Multihull Structure Thoughts

Yes, she is in good hands with her current owner.

He told me about a similar stuffing incident with the boat when it was in the Pacific Northwest where it hit a kelp bed with the full main and spin up which fouled the rudders and everyone was thrown forward and the boat capsized, after which I believe it received its current mast and sails which would have been just prior to his purchase.

I haven’t yet gone for a sail on it. Too busy with my own boats and still recovering from a rotator cuff injury, but looking forward to it next Summer.

Thanks for the stories, I’ll pass them along.

 

This is just a fun post folks. There is a myth that monohulls maximum speed is 1.34 multiplied by the square root of the waterline. That means a 100 foot monohull should have a maximum speed of 13.4 knots. The top 4 finishers (all 100 foot and all previous line honours winners) in the recently finished 630 mile Sydney to Hobart averaged over 17 knots. OK But that is not the interesting part.

The first 15 boats have averaged above 13.4 knots. 2 of those boats are TP 52’s. 52 foot boats are meant to be able do a maximum of 9.6 knots.

Next lets look at boats that have averaged just over 10 knots. The is a 34 and 36 footer that are meant to have a maximum speed of 8 knots. Both these boats are being sailed 2 handed in the 2 handed division and they are running 36 and 37 th overall.

The boat that is running 96 th is a 30 footer that is averaging 7.1 knots. Its theoretical maximum speed is 7.2 knots. At last, we have found a boat that is sailing to its theoretical speed. What is the boat, Malaluka, a 99 year old timber flush decker that has a gaff cutter rig, that has competed in the last 16 Sydney to Hobarts after restoration with 8 th overall (on Handicap, I wonder what the age allowance is) its highest finish.

All the speeds mentioned here are the average speeds for the 630 miles of what was a reaching run of about 15 to 20 knot wind speed. There is a light wind upwind final leg.

The jpegs are of Comanche 100 ft, Law Connect 100 ft (old speed boat), Patrice TP 52, Mitral 34 foot 2 hander and Malaluka 30 foot 99 year old gaff cutter.

 

A more recent design with a similar folding method is shown on page 7 of this thread. And Delaveau Multihull Design https://www.delaveaumultihulldesign.com/explorer-build.php

 

Hi Andrea, The 32R hulls are symetrical in cross section below the waterline, but have a pronounced chamfer panel on the inside of each hull, quite a normal feature in more recent designs as it gives more interior space without adding to waterline beam. Suggest you check out the work of Bernd Kohler, who has several (true) assymetric hull designs - including one or two with narrow versions for canals wtc. DUO900page https://ikarus342000.com/DUO900page.html

 

Hi, another year begins, I hope you will have many days of fun on the water and some evenings dreaming of being on the water. We will start slow with a few boats then do some items on RedRueban topic of small cruising boats. The first boat is a production cat that had a relatively short life but was an interesting attempt. The Virus 8 was designed by Julien Marin for VirusBoats (producers of the Magnum range of trimarans). The Virus 8 is 26.2 x 15.4 foot with a weight of 1570 lbs. The rotating 39.5 foot mast carries a 258 square foot mainsail, 140 square foot jib, 323 square foot gennaker and a 645 square foot spinnaker. As you can tell from the sail area this cat was aimed at performance. The hull length to beam is about 12 to 1. Now we get to the reason I think this boat had a short production run the keels are low aspect ratio fixed keels. The cat draft is 2.4 foot and has fixed underslung spade rudders.

Low aspect ratio keels have been tried previously on a sports cat (the International 23 Crowther cat). They are done for cheap production (no dagger cases and kickup rudders), improved internal space and simpler handling for novice sailors. The downside is the cats are slightly slower in light airs due to increased wetted surface, don’t point as well and can be slightly heavier. The Virus 8 tried to overcome these slight impediments with larger sail area and hiking seats to provide more righting moment in higher winds. Virus 8 video’s give a good idea of this boats sailing capability, it can be fast on most points of sail. Only racing purists would want more performance. Now we reach the problem. The racing purists would choose something else but the cruisers want more space and headroom for there money.

Tests of the Virus 8 lead to these quotes “Not surprisingly she was able to sail a little faster than the wind. And she slices through the waves with her wave piercing hulls just as I had expected her to do. Today the "test pilots" took her up to 15 knots and managed to get one hull out of the water. More to come. And she performs incredibly well upwind…tacking was a little bit difficult at first but with just a little practice it was easy. Keep the speed up (not difficult in this boat) and tack slowly.” And “In difficulty in the very light airs close to the coast, notably to windward (but a code 0 would help), it really came alive once the breeze reached 6-7 knots, to allow the GPS to display values which changed when the wind increased or decreased by 1 or 2 knots.” Translation once the winds are above 6-7 knots you have a very good performer that requires some care in tacking. All as expected with a low aspect ratio keeled performance cat.

