (under $400 with mast, sail, battens, blocks, ropes), low stresses everywere, low sheeting force, the easiest rig to reef, all controls in cockpit, safe caught a back and so on. 20 knot winds get maximum speed of 13.5 knots and several times over 12 knots The buoyancy reserve is OK (quite near 200%). The problem is the drag from beams and nets when the heeling force increases. He will make the ama deeper for next spring. le of sail luff and leach elliptical to minimise losses of upwash-downwash phenomenon. The cruising speed was similar compared to slightly bigger monohulls, the best continuous speed was above 11 knots at side wind. Next I’m going to make a new Junk sail and rigging by using carbon mast and battens to decrease drag and weight and designing each panel to have more camber.

There was a rebuild of various aspects of Ping-Pong in 2005 which was relaunched after a five week rebuild. The main changes were: 1. Bigger rudders (about 100% more area) 2. Higher clearance (from 30 cm to 50 cm) on the cross arms 3. More camber at the new junk sail. The rebuilt boat was test sailed. Ping-Pong in 10-15 knots winds, course to windward, new junk sail work well, new rudders too. Shunting angle was between 90-100 degrees, satisfied. New rudders could have more balancing area in front of axis line, now they are heavier to steer than the old ones while there is some weather helm.

Here you have an easily handled boat that can act as a mini cruiser (last 2 jpegs) that can be built in 10 weeks for under $5000 from hardware store materials. It performs reasonably well and can maintain over 10 knot averages. Interesting and fun.

 

A small repeat but very useful site. This is the Scarab 22 trimaran which is 22.3 x 18.5 foot folds to 8.2 foot. Weighs in foam glass 925 lbs and in plywood 1200 lbs with a total displacement of 2000 lbs. The sail area is 270 to 400 square foot depending on the headsail. The plans are available from Team Scarab for $150 Australian and are PDF downloads. Plans for the Scarab 22 folding trimaran http://www.teamscarab.com.au/scarab22/design.html

The real interest is in the following build site that was done by a Canadian, Oliver who did an excellent job in the build process but as importantly documenting the build process. The site is loaded with good information and Oliver also did really good work checking the structural aspects of the design including a full FEA analysis. Please read the blog. Scarab 22 construction http://www.voile.org/trimaran/

 

The following is a home built tri using Mystere 6.0 catamaran outer hulls, custom main hull assumed to be 20 x 17 foot with a 30 foot high mast. I do not know the displacement. The real interest is in the folding system. A home built version/variation of the Farrier folding approach.

The cross arms are aluminium tubes with square tubing as part of the folding mechanism with some aluminium brackets and stainless-steel bolts. The jpegs give most of the story. The diagram is done by the designer of the W-17 Mike Waters as to how the attachment to the main hull should be done. The concept works well but as you can see it takes quite a few pieces of metal to get it to work well. The aluminium welding needs to be done by a good person and the location and direction of welds is important. Just welding a strip of aluminium onto a tube without understanding how the weld weakens the metal temper of the tube etc can be a future problem in the making.

A simple single full length aluminium tube with a waterstay would be lighter probably stronger and longer lasting. But the folding system is much more convenient for trailing use. How this helps.

 

I keep being surprised by what people “want” in a multihull versus what they need. What prompted this is a person wants a 60 foot Wharram type cat to do some fast ocean cruising. So, I decided to chase down some real information on Wharram’s Gaia 63 x 28 foot weighing 18,000 lbs and capable of carrying 10,000 lbs load, with a “schooner” wing sail rig of 1400 square foot sail area. The claim is the boat can be built in 4000 hours (I think it will take a lot more hours for a home builder) from slightly tortured 11 mm Douglas fir plywood hulls, with stringers and ply bulkheads, covered with glass. The keels included a bog poured in covered with glass to provide reinforcement. It has timber ply crossbeams that are “tied” on to hulls etc.

What we are interested in is the average cruising speed of Gaia. The average daily speeds were 5.5 to 5.8 knots across oceans with peak run averages of 9 to 10 knots. Gaia can top out at over 16 knots but we are talking cruising averages. Wharram and co can sail the boat with 3 adults but prefer 5 or more for comfort. (Practical Boat Owner April 2020).

Wharram’s commentary on another blog “Most of our catamarans can achieve speeds on all points of sailing, of half the apparent wind speed. We have done detailed measurements on the Pahi 63, Spirit of Gaia, and data collected from many of our other designs confirm this. Our catamaran designs with their slim hulls and low freeboard also 'ghost' well in very light winds. The boats will keep moving in winds as light as 3-5 knots, at which wind-strength monohulls generally don't sail at all.”

Now let’s compare this to a series of real cruising cats that have done serious miles. 38 foot Chamberlin 7 to 7.5 knots, 38 foot Mango Oram 8 knots, Beach Marine 10 meter 32.5 foot 7 knot average, Woods 32 Eclipse cruising 7 knots, 28 ft Waller 880 7 knots, 30 foot Wharram 5 knots across Atlantic and Klis 22 foot trimaran 5 knot average for half way around the world.

