Small trimaran with Tornado/Nacra 5.8 center hull

[revintage]

Thanks ttlf,
This gave me an idea. Can´t wrap the beams, as I might want to reverse build and go back to a beachcat with 5.5 hulls and 3.2m beams. Anyway thinking of adding 1.5m cups made of 110x2mm tubing, cut in two halves to be fitted to the center hull. The cups are 106mm inside, that could be built up with epoxy and glass, to fit the 100mm beams. It can easily be done in one layer, using this 660gr cloth/chopped mat. EDIT: Added simple sketch with table of estimated added strength. Note the cups will be clamped at the ends.

 

[revintage]

Finally found a donor for the center hull. Got this odd Tornado for free, but it will be perfect for my build. Haven´t seen it IRL, will pick it up mid-April, 550km from home. Looks like an early 70´s GRP Sailcraft/Reg White UK. A friend of mine will take the other hull and probably build another tri.

 

[revintage]

The tri build will be completed 2023, but I will false start this summer by building the widest catamaran of the available parts. The ladies in the family asks for sun decks, so by adding two removable 18x600x2200mm Paulownia boards this will be taken care of.

Up to six boards can be used on the tri, when in sun bathing mode.

Did a detailed weight analysis and the tri will be a little heavier than expected, at just below 500lbs. To compensate for this I will use a bigger rig: Tornado mast, Inter 20 main and Tornado jib, 23,35 sqm.

 

[revintage]

I have given up on the Tornado hull I was given from the nice guy in southern Sweden. Did some calculations and it will not be economical to make the 1200km trip on my own to collect it, together with time loss and costs for modifying the hull.

Realized I have no time for the catamaran project I was building around my 5.8 hulls(see image), will instead take one of the hulls and combine it with the 5.5 as amas. It will be kind of plug&play as the three have the same beam pockets for 100-102mm beams and the same distance between them, ie the beams will drop right in, without any hull modifications at all. The front beam will be 3.2m 100x3mm with 0.7m 90x3mm outer ends and the rear beam 2.8m 100x3 with 0.9m 90x3mm outer ends, to end up with a beam of 4.6m. I have just ordered 4m 90x3mm together with joining hardware from Germany to arrive next week.

The 5.8 hull is slightly shorter than the Tornado. The amas are 20cm shorter at the stern, 10cm shorter at the bow and 10-15cm lower then the aka. I might need to add a spacer in the aka rear pocket, to make everything line up properly with the ama bows a little down.

So from two old beachcats I get one tri and quite a lot of leftovers to sell.

The sketch is adjusted for the 5.8 aka.

 

[revintage]

Mock up of the boat in 8.5 ft trailer mode. Spacers needed under both beams to lift the akas ca 4" wrt the center hull. Unfortunately the center hull beam pockets are 3cm further apart than the amas. Not a problem though, as the rear beam anyway will be lifted above the pocket as the amas needs a little bow down. The sketch shows the final beam arrangement that allows trailering when "folded".

 

[revintage]

Spacers to lift the amas and also create bow down. A little clumsy but made with standard material.
It could be made otherwise but the idea is to keep the center hull intact, if wanting to reverse the build.

 

[revintage]

Rear beam ready at 17kg. 2.6m center part 100x3 with 22mm low Harken track. Outer end ktubes reinforced 90x3, 300mm overlap. Reworking the coupling with stainless clamp instead of 10mm bolt.

 

[revintage]

This is a simple drawing of the "tube sandwich" above. Still waiting for the 3.75" sleeves to arrive from UK, though.

EDIT1: Also added the readybuilt front beam in its final design, where I am also missing the sleeves.

EDIT2: When trailering the main beam middle 100x3 tubes are removed and the outer 90x3 are slid inside the 1,4m center tube to 2.0m beam. The rear center tube is removed and the overlapping outer tubes stacked and clamped. Both front and rear outer 90x3 tubes are permanently fixed to the amas.
Fits my trailer where 2.02m is allowed.

