Topic to learn from: coupler? Or gearbox perhaps?

Discussion in 'Sterndrives' started by Random_user, Mar 3, 2017.

  1. Random_user
    Joined: Mar 2017
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    Random_user Junior Member

    First of all, I'm Dutch, and I don't know all the names of the parts, so I will be using lots of images, so everyone can understand what I am talking about. I am not that interested in part names, not even the dutch part names. All I care about is their function.

    Context of my question: I want to put an regular car engine (Audi B5 engine, V6 and 2.4L, 165 hp and 230 (?) Nm of torque) inside a small boat. Want to use an old/used sterndrive, and I am unsure about some things. Want to keep costs low, because I am not even sure if it will work or even float.

    Some people on some Dutch boating forums told me I would need a coupler. Unfortunately, they can't really explain to me why I would need one of them, and I had some other toughts. I hope this much larger international forum can help me out.

    A coupler is supposed to help with vibrations, and alignment. It's a bit of a buffer, and it should keep the bearings inside the engine healthy. But I wonder, can't I just use a (frontwheel) car style driveshaft? They have on one side a regular sterndrive flexible joint (don't know the name), and on the other side, a completely different and highly flexible joint. I would think this second joint would be a buffer for alot of vibrations, and would also be a great buffer for forward/backward movement. So, do I really NEED an coupler?

    The only reason I can think of where a coupler is required, is changing gears. I am not sure on this, but it seems that "smaller" outboard engines use something like a "dog clutch", which isn't really a clutch in my opinion. Just pieces of metal, which slam together, giving a big jolt to the propellor. (and the engine) A coupler might be required as a buffer, but I wonder how important this is, and how much of a buffer the coupler would be in the end... Do I NEED an coupler for this purpose? Or will my engine stall when putting it into gear? Of did I miss something about the inner workings of a stern drive?

    Considering the supposed jolts when changing gears, there might be some other ways to help me out. I want to buy an entire car, as a donor. Only thing I REALLY need, is the engine, but it ofcourse also has an gearbox. Not looking at the weight gains, I might consider using the gearbox, to connect to the sterndrive. I see two options here, and I want too explain my reasoning for both of them.

    1: manual gearbox. The manual gearbox has an regular clutch. This would be a way better means of changing gears. It would go smoothly, considering how an dog clutch would work inside the stern drive. It would be soft on the stern drive (changing gears inside the sterndrive, with the clutch engaged for example), and it would be the perfect buffer for the engine, and it's bearings. I could "lock" the gearbox in a specific gear, for example 3rd gear, and never change it. Only using the clutch.
    The other option I might be considering, is putting the stern drive always in gear, and locking that. Then I could use the manual gearbox for forward, neutral and reverse. I know most of you would say: bad idea, you can't upshift while speeding along. But wait a second... I want my boat to be able to go fast, but I also want my boat to go slow. And (car) engines don't like to be used at idle speeds. So I might put the gearbox in 1st gear, and let the engine run at (for example) 2000 rpm, and go slow. If I want to go fast, I shift up to, for example, 4th gear, and use the full rpm range. Not shifting while trying to speed up or when at speed. (I am not looking for something like 65 mph, 40-45 mph is fast enough)

    2: automatic gearbox. The automatic gearbox has that strange "clutch" thingy. (don't know how it's called, don't want to look it up) It would also be a "perfect" buffer for the build-in dog clutch in the stern drive. But I do see some disadvantages here, and I hardly know enough about boats/propulsion...
    With the manual gearbox, I can select gears, and go from there. But the automatic gearbox is different. People told me that the pressure would be too much for the automatic gearbox, to actually change gears. The engine would in this case be locked in 1st gear, with a "slow moving prop shaft". But is this true? Can't an automatic gearbox upshift when you've got "enough hp and torque"? Would the slowing down effect during the shift be really that bad, preventing upshifts? And before I forget, the automatic gearbox also has the disadvantage that it will eat up some of the power from the engine, due to the clutch.

