Multihull Structure Thoughts

[CrazyRU]

This is about a Russian proa blog that started out well then descended into confusion for a period and was built and then sailed. The proa proved to be fast but nose dived in any sort of waves and stronger winds. The structure appeared to hold together but the proa proved to be sensitive when sailing. Again, this was a home designer builder.

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And all these years I was waiting for you to review my boat and, of course I missed the actual review

the boat has never had the nose diving problem. I guess it’s translation misunderstanding.
The bows behaved beautifully upwind and downwind.
The boat has a unique system of managing the center of lateral resistance by playing with two boards located at bows of the main hull. that system needed a period of development and tweaking.
However the boat had been tuned out ever since and it has performed very much as designed, (with a few features being tuned down.)
I built the boat in 2014, however life got in the way and I have not being able to actually play with the boat until 2022. The boat successfully finished three Everglades Challenges, 300 miles unsupported adventure races along Florida west coast, in 2023-2025, being one of the top solo boats.

 

[HelmutSheina]

OM has a scow bow shape been tried on cat hulls?

 

[oldmulti]

HelmutSheina. Cat and tri hulls have had fuller ends but not a formal scow shape. The reason monohull scows exist is to provide more lateral stability on the longest length of the hull. Multihulls have a lot more stability and therefore want a bow shape that cuts through the water best. The only reason for fuller ends in multihulls is to reduce pitching.

There are 2 smaller catamaran designs (16 foot or less) that have scow bows but that is to simplify building in plywood. They do not perform well and are at best day sailor cruisers.

If you want more info on scow designs in the smaller sizes look at the following web site. Monohull scows, catamaran and trimarans pointy end designs. Nautline : Boat plans, plywood sailboats plans, pocket cruisers sailboat plans, plywood epoxy boat, DIY boats, junk sail, plywood catamaran plans Nautline : Boat plans, plywood sailboats plans, pocket cruisers sailboat plans, plywood epoxy boat, DIY boats, junk sail, plywood catamaran plans https://www.nautline.com/sailboat_plywood_plans.php#K395

 

[HelmutSheina]

Thanks OM.

 

[Robert Biegler]

OM has a scow bow shape been tried on cat hulls?

I know of only two examples. There was Jean-Yves Terlain's Gautier 1, possibly the ugliest boat that ever raced. Perhaps not a good example, as it seems to be pointy at the waterline. Those raked pram bows were probably for dynamic lift when immersed.

https://c8.alamy.com/comp/H9EG96/aj...e-1980-plymouth-england-ostar-1980-H9EG96.jpg

Then there is an F18 design, the Cirrus 901. From what I read, it gives away upwind speed for being able to push harder on a reach due to lift at the bows.

 

[calevi]

Any idea what’s going on with the Sketch to Sea HH88 cat project? He finished the boat and then pretty much disappeared. I was a bit concerned about how top‑heavy it might be with all the equipment he added up there, but that’s just my own speculation.

 

[oldmulti]

Thank you Robert for reminding me about Gautier 1. Page 223 of this thread has an item about Gautier 1. The bow shape is a normal up to about half way up bow used in normal sailing conditions. The blunt scow bow used for buoyancy starts halfway up the bow and caused problems in heavy airs. Gautier 1 had many issues from being overweight to having an under powered rig. A bold experiment for its time. In the second jpeg bottom right corner is a side view of the bow.

 

[oldmulti]

Calevi. There is a lot of advertising etc in this youtube but it gives some information about the HH 88 seatrials. : SEA TRIALS: SAILING THE NEW HH88 SUPER YACHT

 

[calevi]

Calevi. There is a lot of advertising etc in this youtube but it gives some information about the HH 88 seatrials. : SEA TRIALS: SAILING THE NEW HH88 SUPER YACHT

I watched the video, thanks! I’m still curious about your take on it. From your perspective, does the HH88’s design seem risky in any meaningful way?