As Paladin said on the wooden boat forum in 2009. “O.K. time to say some un nice words....BIG boats, cruising.....fast......really don't belong together for serious cruising. I have had some big boats, a couple of 44-45 foot monohulls, a 49 foot tri, a 38 foot for offshore cruising and circumnavigation, a 31 tri for circumnavigation and smaller boats. A 31 to 38 foot is all the boat you need for single or double handed cruising. Larger and they are a real pain to handle, a helluva lot more expensive when you sail into a country and need to have it hauled for repairs or refit, a constant fight to stay on top of things, and the price of goodies just about take a cube in price when you get larger, you need much heavier lines fittings, sails, engine and really more people to get from point A to point B. More ocean crossings are made in boats 30 feet and under than any other size. Stop dreaming, go sailing.”

Do you really need 63 foot, space to sleep 10, need 5 people to comfortably sail the boat cruising so that you can average under 6 knots? How about an under 40 foot cat that can be sailed by 2 that will cost you half the up front and maintenance costs and if you have a good design probably average higher speeds. Understand what you really need and buy/build accordingly, you can spend the extra time and money you will save on real cruising.

 

I think it is pretty easy to miss the mark without considering the different sailors "styles" and goals. Gently getting there works for James, there is no doubt the long skinny hulls could be cruised faster by those with different priorities. For sure on any boat getting more speed takes progressively more effort and/or nerves. How hard to work for that knot is a good yardstick for cruising, especially with wide age ranges aboard.

 

You are confusing length with size. They are different animals.

A long multi will perform better (how many of those small cat miles were upwind into a decent seaway for 24 hours?), have a better motion and when it gets gnarly, feel safer than a small one.

The main reason boats come to grief is crew error. When the crew is tired, this is exacerbated. Cold, wet or scared, all make it worse. A large light multi will require less sail and deck work than a smaller one of the same weight and rig, the crew will be more relaxed, more able to rest and less intimidated by the conditions.

While a harryproa fits this description, there are also a few catamaran designers who understand. One is Bob Oram. Wharram is arguably another, although his obsession with ply and cheapness means many of his boats miss the target.

Cav,
Agreed, but it is so much easier with a simple rig and the ability to depower immediately and totally and have the boat sit quietly, if required. Then you can set sufficient sail for the lulls and reduce power in the gusts, which is so much better than reducing sail for the gusts and wallowing the rest of the time. The classic example of this is cruising multihulls reducing sail at night and in squally conditions, "just in case".
A self vanging rig that can be totally dumped by releasing the lightly loaded sheet is a boon in these conditions. If that rig is linked to a simple sheet release activated if the windward hull stern leaves the water, night time sailing becomes far safer and faster, often to the point that the on watch is enjoying it so much, they do a double.
The only rigs that allow this are an unstayed masts with wishbone booms and junk rigs. Unfortunately, the latter are rarely good performers, although some of the new variations appear to be improvements.

 

I like your thinking Old Multi - I don't get the way multis are getting so big. I get a little apprehensive on our very low load 38ft cat - I am a pretty fit 52 year old who is in pretty much the same shape I was when I launched the boat 20 years ago and she is pretty much at my limit.

I don't know how old couples manage large and heavy cats. They would scare me but obviously they do not scare their owners, or they would not buy them. It perplexes me but I need to respect their choices, I just cant see why you need to be so far away from the person you love when sailing. I mean we can have a hull each. Our boat is big - it can take 20 people out for a fun day and hold stores for 2-3 months. Why go bigger? I don't want to. The square cube rule means a bigger boat would be unaffordable for me.

Each to their own though but remember, there is never someone telling you "Don't upgrade" "Buy the cheaper boat" "You don't need that extra equipment". We even have the phrase "Bigger and better" but maybe we should champion "Simpler and smaller". Cost is a big factor for me, as is the fact that I do all the work on our boat except for sails. If she was bigger or more complex I would find owning her onerous. As it is, I get more fun than work which is good.

And hey - as for being half a knot slower than a Mango - well if we ever size up against one I will let you know but I am putting my money on my Chamberlin - she has style, grace and lots of pace!

cheers

Phil

 

Cavalier and Rob. I support the idea that a cruising boat is what anyone wants and the style of cruising/speed of cruising is what they choose. My basic problem is size is a lovely solution to a bit more comfort for crossing oceans but at what cost. Rob, I have stepped aboard the 60 foot modified Harry Proa built in Melbourne. The guy who built it from a 50 foot plan is creative and a fast worker but the boat is according to the guys who sail it a bit of work. Yes it can go at wind speed, yes it handles a seaway but when anchoring, parking it etc its just a big boat. It needs a minimum of 2 people to keep it sailing reasonably and the amount of maintenance it has required is commensurate with any 60 foot boat. (PS folks this boat was not built accurately to a Rob Denny plan as I said it expanded from a 50 foot to 60 footer and had such tricks as 18 mm cored hull sides then because the 18 mm did not bend enough for the bottom some bottom panels had 12 mm core etc. Also the engine and steering systems have to be reengineered, again not Robs design). What Catsketcher and I appear to be agreeing on is a smaller boat may achieve the same end result with less cost and physical effort sailing. Rob I fully agree a 50 foot Harry Proa with a flexible aerorig will be as cheap and faster than a 40 foot cat but in the world of mooring fees being based on size there are other considerations.

