Multihull Structure Thoughts

I had a play around with the numbers on CM for some of my projects but now with the price of good ply it doesn't yield cost benefits imo. When good quality ply was cheap and labor to help with the build was affordable it probably made all sorts of sense. The area where it seems to still make sense is relatively small multihulls with 6mm hull thickness and not needing sheets to be scarphed along the long axis. I put together a half hull as a test on the small mould out of cheap 3mm luan ply and it worked well and achieved the required shapes but in larger builds where shell construction is a lower proportion of overall cost and the risk of having a whole hull side fail I can't see the economies.

Having said all the above if I could get 100 sheets of good quality 3mm ply at the right price I'd still have a go at it. With Gaboon marine ply costing about $100AUD a sheet it isn't viable. I bought Kurt's 43' cruising trimaran plans because I think its a great boat but whether I'd build in CM or not would have to be determined by cost at the time.

 

We have posted about the Scarab 32 trimaran before but this is an update with some additional information. The 32 is 32 x 24 foot with a weight of 5,500 lbs. It carries a 44 foot mast with a 432 square foot mainsail and a 205 square foot self tacking jib. The float displacement is 6,600 lbs. Auxiliary power is a 9.9 hp long shaft OB. The tri can be folded to be trailed with an oversize permit (10 foot wide).

Ray Kendrick and his partner have built the first Scarab 32 which will be used as his retirement boat. The plans of the Scarab 32 have a sloop rig and a daggerboard, Ray’s personal boat is proposed to have a schooner rig and a low aspect ratio keel for his "long term cruiser” Scarab 32. I do not know if the boat is formally launched yet as where he lives have been under a series of floods for 6 months.

The first build was mainly a foam glass build with solid glass, some carbon fibre cross beam caps and aluminum cross beam struts. If good plywood is available you can opt to build the design in plywood again with fiberglass beams. The ply version has glass inside and out. The hulls are chine which makes the shape easy but chine lines are difficult to make look “good”.

The reason for this post is to alert you to some construction jpegs are at: Building a Scarab 32 Cruiser. http://www.yendys.com.au/Scarab%2032.html and a great PDF describing the build of the Scarab 32 outlining all the major steps etc. If you are interested in the design, it only costs $150 Australian and is a comprehensive full PDF design package with 49 drawings.

The jpegs give the idea and the PDF is the Scarab 32 build PDF.

 

I helped a mate build a CM 16' trimaran several years (decades) ago when ply was cheap. The system was quicker and produced lighter hulls than cedar strip. There were a lot of little tricks Kurt had discovered, which made it easier. The one he missed was chopping off the bows, adding a watertight bulkhead and a foam crash bow. Probably no quicker, but a lot less effort getting the bows of the panels together.

I sold the materials for 3 or 4 30-40' CM cats to Aus builders. All of them liked the method and Kurt's service. The boats looked great, floated where they should and the hulls were identical as far as the owners could measure. One of them had some trouble, flew Kurt over and he spent a couple of weeks sorting it out, gratis.

I met him a couple of times, found him to be a nice guy, who stuck up for what he designed, with facts, data and experience to support it. The status quo types ignored what he said about the boats, materials and build method and replied with personal abuse. Not much has changed. ;-)

 

The updated CM method uses a composite bow piece to ease up that area a bit, seems to work out well.

 

I like the foam bow and crash bulkhead idea for anything with a plumb or reverse bow.

 

Today we will talk about a Patent Attorney who did Ian Farriers folding patent. This man was also a major influence in the development in proas. Why is this important, because we are going to talk about a proa that is well described in concept but we know little detail about. This is a Patent Attorney skill, they describe the function of a item well but they don’t give dimensions. A Patent Attorney tries to EG describe a bolt and a nut function but wants the patent to cover all bolt and nut sizes to maximize the patent coverage.

John Pizzey designed and built at least 4 Pacific or Atlantic proas. The proa we will discuss is his last design in about 2013 called “Pi Hi”. This is a Pacific proa of 30 foot length and carries about 400 square foot of sail area on a 32 foot mast. The last real numbers I know about this design. I am guessing the beam is about 8.2 foot. Now we start to quote John Pizzey about the Pi Hi design:

The main hull and float: “The main hull has three steps in each side, like an exaggerated clinker construction, to provide narrow hull progress through the water and waves and flared topsides which provide a centre of buoyancy when π↑ (PI Hi in symbols) flattened, well out to leeward for self-righting. The float is virtually a replica of main hull to the first step. A long-shaft outboard motor is supported on a pivot mount on the central beam structure near skipper so it can be rotated about a fore and aft axis to and from the water and always disposed below the net with the remote controls near the skipper. There is full headroom in the central cabin. The high cabin, probably with vertical outside face or flared cabin side to match the hull has the beneficial effect of providing floatation well out from the CG when π↑ is flattened. A flared cabin side will enable the base of the inclined mast to be located as far as possible to leeward and that is a definite advantage.”

