Multihull Structure Thoughts

Fallguy. CSM is chopped strand mat. When fiberglass was first developed they did not do continuous stands of fiberglass, they did chopper guns which sprayed resin and short strands of fiberglass into a mould. That mix was "strong" enough at the time if you sprayed enough thickness on a given panel. It was also fast in production as some really good chopper gun guys could build up the required thickness by "eye" without measurement. That then became a "product" of a mat of short random fibers using a binder. The binder breaks down easily in polyester but the binder does not breakdown well with epoxy resin. D Halliday of Boatsmith FL is a good builder. But like all designers or builders he uses approaches that suit himself and the client. There are 10 different ways and materials to build a crossbeam, each has its advantages and disadvantages. Its like some Team Scarab tris, you can build in foam glass or you can build in ply glass using the exact same glass layup with plywood substituting for the foam. The difference, additional weight and the need to use epoxy on the ply glass versions. The cost is cheaper plywood than the foam but more expensive epoxy resin instead of polyester, therefore total cost of either version about the same. Why do the plywood core? The same applies to the Coosa top and bottom flanges on the crossbeams. You can validly do the Coosa flanges but why?

 

Oh, I well know what csm is. I used 1708 fabric and 1208 and 1708 tapes in my build. The 1708 fabric was largely used for moulds or tabbing moulds as were the tapes. The idea csm cannot be used with epoxy is a fallacy.

As I stated earlier, the coosa board would be used instead of making a plug and female mould to go straight frp. Unless I am mistaken, it would be less laminating.

 

Back in the day when I built yachts in moulds the foam would be replaced by ply where fittings like jib tracks, winches, staunchion bases etc were bolted through, inevitably this rotted out if things were moved or replaced and not sealed properly.
It’s my understanding that the higher density Coosa board can replace the ply ?

 

Fallguy, apologies for the CSM explanation, it was my misunderstanding of your initial entry. As for no moulds, I agree you could make a shape with Coosa and directly glass over it, as you could with ply. But in the Tiki 46 crossbeams no mould was required, the shape is formed by the Divinycell and vertical web of Coosa. People then can add additional unidirectional glass as required on flanges and biaxial wraps around the total beam. In a later build Boatsmith build fiberglass beams for an Akiri 47 that required moulds as it was mainly glass on both the webs and flanges.

Redrueban Coosa could substitute for plywood as it has similar characteristics but it will need some investigation. Users of Coosa claim that it does not hold screws as well as plywood and needs larger backing plates on bolts etc to minimize pull through. Given a choice between potential rot and larger backing plates, I would use Coosa and the larger backing plates.

 

@ redreuben: because quite often deck fittings are pulled out from their places, people here developped the following technique:
1. birch waterproof plywood is inserted before the final lamination layers, where the deck fittings will be inserted (this birch ply is the strongest ply found here);
2. bigger holes than necessary are drilled through the deck for the deck equipment;
3. These holes are filled with epoxy mixed with wood powder;
4. After polymerization, new holes are drilled through the hardened epoxy, so there is no exposed plywood anymore.
5. Big backing plates are added before the nuts are tighten.
Excuse me please if anyone already knew about this well-known technique, but I found out many professionals don't know about it, and prefere to seal the holes through wooden transoms inside fiberglass hulls by using cheap silicone .

 

F4m, professionals know about it, it’s just time intensive for production built down to a price.

 

Jeff Schoinning once said to me that he sells dreams, builders build the reality. What a lot of first-time builders don’t realise is the reality of deep sea cruising. If you plan well, are lucky and patient you will not hit any winds stronger than 35 knots but the majority of deep sea sailors hit the occasional real storm to hurricane winds at some point in their travels. What you do to handle a difficult situation depends on your boat, your experience and your ability to emotionally and physically handle the situation.

Your boat needs to be built and prepared for a storm from the first time you head off shore. This does not mean you overbuild the boat, as most multihull designs will survive a storm better than you will. This means lockers, hatches, windows and doors etc can securely lock and are virtually waterproof. The boat has a reefing system that is fully setup, has been proven to work in difficult conditions and most of the crew know how to eg reef any sail. You have sailed the boat near its limits to know how the boat reacts under real pressure. Many people are surprised at how hard the steering is under incorrectly reduced sail or how the boats momentum in big seas can affect your steering in a big confused sea. Multihulls can broach or be thrown sideways. Please practice sailing in rough conditions and understand your boat and yourself. Its some of the best sailing education you will ever get. A good boat in moderate weather may become a problem in heavy weather.