The accommodation is basic, 4 berths limited cabin space with a portapotti, a small galley and limited headroom. The construction is fiberglass with foam in many parts. The crossbeams are 2 large aluminum tubes with the mast beam having a stainless steel dolphin striker. The above water chine is used to stiffen the hull and provide slightly increased room. The Virus 8 can be disassembled for trailing.

An interesting cat in a size a lot of people want but it is a very difficult size to provide both accommodation and speed. Richard Woods ELF production cat comes close but is still not sold in large volume. The jpegs give the idea.

 

A short one about what can be achieved if you want to race across the Atlantic. The first cat was created by Darren Newton as a Mirco racing catamaran he built in 1994. It is an open bridge deck tube catamaran. The F26 is 26.2 x 16.4 foot that weighs 2560 lbs. The rotating wing mast carries about 400 square foot of sail. This boat has daggerboards. Reasonable so far.

So, what do you do with a coastal racer at best with limited accommodation. You do a dual handed Transatlantic race (sailed Darren Newton and Bob Beggs) for fun. The Dazcat F26 Clarks Active Air was in the 1994 Transatlantic Race winning their class. Then Bob Beggs decided he would do a single handed Transatlantic race. The F26 has “limited” accommodation, that means two small single berths and some storage. Deck protection was the clothes you wore and comfort depended on the weather.

The F26 was built in Airex PVC foam with e-glass and aluminum cross beams.

Next cat is the Firebird designed by Martyn Smith for Modular Moldings who built 18 of the cats starting in 1986. The Firebird is 26.3 x 17.2 foot with a weight of 1200 lbs. The rotating mast carries 385 square foot of sail. The hull length to beam is 14 to 1. The draft is 4.6 foot over the daggerboards. The rudders are underslung but kickup with part of the stern. This cat was designed for micro multihull racing and at best was to be used for coastal racing.

Pete Goss (ex Paratrooper) successfully raced one (Cornish Meadow) in the 1988 single handed Trans Atlantic race finishing second in class in 23 days 3 hours. Pete endured some serious weather conditions. Several others won several races and micro multihull championships (attached is the back page of the Firebird brochures listing some). A Firebird was used as a trailer sailor across Europe. The accommodation is basic with 2 berths and a minimum of anything else. One person who owned one said he would never sail any more than 300 miles in a Firebird as that was as far as he could go with one over night stay.

The Firebird is a very well built foam uni directional glass throughout with carbon fibre in selected parts like the cross beams. The main mast beam is composite on Firebird and weighed 17 lbs.

Both the above cats were designed and built as at best coastal sailors but in the hands of competent skippers have crossed the Atlantic on several occasions. These guys are tough and are willing to put up with the discomforts that come with small multihulls produce while in rough windward conditions. But if you are capable the boats can reward you with some excellent performances at a minimal cost.

There is only 1 jpeg of the F 26, the rest are of the Firefly.

 

This is a simple tri that was intended to be a dual purpose mini cruiser. The A18 T initially was built as a day sailor with an option to put a small cabin on the main hull.

The tri is 18 x 15 foot with a displacement of 800 lbs The fractional sail plan (from a EG Hobie 16) that has a 26.5 foot mast and carries 218 square foot of sail area. The main hull has a 6 to 1 length to beam ratio. The float length to beam is 13.7 to 1 which is good for fast sailing. The floats flattened-out towards the sterns to provide added lift when sailed hard. The floats have 125% buoyancy of the tris displacement. The multichine main hull has a Prismatic Coefficient of .573 and the floats have a Prismatic Coefficient .63. This means the floats have “fuller ends” relative to the maximum underwater section of the float hull where as the main hull has less full ends relative to the main hull maximum section. This allows the floats to perform better in heavier airs where the main hull may be starting to “plane”. Trimaran design is a little tricky compared to catamaran design. In cats both hulls are basically the same shape and sections, in tri design to get the best performance the main hull and float shapes are different to get the best performance across a wind range and to minimise pitching. The draft is 150 mm to 3.3 foot if board and rudder are down.

The main hull is constructed from 1/4" marine ply with 1/4" stripped cedar decks. The boat is glassed inside and out. The 15.9 foot floats are constructed of 3 mm plywood again glassed inside and out. The cross beams are aluminium with water stays. There are a few bulkheads in the hulls but the multi chine shape provides the fore and aft stiffening for the hulls. The initial build was done without the cabin but was neatly finished for fun cruising with the kids etc. A minimal camp cruiser for a weekend away. No performance numbers were provided but the builder owner was “satisfied” with the performance.

The jpegs give the idea.

