economical coastal cruiser

Discussion in 'Boat Design' started by sandy daugherty, Feb 11, 2010.

  1. Guest625101138

    Guest625101138 Previous Member

    There is some data here on a 50HP outboard:
    http://www.yamaha-motor.com/assets/...otb_2StrokePerf_HPMidPort_50hp_0154-EDG-Z.pdf

    At full power it burns 5.8gph. That translates to about 510g/Kwh at full throttle. I expect at 16kW it will be worse. Probably around 40HP would be best.

    However the big downer with the outboard is the inability to fit a reasonable prop. It will throw about half the power away spinning its little prop madly. Maybe David can solve that issue and find a way to fit a bigger prop.

    Rick W.
     
  2. Pierre R
    Joined: May 2007
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    Pierre R Senior Member

    When you read power curves for an engine and propeller you do not look at the fuel burn figures as that required by the prop at a given rpm less than full power. The excess power above the prop and before reaching the full load state is the power available to drive auxillary components. If the engine is only driving the propeller and little else the engine does not consumer the given amount of fuel on the curve. Its not as good as full load but not as bad as you guys are painting it.

    How many of this type of boat have you built and how many do you have out cruising the waters at present? You get sued if you are wrong on this stuff. Much of this thread seems to be the blind leading the blind with plenty of contradictions and inconsistencies.
     
  3. Guest625101138

    Guest625101138 Previous Member

    There is an easy solution to this. Provide your figures for the diesel and petrol comparison so others can do some basic figuring. You won't be held to account for it. Just helping a few people trying to make some basic decisions.

    If your only intention is to provide criticism without useful contribution why participate.

    Rick W
     
  4. Oyster
    Joined: Feb 2006
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    Oyster Senior Member

    Got a mirror sir? :p Armchair hypotheticals does no one any good either. ;)
    Instead of attempting to outpost everyone across these threads until people loose interest, sit back and take a breath and remember that the varibles involved are vast and wide. Try being a bit more open to people that have actual working boats and setups too that's willing to provide their own life experiences which may also meet their needs for others lurking and reading on their simular needs.
     
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  5. tom28571
    Joined: Dec 2001
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    tom28571 Senior Member

    Pierre,

    My BJ24 typically displaces about 2900lbs powered with a Yamaha T50 and a 13 5/8 x 13 prop that was selected among those available. It has never consumed over 2 gal/hr on many cruises. That covers a lot of different speeds over the length of a typical cruise. I have a typical "slow" cruise speed of 12mph and a "fast" cruise of 17.8 mph and anything in between. Fast cruise is at Yamaha's recommended RPM of 4400. Some of the time will be slower and some faster. Calculated fuel use is from 6 1/2 to 8 1/2 mpg depending on conditions.

    Sure, I'd like to have an optimized propeller but practical considerations limit us to what is available off the shelf. These figures may not match what is considered optimum but they are real and attainable.

    Edited to add that the propeller providing the highest speed was a 15" pitch that loaded the engine and limited top RPM too much. A 14 x 11 was the first bought and it allowed over revving past Yamaha's recommendation. It was repitched to 12" and is used for a spare since I think the 13" pitch works better.
     
  6. Pierre R
    Joined: May 2007
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    Pierre R Senior Member

    I am certainly somewhat critical of you Rick. Perhaps you mean well but your presentations scream of arrogance. Since we only have your posts and not you in person it could simply be your command of the written word. You seem like the rigid analytical engineering type who sees the world through engineering principles and those who don't are doomed to stupidity.

    When you are looking at diesel curves you are not looking at absolutes. You are looking at a guide line and understanding that is key. Missing now from most manufacturers figures is the mean specific fuel consumption per KW at each rpm. I thought this curve was much more useful than the fuel consumption plotted against brake power, shaft power and propeller power. The propeller power is the most obscure because it make many assumptions about the drive line and hull configuration.

    When selecting a diesel you want a diesel engine which will deliver about 55% to 70% of pleasure rated power at the propeller depending on what the torque curve shows for that particular engine and the size of the engine in relation to it's accessories. You want normal cruise somewhere just to the right of peak torque but before a noticeable drop is experienced. After the engine and gear box is selected, the prop is maximized. Not normally the other way around. To many assumptions with to much time and effort wasted on the later approach.

    You want to optimize the diesel engine to the weight of the boat, the accessories you will drive and cruise speed of the boat. This is normally where your big expenses are. After that then optimize the prop to get as much out as you can where the diesel is most efficient. In most cases the prop selected will not be the one that delivers maximum efficiency. Those curves are also full on assumptions. Balance, harmony and low maintenance is what ultimately determines best fit. Not absolute numbers.

