Multihull Structure Thoughts

If you want to see how wrong a mono designer can go with a cat design take a look at the beneteu blue 2. It has been discussed on the forum. Try to find an out of water pic to see how awful a cat hull can get....

 

The first of the pictures presented (which also features at the top of the designer's webpage) is mildly amusing in that it shows this 100 ton 16m wide catamaran sailing on one hull - on a flat sea too! The rig dimensions are not stated but from the pictures they look to be about the same proportions relative to the rest of the boat as one would expect for a much smaller cruising catamaran. Other things being the same, the heeling moment from the sails scales with cube of linear dimensions and max righting moment with the forth power so I cant imagine flying the windward hull to happen with this catamaran - certainly not in the weather conditions depicted. Either these professional designers do not understand the stability of sailing boats or this is misleading graphics being used for product promotion.

Agree this would make a comfy cruising yacht but given the beam the available accomodation would place it well into superyacht territory so maybe you would actually need rather more than $10 million?

 

Hello Oldmulti, thanks a lot for your answer and all, you additionally found out about this design!

In the quote above you wrote about 'pitching'

As not English native ( and may be for them too) could you please explain this three expressions, that are often found in descriptions about catamarans: hobbyhorsing - pitching - slamming ?

Thanks again

 

Andrea. Hobbyhorsing. The bow of the boat is pushed down into the sea lifting the stern up then the bow lifts up pushing the stern down. Hobbyhorsing is this cycle continues as the boat sails along. Some boats with fine ended hulls hobbyhorse even in light airs and the boat slows due to the increased wetted surface and disturbed airflow over the sails. Older designs were likely to hobbyhorse than more modern designs with full end hull shapes. Early Wharrams designs were prone to hobbyhorsing.

Pitching. Pitching is when a boat is going EG upwind, and the bow pushes into a wave then lifts and pushes the stern down. As the boat goes over the top of the wave the stern is pushed up and the bow is pushed down. As each wave arrives the cycle continues. There are ways to minimize pitching. Having fuller end hulls, Have the stern fuller than the bow creating asymmetry in the hull shape. The latest idea is to have very slim wave piercing bows that don't "lift" until about a 25% of the boat is in the wave so in effect the entire boat is "lifted" over the wave with minimal pitching. You have to be a good designer to get wave piercing to work well across a wind and sea range but if it is done well you will have a comfortable boat.

Slamming. 2 versions. Slamming in a hull is generally forward and is a full ended flat bottom bow shape. As the boat goes over a wave the bow slams down (hits hard) sending a small shock wave through the boat. Reduces pitching but is very annoying over a long sail. It also can cause structural problems over a long time. The second version of slamming is when an underwing on a cat or crossbeams on a tri are to close to the water. The underwing or crossbeam is hit by the top of waves as the boat sails upwind or reaching, This slows the boat, can cause structural damage and can be very annoying over a long time especially in older designs with wingdecks close to the sea. In Prout and Catalac type designs crew could not sleep in forward bunks at sea due to slamming on the underwing.

All of the above "bad characteristics" of fine ends, low to the water wingdecks etc can be in a EG cat that may have accommodation but is a slow uncomfortable boat especially upwind. Modern designs have fuller ended hulls that have an asymmetrical fore and aft shape with higher bridgedeck clearances that are shorter in length. Result faster more comfortable boats that pitch less, minimize hobbyhorsing and rarely slam.

Hopes this helps, can anyone else use German terms to help answer Andrea question. No other item today.

 

Seems the Corsair 880 Sport in this year's R2AK has a few structure discussion points. Apparently the main bulkhead, rudder and front beam are all experiencing failures. The boat is apparently brand new.
In other TRI news a venerable F27 is currently the first multihull.