The mast: “The pivoting, preferably buoyant mast is supported centrally on outside of cabin top by a strut which extends from a mid position on the mast to the inside of the float. This provides an inclined pivot axis whereby as the mast pivots from its sailing position its upper end moves inward until the mast is vertical (athwartships) and then back out to the new sailing position. The mast has its minimum lean when locked centrally for non-sailing activities. The roller furling headsails are 3/4 or 7/8 rigged with the drifter and spinnaker set from the masthead. Halliards external and mast sealed, a carbon tube would be best although a round aluminum tube would be cheaper.”

The sails: “The tack of each working headsail incorporates a furler connected to the hull through a strop, preferably a length of chain for easy adjustability for fine tuning and probably tied with shock cord to limit shock loads as the mast pivots to the extreme of its travel. This strop enables the mast to pivot to its new forward position when the forward furler is winched down to a windward position along the fore-beam to provide the necessary sheeting angle. The sail trimming sheet passes from the sail to a turning block on the hull, probably at the end of the aft beam to a set of turning blocks along the aft-beam to a winch beside the skipper. The set of turning blocks is also used to lead drifter and spinnaker sheets to the winches. This sail furling lines pass to respective winches on the cabin top where they can be reached by standing centrally in the cockpit in the roof cutout which also provides easy access into and from the cabin. However the furling lines are interconnected to furl/unfurl together with sufficient slack when they are removed from the winches to enable both sails to be furled.”

Sailing: “The skipper sitting aft under cover has his hand on the rear rocking tiller. The front rocking tiller is pinned at a positive angle of attack to provide lift to windward and to the nose of the main hull which will be heeled about 15° when pressed. The rear “headsail” is furled. With the drifter (isosceles triangle sail with line from each corner, front one pulled tight to windward and rear one becomes the sheet) the skipper can ghost along surprisingly quickly to windward or anywhere else when every other boat has their sails hanging uselessly, including the monohulls with their crew to leeward who can’t get their boat to heel to 15°. This sail can be held onto to windward until the crew protest too loudly, probably about 15 knots, when further windward progress will require dropping this sail about its medial hoist line, too easy, then unfurling the forward headsail and continuing, mostly on one hull and without concern of being caught out by a bullet. Sailing downwind, take your pick, one headsail set; two headsails set wing ‘n wing; a headsail and the drifter; the drifter alone, or a spinnaker, it will all depend on the conditions, your course and your mood. You should be able to utilise barber haulers and poles to achieve what suits you.”

And in answer to a question from another person. “The dynamics of the hull design is probably most important aspect and modern computer simulations should be able to assist in coming up with the best hull form, especially Pi Hi rocker and fullness in the ends for a proa. Flight and Piawatha (2 previous proas John designed and built) were both rockerless although the ends of Piawatha did tuck up a bit. Again size is important as crew weight on a small boat with a lot of rocker will be more effective in raising the bow than crew weight on a rockerless hull.”

The jpegs show the concept of Pi Hi and some hull details etc. When John wrote this in 2013 he was about 70 years of age and I do not know if a version of this proa was built. Tomorrow we will discuss some of the other proas designed, built, raced and cruised. Very interesting concept from a person who has a LOT of experience in proa design, development and sailing.

 

As mentioned yesterday John Pizzey has designed and built several proas before yesterday’s design. Now forgive me I do not know if the details or order of the build of proas are correct. The first I am aware of is a 23 foot pacific proa Piawatha. Piawatha is a Pacific Proa with a Gibbons rig for at least part of its development. The jpegs give the idea of the proa. Again, I do not know the final dimensions of the vessel beyond it was trailable which means an 8.2 foot beam. Several rudder arrangements were tried on this design.

Next came Flight which was a 30 foot Atlantic proa initially. A variety of rigs and rudders were tried on this version and this boat was eventually converted to a power proa.

