Long - Skinny Power Boats

Discussion in 'Boat Design' started by SAQuestor, Sep 24, 2004.

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  1. CDBarry
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    CDBarry Senior Member

    D. Bailey, "The NPL ... " Maritime Technology Monograph No. 4, The Royal Institution of Naval Architects, 1976.
  2. SAQuestor
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    SAQuestor Senior Member

    As I said before, "I searched RINA's archives and publications and came up with a fat zero."

    Perhaps I did not know how to use their search engine properly, but nothing I saw on the RINA site lead me to believe that the cited monograph is available.

    Again I ask, "Can you provide a link or some other information that will lead to the discovery of where one can obtain this information?"

    I'm afraid that just citing the The Royal Institution of Naval Architects isn't much help. If you can, please provide a link or other source for this document. Otherwise it seems pointless to mention this monograph if it isn't available for purchase or viewing.

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    FAST FRED Senior Member

    My lust for a "needle boat" is mostly driven by cruising costs , primarily fuel.

    The referenced 4.8nm/gal is really impressive.

    Is the long skinney boat the ONLY way to get good performance , range and sea keeping?

    I think so , but perhaps others could sugest a way to better 5n/mpg in a usefull offshore cruising boat.
    12K cruise or better ,
    No cargo , besides normal interior,ground tackel and usual cruising stores.


  4. SAQuestor
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    SAQuestor Senior Member

    I agree with Ilan Voyager, this is becoming a very interesting thread. Thanks again to all that are participating.

    Again, taking from separate posts and commenting.

    Portager wrote: “Three reasons; reliability, fuel efficiency and hot water.” And further, “where they are constantly sucking salt laden air through their insides.”

    What’s the difference between a marine-ised diesel and an industrial diesel in this regard? Does the marine-ised diesel have some special air filter that precludes it from “sucking salt laden air”? I don’t mean to be flip, but they operate in the same environment. Operating temperatures are hot enough in both to vaporize any water that they may encounter – though there shouldn’t be any liquid water in the engine space. As for using air – let’s agree that the amount of combustion air needed is equal, then the difference is solely in the volume of cooling air needed to be run over the heat exchanger(s) and exhausted from the engine space. I will concede that there could be residue left behind from moist sea air as it is heated as it passes the heat exchanger. But why wouldn’t one include in the maintenance schedule taking the shrouds off and inspecting/cleaning the heat exchanger?

    Perhaps the concern is the volume of air necessary for proper cooling and how that volume would affect other ancillary equipment normally found within the engine space. The simple answer then is segregate the engine and its need for large volumes of air from the rest of the equipment space, therefore minimizing any contamination of said auxiliary equipment.

    Portager continued: “air cooled engines need to make certain compromises, such as lower compression ratios to prevent premature combustion due to hot spots.”

    OK, I’ll concede that is one compromise, but is that necessarily that bad? I think that may be a judgment call on each individual’s part.

    But to suggest that one can’t have a hot shower because one engine is water cooled and one is air cooled is a misleading notion. Either engine is very capable of driving a high-output alternator charging a high capacity battery bank – and will if the boat is to be independent of marina’s – and therefore a small electric hot water heater will provide those showers just as easily as a heat exchanger off a liquid cooling system would. And if one wants to stick with the heat exchanger concept, circulate the engine oil through an oil to oil exchanger and the route the secondary oil through a water storage tank. Doing an oil/oil exchange will preclude any possibility of water contaminating the engine oil. I’d probably want to use a Gulf States external oil filter system anyway, so including a heat exchanger in that external loop wouldn’t be that big of a deal, IMO of course, and YMMV as always.

    Portager continued: “lower efficiency which is the bane of long range power boats.”

    Very true, but when comparing fuel efficiency we must of necessity take into consideration exactly how much power is actually being used. For example, the Deutz specifications for the F3L2011 engine specify 218 grams of fuel per kWh of output. This engine has a 34kW sustained output, but I doubt whether we’d cruise with the engine running its maximum, so for arguments sake let’s halve that and say we’ll run it at 17kW. So if I do the math correctly, that means that the engine will burn 3706 grams of fuel per hour. That translates into about 130 ounces and that translates into just a smidgeon over 1 gallon per hour.

    So if we can produce a hull that will travel ‘x’ miles on that 17kW(~23hp) then we’ve got an x efficient boat. It’s my understanding that at least three factors contribute in a major way to how efficient the hull can be propelled, total displacement, waterline length and Cp.

    Let’s say we do the hull design really well and the total displacement is a light as practical and that 23hp will shove the boat along at 6 knots. Then we’ll be getting 6nm/gal. Let’s say we’ve done an even better job of optimizing the hull shape and that 23hp shoves us along at 8 knots. Then we’re achieving 8nm/gal. But maybe these numbers are just SWAG’s and aren’t realistic. Dunno.

