Motor yachts for long range cruising

[Simi 60]

Originally Posted by barnakiel

I would get a power cat. Not just comfort underway and anchored but think fuel economy.

b.

We thought power cat but after doing the math got what we have instead.
To get a power cat that has the comfort level and carrying ability we take for granted would have cost easily 6X more, more likely 10X.

Fuel usage is not bad, we use about 13lph doing 7.5 knots @ 1100 rpm with a single 350hp engine pushing 65 tonne through the water.
Comparably cats we looked at would burn double that with engines x 2.

Of course smaller cats would use less fuel but comfort and load carrying ability drops off dramatically and they still cost more to buy than what we have.

[SouthernPride]

53 MY Hatteras here.

I stick to the east coast USA to Bahamas, Caribbean, Gulf. Enough fuel to traverse all but carry and extra 300 gallons diesel. Running 11 knots +/-
gives me the best fuel consumption per NM.

Good ride in 3 to 4 foot seas.

All electronics upgraded, yard inspection every year, engines maintained as per instructions. replaced generator, moved to several 12 volt options available today, solar power.

Quite happy...(just me, and short visits by female species)

Good Luck

[Dougtiff]

Don't know what your budget is, but check out "diesel duck ", long range, low burn rate, steel, most built in China, by an american, who owns the yard, used ones come on the market from time to time, had a friend who owned one, very impressive.

[barnakiel]

Originally Posted by Simi 60

We thought power cat but after doing the math got what we have instead.
To get a power cat that has the comfort level and carrying ability we take for granted would have cost easily 6X more, more likely 10X.

Fuel usage is not bad, we use about 13lph doing 7.5 knots @ 1100 rpm with a single 350hp engine pushing 65 tonne through the water.
Comparably cats we looked at would burn double that with engines x 2.

Of course smaller cats would use less fuel but comfort and load carrying ability drops off dramatically and they still cost more to buy than what we have.

I am with you about the cost - I understand you mean the price of the boat. Yes?

But I am lost at your fuel usage calculation.

Quote: "... Comparably cats we looked at would burn double that with engines x 2...."

How is that a cat that has an easier driven hull will require more power to drive it to the same speed? I mean, there will be 2 engines (a good thing likely on its own) but each would need to push only at 50% of what a single, one engine does in a mono hull. Hence fuel usage should be same. Actually less because of easier mentioned easier driven shape.

Fuel usage is displacement related, not number of engines related. Eh?

PLS update me on where I am off.

Cheers,
b.

[Simi 60]

Originally Posted by barnakiel

I am with you about the cost - I understand you mean the price of the boat. Yes?

But I am lost at your fuel usage calculation.

Quote: "... Comparably cats we looked at would burn double that with engines x 2...."

How is that a cat that has an easier driven hull will require more power to drive it to the same speed?

Most decent sized power cats in the 18 to 20m range that are actualy capable of being liveaboard passagemakers have 300+ HP x 2
Logically they will use twice as much fuel as 300hp x 1

[SV Bacchus]

Originally Posted by Simi 60

Logically they will use twice as much fuel as 300hp x 1

I see your mistake. You mixed up boats and logic. What may seem logical in other situations doesn't hold true with boats, at least as a rule.

[Simi 60]

Originally Posted by SV Bacchus

I see your mistake. You mixed up boats and logic. What may seem logical in other situations doesn't hold true with boats, at least as a rule.

Explain how 2 x 300hp running at 1100rpm uses less fuel than 1x 300hp running at 1100rpm?

[a64pilot]

Originally Posted by Simi 60

Explain how 2 x 300hp running at 1100rpm uses less fuel than 1x 300hp running at 1100rpm?

I think he was teasing.
However it’s not quite as simple as that.
Yes fuel burn will be half, but speed will be lower too, likely not half though. Range often becomes more of an issue than fuel burn.
I have found that a sailboat is a phenomenally efficient boat under power. I know we are not talking sailboats but I think it exemplifies that a hull designed to be run at hull speed or less and designed with being as low drag as is absolutely possible can be extremely efficient when compared to a planing hull being driven by motors large enough to plane.

[Simi 60]

Originally Posted by a64pilot

I think he was teasing.
However it’s not quite as simple as that.
Yes fuel burn will be half, but speed will be lower too, likely not half though. Range often becomes more of an issue than fuel burn.
I have found that a sailboat is a phenomenally efficient boat under power. I know we are not talking sailboats but I think it exemplifies that a hull designed to be run at hull speed or less and designed with being as low drag as is absolutely possible can be extremely efficient when compared to a planing hull being driven by motors large enough to plane.

We are full displacement, not planing and run at hull speed or less with near zero wash doing 7.5knots.
The powered cats we looked at that are comparable in comfort, range and load carrying ability (and they are rare as rocking horse sh1+) were doing 9's and burning 30+ litres/hour, some considerably more again.
Not only double the burn but they also cost over $1,000,000 more to buy as well.

I do miss the shallow draft.

[barnakiel]

Originally Posted by Simi 60

Most decent sized power cats in the 18 to 20m range that are actualy capable of being liveaboard passagemakers have 300+ HP x 2
Logically they will use twice as much fuel as 300hp x 1

I am still lost.

My thinking is:

For any given displacement = X the amt of hp to get it to a specific speed is fixed.

Hence, on paper, a 10t mono hull trawler will call for say 200 hp to get at say 6kts.

Hence, the same trawler, now twin screw, will still call for 200 hp to get at say 6kts. Except now it is 100hp per screw.

Hence, a 10t cat, with two engines, will still ask for 100 hp per screw.

To say all the boats, on paper, if displacement is fixed, will use the same amount of hp to get to the same speed.

And fuel consumption is first order hp related.

In real terms, the cat should burn less than a monohull, as cats tend to heave easier driven hulls (the need fewer hp to get to the same speed).

Where am I wrong?

barnakiel

[SV Bacchus]

Originally Posted by a64pilot

I think he was teasing.

Thanks for catching on a64, it was light humor.

Seems to be a very hot issue for the gentleman so maybe he wasn't able to see it!

[SV Bacchus]

Originally Posted by barnakiel

Where am I wrong?

barnakiel

Hey B,

I don't think you are wrong but it would take someone better versed to explain it than me. I think you made perfect sense.

[Simi 60]

Originally Posted by barnakiel

Where am I wrong?

Real world numbers vs on paper theory
Real world numbers for us are 65t, 315hp monohull trawler uses about 100hp to do 7.5 knots, so less hp for 6kts - for that 7.5 knots it uses about 13lph


Domino 20 powercat 300hp x 2
possibly one of the most efficient passagemaking powercats around but well over $1 million price difference to ours
Range:@10Kts: 6,000 NM
Average Burn: 2l/mil or 2M or 5GPH

Arctic Northwest Passage: Power Catamaran DOMINO is for Sale



Sher Khan 22m catamaran, almost $3 million price difference to ours
Powered by the Economical and ultra reliable Gardner 8lxb @ 160hp x 2
Fuel burn ; 32Lph @ 10 Knots cruise or 3.2l/nm

https://ensignbrokers.com.au/ensign/...-22-5m/154067/

And these two are the most efficient , comparable in comfort passagemakers I found.

[Simi 60]

Another a bit smaller
Uses 19lph @ 10

Power Catamaran World: Hero: Bill Shuman's dream powercat

[Simi 60]

Another, not really a passage maker as it doesn't have the tankage but
350 x 2 @ 10kts burns 40 lph
https://www.boatsonline.com.au/boats...tamaran/155611