Multihull Structure Thoughts

I like your site, TrimaranMan.

 

Folks I still have an eye operation to go so I will only be doing this item and will return in a week or so. This update is of a very popular concept drawing in November 24.

This is a significant update on a design done by Eric Henseval (from France) for a build in Poland. It is a plywood build and is listed as “easy to build” for the professional or home build design. This is a fast cruising trimaran that has many sail options on a racing type rig.

The “DIVINITE 8.50m” plywood trimaran is 27.9 x 18.4 foot with a weight of 3,020 lbs and a displacement of 4,480 lbs. The 35.8 foot mast carries 510 square foot upwind with a 316 square foot, a 164 square foot fore triangle, a 193 square foot solent, a 102 square foot staysail and a 538 square foot asymmetric spinnaker. The main hull length to beam is about 10 to 1. The length to beam on the floats is 16 to 1. The draft ranges from 1.3 foot to 5 foot over the central hull daggerboard. There is 440 lbs of fresh water ballast per float. Transferable from one side to another with a smart plumbing system. The engine can be a 10 HP outboard. The cross beams are demountable by bolts so the whole tri can be transported in a single 40 foot container. The hull shape is dory single chine in the main hull and I presume in the floats.

The accommodation comprises of a main saloon with 2 seats/berths with vision 180° when sitting looking forward, convertible in double berth. The main saloon has 6 foot headroom and also has a galley, chart table, ice box location and a porta potty. There is a double berth forward. There is storage in the floats.

Construction is a plywood epoxy with e-glass on many external surfaces. The hull bottoms are 12 mm plywood. The hull sides are 9 mm plywood with the bulkheads being 12 mm except the main beam bulkheads which are 25 mm plywood. All bulkheads have timber edge framing. The hulls have stringer support at about 300 mm centrelines. The decks are 9 mm plywood with deck stringers where appropriate. The 150 mm aluminium tube cross beams that are bolted vertically onto the hulls. Not shown in initial diagrams but I would be certain they will be there are waterstays. Chine lines etc are taped seams. “Easy to build” is Eric’s claim. Eric has designed many smaller multihulls before and really knows how to design simple to build effective cats and tri’s. I will accept his words.

No performance data but the rig, light weight and hull shape indicates high average speeds will be possible EG peaks near 20 knots and easy 8 to 10 knot averages in short bursts. But remember this is a high performance cruiser not an outright racer.

The limited jpegs will give the idea for this excellent, much easier to build than a farrier, high performance cruiser.

 

Featured in post #2881, here is video footage of the ModX in the flesh:

 

It’s been so quiet around here with OldMulti away.

Hope you are doing well OldMulti!

Thought I would post another to help tie everyone over until he returns.

Our summer sailing/mooring season has started as our offshore waters calm, with boats making the annual pilgrimage from our harbors on the south side up to the Northshore’s Bay of Hanalei on the Hawaiian island of Kauai.

A few weeks back I accompanied some friends on the boat I covered in post #3027.

Here is a little video documenting the adventure:

 

Hi. Finally got the medical all clear will be back tomorrow. Have fun.

 

Welcome back we missed you.

 

Westerberg is a specialist aluminium boat and trailer manufacturer in Albany Western Australia. The waters off lower left of Australia can range from calm to full gales that come from the Antarctic. In short you need a good riding boat that can handle difficult conditions. The Wildcat 6.6 and 7.2 meter cats are trailable and can handle bad weather if required.

Ther Wildcat can be either 6.6 (21.6 foot) or 7.2 (23.6 foot). All other dimension are the same so we will focus on the 7.2 cat. The 7.2 is 23.6 x 8 foot with a loaded weight of 7600 lbs. The power is 2 x 200 HP Suzuki outboards with a total of 500 litres of fuel. Cruise speed is 20 knots but peak speed is near 30 knots.

Thers is a head in one hull bow and storge inn the other hull bow. The pilot house provides seating for wet days. As Westerberg is a custom builder cabin configurations etc can be modified to suit. This cat is intended to be a fast coastal fishing craft for pleasure or a professional so there are limits to the modifications that should or can be done.

This cat is well built and strong with an aluminium hull and underwing of 5 mm. The tread decks are 4 mm and the cabin top is 4 mm. There are aluminium bulkheads with limited “stringers/chines” in the sides and ribs on the underwing.

