The purpose of this project is to design and mass-produce kits for a floating tiny house that can sail. It combines high-tech modeling and fabrication and low-tech assembly that can be carried out DIY-style on a riverbank or a beach. This boat is a four-bedroom with a kitchen, a bathroom/sauna, a dining room and a living room. The deck is big enough to throw dance parties. It can be used as a river boat, a canal boat or even a beach house. It's rugged and stable enough to take out on the ocean.

Saturday, October 19, 2019

Engine Mount Design

Deployed — Stowed — Raised for maintenance

Quidnon is rather indifferent to choice of engine: just about any outboard over 25hp will do. But the leading contender right now is Yamaha T50 or T60 (the number is the horsepower rating and the T stands for high-thrust, which is bad for high-speed planing and good for pushing a heavy barge). The engine is installed in an engine well, making it an inboard outboard, if you will.

This arrangement presents a few design challenges:

• Normally outboard engines are hung directly on the transom. When not in use they tilt until they are out of the water. But in an engine well there is no room for the engine to tilt; instead, it has to slide up and down inside the well.

• Normally, control cables for the throttle and the shifter are led forward from the engine, but in an engine well the engine is up against a bulkhead, so control cables have to execute a tight 180º turn as they exit the front of the engine, which is something that cables can’t do.

• Also, engines are usually bolted into place (they come equipped with clamps, but these are far less secure than bolts). But bolting the engine into place when it is in the engine well would require reaching down, and perhaps hanging down, into the well—a very awkward working position—and this would have to be done every time the engine has to come out for maintenance.

• Lastly, what happens when the engine hits a submerged rock or some other obstruction? Does the engine’s lower unit get destroyed, or does it just get banged up a bit while it is the engine mount that fails. And when the engine mount fails, how does the owner repair it on the spot using provided spare parts and without having to haul out the boat?

Quidnon’s engine mount design solves all of these problems.

Backing up a bit, some contraption—be it a shop crane, a hoist or an improvised A-frame—is used to lift it into place, usually with the boat ashore. In exceptional circumstances two or three big, strong men can simply lift it into place with the boat backed up to a floating dock, but this is a risky operation. On Quidnon, which is designed to never need a haul-out, it has to be possible to install and remove the engine with the boat in the water.

This is done using a swinging hoist that is part of the aft deck arch. The hoist is used to lift the engine off a floating dock or a dinghy, lift it up to the deck (a rise of 10 feet/3m or so) swing it toward the engine well, and install it onto the engine mount. This would have to be done repeatedly because outboard engines don’t last that long, with 1200 hours being the typical point at which people give up on trying to make them run reliably and buy a new one.

Someone who motors all the way down the Intracoastal Waterway and back every year, putting around 300 hours on the engine each time, usually needs to replace the engine every four years. A lot depends on the amount of preventive maintenance, and with enough care that number can be doubled to eight years. A complete overhaul can stretch it out to ten. But Quidnon’s expected useful life is at least 30 years, so it will need to be repowered at least three times, and perhaps as many as ten. Luckily, outboard engines don’t cost that much. A Yamaha t50 with 0 hours costs around $10k. Now, $100k is quite a bit of money for most people, even over 30 years.

The amount of preventive maintenance an engine receives is generally a function of how easy it is to get at. Impossibly awkward and cramped engine spaces that are common on sailing yachts with inboard diesels will quite predictably receive less than the optimum amount of attention from their owners; but if the engine can be pulled out and placed on a stand without so much as breaking a sweat, working on it and tinkering with it will be a pleasure and it will receive all the care it needs. Quidnon’s dedicated engine hoist incorporated into the aft deck arch and the design of the engine mount are intended to make working on the engine easy and pleasant.

The engine mount consists of just seven major components:

• Four brackets that are attached to the forward bulkhead in the engine well, two at the top of the well and two at the bottom

• Two rods that run vertically between the two sets of brackets

Upper bracket
Lower bracket

• A slider car which slides up and down on the two rods and incorporates a large, solid piece of hardwood to which the engine is bolted


The brackets and the car are welded up out of A500 steel and subjected to the same galvanization process used for anchors and anchor chains. They consist of tubes, square and rectangular pieces of channel and plates.