    Reason for considering a gearbox would be money. I imagine there isn't a bolt-on coupler for this type of car engine. I would have to get a company to modify my flywheel, or to build me a custom coupler, which can get expencive, while I already have an gearbox. (still need to buy the engine/donor car, so I can find an automatic of manual gearbox for that) And it's been made to function and fit propperly. With both the gearbox and coupler options, I would need to get a custom made driveshaft, so I keep that out of consideration. (the engine will be more to the centre of the boat, due to balance/small boat)

    Sorry for the long post, but I really need some help on this.

    *PS: tryed to put in an image/attachment with that "flexible car axle joint", but I can't figure out how I can put that in the propper place of this topic.
     

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  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    A coupler is a part that bolts to the flywheel, so that the shaft that goes to the sterndrive can be coupled to the engine. You don't need a gearbox with a sterndrive. They shift internally. However, they are severe shock loads on boats, and the coupler helps from them transferring to the crankshaft, etc.
     
  3. Random_user
    Joined: Mar 2017
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    Random_user Junior Member

    Thank you for that reply, but I doubt that you have fully read/understood my topic.

    -I've hinted on the costs of modifying my flywheel to fit a stock coupler, or get a custom coupler >>> I know where it goes to.

    -I know a coupler normaly goes between the engine and the stern drive. To be more exact, between the engine and the driveshaft. This can also be seen in my topic.

    -I know I don't need an gearbox, and I already said something about the internal sterndrive gears/clutch thingies. But you clearly didn't read my post, because I was mentioning another kind of benefits of (stock) gearboxes. The clutch assembly for example, to dampen the (sterndrive) gear changes.

    -I know there are big shocks on a boat, which will put a big load on the crankshaft. This entire topic is about that subject, and how to cope with the stress in the entire system.

    Please, READ again, and do a more indepth reply.
     
  4. Scot McPherson
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    Scot McPherson Senior Member

    Part of learning how things work is knowing what to call the parts. Otherwise you are in THIS situation where the two people cannot understand each other.
     
  5. gonzo
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    gonzo Senior Member

  6. Random_user
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    Random_user Junior Member

    I expect to make lots of RPM. I would not trust myself when trying to drill accurate holes. But enough about the coupler.

    What about the gearbox idea? Especially the manual version. Why should I use one,, and why shouldn't I use one. Might need to add that I want the boat to function for about 5 years, and using it a total of 500-600 hours in total before bringing it to the junkyard. (I would call that a succesfull second life for the pile of parts I intend to use, boat hull included)
     
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    A manual gearbox (transmission) isn't necessary, nor desirable, except in rare applications, which yours likely isn't. In this case an automatic would be a better choice. The strange thingie is a torque convertor and it's not a clutch, though does transmit rotational energy to the transmission, with sufficient RPM at the engine. A clutch (there are several types) is a physical linkage between the two (engine/trans), while a torque converter is a fluid coupler.

    The only time you'd want to use a manual transmission is on a straight shaft setup and this was fairly common when I was a kid. We'd take an old 3 speed and remove the gears we didn't need, but retain the clutch. On an outdrive, you'd screw with the lower unit gear ratio, by adapting a manual transmission to it. Technically, you could use whichever gear was 1:1 or close to it, but a lot of complexity (welding, fabrication, shift and clutch linkages, etc.) to a much simpler set of issues.

    From the way I understand your situation, you simply need to marinize the automotive engine and make an adaptor plate for the bell housing. This will let you marry the engine, to the outdrive, without any home brewed contrivances. In fact the adaptor will be the easy part, as any reasonable machine shop can mill one up fairly cheaply. The butt kicker will be the exhaust manifolds and cooling issues.

    Unless you plan on a dry exhaust, which typically requires a fully exposed engine bay, you'll need water cooled manifolds. You'll also need a heat exchanger (or keel cooler or similar) to control engine temperatures. Heat exchangers or coolers can be easily adapted to any engine, assuming it's big enough and you can get a thermostat cool enough (boats run much cooler than automotive applications). The exhaust manifolds on the other hand will be the bear, unless someone can weld up a set or a manufacture is using this particular engine in a boat.