    But let’s get really crazy – try this one - http://dieselducks.com/Troller 50.html - scroll down to the very bottom of the page – for ~7 knots @ 13hp. So doing the math conversions (13hp = ~9.7kW = ~2115 grams of fuel/hour = 75 ounces/hour = .585 gal/hour) means this particular boat MAY get almost 12 nm/gal @ 7 knots. Using the widely accepted .06 gallons of diesel per horsepower hour figures out to .78 gallons per hour to produce that 13hp – so that equals just shy of 9 nm/gal. Regardless of what figure you choose, that prediction ain’t too shabby for a 50’ boat displacing about 32 tonnes!

    And as Buehler says, “Here's figures my computer developed. Please keep in mind they refer to calm conditions which means no tide or wind. In real life you're generally pushing against something but just the same, they give a good reference and in one case, we found the 38' DUCK actually surpassing what the computer said she could do.”

    So to answer Fast Fred’s recent query, it doesn’t appear that long and skinny is the only prerequisite to decent fuel efficiency.

    Portager continued: “First diesel is intrinsically safer than gasoline.”

    No question about that. But just because it is does not mean that one has to rule out a gasoline powered outboard. If >I< (YMMV) were going to power a boat with an inboard engine it would be a diesel. But if the design worked well with an outboard, then a 4-stoke of appropriate size couldn’t be ruled out.

    Gasoline tanks can be built and placed in accordance with Coast Guard and ABYC safety regulations and be safe for usage.

    As for 4-stroke reliability… as others have said: if I were only cruising close to the coast or on rivers and lakes and if the design worked well with an outboard, I wouldn’t be hesitant about choosing that direction. As always, YMMV.

    Finally Portager’s comments about ply/epoxy and aluminum. All valid and something to be taken into consideration. But Ilan Voyager expresses my sentiments exactly. He said, “I do like aluminum but I think that all the work and cost of the insulation annihilates any advantage in small boats; a metal hull without a thick insulation under the tropics, no thanks.”

    As for the Parker Dory and its flat bottom. Again as several folks have said, it’s all a personal choice.

    Phil Bolger has lots of designs that utilize flat bottoms – whether sharpies or dory style hulls. He’s apparently well aware of the pounding that occurs and has designed a couple of solutions. One I’ve seen is nothing more than a flat disc that intersects the waterline forward. This eliminates the acute angle between the water and hull, thus reducing the irritating slapping of small wavelets when anchored.

    In dealing with larger waves he has designed a ‘cut-water’ for several of his designs. This appendage acts much like a traditional bow shape and does not allow the waves to see a flat bottom forward and therefore greatly reduces any pounding usually associated with a flat bottom meeting an oncoming wave while keeping the inherent ease of building a flat bottom boat.

    If, like Mike, your concept is for a transportable boat, then the choices available seem to narrow. But if you’re not limited by height and width restrictions, then the choices are much more numerous.

    The point of starting this thread was to solicit ideas and discussion on what choices are available for those of us that want to be able to transport our boats to different cruising grounds each season. 10miles/gal fuel mileage would be great when on water, but that same fuel mileage on land at 60 mph is even better!

    I’d like to suggest that no one person has all the answers. They >might< have some that are appropriate for their personal circumstances, but to learn and consider viable alternatives we must keep an open mind and not reject out of hand ideas that don’t fit our preconceived notions of what is right and proper.

    My personal progression is but one example. A few months ago I rejected Bolger’s designs out of hand because I simply disliked the boxy shapes that many of his designs employ. In his boxy designs form follows function without regard for conventional aesthetics. Because I didn’t >>CHOOSE<< to look beyond the (to me) ugly square-ness, I completely missed the brilliance of the underlying engineering.

    In July I took a trip to the coast with Chuck Leinweber of Duckworks Magazine (http://www.duckworksmagazine.com) to see a wooden Diesel Duck being built (pictures of this particular boat and discussion of Buehler’s designs available here - http://groups.yahoo.com/group/BackyardBoatbuilding2). The discussion during that trip caused great pause in my “conventional” thinking. I started looking at alternatives that would allow me to achieve the goals and requirements of my retirement boat.

    I’ll be so bold as to suggest that if one wants to learn about some alternative marine engineering, look at two of Bolger’s boats – the Tahiti and the Sitka Explorer.

    The complete treatise on the Tahiti can be found in the magazine Messing About In Boats (MAIB) volume 17, no’s 12, 13 & 14 from November and December 1999. An update is in volume 19, no 22 from April 2002. Apparently this design is afloat in the Florida Keys and is nearing completion.