The two rods are of stainless steel because they have to be smooth to keep the slider car from binding up and can’t have a surface finish because it would wear through over time. The rods have caps welded to their top ends to keep them from falling through the brackets.

The brackets and the rods are not in direct contact. Instead, neoprene rubber inserts are used to isolate the galvanized steel from the stainless to keep them from galling together through galvanic action, to dampen the vibrations in the rods (which would otherwise ring like a bell at certain engine speeds) and to prevent engine vibrations from being transmitted to the brackets, the bulkhead and from there to the rest of the hull.

The car which slides up and down on the rods and on which the engine hangs uses similar inserts but of different material: Delrin plastic instead of neoprene rubber. This material is slippery and allows the car to slide easily. The inserts are forced into the pipes at each end of the car and slide freely on the rods.

The order of assembly is as follows.

• Hoist the engine aboard
• Bolt the engine onto the car with it hanging above deck
• Lower the engine into the well and skewer it into place by dropping in the two rods

There are a few more minor details:

• When the bottom of the engine hits a rock, the bottom two brackets are the designated points of failure. What fails on them is not the brackets themselves but the nuts that hold them against the bulkhead. The nuts are stripped off the pieces of threaded rod onto which they are threaded. In turn, the pieces of threaded rod is screwed into a socket that is installed from the opposite side of the bulkhead.

Designated point of failure marked in red

The repair procedure then involves lifting out the engine (it is left hanging on a lanyard, which is the usual precaution to losing it), removing the stripped pieces of threaded rod (they have a slot at one end, to accept a screwdriver), screw in new pieces of threaded rod (provided as spares) and reattach the brackets using fresh lock washers and nuts. Then the engine (with the damaged bottom unit replaced or repaired as needed) can be put back into place and into service.

There are a few more elements to the design that are small but critical:

• A small custom 3D-printed part to make it possible for the control cables to face aft and up instead of forward.

• Lanyards for each bracket, so that they don’t go swimming if they are torn off the bulkhead in an underwater collision.

• Clips to keep the rods from falling out in a capsize.

One last element of this design will most likely need to be determined experimentally: how much and of what kind of sound insulation to install inside the engine well to keep the noise level in the aft cabins low enough so that people can sleep soundly with the boat moving under engine.

The engine mount was the last important conceptual part of the design that needed to be completed. Now that it is, the work of putting together detailed construction drawings can begin. It’s taken a long time, but we have finally arrived at that stage. Thank you for your patience!


  1. I'm thrilled to hear that the Quidnon is just about ready for mass production and look forward to the opportunity to purchase full working drawings. There is, of course, the question of what they will actually cost before one can start to assemble here.

    1. I'll provide a spreadsheet for costing them out based on location, local labor rates and choice of materials.

    2. How about for a "Mini Quidnon"? I'm finding that something about half that size or a little less would be preferable for me right now (moneywise& passengerwise). Would the plans be the same, just halved?

  2. Congratulations for reaching this stage and all your hard work. I too am looking forward to purchasing plans and assembling a Quidnon. Can you please confirm the cost? Many thanks.

    1. There will be a spreadsheet for calculating costs based on choice of materials and equipment. They can vary by a factor of 10 depending on what you choose and where in the world you are. For example, comparable quality plywood is 9 times cheaper in Russia than in the US.

  3. In the diagram with the nut that can strip off, why not make the hole that accepts the threaded rod go all the way through, and make the rod a regular hex bolt with the head on the left? The slots may become stripped and the threaded rod may corrode on, which typically means drilling out the bulk of the rod, then drilling at an angle (good luck with an easy out) to make a face for a punch (times two if one wants pure torque to pull the rod---two people hammering to turn the broken rod).