    Even with all the fancy computer programs out there, propeller selection is still in the art form category.

    Rick do you know the assumptions made by the writers of the computer programs you are using to give optimum absolutes? I admire your passion and willingness to help but yacht design is still an art form. That is why the field of truly great yacht designers to the number practicing is small. Computers have not leveled the playing field and in fact have taken yacht design by amateurs in the wrong direction. There are plenty of disasters out there to prove it.

    Am I a yacht designer? No, but I am strongly thinking of putting the nose to the grindstone to learn how to be a great one. Seems like it would fit my personality perfectly. I am one of those rare birds with engineering degrees, patents, time and money who is also a touchy, feely, creative abstract thinking artist type who can communicate and teach.
     
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  7. fcfc
    Joined: Feb 2005
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    fcfc Senior Member

    This thread is stalling.

    For those thinking building a 40 ft lightweigh boat, you should check this site : http://www.fram.nl/workshop/figures/timeandcosts.htm

    On project cost, you can click on the legent of the pie chart to understand what it contains. You will see that the price displayed does NOT include engine, sail hardware, hardware interior, instruments etc ...

    At the listed stage, it is mainly bare empty hulls, tho external finished and painted.


    Second, the trailerability of a 40 ft boat a bit strange.

    I have already said than one practical limit is 25 ft, 4500 lbs (2000kg) weigh trailer included, 8ft6in beam. At this stage, the boat can be really said trailerable.

    The next limit is 36 ft 11m (the 12m limit is the whole trailer length including tow bar and coupling up to the rearmost light. rear overhang limited to 40 cm (1ft 4in)). 3500 kg (7700 lbs) trailer included. That leave some 2600 2700 kg (5900 lbs) for the boat in trailering state. And this level of complexity and price (trailer price, towing vehicule price, boat price), adding an overwidth permit to 3m (9ft 10 in) is near nothing. And at this stage, it is not trailering, it is an expedition to plan and prepare long before.


    Third, still no budget. Under 50 000€. There is simply no money for a diesel. Whatever the technical considerations.

    Between 50 000 and 100 000€, you may have money for a diesel, if you severely restrict the hull and interior layout. ie an near empty 30 ft hull with diesel.

    You need to target over 100-120 000€ if you want a 40 ft hull with some efficient diesel.

    PS Trailerability is for European countries.
     
    Last edited: Mar 18, 2010
  8. u4ea32
    Joined: Nov 2005
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    u4ea32 Senior Member

    fcfc, the trailering regulations are far from consistent internationally. And within the USA, they are contradictory. It seems the EU is currently trying to make things more consistent, while the US seems to be making things less consistent. But I think the EU has no more chance of achieving uniformity of regulation than the USA.

    Ignoring regulation for a moment, and just speaking of what is easy to do:

    Its quite easy to tow very long loads -- even 60 or 100 feet long -- if the beam is narrow, the height is low, and the weight is low. For example, its really quite easy to tow a mast trailer.

    The height is important because trees overhang roadways. So the practical height limit is the height of garbage trucks, as these generally "trim" the trees on many roads! So the height on trailer should not exceed about 12 feet in my experience.

    The practical width limit is 8.5 feet in my experience. Mine is 8.33 feet, and there are MANY launch ramps where I have inches on either side of the boat getting through the gates and other obstacles.

    Any oversize permit is really a huge pain. They are usually cheap, but it takes visiting some government office to get one, and there are usually horrible liability stipulations: in California, if you are towing with a permit and there is an accident of any kind, its YOUR FAULT and the towing permit is nullified, which probably means your insurance is invalid.

    With respect to weight, that is also not much of a problem. My truck cost new $30000. So its not expensive. Its a Ford F350, so its not a commercial truck. Its actually easier to drive towing 12000 or even 14000 lbs than it is driving it empty.

    My parents used to tow a 4000 lbs 24 foot sailboat on a 2000 lbs steel trailer with all the crew (7) and all the gear in the van -- and the van was a 30 HP VW combi! Hydraulic brakes were essential, as was patience (zero to 60 in, well, never happened!).

    So you can easily and safely tow quite a lot.

    Now, with regard to regulations, its much less clear than you suggest, even in the EU.

    In the USA, and probably in most places on Earth now, 53 foot containers are becoming pervasive. International treaties are involved in shipping, and these override local restrictions in many cases. So there may be regulations stating nothing over X feet long, but there are also international treaties signed by many (more and more) countries that guarantee unimpeded transport of 53 foot containers, and these are usually pulled by tractors that are 25 feet long. That's a long vehicle! Now it may be true that commercial licenses may be required but in the USA, a commercial license is never required until the weight of the trailer exceeds 25000 lbs. Has nothing to to with length or width of load.

