Multihull Structure Thoughts

bajansailor. I have not seen or spoken to a Spronk cat owner in Australia. I have seen an about 50 foot lapstrake cat with fine sterns at a distance in QLD at one point but could not locate the owner to understand if it was a Spronk. Peter Spronk's cats were spectacular for there time. Well designed and built bar one detail which was the underwing clearance, but they seemed to work in Caribbean waters. I am sure you have done some inspections on them in your time, how did the owners rate them?

 

There are currently four Spronk cats engaged in day charter operations here in Barbados.
Two brothers here, Peter and Graham Allen, each have a Spronk catamaran (both called Stiletto, which can get a bit confusing), and they do rate them very highly indeed = they have owned their boats for at least 20 years now, doing day charters with passengers on coastal cruises including stops for lunch and snorkelling with turtles. The boats themselves are both approx 40 years old now, and are maintained to a high standard. I have had occasional surveys on both, and I remember noting that they were built with Bruynzeel marine plywood and pretty much all of their timber is still original.
Graham has the smaller (45') Stiletto - here is his website. He also still has his original Stiletto 27 catamaran (built in Florida by Force Engineering in the 70's)
Stiletto & Supercats Catamaran Cruises & Charters - Barbados http://www.actioncharters.org/

Peter does not appear to have a website, but there is a photo of his Stiletto Spronk cat at this link - he also started off with a little 27' Stiletto back in the 80's.
Stiletto Catamaran Cruises - Go Barbados https://www.gobarbados.org/stiletto-catamaran-cruises/

The other two Spronk cats are owned by Ryan Roach of El Tigre sailing cruises - they both have schooner rigs. and are very popular in the day charter trade here.
El Tigre Sailing & Turtle Snorkeling Cruises - Barbados https://www.eltigrecruises.com/

Rubaiyat used to be based here some years ago, but I think she now operates out of Grenada.
50 ft SPRONK 1979 Spronk 50 RUBAIYAT Aruba yacht for sale - | iyba.org® https://iyba.org/mls-detail?id=83606&vessel=2783307&title=1979-spronk-50-spronk-50-rubaiyat

 

This is the first of 2 items about the same size of tri created by the same designer John Marples with one difference the hull shape. Back in the 1990’s the 3 meter or 10 foot tris were popular and used in local racing for kids to 80 year old kids to have fun with. They did not reach great speeds (less than 10 knots) but felt like they were going fast because you were so close to the water. John along with many others designed boats for the class which had only a few basic rules 10 x 8 foot with a weight including crew of 380 lbs with a maximum sail area of 60 square foot and a spinnaker of 70 square foot. the boat weight was around 150 lbs. Helmsman must sit in one place and cannot move around to achieve different weight distribution. Any construction material was allowed.

Then in Italy a 10 foot class was introduced that was 10 x 10 foot with a maximum sail area of 86 square foot with an 86 square foot spinnaker. Any construction material again and limitations on bowspirits and rudders to keep the boats to 10 foot.

John Marples did his designs to the 3 meter rule as the tris with 8 foot beam could be trailed as one unit. The first Marples design we will look at is the Constant Camber 3-meter is a cat-rigged solo harbor racer and trainer. A spinnaker is available for downwind sailing. All of the sail controls (main sheet, vang, downhaul, and outhaul, and the spinnaker guys and sheets come to you in the cockpit. This is a Constant-Camber version of the Seaclipper 10. The CC 3 meter is 10 x 8 foot, weighs 150 lbs rigged and displaces 380 lbs with crew. The mast is 17.9 foot tall and is made of a 52 mm aluminum tube in the lower part, a 47.5 mm mid part aluminum tube and a 44 mm aluminum tube top part of the mast that carries a mainsail area of 60 square foot with a 70 square foot spinnaker. The draft is from 0.9 to 2.5 foot over the daggerboard. The main hull beam is 2.1 foot which means an about 6 to 1 length to beam main hull.

