Multihull Structure Thoughts

Cavalier mk2 is correct, Funamblue is an Atlantic proa. I don't know if I am coming or going with these proa's.

 

Heads or tails? Usually 50 % chance of being right. I think for a cruiser I would want to be able to tack at times like a outrigger for narrow places then go back to my usual configuration for long boards. Ocean racers just need to set up one way.

 

Many people like Wharram cats for their simplicity, relative ease of building with common materials and have a proven track record. But the trade off is, they adequately perform with reasonable sea keeping capability. Different people have differing reactions to going to sea. Some don’t get sea sick no matter what the boat. I prefer full ended cats or tri’s that minimise pitching which reduces any sea sickness. If I am a fine ended cat that pitches more, I feel very uncomfortable. Result, some designs suit some people whilst other people suit other designs.

Hanneke Boon (Wharram fame) wrote an article in late 2023 about the Pahi 63 performance and sea keeping qualities. A Phai 63 is 63 x 28 foot and a displacement of 28,000 lbs with a schooner rig of 1400 square foot of sail area.

Hanneke wrote: “Later in the voyage (global voyage 1992 – 1998) we sailed up the Red Sea and spent 12 days non-stop tacking to windward in Force 7-8-9 head winds and around 4m high steep seas. We were heavily reefed with 3 - 4 reefs in the Foresail and a reefed Staysail. The Mainsail was never used at all. Maximum speed we could sustain was around 5 - 6 Knots as the seas were so violent. Angle between tacks on the chart averaged around 120 degrees and we made good on average 50-60Nm every 24 hours (not counting the times we had to heave to when conditions were extreme). The whole voyage we were using our self made self steering windvane, which worked excellently. We were the only sailing boat that sailed up the Red Sea, all others used motors. We were very glad of the (lashed) flexibility of our boat as at times half a hull was in the air as a hole appeared between waves.”

Hanneke also wrote: “Many opinions thrown about by people about V-eed hulls being no good etc. refer to roughly built early Wharram Classic designs, often having blunt stems and big gaps round sterns and rudders, causing bad windward performance. For the last 40 years the Wharram hulls, underwater streamlining and sail rigs have improved and they sail as well to windward and are faster than most cruising monohulls. A well designed V-eed hull has qualities most people do not understand. You need to spend time sailing on one to come to appreciate their kind sea motion.”

The article also included the 2 jpegs of the performance of the Pahi 63 (shown below). In summary, in fairly smooth seas and lower wind speeds, the cat can do between 50% to 90% of wind speed. In stronger winds and 5 to 6 foot, occasional 10 foot seas the cat can sail at 35% to 60% of wind speed. In short better than most cruising monohulls, matching most heavy French cruising cats but below the average speed of high performance cats or tris.

Wharram designs meet the requirements of many but if you want higher performance, higher pointing multihulls more modern designs will suit that market. Only downside is those modern designs probably cost more money.

The 2 jpegs provide the Hanneke Boon performance plots based on real actual sailing experience.

 

I agree. The first time I "tacked" a shunting proa in 2009 I was concerned that I might get stuck by lightning even though it was a clear sunny day ;-). This was in P52 limping into a marina at Aransas Pass Tx with a jury rigged mast with the top 6' missing and a shredded sail. The geometry of the situation approaching a bulkhead to tie up to , the wind direction and preferred orientation of the boat it just made sense.

My current proa, QB can easily tack if the aft sail is reefed down to clear the aft shroud. I usually just reef both sails to the same point and maneuver slowly until I get out into open water like leaving Port Mansfield for this years TX200.

 

Hi. For a speed reference point, an owner of a Farrier 36/39 slightly modified tri and a Farrier 25 C had this to say about averages speeds over longer distances.
"25-32’ monos on the ocean tend to see 5-6kts overall. 32’-40’ should bump up to 6-7. 50’+ performance cats usually can avg 10, thanks to waterline. F36/39 NeheNehe crossed from Mexico to Polynesia at about 8.5 knot avg. Ravenswing’s (the 36/39) target is right there too. I’ve had upwind 500 mile trips only seeing 6 average mostly because of intentionally slowing the boat to avoid pounding/slamming. In our tris, I’ll say average speed is totally dependent on sea state. 7 kts was my F27 target for coastal trips off northern California." Greg F36/39 hybrid & F25C #15

 

So the Pahi can do 9 knots upwind and yet allegedly averaged about 2.3 knots upwind VMG on the passage that was mentioned? I've never sailed a boat that loses speed so dramatically upwind in heavy conditions.