    Sitka Explorer is described in MAIB volume 20, no. 6 from August 2002. Apparently someone has commissioned the full design and it will be complete sometime this winter.

    MAIB can be reached at 978-774-0906. I have NO CONNECTION whatsoever with MAIB and mention this only as a community service.

    The point? Think outside the conventional box. There may be good and valid reasons for >>NOT<< doing something too unconventional. But that doesn’t mean that we should accept at face value the ‘conventional wisdom’ of the industry.

    Progress – whether incremental or by leaps and bounds – is only made when someone has an epiphany or questions the status quo.

    So I sincerely hope that we’ll continue to explore alternatives in this conversation.


  5. Portager
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    Portager Senior Member

    I agree with most of Ilan Voyager ‘s comments with the following exceptions.

    I beg to differ with that miraculous conclusion. A monohull can support an 8:1 L/B, it all depends on the center of gravity to center of buoyancy height. If you don’t get the height out of proportion to the beam it won’t require too much ballast. Besides this is a lot of comparing apples to oranges. Multihulls have a less efficient structure and higher wetted surface area. In addition when you scale a multihull down you risk pounding on the wave tops. I prefer monohulls because years of research revealed that they are susceptible to structural torsion in beam seas and they have high inverted stability (turtle).

    I do agree that Aluminum boats must be insulated, but I didn’t realize that installing insulation was so costly and complex! To think that I was lead to believe that was the easy part.

    I guess I shouldn’t mention the mass of empirical evidence to the contrary.

    I took a closer look at the Duetz engine. It really isn’t air cooled it is oil cooled. You could probably make it work by using an oil plate cooler or keel cooled. You could also use an oil to water heat exchanger to heat water. You don’t need to worry about water leaking into the oil through the heat exchanger since there is solid metal separating the liquids.

    I checked Buehler’s calculations and they don’t agree with Conch’s equation or Dave Gerr’s equations. I’ll do some more calculations tomorrow, but I don’t believe a Duck with a 44’ 7.5” LWL, 15’ beam and displacing 69,668 lb is going to provide 12 nm/gal @ 7 knots. Portager is an efficient design but with a weight of 32,000 lbs light, LWL 46.75 feet, beam 12 feet it only does 4.5 nm/gal @ 8 knots.

    Why not try thinking outside the box once in awhile? Open your mind to new possibilities they might surprise you. :D

    Mike Schooley
  6. CDBarry
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    CDBarry Senior Member

    You should be able to borrow it through inter library loan, or perhaps it will be at a university library nearby - it is widely held. Also, send an email to publications at RINA and just ask. Finally, there is always Amazon, eBay and the various used book online sources. Finally, a significant amount of the information is exerpted in SNAME's PNA.
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    FAST FRED Senior Member

    Good fuel milage at slow fat boat speeds are EZ .
    Our 33ft cutter is a Maurice Griffiths design (Lone Gull II, blown from 24lwl to 28lwl 33loa).

    With over 4000 hours of engine operation since the mid 70's the fuel consumption is 3/4 gal per hour at 6- 6.5K normal cruise.
    Volvo Md3B 1 to 1.91 reductiohn with 19X13 TWO blade propellor.

    The two blade is more efficent under power , and quite easy to index and lock behind the deadwood. DL 333, Bwl 10.6 at cruising 17000lb displacement.

    A fat, not light boat, but restricted by the beam from ever going more than 7.2 or so , even with a gale blowing.

    The question is how can I doubble the cruise speeds on the same fuel?

    I think its impossible , but to doubble the speed to 12 or 13K on 3gph may be doable.

    The low & hull profile if an early Commuter with 8 to 1 lb ratio or better, along with a very light simple interior should take care of the boat part.

    For the engine & drive the problem becomes one of maximizing the output.

    Certainly 2 engines , one of 70 hp run at about 50 should be in the 2 1/2 to 3 gph burn for long range work and a second high power at what ever is affordable would allow splendid top speed when required.

    There are multiple engine drives from LST and other military surpluss sources so the price would not be out of line.

    But carring a large engine for very rare use doesn't make loads of efficency.

    My concept is to use a truck transmission for the multiple speeds.
    YES they are cont duty rated .

    An very fresh truck engine/tranny of 250 hp is quite inexpensive , and the exhaust manifold is OTS.(Off The Shelf)

    By setting the boat to run at top speed in a lower reduction gear , the tranny could be shifted up to increase the loading at low (1200 to 1500RPM) distance cruise .

    Egt gage and the mfg fuel map would be required.

    The semi submerged prop system looks ideal for ease of onboard repair and efficency.One of the nicest concepts of the propsed surface drive would be the ability to take the ground with out damage.

