Multihull Structure Thoughts

Today is the second part about foils, fiberglass foam cored daggerboards mainly. Foils on high performance multihulls are to control the boat and resist leeway. The best foils tend to be high aspect ratio and by default are long (deep) into the water. Result occasionally they act as a default depth sounder. The best daggerboard foil shape depends on the capability of the boat. Some boats run 15% foils others 12% NACA sections etc but a well shaped foil improves the performance of a boat especially upwind. Now we come to the construction of the daggerboard. There are several options each have their advantages and disadvantages and more importantly significant weight differences. The main options are Western Red Cedar Core with glass strengthening and coverage. WRC core for about 25% with a balsa front and rear with glass strengthening and coverage. Or a WRC core for about 25% with a Corecell type foam from and rear with glass strengthening and coverage. A full WRC board can be 3 times the weight of a foam glass board and twice the weight of a Balsa based board. In a EG 30 foot cat 2 foam glass boards could be 60 lbs lighter than 2 full WRC boards.

A fiberglass foam cored board should have a PVC foam core (about 5 to 6 lbs per cubic foot) EXCEPT there is a solid insert of WRC in the 25% of the fore and aft width at the maximum chord width. The WRC insert should be shaped as per a part foil section but be about 4 to 6 mm thinner than the full thickness of the board to allow layers of fiberglass to be laid on the outside for strength. The WRC insert should be wrapped in 2 layers of 400 gsm e-glass biax in epoxy to “seal” the WRC insert. Next you add the foam core to the forward and aft edge. The foam can either be hot wire cut to shape (aircraft wing building technique) or foam panels are glued together and hand sanded to shape fore and aft.

High density insert are put into the board at “known” stress points. EG on the aft edge of the board where the board would exit the hull when fully down and the top forward edge of the board where it rests in the case when fully down. Also additional hard points are put in for EG saddles used to guide tie down ropes for light boards that float up in their cases.

When the board is fully shaped and the uphaul rope groves anb turning box slots are inserted in the board prepare the surface for the final glassing. Next lay 1 layer of 400 gsm e-glass biax fully around the board to stabilize the foil shape. Depending on the size of the board lay EG 6 layers of 400 gsm unidirectional the near full length of the board over 40% fore and aft of the boards surface at maximum chord. If you are using carbon fibre unidirectionals may be 4 or 5 layers.

The final EG 2 or 3 400 gsm biax layers then are wrapped around the full board and the board is faired to full shape for painting. With foam glass board constantly check the rear edge of the boards as any serious knocks can crack the edge allowing water ingress.

Finally, another approach to fiberglass board making was developed by Malcolm Tennant and is commonly used in New Zealand. You have a Sheetmetal shop fold a sheet of 16ga aluminum or steel down the center to 45 degrees to act as the mold. If they have the dies of the nose radius you want that's great but usually you have to sweep an epoxy fillet into the mold at the desired radius. The open top edge has a 90 degree fold to keep the trailing edge straight. The V metal mould has temporary supports whilst you lay the fiberglass into the mould of the desired skin thickness. A preprepared insert timber or fiberglass board insert is then placed in the glassed metal V mould at maximum chord. Before the glass is cured, the metal V mould and glass is then forced into a Wooden timber frame then the 2 trailing edges are clamped together. The glass foil then cures and then can be removed from the metal mould. The jpegs describe this better. Originally Tennant said to fill the core with Styrofoam beads mixed with epoxy but if the skin thickness was increased slightly the additional core material was not needed.

Please understand boards need to be well shaped and constructed to take the loads imposed on them. Choose the technique you prefer and do them well. But keep the original mould, shaping devices etc because in the real world especially if cruising you will probably need another one. The final jpeg is a very high performance board structure, not recommended for a home builder.

 

The final in the mainly dagger board series. Plywood dagger boards are popular in smaller multihulls. They are cheap and relatively fast to build and only require a EG 300 gsm e-glass cloth finishing wrap around them. Ok it the multihull is a cruiser below about 22 foot where the loads are low. This is a simple compromise if light weight and high strength are not required.

The problem with plywood boards is the plywood. Solid plywood boards have at least 35% of the grain fibres of a plywood board go across the board, only 66% of the grain fibres are running vertically providing strength. Some cross fibres are needed but not 35% of the board weight. Therefore, plywood boards are 25 to 30% overweight. In a board that weighs 20 lbs a 5 or 6 lbs overweight is not going to be a problem but if it’s a cat with 2 rudders and 2 daggerboards you could save 24 lbs. Secondly plywood boards should not be high aspect ratio as they become “relatively” weaker the higher the aspect ratio. If you have a Chat 18 or a Jarcat 20 the plywood boards are OK.