People also need understand where and how to use the safety gear on board. Finally, and most importantly know your personal limits. I personally know a 34 foot tri and a 37 foot cat that were lost in moderate 30 to 35 knot conditions because in each case the 2 person crew just ran out of energy and made poor decisions after being awake for 24 hours. One person lost his life when sweep overboard before the boat hit a rocky shore.

Read and learn from experienced people, with one of the better series of free books by Steve Dashew. I have mentioned these books before and they are not small downloads but their words are very educational. The site is SetSail FPB » Free Books https://setsail.com/free-books/

Also, the following catamaran based severe weather sailing has many stories of handling catamarans in storms from those who have experienced a real storm. The PDF can be clicked on below or obtained from the following web site: https://www.hisse-et-oh.com/system/...in_severe_weather_(March_2014).pdf?1419944544

The jpegs are general, the PDF is 2 meg and very informative.

 

The following is about Farrier tri’s but again the knowledge is applicable to many multihulls. Ian Farrier designs were very good and his plans were among the best allowing a home builder produce a quality tri or cat that, if built to plan, could sell for more than the tri or cats build cost. Ian also produced excellent supporting documentation including the following sailing manual.

The manual describes the boats, their systems and how to use those systems under various sailing conditions. I wish all designers would produce documents like this. It would help all future owners to understand why they have to build things a certain way to achieve cruising or racing outcomes.

The document can also be accessed at:

http://chesapeakemultihulls.org/wp-content/uploads/2019/07/2012_Sailing_Manual.pdf

The jpegs are just general. The PDF is 3 meg.

 

Here is what happens when a person finds free plans on the internet, likes the design then builds with the materials that are available to them. We have featured this design before but the home builder has gone further in his construction. He has requested comments on the web, has received some and is still proceeding as he is too far into the build.

What is the cat, the Rival 21. The designer and original builders of the boat (Sergio Marques and Chico Armond) created 21 x 11 foot without wings. The total beam with wings is 13.9 foot. The base design is for a 650 lbs weight. The rotating 29 foot mast is probably from EG a Hobie 20 or 21 as is the 222 to 300 square foot of sail area. The main is 183 square foot. The hulls are slightly asymmetric with a hull length to beam is 16.5 : 1. There are deep boards and kickup rudders. The designers say the actual weight of the boat full loaded (eg engine, ropes etc.) but no crew is 870 lbs. Each hull should weight about 210 lbs complete.

If the design is built correctly, it is plywood with 8 mm ply bulkhead, 6 mm ply hull sheets with 18 x 36 mm gunnel strips. A light fiberglass cloth covering in epoxy. The crossbeams on the plans indicate a 52 mm aluminium tube but reality of the jpegs say about 95 mm aluminium tubes for crossbeams. I think 95 mm tubes are about right.

Now the guy who found the “free plans”. His built the bulkheads from 8 mm ply then skinned the hulls in 9 mm “waterproof” MDF chipboard with the 18 x 36 mm gunnels. The first hull weighed 220 lbs without deck or daggerboard case and other associated hull hardware. In spite of some advice from others the build continues. It will be interesting to see the longevity of the hulls. I know of a least one steel mono that got half way around the world with a MDF internal structure before it had to be rebuilt internally.

The jpegs give the idea of the original boat and a few of the “build”. The “free plan” is also shown.

 

I may insert a fraction of thread hijacking here, apologies in advance.

Going back to the post on this thread from December 31 last year, in regards to the junk rigged 38ft wooden catamaran named Kaimiloa built by Eric de Bishop 1931 in Hawaii, did anyone else notice that the boat sailed 160 mile days on the long voyage back to Europe. IMHO 160 miles a day is pretty good. For those on a budget buying say a 30ft monohull a reasonable days cruising might be 100 miles or so, thus 160 seems quite good. I was thinking why such a low tech boat sailed so fast. Maybe there was a lot of downwind sailing, but it seems that the vessel was intrinsically quite fast, what I mean by that is a 38ft catamaran is intrinsically a quite fast vessel. So we have a low tech simple technology on a fast layout giving quite reasonable performance. Now for modest money most would find a modern 38ft catamaran expensive, so may have to settle for a vessel of smaller size and thus slower intrinsic speed. The modern styleis perhaps is to take a smaller boat with lower intrinsic speed yet use high tech materials to make up a bit. Example stainless steel fittings, modern goose-necks, roller furlers, self tailing winches etc etc. Perhaps the major player in a simpler style is James Wharram.