 

I always thought she was a fascinating boat, and I think I remember building a cardboard scale model as a kid. But while she may have been "cut up due to politics" it's also fair to say that she was only created due to politics. And didn't Delages' previous boat, the "slanting proa", capsize at the start of a Transatlantic race when the slewing line slipped? Does that not perhaps indicate that his ideas could have been impractical? I'm just always very cautious about claims about speeds and potential breakthrough designs when many such claims only come through the completely biased source of the designer/builder.

 

Seems like they adjusted the speed for comfort and safety. That is good seamanship,the boat can go faster but if the crew gets tired or something breaks you may not get to your destination. Cruising, not racing, also interesting to see that reefed way down the wing gaff rig could take them to windward against those kind of seas, the Red Sea isn't really a Sunday sail upwind.

 

120 degrees between tacks and 50 to 60 miles a day made good to windward doesn't sound very good.

 

No it doesn't. It sounds like a schooner with the main furled and a heavy reefed foresail getting the bows blown off a bit by the wind and waves. Some main would help with that, maybe Hanneke will let us tag along on a voyage to try some things out.

 

A trysail on the mainmast might be the easiest solution to work with the reefed foresail.

 

John Slattebo developed the Slatts 22 as a hydrofoil stabilised tacking outrigger. The Slatts 22 is 22 x 12 foot weights 390 lbs and carries 228 square foot of sail area on a 28.5 foot aluminium mast. The idea was to create a fast day sailor for people not requiring hiking out etc. The submerged T foil is a NACA 012 section of 2.5 square foot area has an angle control in the cockpit via a morse cable. The angle control can move the foil plus or minus angle of attack over a 22 degree range. On one tack the foil provides lift on the other tack the angle of the foil is put down and the foil pulls the float down under the crew’s control. According to a report in a 1989 Multihulls the boat can sail at about the same speed as a Hobie 16 without needing to hike out etc. The boat is built of 6 mm divinycell foam with unidirectional and bidirectional fabrics in polyester resin. The foil is foam glass. The cross arms and foil support strut are 6061 aluminium.

There then appeared 2 further versions using the Slatts 22 main hull. The first was “Different 22” which was a modified version still with a foil but laid out differently. To quote the new owner. “I decided to modify it and the modifications were significant enough that the designer, John Slattebo, asked me to no longer call it a Slatts. There are no hard feelings, he just feels that it no longer represents his design ideas. All I did was add a couple of benches and a tiller and move some jib blocks around. So, it's a Different 22.”

The next version of the Slatts 22 was again done by John Slattebo and called “Tipnot” this version does not have the hydrofoil but has a larger outrigger and a sliding beams to allow an 8 foot wide trailering width. The float is 16.6 foot long (the original was 12.3 foot) and weighs 40 lbs. This appears to be a cross development with wings like the Different 22 but Tipnot does not have the hydrofoil. It is a “classic” tacking proa.

The hull structures again are 6 mm divinycell foam with unidirectional and bidirectional fabrics in polyester resin but the cross arm are supposedly made out of car exhaust tubing. Car exhaust tubing can be between 40 mm to 100 mm with 1.2 to 2 mm walls. Depending on the brand, it can be made of stainless steel. I don’t know the size used here but it is an interesting approach to cross arms.

Each of these builds had the same intention of being an easy to sail performance day sailor that does not require hiking out but could match it with an EG Hobie 16.

The jpegs start with 2 of the Slatts 22 original, the next jpeg is the “Different 22” and the final 3 jpegs are of the “Tipnot”.

 

This is a James Turner designed South African built by Vision yacht catamaran that is a real cruiser. Why, it has options like a real workshop in the starboard bow, it has a real navigation area, the main saloon has 6.75 foot headroom, it has 3 queen size double berth cabins (not 4 which is the default in this size cat), a really practical helming sail handling position etc.