    And the way trailers are measured is almost laughable in the inconsistency. Often, the length is measured between the "king pin" (trailer hitch) and the aft most axle. Often, there are stated overhang limits. Often there are overall length limits. Often there are height and width limits. But things like mirrors, lights, awnings, steps, ladders, winches, and other "accoutrements" are not measured in width and length. Usually, all these various measurements do not add up.

    Given the 53 foot treaties, and that "accoutrements" excludes anything that can be bolted on (such as outboards and swim platforms) in my experience and understanding the largest simple-to-trailer boat throughout the USA is 53' long and 8.5 feet wide and 12 feet high on the trailer.

    Given the realities of future fuel costs and so fuel consumption while towing remains reasonable, I think 3500 to 4400 lbs (2 metric tons) is a good max weight on the trailer, so the tow vehicle can be reasonable (such as a BMW 1X diesel or a VW Tiguan diesel).

    And with respect to budget, which I agree is very important: The same boat can cost from $20K to $300K, so its really your choice. If you build it yourself, you might do it for $20K. A cheap builder, maybe $100K. A good builder, $200K. A High end builder, $300K. So I don't think budget is important FOR THIS FEASIBILITY STUDY.

    If you really want to build the boat being discussed, I suggest you do the necessary things: once the feasibility is demonstrated (still debatable), draw up some preliminary drawings and scantlings, and ask MORE THAN ONE builder for an estimate.

    I've done that, so my design (that has some features similar to what is being discussed) is within my budget. Some of the things I learned from shopping the design to multiple builders includes:

    1) The shape of the boat is irrelevant to cost. Hard chine, round bottom, compound curves, tumblehome, developable, very much non-developable, gunwales (round unified gunwales, hat section, box section, etc), boxy, aerodynamic, ... NONE of these make a measurable difference in the cost of a boat. The time it takes to make the one-off mold is measured in less than a few dozen hours regardless of the shape. Again: one-off molds are CHEAP even when quite complex.

    2) Unlike shape, materials do make a difference to cost. The cheapest one-off construction method is glass/foam (vinylester is a little cheaper than epoxy, but not enough to matter). Aluminum is more even if very ugly. Cold molded is even more because of the tremendous increase in labor (all that sanding and fairing between laminations that is not needed with glass). Traditional wood is MUCH more. Interesting, but Carbon/Nomex is only about $10K to $20K more than glass in this kind of boat.

    3) By very far, the biggest contributor to cost is SYSTEMS and FINISH.

    Note that I got budgeting numbers already, and I am still far from being done designing. The length keeps changing from 40 to 45 to 53 feet, the hull keeps changing from displacement to planing, the powerplant keeps changing from outboard to inboard diesel, from one to three.

    But I keep the displacement as low as possible, and the systems as simple as possible, and the finish as simple as possible (but still very high quality).
     
  9. erik818
    Joined: Feb 2007
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    erik818 Senior Member

    Fcfc,
    The figure 270g/kWh (or 0,3 liter/kWh) is a typical figure for small inboard Vetus diesel engines, a company which provide data on fuel consumption as a function of rpm. Data provide by Solé are not as explicit, but at max power, the data sheet for Solé motors give about the same fuel consumption.

    The fuel consumption data I have on the Yamaha outboards are the best I can get hold of. It’s been much more difficult to gather fuel efficiency data on gasoline outboards than on inboard diesels. With nothing else to go on I have to assume the same optimist factor for the two sets of data, so I still believe the relation 17 hp to 10 hp for one hour per gallon fuel is correct.

    The actual difference in efficiency isn’t as large as that. Diesel contains more energy per volume than gasoline.

    The weight of a 30 hp diesel with transmission is about 150 kg. Add 30 kg (guess) for propeller shaft and propeller and we have 180 kg. A 40 hp modern four stroke outboard weighs 90 – 100 kg. The difference is about 90 kg (200 lbs) Some of the weight difference will be offset by the lower weight of diesel fuel for the same range.

    Adding the price difference into the equation provides all the necessary inputs to come to any conclusion you desire. I prefer an inboard diesel but see no point in arguing that an outboard is wrong.