The next proa I am aware of is PI which was a 30 foot Atlantic proa again. There is a patent document available about this design which is included in the attachments. Again, little detail but this proa was raced in the Brisbane Gladstone race and local events. With the right crew on board, it was fast but with people of limited experience it could be difficult for them to get good performance from the design. I have tried many rudder combinations: inboard; in main hull and in the float; formed as articulated ends of the hull; as well as hung from the side of the main hull and from the float.

The final form used in Pi was a spade rudder at each end of the float, one a balanced spade steered manually by a wheel which rotated about a transverse axis and the other a symmetrical spade adjusted, and held against rotation by a hydraulic ram and operated from a button next to the helm. The electrically operated spade could be adjusted to provide lift whether at the front or the back and the boat steered with the other rudder, whether at the front or the back. This improved windward performance remarkably as both rudders were at all times providing lift to windward. I would always incorporate an arrangement in which I could take this advantage which is peculiar to proas.

The rudder shafts of Pi were inclined slightly fore and aft and I made foils to sit underneath the rudders at the same angle such that the rear foil would always be horizontal and the front foil inclined with a positive angle of attack equal to double the inclination of the rudder posts, so as to positively lift the float bow. I never fitted these foils as the lift in Pi came mostly from the sails. She was already extremely radical but surprisingly successful after sorting out a few teething issues. On Flight I eventually abandoned the articulated ends and went to spade rudders in cases so they could be raised for beaching. Flight, with no rocker, floats in less than 6 inches of water from memory. I prefer to leave both rudders down with the front locked at a positive upwind bias.

The next proa was Addwater proa, Flight, is a narrow flying proa which is self righting from a knockdown, proven on countless occasions. It utilized a rig canted off to leeward. The cant angle was fixed bit it could be made adjustable for wind strength, laid off for heavy winds and only slightly off upright for light winds, this allows the sail weight to curve the sail to the airfoil shape and enables the boat to sail in a breeze so light every other boat has stopped. In such conditions, Flight would keep sailing and be readily controlled, shunted and sailed in any sailing direction giving great pleasure. In this situation the big isosceles triangle sail is tops - like a big reacher.

The final proa is a modified Pi due to medical issues, Pi was converted to a power boat with a large covered cockpit. It was 42ft long, a 100HP outboard alongside the main hull and a 50HP on the float. Pi powered does 20+knots flat out and cruise at 10 knots using about 10 liters per hour.

John also in 2013 designed Pi Hi as in the previous post. To give you an idea of John Pizzey words please look at the following web addresses:
Proa File | The Proas of John Pizzey - Part 1 https://proafile.com/multihull-boats/article/the-proas-of-john-pizzey-part-1
Proa File | The Proas of John Pizzey - Part 2 https://proafile.com/multihull-boats/article/the-proas-of-john-pizzey-part-2
Proa File | The Proas of John Pizzey - Part 3 https://proafile.com/multihull-boats/article/the-proas-of-john-pizzey-part-3

The jpegs start with the 23 foot Piawatha, next Flight, next PI and the motorized version of PI. The final PDF is John Pizzey proa patent.

 

This is 2 parts, written by Chris Morejohn who was a part owner of Hellsbay boats who produced boats between 16 and about 24 foot. The jpegs give and idea of the 16 and 18 foot models The 16 foot Microskiff performance, with “a big-water ride” is 16.3 x 5.9 foot and weighs 595 pounds. Powered by 60 to 70 HP outboard. Draft of hull is 0.6 foot. Hellsbay boats now do Carbon Innegra ™ hull, Vacuum-Infused Core Cell ™ construction throughout entire structure, Carbon fiber stringer system and 100% Vinyl ester resin. This is not about multihulls but the “true” costs of building a 16 to 18 foot power skiff in about 2002. The numbers will be different today but you will get the idea of how and why some skiffs cost what they do. I have edited the original post to make it shorter but the concept is the same.

Chris from here: “With my basic information presented here you can go and look at your skiff or any other and add up the numbers to get a good idea of what it's original cost was, is and where all your hard earned money is going.