The Vision 444 is 44.4 x 24.66 foot with a weight 17,650 lbs and a displacement of 22,650 lbs. The 60 foot mast carries a 720 square foot mainsail and a 315 square foot self tacking jib. There are options in rig and sails available. The draft is 3.85 foot over fixed mini keels. The engines are 37 HP inboard diesels. There are 880 litre fuel tanks and 970 litre water tanks.

The accommodation has in the port hull 2 double cabins with heads and in the starboard hull a owners cabin with a double berth aft, a large toilet shower forward with a tool shed/workshop forward. The main saloon has a U shaped galley, seating table area and a real navigation area. The cockpit is interconnected to the main saloon. The helming sail handling area is a few steps up from the cockpit. A simple effective approach.

The construction is E-glass, foam sandwich throughout with all components Vacuum Resin Infused with Crystie Vinyl Ester Resins. Crystie Spray Gelcoats are used then the hull is spray painted to suit. All furniture is Vacuumed Foam Sandwich Furniture components that are structurally bonded to hull and the underwing. All lockers painted out with Grey Polyester Topcoats. Any solid and veneer wood surfaces are finished with Waka Waxed Oil Finishes.

This is a 250 mile day cat in good conditions with peaks probably near 20 knots. But this is a solid cruiser that will sail according to the sea conditions not outright speed.

The jpegs give the idea of a good cruiser.

 

Circa 1983, I remember having seen Guy Delage entering Funambule at the Moulin Blanc Harbor in Brest, with plenty of wind under sails alone and maneuvring the sails to enter
forward then backward in a rabbit hole like a car in a parking! Only a very well designed / sailed Proa is able to do that.

 

The Aura 51 cruising cat is the latest model development from the French builder Fountaine Pajot done by the naval architects are Berret-Racoupeau. This is the next development from the Saba 50 which Fountaine Pajot sold 300 of the $1 million plus cruising cats. Result is the Aura 51 is a very important development for the company and appears to meet the market requirement of a good charter cat that can also severve as a very good private owner cruising cat.

The Aura 51 is 51 x 26.5 foot with a weight of 39,903lbs. The 76 foot mast carries a 1023 square foot mainsail and a 635 square foot genoa. The draft is 5.5 foot over the fix low aspect6 ratio keels. There are 2 x 60 HP or 2 x 75 HP inboard diesel engines. The engines drive the cat at 8 knots when cruising. On the main cabin roof there is a 2000 watt solar array that provides the batteries with enough power to run most of the ancillary items without a generator if required.

The rational of this cat is aimed at the charter market. The basic layout is 4 double berth cabins with ensuites in nthe hulls or you can have a 5 double berth or 6 double berth cabin layout with ensuites in the hulls. The main saloon and under cover cockpit combine into one large space for seating, galley and entertaining. The sliding doors separating the main cabin and cockpit can be fully opened. This cat has all the accommodation that any private owner would need in a cruising cat and for charter work the 6 double berth cabin arrangement would still provide a comfortable boat for all the guests. The helming sail handling raised cockpit is connected to both the l;ower cockpit and fly bridge accommodation. The view through the main cabin windows is very good with 360 degree vision.

The composite construction is straightforward combination of resin injection and infusion with balsa core in the hulls and Divinycell foam in the deck. High-tech composite materials constitute most of the structure of the hulls, flybridge, decks, bulkheads and furniture. Fountaine Pajot has perfected a resin injection and infusion technique that makes the catamarans considerably lighter while maintaining consistent quality.

One of the few tests I have read of performance said: “The Aura 51 moved well in the 5- to 8-knot northerly, making over 4 knots close hauled, and an even 4 when cracked off on a beam reach. A company rep suggested that in better breeze, the boat would generally make speeds about half that of the true-wind speed.” If a cat this size can move well in light airs then it indicates a cat capable of 10 knot averages and peaks near 20 knots. Not a racer but a good cruiser.

The jpegs give the idea of a good high end cruising cat.