    Lastly, there's nothing cheap about making these types of changes to a boat. Adaptors aren't too bad, but all the related marinization stuff is costly with gas engines. You'll need a new alternator and starter minimum and will likely have other concerns too, such as cam profile, much lower output with the automotive power settings. Additionally, if the engine is ECM controlled, you'll have to deal with a new fuel map and multiple adjustments, just to get it to start and run properly. Most commonly, you'd want to use an engine that has a marinized version, so the parts are available. This means couplers, bell housings, marine alternators, etc., are all available and it's just a matter of swapping out some parts. With your envisioned scenario, you'd have to manufacture, modify and fabricate most of it, which generally isn't inexpensive. In fact, I'll bet once you look into the costs of this type of conversion, you could just as easily find a good used marine engine, that'll bolt right up, for similar money.
     
  8. CDK
    Joined: Aug 2007
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    CDK retired engineer

    You misunderstood the coupler concept. It is just an iron plate that replaces the clutch assembly. You could leave the clutch plate in place if you manufacture a drive shaft with a matching splined end, but you'll find it is far easier to drill some holes in the flywheel and use an off the shelve Mercruiser of Volvo coupler plate.
    And of course like PAR wrote, you need an adapter plate for the bell housing.
    All other home brew solutions will put the engine further away from the stern drive and complate your project.
     
  9. Random_user
    Joined: Mar 2017
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    Random_user Junior Member

    @PAR, thank you for doing an in depth reply. I'll have to think about gearboxes again. I tought automatic gearboxes would have a difficult time shifting because of the constant pressure on the system, and the drop in speed between the shifts. But if I understand you correctly, it would still be better then a manual transmission.

    On the manual transmission option, you "down vote" this idea because of the added complexity. In a normal or commercial setting, I would instantly agree. But this is supposed to be a 2 year project for my girlfriend and me, and building should be 80% of the fun. Using the boat being the other 20%. So making everything fit would be part of the challenge, with the sidenote that we want to have SOME chance of it all working.
    You also talked about the 1:1 gear ratio, coming out to the gearbox. I get that, that way you have a good rpm to the sterndrive. But as I stated, car engines don't really like to idle, and about 80% of the time, the engine would be close to idle. (speed limits in my area, with few places where you can go fast) So that's why I would consider a gearbox, with a much lower high-end speed for one of the gears. Or am I missing something here?

    Could you explain to me why I would have to marry the engine to the outdrive? Due to balance, I want to put the engine as much as possible forward. (like almost touching the backs of the seats in this 2 person boat) Using a relative long driveshaft, with an coupling like I used in the attachment, it should work. (but I have seen many sterndrive/engine pictures, where they both were connected) We also intend to reinforce the boat/hull big time, and add an aditional frame to the sides. This frame should also go to the stern (and area where the sterndrive is connected to the boat).

    Our first goal is to make the most basic technical parts function. Test if the boat is going fast enough, if it sits on the water nicely, nothing breaks, and ofcourse the boat should not sink. So at first, we would be using an fully exposed engine bay. We will be testing things, with stock manifolds. (why spend the time, when the boat might sink or magicaly disapear in a thousand pieces)

    Depending on the amount of play in flotation, we will add the other parts. My first idea was a custom home made simple exhaust manifold, with short pipes upward, with a regular car mufler. (having a nice sound is something I like, it's something different which you don't hear that much on the water) We could heat-wrap the exhaust manifold and headers. Yes, I know it can and will degrade the metal, and it will most likely not be happy when wet... But keeping it dry should help, and it should keep a large portion of the heat outside the engine bay. We would also be using heat exchangers for engine cooling, and I have some ideas on that. I am also considering using 2 car radiator fans, which would be pulling in air from the inside of the boat. (on both sides of the chairs) I think this goes a long way towards cooling the engine(bay). It would also prevent spray water, because we should be pulling air from a dry area. And in the end, if heat is a problem, I could always try and build myself a water cooled exhaust manifold. "Good enough" is good enough, don't need to squeeze every last hp out of the system. If it works well enough, it's perfect.

    Talking about costs... We intend to use lots of used parts. Our budget is around 5.000 euro, to get it all working as we intended it to work. Yes, for that money we could get an older used boat with inboard, and pull all that stuff out. But where is the fun in that? Remember, 80% of the fun is building it, 20% is using it. (at least, that's how we intend it to be) The road is more important then the destination. We also like somewhat origional ideas... But my main concern would be: might it be possible, and what are my options.

