9m Steel Catamaran; thoughts?

Discussion in 'Boat Design' started by rustybarge, May 20, 2016.

  1. rustybarge
    Joined: Oct 2013
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    rustybarge Cheetah 25' Powercat.

    Can a small 10 mtr cat be built in steel?

    Here's another one from the Shetland islands in Scotland , but was designed for use on a fish farm in sheltered waters.


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  2. Richard Woods
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    Richard Woods Woods Designs

    I'm sorry. To clarify, I meant for recreational use. The flat fronted bridgedeck, above, would certainly limit its use to sheltered waters!

    RW
     
  3. rustybarge
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    rustybarge Cheetah 25' Powercat.

    In fairness, I can't disagree with you. Lol.

    But ...

    I've seen literally thousands of abandoned home builds on the internet because ply, foam sandwich and GRP construction is painfully slow and takes thousands of hours of work to complete a project .

    We all know cats are hyper sensitive to weight because of the limited buoyancy in the slim hulls. But when you consider that an average general purpose cruising cat like the PDQ34 easily attains 15kts on 20hp/ton in a big heavy design all be it in GRP. So the Bowen weighs in at 6.5 tons in steel, instead of a similar ply design at 2.5 tons, but would only require twin 75 hp diesels to push it at the magic 15kts.

    In fact I've penciled in 10-12kts it's as the most likely cruise, and estimate about 10-15hp/ton as a probable power requirement at that speed ...?

    There is a massive choice of low power diesel engines in that power range at very reasonable cost.
     
  4. Richard Woods
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    Richard Woods Woods Designs

    I think you also need to check out, for example, the Aspen 32 and Endeavor cats. I thought the PDQ had twin 110hp?

    Most of those boast of 2mpg economy, which you may find more than you'd like. yet all are maybe half the weight of a steel boat, so you'll need bigger engines and use more fuel

    RW
     
  5. rustybarge
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    rustybarge Cheetah 25' Powercat.

    Here's my SOR if anyone would like to make suggestions ...

    Less than 12 MTR to fit typical Med marinas smallest space.
    Cheap and quick to construct as home build.
    Stable at anchor; planning to anchor out a lot.
    Small diesel engines/ twins for safety .
    15kts Max run for shelter; 10-12kts cruise.

    Large covered cockpit/ open plan saloon/ galley up.
    Cabins secondary consideration; one double , kids sleep on couches.
    Full standing headroom everywhere.
    Would like FB, but maybe too heavy .

    Summary: cheap to construct and run , manageable size for 2 pax to coastal cruise warm Mediterranean climate.
     
  6. whitepointer23

    whitepointer23 Previous Member

    ok i have to bite. why do you keep saying ply is a slow and tedious construction method, i find it is the opposite. as far as abandoned projects go i see mainly steel yachts advertised here as incomplete . i don't know if its the tedious grinding and welding that is the reason but i suspect its more to do with steel projects being larger , usually 30 to 50 ft. the owners work on them for so long they lose interest or get to old to finish them. i can think of 4 or 5 for sale at hull and deck stage without even looking .
     
  7. rustybarge
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    rustybarge Cheetah 25' Powercat.

    OK; I fell in love with the 30' Devlin 'Slipknot' picnic stich and glue epoxy design, and I noticed on the website that Sam Devlin actually builds these designs to order in his own workshop. So I though to myself ' this a pretty boat, I wonder how much a ready made hull and superstructure in ply would cost?'

    In steel a 30' boat would be about £30-35k, still in primer coat.
    Alloy about twice that amount, plus a bit...lol.

    I waited for his email with a rising sense of excitement....$186k plus shipping...this reflects the thousands of hours work to assemble, sand and fair the hull and superstructure . no paint included, no windows, no engine; just the structure . Not sure how many thousand hours Richard estimates for his Scoota 30' , but you can buy a finished ply boat for $ 120k ; not sure what state of finish that includes.

    I have nearly zero experience with epoxy, except the dinghy I built , but my take on the process is:
    The ply hull dry assemblies at the same speed a steel; stitching is a little bit slower than tack welding ...
    Then putting tape on the joints is a bit quicker than continuous welding.

