Building a 21' cruiser with inboard diesel and auto

Discussion in 'Projects & Proposals' started by lucas12, Mar 23, 2006.

  1. lucas12
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    lucas12 Junior Member

    I've been trying for 3 months to find my ideal boat, but no luck.
    So being a motorhome designer I've decided to make my own.
    What I was thinking was using a glass hull 21' that is very ocean worthy but a planing hull, and converting it to inboard/shaft drive using a car diesel to be marinized 2.0 turbo diesel with the auto 3 speed.
    The idea is to take on water ballast for rough seas that decreases volume (weight) at speed (calmer water) so in essence the boat would act as a semi displacement or a sport fisher (planing hull) all the interior panels would be alumium honeycomb which is 11kg per 8'x4'x 20mm board with incredible torsional stiffness, this would also do the bulkheads etc.
    My question to anyone the wiser (which wouldn't be hard) is "What could be wrong with the concept if any ?
    Oh the other factor is I want to spend $20,000 and so far looks achievable.
     
  2. lucas12
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    lucas12 Junior Member

    I'll make my own reply then

    I've read just about every thread involving "using auto running gear" and there is definately one side of the fence or the other, yet no examples of proof as to what works and what doesn't. I've also come across some examples of people using 2 speed autos in ski boats and they work fine, one comment was some people turn the auto upside down to enable servicability, even that seems drastic, as it's not hard to pull out an auto once every blue moon. As far as marinising and air flow and cooling, I can't believe marinised basicly means being able to pump cold salt water into any engine, that's insane engineering ! no wander boat motors are so unreliable ! No offence to any purists but you're all being ripped off buy the greatest consumer scam ever.
    Fair enough when T model fords were around, but it's 2006 and we can almost catch a plane to the moon, and we're still pumping cold, corrosive water through an engine that generates heat and relies on heat soaking in order to run itself in, a piston is round so is the matched bore, if you pump cold water down one side and have hot on the other even a few deg it's going to last a very short while as they seem to. God help the poor engine if it ever ran dry even for 1/2 a second.
    Another suposed down side to the Auto gear problem was the electrics, I went on the hunt looking at new boats over the weekend, the electrical design is the same as Toyota, I wouldn't use a petrol engine as the engine bay wouldn't have enough airflow but if I had a car that had the slightest hint of petrol smell I'de take it off the road, because it's illegal ! and dangerous, so why let a motor in a boat get to that stage ?
    Anyway I'm sure I'll have some challenges getting the set up right, but for $2000 as aposed to about $20,000 or so for the same power theres no contest especially when actual thoughtful engineering has gone into it.

    If you can't join em beat em !
     
  3. tom kane
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    tom kane Senior Member

    There are a lot of contradictory opinions about how a boat should be designed (especialy in boating forums)and like you I am not impressed with many boats that are supposed to be professionaly designed.That includes hull and propulsion.Like you say salt water running through any hot engine is silly,and of course there are alternatives.How you design your boat may be dictated by your local Boating Regulations and resale value,as your boat design may not impress others.I believe you have good ideas which are practical,but can you put them into practice,or more likely will you be allowed too.Automatic gearboxes from autos have been much used in boats, some with direct drive instead of torque converters,but correct ratios are a problem used in boats.Five speed automatics for boat have been used.If you do plenty of research about what others have done and study, you should have a lot of fun,but it will be expensive unless you can do the work yourself,as it will be difficult getting others to comply to your designs because it is not conventional and well understood.
     
  4. lucas12
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    lucas12 Junior Member

    Thanx tom, someone who thinks latteraly is always worth listening to.
    I will be doing all the work, I've done some pretty awesome conversions of cars and buses, my ideas are always based on budget and not losing money when I sell.
    Since you mentioned "hull design and propulsion" that's my only grey area left, I've thought out the whole cooling and ventilation system as well as controls etc for the engine and the shaft. I even joked about using PARK on the auto to drop the anchor LOL. It's not that silly ??
    I did ask around about putting a skeg on a planing hull, one theory was it won't want to turn, and if you did at high speed, it would lean out not in, but if it was shorter and curved would it follow the curve of the turn or is just a theory, because I can't remeber seeing a displacement hull leaning into a turn ???????
     