 

Small cruising multihulls can be as short as 21 foot and I have limited the length to 27 foot. All of the boats listed below have done at least 2000 miles non stop in open ocean. The real issue is what is a cruising boat? A Tiki 21 has circumnavigated, but could you live in a narrow single berth with no seating headroom, minimal storage and payload capacity. In reality you need a minimum of 500 lbs payload capacity for each crew including associated water and stores etc. I think the minimum accommodation would be 2 single berths that are at least 2 foot wide, there is sitting headroom in an enclosed cabin and there is an area for a galley and a porta potti.

By this definition a Tiki 21 is a weekend camp cruiser, a Tiki 26 is a month long cruiser. Longer durations than this depends upon the willingness of people to put up with discomfort. To quote Bernard Rodriguez who sailed Amistad (Dart 25 ft Piver trimaran) to England in 1968 and entered the Observer Single-Handed Transatlantic Race (OSTAR). He described these passages, especially the race back, as harrowing experiences. Seaworthiness was not the issue. With high buoyancy floats, and a huge strength-to-weight ratio, Amistad is a very tough, fast, safe little yacht. But her “cabin space” is so tiny as to hardly deserve the name. What you go through offshore, trying to live, eat, sleep, and navigate in something like a 4 x 9 foot space with 5 foot headroom is almost beyond description.”

What is being said is cruising is a phycological game as much as it is a physical game. If you want to see the world and voyaging is a chore, being in a small confined space will only lead to problems. If it is adventure, challenging yourself, testing your limits and really getting off the beaten track for long periods then small boats cruising can provide a view into some very interesting worlds, then many discomforts of small boat cruising will be tolerated.

If you can live in a small tent for a month, you may find an under 23 ft boat OK, but if you and your partner like RV’s, apartments or houses the only 3 boats in this group will be OK over the long term for most. They are the Heavenly Twins, Catalac 27 or Farrier F 27. They provide the wide bunks, separate galley, separate toilet space and some internal seating room.

Tomorrow we will talk further about the boats performance, capabilities etc. The first jpeg is the table of boats and trips. These are a subset of what I found but it gives the idea. The other jpegs are some of the boats mentioned. PS I do not support an inexperienced person doing a long trip in any of these boats, please gain experience in EG heavy weather sailing, long periods of living aboard etc before you try any trans ocean sailing.

 

The above mentioned micro multihulls are all still quite luxurious in comparison to the tiniest monohulls that have crossed oceans - here is an interesting article about them.
Smallest boats: The bonkers world of Microyacht adventures - Yachting World https://www.yachtingworld.com/features/smallest-boats-the-bonkers-world-of-microyacht-adventures-141574

They mention the 3'10" long boat Big C, which will be setting off across the North Atlantic next summer, from west to east - with a 6' tall bloke on board.
More about Big C on her Facebook page -
Big C Atlantic Challenge https://www.facebook.com/profile.php?id=100082612007911

 

Part 2 of small cruising multihulls. Of the really small multihulls (below 23 foot) only Rory McDougall on Cooking Fat (Tiki 21) did repeat ocean sailing over many years. The Berque Brothers, Thomas Firth Jones, Tony Bigras did only one substantial multihull trip on each of their smaller boats before they on sold their boats. In each case they had no doubts about the boats seaworthiness but there was insufficient space and payload capacity for serious cruising. The Berque Brothers, for example, went across the Atlantic and cruised Florida for 2 years in a 14 foot monohull comfortably.

From 23 foot up the interior space and payload capacity was sufficient for the boats to be practical long distance cruisers. EG Kliss (23 foot tri) sailed from England to New Zealand over several years. Tom Corkhill sailed his Clipper 25 foot trimaran from Brisbane to South Africa before being capsized by a wave. The Seawind 24 open bridge deck cat with 2 adults and 2 children spent a year sailing the Pacific before they stopped due to a son’s medical issues.

On the topic of speed every boat in this group will sail 4 knot to 8 knot averages. The F 27 will do 10 knot average’s if pushed but that is not cruising reality. It did not matter what size of boat I sailed on under 50 foot in cruising mode, we would sail at about 8 knots maximum for both comfort and ease of sailing. You could have a smaller jib and reefed main which would still give a comfortable speed with minimal requirement to do any sail handling if the wind started to rise. PS some of these boats can peak at over 18 knots but the Heavenly Twins and Catalac are 13 knot peak sort of boats.

Now we come to the topic of seaworthiness. Two Rabbits (Wharram 22 foot Hinemoa modified around the deck for more internal volume) went through a hurricane. Several other boats have been through 50 knot plus wind storms. All of them survived. The major worry for most was not the wind speed but the wave action. Small boats can be thrown over by a breaking wave crest. Lock Crowther had research done and the general conclusion was any waves larger than the beam of the boat could lead to a capsize. The most effective way to negate the problem is to un a parachute or drogue off the bow or stern of the boat. This is an art form that needs to be practiced with very good equipment EG swivelling shackles, good retrieving lines, strong sampson posts firmly attached to the boat etc. The majority of these guys were conservative in their speed and boat handling.