    Regarding prices, a brand new 27 hp diesel inboard can bought for approximately €3,000. The catch? From the ad: “Kinesiska dieselmotorer av mkt hög kvalitet, tillverkade med västerländsk förlaga.” Translated “Chinese diesel engine of very high quality, manufactured from a western original.” The motor could be a good buy, but not without risk. If you want to attempt Swedish you can check their home page www.rrun.se.

    Erik
     
  10. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    While I have long been a fan of the Atkin style boats I was delighted to get the latest issue of the West Epoxy co "Epoxyworks".

    There they show a boat built here in Fl to revised Atkin plans that cranks out a claimed remarkable 30mpg.

    http://www.stormportboatworks.com/moreinfoandbasicspecs.html

    Is the web site , and since it could only benefit the builders I have copied and pasted some of the site,


    "The Oyster Cracker has all the features the discriminating flats fisherman desires.Deck configurations can also be custom tailored to your needs. Shallow draft, uncanny fuel-efficiency , total weed less ness, and environmentally friendly running are some of the strong points that this boat offers.

    Her uncanny fuel efficiency is due to a three cylinder Kubota , diesel motor. This ultra-clean burning motor surpasses California emissions for the year 2015 ! At 12 kn. cruise, the dependable power-plant burns less than 1/2 gallon an hour. Fuel consumption does not change much at 18.kn.. top speed.That's over 30 miles a gallon!

    With two men and gear, the boat floats in 10" and maintains a 8 " draft at any speed.This unique tunnel-hull does not need a " hole shot". The boat will run over a floating crab trap warp without tangling.The 10 inch prop is well protected and totally weed less. Thick Lilly pads and grass are pushed to the side. Hydrilla is no match and is chopped to bits.

    The Oyster Cracker as shown is loaded with features. The elevated console has a built in tackle center. Leaning-post w/rod holders, Large forward casting deck with live well in step, Rear casting deck, and optional live well- cooler.raw water wash down pump w/ hose storage. Tee Top w/rod holders. Under gunnel lites and rod storage. Cockpit is self bailing.
    This boat was designed to be easy to maintain.Cooling of the motor is accomplished with a keel cooler. This is a closed cooling system. It eliminates the problems associated with raw water cooling. The motor compartment is an "oilers" dream. Easy access to motor from front and rear. There is a small pump on the motor for changing oil.

    Environmentally friendly aspects include:

    Well protected prop that will not scar grass beds and is manatee friendly; ; Mercuery-free bilge pump switch. The ultra-efficient motor will even burn bio diesel fuel; and boasts an incredible efficiency of over 30 mpg (less than 1/2 gallon per hour). She actually surpasses California emissions standards for the year 2015!

    Superior Construction: Oyster Cracker is not a plastic boat. These boats are built to last and survive many hard groundings in our rocky coastal environment. Her innovative epoxy-plywood composite construction has proven to yield a superior and far stronger hull then those slick poly-production boats. Competitive boats, both sail and power, have discontinued the use of all glass construction in favor of the epoxy-wood composites. The reason is simple. After repeated use, the "all-glass" boats soften. They become less responsive. This is due to cyclical loading. Marine grade plywood can withstand 700 times the cyclical loading and still maintain its original strength. High quality, growth sustainable marine plywood is used as a core material. This wood is totally encapsulated in epoxy and cloth - inside and out.

    The Oyster Cracker has a unique tunnel hull. Water to the tunnel is supplied from both sides of the hull instead of from the bottom. The boat does not have to be built light weight to achieve optimal shallow draft. The bottom of this boat is over 1 inch thick! A fabric called Xynoll covers the bottom. This product has a greater abrasion resistance than Kevlar. Even after a hard grounding, your need for repairs, if any, will be limited to the bottom paint only.

    The 10 inch propeller is well protected by a large foot or sole plate. It does not protrude below the boat. The 25 hp Kubota diesel motor is ultra-clean burning and incredibly efficient in this installation. These motors are built to last a lifetime. When your buddy is changing out his high dollar outboard, you will be changing the oil in your dependable little motor.

    Please remember; Storm Port Boatworks main priority is to deliver the highest quality and value in the boat you desire. All of our boats are built with the environment in mind. Ordering a boat from Storm Port Boatworks makes you a leader in the "Green Revolution".You can be proud that you are reducing the impact to our fragile marine environment. You will be able to enjoy boating at a fraction of the cost of any boat of comparable size. Show people you care. You are aware!

    The Classic Cracker has the same construction and performance capabilities of her sister ship with out the bells and whistles. This boat has limitless commercial or tender possibilities. She is also a good example of how deck configurations can be customized to suit the potential owner."

    A 30 mpg boat at 12 to 18K would be a remarkable deal.

