40' displacement powercat

The concept:
A robust coastal cruiser, comfortable for a week at a time, and longer on occasional expeditions.
The boat is also my apartment when I work in Auckland.
Because of that I head out to the Hauraki Gulf islands to overnight solo, one or two nights a week.

We wanted:
1. Easy to handle solo, even in the 20 to 30kn winds we often get down here
2. Had to fit in our well located 12m marina berth
3. Good cockpit space for fishing and diving
4. Good fuel efficiency, particularly at higher speeds
5. Walk around master and good size guest berth
6. Separated shower and heads
7. Twin helm seats
8. Reverse sheer windscreens to keep the sun out of the boat
9. Good cockpit seating
10. Ability to sit on the beach

We are catamaran fans having circumnavigated a Grainger 46 a few years back.
Since then we have had two Roger Hill planning alloy powercats.
This time we wanted to try displacement for softer ride and better efficiency and range.
We tweaked the accommodation layout on one of Roger’s proven hulls and asked him to develop a GA.
We then engaged Alloycats to do the build.
Alloycats had built our last two powercats (we bought those two used) and are 2 miles from our house.

The main problems for powercats are:
a. you have to be careful with weight
b. engine access is usually bad

Roger added 50mm more draft for our build to cope with the 1000l fuel and 400l water we wanted.
We also went with twin heads and showers.
It’s nice for guests to have separate facilities but mostly it allows an access door in the rear wall of the shower.
That allows easy access to the front of the engine where service items like the alternators and raw water pumps are.
The rest you get to from a deck hatch.

The renders aren’t quite where we ended up but we started with this.

Wow!! That looks amazing!!

A video of one of the earlier models. From the 45s mark there is some nice drone footage of it underway.


That one had twin Hyundai 270hp and this is the fuel burn achieved.



But this is a builders thread so here we go.
Roughly a year ago now.

darkside said:

A video of one of the earlier models. From the 45s mark there is some nice drone footage of it underway.

That one had twin Hyundai 270hp and this is the fuel burn achieved.

View attachment 125746

But this is a builders thread so here we go.
Roughly a year ago now.

View attachment 125747

View attachment 125748

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Wow!!

Looks great. Is that video a rendering or real? (Seeing on my iPhone).

What happened if you stretch it to 50’ plus? Can you get larger stateroom and better engine access? How much beam does that add?

Looks very efficient and well done for space.

Beautiful and inspiring! Can't quite tell whether there is a center nacelle to reduce / deflect pounding beneath the bridge deck.

when will the boat be finished? Are you happy with the builder?
Which power plant did you choose the Yanmar 4lv or the Hyundai 270s as I noticed the owner of MAGGIE(another roger hill 12m cat) used the Hyundai V6
The changes you have made to the original design are fantastic, well done.
contemplating one myself

Yes Roger designs larger displacement cats, this one around 50'

https://www.powercatsnz.com/index.cfm/designs/power/16m-composite-displacement-hull-power-cat/

Yes there is a small nacelle

My guess around 3 months to launch but we will see.
The build is more or less as I expected, better in some areas, not quite there in others.

I really liked the idea of a small 6 cylinder Hyundai for smoothness but the reported superior Yanmar support won the day. This will be my eighth and ninth Yanmars so I'm getting to know them a bit.
We did order 4LVs but couldn't get any.
We ended up with old school mechanical injection Yanmar 4LHA-STP
With the 4LHA we get 25% more capacity for the hp and with that probably better long term reliability.
We loose a bit of efficiency, we don't get instant fuel burn readings and the bigger capacity engines weigh 30kg more (each)

I've seen Maggie anchored out but haven't met the owner.

Fantastic thread - great to see what you're doing and why. Love to see how the design matches your needs.

More shots of the build.




Lots and lots of welding.

A few more. Hopefully they end up the right way up.

Great vessel. Following?

Nice!
You've got to love a well-conceived plan.

Fantastic design and build, how long has the build taken so far?

How is it that you can install mechanical engines in New Zealand? I would think they would required strict emissions compliance. Perhaps Tier III or IMO 3

Just ticking over a year so far.....

No emissions rules for off highway in New Zealand. Same as Australia as it happens.

Mako said:

How is it that you can install mechanical engines in New Zealand? I would think they would required strict emissions compliance. Perhaps Tier III or IMO 3

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darkside said:

Just ticking over a year so far.....

No emissions rules for off highway in New Zealand. Same as Australia as it happens.

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Glad Mako asked the question and you answered.

I have seen non EPA or IMO engines for sale in Australia and maybe New Zealand which made me wonder if the webpages were correct or just out of date.

Thanks,
Dan

Plenty of checking to get the front screens set up correctly.





Detail starting on the stern step

looking good, you must be getting excited as it nears completion!!

I realize that the word "displacement" means something entirely difference in the catamaran world. 25 knots with minimal fuel tankage hints at quite a different SOR than most people who buy/build displacement monohulls. Still, it's rather amazing that you can reach that speed with moderate hp.

Joining this thread to see more. My new boat has two double berths forward, too, but they are set out parallel, not like your 90° configuration.

My new-to-me boat is 12m, 5.03 beam, 1.1m draft with liftable stern drives.