There are 2 ways to improve plywood boards. The first is simple. Make the board a higher aspect ratio and add unidirectional glass over 40% at maximum chord down either side of the plywood board then wrap the board in 2 layers of EG 300 gsm glass cloth. Improved performance and strength although similar in weight.

The second approach has been developed by Bernd Kohler. Kohler uses thin plywood side panels glassed over on both sides with a light cloth (EG 200 gsm e-glass). The fore edge of the plywood panels are glued to a shaped nose panel or have a strong bog poured into the nose section and allowed to set. A square spar covered in carbon fibre is glued to one inner face of a glassed plywood panel at maximum chord. Glue is then placed on the spar where it will touch the other inner face of a plywood panel. The plywood panels are pulled together and glued onto a shaped rear spar and left to cure. Once the board glue has set the board is faired and a final glass layer is wrapped around the board. These boards are light and strong. They are half the weight of solid plywood boards and take about the same time to make as they form a natural foil shape versus having to shape a plywood blank.

The jpegs give the idea. The first 2 are solid shaped plywood. Kohler boards are next.

 

Jzerro and Ryan Finn have rounded Cape Horn and are heading to San Francisco. Jzerro is the Russell Brown designed and built the Pacific Proa that was first sailed in 1994. Jzerro is 36 x 22 foot weighing 3250 lbs and displacement of 4500 lbs. It carries a 36 foot rotating aluminium wing section mast, 95 mm x 190 mm (another report says 200 mm), supported by spreaders and weighs 160 pounds with all standing and running rigging. The sail area of main and genoa is 600 square foot. The float is 26 foot long.

Jzerro was built from 2 layers of 4 mm ply covered with 200 gsm cloth in epoxy over 19 x 32 mm stringers at 150 mm centrelines, frames and bulkheads at point of cross beams and crash bulkheads. The main hull is slightly asymmetrical requiring a wooden keel structure. The pods on all his 36 foot plus designs carry a double berth and serve the very important function of providing stability to 90 degrees if the proa is caught aback. The cross arms are timber plywood boxes. The cross arms were strengthened with carbon fibre in Australia after Jzerro broached on a bar entrance flexing the cross arms as it was pushed down the waves float first.

It has done thousands of miles in Russell’s hands and was sold to Ryan Finn. Russel Brown considers Ryan Finn a very competent Proa sailor. After initial sailing of Jzerro Ryan decided although Russell Brown had sailed Jzerro double-handed across the Pacific, Ryan Finn needed to modify the boat for solo sailing. “The biggest thing was I needed new sails and I wanted the sail handling to be a lot different. So I’ve moved a lot of chainplates for the headsails on both ends, and added medium roller furling sails on halyard locks,” recalls Finn. Finn has opted for wind instruments on a static pole on the ama, rather than masthead units on the rotating rig, for simplicity. However, he points out: “Because you’re going forwards and backwards, you have to recalibrate the autopilot every time you tack. Everything has to flip 180°, so it’s kind of complicated. I’m getting used to it, but I don’t know how many proas there are sailing that have autopilots!” Accommodation on Jzerro is limited within the main hull and leeward pod that extends outboard – and although Jzerro’s ply interior was beautifully crafted, Finn describes the sink as his sole luxury. Solar panels and a fuel cell were installed for power, with Iridium GO! for communications.

Ryan had been harbouring a dream of sailing around Cape Horn and trying to break the single handed New York to San Francisco via Cape Horn record (14,000 miles journey). On Thursday, January 21, 2021, Ryan Finn departed from New York to San Francisco via Cape Horn while attempting the record. Things were looking good for Ryan upon his departure, aside from the fact that the drinking water load was heavy on the boat and there were minor equipment hassles. Ryan had planned to finish half the water by Cape Horn, which would lighten the load for the remainder of his trip. Assuming Ryan took 4 litres of water per day for 80 days the water load would be about 715 lbs. This is a substantial load of water on top of all the stores and equipment required for 80 days at sea all going well.

Then, on January 22, Ryan heard a big "BANG!" Not exactly an exciting thing to hear on a solo trip at sea. He discovered a hole right above the water line on a forward end of the pod. Ryan explained that the "water was rushing into the boat like an open fire hydrant." It did not help that the boat was skipping and taking dips into the sea. Ryan then quickly situated the boat, so that he could take swift action to get the water out fast and make some repairs. It took Ryan an hour or so to make necessary repairs to patch the hole. He reached out to Russel Brown, the architect of Jzerro, and Ryan moved Jzerro to Russell's parent's property in Mob Jack Bay, Virginia. Once the weather warmed up, repairs were done and Ryan started plans for another record attempt late in 2021. Additionally, Ryan got a water maker for the next trip along with a hydro generator, so that the over load of drinking water on the boat was reduced. He also improved the electronics.

