Super-Lightweight displacement boats Vs. old fashioned heavyweights.

tadr said:
Power VS speed for PL 46 and 56 at stated displacement.

View attachment 36133View attachment 36134

Note the Gerr method B goes straight up as you expect with a traditional full displacement curve. That method is not applicable. Also note the Groot and Gerr A are rather similar in the 10-14 knot range, which is somewhat believable.
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Just looking at a single volvo d3 150hp at 1800 revs gives 100hp/9ltr/hr.
Tthat equals 9ltr/ hr at 10 kts= 0.9ltr/ nm= 5mpg.........

That's a very good number for a 46' boat at 10kts.

Twin d3 110hp looks like 1700revs/ 50hp each/ 1gal hr each.....also 5mpg.
 
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rustybarge said:
Just looking at a single volvo d3 150hp at 1800 revs gives 100hp/9ltr/hr.
Tthat equals 9ltr/ hr at 10 kts= 0.9ltr/ nm= 5mpg.........

That's a very good number for a 46' boat at 10kts.

Twin d3 110hp looks like 1700revs/ 50hp each/ 1gal hr each.....also 5mpg.
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But as someone noted back in the thread, she is a very small 46' boat. Her beam is about that of a typical 32' trawler yacht.
 
MapisM said:
Why, exactly?
I can't see what there's to like in buying a 46 footer and actually get a 32'.
If fuel efficiency is your top priority, just go for a catamaran.
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Cats are very sensitive to load, because of the narrow hulls. Once the hulls start to sink low into the water the bridge deck connecting the two hulls will start to hit waves, pushing the boat backwards in rough weather.
planing hulls are also very sensitive to weight, but not to such an extent.

the 56' slim design will take 1000gals, which should give a massive cruising range of over 2000 miles!
the main attraction I see is being able to fill up in a cheap duty free port like Gib ( maybe Algeria?) then cruise around the med for the rest of the year on the cheap fuel, that would really save a shed load of money.
 
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Save money compared to what?
It doesn't make sense to say that a Privateer 52 burns more fuel than a boat which is actually MUCH smaller.
You might as well get a proper smaller boat, and save even more money overall...
 
MapisM said:
Save money compared to what?
It doesn't make sense to say that a Privateer 52 burns more fuel than a boat which is actually MUCH smaller.
You might as well get a proper smaller boat, and save even more money overall...
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Using the top speed of the slim hull design( a bit unfair):
At 14kts with twin 150's... 2250revs/100hp each/14ltr each = 28ltrs/hr...= 2.25 mpg.
and the deck sq ' as a guide to size if the boat, we get 56 by 13= 728 sq'

the Fleming 55', which is quite slim as well considering it's weight:
cruises at 10-15kts 0.8mpg on twin 500hp
56' by 16, that makes 896 sq'

lets look at the st44:
1mpg at 14kts on twin 300hp
45 by 13 gives us only, 587 sq'

So the slim design is a lot bigger than the next class down, the ST 44, and with twice the fuel economy of the swift trawler.
 
rwilson said:
oh well if your numbers come in then you can, but then if they did fuel burn would be less of an issue!!!
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Now i'll argue the disadvantages:

How on earth could a flat bottomed hull be considered a offshore passage-maker?
I can't think of another design with so little deadrise.
I would imagine breaching on the top of large waves would be a real possibility.
 
rb,

in real life, LOA is a factor determining mooring fees and taxation (where it's applicable like down here!)
as many have mentioned fuel is a relatively small part of the overall annual costs.
If you then consider this, the winner I'm afraid is the fattest shortest planning hull that accomodate your needs.
I've not examined the plans of the ST44 vs this 52 but I'm pretty sure the 44 has loads more useable space due to the extra beam so it needs a large weighted multivariable equation to get any results.
Of course you can just say, "oh, I really LIKE that" and be done with. Just don't try too much to justify your decision as it doesn't seem it works :p

BTW, I'm not saying I don't like the 52, but I'd not be able to afford the 15m+ crazy taxation :(
Plus it would need stabilisation..

cheers

V.
 