  5. tom kane
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    tom kane Senior Member

    I am sure you know that you can beef up auto boxes like the racers do by adding extras plates and redrilling the crutial holes ect.,to take big HP.The gear change is much better than clonky outboards or inboard/outboards and change at higher RPM,especially diving into reverse when you need it.There are some interesting books written by top American(must be top) power boat drivers if you have a look around,I have titles somewhere.A trimmable shaft drive that can be run as a surface piercing drive or as as a conventional shaft drive would be a good choice for an adverturous designer especially with say a modern five speed auto box,and tops in handling all sea conditions and docking and long service low maintenance.Changing down a gear or two in heavy seas gives better control.
     
  6. lucas12
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    lucas12 Junior Member

    Hi tom, I had a guy in south Australia lined up to source the hull, but he's no longer got the moulds, so I'm looking for an appropriate hull in plan form, to form up to 28' x 8'.
    Bruceroberts never returns emails so I've given up on that, Glen L has alot on offer all with 18deg deadrise. Would that hull design suit with prop below duck board, My main trips will be ocean up 5 km off shore on the east coast of Oz the idea is to travel to an area, launch and travel up or down the coast line for 2 weeks at a time, and camp ashore on rough nights with my 2 kids, the design criteria is to be able to manage 2 toddlers, a boat and everything else in reasonable comfort and safety. The worst case senario is big swell and being able to turn around and head back to shore in good time, as well as fish comfortably on chop. Don't worry people think I'm mad with what I get the kids involved in, but at their tender ages they absorb like sponges and adapt very smartly, each new challenge gets easier for them and they love it. No kid of mine will ever get a playstation. I looked at surface drives and the engineering seems fairly robust and simple, is that really the ideal drive ? And what are 'Trim Tabs' ?
    Simon
     
  7. lucas12
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    lucas12 Junior Member

    I know what trim tabs are now, how basic, it would be easy to make a set with air cylinders compressed off the engine and regulate the pressure (set and forget) Do you think they are an economical alternative to a surface drive with economy sacrifice ?
    Cheers Simon
     
  8. lucas12
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    lucas12 Junior Member

    I've been researching all night and just had to add one more thing before I get some sleep and get ready to solve other peoples problems tomorrow at work. On the motor homes I pressurise the chassis and containment and storage areas to keep dust out, just with a duct from the outside airflow, if I use a compressor like a modified auto aircon compressor to operate trim tabs I could also make the hold area leak proof to 1 or 2 bar, the seals would also be pressurised to seal airtight and the bulk heads would take less stress as the hull area would become structural against force as a whole. It might be overkill especialy if I spring a leaky seal and the thing farts !

    Simon
     
  9. tom kane
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    tom kane Senior Member

    Building a 21 cruiser with inboard diesel and auto

    If you want to keep up to date in system controls,research interceptor plates (which react faster) instead of old trim tabs.
     
  10. lucas12
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    lucas12 Junior Member

    Thanx tom, I'm going to take all the info I've collected and see how I can come up with a designed outdrive system that is ecconomical to produce without castings, solidedge is good as a design tool especially sheetmetal, which if it can't be folded the software won't flatten the model, during my research and modeling for Motorhome componentry I've established cheap ways of replicating injection moulding, instead of expensive dyes, I've come up with materials and mould designs formed on CNC that can be vacuum formed, I'm currently working with a fibreglasser to educate him on vacuum techniques and cheaper pattern making techniques to be able to quickly change mould sections with costs covered on the first unit sale and profitabilty there on. Hopefully in a year or so my boat will be on the water.
    I guess my only hurdle will be acceptance of it's engineering, but saying "Hey we're not stupid enough to pump salt water into our engine" I might ruffle some feathers ? The intension is to create from the 'KISS' principle 'Keep It Simple Stupid' so that the hull design should be 'Basic' to pruduce the mechanical components will be cam type in function from standard sections and lazer cut components (raw but clever) and eventualy maybe even a steam engine (hey were surrounded by free fuel) and webasto make very efficient burners that could just about burn any fuel as a flame producing fuel perhaps fish oil ? I've been hooked on the issue of oil reserves lately and saw a show on SBS last night that pretty much confirmed what I keep preaching "Theyre not going to tell us when it will dry up, we'll just wake up one day and they'll be none left" No plastic, no rubber, no transport, no food, no medicine, .................. and so on. The world is 25% iron and I'm guessing 65% water, Iron burns well, and water expands 70,000 times on combustion.
    Food for thought !
     
