What sort of efficiency can a 35'-40' planing hull make.

[Dave_S]

I'm considering a power boat for coastal cruising the Great Barrier Reef. The day to day running costs are important to me but I'd like to travel at planing speeds when possible. What would be good options in the second hand market and what sort of litres per nm might I get planing V's displacement speeds. Do you cruise with one engine or two ?

I'm more a fan of the older designs (not too old) than the sleek modern boats but that may be a conflict with efficiency?

I'm thinking of AU$100,000 to AU$200,000 purchase with one large comfortable cabin with head and shower.

What would you recommend I research ?

[Simi 60]

Zero sort of fuel efficiency


Displacement hull carries a better load and uses much less fuel.

[Tin Tin]

Semi displacements like the Fairway 36 economical at half speed, but can plane if you are in a hurry, consumption and speed related to engine HP anywhere from 150 - 350HP+. A better option may be a displacement power cat if you can find one with high hull clearance and narrow hulls (eg Schionning, Grainger etc), will do 15+ knots with smallish motors eg 75- 100Hp * 2

[Pizzazz]

I would get the biggest powerboat you can find in your budget with the newest engines. Fuel consumption on a plane depends largely on two factors, displacement and transom angle (the shallower, the more efficient but the ride quality is worse). You can expect around 2 nmpg at 10 knots and 1 nmpg at 20 knots. A good rule of thumb for nmpg is 20/speed in knots for boats in the 30,000 lb range.

If you look at your long-run costs, fuel is not that much but it really depends on how much maintenance you need to do on the engines. If you start replacing major parts, it gets very expensive very quickly. It is better to recondition older parts but it is not always possible.

The benefit of a powerboat is less time on passage. You can pick your weather windows and cover 150 nm in daylight or 300-350 nm overnight. You arrive at your destination refreshed, showered and well dressed. Unfortunately, many operators of older boats then need to use the saved time to get right into maintenance. So, it is kind of a trade-off.

I personally do not get displacement power boats. You average 6-7 knots, you lose the romanticism of sailing, your fuel consumption is not significantly better, you cannot outrun weather. But if you have a well sorted out boat with good sound isolation, and lots of time, it can be quite enjoyable.

[Simi 60]

Originally Posted by Pizzazz

I personally do not get displacement power boats..

Well that's obvious

You average 6-7 knots, you lose the romanticism of sailing, your fuel consumption is not significantly better, you cannot outrun weather.

We average 7.5 to 8.5 burning 15 litres/hour on a 60 ft 60 tonne boat more comfortable than many small apartments.

And we don't need to outrun weather.
Planning, pick your times.

[Galumay]

I know when we were looking for a motor vessel, it was hard to find anything on the Oz market that was both planing hull and economical. The closest, as someone else mentioned was some of the power cats. Tough finding something like that in the market in good condition for $100-200k too. I try to work in Litres per Nautical Mile, makes it easy to compare across different speeds and hull types.

So your slower displacement boat with an efficient diesel will do around 1L/nm at best, my 8m planing hull used to do about 2L/nm and I reckon you would probably be looking at around 4L/nm for the size boat you are talking.

Good luck with your search!

[rocks]

We ran a 10m and about 4700kg fibreglass, LeisureCat with twin 250 hp outboard. The boat was best at about 16 to 22 knots in a 2m to 2.5 swell.
kts lt/hr
brace yourself 6 10
brace yourself 14 37
brace yourself 22 67
brace yourself 24 72
brace yourself 31 104

[NBs]

Hi,

I have experience 38 feet 2 x 265hp fly bridge planing hull boat about ten years.

I cruising about 6-7 kn 1,4 l /nm and 23-27kn about 3 l/nm.

Now i have SD hull whith long keel 41 feet and 6-7 kn 0,7 l /nm and 18kn 3,3l/nm, single 385 hp

Planing huli is not work nice under hull speed, boat move like snake and if you ran only single engine fuel consuption its about same whit twins.

some gearboxes do not like to rest, but can be damaged by poor lubrication, as well as heat build-up if you drive a single.

I'm also thinking about the equation of low budget and old big diesels, they can bring joy for a long time or quickly a big problem, so use an engineer to check the diesel engines.