The first thing you have to know is what the materials cost the builder. If you build lots of boats then you can get a slightly better discount on goods bought wholesale from either the manufacturer or the vendors that buy in bulk and resell to you. Most flats skiff builders are building a small amount of boats a year. Less than 200 is the norm. Small shops maybe 30-40 a year. The difference between these two shops will differ in buying power by very little between the two. The smaller shop will have smaller overhead verse the big shop with employees and all that goes with size. So, if a small time builder is producing 20 skiffs a year with low overhead but is charging the same or more than the big shops the potential for profit by a per skiff basis is way more than the bigger shop. But that profit is limited to 20 skiffs so the bigger shop can be way more profitable in the long run. I will be describing here a materials list that will fit any of the top end skiffs I built in 2000-2001 from 16'-18'.The only real difference in cost will be the slight added amount of fiberglass materials for the slightly longer hull and the added length of the rub rail. All the hardware is the same for most all skiffs. The time difference to add this hardware to a 16' skiff verse an 18'er is nothing. The fiberglass labour to build the bigger skiff comes to about 12% more. The prices here are from 2001. I will show a basic break down of one of my skiffs.

PARTS AND HARDWARE: This is all the hardware, rub rails, electric wires connectors, cushions, battery's everything needed to put the skiff together. $1,627.00

HYDRAULIC STEERING: This is what the whole setup costs including an Edson wheel. $1,114.00

GELCOAT AND RESIN: - 14 gals. For hull average, - 10 gals. deck , hatches, - 2 gals stringer, - 4 gals. Bulkheads, - 4 gals cockpit floor, - 4 gals misc, for tabbing in parts

38 gal total but will vary a bit between hull lengths by about 10-12%, $15.00 a gal. For vynelester resin= $570.00

GELCOAT: 7 gals. For entire skiff about 5% difference between lengths. $120.00

FOAM CORE: Either Dyvinycell, Kledgecell, or to me the best core, Corecell. For the 16 foot flat power skiff:

- 180 sq. ft. Hull shell 3/4", - 108 sq ft deck 3/4", - 42 sq ft floor 3/4", - 48 square foot bulkheads 3/4" and 1/2", - 12 square foot stern 3/4" hard foam, 4.5 sq ft tower lid 1/2" - 3 square foot misc deck supports. 1/2",

- 6 square foot rod racks 1" hard foam, Total of 403.5 square foot Core in varying thicknesses, densities.

- 7 gals bonding putty, - 3 gals bonding resin used, total of $ 1,516.00 to bond core in skiff.

FIBERGLASS CLOTH, KEVLAR , CARBON FIBER CLOTH: Following is the layup schedule that I have used on most of the skiffs built during this time period. Technique improved over the years of building EG vacuum bags but the original hand built with roller and bucket is still going after 32 years. (Chris sold out his share of the business in the early 2000’s and as you will see the boat manufacture has changed a bit)

HULL LAYUP: - gelcoat. Let cure, - 3/4 oz. skin out CSM. Let cure, - 1-1/2 oz CSM, - 10 oz. layer Kevlar cloth, - 1-1/2 oz. CSM Above three all at once, let cure - fill in strakes with putty, let cure , agitate hull skin for core bonding,

- bond core. Let cure, - fair core , fill voids, - 3/4 oz. CSM, - 7 oz. layer eglass cloth laid up with Matt all at once.

DECK, HATCHES, COCKPIT LAYUP: - gelcoat let cure, - 1-1/2 oz. CSM let cure, - bond core let cure, - fair , fill voids, - 3/4 oz. CSM, - 7 oz. e-glass cloth, all at once with CSM

BULKHEADS: - one layer 7 oz. e-glass cloth on bare core.

STRINGERS: Depending on floor size, stringers vary a bit. Described here is a simple hat stringer. Some I use are shaped like an H. The core is doing all the work, the stringer is just to support the floor. If the deck and the entire skiff is bonded as a whole then you do not need lots of thickness. In skiffs that have their decks riveted on or screwed on then it's a whole other story.

- 2 - layers 1-1/2 oz. CSM with a 12" strip of Carbon unidirectional laid down the middle all at once.