 

The Race to Alaska is proving to be a tough race this year. 30 knot winds are forecast for the next few days and several boats have dropped out but we will focus on the Farriers. The lead Farrier is an old F27. The start field included F 25 C, F 28 and a recently built Corsair 880. As Cavalier mention the 880 had a bulkhead problem with the bulkhead separating from the hull side over a short distance and other issues. But let’s look at The Race to Alaska course. Its 800 miles long between from Port Townsend to Victoria BC then a second start from Victoria BC to Ketchikan Alaska. It can be sail outside Vancouver Island or on the inside passage of Vancouver Island up a series of tidal effected, log strewn straights. Less waves more obstacles.

Your race course selection effects your race chances. Boats that have structural problems can be from sailing forces or as the Farrier “Trimorons” found the hit something hard and had there mainhull filling with water which required beaching. Very damaged daggerboard and case. All I am saying is don’t assume that a failure in this race is all about sailing forces, some of the problems may have been caused by a log hit earlier, before the failure. The next problem with the Farriers are several rudder failures around the pins supporting the rudders and the cassette cases supporting the blades. Again, this could be sailing forces or hits on logs etc.

This race is very weather dependent and requires skilled people if you want to be a race winner. You also have to be very creative in solving problems. “Trimorons” have a broken tri laying on a remote beach with little access that needs to be lifted onto a trailer which is 100’s of miles away. This race is a challenge. To quote the owner on Facebook “We’re out. Trimoron. Tonight at about 10pm (still twilight) we were escaping the furious winds in Johnstone strait to anchor in Blenkinsopp Bay. We hit something underwater a long way from shore, think it was a rock. It cracked the daggerboard case and we started filling up with water. We got the mainsail down headed towards shore under the storm jib and put out a pan pan. (Huge shout out to Team Monkey Fist already anchored there who instantly responded that their team was getting dressed and on their way). Thanks also to fishing boat Epic(?) and to James and the coastguard team. We’ve grounded/beached the boat but the centreboard is jammed down, everything is a soggy mess. The coastguard wanted to take us off. Vlad refused to leave his boat and Jeff stayed with him. They’re resourceful guys and will manage between the boat and the shore (where team Mike n Marty saw a bear earlier) but need help.”

Now another small item I found in the Farrier blogs which interested me. The performance of a F 28R versus older F 24 or F 27’s.

Re: R2AK Trash Talk, anyone?
From: Garry Sagert
Date: Sun, 11 Jun 2023 00:37:42 AEST

Our F-82R (similar to F-25C Mojo) is VERY weight sensitive so we prefer to sail double-handed. Even so we basically sail boat-for-boat with the "slower" production F-boats (e.g. F-24II, F-27) up to about 8 knots of breeze, and our advantage comes in 8+ knots of breeze when we can leg out due to our lighter weight and greater floatation (i.e. righting moment).

We once sailed a longer multi-day race with three people and overnight gear and the impact of the third person on boat performance was astonishing, and our ability to leg out on the "slower" boats all but disappeared. In retrospect it's not really that surprising given that each person and gear adds ~10% to the sailing weight of the boat. We can preserve some of the performance advantage in longer races (e.g. Swiftsure) by sailing with three smaller crew members, but we still have to be very meticulous about only bringing absolutely necessary provisions. All of this is to say that by loading up Mojo with four crew and provisions for ~5 days they have basically turned a blistering fast F-25C into an F-27 in terms of performance.
Garry Sagert F-82R “Unleaded”

In short don’t assume carbon fibre will win you races. It just reduces weight if well done. You lose the advantage of weight reduction if you go and load up the boat with people and food etc.

The web address for R2AK is: Race to Alaska Explained - Race to Alaska https://r2ak.com/r2ak-explained/ See you tomorrow.

 

The Gunboat 90 is an interesting boat, yes its large, yes it sold second hand in 2018 for $11 million dollars, yes it is fast but it was sold after the owner said he wanted a faster smaller boat for his family to sail. He now owns the Eagle 53 partial foiling cat. So, what was “wrong” with the Gunboat 90? The Gunboat 90 (named Sunshine) is 89 x 41 foot with a length of 97 foot over bow sprits etc. The shell weight is 59,600 lbs, the displacement is 82,799 lbs. The 110 foot high carbon fibre Hall mast carries a mainsail of 2012 square foot, a genoa of 1345 square foot, a gennaker of 2368 square foot, a spinnaker of 2490 square foot. The length to beam is over 13 to 1. The draft varies from 6 to 11 foot. The power is twin 190hp Yanmar diesel engines allow a cruising speed of eight knots, topping out at 12 knots.