The major difference between the 2 designs is the CC 3 meter is Constant chamber round bilge. The hulls are laid up from 3 layers of 1.5 mm western red cedar. There are some veneers use in some cabinet construction that may be able to be used. One mold allows you to do the halves of all three hulls. Then the hull haves are joined at the keel lines and the bulkheads are put in place and with some slight torturing of the hulls the bow and sterns are joined. Result 3 hulls ready to be decked and have the 52 mm aluminum cross beams attached. Sounds simple and in theory all could be done in 100 hours. I have only read a few build reports but 100 hours sounds optimistic.

The performance of the tris according to John is about 4 to 5 knots upwind and about 6 knots off the wind, sometimes faster if you are brave enough. But be warned these boats require good skills to get the best from them, a good 3 meter has 13 ropes going to the dashboard in the cockpit which need adjusting to get the best performance, result you steer by foot pedals as your hands are busy.

There were quite a few Constant Camber 3 meters built as shown by the jpegs. Tomorrow we will discuss its sistership the Seaclipper 10.

 

The Seaclipper 10 is the second John Marples designed 3 meter trimaran. The Seaclipper 10 was a chine hull design that was perceived to be easier to build than the round bilge Constant Camber 3 meter. The Seaclipper 10 is 10 x 8 foot, weighs 160 lbs rigged and displaces 360 lbs with crew. The mast is 17.9 foot tall and is made of a 52 mm aluminium tube in the lower part, a 47.5 mm mid part aluminium tube and a 44 mm aluminium tube top part of the mast that carries a mainsail area of 60 square foot with a 70 square foot spinnaker. The draft is from 0.8 to 2.9 foot over the daggerboard. The length to beam on the main hull is 6.1 to 1. Again, the Seaclipper is sailed from a seated position with foot pedal steering and control lines coming to a dashboard in front of the helmsperson.

You will notice the slight advantage in reduced displacement, better length to beam and increased daggerboard draft of the Seaclipper 10 over the CC 3 Meter. According to John Marples in racing in Seattle the chine Seaclipper 10 was slightly faster than the round bilge CC 3 Meter. As Richard Woods will tell you, a well designed chine hulls have minimal impacts on performance. In the case of the Seaclipper 10 the longer underwater length and resulting higher aspect ratio of the daggerboard would help and the slightly better hull ratios would also assist.

The build of the Seaclipper 10 is mainly 6 mm plywood (covered with 120 gsm glass in epoxy) with 19 mm gunnel timbers etc. The dory bottom has stitch and glue taped seams with the side panels. The dashboard is 12 mm plywood. At the cross beams there is 40 x 40 mm timber. The mast and daggerboard boxes are 6 mm ply with reinforcing timbers at the corners and both have 120 gsm cloth on the inside. The decks are 6 mm plywood. Marple’s suggested exterior plywood be used. I will do an item on a 10 x 10 foot tri tomorrow that uses 4 mm ply throughout.

The jpegs give you some idea of the build and samples of the Seaclipper 10 sailing. Again, a great fun boat which if you are a first time builder will teach you a lot about boat building and multihull sailing. That’s if you can get it away from the kids.

 

A short one for the people interested in Sail GP. The 50 foot foilers did 3 races in Sydney Australia yesterday with its 30 to 40 klm/hour winds. Speeds up to 95 klm/hour with the France winning all 3 races and USA doing well. BUT do not expect any racing today or in the near future. The NZ cat was hit by lightening in Singapore destroying the rig, electronic and hydraulics. This meant NZ used the "spare" boat and a borrowed wing whilst a new cat is being built in NZ.

After the racing in Sydney yesterday they were lifting the cats out as a storm front came through. The last cat to be lifted out was Canada's and the wing was still on the crane when a massive gust hit and the wing went out of control dragging the hulls then hitting its accommodation tent destroying all in its path. People running everywhere. Result new boat and wing required. Sundays racing is cancelled. NZ boat builders working overtime. NZ event and maybe San Francisco events delayed.

I knew these cats could fly but this is beyond my expectations.