- 40 yds 3/4 oz. CSM, - 40 yds 1-1/2 oz CSM, - 14 yds 10 oz. Kevlar cloth, - 32 yds 7 oz. e-glass cloth, - 12' Carbon unidirectional cloth. Material Costs total $ 615.00

TRAILERS: Vary in cost but have a very high markup from whole sale from - $750.00 standard trailer to - $ 1,300.00 top of the line

ENGINES: All boat builders that have boat dealers can buy their engines from the manufactures if they can afford to be affiliated with them. That means you have to be able to have enough boats going out the door to be able to sell to dealers at a discount so that they can resell at a profit. If you can buy $100,000.00 dollars worth of engines up front then you get them for a great price. The deal is they go on the boat and boat dealer sells the boat and only he gets to do the warranty work or future maintenance on it. As a builder once out the door it's out of your hands. Now as a boat dealer engine sales shop you can buy engines from the manufacturer but at not as great a savings. What the manufacturers do is give them rebates for every engine sold. Sell a lot of engines and you make your profit from this. What does all this BS mean, if you are a small shop what you do is find a motor dealer and get him to sell to you at just above his cost with him getting the rebate and you maybe passing the savings onto the customer. What you are really after is the boat sale with lots of options to install.

A Big foot Mercury 60 hp cost whole sale $ 3,544.00 with the prop costing $210.00 more.

So, the materials and component parts add up to: - $1,627.00 parts, - $ 1,114.00 steering, - $ 570.00 resin, - $ 120.00 gelcoat, - $ 1,516.00 core and bonding putty, - $ 615.00 fiberglass cloths, - $ 750.00 trailer, - $ 3,754.00 60 hp Merc

A Total of: $ 10,066.00 for the total boat cost in materials wholesale to get it out the door in 2000-2001.”

So far, we have only talked about the materials used and costs. Tomorrow we will talk about the labour and add on expenses to build a 16 to 18 foot skiff. As you can see from the above the actual shell structure only uses EG 24 out of the 38 gallons of resin. Just adding up the shell surface area and “calculating” the cost of a shell, you may only estimate 65% of the EG resin you may require. Also, if you are going to build a one off you will use more materials, have more wastage and have higher costs than a professional production builder. The jpegs below are samples of the type of boat being discussed.

 

Part 2 of the Skiff build. This is about the labour and additional costs in the build of a 16 to 18 foot monohull power skiff.

You have all the materials you need to build a skiff, you now need to build the dream skiff. You will need cash to get your shop and build your plugs and molds and then your first hull. If you can do all the design work your shelf, all the plug and mold work on your own and then build the skiffs on your own you will save a ton of cash. But you will only build a few skiffs a year. This I did in my early years making a living but could always see that if I could just build five times the amount I could then make a good profit. Thus in come the employees the added costs and so on. By the time I sold out my share of Hells Bay Boatworks to my partners we were a well oiled machine with many boat models, a very low overhead as we owned everything built to date and only had the mortgage to pay and the standard cost of having employees.

LABOR , EMPLOYEES:

This is a break down of what I think your average hired fiberglass workers, riggers should take to build a skiff. The hours I show here can vary a bit but not widely unless you have very new, or very slow workers. If you are infusing a skiff with high tech epoxy resin the labour is about the same or less with a crew that understands the process. The rise in cost is in resin only. But you want to put in all these new fancy cloth weaves that sound so great on paper. Not for me! Waste of money. I feel all the hybrid Biaxal take up more resin, and are prone to high impact shattering because of the way they lay. An infused epoxy hull with these cloths having to be pulled and compressed over many tight lifting strake angles is a pain in the butt. As soon as your hull has been lifted out of the mold go and look at it to see all the little air bubbles and resin pockets in the cloth and Chines. But oh! When we go to paint over all this you can fix it then. Not for me.

Ask your builder why a hull that is so light with so little resin used and so little cloth needed costs so much. Do the math, a 375 lb skiff can't have too many gallons of resin and cloth. The cores the same pretty much for all skiffs.

TO BUILD A SKIFF - THE HOURS: - wax molds. 2 days, - spray gelcoat all parts. 1 day, - skin all parts, layup all parts 2-3 days, - core boat - by hand , Vacuum bagging, or infusion. 3-5 days, -finish glass all parts. 2-3 days, - remove parts, cut , trim parts. 2-3 days, - assemble boats from all parts. 7-10 days - rig skiff, carpet, tower all hardware. 3-4 days, - rig skiff electrical. 2-4 days, - install motor, steering 2-3 days, - finish details, fix dings etc. 1 day

Total 27 days x 8 hours a day = 216 hours to build, rig an average skiff as described without options. 39 days max worst case scenario. If this is happening you need to see what's up to get the hours down. Let's split the difference on the two and end up with 280 hours to finish. 280 hrs. X $ 20.00 US average wage cost back then = $5,600.00

Workers costs back then were from $11.00 an hour to $ 18.00 with most in the $ 13.00 an hour area. The two shop foremans wages were more. The wages of the owners are included in my estimate. We had a health plan for all employees. We gave out bonuses every year to all employees.