    On a side note, we only payed 250 euro for our boat. We will mainly be using the hull shape, and build on that. (max hp for an outboard would be something like 30-40 hp) We will be building the boat inside an simple garage box, and that's also where the boat will be stored when we aren't using the boat. Because of this, we think me can skip most of the marine conversion parts, such as the alternator/starter and such things. Building the system so it is very unlikely to get really wet. If the boat explodes in a worst case scenario, while we can walk (swim) away from it, we would be somewhat ok with it all.
     
  10. Random_user
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    Random_user Junior Member

    I was looking at this kind of couplers. Those are the ones I mostly find when using google: https://www.perfprotech.com/coupling-assembly-76850a2/product/113192 I also agree that an coupler plate would be way more easy to create.

    But about the bell housing, and fixing the engine directly to the sterndrive... This would make the engine package to heavy in the back. Remember, it's a small boat. (which was never intended to get an inboard engine with 4 times as much hp as an outboard would be using) Because of this, we NEED to put the engine away from the stern.

    If you are wondering what kind of boat we are using for this project, it's a trifoil 70. A +/- 4 meter long cathedral hull boat. We are going to raise the stern for some extra flotation, and reinforce it alot so it can take a pounding. (she hasn't been in a small faster boat ever, but she really likes rolercoasters, I like strong small fast boats during storms)

    If all the mechanical things work good enough, we are going to redesign the entire top, making it better in plowing trough big waves/keep us dry.
     
  11. PAR
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    PAR Yacht Designer/Builder

    You are misunderstanding some basic concepts with drives and boats in general. If you want to add to the complexity and cost of the project, add a transmission, manual or automatic. Both can be made to work, but not easily, for mostly the same reasons as well.

    I'm concerned about your "extra floatation" ideas and the drive's ability to handle a dramatic HP increase. Maybe you can post some photos of the boat, possibly with a sketch or two of your proposed changes, particularly to it's shape and CG location.

    As far as engine placement, well you can run a simple "jack shaft" setup, which will let you place the engine as far forward as you like, but if you guess wrong, you'll need to redo the jack shaft, possibly bearings too, until the boat trims properly. This is an extremely costly way to engineer things. In small boats, it's very difficult to bury the shaft below the sole, making for an odd centerline hump, at the very least.

    How was the boat previously powered? Engine type (family), drive type, etc. Lastly, you might be shooting too high with a huge power increase, particularly on that type of hull, which has a lot of drag associated to them. Your engine doesn't weigh all that much, particularly compaired to a the maximum size outboard the boat likely originally carried. Getting the balance right should be done on paper as best as practical, before she's launched, to minimize surprises.
     
  12. Random_user
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    Random_user Junior Member

    Uploaded some pictures with sketches in it. (used paint, have no fancy photoshop skills)

    To start off, the boat should only start sinking (with flat water) when the weight gets above something like 2100+ kg. Very rough measurement, I know, but it is likely more. (with flat water/no waves) This is when the stern, where an outboard would sit, get's raised to the stock back height.

    Origionaly, the boat was made to use outboard engines. Found an older topic on these forums, with "some" boat specs. http://www.boatdesign.net/forums/fi...ding/strommens-vaerksted-14-trifoil-4597.html It states it could handle a modern 40-45 hp engine. I will however rebuild the back end, due to wood condition. So I can build it as strong as I need it to be. I will also reinforce the bottom/hull, and build a frame to keep the sides connected to the bottom/back end. I will also reinforce the front part, so it can take a big beating. (strength before performance)

    I only have the boat (and a trailer) so far. I can get a stern drive, which is good for the intended amount of HP. (stock engine hp would be 165, and 230 Nm of torque... But the engine will be older, so who knows what remains) Origional top speed of this kind of boat would have been somewhere around 66 km/h. If I manage that, or maybe get to 75 km/h, I will be really happy. I want the inboard engine as a hobby project, the looks (maybe add an old crappy outboard engine on the back for fun), the sound, and the idea that the boat can do top speed under most weather conditions. Unknown if this all works out, that's part of the fun. Turning this very stable boat into a rolercoaster, is fine by me. That's where the added strength comes in.

    I imagine I can use the hydraulic trim, to get the best performance out of the sterndrive. Keeping all of that stock would mean it would just work.