vas said:
rb,

in real life, LOA is a factor determining mooring fees and taxation (where it's applicable like down here!)
as many have mentioned fuel is a relatively small part of the overall annual costs.
If you then consider this, the winner I'm afraid is the fattest shortest planning hull that accomodate your needs.
I've not examined the plans of the ST44 vs this 52 but I'm pretty sure the 44 has loads more useable space due to the extra beam so it needs a large weighted multivariable equation to get any results.
Of course you can just say, "oh, I really LIKE that" and be done with. Just don't try too much to justify your decision as it doesn't seem it works :p

BTW, I'm not saying I don't like the 52, but I'd not be able to afford the 15m+ crazy taxation :(
Plus it would need stabilisation..

cheers

V.
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some very good points.

Few of us can afford the capital cost of a new 40' and above boat. it's going to be £500k or more, and in a couple of years after depreciation that will probably look like £300k. But more importantly if you factor in extensive cruising over the summer months at £7 a mile, plus maintence etc etc, your will be in the top 1% of high income earners.....just a guess: you will probably be earning well in excess of £500k a year after tax. Actually maybe considerably more will be needed after the expense of running a house, car, school fees ect.

Me, i'm retired. I don't have that sort of disposable income.

So a self build done on a miserly budget with ultra low fuel consumtion keeps the dream of an around the med cruise alive.
the slimline hull design is really a fast motor yacht design.....don't panic, without the sail!
 
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I'm with you on that!

so, if only you could built on the cheap a nice fat f/b sailboat at around 40-45ft with decent aft deck and an airy sliding door saloon with standing height and floor level 1+m above waterline. Yep, 8knot hull speed with 1.0+mpl would make a perfect kit.
Have another 15yrs before I can start thinking about it :D
And don't mention cats as they're too expensive to moore or keep on the hard.

cheers

V.
 
vas said:
I'm with you on that!

so, if only you could built on the cheap a nice fat f/b sailboat at around 40-45ft with decent aft deck and an airy sliding door saloon with standing height and floor level 1+m above waterline. Yep, 8knot hull speed with 1.0+mpl would make a perfect kit.
Have another 15yrs before I can start thinking about it :D
And don't mention cats as they're too expensive to moore or keep on the hard.

cheers

V.
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I'm searching for the holy grail!
have you seen that cartoon of a jumbo jet, with helicopter rotors for vertical lift off, and floats for landing on the sea, and opening front to take cargo loads, all powered by a tiny ram jet engine......:D

a hovercraft is the answer!
 
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comparing the passagemaker- lite to the Dashew 64' windhorse design, there appears to be some
differences.
the Dashew bow section, fine entry:

View attachment 36176View attachment 36174


Dashew...........................Passagemaker-lite
View attachment 36175View attachment 36177

and the Passagemaker- lite:

image_zpsc27f891d.jpg
 
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rustybarge said:
comparing the passagemaker- lite to the Dashew 64' windhorse design, there appears to be some
differences.
the Dashew bow section, fine entry:

View attachment 36176View attachment 36174


Dashew...........................Passagemaker-lite
View attachment 36175View attachment 36177

and the Passagemaker- lite:

image_zpsc27f891d.jpg
Click to expand...

First off, Steve was busy selling sailboats when I designed the PL46 in 2001.

Of course they are different shapes they were designed by different people. Steve is using sailboat forms and relying on length to attain speed, I'm designing powerboats starting with basic naval architecture and forms originating in WWII patrol boats. I don't know which design it is you are comparing but Dashew's smallest powerboat is I believe 62', almost 20' longer than the PL46. If your comparison is with Windhorse at 82', she is almost twice the length of the PL46. That means the hulls (as they are operating at the same real world speeds) are working at completely different speed/length ratios which calls for different hull forms. I think Windhorse would run up to a S/L of about 1.4 or so, whereas the PL46 is designed for a maximum S/L over 2. The higher speed/length ratio requires (for lowest resistance) a higher prismatic coefficient, this manifests in fuller ends and a smaller(relatively) mid section. A lower prismatic means a larger midsection and finer ends.
 
MapisM said:
Why, exactly?
I can't see what there's to like in buying a 46 footer and actually get a 32'.
If fuel efficiency is your top priority, just go for a catamaran.
Click to expand...

What I said was "Her beam is about that of a typical 32' trawler." There is quite a bit more volume than a 32' trawler, it's just arranged differently. If you value privacy this can be a plus. Also you can spend your cruising days 20' forward of the engines, instead of standing on top of them. And her motion in a sea, especially pitching, will be far smoother than that of a shorter, wider boat.
 
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