 

[revintage]

Main beam and fittings ready. After next weeks ski vacation it is time to make the fittings for the rear beam I built earlier.

 

[SolGato]

Looking good!

A cheap an easy way to protect the beam tubes from galvanic corrosion due to strap contact is to spray the underside of the straps with a few coats of PlastiDip.

I’ve deep doing this with my aluminum electric motor housings and stainless mount straps which get submerged in saltwater.

The nice thing about spraying a thin layer of rubber onto the strap versus using pieces of rubber or plastic is that a thin layer doesn’t expand or contract as much as a shim, so the clamps remain tight without any slipping.

It can also easily be touched up by spraying again if you need to disassemble and find that the rubber layer has been disturbed.

 

[revintage]

Hi SolGato,
Thanks for a great trick that can be worth trying. As I only sail inlakes, the corrosion problems are far less, than for you guys sailing on the ocean. So far I have used 70 μm self adhesive vinyl film on stainless surfaces that come in contact with aluminium for mast fittings etc..

Found another image that, to the far right, shows the clamping and locking method, used for the sliding beams. The stainless clamps are actually for joining car exhaust systems. To avoid metal against metal I use a 140 µm self adhesive PE- tape, that makes it easier to insert the tubes in each other while minimizing play. Actually the clamps will need to be isolated from the aluminium too.

 

[revintage]

Did a mockup of the cockpit frame on my Frankentri build today. With the hull DWL horizontal I set the frame to be horizontal too.

Doesn´t look nice at all, maybe a little slope rearwards is the way to go, although not as much slope as the Nacra hull deck? Is there a rule of thumb of how to do it, a little slope might be helpful, as to drain spray to the rear?

Thinking of lowering the top of side tubes, that is now 8cm above, to be flush or ca 2
cm above the rear rectangular crossbar(red).

The track on the rear crossbeam(situated just behind the crossbar) is about 4cm above the crossbar top.

 

[SolGato]

Agree that a rake toward the rear would be more pleasing to the eye and help knock down spray, and it might even provide some lift at speed going into the wind (my trampolines do on my beach cat), and I would think should also help keep the stern planted downwind so wind doesn’t get underneath and push the bow down.

Assume you are familiar with this boat?

If not, check out some of his videos of it sailing. It’s a great performer.

 

[revintage]

Hi Solgato,
Certainly familiar with Outlaw as Christofer is a friend of mine and the one who led me in to the trimaran path. Last time I visited him I bought the other hull from the A-cat he uses as center. I am rebuilding the hull for my 6x6m trimaran foiler, that partly can be seen to the left in my first image.

Did some thinking yesterday evening and realized the 80x40x3mm tubing(purple) is not enough to lift the rear of the amas to achive a healthy bow down. It was also close to impossible to turn the bolts inside them. Just ordered 100x50x3 tubing instead.

With 10mm of the 70mm tube protruding over the crossbar top, it will result in a lowered rear end of 50mm. There will be another 50mm tube(blue), with its top flush with the crossbar top, 300mm inside the 70mm tube to form the front edge of the cockpit seat.

Maybe better I take a new image when ready instead of drawing clumsy lines .

 

[SolGato]

I figured you knew the boat.

If I’m not mistaken you’re planning for a ridged cockpit (versus net) and have already budgeted the weight for it but haven’t yet decided on how it will be constructed?

Not to be a backseat designer/builder, but if you have access to airplane salvage or surplus and can get your hands on some Nomex panels the light weight and rigidity will blow your mind.

The guy who owned and modified my 30’ Cat hulls purchased a bunch carbon fiber sandwiched Nomex from a surplus yard (it’s used for flooring in commercial airplanes for example) and had constructed an amazingly lightweight ridged cabin and cockpit from it. Incredible stuff.

Sadly the interim owner cut up the cabin and threw it away, but he did save a few larger pieces which came with the hulls which is how I became familiar with it.

Somewhere I have a link to a source that manufactures and sells all kinds of honeycomb core paneling available in various sandwiching and core materials, and the pricing for some of it isn’t all that bad.