The accommodation is large, look at the jpegs, you have space for 4 double berth cabins with ensuites and 2 crew cabins in the hulls. The main saloon and cockpits form a large area for socialisation, food preparation and entertainment with such things as 40 inch TV’s etc.

The hulls are a composite construction of vacuum-bagged, epoxy foam sandwich and Aramid Honey-comb Nomex with carbon fiber inner skins and Kevlar outer skins for impact resistance. Built by South African yard Gunboat, Sunshine was delivered in 2010. This structure is very well designed and built.

The result the Gunboat 90 is capable of 400 mile days, has peaked at over 25 knots and has raced successfully around the Caribbean. So why did the owner and his skipper on a sunny afternoon chat about a new faster cat? Because the Gunboat 90 was not radical enough. It was fast but the prospect of foiling around a race course with a reefable wing sail was of more interest. Also, the owner did not need such a large boat for his family sailing. Result the Eagle 53.

The jpegs give the idea of the Gunboat 90. Please look at the Polar diagram to get an idea of the speed capability.

 

The R2AK F27 in 2nd is out with bulkhead damage. 4 guys and stores in big wind and waves so probably weight related is the current guess.

 

This is about a new custom design by Grainger Designs. The concept evolved from a series of highly motivated discussions with a couple of veteran trimaran sailors who found themselves boatless and lusting after the next live aboard sailing adventure. The sailors in question are Jason and Clo from Sailing Spirit, a 40 foot ex racing trimaran that has travelled half way around the world. Little detail of the numbers are available so I will give you my GUESSES. The TR 50 cruiser is 50 x 36 foot with a weight of around 18,000 lbs and a displacement of 25,000 lbs. The 70 foot carbon fibre mast probably carries a 950 square foot mainsail, a 450 square foot jib and a 800 square foot Code 0. The draft of the tri is interesting. The floats have large fixed fins that draw 5.25 foot at rest and when healed can draw up to 8 foot. This removes the need for daggerboards in the main and float hulls which lightens the boat, minimises noise, simplifies upwind work and reduces build costs. This is a very logical approach for a cruising trimaran.

The following is an edited version of Grainger’s website.

Jason and Clo spend some time comparing the concept of a 50 foot cat to see how it would stack up in terms or accommodation, performance and style. In spite of having more cabins and about three times the interior floor space of the cat, the cat soon took a back seat in the discussions. It was always going to be a trimaran. Jason and Clo (who are professional delivery skippers) spend a lot of time on the water, they have seriously minimal requirement in terms of creature comforts and gadgetry. They have a pretty good idea of what works for them on a cruising boat. The emphasis for the design work was to be on the sailing qualities of the vessel and keeping things simple for minimum maintenance and affordable build cost. Two double cabins and a single bathroom was all they required.

For a trimaran that will do a lot racing the emphasis is on high buoyancy floats with a lot of buoyancy low down to minimise heeling and get main hull to lift as early as possible. For a cruising trimaran we still want to keep a lot of buoyancy in the floats but the emphasis is on a more V shaped section rather than U shaped for a gentler ride in more animated sea conditions. We achieved the combination of the V shaped hull form with high buoyancy by increasing the float profile. This form will provide a softer motion upwind at the expense of slightly increased wind profile. Fixed fins on the floats don't add much to the draft and provide good upwind performance without interfering with the interior layout.

Design of the helm station and access to the sail controls is at the heart of the efficient functioning of a sailing yacht. Twin helm stations aft in the cockpit with sail controls readily at hand keep the helm person in close proximity to rest of the crew and guests. The helm has good visibility from the seated or standing helm position, and even better visibility over the cabin top by standing on the side deck. In adverse conditions the helm person can also benefit from the protection of the roof that extends right to the forward end of the aft cabin. An optional tiller steering arrangement allows for helming from the aft beam sitting or standing.

