High end vs low end cruising catamaran

cando2 said:

Mulkari. Besides performance hull shape, what are those other improvements you wish to make? Will you be building inside with a concrete floor or outside under a tarp? How long do you anticipate it will take to complete? I'm struck by how inexpensive your current boat was to build compared with how much you expect to spend on this future build; why so much more? Regarding your 1.5x your current displacement goal, I'm guessing even a 13 meter boat will render a displacement of 2x plus, which wouldn't be a bad thing. There is a prominent US designer who has been designing tube cats for over 3 decades. He can do slight mods to stock plans for little extra cost. He is known for least costly high performance cruising hulls with a quick build system which are worth looking at IF you are clever and have build skills above average, do not require perfection, and can live with slight variations between hull builds.

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Other improvements kick up centerboards , beachcat style kick up rudders, better crosbeam design. I don't want any mechanical parts inaccessible under waterline. I will build inside in a small hangar with concrete floor. I'm, guestimating around 5 years to get to sailable stage, then things like finishing interrior can be done later.
You misunderstood about 1,5 size factor. I meant not displacement, but length and beam, If current boat is 9.5 m hull length then new boat would be 14 - 15 m long with around 1.9m wide hulls and around 7.5m total beam. Displacement would be guestimating around 9 tons. Ideally I would like around 3 ton payload capacity so 6 ton empty weight would be target.
Cost I just guestimated, if I manage less then great. When I built my current boat I initially estimated around 15k euro which when considering new sails I bought later was pretty spot on. Now things are more expensive so if just scaling cost by displacement then I arrive somewhere at 100 - 150k .
Can you post a link to that designer?

Rumars said:

Do the right thing and insulate the hull, regardless of what it's made of.
Dix has a ply cat where he fits EPS between the stringers and follows up with a thin ply panel glued on top. This way you achieve a smooth interior, wich is a big thing for stringer frame ply builds.
If you go composite you can carve a male mold out of foam and sculpt the interior into it afterwards. With intelligent design this way you could even build the hulls single skin using polyester resin, wich would probably be the cheapest.

I am going to say the heretical thing: for a true cruiser buying diesel is more advantageous then buying new high performance sails. Even at 2€/l diesel will economically be better. Your boat will be big enough to need proper inboards anyway, so there's no added cost for the engines.

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Yeah insulation is a must given where I will sail, it's great in hot tropics too. I'm looking forward to wood and plywood build. I like to work with those materials and here I can buy plywood suitable for marine use directly from factory at great price.

I'd really like outboards, diesels are heavy and expensive, have to be located inside, need shaft or saildrive that can't be serviced on water and even minor grounding can cause expensive repair. Given experience with my current boat cruising Baltic and North sea I use my 6 hp outboard motor very little mostly when it is really zero wind and to get up and down river where my dock is located. My current boat sails really well. If there is 3 - 6 knot wind on beam reach I usually sail same speed, if wind angle allows for asymetric spinnaker then maybe even little faster.

I've insulated plywood boats with eps and a layer of 2.5mm plywood cover. Never had a squeak, even in rough weather. There is no need to glue it, but if you want there are inexpensive adhesives specifically for the application.

What squea

Mulkari said:

I'd really like outboards, diesels are heavy and expensive, have to be located inside, need shaft or saildrive that can't be serviced on water and even minor grounding can cause expensive repair. Given experience with my current boat cruising Baltic and North sea I use my 6 hp outboard motor very little mostly when it is really zero wind and to get up and down river where my dock is located. My current boat sails really well. If there is 3 - 6 knot wind on beam reach I usually sail same speed, if wind angle allows for asymetric spinnaker then maybe even little faster.

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With an open deck cat it diesel doesn't have to be expensive and complicated. Lift a mechanically controlled diesel out of an older car/tractor, install on deck including radiator. CV joint out of a big 4x4 car including wheel bearing enclosure, pipe and you have a swiveling longshaft drivetrain. Dry manifold, water injected downstream via a small pump fed from an inlet near the propeller. Sound enclosure over it to serve as deck bench or table.
A 10t 14-15m cat will need a 40-60hp engine if it is to be a go anywhere boat.

You should also add a two direction thrust bearing.

Rumars said:

What squea


With an open deck cat it diesel doesn't have to be expensive and complicated. Lift a mechanically controlled diesel out of an older car/tractor, install on deck including radiator. CV joint out of a big 4x4 car including wheel bearing enclosure, pipe and you have a swiveling longshaft drivetrain. Dry manifold, water injected downstream via a small pump fed from an inlet near the propeller. Sound enclosure over it to serve as deck bench or table.
A 10t 14-15m cat will need a 40-60hp engine if it is to be a go anywhere boat.

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That's definitely an option similar to drive trains of many boats in East Asia although outboard is more plug and play solution saving time. Also it is something that can be upgraded later if outboard is found to be inadequate. Not sure if there are high thrust versions of 40 - 60 hp outboards like there is for 9.9 hp Yamaha.

gonzo said:

You should also add a two direction thrust bearing.

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That's what the wheel hub is for, it contains two opposed tapered roller bearings. The housing needs two trunions as pivot points, those run in plain bearing mounts fixed to the cats beam. That's so you don't have to pivot the entire engine as the asians do.

Mulkari said:

Not sure if there are high thrust versions of 40 - 60 hp outboards like there is for 9.9 hp Yamaha.

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That is exactly the problem, it's a difficult beast to find. The mounting is also to be considered, usually some sort of sled or motor well. This isn't to say that it's impossible, you can use outboards even at this size, but it's definitely not as simple as on a smaller boat.
The pivoting longtail on deck is also a more complex installation then the usual saildrive or shaft, so it's rarely seen.

The new trucks usually have ball bearings. They can take some lateral load, but I don't know how much continuosly. I know some older equipment has tapered rolled bearings, so those should be fine.