 

The final of the 10 foot sailing trimaran series. The tri in the jpegs is a design for an Italian guy and it looks good but once you download the PDF’s you find the design and detailed plans are done by Eric Henseval who worked with VPLP in there racing division working on 60-foot ORMA multihulls, including Alain Gautier's FONCIA 2, Groupama and Belgacom. He has also designed the 18 foot performance cruising Sardine Run trimaran and Sardine Twin catamaran along with many monohull racers and cruisers. A reasonable resume.

The 10 foot tri is 10 x 8.85 foot with a weight of 155 lbs and a displacement of 325 lbs. The 19.5 foot mast above deck carries an 86 square foot mainsail including mast. There is an optional 86 square foot spinnaker. The mainhull length to beam is 8.5 to 1. The draft is from 0.75 foot to 2.5 foot with the board down. The floats displacement is 100% of full displacement. Again, the design is to be sailed from a seated position steering with your feet and all sail controls are connected to the dashboard in front of the helmsperson.

The construction of the shell is 4 mm plywood. Aft beam bulkheads are 8mm thick Forward beam bulkheads and transoms are 8mm thick. The mast beam bulkhead is 8mm thick. The maximum section of wood beams is 95 X 70mm. The external shell is covered in epoxy glass cloth of 180g/m2. The hulls and deck are taped seam with all glass strips 300g/m2, 100mm wide. Central hull clamps: wood 12 X 30mm, floats clamps: 22 X 22 mm. Not specified but other 10 foot designs have aluminium crossbeams of from 45 mm x 2.8 mm walls to 52 mm x 1.6 mm walls. If you are doing a pure racer think about the aluminium beams but be careful as they are on the edge for a boat that has a very tall rig.

The plans can be downloaded from the following web site. Growing the 10 Foot Trimaran Class | Small Trimarans http://smalltrimarans.com/blog/growing-the-10-foot-trimaran-class/

Download the 8 PDF’s which contain the line plans, plywood sheet patterns, structural detail etc.

The jpegs give the idea. Have fun.

 

The TOUCHWATER is designed as a wave piercing semi-displacement sailing catamaran, not following class or regatta restrictions. In its original version it was an 18 foot sport catamaran, comparable to a formula 18 concept. The cat can be a Una rig, have jib, spinnaker and can have trapezes for one or 2 crew.

Now we get to the hard bit, the dimensions of this cat can be from 16 foot to 19 foot with a beam from 7.5 foot to 8.2 foot. The weight is from 313 lbs to 360 lbs, The mast length can range from 26 foot to 30 foot and carries from 140 square foot to 172 square foot in the mainsail and can have a small jib as well. The draft over the 4 (yes 4) fixed fin keels is 1 foot. There is a fixed hydrofoil option available. The length to beam is approximately 12 to 1 depending on the length of the cat. The cat is configurable to suit the needs of the clients. Some clients want a narrower cat for trailing, some want a jib, some want the foiling option etc. There is also a 13 x 6.5 foot cat version available.

The foiling option system works automatically. While sailing, the boat is lifted by the leading foil at the hull nose and the main foil at the fins. The leading foil is planning on the water surface. By this, the hybrid foil system reduces the drag of the hulls and provides more speed. Translation, the hull shape without foils is basically a planning hull shape, the foils try and use the planning capability to control the foil angle to create lift. Interesting, but I would need to see it in action to judge its effectiveness. The hydrofoil system is designed for reliable operation in stronger winds, being effective from approximately 3 Beaufort onwards.

Now we get to the very interesting part the structure. It’s aluminum. There are a series of pressed aluminum panels that appear to be tack welded together (and I suspect glued) to form the hull shape. The hull length can easily be changed by cutting a panel down or changing the bow shape (from axe to more vertical) but the basic pressed chine hull shape remains. The aluminum thickness is not specified but I would guess about 1.6 mm thick. With the many chines and some curvature, the hulls should be stiff enough but don’t step on the wrong spot as it probably will dent but will still be watertight.