    1. It's actually a lot simpler than that. The anchor and the threaded rod, and the nut, are stainless steel, and will take a really long time to corrode. In general, all that will be needed is installing a fresh threaded rod, washer and nut. If for any reason the threaded rod is stuck inside the anchor, then the anchor will need to be pounded out (it is caulked in) and a new anchor installed. Since all the holes are above the waterline, this won't involve taking on any water. The repair procedure should require a minimum amount of time dangling in a bosun's chair inside the engine well with one's feet in the water.

  4. In the spirit of K.I.S.S why not the traditional mounting in a rear compartment just above the waterline with permanent bulkhead mounting and teardrop openings with latch in place dogs for when it is tilted up? Reuel Parker designs nice ones for his sharpies and scows. The simpler the system the better, especially in a vessel that needs engine assist to claw off a lee shore.

    1. I like Reuel Parker's designs, but this time simpler is definitely not better. First, there is the problem with cavitation with transom-mounted engines in any kind of wave, especially big standing waves at harbor entrenses (which I have encountered a lot). Second, the opportunities to sail during a passage on one of the major rivers (Volga, Ob', Lena, Yenisei) are rather limited, and so there are a few thousand km of motoring. Third, have you tried working on a transom-mounted engine while it's transom-mounted? Not fun, and any little part that gets dropped overboard results in weeks of delay and hundreds of dollars in express shipping expense.

    2. NOT transom mounted.... in a dedicated well. Same removal by halyard to work on it. Props well beneath hull for no cavitation. All this dogma from a guy who once welded up a side mounted, swing up 8 hp outboard which failed miserably on a Pearson 32. Should have built in a Parker style well. James Baldwins ATOM voyages site has a great article on the "inside outboard" and is the same concept. Point well taken on river voyages.... efficiency rules. Fair winds, good tides.

  5. Dmitry,,,
    Lookin good, dude, with plenty of room for different engines & shaft lengths/prop configurations. As per usual, I like the way you think about problems and your usually-well-thought-out ways of solving them. (I still think you’ll come around to using expanding foam, conduits and centering devices to strengthen and make the masts float without losing usability or additional functions.)
    Personally, I don't like the idea of doing any maintenance over water, as the sound of a certain ‘splash’ some forty years ago still resonates in my reptilian brain like it was yesterday. (Given what I’ve found while diving, I can attest that once overboard, items rarely are retrieved, no matter whether from pond, lake, river or ocean.) I like your idea of pulling the engine/mount-car as an assembly to maintain on deck; raised and lowered with a hoist, block and tackle or come-along, with few ‘opportunities’ to invite disaster aboard. Also, in MY Quidnon, everything entering the engine well will be attached by lanyard.
    I’ve heard of alternating layers of bubble-wrap and heavy-duty aluminum foil spray-glued in place works very well, so I might try that lining the well. Or perhaps fitted and glued in place 'fireproof' acoustic ceiling tiles? In addition, I'd try to augment sound isolation w/ a layer of rubber between the engine mounting bracket and the 2 x 14 chunk of wood it’s bolted to, as well as to sandwich a layer between the rod bracket pads and the bulkhead (and backing plates, if any, too).
    Perhaps I missed it, but how is the engine raised and fixed in place while in the well and under way? How does one raise or lower and start the engine quickly if needed? Gravity will lower it to a bottom (lowest) point, but how is it easily raised and kept at the intermediate stowed or upper positions?
    Lastly, have you narrowed down where the initial Quidnon will be built yet, and if the build will be recorded for use as an instructional video(s)? I’d love to see a fleet of Quidnons rafted together at the Annapolis boat show, just to show some of the various iterations a Quidnon might become after the initial build. Thanks Dmitri. Quidnon just seems to get better and better, and it’s only just begun.
    Best to you and your Quidnon progeny,,,locojhon

    1. I too lost an outboard overboard once, directly in front of the Coast Guard station. It's there to this day, I am sure.