 

[oldmulti]

Calevi. The HH88 is designed and built by some of the best in the business. The basic boat is good, but it is designed for a purpose to be a luxury cruiser. Result, the HH88 has a lot of internal space, a lot of windage and a lot of technology, internal fitout items etc to meet the luxury cruiser category. The HH88 appears to have a strong light structure which keeps it relatively light, the fit out uses light materials, the technology and the rig are appropriate. Now we get to your concerns about the HH88 is top heavy.
Stability in the HH88 will be very large due to beam and weight, the crew will be taking sail off in strong winds because of potential rig damage more than a stability issue. BUT the HH88 will not be the best going upwind due to windage and the second issue thee HH88 hull shape (designed by some of the best designers in the world) should be optimised to minimise pitching. The HH88 should still be relatively fast but I suspect the owners will sail at a speed for comfort not outright speed.
I have sailed and helmed on 80 foot charter cats. They could average 10 to 12 knots while the guests were comfortable, but the helm was not as responsive as fast performance racer cruisers.
Translation the HH88 should be a good reasonably fast luxury cruiser. If you want more performance and less accommodation there are other options out there. Have fun.

 

[oldmulti]

The Outremer 48 is a new version of the Outremer line due for release in Spring 2026 in Europe. The design team is VPLP Design, Design Consultant Patrick Le Quément and Interior Architect Darnet Design. The builder is Outremer in France. The Outremer 48, its successor to the Outremer 45, takes all the traits of its predecessor and refines them delivering more performance, improved ergonomics and a modern aesthetic. The idea is to deliver performance somewhere between the Outremer 45 and the 4X while delivering more comfort to long-distance cruisers.

The Outremer 48 is 48 x 25.25 foot with a weight of 23,500 lbs and a displacement of 33,600 lbs. The carbon Fibre fixed mast carries a 882 square foot mainsail, a236 square foot staysails, a 376 square foot solent, a genoa of 1,076 square foot, a gennaker of 1,615 square foot and a spinnaker of 1,936 square foot. The draft is from 4 foot over the rudders to 7 foot over the daggerboards. The standard engines are 2 x 40 HP Yanmar diesels.

The accommodation has either 3 or 4 double berth cabins in the hulls with a shared head shower in each hull. The hulls are narrow (probably 11 to 1 or greater) with the double berths going across the hull width about the soft chines. The main salon has a large galley, a navigation helming position, a table and seating area. The attached cockpit has external seating under a roof top. The semi raised external helming and sail control position is on the port side of the cockpit.

Sail handling is improved by the self tacking jib whose jib track is brilliantly incorporated in the leading edge of the main cabin roof. Thee overall design is very well thought through to provide a good balance between accommodation, helming and sail control. In short a good high speed cruiser.

The construction is advanced composite materials with vacuum-infused construction methods contributing to a structure that is both robust and light. The sandwich construction above the thick solid fiberglass bottoms saved weight. Carbon is used to re-inforce high stress areas. Built in dedicated, high-tech facilities in Lorient, also home to ORC Catamaran. Outremer is part of the Grand Large Yachting Group that employ tight quality control at each stage of production.

The performance is 10 to 12 knot averages with peaks over 20 knots. The jpegs give the idea.

 

[oldmulti]

Pirogue 460 tacking outrigger canoe is designed by Jérôme Delaunay – Naval Architect Plans Nautline .com. The proa is a day sailor that can be easily built in plywood from simple plans.

The Pirogue 460 is 15 x 12.5 foot with a weight of 135 lbs. The design can carry 3 adults. A lateen sail of 55 foot is on a 15 foot free standing wooden mast. The length to beam on the main hull is 10 to 1 at the waterline. A leeboard can be used as lateral resistance.

The build is plywood and timber. The hull can be built from 5 sheets of ACX plywood 6 mm thick. The tacking proa can alternatively be built from 8 or 9 mm plywood with reduced payload capacity. The design is stitch and glue with light glass layer externally in epoxy. You can use a cheap polytarp sail on a wooden mast and boom.

This is a fun cheap boat for sheltered water. The jpegs give an idea. PS The plans are cheap.