To quote the company “The hull plates of the aluminum catamaran are produced by CAM controlled laser cutting. In the following stamping procedure parts get their characteristic profile. The shape not only causes the efficient hydrodynamics of the multi-chine hulls with lateral drift resistance and semi-displacement characteristics. The profile also is adapted to increase stability of the convex hull shape by using the thermal stress of the subsequent welding process. Hull structure, appendages and rudder equipment are made of aluminum alloys No. 5083 and No. 6060. All parts of the foil system are made of aluminum. Ductility of the material gives strength and robustness. And corrosion resistance makes the system maintenance-free.”

As you can see from the jpegs it can sail reasonably well with a performance that can match many beach cats. The windward performance is good with the fin keels.

The jpegs give the idea.

 

Second part of jpegs of the Touchwater aluminum catamaran.

 

The knife edged wave piecing profile of those aluminum hulls is impressive!

 

The NV 47 is a cruising motorsailor conceptual design from a Canadian BoatBuilder in about 2010. The NV 47is 47 x 23.7 foot. The displacement is unknown. It has a 52 foot wing mast with a about 600 square foot of mainsail and 400 square foot of genoa. The chine planning hull shape has a length to beam of 16 to 1. Th draft over the rudder is 5 foot. No engine power is specified. These are thin planning hulls which are to have additional support of foils to help lift the hulls to planning. The designer says “foil assisted don't need a wide hull surface to carry the weight… We hope to plane at 13 knots cruise at 18 to 20 knots under power. Its and experiment for sure.”

Again a quote from the designer “NV47 Hydrofoil Assisted Catamarans is a new addition to sailing catamarans and will have a Omer Wingsail and we will have that rendering soon. The NV47 Options Include 4 queen beds, 3 helm stations and diesel electric drives. The large cabin space with a galley, large dining area and 2 full bathrooms. There is a roomy aft deck with swim platforms and dingy davits.”

The construction was to be foam glass done by resin infusion then I read this line “There's just me out in the building, you'll not see me for a few years. Hard and on my own... thanks to infusion. Keeps me out of trouble and a nice quiet shop.” This is a very big single person project, especially when you are the lead designer experimenting with foil assistance on a thin hull planning hull approach. If anyone knows anything more could they please advise.

The jpegs give the idea.

 

Re the NV 47 - I wonder how much the helmsperson can see from the outside helm station looking through the windows of the deck saloon - and how tall one has to be to be able to see over the roof when standing at the helm?
Re the accommodation layout, surely it is not very practical to have the only access to the aft cabins going through the heads compartments?
If you are in the aft cabin, and want to go up on deck, and somebody from the forward cabin is in the heads on a long session, then you have to wait patiently, or climb out through a deck hatch (I hope there are large enough hatches in these cabins )

 

The NV 42 is the second design done by a Canadian guy to be a 42 foot motor sailing Hydrofoil Assisted Diesel Electric Hybrid catamaran. The cat is approximately 42 x 22 foot, displacement unknown with a biplane rig. The masts are 55 foot high carrying about 550 square foot per mast. Again there are thin asymmetric chine hull (virtually half a deep V) with a single foil assist for additional lift. There is a single central daggerboard. And a cut off transom as in a power boat type hull. As mentioned above the power is a Diesel Electric Hybrid, but there is no mention of the power or how it drives the cat.

The accommodation is 4 double cabins, large salon, 2 full bathrooms and a large aft deck. The designer states “Salon cabin forward design Increases interior space”. The design also has “2 outdoor helms and 1 inside helm and navigation station”. The entire design is aimed at single handed operation.

The designer claims “Planning hulled Hydro-Foil Assisted Catamarans offer stability, speed, and fuel economy.” Again, I have seen no evidence of one being built. I would need to understand how the one foil system would handle the variations of the rig pressure which would tend to pitch the cat bow down under some circumstances versus running under power which could have the nose pitch bow up. This is a large range of angle of attack to the foil which means it either needs to be adjustable or the hull design is very good.