The next attempt for the San Francisco via Cape Horn on Tuesday, January 18th 2022. He will be attempting the word record for the fastest single handed route to San Francisco. The current record for this trip is 81 days, and Ryan plans on making it in just 70 days! Ryan headed down to South America, hugging the Atlantic Coast. Once there he worked with weather routers and got around the Cape Horn as fast and as safely as possible. Ryan is aiming to have an average speed of 10 knots throughout his trip. "I am feeling pretty confident that this can be done," Ryan Finn stated. Jzerro features Headsail Furling (ELHF) Systems, Engineered Synthetic Standing Rigging, Torque Rope for the storm jib, and Dux Running Rigging.

On the 24/3/2022 Jzerro average speed was 11 knots with a maximum speed of 17 knots. Jzerro has sailed overall 10,500 miles and is averaging 215 miles per day overall, good for a single handed proa that has rounded Cape Horn in winds up to 45 knots mostly on the nose and 35 knots winds were considered “reasonable” sailing weather. Jzerro, Russell Brown and Ryan Finn again are reinforcing what can be achieved by a well designed and built proa. But the most important part of these boats is the skill of the skippers who sail them. If you have the skill and seamanship, you can achieve things like, to quote Ryan "I am making 9.5 knots in 5.5 knots of wind".

The jpegs are of the original build and Jzerro as she is for the record attempt.

 

I though I’d add this one to the thread since I just purchased one, could not find mention of it using the Search feature, and had collected what info I could find during my pre-purchase research.

I will present it in similar fashion to OldMulti and hope he approves

The following info comes from what looks to be a July/August magazine article from 1979.

At that time, the Viva 27 was marketed as “The fastest production weekender in the world”. It is an approximately 27’ x 16’ Bowie Houghton designed trailerable Catamaran with folding beam tubes that hinge in the middle to allow the hulls to collapse inward on the water to reduce the beam to under 8’ during trailering and launching.

With a displacement of 1750lbs, and Main sail area of 375sqft on a rotating mast with an additional 200sqft Genoa on roller and a 625sqft Spinnaker, the Viva 27 with its hull mounted dagger boards (which are adjustable for balance), has a draft of 11” up and 5’ down, and is said to reach speeds of 12-15 knots in average conditions and 20 knots in ideal conditions, and is stated to have an IOMR rating of 1.05, thanks in part to its computer designed hand laid polyester/fiberglass hulls.

Each hull has storage/accommodations for a single bunk and sitting headroom with the hatch open, not unlike a Stiletto Cat, but the Viva 27 features large flush hatches for access as opposed to pods, with rudders hung at the transoms connected to a crossbar and tiller for control much like a Beach Cat.

Please see attachments below for more info and photos of examples.

 

A short one about a New Zealand open wing deck racing catamaran called Crazytrain. Crazytrain was designed and built by Greg Martell who is a professional boat builder with 30 years’ experience. The cat is 30 x 17.5 foot of unknown displacement (guess 3000 lbs) with a 45 foot aluminium mast carrying about 500 square foot of sail upwind. The square head carbon mainsail in later jpegs looks like a very powerful addition to its sail inventory. The length to beam at the gunnels is 10 to 1 with the length to beam at the waterline of about 15 to 1. The daggerboards are deep with a draft of about 6 foot. The transom hung rudders are daggerboard type. There is a central pod for an outboard, additional stiffness and storage of miscellaneous items.

The cat performs very well with 15 to 18 knots normal in the right conditions and reported peaks of over 22 knots. Crazytrain can match it with New Zealand 8.5m Multihull Class boats on a race course and has finished fourth over the line in the NZ Coastal Classic. The Coastal Classic has all types of boats (about 200 to 300) including racing multihulls up to 60 foot. The internal accommodation has some berths in the hulls and limited “camping” type facilities.

Crazytrain is a Stressform (tortured ply like a Tornado cat) plywood and epoxy construction and is built from four millimetre gaboon plywood, sheathed with 300-gram boat cloth and epoxy. The 3 crossbeams are aluminium tubes with the mast support beam having a deep dolphin striker. I have little other detail about the cat so if our NZ friends can add any detail it would be appreciated.

An interesting design, built to a budget, that is fast and by the looks of jpegs a lot of fun. The jpegs tell you more.

 

Oldmulti, Do you know of anyone building with tortured plywood? I'm learning the hard way, but it's going okay. Surprised the Crazytrain could get away with 4 mm ply. That's what I'm using, but it's very thin and flexible. I'll use 200 gsm. carbon both sides.
Wish there was some interior shots of Crazytrain

 

I’ll second what Russell said, tortured ply fascinates me, particularly some of the NZ 8.5 boats and Gary Baigents work.
I also like the look of the hull shape at least of the Selway Fisher Cat 254 in 6mm
I’ve had a few thoughts about using melamine coated thin ply to fold up a female mould, I think it could be a fast and economical way to create a mould for infusions.
Russel, photos look great, what is it ?