  11. Gilbert
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    Gilbert Senior Member

    cold water on the cylinder liner??

    Most marine cooling systems do not have cold seawater going into the engine block. The raw seawater is normally pumped through one side of a heat exchanger and then into the water jacketed exhaust manifold and then, if it is a wet exhaust, out the exhaust pipe. Systems using raw water are most often intended for fresh water, and those intended for salt water use usually have heavy castings to give reasonable life with the corrosion that can be expected with salt water. Then there are closed systems with 'keel coolers' which transfer the heat to the water outside the hull. You could even use a closed system with a radiator but that would require getting rid of a lot of hot air.
     
  12. lucas12
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    lucas12 Junior Member

    What I had intended to do was lay the aluminium radiator in a tank that the raw salt water is pumped into, which would then pass through a s/s jacket over the exhaust, basicly the same thing, as far as air cooling, diesels run colder than petrol engines, so I was going to keep the viscous fan with air being taken in through a grill on the engine cover (box) and duct out as much as possible to the stern. once I work out my weights of the boat I'll have to try to work out how much torque is needed to push at 1:1 in top gear at say 30 knotts at 2500 rpm, I think a 2.0 turbo diesel will have enough torque and hp to hold the prop against the water at 2500 rpm, It's alot easier to work out a cars requirements, with some experience, so I'm flying blind a bit. It's a new factor for me (calculculating power, drive ratios, and constant wheel spin)
    I need to do prop research !
    As far as hull design I've got the basis of ideal deadrise, for the length of the plane but what is the ideal length of the plane in % of the boat, in other words "When does the keel start to rise up to the bow" I would guess that would depend on the engine position, seeing that I'm centraly mounting the motor, does that mean my planings section (flat from the side profile) would start to finish just ahead of the centre of balance, or just behind to give a softer ride ??????
    I still can't determine from other design plans what dictates inboard position centre, stern, or out board, when the hulls all look the same on the PDF's
    But the designers state what the engine layout can only be one for the model. or does it purely depend on weight distribution of the whole vessel ??
     
  13. lucas12
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    lucas12 Junior Member

    I've read a few threads on hull design, NUP ! I think I'll build my first boat hull from plans and look at it later when I've got kids who are independant and associated staff as well ! I've decided on Glen L's Monsoon 22' cruiser which should be do-able as a plug made from cheap ply and glass then pull a mould. Most of the mechanical components can be sourced from general suppliers for the surface drive, which at this time will be a porche CV joint and some other fabricated bits. Can't wait !
    30 knotts is specified to req 180hp for the monsoon 22, hopefully a diesel with the right torque and 0.8:1 top gearing will reduce the hp required to about 100hp.
     
  14. tom kane
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    tom kane Senior Member

    It sound as though you are having a blast with this project,and using standard parts to build a good surface drive can be easy even if you use dynamic or passive steering.You do not realy need a lot of trimmability with surface drive but if you build a drive with 20 degrees of trim you can run the drive as a conventional drive if you do not like the surface drive option,and use standard design props,which are cheaper and you can access a bigger range of pitches without being held to ransom by a surface drive prop supplier.
     

  15. Willallison
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    Willallison Senior Member

    You can't simply change down gears, use less power, and still go the same speed. Sorry to pout cold (salty;) ) water on your plans, but that aspect of your plans simply won't work.
    Propellors are optimized (generally) to give the highest speed at an engines max revs. At any other speed they are less efficient. There's a reason why you don't see boats running around with variable transmissions....
    Sure there are 2-speed gearboxes available, but generally they are installed in one of two applications. Underpowered boats can benefit as it allows them to get onto plane with engines that would otherwise be overloaded. Also, high speed boats - particularly with surface drives that have huge blade area that is too much for the engine at slower speeds - can benfit as it allows then to fit higher pitch props.
    It's not that the boat won't work with a multi-speed box, it's simply that it's complexity for complexity's sake. There's no real gain over a 2-speed system, which can be achieved in other ways - like a torque-shift prop for isntance.

    Nonehtless - I admire your adventurous spirit!
     
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