 

[oldmulti]

After building several tris with canoe type main hulls Tom Flanagan from Anacortes Washington in 2019 decided to build a lightweight carbon fibre tri for day sailing around his area. On a lot of his tri’s e used a wingsurfer mast and made his own lightweight polytarp sails. This tri’s sail was made from lumber wrap (house insulation wrapping).

The tri is 15 x 6.5 foot with a weight of 160 lbs. The windsurfer mast carries about 100 sqquare foot of sail. The length to beam at the waterline of the main hull is 11 to 1. The floats are 11.8 foot long. There is a Hobie pedal drive in the main hull. Draft is unknown.

The main hull is 2.1 foot wide allowing a person to sit in or on top as required.

The construction is carbon fibre, fiberglass over pink roofing foam 15 mm thick. The hulls have bulkheads under the carbon fibre cross beams which are glassed to the hulls. The main hull was built on a wooden male mold which was constructed from stringers and a layer of 3 mm plywood. The wooden male mold then had to be faired before the fiberglass foam hull was constructed on the male mold.

I will quote Jim for performance: “As far as performance goes l only have clocked myself on time and distance (no GPS). With a modest 12 – 14KT, I can scoot along at 5 – 5.5 Kts.”

The jpegs give an idea of the tri and the male mold used for the main hull.

 

[oldmulti]

This is a short one for those who desire real design information to understand either how to home design or check how to build a multihull structure. The information contained in this group files is mainly about composite builds. There is also a excellent news group that can provide updates etc.

To give you a sample of what is available the logon is: Log In https://fct.groups.io/g/main/files/F-9BeamPlans.pdf

You need to join the group and you will need to go to the home page: main groups.io Group https://fct.groups.io/g/main

If the moderator accepts you, it will be a free entry and no ongoing costs.

There is a lot of information in these files which will improve your knowledge.

Look up the following when you get in:
Log In https://fct.groups.io/g/main/files/Farrier%20Archive%20Project

The 1 jpeg will give an idea.

 

[oldmulti]

This item is about a Gary Dierking design called a Wa’apa. The NSW builder Aaron de Ruiter modified the design by changing the rig and rudder to suit his sailing conditions on the Hawkesbury river. The majority of the design was the original plan but the modifications suited the environment better. Wa’apa can be built in either a 16 foot or 24 foot version in either a lightweight or more rugged construction. The Wa’apa can be set up as a tacking tri, tacking proa, pure proa with either a lanteen or Bermudian rig depending on your build and preference. The Aaron Ritter version was built as a tacking trimaran with a lug sail rig.

This version is the 16 x 11 foot version (can be disassembled to about 4 foot wide) in a light weight construction. The weight of the main hull and floats total 90 lbs with a total weight of about 150 lbs. The length to beam on the main hull is about 11.3 to 1. The floats length to beam is about 10 to 1 when push down to the chines. The 14 foot solid wooden mast (60 mm max width) carries an 89 square foot lugsail from Mike Storers OzGoose design. The lee board on the main hull provides lateral resistance. The rudder is kickup to the OzGoose design offset from the main hull.

This tri is purely a daysailor with either in hull seating or on small wings either side of the main hull. 2 adults is the maximum load.

The construction is ply and timber. The dory bottom main hull sides, decks are 3 mm plywood and a 6 mm plywood bottom. The main hull has 18 x 25 mm chines, 18 x 30 mm gunnels and 3 mm plywood bulkheads with 18 x 25 frame edgings. The box section floats (attached on edge to present a V bottom) are 3 mm plywood with 16 x 16 mm stringers for the float chines. There are attach by a solid cross beams 70 x 70 mm of laminated timber. The cross beams are web strapped or tied on to the main hull and attached by bolts to the floats.

The performance is good and to quote Aaron writes: “I’m really pleased with how the new sail went. I thought that I might be overpowering the boat but she really handles the extra sail area without a problem. On the sail back from the beach to the launch site I was sailing from a beam to broad reach and got the boat up to 9.4 knots — plenty fast for me!”

The limited jpegs will give the idea.