    The largest compromise for speed / efficency would be the need to use a 2 or 3 chine hull to lower building costs & time.


    Bus coach conversions , the orig insulation is tossed and spray foam is used.
    Relativly cheap , and the interior is faired using a body shop "Jitterbug" (air file) with very little effort .
    BUT one HECK of a lot of dust to vacume up!

    The foam selected should be non burning , and a simple wall finish is simply glued on, or pop riveted to framing.
  8. Portager
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    Portager Senior Member

    The problem with surface piercing propellers for this application is they are very inefficient at low hull speeds, which is where your high efficiency drive would operate. I believe a controllable pitch propeller (CPP) would be a better application because they provide high efficiency over a wide speed range. Note: a variable pitch propeller (which is a propeller with a constant pitch that varies with radius from the hub) would provide higher peak efficiency but the CPP provides high efficiency over a broader range.

    If your interest is high efficiency at moderate speed like 6 to 8 knots, but the ability to also achieve higher speed such as 10 to 12 knots, then a semi-displacement hull and a CPP will provide that capability. This could be done with a length of 36 to 64 feet. To achieve IMO offshore stability with minimum weight, i.e. nearly zero ballast would require a beam of ~10 feet, so the L/B would be 3.6:1 to 6.4:1.

    On the other hand if your desire is to obtain the highest possible efficiency at 10 to 12 knots, then I believe a long skinny design is required. To be highly efficient at 10 knots will require a V/SQRT(L) of 10 which equates to a LWL of 100 feet. Again the minimum beam for minimum ballast weight would be ~10’ so the L/B is 10:1. At this L/B your structural efficiency will suffer so it might save weight to increase the beam to ~12’.

    From a transportability standpoint, a 100’ length would be very difficult to transport. Even though you could get an over length permit, you would need to hire pilot cars in many areas and it would be difficult to negotiate corners. You would probably need steering on the trailer axels, which increases cost, complexity, …

    A good compromise between transportability and cruise efficiency would be to keep the LOA below 65’ and the beam below 12’. This would be transportable without pilot cars except on some two lane highways. The L/B would be 5.4:1 and the efficient cruise speed would be about 8 knots. With a semi-displacement hull and light weight design maximum speed could be 12 to 16 knots depending on maximum power.

    To increase maximum speed much over 16 knots would require a planning hull and massive engines instead of a semi-displacement hull, which would be detrimental to cruise efficiency and sea keeping in rough seas.

    Mike Schooley
  9. Ilan Voyager
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    Ilan Voyager Senior Member

    Some precisions.

    That's becoming interesting more and more...

    1/ Nothing at RINA. Visibly the internet archives begin with the year 1990. I made a search in internet and I've found a few informative pages on displacement boats with a small illustration of NPL series hulls..

    http://books.nap.edu/catalog/5870.html (a bit arid...maths)

    I did not made a search in http://www.nationalacademies.org/ where you can find a lot of treasures after digging a lot, the naval libray is impressive.

    A few words about NPL series hulls: these hulls are a shape that can be simplified in triple chine without a great loss of efficiency.

    Surely RINA will sell the doc it against some good english pounds.

    2/SAQuestor post

    **The ciphers given in http://dieselducks.com/Troller 50.html are totally false.

    There are the ciphers I've roughly estimated in hurry:

    ratio length/width at LWL 3.41 meters; it's normal, nothing slim.
    At displacement 31.63 metric tons;

    V/L .. Knots ..... HP claimed Rough HP
    1 ..... 6.96.... . 12.9 96
    1.1.... 7.65...... 19.8 116
    1.15.. .8.0....... 24.3 126
    1.20... 8.35...... 31.5 138
    1.25... 8.70...... 42.4 149
    Following; out of limit of hull speed at 32 tons
    1.30... 9.04...... 57.3 161
    1.35... 9.39...... 77.9 174

    The induced skeg loss factor of the propeller, correction of hull speed and correction of shape are not included.

    The max hull speed counting the displacement and shape is 8.5 knots at best. With the old 100 HP this boat was running at about 6.0 knots, a common speed for fishing boats a few decades ago.

    I estimate, by smelling this boat with my engineer's nose, that it needs at least 200 HP, gearbox 5/1 and a propeller of diameter pratically 2 feet to move at 7.0-7.4 knots cruising speed. Navigating in dangerous places as North Brittany (France) with tide currents and strong winds I would put 300 HP to be sure to arrive at the harbour.

    A lot of internet sites give false infos, or unbelievable claims...Dynacam engine and Bugatti boats (poor Ettore, he must cry in his grave) which with its pics of old russian WIGs and other stupidities attain the level of the total fake are a few examples among dozens of other.