Construction: PVC foam cores/epoxy infused with glass and carbon reinforcements engineered to ISO12215-17.

The jpegs give the idea of a very interesting design, I hope we see it on the water soon.

 

A general update on some structural failures in the Race to Alaska Farrier tris. From the Farrier owners web site.
"Re: R2AK - Structural Failures - A Cause for Concern? From: Garry Sagert Date: Fri, 16 Jun 2023 03:42:05 AEST

I was talking to Eric Pestou, an engineer (also an F 27 R2AK competitor) about this very comparison with aviation vs. boat design.

The thing with aviation is that the loads are relatively predictable because you're only dealing with one "fluid" (i.e. the air) and beyond a certain load factor the wings will stall and the load won't get any higher.

By comparison with sailing you're dealing with the interface between two different "fluids" (i.e. air and water) and the water part of that can introduce very unpredictable loads depending on sea state.

Francois Perus (880 designer, construction issues at Corsair not his "fault") says that because of this unpredictable loading it's very difficult to do finite element analysis (FEA) on an entire boat system, especially within the context of production boat companies trying to turn a profit, so designers and builders tend to rely heavily on past experience.

Then you add the highly manual (and therefore somewhat inconsistent) manufacturing process and it's not surprising that new boat models have teething problems."

Garry Sagert F-82R “Unleaded”

 

Whilst we are on Grainger design, I noticed that Tony is now saying he is designing multihulls that are longer for a given accommodation, as it provides a better performance and sea comfort. The I looked through his designs on his current web site and found the shortest design is 40 foot catamaran or a 36 foot trimaran. His earlier designs like the Raku 32 still exist but as a production build and the Raku 35/6 has disappeared. From another source Tony appears to be focussing on larger new designs or semi production kits of his larger catamaran or trimarans. People who want smaller designs appear to not be catered for.

So, an update on the Raku 32. It is now being built by a Polish company, promoted by Roland Gaebler, a German (who helms a Decision 35 catamaran), who has helped develop a performance version of the cat. The Raku 32 is 32.15 x 17.2 foot with a weight of 6,650 lbs. The standard model carries a fixed aluminium mast of 48 foot carries a 440 square foot mainsail, a 225 square foot jib, a 616 square foot Code 0 and a 904 square foot Gennaker. The Performace rig has a 52.5 foot carbon fibre mast that carries a 495 square foot mainsail, a 23939 square foot jib, a 602 square foot Code 0 and a 995 square foot Gennaker. This is a lot of sail for a 32 foot cat. The length to beam on the hulls is 13 to 1. The draft is 5.5 foot over the daggerboards. The power is outboards of 10 HP.

The Raku 32 will move very well under either rig if built to weight and is not loaded down with excess crew and stuff. A estimate of speed says 10 knot averages will be possible with peaks around 20 knots. The price start at $270,000 US to $324,000 US for the performance version.

The accommodation is 2 double berths forward on the wingdeck, a single berth and toilet in 1 hull and a galley and single berth in the other hull. The saloon connects to the cockpit to have a large social area. The hull headroom is 6.2 foot and the saloon headroom is 5.3 foot. The steering can be tiller or wheels in aft corner of the cockpit.

Construction is foam e-glass with vinylester resin. There is some carbon fibre reinforcement in bulkheads and roof structure.

This is an excellent fast smaller cruising catamaran that will good fun for those that can afford her. Pity the design is no longer available for the home builder.

 

When I look at that Grainger tri I see echoes of Ed Horstman's hull shapes. Those fat V or whatever you want to call them make a lot of sense in a boat used in variable water.

I emailed Mr Grainger a short while back. His reply was lightening quick and right to the point. I've always had a high opinion of his work but he made it clear that he is focusing on those larger boats now. I guess there isn't money in the smaller ones ?

Obviously I don't understand the market. I couldn't imagine anything worse than a 90' carbon cat...well maybe I could imagine SOMETHING worse but...