This cat has an excellent hull shape and according to one experienced tester is the softest riding cat going into waves he has driven. A nice example of what can be done in a aluminium fishing cat.

The jpegs are mainly of the Wildcat 6.6 but the first jpeg is of the Wildcat 7.2.

 

This Crowther designed 40 foot catamaran was built in France in 1992 under the Cantana brand. The basic design was done in the mid 1980’s. This cat started the higher performance cruising catamaran trend. It was partially commercially successful and many were produced.

The 40 is 40 x 19.4 foot with a shell weight of 10,300 lbs and the displacement is 22,600 lbs. The 57 foot fixed aluminium mast carries a 527 square foot (6 full batten) mainsail, a furling 371 square foot jib and a 842 square foot Hood spinnaker. The draft is between 2.6 foot (over rudder and skegs) and 8 foot when the hull based daggerboards are down. The engines are 2 x Volvo Penta 28 hp diesels.

The accommodation is where this cat is considered “old fashioned”. The wing based double berths are narrow compared to modern cats and the head shower are aft in the hulls with access to the engines through a bulkhead hatch. The wing deck cabin contains a smaller U shaped seating (smaller due to wing deck bunks limiting available space. The galley on the aft cockpit/cabin bulkhead which only allows a 2 foot wide doorway. The cockpit is smaller than other cats of this size. Most later 40 foot cats have wider beams allowing more cabin/deck space and larger hulls with chine steps allow wider berths.

The performance of this series of cats was good. The were fast and very seaworthy with 10 knot averages and peaks of 20 knots possible.

The 5.8 meg PDF provides insites into the construction of the cat. The build started with a polyester unidirectional fibres on PVC foam structure but evolved into vinylester and epoxy resins.

Get a good used version of this cat and you should be a happy person if you are not going to be sailing with a crowd. The jpegs give the idea.

 

Many people think that a well rounded hull shape is the ideal. In terms of ultimate performance it may be but for most people who just want a relatively fast boat for the occasional race and a lot of cruising is the effort of a light weight round hull shape worth the extra build time. The following 2 trimarans are examples of good boats that are relatively light, simple plywood builds that may not go as fast as Farrier tris but will sail well and surprise many as to their seaworthiness and speed.

The Marples Seaclipper 28 has been around for 30 plus years and many homebuilt versions have travelled long distances. Speeds of up to 20 knots have been reported. Seaclipper 28 is 28.5 x 18.5 weighing 1900 lbs displacing 2650 lbs with a 32 foot mast carrying 166 square foot main and a 205 square foot genoa. The length to beam on the main hull is 8.5:1.

The Divinite 8.5 is a new design by Eric Hensval of similar dimensions with more modern hull shapes (mainly in the floats). The “DIVINITE 8.50m” plywood trimaran is 27.9 x 18.4 foot with a weight of 3,020 lbs and a displacement of 4,480 lbs. The 35.8 foot mast carries 510 square foot upwind with a 316 square foot mainsail and a 164 square foot fore triangle. The main hull length to beam is about 10 to 1. The length to beam on the floats is 16 to 1

Now let’s compare the hull shapes. Both have a single chine dory hull shape on the main hull. The Seaclipper 28 has a deep V float shape. The Divinite has a flat bottom narrow hull float shape.

Both of these tris would have relatively easy to build hull shapes especially in plywood. The deck portions of the hulls vary in complexity. The Seaclipper can have a flat low headroom deck or a standing headroom cabin with slight wing deck extensions. The Divinite has full headroom cabin with wingdeck extensions.

Both boats are mainly plywood with timber support. The plywood is mainly 9 mm with some 12 mm in both boats. The crossbeams on the Seaclipper can be solid or swing wing timber structures. The Divinite has 150 mm Aluminium tubes with waterstays. Both systems are easy to do and both boats are transportable and will fit into a 12 meter container.

I suspect the Divinite will perform better in outright speed due to a bigger rig and better float hull shape but I think both tris will be equally seaworthy with similar average speeds when cruising. Simple hull shapes like this work very well if well designed by good designers. Compare the cross sections of the main hulls of both boats and you will find a lot of similarities. The floats are where the major differences are.

The jpegs give the idea.