    That shows that everyone must have a very critical eye, and to check the veracity of the claims.

    ** Whatever you shall do, a flat boat will pound. For me, the V is easier to build and stronger in chine building: the triangle is the lone geometric figure that cannot be deformed and you have a strong keel instead of a floppy flat pannel. Flat boats are acceptable only in very small boats, or in lakes and calm rivers.

    2/ Fast Fred post

    The facts are stubborn, and hydrodynamics applies to all thing going on water:
    so I do totally agree with the searchers of the english DERA, the engineers's pool of the french DCN, some PhD guys of the La Haye Naval Institute plus a bunch of australian and neozelandese designers of the fastest ferries of the world, who think all together, after an extensive and costly research, that the most energy efficient ship for some applications is a slim hull with a ratio around 8 to 10 and thet the best configuration with slim hulls is the TRIMARAN.

    With so innovative designs, progress are cautious and slow as the finantial risk is great; the success of the campaign of validation and evaluation of the RV Triton will probably speed up the process. Various navies are now very interested by trimaran frigates.

    I agree also with Nigel Irens, one of the best naval architects of the world, plus Mrs Morelli and Melvin, who are among the top cream of the yacht design. They have access to all needed data and have experimented hydrodynamicians to give them a little help.

    The 4.8 nm/gallon average at 8.93 knots of Yanmar Endeavour (only 40 feet long) was made while crossing The Pacific, thus the boat was fully loaded at the beginning of the trip. It may be improved as this boat was powered by 2 small (27HP) diesel outboards: small fast revving (4500 RPM) diesel and small fast spinning propellers are not the best combination for efficiency. The 12 knots top speed is gotten fully loaded. These ciphers are not computer calcs but true facts coming from the use in sea.

    The most interesting fact is that these results are obtained by very simple means; a hull, 2 outriggers, common engines and a lot of strong thinking.

    3/ Portager Post

    First I remind we are discussing about 35-60 feet slim power boats.

    As I'm not christian, I refuse the word miraculous about my assertion "A small monohull with a ratio of 8/1 would be dangerous". It is the result of simple arithmetic; take a 40 feet hull, so 40/8= 5 feet at the LWL. Try to add the accommodations. Everybody with some experience will think immediately: dangerous.I guess that the medium term in a small monohull boat is about 5/1.

    There are 8 to 10/1 monohulls (I've sailed on them in the Navy) but these boats have a very huge difference in size.

    The wetted surface and structure unefficiency doesn't seem to bother the modern sail and power multihulls (I do not speak about a Arthur Pivert tri, or some crappy cat of the 60's) for going fast and to be efficient; you have just to sail on one of these boats to be convinced, and to see the results obtained.

    Structural enginnering problems are solved since 15 years and the pounding is known only by badly designed multis. Ask the Australian which use 20 feet power cats in rough sea.

    About inverted turtle position, I prefer to stay in a inverted multi, whose design had foreseen this eventuality and organised the survival, with food, water, radio etc that to be on a rubber life boat with the monohull being one mile under my feet. A french multihull joke says; "while capsized, multihulls float inverted, monohulls sink upright".

    I shall add that power monohulls may float also inverted, and a part some specially designed rescue boats I do not know self-righting power monohulls. It seems you're mixing power and sail boats stability facts.

    The facts are there, the remainder is an old academic discussion, which seems to be closed long time ago at least for europeans and australians.

    I understand perfectly that you do prefer monohulls and it's your own right that you have not to justify or rationalize.

    About metal boat insulation cost and time: just make a excel sheet of the cost (work even free it's spent time, and materials) of foaming, paneling and finishing the inside with marine standards of a 50 feet metal boat. calculate also the (heavy) weight. You'll be astonished. Finishing is the hardest and longest part of boat building. The hull is no more than 25% of materials cost and time of a living aboard boat. I have a (too, my beard is white now) long experience of this fact.

    About lightning: many mine sweepers are in fiberglass now, with a lot a fragile electronics. Lightning should be a big concern but it is not a problem with the normal protection technics. I maintain that "Lightning is not a concern if you take the precautions needed whatever the hull material". I won't detail here the very well known technics of lightning protection of a boat. It's probably be a good thread subject.

    About Deutz engine; you're right and I was mistaken. I thought it was the common air and oil cooled engine. I've downloaded the PDF and truly it's an interesting engine for a small boat. Worth to be marinized. So the noise and corrosion concern have to be thrown in the garbage.

    About Duck boat. We agree together that the given ciphers in the internet page are impossible.

    The last; Portager is a nice boat, even if I prefer multihulls.