Regards

NBs

[ranger58sb]

Originally Posted by Dave_S

I'm considering a power boat for coastal cruising the Great Barrier Reef. The day to day running costs are important to me but I'd like to travel at planing speeds when possible. What would be good options in the second hand market and what sort of litres per nm might I get planing V's displacement speeds. Do you cruise with one engine or two ?

I'm more a fan of the older designs (not too old) than the sleek modern boats but that may be a conflict with efficiency?

I'm thinking of AU$100,000 to AU$200,000 purchase with one large comfortable cabin with head and shower.

What would you recommend I research ?

Planing and fuel economy in the same sentence is an oxymoron.

OTOH, efficiency is a slightly different concept, so... yes, there are some planing boats that would use less fuel than some other planing boats... while planing.

Not easy to research, but one way would be to look at engine manufacturer's specs for their fuel consumption curve at various RPMs. Then assume that your usage would fall somewhere between "on plane" and "200 RPM off the top."

Then, if you can, find boat reviews that describe planing speeds for various models.

Compare all that.

And you'll see the "liters per NM" guesswork will be all over the map. Our last boat (42', twin 450hp diesels) at cruise used about 26 GPH at about 20 kts, so .77-ish GPNM. (Whatever that is in liters.) Our current boat (58', twin 900-hp diesels) could be running more like 40-50? GPH at about 25 kts... but I haven't yet had time to fully research/test our power/speed curves.

Cruising on plane in a twin screw boat almost always has to happen using both engines. Part of that is about gears; some gears can free wheel (usually only up to a certain speed), some can't (need to be locked down). This also often influenced by dripless lube systems and crossover lines, etc.

Newer electronic common rail diesels tend to get you better fuel "economy" than older mechanical diesels.

Don't know your market there, so can't suggest boat makers or models. Link a few that catch your eye, and folks here could probably comment better.

You will find making yourself a decent and semi-detailed list of criteria (over and above engine stuff) of what you need, want, would like to have, don't want... will help you a lot in the long run.

-Chris

[Pete7]

Dave, are you thinking petrol or diesel?

Pete

[rslifkin]

In the 40 foot range, I'd expect a moderately efficient planing hull with modern-ish diesels to achieve somewhere around 0.9 - 1 nautical miles per (US) gallon at its best planing cruise and somewhere around 2.5 - 3.5 nautical miles per gallon at around 7 kts for slow cruise.

It will vary a bit between boat designs, and lighter weight boats will burn less (especially on plane) than heavier ones. Handling at lower speeds (and therefore the ability to slow down to save fuel) will also vary between designs.


With gas engines, fuel burn will be significantly worse. My own 38 footer (moderately heavy at just over 27k lbs loaded without people) with 1980s tech gas engines gets just over 0.5 nautical miles per gallon on plane at 17 kts and somewhere around 1.2 - 1.3 nautical miles per gallon at 6.5 - 7 kts.

[Dave_S]

Originally Posted by Pete7

Dave, are you thinking petrol or diesel?

Pete

I'm open to what's available, I'm not keen on diesel smell but I would consider either.

[old pirate]

Dave, we came to the same descission a while back. So sold our Leopard sailing cat and started the long looking and learning process. After nearly 2 years we settled on a Dominator 38 which suits our outdoor style living compared to the 36 footers. Also a single 350hp engine as we plan to do the miles. Lizard island this year ! Cruising at 8kn (1400rpm)we consume 9 litres ph. 9kn goes up to 11 litres per hour. The boat does plane, but we haven’t spent much time there yet. I suspect about 30 litres per hour at 15+ knots. She tops out at 18knts (2200rpm). If speed is needed.
Like sail boats ,some makes their hulls are prone to osmosis. Also the fuel tanks have to be replaced in these same boats, preferably before they start leaking !
There were so many variables. We opted for the single engine. Have bow and stern thruster to assist docking. So far very happy.

[boatpoker]

The boat in my avatar cruises at 7.2knts using 0.75gph. or about 9 nautical miles per US gallon

[boatpoker]

My previous boat (below) with a single engine TAMD60B travelled at 10kts using 1.6gph and at 21kts using 8gph.