Total costs of materials and labour. The two costs ; $ 10,066.00 materials, $ 5,600.00 labor for a total of = $ 15,666.00

Now we have to add in the mortgage, building insurances, advertising, extra employees like the secretary, alarm company, electric, waste disposal of acetone, lawyers, company trucks, inventory, future plug and mold building, tools needed, dinning out smoozing clients and so much more. In today's Internet world you can do very well advertising through facebook, instagrame, and other venues for very little.

To wrap this thought process up the average cost for a top end skiff out the door in 2000-2001 cost about $18,900.00 to $20,000.00.

Again we are seeing the shell "build" takes about 12 of the 27 days. The rest of the time is spent on internal building, finishing, installing equipment, selling etc. One off boats would take longer. the jpegs give a small idea.

 

I just built some tortured ply hulls from 4 mm Okoume and the cost seemed very reasonable compared to the 4 sheets of 1/2" foam it took to make molded decks. The decks took lots more resin, carbon, and glass than I had expected as well. The hulls were hand laminated with 200 gsm discount carbon inside & out, which didn't take as much resin as I had expected. Finished weight 160 lbs each at 27' long

 

Another data point.
Next year we are running classes in Fiji to build 8m (26.5') versions of the mini cargo proas I was involved with in the Marshall Islands a couple of years ago: 7m (23)' long, 6mm (1/4") ply and stringers with 200 gsm (6 oz) glass. 2 people could carry the lee hull which weighed about 80 kgs (177 lbs).

The Fijian boats are 10mm (3/8") H100 PET foam (environmentally preferable to pvc foam and a little tougher but 25% heavier for similar properties) with 400gsm (12 oz) glass outside, 200gsm (6 oz) inside.

The sample pieces we have made use 200g/sqm of resin each side to fill the foam. The hand laid glass uses 1.3 times the glass weight, incl a filler coat. 1.5 times when the joining fillets are added. These are as expected.

So, 1 kg (2.2lbs) of foam + 600 g of glass + (600g x 1.5)+.4 of resin = 2.9 kgs per sq m (10 ounces per sq').

The 18 sqm (200 sq') of hull, decks, cockpit and bulkheads will weigh ~50 kgs (110 lbs) with a freight capacity of 1 tonne/ton.

Materials costs ($US):
200 gsm glass $1.10 ($0.10c per sq')
400 gsm glass: $2.20 ($0.20c/sq')
H100 PET Foam: $12 ($1.12/sq')
Epoxy: $9 per kg ($4/lb)
Sq m cost: $27 Hull materials cost: $470

4mm okoume/gaboon ply costs $US24 per sq m, weighs 1.85 kgs per sq m, plus resin, glass, keel bog and stringers.

The students will build 2 boats (incl sails, spars and rudders) during the 3 month course, at the end of which we will use the boats to teach sailing and seamanship. They will then return to their villages to build, maintain and sail their own boats.

The plywood Marshalls boat was sailing after 5 weeks with a borrowed rig and rudder/paddle, but there was a lot of setting up, timber and ply scarphing, stringers, epoxy coating and other work that is not required in the foam boats.

 

Big warning, this proa was designed by a university professor as an homage to “traditional Micronesian ocean voyaging sailcraft (generically, Proa)”. He has built the proa which he described as a “new kind of asymmetrical multihull sailcraft that leverages modern (and mostly sustainable) materials and methods to create new synthesis that is a viable solution for pressing economic, social and environmental needs of island and coastal communities.” He is not into numbers or details in his writings and I do not know if he has any naval architecture support.

Back to the proa “Orthogonal”. “Conceived as a technological "middle way" to exploiting advantages of modern materials but designed to be built on a beach with simple hand tools. Orthogonal also seeks new design solutions for shunting sailplans. The goal is to design and build fast, cheap, easy to build and maintain, easy to sail, safe, ocean going sailcraft of a range of sizes for inter island travel and trade, fishing and other uses. We are now well into the Orthogonal project and have a 30’ outrigger craft mostly built.”