    Now the hardship starts ..lol. Sanding, wetting out, curing, sanding, etc etc ..
    Then after thousands of hours of very boring dirty back breaking sweaty work you have to fill and fair the rough surface to get an even smooth paintable surface. Steel is already smooth and even; OK you have to grid out the welds at the chines, a reasonably quick process .

    Phew, I'm exhausted just talking about it!
     
  8. Richard Woods
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    Richard Woods Woods Designs

    Sam does really good work, you pays your money...

    We paid an hourly rate for our Skoota 28. As you see it in the videos it took 2300 hours to build. another one would be quicker, Josh estimates 1800 hours. The USD120,000 includes engines deck gear etc

    Not yet sure how long the Skoota 32 will take, I'll post photos of the first hull later this week, when I get them. obviously the second hull will only be a couple of days as the mould is now made (which took about 2 weeks)

    I have seen many steel boats that needed filler because of weld distortion (read Eric Hiscock on Wanderer 4 for more). Most workboats don't bother to get a yacht finish. You can get the same no filler finish quickly in wood. It is the finishing that takes the time

    RW
     
  9. rustybarge
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    rustybarge Cheetah 25' Powercat.

    Aha, I didn't realise the Skoota 32' was a GRP moulded boat.

    Will this be available as a hull/superstructure kit for home finishing and do you have a ball park idea of the price?
     
  10. Richard Woods
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    Richard Woods Woods Designs

  11. rustybarge
    Joined: Oct 2013
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    rustybarge Cheetah 25' Powercat.

    Thanks, had a chat with Ian.

    He will supply a kit with the finished hulls, wing deck and roof (two pieces), with flanges ready for the home builder to join together and laminate; temporary bulkheads fitted for transport, for £50k.

    Complete shell ready for fitting out £115k.

    A finished boat fully fitted out is £150k.
     
  12. serow
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    serow Junior Member

    These are referred to as plasma cutters. They are very handy and can do a good job.The nozzle is on the end of a lead like a mig welder and has to be guided along the chosen path. By far the best way is to somehow fix a guide offset by appropriate dimension, about half the diameter of the head[head dia say 25~30mm] otherwise it can get a bit like one of those fairground games where you have to guide a handle around a wire without ringing a bell.
    The cut is about 2#3mm wide, but if you stop you get a small circle and it can be a bit messy to start again. For 3mm you can easily get one to run on 240 volts. They need an air supply to blow the spark into the steel and create the burn. Consumables are nozzles and air. I guess they are slightly more expensive than mig welders. A half decent Sealy one will do you, even though it might be a bit clapped out at the end.
    Don't even consider a jig saw for this project. Your teeth will fall out.
     
  13. rustybarge
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    rustybarge Cheetah 25' Powercat.

    I grew up on a farm and we used cutting torches and stick welders , so I'm looking forward to trying out a plasma profile cutter. Its interesting to see how much steel kit suppliers charge for cutting steel, if you click kit prices link on this site it shows you weights of the precut parts which seem to come in at about €2k/ton.

    https://www.bonitoboats.eu/products.html

    The price of steel plate in Europe at the moment is €300/ton, so cutting your own patterns and descaling and priming the steel will save lots & lots of money. Of course the big commercial plasma cutters cost hundreds of thousands of pounds, so they have to get a return on their investment.

    I think the lesson home builders is cut fabricate and weld everything yourself; the moment you buy in ready made stuff the costs will escalate out of control.
     
  14. serow
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    serow Junior Member

    You're certainly right about it costing a lot more. At the moment a laser quality 3mx1,5m x3mm sheet will be around £65-75 which is getting on for £1000/T.
     

  15. serow
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    serow Junior Member

    ....1000/t. Cutting may be another £40-50 so you're getting to the £1500/ton which is not a million miles out. As to time saved who knows. Cutting it by hand, fairing it etc will probably take longer than the assembly and welding, but of course you're not paying anyone so I agree with your comments. Of course you could also mine the iron ore yourself and make a further saving. With a plasma cutter, angle grinder, mig welder and mainly enthusiasm you'll be fine. You could reserve any professional cutting for really tedious small parts.
     
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