The cat was offered as a foam glass kit. I suspect the design is a concept as the NV 47 cat was but as I said about the NV 47 the designer is trying to do all things to all people cat which is a very hard task especially when you are developing thin planning hulls with foil assistance. Weight distribution is a major issue, fuel usage and sailing pressure effects especially with a biplane rig are other factors. I hope the designer has considered it all.

The limited jpegs give the idea.

 

The Tiki 38 is a popular well known Wharram design. The standard Tiki 38 is 38 x 20.3 foot with a weight of 7,220 lbs and a displacement of 12,200 lbs. The standard rig is a ketch rig with 30 foot masts and 225 square foot wing sails on each mast. The jib and staysail are 140 square foot each and a 536 square foot spinnaker can be carried. The draft is 3 foot loaded over its semi low aspect ratio keels. The standard Tiki 38 is built from 9 mm plywood with timber stringers and plywood timber edged bulkheads with timber ply cross beams. All epoxy coated and e-glass covered exterior surfaces. Further details on page 68 of this thread. So far so good.

Wharram Tiki 38, if built to plan, sails well, are ocean capable and if well maintained, long lived. But as per usual some people like to modify things. The result was the first jpeg.

The were two Tiki 38’s built in Asia by a professional builder for an Australian and a New Zealander. They were “Improved by the builder” who modified the structure and the hulls (built in cedar strip planking instead of plywood). The boat was completed with honeycomb decks, honeycomb sandwich interior and furniture. The final result is a lighter vessel, that floated about 125 mm above the expected designed waterline which indicates about 2,200 lbs less weight with a slightly fuller waterline.

Now we get to an interesting problem. The NZ owner found the build was not to agreed standards, basically kept the strip plank hulls, took the hulls to NZ removed substandard work and completed the Tiki 38 above the hulls to the original plan. The Australian inspected the near finished project and refused to accept the vessel and started legal proceedings. The builder took over the Tiki 38, sold it and it broke up in a small storm resulting in the first jpeg. On the Wharram web site at:

Dodgy ‘Professional’ Builders – A Warning | James Wharram Designs https://www.wharram.com/news/2009/dodgy-professional-builders

Are the following comments in August 2009 By Hanneke Boon

"We would like to draw attention to the problems people have experienced by ordering their Wharram catamaran to be built by the ‘RB Power & Sailing’ yard of ***** ********** in Pattaya, Thailand.

The first boat built was a heavily modified Tiki 38, of which the owner refused to take delivery and which since being launched in February 2009 has broken up at anchor. The second Tiki 38, which was being build for Warren Matthews, was removed from the yard last January for finishing in New Zealand, after the owner discovered serious deficiencies in the build.

Practices like these are the reason for James Wharram Designs setting up Franchised Yards, where the owners can be sure to get a correctly built, high quality Wharram Design. RB Power & Sailing is NOT a franchised yard! Currently franchised Wharram yards include Andy Smith Boatworks in Bohol, Philippines and Boatsmith in Florida, USA"

A little research found the following comments from Wharrambuilders forum. Strip planked Classic? https://wharrambuilders.ning.com/forum/topics/strip-planked-classic?overrideMobileRedirect=1

Reply by Budget Boater on March 29, 2014 at 7:43am

“The strip planked Tiki38 to which you are referring was improperly built and abandoned by the owner with a very substantial lawsuit that followed. To the best of my knowledge, the boat broke up in a small storm and was lost. Beyond that, you have to do what turns you on. However, if you are that into strip planking, why build a Wharram that was not designed to be strip planked? Instead look for those catamaran designs that were designed to be strip planked, like a Chris White Atlantic series.”

Reply by Andrés on March 29, 2014 at 7:53am

“The history of this boat is very sad. The owner was not happy with the builder final product and refuse to take the boat as it was. The builder take the boat to himself and all the money of the builder (U$ 70.000 if I remember well). The owner lost everything. Then the builder sold the boat and it ended like this.”