    3/ Fast Fred second post

    A truck transmission: Why not? I have seen and tried a 45 feet shrimp boat in Senegal fitted with a truck transmission and engine. They changed of gear with the boat stopped. It worked very well, and the boat was a good one. On a such boat, size and weight were not a problem, but truck engine and transmission are truly bulky and heavy.

    The nicest feature of this boat that this boat has been conceived with the help of an engineer of the Arsenal de Dakar by local fishermen and built on the beach between 2 coco trees by local artisans...

    4/ Portager second Post

    As surface piercing props come from competition, they are perceived as designed only for fast boats. The surface props found in the american market are designed only for fast boats with "fast" propellers.

    But surface props work very well also on slow boats if designed for this purpose:
    Mr Sholz ( www.levidrive.com/ ) makes very efficient surface props, designed by Sonny Levi, for small fishing boats in Malaysia.
    The harbour captain's service boat of the Vieux Port at Marseille (France) uses 2 surface props...it pushs like a tug and it's used sometimes as tug.
    Mr Dorado, naval architect in the south of France has designed successfull working boats with surface propellers.
    The nice feature of surface props is when too charged, they slip instead of cavitating, and thus give like a kind of automatic gear box effect. The other advantages have been already said.

    Pitch controlled propellers are very expensive, and I'm afraid, on small boat, of the reliability.

    I agree with the analysis which follows in your post for monohulls (we are far of the 8 or 10/1 monohull...)

    To end this too long and surely boring post, I think that for a 2 persons a 40 feet live aboard is enough, with possibily for 4 during short period. My personal tastes go to a 40 feet trimaran, maybe foldable with a 90 or 100 HP engine. With small boats, small problems...

    Best regards to all.
  10. SAQuestor
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    SAQuestor Senior Member

    OK - I've never built one. But...

    "The main propeller is NiBral, 30" x 21" with a 3 to 1 gear reduction. The saildrive prop is a folding, geared, bronze 15" x 10". At 1400 rpm the main engine drives her about 6 knots and uses approximately 1 ½ gph. The sail drive unit can move her about 3 mph."



    "A very interesting trip From Zhuhai to Yokosuka Japan via Hong Kong. All told the trip took 9 days 22 hrs and 15 minutes for the trip including 2 hours dead in the water. Thats an averag of 7.34 kts. All in all, not too bad."

    Unfortunately Don doesn't give fuel usage, but the engine is a small 4cyl. Cat. Didn't take the time to look through his entire web site to see if he mentioned the exact size.



    "John Deere 4045 135 hp low pressure Turbo diesel marine diesel with ZF Hurth 2.78:1 marine transmission."

    Since these folks live in Hong Kong they don't have any long voyages to report on.




    I chose a 78-hp Perkins M80T turbo diesel, identical to the Volvo TMD22. Not just because I got a good deal on this engine, but the lively 2 liter motor of the newer generation will do for sure 20,000 hrs. of service without critical, expensive, technical hick-ups, as long as the engine gets its oil and filter changes and the changing of the timing belt once awhile. Being designed for the automotive and farm equipment use, it has a self bleeding Bosch diesel fuel system and a 400 hr. oil change period. The 4,000 Perkins network outlets in 160 countries and the countless Volvo outlets are providing rapid supply of spare parts and responsive one-stop servicing on all factory specifications.

    Nowadays diesel motor technology is changing fast. I wanted to go away from the heavy weight, slow turning, not responsive, but fuel gulping iron brute of the dinosaur age. This motor, with the 2.74 Hurth gearbox, coupled with an Aqua Drive to a 40 mm (prox. 1-1/2") prop shaft of a 20" CP Propeller System, from West Mekan (Konrad Skibenes) will propel "Diesel Duck" just fine without killing our wallet when paying the fuel bill."


    I point out these links and quotes not to be argumenative per se, but rather to show that perhaps the traditional calculations aren't always as accurate as we'd like.

    Since Mr. Buehler isn't one to exaggerate, I respectfully suggest that your figures of needing ~6x more HP - 19.8 vs. 116 is too far off to be true either.

    1.1.... 7.65...... 19.8 116

    116*.06=6.96 GPH and a total range of .... Well he didn't spec the fuel tank size on the troller, but if we look at a similar boat of Buehler's, http://dieselducks.com/Duck48study.html the fuel tanks there are spec'd at 900 gallons.

    The speed at V/L 1.1 is similar - 1.1..... 7.44.... 13.7 for a range of 8147 miles.

    So let's take (for approximations sake) the same ratio and thus 13.7hp becomes 80hp using your calculations. Using the 80hp figure and the range drops to a palty ~1400 miles, a ~6750 mile loss.

    Perhaps George's calc's aren't exact, but I'll also suggest that he'd not sell any plans and no one would build an ocean crossing power boat that had a range of less than 1400 miles on 900 gallons of fuel.