      Maintenance over water is a pain. At the very least a tarp should be hung below the engine to catch any falling parts. Transfer pumps get rid of the need to regularly remove the oil drain plug, although it does need to be pulled periodically to clean off the metal flakes that accumulate on its little magnet.

      There will be a hoist to raise and lower the engine, hooked to the bracket car at the bottom. Where it gets attached at the top is to be determined. It could be a simple crab winch with a handle.

      Where the first Quidnon is going to be built is still a mystery to me. Certainly, having someone film the entire process and put the result on Youtube is an excellent idea.

    2. 2lb closed cell spray foam at a 50mm (2") acts as a vapor barrier, is air tight, light weight, has an R value of 10-12, wont soak up water, ever, will not rot and it floats, sounds like a boat builders dream. Glad I'm not the only one seeing the marine advantage for it's use. And anything it's sprayed on, wood, metal, glass, plastic, moves the 'dew point' to the outside of whatever it is sprayed on, neat feature.

  6. Hi Dmitry! A few years ago I acquired a customized MacGregor 25, with an engine setup very similar to what you describe, except necessarily transom-mounted as a retrofit. Just let me know if you'd like photos of this design, for an "in the real" reference, though it looks like you've got it all figured out. Anyways, just thought it serendipitous.

    And congratulations on this milestone! Your engineering and dedication to this project is inspiring.

    1. I am familiar with McGregors. They are about the only shoal draft sailboat designs commercially available. The two problems with transom-mounted outboards are cavitation and the exposed location. Also, transom-mounted outboards are thief magnets.

    2. I just thought it interesting that the previous owner of this MacGregor (unknown to me) went to such lengths to completely re-work the transom for a similar "elevator and car" engine mount, including a dual-rudder system and mainsheet traveler integrated into the top of the engine mount framework/stern rail. It will be useful for engine maintenance and removal, at least.

      My sailing knowledge is still very limited, but I've learned a lot in the past few years attempting to keep up with the Quidnon's design. The MacGregor is intended to be my starter boat, to learn on the Chesapeake and ICW. It was cheap and came with new sails and some nice hardware. Shoal draft/ swing keel will come in handy in the ICW.

      I'm hoping my next boat will be a Quidnon *grin*

    3. McGregor 25 is a perfectly good choice for a commercially built shoal draft sailboat. I looked at their designs very carefully at one point. The idea of an aft deck arch with a sheet traveler mounted on top of it is a brilliant idea; I wonder where the boat's previous owner got it.

  7. Cool, happy to see the progress on this project.

    mech design comments:

    No bushings? Delrin is okay but it isn't the best bearing material, and also for marine application, i wonder about its water absorption, UV resistance, etc. (this is a reflexive comment, i was a mechanical engineer earlier in my career, and boss was constantly pushing Delrin on me, or worse, having the shop substitute it without asking... it's worth a little time looking at better plastics trust me).

    With bearings in particular, modern polymer bushings are well worth the buck or two you pay (i.e. less likely to bind / require gorilla service / end up deformed). Adding them is a low design impact.

    The other thing to watch for in two-rail systems is shaft misalignment and overconstraint. (seems too stupid to mention, but again, been there enough times). I would design the car to accomodate some misalignment and overconstraint by, perhaps, mounting the bearings in tolerance rings (if suitable stiffness is available in your size). In any case, save some working room in the design in case you end up needing to do these things later, and pick material sizes (diameters/fits) that are common for bearings.

    (The other trick for overconstraint is hole-and-slot rather than two-parallel-axis-holes, but that leads to the potential problem of not enough interference rather than too much).

    For the intentional-break part, which is quite clever, I've seen shear pins used for that. I think that lets you control the level of force better - maybe you care, maybe not. On a related note... once the bottom support breaks, you have this long lever arm that will want to rip out the top one too, no?

    Anyway, good stuff and good luck!

  8. Hey Dimitry. Looking good! Have been following the Quidnon build for a while. Re your engine mount design, I can't work out how you will easily reach the bottom of the leg when its time to change out gear oil or tinker with the prop?? Cheers


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