9m Steel Catamaran; thoughts?

The paint on my boat is now over 15 years old, but on fresh water. It has worn thin in places, but with no peeling patches.I applied 3 zinc primer undercoats and two top coats with rollers , so the coats were thick.

I suppose you could call modern epoxy paint systems steel/epoxy sandwich...lol.

 

Seems you know the price of coatings.

A while ago someone was on here wondering about cheaply (the price of steel had crashed) building an 85" Bruce Roberts steel yacht. In a couple minutes I figured out a rough price for coatings and it came to $80k IIRC.
Never heard back from him.

I think Bruce Roberts offered a steel cat plan,looked on his site and couldn't see...maybe email him.

 

I've seen the Bruce Roberts steel Cat somewhere on his site; its a massive 60' by 28' motor Cat which can Max out at 10kts. He's keen on his radius half pipe bottom chine instead of a normal hard chine; a lot of extra work for what gain?

Where would you find moorings in the Med to tie up a boat with that massive beam?

 

I'm fairly sure he had one in the mid 30's foot range, but for sure I recall it was a rather a homely thing...

 

Apologies for taking so long to reply - I've been rather distracted by other things happening.
The shell plating on Rumpy Pumpy is generally 4 mm, although the keel plates are (I think) 6 mm.
The hull frames were plasma cut from flat plate - however they did wobble about somewhat when setting up, and they only 'stiffened up' when some flat bar longitudinals were tacked in.
If I were doing it again (in either steel or ally) I think I would either weld flanges on to the frames cut from flat plate, or build them from unequal angle bar (and if in steel, ideally blasted and primed before assembly, similarly the shell plating).

Re the Boden design, it looks like a typical cabin cruiser design transposed on to a catamaran hull - and I don't think that works very well.
And I am not too sure about that pronounced step in the side elevation in way of where the stern tubes are - looks like this would cause a lot of extra form drag, and maybe upset water flow to the propellers?

You had previously posted this :
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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.
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I think that a cat like Janthina (in the scanned pages attached) would fit this SOR - except that she is plywood.
Although it shouldn't be too difficult to re-design her with chined hulls for building in steel - you would have to be very zealous with your weight calculations though.
Most of the accommodation is on the main deck, rather than down in the hulls, and she has her wheelhouse forward like a trawler, rather than the aft wheelhouse on the Boden cat.
And she is less than 12m LOA as per your SOR, and with two small diesels and 500 gallon fuel capacity she apparently can do 2 mpg (and probably a fair bit more if you slow down a bit).
The article about Janthina is also online, with Google books - https://books.google.com/books?id=9...A135&dq=janthina#v=onepage&q=janthina&f=false

Just for general reference, re forward wheelhouses, here are the range of Ranger tugs for design ideas, although I appreciate that they are monohull rather than catamaran.
http://www.rangertugs.com/models.aspx?itemid=2634&pagetitle=Build A Boat/Models

Similarly the range of Nordic tugs :
http://www.nordictugs.com/models/

This is an interesting trawler type of power cat, but her hull form with the wave piercing bows would be more complex to build in steel, and she would have to be scaled down a bit to be under 12m.
http://www.trawlercatmarine.com/recreationaldesigns/tmd45.html

 

>>The hull frames were plasma cut from flat plate - however they did wobble about somewhat when setting up, and they only 'stiffened up' when some flat bar longitudinals were tacked in.
If I were doing it again (in either steel or ally) I think I would either weld flanges on to the frames cut from flat plate, or build them from unequal angle bar (and if in steel, ideally blasted and primed before assembly, similarly the shell plating).<<

I've only built with fabricated frames , but I've seen lots of shipyards build from plasma cut bulkheads and frames. Besides having to spot weld angle iron to keep them straight and true for the plating, the other problem is that you can't adjust the size of a frame cut out of one piece of plate once its in place like you can with a spot welded frame made from angle, which can be ' adjusted ' in situ to fit the precut hull plating .

Jantina is exactly what I'm looking for , a sort of small explorer yacht.

Here's some more photos ive already posted in the thread of a tunnel cat design built for wind farm servicing in Ireland....but in alloy.a very similar design to your suggestions.

 

The SMS Coastal Cat looks very neat - but even built in ally she is very 'tubby', rather like a tug - and she would have to be even more tubby if she was built of steel, AOTHBE.

Here is an interesting cat - just under 12m, all accommodation on main deck, and with a possibility of a flying bridge.
http://www.multihull.de/flatcat/FlatCat_Power_de.pdf

 

Nice design; there's little doubt that's its much better to go for a galley- up, as well as the saloon all on one level. You would need at least 40-50' in a very wide beam to make use of the hull spaces without taking away from the width of the living space in the saloon.

IMO most boats seem to chugg along at 8-10kts whatever their design, so the weight of steel construction may not be a big a disadvantage as you would first imagine; and in a steel cat you still have a 15kts run for shelter option in a pinch.

There appear to be lots of options available to build on a flat deck cat hull.

 

Hi Rusty, I'm wondering if you have made a final decision yet re the steel Boden cat?
If not, then have a look at this design from New Zealand - they note that it can be built in steel.
http://devilliersyachtdesign.co.nz/10-5m-alloy-house-cat/
And although they say 'aluminium only' for the deckhouse, I guess this could be built in (eg) ply/epoxy on to the steel hull.

 

Thanks, that's an interesting design for steel construction. The kiwis are masters of the catamaran and because their seas are notorious for steep waves they always give due consideration to bridge deck clearance.

I just came across this old alloy charter Cat from the '70's at a very reasonable price ; it has twin 50hp diesels that top out at 8kts, but the hull form looks like it might work at a faster speed with bigger engines.

There's a video at the bottom of the page that gives an idea of the hull form .

http://www.findafishingboat.com/alicraft/ad-79481