Permalink Reply by Budget Boater on March 29, 2014 at 8:14am

“From my recollection, the builder had discounted, or dismissed, the inherent strength of plywood, and the structural parts of the boat (beam troughs, keels, mast cases, etc.) were not built to withstand the stresses of the sea. I do remember seeing a photo of a beam trough locating pin hole that had ZERO wood of any kind in it - just foam and a thin layer of fiberglass.”

Reply by Marty Peters on March 29, 2014 at 10:27am

“***** Benetti built that 38 in pattaya and he was/is a well known crook and scam artist. His yard was raided by Thailand police and I believe that he is still under arrest awaiting trial for fraud etc etc. he also built another 38 that had lots of issues and was taken by the owner and finished by a New Zealand yard after removing the substandard work. It turned out fantastic in the end. I think the name was natural high.”

No further comment required. I could direct you to further commentary but accept the structure did not follow the Tiki 38 plans EG material substitutions etc. As said the Tiki 38, if built to plan and well maintained, will serve you well. If you wish to modify a design, get approval from the designer first then choose a competent proven reputable builder and then monitor the build. Cheap usually means short cuts. The jpegs give the idea of the boat that broke and the standard design.

 

The following is about a few of Schionning power catamaran designs. The Growler 650 VT and Growler 710 VT. These 2 designs are very close in concept and the majority of there dimensions. The 650 VT is 21.3 x 8.2 foot with a displacement of 2860 lbs. The draft is 1.2 foot over the hull. The length to beam is about 12 to 1. The power is two 50 to 90 HP outboards which will cruise the cat at 15 to 25 knots with a top speed of 30 knots. The 710 is 23.3 x 8.2 foot with a displacement of 3630 lbs. The length to beam is 14 to 1 for the 710 VT. The draft is 1.25 foot over the hull. The power is two 50 to 90 HP outboards which will cruise the cat at 15 to 25 knots with a top speed of 30 knots. The underwing clearance is 1 foot for both cats.

The VT (Vapour Trail) series has a patented deep V with side planning chine hull shape that is claimed to be fuel efficient and provides good speed in a variety of conditions. The shape has been tested on many cats in the range and according to reports appears to work as advertised.

There are three versions of the Growler 650 VT and 710 VT available: The Sports, Fishing and Cuddy Cabin. Each has a slightly different layout and set-up depending on the intended uses. A Fishing version has a hard-top cover that provides much needed shade when out on the water, as well as plenty of space to work while remaining extremely stable in even the largest swells. They have excellent load carrying capabilities, and can be loaded with equipment and passengers more so than other boats of similar size. A small fridge can be installed, and there’s plenty of room for eskies etc. The Cuddy Cabin has a roomy cabin, with a double berth from which a table extends to create a dinette if required. A small fridge, small gas cook-top and port-a-potty can also be installed if desired. The Cuddy can also be trailered and stored in the driveway during the week. Built from balsa-core Duflex panels.

The construction of the Growler VT series is mainly kit based with Duflex panels (e-glass either side of Balsa) provided and premarked for scarfing and cutting to form full length hull and underwing panels. Additional glass taping, bogging etc is done to join the panels, then a final glass layup is done to provide strength as required. It is faster than a build from raw materials but your saving in time is paid for in the additional cost of the “kit” and your need to still do a fair bit of finishing work. The very big advantage is the provision of a chipboard full size guide mold which establishes the boats shape very rapidly minimising any future problems.

Kits are an excellent way of simplifying a boat build but it is only about a third of the time required. The other 65% is finishing and equipping the boat with pluming, electrics, fairing, painting, installing engines, steering mechanisms, safety gear, furnishings etc.

Like all Schoinning designs the plans are not cheap, but if these designs suit your needs have fun. The jpegs give the idea.

 

That looks like a well thought-out kit.
I've never worked with Duflex, but I'm interested. I've heard that end grain Balsa can be infused, which would make it very long lasting.
How is Duflex made?