    If Rick could work out one of his 80% efficient prop setups given the design constraints we are looking at progress!

    Kept skinny (8ft6in) and since the builder claims (as Atkin did) that weight is no problem the boat could be built of not super sophisticated (like plywood) materials and the cost kept down.

    Will be interesting as up till this point only Rescue Minor was avilable as a yard stick.

    Since this yard is thinking of bigger boats REAL performance numbers will soon be avil'able.

    Here's to it!

    FF
     
  11. Guest625101138

    Guest625101138 Previous Member

    For propellers I know exactly the assumptions used as they are programs I have created. My designs get within 1 to 2% of actual measured efficiency. They are more accurate than any empirical curves you will find because I determine blade characteristics at actuall Re# for the conditions. I also adjust for cavitation and can apply a wake factor if I determine the hull shape warrants it.

    The speed predictions program I have developed for slender hulls will give calm water power predictions, hull and prop combined, within 2% across a wide speed range.

    I know there are very few NAs participating here who understand prop design because of the information they offer here. I have also had three requests from universities working on efficient boat projects to provide prop designs for them. Anyone with a bit of interest and basic knowledge can quickly gain better insight into the physics of props than most NAs here have with a few hours spent understanding JavaProp. You might class them as instant experts but they will be better placed for assessing prop performance than anyone applying empirical curves.

    It took me a couple of years to develop my software but it has been worth the effort as it gives me great flexibility in designing props - I understand the fundamental physics, few NAs here do. They just go to the curves, which are useless if you want an efficient prop.

    So as far as prop design goes I know exactly what the software does.

    The hull drag software I use was developed by a mathematician I have great regard for. I understand the maths behind it and I have extensively tested its results at a scale relevant to the application here. I doubt there are many people who have built and tested the range of slender hulls I have tested.

    So as far as props go and hull shapes for low drag I can provide accurate data for making decisions on. I am in a very good position to help with feasibility and what is possible within certain constraints.

    Rick W
     
  12. Pierre R
    Joined: May 2007
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    Pierre R Senior Member

    Rick you sound exciting and I wish that I could put faith in everything that you say but there is simply too many inconsistencies throughout your posts.

    You had me going there for a while on props until you tried to size and engine and determine its performance. I knew then that you did not understand loading and diesel engines. As soon as I knew that I knew that you could not optimise a prop the way you are trying and mate it to a diesel engine. Variable pitch props are the closest you will get to the kind of data that you have been providing for fixed pitch props. You would either overload or not have enough pitch much of the time.

    I am aspiring to learn but I do have a good idea of what will work and what will not. I intend to build my retirement boat within the next 5 years.
     
  13. Guest625101138

    Guest625101138 Previous Member

    You will find in posts a couple of days ago that I said variable pitch was the best choice to get the best from the diesel. However I also note how Tom has overpropped his little diesel to improve the efficiency.

    Also if you go back you will see I took at a stab at the difference specific fuel consumption of diesel and petrol and asked others to contribute accurate data if they had it. I asked for fuel maps if anyone had them as it is not something I have any current interest in.

    My real interest is in solar power and electric drive. So I take greater interest in what is currently available in this technology.

    Rick W
     
  14. Willallison
    Joined: Oct 2001
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    Willallison Senior Member

    I don't profess to be an expert in every field of yacht design... few honest qualified people would. Props are one of those grey areas for me... where I would defer to the greater expertise of others. There are some fundamentals of prop design that any comptetent desgner ough to know. In my view, some of Rick's posts would suggest that he fails to fully comprehend some of those fundamentals.

    The failure to understand that a prop operating virtually at the surface is likely to suffer from ventilation problems is one example.

    Another can be found here:

    http://www.boatdesign.net/forums/props/prop-doing-bad-29864-3.html
     
    Last edited: Mar 18, 2010

  15. Guest625101138

    Guest625101138 Previous Member

    You would be a fool to put faith in any unpaid advice or opinion without testing it.

    I have a fair track record on the forum for giving free advice that people weigh and try and get the results I predict. I often get notes of appreciation and I get many direct requests from all sources.

    I have attached an example of the recognition I often get. I am happy to help. The more trying and improving on my ideas the faster I progress. I could not hope to build and tests things at the same rate 50 people can.

    When I first started making props I even sent one, at my cost, to a fellow in the US to test. It is cheap education in the real world. I have paid for parts built by a friend in the US to test and share my views on his creation.

    Vic Garza (porta) is probably one of the few who has followed my journey with boat testing over the past decade and has provided me with some great ideas to explore.

    The forum should be about learning not sniping.

    Rick W
     

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