 

I thought I was miss reading something but Morelli and Melvin were designing foils for pontoon boats. Pontoon boats being the aluminium cylinder flat deck party boats for motoring in bays and lakes type boats. About 50,000 of various sizes of pontoon boats are sold in the USA each year. Some can get to 35 knots with big enough outboards but I did not think of them as being “performance” machines.

The company Hydrofin “guarantees you an extra 20% performance in the higher speed ranges when you fit a hydrofoil fin on a 2 to 2.3 foot cylindrical hull. Interesting. What do they mean in performance gain. For the same speed through the water the hull with no fins would need to be revving at 5000 rpm (150 HP Mercury outboard). The same hull with the same weight (3000 lbs) and outboards with Hydrofins would achieve the same speed but the outboards would only be doing 4100 revs. Lower revs mean less fuel.

Now to achieve this efficiency gain the foils start lifting at 15 MPH and the foils need to generate 1200 lbs of lift at 30 MPH. To achieve this lift, the angle of attack of the foil has to be 1 degree up at the front. But the real trick is where the foil is placed to produce the lift. First you need to find the Centre of Gravity of the total boat and secondary gear in normal motoring state. Then you need to place the foils 6 (152 mm) to 9 (229 mm) inches forward of the Centre of Gravity. Hydrofin kits come with an attachment plate, glues and very good instructions on what a professional attachment person needs to do.

The foils themselves are 6061 aluminium and any attachment bolts are 316 stainless. The major backing plate to a foil is aluminium.

The performance test results on pontoon and 3 hull tritoons have backed up the performance claims of 20% improvements. Morelli and Melvin were initially skeptical when asked to do this work but once they did the analysis and design understood what the customer wanted. Pontoon owners who wanted more speed often repowered their craft with bigger engines for many times more than the cost of a set of foils which achieved the same speed increase for less fuel.

The jpegs give the idea.

 

Well... it does sort of beg the question ; when will we see them on sailing cats/tri's ?

 

I’ve been following the adoption of foil assist on pontoon boats for a little while now.

There are some very simple kits available that consist of a few brackets and a foil section that spans between the pontoon hulls that still allow for easy trailering and launching that give all the positive benefits of higher speeds, quicker planing, and better fuel economy.

The impressive results have inspired me to incorporate foil assist on my 30’ Solar Electric Cat in an effort to increase efficiency and smooth out the ride.

M&M has also worked with builders like Aquila to incorporate foil assist with impressive results.

 

Poulain 901 tri started as Van Peteghen-Lauriot Prévost design in 1985 and was built at CDK. It was designed to be 75.4 x 53.4 foot displacing 19,000 lbs with a 97 foot mast. The original build tried to meet these numbers but ended up being 75.4 x 53.4 foot displacing 30,400 lbs with a 85 foot mast. So how did this tri after modification end up being an 88.5 x 53.4 foot displacing 36,500 lbs with a 105 foot mast. The modifications also lengthened to floats by from 70.8 to 87 foot. These are a lot of changes for an old design. Why? Because the base structure was good but when Charal wanted a tri for serious racing they provided a 15 million Euro budget to up grade the tri in 1994. The tri was now seriously fast but this is not the end of the story. Sports Electra was the next sponsor who took on the tri and Olivier de KERSAUZON sailed it around the world in 71 days. Next with new rudders and deck plan under a new sponsor IDEC, Francis JOYON sailed the tri solo around the world in under 73 days. After more record breaking the IDEC (Poulain 901) tri completed a transatlantic run in 2008 and ran aground and destroyed near its home point in France.

This boat succeeded because of 2 factors. It was well designed and built at the start. The initial structure was PVC foam with Kevlar and epoxy all round. And the second factor people recognized the basic structures potential and put some serious money into the upgrades and modification. The upgrade budget of $10 million US plus in 1994 was serious money but the sponsors were rewarded with many racing successes. Olivier de KERSAUZON and Francis JOYON were French national hero’s and provided sponsor with days of prime time news coverage etc.

In the final configuration IDEC was 88.5 x 53.4 foot displacing 36,500 lbs with a 105 foot rotating wing mast carrying 3,440 square foot upwind and 6,400 square foot down wind. Draft was 14 foot. The average speed around the world was 17.6 knots with peaks over 30 knots. This is one very large boat to single hand around the world at these speeds.

The jpegs give the idea of an excellent tri.