The numbers give an idea of what is required in the design of a small cruiser. A minimum length of about 23 foot will allow about 1000 lb payload capacity and a boat that has a sail plan and righting moment that will handle at least 23 knots wind speed before capsize. You would be reefing at under 20 knots of wind speed.

In short, if you have a sense of adventure AND you have sailing/seamanship experience, then enjoy your long distance sailing in a smaller boat BUT be mentally prepared. Joe Culprit who built and sailed the 54 foot trimaran Virgin Fire started sailing a 29 foot Warrior tube cat for months. Joe stopped sailing the Warrior because it was “closing in on him” and he felt trapped. The Warrior and Joes sailing skills are very good, it was just a mind limitation. A few jpegs give boats and some internal space idea.

 

Small cruising multihulls jpegs part 2.

 

The jpeg associated with this post "small offshore multihulls" has Miss Cindy as 3304 lbs displacement. She actually weighs a little over 1000 lbs at full load. This makes her righting moment around 3000 ft-lb instead of 9730 ft-lb. Also, in Tony Bigras book, Travels with miss Cindy", he claims 15 knots as top speed instead of 17 knots

 

Re the 5 metre Berques cat in post 3040 above, here are some photos of her that I took here in Barbados 13 years ago.
I just happened to see her at our only haul out yard and was quite intrigued by her then.
I think that she might have been shipped here, and was going to be launched soon - she did not look like she had just sailed across the Atlantic.

 

David. Thank you for the correction. We will take Miss Cindy upper displacement according to Tony web page at Travels with Miss Cindy. Specifician and Equipment. https://turtleislands.net/tmc/specequip.html This is 1100 lbs. This will lead to a righting moment of 3245 foot lbs and a maximum wind speed of 17.5 knots before capsizing (the 17.5 knots is not boat speed, it is wind speed). I miss read the displacement number from the calculation table I used for these boats but the capsize wind speed was correct. The numbers in the table of 17 knots or 23 knots etc are the wind speed that will cause a capsize if the sheets are hard on in a close reaching or upwind situation. But thank you for pointing out the mistake.

As of the September 2022 Miss Cindy was for sale after Tony Bigras did an upgrade. Price was about $5000. It is on his web site. Miss Cindy for sale https://turtleislands.net/mc/MCForSale.htm

 

This is about boat size versus materials. I will only focus on 1 component, cross beam of Wharram cats. We will speak about the Tiki 21, Tiki style substitute (plans available from Wharram) cross beams for Tane or Tanenui (27 foot), Tiki 46 and Phai 63 beams. If you think a Phai 63 in only 3 times longer than a Tiki 21 therefore should only take 3 times longer to build, you will be surprised.

The Tiki 21 has 3 cross beams each of 120 x 20 mm top and bottom timber flanges and a 15 mm vertical plywood web. The beams are 12 foot long and are 175 mm to 125 mm high.

The Tane or Tanenui has 3 Tiki type beams that have 120 x 19 mm plus 2 layers of 88 x 19 mm plus a 32 x 32 triangular timber insert on the top and bottom flanges of the 2 layers of 15 mm plywood vertical web. The beams are 12.5 foot long and 200 mm high.

The Tiki 46 has 4 full beams and a half beam that have 140 x 70 mm laminated timber top and bottom flange with 86 x 56 mm corner flanges. The 2 layers of 19 mm plywood make the web. The 4 main beams are 24 foot long and 450 to 360 mm high.

The Phai 63 has 4 main beams and 2 secondary beams fore and aft. The main beams are 146 x 76 mm timber flanges top and bottom with 76 x 52 corner triangles on a web of 2 layers of 19 mm plywood. The beams are 28 foot long and 390 to 350 mm high. The 2 secondary beams are the same structure but about 300 mm high.

In all the above I have not included any secondary timbers and bogging of corners or fiberglass over the beams etc. The jpegs below (all from the web) show you the designs and concept.

Now let’s compare the materials to build the Tiki 21 beams versus the Phai 63 beams.

All 3 of the Tiki 21 beams would take 18 square foot of 15 mm plywood and 1.9 cubic foot of timber. All 6 of the Phai 63 cross beams will take 436 square foot of 19 mm plywood and 56 cubic feet of timber.

The Phai 63 takes 24 times the amount of plywood and 29 times the amount of timber to build the beams than the Tiki 21 beams. The cost of the beams for a Phai 63 will probably pay for a complete Tiki 21.

Translation of the above, don’t build a boat bigger than you need, big boats cost a lot of time and money. PS please don’t use the above crossbeam specifications in any other design, Wharram design unique cats that require a specific type of beam for there purposes. Hannke Boon has warned others against putting EG aluminium beams on a Wharram as they do not have the design characteristics suitable for a Wharram cat.

The jpegs give the idea.