    Please, before you dismiss this as hog-wash, spend the time to do the research on Buehler's built boats and you'll find that more than several have indeed crossed oceans putting along happily at ~6.75-7.25 knots and burning about 1 gallon per hour (depending on conditions of course.)


  11. Ilan Voyager
    Joined: May 2004
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    Location: Cancun Mexico

    Ilan Voyager Senior Member


    I have worked on the design (alone or in a team in the Navy) and/or built something like 143 boats if my archives are good in about 33 years. Actually I'm working on the number 144 a 35 feet diving boat. This variety goes from the prelimanary sketches of one aircraft carrier to a sailing dinghy of 3.2m, passing by fast patrol boats, duty boats, tugs, power yachts, fishing boats ( 35 built from 8 to 50 m), racing multihulls and so on.

    While working for a client, I'm able to calculate the speed of a work boat if the shape is well known within 1/10 of knot, and estimate the consumption at 1 liter hour, as these results are guaranteed by contract with heavy penalties if the intended speed and consumption requirements are not fulfilled within a certain very small percentage. Ask to any naval architect or engineer working in this field and he will tell you the same thing.

    That I guess is that Mr Buehler confused the ciphers of the 50 feet with another boat (38 feet I do not remember) he was talking about in the same internet page.
    I didn't said that Mr Buehler was a hustler. I've simply said and Portager will agree that the ciphers were impossible, as the boat weights about 31683 kg for less than 14m of LWL.

    The Gerr formula without any correction of shape (double ender, skeg etc as I have not the hull's coefficients) gives a max hull speed of about 8.75 knots.

    The other examples you give are from different boats and we do not know exatly the hull shapes and coefficients (As I have seen without paying attention to details the shape is very different; look at the sterns).

    A good semi displacement fishing boat of 15 meters of LWL weighting 32 metric tons can make easily 7 knots with 100 HP and 9.9 knots with 200 HP, but need only 51 HP to get 5 knots... but it's not and old double ender in transverse bottom plaking style; a such boat creates an enormous drag while tempting to approach the 7 knots because of the stern and the drag penalty of keel and skeg shape.

    I'll follow your advise and I'm going to discover the Mr Buehler's boats in detail. I'm going also to look in my old books about power calculations of true displacement boats, it's good to read again the old classics...

    My statement about some internet sites (look at the "bugatti" site and you'll understand) remains valid.
  12. SAQuestor
    Joined: Sep 2003
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    Location: San Antonio

    SAQuestor Senior Member

    I've snipped a good bit.

    I'll not dispute your knowledge and experience, and bow to your long career.

    Besides, this discussion has taken a turn away from how to get a long skinny monohull power boat to be its most efficient.

    If possible, I'd like to see the discussion get back on that course.


  13. Ilan Voyager
    Joined: May 2004
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    Location: Cancun Mexico

    Ilan Voyager Senior Member

    It would be very sad to start a dispute while we are here for our pleasure, to meet interesting people, and to exchange ideas.

    Surely, there are always subjects of disagreement as esthetics, monohull versus multihull, marinisation of engines etc but that never has to come to dispute.

    As anyone can make mistakes, I'm going as I said in a former post to re-read some old books about the displacement boats of Mr Buehler's style.

    For example the ciphers given by http://www.rusty-duck.com/construction/specs.html
    are consistent. The hull has a wide stern: a very rough calculation gives a hull speed of 8.8-9.2 knots, a speed of 2.7 knots with 18 HP (close to the about 3 knots), the "about" (that can be somewhere between 5.6 to 5.9 knots...) 6 knots at 1400 RPM of a torquey slow revving N.A. Lugger 105 HP with a 3/1 gearbox and a 30" x 21" propeller (a good combination with such a boat) is "normal" and within the range of the engine.
    We are far of the 6.96 knots with 12.9 HP of the troller 2050...

    We'll be back to the subject of this thread. If you feel I have been rude, please accept my excuses, I did not wanted to be rough.


  14. Tad
    Joined: Mar 2002
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    Location: Flattop Islands

    Tad Boat Designer

    Excellent, very nice discussion.

    And Ilan is to be congratulated on pointing out mistakes where he sees them. Take everything you read not as gospel, but as one side of the story. Check technical assertions against your own experience and with other published references.

    This paper includes some lines from one of the NPL hull series. NPL Hull
    The form is close to where I ended up when creating my Passagemaker Lite series of hulls. This particular NPL form is very fine forward; the PL hulls are slightly fuller. I would love to compare seakeeping of the two with tank or software.

    I include some writing I did a while back on comparing the efficiency of various hull forms. This was in reply to Harry Bryan's article in WoodenBoat # 170 on fuel efficient displacement hulls. I would like to get some trimaran data to include.