 

There has been some Farrier trimaran structural failures in this year's R2Ak. My friend Vince wrote some thoughts about them. The trunk failures were from grounding:

Has the Trimaran carnage given you any reason to rethink any of your design choices?
Lessons I take:
1. Where you have a bulkhead that is cut away to allow passage from the forepeak to the main cabin, that bulkhead needs to be extremely strong. It is not sufficient to simply wrap a piece of three-quarter inch foam with some glass. You need a true hat section ring frame with a **** ton of carbon.
2. transferring the load from the lower folding strut to the ring frame via a bolted connection through the hull itself, does not work well. That simply pulls the hull up away from the ring frame. You need either composite chain plates that are attached directly to the ring frame and penetrate through the hull, or maybe a giant composite saddle that wraps around the ring frame, and then drops onto the hull. You then through bolt with giant washers and g10 backing plates, so that you are effectively pulling on the ring frame, not on the hull.
3. The new 880 is a perfect illustration of how chasing power can backfire. It is a relatively heavy boat with big, flat bottom floats and a big rig. It can be really fast, but the stresses must be much higher than the f31 upwind in short seas and heavy air. It needs another 150 pounds af carbon structure at least (my considered and completely unqualified engineering opinion.)
4. farrier’s daggerboard case laminate spec is inadequate. My case broke, trimoron’s case broke. I am aware of others. That is not acceptable. The board needs to go first always.
Centerboards starting to look very good.
5. Rudders and cases are often marginal, and made more so by ignorant DIY. Farrier’s original kickup design was crude and heavy, but I never heard of it failing. The daggerboard rudders have been more problematic.

 

Oh, and it looks like my solo R2AK record is about to be broken by Eric Pesty sailing an F-24.

 

This is a story about a company wanting to explore options before they commit to a new design. Seawind catamarans sought a new larger design for production. Eventually Seawind chose a Reichel Pugh 52.5 foot fiberglass composite design (the Seawind 1600 Passenger). An alternative proposal for Seawind was from De Villiers Yacht design in New Zealand. The 525 cruising cat is based on an existing hull design but had a complete rework above the gunnel level with new deck, interior and cabin top. Basic first, the 525 is 52.5 x 25.7 foot weighing 32,400 lbs. The 70 foot aluminium fixed mast carries 1631 square foot upwind and has Code 0 and spinnaker options. The draft over the fixed low aspect keels 4 foot. The underwing clearance is 2.75 foot. The power is 2x Yanmar 4JH57 diesels driving through a shaft to propellers in a skeg rudder combination.

The name chosen by De Villiers was the Seawind Endurance 53. The reason is this cat was a strong design intended to be built from mainly aluminium. As I said, he had done similar cats previously for extended cruising sailing, the DVD 52 foot Aluminium Cruising Catamaran – Design #163 / #183 /#226, and for this design (#232) used the same hulls but modified the topside. This could have been the first aluminium production cat for Seawind but I suspect Seawind choose to stay with composition fiberglass production for consistency and I also suspect these designs were proposed at the time Seawind and Corsair were getting together. Choices had to be made.

The accommodation spaces are generous. In 1 hull is a guest double bedroom with ensuite and a real work shop forward (or alternative sleeping cabin) in the other hull is a master suite with a double berth, seating and a full ensuite bathroom available. The main saloon has a full galley, seating, entertainment area and a navigation helming station forward. The deckhouse roof extends aft to cover the aft deck lounging area which allows for a 3000 Watt solar array. Aft is a cockpit with dual under cover helming stations. All of the sail control lines are led aft through the house side window sill coamings to dedicated winching stations alongside each helm and there is a self tacking jib to simplify sail handling. Again, on a cat this big electric winches would be a big advantage.

Performance is not mentioned but with the sail area and relative low displacement this cat could do 10 knot averages and peak at 20 knots in reasonable conditions.

A nice conceptual design for those who really want to sail a go-anywhere ocean voyaging catamaran.