So from here we do an educated guess about the numbers of a combined Pacific and Atlantic proa. The proa is 30 foot long with 30 foot long float. The “schooner” rig masts are 30 foot high with a 200 square foot jib on each mast. “The key to Orthogonal’s design is that both sails are reversible in the sense that either vertical edge can be the luff (leading edge).” The jibs can either be shifted to each “forestay” or as is Bolger proa had 2 “leading” edges and a maximum sail draft at the mid point of the sail. With a boom at the bottom of the sail it can be “tacked for an aft easily. But if you are going to use the boat as a tacking proa the boom would cause a problem.

The main hull has a daggerboard for lateral resistance and a kickup rudder at each cross beam point for steering control.

The proa is mainly built from plywood which is mildly tortured to create an asymmetric shape in the main hull. All wood-wood joints are made using epoxy filleting. The float is symmetrical. The crossbeams for Orthogonal “are conceived like conventional masts – compression members held in place by stays – in this case one fore, one aft and one under. The beams themselves are of unique construction – four aircraft grade aluminium tubes in a triangular arrangement, wrapped helically in both direction in fiberglass cloth bonded with epoxy, with the interstices filled with liquid polyurethane foam. This created a light, strong and rigid spar.”

I think the limited jpegs will give more information. Simple design, I hope it works.

 

This is about the performance of the James Wharram designed Tiki 21. The Tiki 21 is 21 x 12 foot with a 800 lbs build weight and load capacity of 800 to 1000 lbs. The hulls are 3 foot wide at the gunnels. It has a 23 foot mast with a “wing sail” 140 square foot main and 80 square foot headsail. The draft is 1.2 foot. There is outboard rudders hung on a skeg but does not require a kickup. The engine power can range from 2 to 8 HP outboard.

Tiki 21 if built to plan are ply and timber mainly including the mast and crossbeams. The hulls are 6 mm ply using new epoxy/glass stitch & glue techniques. There are timber gunnels and diagonal stringers. The gunnels and stringers are 12 mm softwood timber. The 6 mm plywood bunk shelf and bulkheads are major structural components to stiffen the hulls and are bogged into the hull. The keel lines are 15 mm plywood with epoxy bog and glass. The deck and hatches are 6 mm ply. The cross beams on the plan are 100 x 19 mm top and bottom flanges on a 15 mm plywood web. The mast is a timber “birdsmouth” build or an aluminium tube. Claimed 400 hour build time but if you are a first timer it could be 1000 hours.

Now we talk about performance. The first is a built to plan Tiki 21 that has done 3921 nautical miles in local and coastal sailing.

Fastest indicated speed: 16.4 knots. Fastest corrected speed: 14.9 knots after adjusting for tide etc

Fastest corrected average speed over one nautical mile: 12.6 knots. Fastest corrected average speed over one hour: 10.2 knots

Fastest corrected average speed over a sailing trip: - 8.6 knots/17.3 nautical miles (reaching). - 8.4 knots/11.2 nautical miles (reaching)

- 7.8 knots/15.9 nautical miles (beat/close reach with the tide). - 6.5 knots/25 nautical miles (close reach).

The next Tiki 21 is “Cooking Fat” is a “built to plan Tiki 21 hull shape” in GRP with slightly modified decks. Rory McDougall sailed the cat around the world in the 1990’s either single handed or with a crew on some legs of the journey. Let’s look at the performance of the global trip.

Total distance sailed - 28,000 nautical miles
Daily average distance (calms & storm survival included) - 90.6
Average speed - 3.77 knots
Daily average distance ( calms & storm survival excluded) - 104.6
Average speed - 4.36 knots
Best days run - 176 miles under wind-vane; (7.33 knot average over 24 hours). 210 miles by hand-steering (8.75 knot average over 24 hours)
Worst days run - 30 miles backwards!

An interesting summary of the days at sea.

Downwind - 106.5 days. Beam reach - 70.5 days. Close hauled - 90.5 days.
Becalmed - 28 days. Lying-a-hull - 9 days. Towing a drogue - 1 days. On sea anchor - 2 days. Heaved-to - 1.5 days. Total days at sea – 309.

The difference in speed between day sailing and ocean crossing is clear. Both these cats are basically the same with similar displacements and rigs. During day sailing you can push harder in “calmer water”. Cooking Fat at times was dealing with 20 to 30 foot seas. Secondly Rory is a very good seaman depending on a windvane self-steering for a lot of the trip, result 4.36 knot averages. Also please note the amount of time Cooking Fat spent going upwind. Good windward performance is very important for long distance sailing.