 

Russell. I am guessing the floats to the tri are coming along, the shape looks good. If you can contact John Tetzlaff full time sparmaker and part-time multihull designer/builder in NZ you will reach a man who has done several tortured ply cats of 4 mm ply glass covered. There are is a good article at https://multihull.org.nz/wp-content/uploads/2019/07/2005-09_Attitude.pdf
The pdf is attached. Attitude and several sister ships have been heavily raced in NZ bay and coastal racing and have lasted very well. Crazytrain is just one of the many versions of tortured ply cats and tri's that have been built in NZ starting with Bamboo Bomber by Malcolm Tennant. Gary Baigent who built the original Bamboo Bomber would consider 4 to 4.5 mm ply to heavy for his tris as he prefers 3 mm as it can handle the curves better. But I also suspect he designs are more experimental judging by EG Frog a foiling tri. But he did a design for a 36 foot Around Britain tri for a guy again in 3 or 4 mm tortured ply. Gary is very approachable and willing to talk. He has made comment on this thread. Some jpegs below may help.
An interesting article about Gary is at PressReader.com - Digital Newspaper & Magazine Subscriptions https://www.pressreader.com/new-zealand/boating-nz/20181101/283841509416216

Also the ply Tornado guys learnt a lot about tortured ply and how to accurately control it when building maybe you can find an old builder in that world.

Also please remember Gougeons' book for more ply folding details. Sorry I cannot immediately connect you with someone.

 

Russell,
I think Gone With The Wynns posted a video recently racing on Crazy Train and another similar cat. Whether or not you enjoy their content, they do touch briefly on the interior and show some decent racing, although it is obvious that they have not filmed aboard a race boat before.

 

Gone with the Wynns



we've got a TP 52 just below us, well run over the top of him

 

Russell. This may help. John Tetzlaff JT 8.5: jtspars@xtra.co.nz

The jpeg is of the 36 foot devils 3 from Gary Badgient.

I cannot comment on the skill or knowledge of this site but it may provide some clues. M.B. Marsh Marine Design http://marine.marsh-design.com/

 

Thanks for all the links. I'm so relived that larger boats are being built with 4 mm ply and getting away with it. It seems impossibly thin. The interior shots of Crazytrain showed only one stringer per side, so hard to imagine it's stiff enough.
Thanks for the contact for John Tetzlaff. I am trying to write about the process, so photos, history, and know-how are of interest.
Was anyone doing it before the Gougeon's? They started in the very early 60's I think.
What's a Selway Fisher cat 254" Redreuben? Yes, I think molds could be built this way, either male or female.

 

This one
Large Catamarans https://www.selway-fisher.com/YachtCats.htm

Second from top.

 

Russell. The following may help. First is Epsom Salts a JT 8.5 with some good sailing videos. Top speed 24.6 knots with several Coastal Classic runs.
Epsom Salts/ Ice Breaker - E 5.9 https://m.facebook.com/Epsom-Salts-Ice-Breaker-E-59-1714837932118747/

The earliest “tortured ply” float was mention in AYRS publication Number 23 Outriggers 1958. Trident 18 foot tri on page 21. 5 mm tortured ply float with glass covering. Booklets – Amateur Yacht Research Society https://www.ayrs.org/booklets/

Next is a site that mentions Uffa Fox experimenting with tortured ply and Mosquito bomber plywood aircraft using some tortured ply in 1940’s.

Compounded (tortured) ply construction. https://www.boatdesign.net/threads/compounded-tortured-ply-construction.54151/

stressed ply multihull https://www.boatdesign.net/threads/stressed-ply-multihull.32521/ has a few jpegs of Selway Fisher 254 cat build

Next is Best home build multihull designs https://forums.sailinganarchy.com/index.php?/topic/93021-best-home-build-multihull-designs/page/2/#comments SAMIN near the bottom of the page and on previous page Jpegs below 2010.

Some jpegs below of Samin floats and Selway fisher cat.

 

What a treasure trove of information. Thanks Oldmulti and Redreuben. Besides the Gougeon and Tornado info, there's not much actual technique info available. I'm documenting my design & build carefully and will publish it somehow, so knowing more of what others did (and got away with) is good. I'll contact John and also see if I can get permission to use some of the photos you have posted. Maybe the Gougeon's were the first to use the Tornado style tortured plywood. Critical parts of the process missing from their
book though.
I enjoyed the model building and design, but had some big surprises with the full size (27') hulls.