SK has 1,200 litres of fuel, and the same amount of fresh water. When my wife is aboard, that water is needed! I really like your pilothouse design (my wife and I have discussed converting our bridge to a hard top and cabin with the forward facing windows your new vessel features). I like the design of your vessel very much.

Your vessel is much faster than mine; at 3,250, the two 285 hp Volvo Pentas push her along at 14kn, and most of the time we cruise at 2,250 rpm, which is 9–10kn. Watching that Kingfisher 1200 video, I could not help thinking that on water that glassy, any boat will fly along smoothly. I would like to see its movement in a 3m sea, but these videos are hard to find! We do not know the displacement of our vessel, nor the builder, but the overall design and thinking seems to be similar to your (our engines are set further back in the amas, and are balanced by the four fuel and water tanks). Our engine space is too tight for my liking, but both are serviceable.

Sincere thanks for starting this thread. Are you planning to leave the aluminium bare on the exterior?

Kit_L said:

...
Watching that Kingfisher 1200 video, I could not help thinking that on water that glassy, any boat will fly along smoothly. I would like to see its movement in a 3m sea, but these videos are hard to find! ...

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Yeah, my wife and I had the same discussion. That boat looks great flying along on that flat water.... But how does the boat behave in the 3-4 foot, steep waves we always seem to find?

Later,
Dan

The video was more to show the lack of wake at moderate speed. It is glassy for sure, but a bit of a lift, the entry looks quite smooth to me.

My guess is that the displacement version will be a big step up in comfort on my last two planning versions. I've done about 15,000nm in those two, some of it in pretty snotty seas. Only once coming around East Cape into breaking head seas was it beyond safe so we bore away and sheltered in Hicks Bay. It gives you a bit of confidence.

That fuel burn/speed is a lighter version, we aren't expecting quite that good.

My wife circumnavigated with me and is good with water. Also good water is pretty easy to get everywhere here in NZ.

Yep she's definitely displacement.

dannc said:

Yeah, my wife and I had the same discussion. That boat looks great flying along on that flat water.... But how does the boat behave in the 3-4 foot, steep waves we always seem to find?

Later,
Dan

Click to expand...

It's for real, even in some chop.
Here is a clip of DOMINO running 11-12 somewhere between New Caledonia and NZ. Maybe not your 3-5' steeps but some seas, nonetheless.
The DOMINO hulls are of similar design concept as those that Darkside is building, just scaled up a bit. We have found it pretty smooth ride even in water that is not nearly flat. Compared to what my heavy monohull would do with this sea state, DOMINO is really quiet in those conditions.

https://youtu.be/muRWaPMMZtk

darkside said:

Yep she's definitely displacement.

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That's a real knife entry, there. I can imagine that profile going through a good portion of any wave.

Ours is a similar shape (but plywood and glass), and on the delivery trip, we were heading into 1.5m NE swells, with chop on top—and I was concerned when we rounded the headland and pointed up the coast. I needn't have worried. We ran at our top cruising speed (13kn) all the way up the coast to home. I was amazed at how smooth the ride was, and the 'air cushion effect' I had heard about was really evident: when we launched off a wave, the descent was soft, and sometimes you could hear the air being pushed out. There was zero slamming.

I have to say I have gone to the Dark Side, too, and, so far, very happy.

Glass over plywood is a great construction method and very common in NZ. John Spencer, who designed Transpac winners using that method said he regretted not calling it "composite" or "exotic". I see the funky RM 1250 sports yacht from France are picking the method up again. Really good for one offs.
The air cushion effect is real, but perhaps more important at higher speeds. Do you get much "cat sneeze" or spray out the front when a big wave comes up between the hulls?

Make no mistake; if I were building a boat as you are from scratch, I would re-do this one or one like your in Al; many reasons. Yet again, as you say, encapsulating plywood in glass has a lot going for it. We'll see, as our experiences unfold with this new boat. Completely understand John Spencer's comment too. As long as no water can get into plywood, it is an absolutely marvellous construction material, and immensely strong.

Re. cat sneeze: no, not on that trip, but I can't see that as any major problem; a lot better than green water over the bow (and at helm position; something we see on our Marine Rescue vessel regularly). and we were in relatively small seas. I will comment further on this aspect as I test the boundaries.

One advantage of the design of my boat is the height of the bridge; I can see all four corners of the vessel when docking. I imagine that with Ahi that there will be blind spots. OTOH, if single-handing, I have to sprint down the upper level ladder (or the one to the main deck) in order to place a line—so this may not be much of advantage!

Thanks for all the pictures- subscribed!

GoneDiving said:

Great vessel. Following?

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Not sure why but I'm not getting email advice of updates to this thread. How do I fix that?

Thanks ?

Very nice! You are a hair smaller than I am in all dimensions and I opted for P&S side doors and decks - which cost a fair amount of usable interior space. So I ended up with a single cabin layout, but otherwise we are very similar.

I'll be interested in watching this come together. BTW - how do you get to the forward part of the engines? I put in a removable hatch on the side deck for engine access forward, but it doesn't look like you have space for that.

Congratulations! Great layout!!!!