    Looking at the images, the only time you are inside the boat, is when you sit in one of the chairs. Front and back are idealy covered. (with the sidenote of engine heat, and possibly no engine lid)

    I did not draw in an engine, and that's up to your imagination. But I intend the engine to go as close to the chairs as possible. It should also be as low as possible. The boat currently has a foam filled floor. (with water in it) The entire floor has to go, because of the water in it. But also because I want to reinforce everything. A new floor will only be created under the chairs, and where your feet would go. In the pointy bit of the front of the boat, there won't be a floor. There will also be no floor in the back/engine bay.

    Please keep in mind that 80% of the fun will be building all of this. If it has been a waist of money, we still would have had the fun together. (also, having your girlfriend/wife/whatever your relationship status interested in a shared technical project, would be worth all the time and money) If the performance and/or handling is crap, it's at least crap we made while having lots of fun.
     

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  13. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Your ideas are simply ill advised at best, because you really haven't the necessary understanding of the dynamics involved. The best thing you might endeavor would be to make the proposed changes to the deck cap, but to just install an outboard. The boat appears to be way too small for an inboard, jack shaft and out drive setup. It's too small for a standard out drive arrangement and you estimations of the weight for this boat are just not even close (by a huge amount). Guessing isn't wise, unless you go no further from shore than you care to swim back to. The math isn't hard, though you do need to understand what formulas and calculations to use and perform. A used outboard can be had cheap and you'll still have lots of work to do, to get this puppy working again.
     
  14. Random_user
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    Random_user Junior Member

    Ill advised at best: I already know that, and there was a reason why I didn't come with pics and drawings right away. I know people are complaining about boat length, but that doesn't mean I like a challenge and an experiment.

    I know it would be way more easy, and possibly cheaper, if I would make the deck cap changes and get a used 90 hp outboard engine.

    The boat indeed LOOKS to small for an inboard setup, and that's the whole point. I bought this boat because of the hull shape and it's length. Getting a larger boat would mean the surprise effect would be gone. (suprise effect if it all works as intended)

    Guessing isn't wise... But it's a start. I've added another attachment, with some measuring. You can hopefully invision why I did measure at these points. If you take these measurements, you could draw a rectangular box. It should al fit somewhat inside a rectangular box of 53 x 133 cm. And I think it's a but to small.

    The boat is 4 meters long. But you can't use that 53 x 133 cm box all the way to the front. So I guestimated 3 meters. So a box of 53 x 133 x 300 cm would be the same as my boat, looking at buoyancy. (and I think it's a bit of an understatement, considering how the boat hull looks) These measurements are without the added height. This box has a displacement of 2114,7 liter, giving me a lifting power/buoyancy of 2114,7 kg. I intend to use half of THAT buoyancy number as the total weight the boat can weigh when finished. The raised back, and partly closed off back (depending on engine heat), would give me some protection against waves flowing over/into my boat.

    You might notice the NL sticker on the back of the boat. It's an "country sticker", meaning NetherLands. Small flat country, with lots of water ways. And in my area, lots of lakes. But not THAT big lakes... Water sports is also big in my area, and our country has a huge population density. With a life vest, I could swim acros any lake the Netherlands has. And there are some HUGE chances someone would pick me up when I would be only a fifth of the way. And I also already mentioned that I do take into account it all might sink. But in that case, we still had lots of fun building/creating.

    Not sure where to add this to my reply, but... I want to use this particular engine because it's short and a V6, giving me more space to put in a driveshaft. Putting the chairs as much in front as possible, would give me about 2 meters of space length wise, to put all the driving gear in. Not sure what an automatic/manual transmission would do to the space, but that's something to consider when I get the donor car. And I am not sure what you mean by "jack shaft". Used youtube as an search engine, and found vids like this one: https://www.youtube.com/watch?v=WARHpBeS_-4 This doesn't look like what I want to use, so I will add another picture. A drive shaft as I intend to use, can be short. In a front wheel drive car I once owned, the smallest of the two driveshafts was like 40 cm. So because of that, I think a driveshaft like in the image, might work.

    *PS: images represent the idea, they are not the exact parts I will use, but represent the type of connection I am considering. No gearbox included in this example.
     

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  15. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    All your description of changes indicate moving weights forward, including the crew. It will get the boat down by the bow, which creates a huge set of problems.
     
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