    The comparison of MPG without regard to either load (displacement/weight), or time (speed), seems an incomplete discussion. There is a very useful comparison of speed/power/weight called transport efficiency (Et ). With this coefficient, plotted against a dimensionless speed, we can compare the efficiency of displacement, semi-displacement, and planning hulls.

    Transport Efficiency takes into account not just the power required (in effect MPG), but also the weight (displacement in the case of a boat) being moved, and the time required to move that weight (speed).

    Et = W * v / Pd * 550

    W is operating displacement, in pounds.
    v is speed in feet per second, (knots * 1.6889).
    Pd is the horsepower required for the above v.

    For Rambler I guessed at a cruising weight of 1600 pounds.
    6 miles per hour is 5.2 knots is 8.798 feet per second.
    I took the power as your stated 3.2 HP.

    Et = 1600 * 8.798 / 3.2 * 550
    Et = 7.998

    Plot this against Volume Froude Number, (see WoodenBoat # 137)

    FNv = v / (g * disp.^.666)^.5

    v is speed in feet per second.
    g is acceleration due to gravity, (32.2)
    disp. Is displacement, this time in cubic feet.

    FNv for Rambler is .53 . This is about mid-range for displacement boats. Displacement hulls operate at a FNv of 1.3 or less, semi-displacement hulls at FNv of from 1.0 to 3.0, and planning hulls at FNv of 2.3 or more. (This is certainly open to debate!!)

    Piquant, designed by Francis Herreshoff and W.J. Strawbridge in 1950 was close to the ultimate in performance for a displacement hull. She was 47’ by 6’6” and double ended, displacement was 6700 pounds. Twin 35 HP gas engines burned 3 gallons of gas per hour for a cruising speed of 16 knots. Top speed was 20 knots. I calculate her top speed Et at 5.88 and FNv at 1.26. A fairly high speed is possible if the boat is very light.

    In the early 1970’s Bill Garden designed Clam, which he termed a doomsday cruiser. She is 42’ by 8’ and of very simple vee-bottom plywood form. Her power was a Gray 4-69 gas engine, developing 15 HP @ 1800 RPM. Cruising displacement would be about 9300 pounds and she has bunks for 4, an enclosed head, and galley. Mr. Garden calculated a cruising speed of 6 knots using 10 HP, 1575 RPM, using one gallon of gas per hour. I calculate an Et of 17.13 at a FNv of .34. A big boat going very slow can be very efficient.

    Another efficient hull is Phil Bolger’s Slicer, 29’ by 5’2”, a plywood vee-bottom hull of very light construction. Her displacement is about 1700 pounds and she achieved 18 knots with a 15 HP outboard. This is an Et of 6.26 but at a FNv of 1.79, which is well up into semi-displacement territory.

    Just for fun I ran the calculations on a typical SUV to see how it would come out. A 5000 pound SUV gets 25 MPG on the highway, we’ll call that cruising speed. Working backwards I calculate about 56 HP is required to maintain 65 MPH. That gives me an Et of 13.9 at a FNv of 3.92. This is a transport efficiency far better than the best planning hulls. Regarding the effort required to move a land vehicle as opposed to a waterborne one, I think you missed the difference between the force required to accelerate a mass and that required to maintain a mass in motion.

    Running through the published figures for the Hinckley 29 I come up with an Et of 1.81 at a FNv of 2.11. This is below the efficiency of the best planning boats and also below the performance of her big sister, the 37’ Picnic Boat. This probably reflects the smaller boat’s higher beam/length ratio.

    Looking at your performance figures (37 mph for 200 HP) and guessing a weight of 5000 pounds for the Parker 23 gives some interesting results. I get an Et of 2.46 at a FNv of 2.23. This is better than the Hinckley and is probably a reflection of the greater propulsive efficiency from the outboard as compared to the waterjet.

    The ultimate Et is a moving target as improvements are made in hull form and propulsive efficiency. I’m sure all the vessels above could exhibit improved Et with better underbody fairing, different propellers/gearboxes, and optimized forms.

    Thanks for adding fuel to the debate and opening the discussion.

    My best to all, Tad.

  15. SAQuestor
    Joined: Sep 2003
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    Location: San Antonio

    SAQuestor Senior Member


    Thanks for the enlightenment on Transport Efficiency. Excellent.

    The point I quoted above is just a quibble - but I've not seen any 2 1/2 ton SUV achieve 25mpg. Take 3/5ths of that number - 15mpg and I'll not quibble.

    I just don't think giant SUV's are all that efficient on their own.

    And as always, YMMV (Your Mileage May Vary) :D



    Going back to the boat discussion.
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