Aluminum Semi-Displacement Catamaran Build

A few shots of the main cabin and framing.

The first is the platform for the mattress.

The second is the companion way - steps are bent into shape, but have not been welded in yet.

The last two shots are the framing structure. They don't really tell you much, but they are great to look at.

A couple shots of the starboard side deck and ER. Engine is still just sitting in place. It gets moved aft a foot or so when it's actually mounted to the stringers.

Despite having to potentially work on the engine in the rain or under a beating sun, I wanted the ER under the cockpit platform rather than under the saloon sole.

I love diesel engines, but I think there's a lot of advantages to having them out from under your feet. It's much like the relationship with my wife - I love her, but sometimes a little distance is a healthy thing.

Which engines are they again? Love the aluminum placard detail! But, your anti vinyl edict needs examination, because I think your ship needs a diagonal color band like the big boys have. I’m going to put one on mine in blue, really gives it an official look.

Engines are JD 4045-AFM85's.

Yep, I'm anti-vinyl I guess. But the builder just put a vinyl wrap on the house of a high speed cat that's just ahead of me on the shop floor. The wrap looks good, but it's not for me. BTW - the cat that's just ahead of me got sea trialed recently. Apparently the two Arneson surface drives and the Cummins engines move that thing like a scalded cat!

I’ve been aware of arneson surface drives for many years, and I still feel like I don’t understand them at all!

Sea Word said:

I’ve been aware of arneson surface drives for many years, and I still feel like I don’t understand them at all!

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That's because they operate on the principal of Magic. I could explain it, but a magician never reveals his secrets.

According to the Keeper of the Schedule - we seatrial in 12 days. Call me a pessimist, but I see more than 12 days of work to do.

But to their credit, it looks more like a boat than a pile of aluminum. Although one of my co-workers just said it looks like a toaster.

Bkay said:

According to the Keeper of the Schedule - we seatrial in 12 days. Call me a pessimist, but I see more than 12 days of work to do.



But to their credit, it looks more like a boat than a pile of aluminum. Although one of my co-workers just said it looks like a toaster.

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Looks Awesome!

Congratulations [emoji322]

Very exciting!

Would like to see some engine room pics if possible

Definitely prefer the aluminum logo.
My John Deere dealer put one of those 4045AFM85s in his play bay boat. Says it top ends at 27 knots and comfortably cruises at 22 knots. Boat name is Deere Lady. I'm curious to see how smooth they are in your aluminum boat. I have the 4045TFM75 in my trawler, and am extremely pleased with its performance.

Ted

cardude01 said:

Would like to see some engine room pics if possible

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Certainly. Although the only engine room pics I have show just an engine shoved in there and no other equipment. I'll post some more detailed pics once we get engines and running gear in place and some of the other equipment is put in.

It may have to wait till I make another trip down there. Sometimes technical photos showing details are hard to come by unless I shoot them myself.

O C Diver said:

I have the 4045TFM75 in my trawler, and am extremely pleased with its performance.

Ted

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Glad to hear. I've not had JD's in a boat before, but I have had them on land based equipment. I'm hoping they are worth the price!

A sister ship (near cousin actually) to mine had the same engines and I was very pleased with the low noise and vibration at virtually all running speeds. Engines were quiet enough that you could hear the oil can effect...I guess that's a plus.

Bkay said:

Glad to hear. I've not had JD's in a boat before, but I have had them on land based equipment. I'm hoping they are worth the price!

A sister ship (near cousin actually) to mine had the same engines and I was very pleased with the low noise and vibration at virtually all running speeds. Engines were quiet enough that you could hear the oil can effect...I guess that's a plus.

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The counter rotating balance shafts do an excellent job of reducing vibration in the 4 cylinder engine. You will likely find that you will have to adjust the idle up a little (still within manufacturer's limits) to have a smooth idle. At the bottom end of the idle range, the counter rotating balance shafts are ineffective and it just feels and sounds bad.

Ted

For those interested in such things - which is probably 98% of the people reading a build thread - electrical work has started.

Initially I was scratching my head wondering why they put the starboard engine master switch on the left and the port master switch on the right. Then in a blinding flash of the obvious it dawned on me that this panel will be mounted facing aft so the controls will be intuitive. I guess that's why you boat drivers use port and starboard and not left and right.