 

Well Wharram markets that thing as a tribal boat, not a couple's craft or even family cruiser so I think he'd agree about sizing for smaller crews. As advertising it is a great hook to pull into port with.

Yes, a rig that can luff from any wind direction is great Rob, I used one on my sailing canoe to stay out of trouble. One good thing about the old Nicol rig is the even split between main and fore triangle lets you have a genoa of decent size on a furler versus a fractional rig, very fast to adjust for conditions and easy to ad light weather sails like a big chute. Those picturesque Gaff mains warrant more hands on deck but it looks fun.

 

Did you account for the HP allowing flipped bows on the long hulls? To me that makes it ride like a 50, and cost like a 40, or cheaper.
As the bows are crush zones for collisions at sea, it makes sense in all kinds of ways.

 

I mentioned Mike Waters W 17 daysailing tri a few items ago. The tri is 17.1 x 13.9 foot and can fold to 7.2 foot, weighing 410 lbs and displacing a maximum of 1000 lbs. The 24 foot wing mast carries a 120 square foot main and 47 square foot jib. There is a 200 square foot cruising rig option. Mike is an excellent boat designer who thinks logically about his designs and has written/blogged extensively about the rational of his design work. He has come to his own conclusions about simple easy to build hull shapes etc which have resulted in a good design that performs well.

The W 17 is a ply timber construction or hulls and cross beams. His wing masts are build at home friendly. I will not detail much of the design as the jpegs will give the hints and Mikes web site gives a lot of valuable build hints and information. The site is W17 Trimaran | Main Page https://smalltridesign.com/W17/greybox/W17-Trimaran.html

This appears to be a real fun boat for fast bay and lake sailing.

 

For many cruisers, the ability to sail comfortably upwind and down in light and heavy air and to get off the fabled lee shore in a gale with a fouled prop is much more important than "speed".

Zero cost, if you are comparing boats of the same weight (and fitout).

That design is about 15 years old and it has been constantly updated since, see below . The 2 guys who sail it are amazing. They are both well on the wrong side of 60, probably 70. They are good sailors, but neither of them could sail any of the cats you mention single handed.
I would argue that none of the owners of those cats could comfortably sail their boats single handed (ie, no autopilot) either, if "sailing" includes reefing, gybing and tacking in a decent breeze and sea, changing headsails, unanchoring on a lee shore and leaving/entering marina berths in a strong wind.

Only the comparatively low and narrow leeward hull on the Harryproa is 60' long. The boat weighs about 4 tonnes (incl electric motor, gen set and batteries) and has less frontal area than most 40' cruising cats. Consequently it is easier to anchor as a smaller anchor is required.

Low speed manoeuvring is difficult as they chose a daggerboard and small rudders instead of the designed large rudders/no daggerboard. The fore and aft configuration of these means it steers better than most cats. This is really noticable when being blown onto a jetty or wall. Angle both rudders at 45 degrees, engage the (single) motor and the boat crabs sideways. This is easier than on a twin engine cat, and would be hard work single handed on an outboard powered cat.

The rig is the same as on several other harryproas. Due to the single, lightly loaded sheet controlling both sails, the ease of shunting compared to tacking and gybing and the ability to completely depower the boat on any point of sail they are all as easy or easier to handle single handed than most cats. The stronger the wind, the bigger this discrepancy becomes.

You are confusing weight and size again.
Two similar weight (and fitout) boats will cost about the same. The smaller one is using materials less efficiently.
If you use a rig that requires a lot of physical effort (sheeting on headsails, hauling down mainsails while running square, extra sails and all the things that go wrong with them) then you are correct, the smaller the rig the less effort will be required. But a low effort rig without all this physical labour is a much better solution and a much larger one can be handled for the same energy and usually a lot more safety.
"may achieve the same end result" ignores the benefits of performance, comfortable motion and safety that come with size.

Higher marina fees vs more speed and lower build cost (and better motion and safety) is a pretty good trade for most people, especially cruisers who avoid marinas whenever they can.
The latest Harryproas have an optional tender which is big and powerful enough to enable anchoring offshore or a reasonable distance away, avoiding the need for the mothership to use many marinas. A 25' tender visiting the marina for a couple of hours is a lot cheaper and more convenient than parking a 40' cat on a marina end tie, which is a pretty miserable place to "enjoy" your boating time.
If you want to reduce marina fees, trail your boat or fit it in a container, it is a trivial task to build the Harryproa lee hull with removable or folding ends as ERuttan suggested.

What are the "other considerations"?