If anyone has read Buehlers Backyard boat building, his main point seemed to be that a simpler vessel (less refined) but built a bit larger would give similar performance to a more advanced style of boat but of smaller size. Buehler was referring to monohulls, it may be that there is something to be said for applying this to multihulls

If just to say you want a boat but have little money, it could be that the ocean is pretty much the same as it was in 1931, that is nice at times, but also very bad at times. Now if your lazy, or lack the motivation to spend 2000 hours building your boat, it might be possible to have your boat built in similar style to 1931 boat. Now Kaimolo weighed 16800 pounds or 7 and a half tonnes. Now in west africa and also in Indonesia, hardwood sells for 500 US dollars a tonne (I kid you not). Now this wood may come in large pieces such as 10 inches by 8 inches, and thus need milling to get down to appropriate size. Now as to labour, in many many many countries people are living on less than 2 US dollars a day. In Nigeria 60 percent of the people are living on less that 2 dollars a day (please dont ask me where all the Nations Oil money goes, I dont know).

Just say your paying wages at say 1 dollar an hour, your 7.5 tonnes is 4000 dollars for timber, your wages are perhaps 2000 dollars based on 2000 hours build, and then you have accessories which may be very useful, things like sails, anchors, a radio, solar panels, a bilge pump, lines, compass, windows, maybe some epoxy resin, nav lights, electric fan, a stove. Note there may also be 'fees payable' to various officials for permits, permissions etc to allow a build to proceed

Lastly please find an example of what I am getting at, here is a link to a 48ft outrigger canoe built in Papua New Guinea in 2012. Cost was 5000 Australian dollars, which back then was about five thousand US dollars. Obviously this is just a big open canoe with no cabin and not really suitable for cruising the world, and without epoxy encapsulation may rot out after 20 or 30 years. Also it may be that when not in use they are stored on islands to dry out, which may extend their lifetime. You can also put the word - sailau into youtube, and you can see the canoes of South East Papua New Guinea. I give the 48ft canoe link as an example because in some way it gives the cost of boats in poorer nations. Is there a realistic way of using the lower timber costs and lower labour costs I am not sure. I am a member of an Indonesian boating group of facebook, and local builders are selling quite large wooden boats to local buyers for very little money. Now mostly these are engine propelled, not sailcraft, and obviously lack modern amenities, I may be able to provide examples in near future

The Vessel https://climatechallengervoyage.wordpress.com/the-vessel/

 

Peter Australia. Your thoughts about cheap multihulls that can achieve reasonable speeds is interesting. The 2 separate aspects are “cheap boats” and reasonable speed. I will deal with speed first.

This is a generalisation but the average daily speed of most monohulls is about the square root of their waterline length multiplied by 24 to equal daily runs. Most cruising cats or tris average daily speed is about 1.3 times the square root of the waterline multihull by 24 to equal daily runs. Lets see how it works.

Kaimiloa 1930’s cat waterline is 29 foot the square root is 5.4 multiplied by 1.3 = 7 knots multiplied by 24 hours = 168 miles per day. Eric claims between 150 to 165 miles per day.

World Cat a Choy 43 foot catamaran went around the globe. It has an effective 40 foot waterline whose root is 6.3 x 1.3 = 8.2 knots x 24 = 197 miles/day. World cat averaged about 200 miles/day.

A Heavenly Twins catamaran “Terrapin” sailed around the world has a waterline length of 21.5 foot. The root of the waterline is 4.6 by 1.3 = 5.98 knots x 24 = 143 miles/day. Terrapin averaged 120 to 130 miles/day with peak days of 180 miles/day.

Cooking Fat a Tiki 21 that went around the world has a waterline of 18.5 foot has a root of 4.3 by 1.3 = 5.6 knots x 24 = 134 miles/day. Cooking Fat daily average distance 104.6 miles/day around the globe with an average speed of 4.36 knots (through water) and a best day run 176 miles under wind-vane and 210 miles by hand-steering.

Miss Cindy 16 foot ocean crossing Bigras cat has a 16 foot waterline with a root of 4 x 1.3 = 5.2 knots x 24 = 125 miles/day. Miss Cindy averages about 4 knots with peak days of 135 miles/day. Miss Cindy can peak out at 15 knots with wave assistance.

