40' displacement powercat

It seems the gauges were reading under by 150 rpm when the tech checked with his more accurate gear. Should be back in the water this week.

Our first night on board out to Mayor Island. A few things to work on, no surprises there.
Overall super happy.

Looks terrific, darkside! Worth the wait, I trust. Perhaps I missed the detail in previous posts, but apparently steering from the inside station is by way of a jog-lever, yes?

There is a small wheel, but the centrally placed auto pilot will do most of the work.
Near docks I don't touch the wheel anyway.

darkside, did you decide to leave the pitch as-is, in the end? If the tech's gear was reading under, the pitch must be nearly perfect. or perfect. Again, congratulations!

Yep the pitch came down from 23.8" to 22"
Now hits 3450 on the rev counters which is actually 3300 rpm apparently.
Early days but fuel burn is 2.6l/nm at just under 20kn (in quite lumpy seas)
I think that is 1.46nm/g or thereabouts.

The graphs say if we slow to 15kn we should see 2l/nm.



For those that are thinking of Starlink this is the speed test pic at 19kn.

That is truly incredible fuel consumption. 15kn at 2 litres/nm will get you a long way; from memory our KAD-300s use 35 litres per hour EACH at 15kn (so Suu Kyi's consumption is 4.6 litres/nm).

Ahi is a brilliant boat, both in concept and execution. Wonderful.

"Ahi" is indeed a great success story. I have quite taken by a few of Roger Hill's designs. In some ways prefer them to those of Malcom Tennant (who was sadly lost to the industry too soon). Both world leaders in cat designs IMO.

I would also like to "dip my lid" to your input into the outcome. Very well done. Enjoy!

Well done indeed!

darkside said:

Early days but fuel burn is 2.6l/nm at just under 20kn (in quite lumpy seas)
I think that is 1.46nm/g or thereabouts.

The graphs say if we slow to 15kn we should see 2l/nm.

Click to expand...

Absolutely fantastic! We're at 2.6l/nm at about 10kn and 2l/nm at 8 while much heavier and longer. Those are great figures in flat seas, let alone lumpy

McArthur as you say you a shifting a fair bit more boat around than we are.
Also we have a perfectly clean hull, not much personal gear, although the tanks were all full.
As I said early days, it will take some more miles to get it accurate picture.

We ran the delivery trip to our marina this weekend.
Around 135 miles for 340l of diesel or 2.5l/nm at 18-19kn the whole way.
Nice stop at Great Mercury island.
Really happy with the performance and ride.
Quite a bit of spray over the bow.
The keel bar is square edged and with the plumb bow a fair bit of spray is thrown.
We will narrow the leading edge and modify the small deflector the builder added.

Truly excellent.

darkside said:

We ran the delivery trip to our marina this weekend.
Around 135 miles for 340l of diesel or 2.5l/nm at 18-19kn the whole way.

Click to expand...

Gotta be happy with that

Fantastic. That’s 1.5 nmpg. Very very good at 18-19kt!

I like.

Just read your delivery trip notes, impressive. I’m also following the construction of “Celeste at G&T Marine. What are your thoughts on Diesel outboard power for the RH 12m.

Some of Rogers planning designs have large outboards, typically 2 x 300hp four strokes on the 10.4m. Most displacement catamaran designs stop at around 60hp for the outboards like Rogers 10.2 and the smaller Schionning Prowlers.
Have a look at the E35 from Argus boats that uses 90hp
Argus Boats - E35 Cruising Power Catamaran

For our skinny hulls the weight of larger diesel outboards would be a challenge.

darkside,

That Argus E35 looks exactly like what we want next, in the base configuration. I note that the first E35 debuted in 2011, and the site's copyright is 2011, also. I have written to the site's owner to see if the company is still in business. I have been inclining to outboards for some time now, after two years on our present vessel and seeing how we actually use her (rather than how we think we might use her!).

I have read the Argus site from top to bottom; the systems are really impressive. The layout would suit a couple who prefer to sleep separately, and Roger's design uses the hull space for the two cabins rather than the forward spaces as our design does. This means no snoring disturbance!

The fuel consumption at our preferred cruising speeds is really impressive, too. I will report back if I hear from the site's owner.

Not sure if Argus are still in business.
This review from 2019

https://www.tradeaboat.com.au/news-reviews/7601-argus-e35-review

Yes, sadly, that seems to be the case. I am in contact with Tony Grainger, of graingerdesigns.net and Raku Catamarans, and he says the same. If I hear back from Gary Pacey, will add here. It's interesting to me that the kind of vessel we are interested in here (Ahi is a perfect example); IOW a FD cat with modest power requirements and very fuel efficient, two cabins, and decent solar systems so owners can cook without a generator seem thin on the ground (water). Why, one has to wonder?

Tony designed Infinity a Grainger Ocean 46 that we circumnavigated from 2001. He may remember that boat.
Another option is the Bob Owen/Tiberius Shiraz that you can Google.
Also the Arrow Cat 42, but that is faster and burns a reasonable amount for a catamaran

That Tony designed the yacht you circumnavigated in is a massive testament. Yesterday in a brief flurry of emails, we have spoken about a 40' re-model of one of his Sensori powercats, and will report back here if that develops. I am inventing a new acronym now:

FDFE cats (full displacement fuel efficient cats!).

I did google Tiberius Bob Owen:


but can't find any other details;

and the Arrow cat is lovely, but defeats the basic purpose of the FDFE cats we are discussing here, I think.

In Qingdao today and looks like a couple of Hill catamarans in the marina. Hopefully licensed.
That's China's chart datum behind them.

Quite some trailer boat.

I watched both the videos; thank you. And they gave me a number of ideas. I am seriously considering replacing my Volvo Pentas with Suzuki DF140 outboards, mounted on pods. If I do go ahead with this, I will start a new thread. I will have to replace my hydraulic anchor winch, too (driven off the starboard engine).