I will have more tomorrow. The jpegs give an idea of the standard Tiki 21 and Cooking Fat.

 

Scarab 32.

The folded beam is 3775 mm. This may or may not be trailerable in your juristiction. It isn't in queensland without a commercial wide load permit. Oversize is limited to 2.9m as I recall. Unfortunately this isn't spelled out specifically on the website.

The plans are on sale at the moment for $100AU which is a remarkable bargain if it suits your purpose. I have the Avalon 9 plans. This boat could easily be stretched to 9.9 meters and built in foam and might suit somone looking for a boat that trails at 8'. It could be built with the simpler newer beam attachment system of the 32. In fact if you bought both plan sets (still ridiculously cheap) you could mix and match to build the boat YOU want, eg an 8' trailerable boat with centerboard, foam construction etc.

Plans for the Scarab 32 folding trimaran http://www.teamscarab.com.au/Scarab32Des.html

The price of the plans for the Scarab 32 folding trimaran reduced to $100 (normally $150) until the end of September.

Plans for the Avalon 9 metre folding trimaran http://www.teamscarab.com.au/Avalon9Des.html

 

Part 2 of the Tiki 21 performance. Today we will discuss some of the learnings about sailing a Tiki 21. A Tiki 21 is 21 x 12 foot with a displacement of about 1800 lbs full loaded with a 23 foot mast and about 240 square foot of sail. The mast can be a round timber mast of 100 mm diameter with 20 mm walls. The aluminium mast is 100 mm with 3.2 mm walls and no taper.

First the sail to discuss is the wing sail mainsail. The mainsail has a sleeve that fits around the mast and in theory is able to be reefed by pulling the sail down around the mast. Problem. When the mainsail is wet the friction between the mast and sail cloth creates problems. Some owners put zips or Velcro in the mainsail to allow the sleeve to be “opened” to allow the mainsail to be more easily lowered. Rory McDougall (global Tiki 21) comment is: “Mainsail is sleeved around the mast. My sleeve is permanent - no fasteners. It installs to mast when mast is down. I didn't want any zip or Velcro failures when I was crossing oceans. If I needed to repair it, I can't take it below anyway. For me it is the best mainsail solution for a cat!”

Next, Rory said “The mast definitely pumps when going to windward. So, it is important to build a strong mast base for the Tikis. You will always get some movement on a beamed cat. You can keep tightening the rig but you will just bend the boat - even the racing multis get this. A 3 stay rig with mast base that allows for some movement is simplicity itself. The lee shrouds will always have some slack when pushing hard to windward. The downside to this is that I have had one of the wires unravel under the top swaged loop after 5 years sailing round the world.”

Rory also said: “I do always prefer hanked on jibs for simple safety and better performance. I had a working jib on Cookie with reef halfway up to give a #4 size. Later on, I added a storm jib and a huge drifter for light winds. Last sail I added was a genoa that filled gap between working jib and drifter. Genoa is brilliant as is same size as mainsail (140 square foot) so makes helm very balanced.”

On heavy weather sailing “After leaving the Canary islands:’ we were bashed by F11 winds, accelerated between the steep mountainous islands. COOKIE rode out the storm very happily to a 1 square meter sea anchor and 250 feet of nylon warp set over the sterns. She tended herself, allowing us to stay dry below and to rest. In fact, the situation felt very settled and relaxed.” Seas got up to 30 foot.

On the approach to New Zealand. “The final approach became difficult and became an endurance test: “A succession of low pressures bombarded us, sweeping up from the southern ocean, creating rapid weather changes and plenty on work on deck. The weather gods wanted the last word with three gales in succession, forcing me to lie-a-hull for 7 days.” Rory said: “Undoubtable, I owe my life to the fact that COOKIE is a deep-displacement, low freeboard catamaran built for strength and not lightweight speed.”

Rory sailed Cooking Fat in the Jester Challenge in 2010 (he came second over the line). Single handed from Plymouth to Newport, Rhode Island. He completed the “upwind” trip in 34 days at an average of 104 miles/day. He sailed back across the Atlantic from Rhode Island to Lands End in 22 days. Peak mileage on the return trip was 170 miles in a day.

Tiki 21’s are at best camper cruisers, but they are very capable of travelling long distances in competent hands. Please understand Rory could survive weeks at a time in conditions most of us would only tolerate for a weekend. A very good cat that is a great introductory boat.