The above are a variety of cruising boats of all sizes that have done real long distance sea miles. None of the above cats are great windward machines including the 43 foot Choy. Modern cats with deep foils could increase daily runs but the majority of the sailing by these guys is generally reaching to downwind sailing if they can arrange it. The speed generalization appears to work reasonably well. It also supports the theory that longer is potentially faster but what is fast enough? Its up to you. Most monohull cruisers are happy once they do above 120 miles/day. A Heavenly Twins can do 120 miles/day and that cat is not a “performance cruiser”. In short, any multi above 25 foot will probably perform well in speed terms. Stability needs to be reviewed in shorter multi’s.

Now we get onto “cheap”. I can find you a cheap second hand 33 foot plywood tri for under $US10,000 that could take you half way around the world if you are prepared to maintain it. I can find you a fiberglass Seawind 24 that has crossed oceans for $A10,000 etc. I can find a ply Piver 30 foot for under $A5,000. Each of these boats will take you places with some accommodation.

You can “build” a cheap boat from lower quality materials and second hand gear etc and have fun. But I have found building cheap often is more expensive than buying second hand cheap. There are several 30 foot minimalist $1000 boats out there BUT they are higher risk especially beyond bay sailing. As the guys from Fusion catamarans said to me. You can buy a kit and finish it cheaply but when you sell it you lose out big time compared to someone who built the boat well with reasonable gear.

I would love to tell you how to build a boat very cheaply and advise the countries to do it in but a little research on the web will give some very clear indications of some of the bad experiences that have been had by others. There was a 38 foot cat that disintegrated in 2 years due to “buc-buc’ a wood boring beetle that chewed through the branded BS 1008 ply that was built in Asia. The ply was labelled BS 1008 but was junk, the builder took short cuts and the owner could not be onsite full time to ensure the build and material quality. Yes, there are many ethical foreign builders but you also have to deal with government officials who see you as a “rich” person and would like a contribution to allow your vessel out of the county etc.

Buying second hand of an undesirable type of boat (eg plywood trimaran) can be a real bargain if your prepared to maintain it properly. Buying smaller often helps reduce cost. The trade off is often the amount performance and/or accommodation you can get for your dollars. The jpegs are of a few boats mentioned above.

 

Going off topic, many many many apologies. It is boats but not multihulls. Please find some examples of Indonesian boats. The boats are high quality but I dont know if the style is suitable for multihulls, in that they use thick hardwood planking which would make the vessel heavy and slow, unless of course it was scaled up. The timber is not sustainably sourced. Sumatra is almost fully gone, Java timber is all long gone. Borneo is half gone, Irian Jaya in next, when they finish with Borneo they will go there, once Irian Jaya is all gone, then there will be little timber and people will complain.
tacking-outrigger.com Modern Indonesian Boats http://www.tackingoutrigger.com/modern_indonesian_boats.html

 

It is Antoine Richer, here is his CV :
https://www.linkedin.com/in/antoine-richer-naval-architect/?originalSubdomain=vn

 

Vik 71 (Ksenia 69) catamaran is a design by Eric Larouge. The bridge deck cat is 23 x 14.6 foot that in one version can be disassembled into a 7.6 foot package for transport. The weight is 2000 lbs and the displacement is 3500 lbs. The 30 foot fixed aluminium or rotating wing mast of 20 square foot mast carries a 215 square foot mainsail (with 2 reefs), a 130 square foot jib (can be on a furler), a 33 square foot storm jib (280 gsm about 6 oz) and a 440 square foot spinnaker (48 gsm about 1 oz). The headstay and the majority of rigging is 6 mm 1 x 19 stainless steel wire. Halyards and most ropes are 10 mm with 12 mm sheets. The hulls draw about 2.1 foot and have NACA low aspect keels and spade rudders. The length to beam on the hulls is about 7.5 to 1.

The intention of the Vik 71 design is to offer adequate comfort to a small family for costal cruising. The central pod has a small galley with 4.8 foot headroom (could have a removable hatch above the floor space to get 6 foot) and accommodates a dinette which can be converted into a double bed. The floats have two extra berths and the toilet.

I do not know if Eric Larouge is still designing as in France if a designer is “retired” he cannot sell his designs but I will assume he is still active. The design can be built home built from 10 mm PVC foam with biaxial cloths on either side in polyester or vinylester resin. The low aspect ratio keels are solid glass with a grounding shoe on the keel bottoms. In the home-built versions the bulkheads are plywood with tapes are biaxial with epoxy.

This is a wholesome small cruiser that would make a great fun coastal cruiser. The jpegs give the idea with the last 2 jpegs of a similar VIK 8 meter cruiser.

 

It is Erik Lerouge, here is his web site with his email address : elyd@orange.fr
Erik Lerouge http://erik.lerouge.pagesperso-orange.fr/catamaran.htm