So far I'm pleased with how things are shaping up and I've only had a few gripes which have all been addressed. Fingers crossed!

I had some questions about the engine rooms. Here's a few shots as they stand now - not much to see yet.

I have port and starboard ER's. I'm trying as hard as possible to keep anything out of the ER that doesn't deal with propulsion or steering. But my tank rooms are filled with...well, tanks. So some things will have to go in the ER.

First shot is from cockpit with large hatch visible. Second shot is the same thing. Third shot is aft end of ER with rudder bearing and last shot is from forward of the engine looking aft.

Access to area forward of the engine is through a weld-in hatch on the side decks.

The PDF shows the basic layout of the starboard ER as shown in the photos. I'm making a few changes to this layout to improve deficiency. But this is a decent enough overview.

Looks like it'll be pretty cozy working on that engine.

ssobol said:

Looks like it'll be pretty cozy working on that engine.

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You're right, there is no excess space. Certainly better than some boats I've worked on, but not great by any stretch of the imagination.

I made a Visit while on a business trip in that general direction. They are making progress, albeit slowly.

Here's a few progress pictures. The exterior looks the same - but I understand they have finished about 90%+ of the finish welding, which takes time but doesn't make an obvious difference.

They have the port exhaust and raw water intake roughly fit. Raw water is drawn via standpipe with clean-out on top. It's a little longer raw water circuit that I'd like, but their engineers needed to find a location with sufficient blocking and bracing to ensure sufficient strength of the stand pipe. Which meant they were limited to areas near the watertight bulkhead where they could weld bracing in. Everything's a compromise.

Rudders are welded stainless steel (I don't recall the grade) and are framed with an eliptical profile. They will form the profile with epoxy and foam and cover the whole thing with fiberglass.

The rudders are being made at Winter's Custom Yachts. Once the rudders are finished, they are ready to go in with all the running gear.

Mast is dry fit here. Looks sufficiently manly!

And finally, some wiring is going in!

What’s the thinking behind the Fiberglass covered rudder?

Sea Word said:

What’s the thinking behind the Fiberglass covered rudder?

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Well, these cats like to go in a straight line...they like it a lot. So a simple plate rudder won't give adequate turning motion. The NA who designed this boat, and a number of other similar hulls, specified an elliptical rudder. The basic elliptical shape required is almost impossible to get in all metal construction so he uses a plate with 90 degree flanges (they are not really a flange, but I don't know a good boat word for them) to provide the outline of the shape. Epoxy or some other non-water permeable filler is used to provide the body of the shape.

Really, as I understand it, the fiberglass is nothing more than a skin on the epoxy to provide tooth for bottom paint.

Here is a similar example from Dennis Harjamaa's personal boat. Although in this case, I believe he used aluminum for the frame and epoxy thickened with fillers to round out the profile.

Bkay said:

...(they are not really a flange, but I don't know a good boat word for them) ...

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Ribs.

Also, could you not approximate the elliptical shape with a series of flat sections. For example, something like this? Don't know how the price would compare.

Interesting. At the speeds this hull is expected to see I’m surprised it makes a difference vs flat plate. And as a metal worker I’m surprised they can’t just bend SS sheets to cover the framing they have laid out, for an all metal solution. Not that it matters I suppose, it will work great, just odd that the only glass on the whole ship is the rudders.

ssobol said:

Ribs.

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There you go. I knew someone would come through!

I think a series of flat plates would be more difficult to build and at greater labor cost while providing lower effectiveness. You'd also have to decide how you were keeping water out - oil filled or some other method.

There are obviously other ways to solve this problem, but this is how the NA solved it and how we built it.

Hey it looks like you got moved outside?!

Oh that’s not your boat. Still asleep

Btw, did I already show you my home brewed aluminum 24vdc welder? You might want to set that up for repairs or additions “on the road”. Just connects to 2 car batteries, or if your house is already 24v then a simple plug into that. It works excellently. I’m still trying to work out a heat adjustment but without any adjustment it works for materials from 1/8” up to “anything thicker”.

Sea Word said:

Hey it looks like you got moved outside?!

Oh that’s not your boat. Still asleep

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Yah, that's just wishful thinking! I'm not watertight yet anyway. As you can see, windows and doors are still in boxes (although they have been test fitted).

One nice thing, they have so much space on the construction floor that you don't really move outside until launch time. Guys work much faster and better indoors as long as they have room.