Short Shaft Outboard Thoughts

By Captain Larry Jarboe

Yesterday, the sun came out and the wind died down enough to try the 2 cycle 2.5 Mercury short shaft outboard (an old rebranded Tohatsu) that I picked up for a hundred bucks. It now has a new carb and an aluminum prop. Essentially, with some minor changes, it is souped up to become the 3.3 hp Merc motor that is still marketed around the world where 2 cycle outboards are not discriminated against.

Notice, I mounted it on my vessel using the smartly designed W700 transom bracket that allows for long or short shaft outboards. Also, I put a concrete block in the bow to help balance the load.

Turning the bracket upside down for the short shaft also means the motor is another 6 inches aft. This is necessary to tighten the motor clamp bolts which are down between the two hulls.

That extra distance aft requires a level of dexterity to reach. After some personally challenging contortions to face astern, I started the motor. Then there were equally challenging physical maneuvers to spin around while underway. That nice lightweight motor (28 lbs.) has no neutral, only forward.

The motor does turn up sufficient torque to make the boat plane smoothly. But, the lowered transom digs into the water during the transition thus throwing water into the face of the engine. That is not good, at all.

Putt putting around was fine. Planing the W700 with the short shaft motor is presently unacceptable. Maybe, a joystick option or more weight in the bow might alleviate the lowered transom grabbing water. Or, a spray shield installed in front of and under the transom bracket. I, personally, want a daily driver with minimal maintenance issues. And, easier reach to start and service the motor.

Yoav, has consistently been recommending the log shaft outboards. I thoroughly concur. The short shaft Mercury would make a good display engine for sales but it runs so well I am putting it up for sale and looking for a 3 hp long shaft as the most ideal power source for my application.

Also, Yoav’s recommendation for Tohatsu small outboards is right on. The Tohatsu engines are probably the most affordable and dependable small outboards on the marine market, today. Mercury, Nissan, and Mariner use the Tohatsu power head and drive that they rebrand with their own logos. If you remember to 1) always use non-ethanol fuel and 2) after each use, flush with freshwater, while 3) running the carburetor dry, and 4) store upright, your engine will last a lifetime.

However, until my short shaft outboard sells, a transom well will not be too difficult to construct. And, some yoga exercises prior to getting underway might not be too terrible. Easier than a Zumba class…

Larry J.

Read much more and see pictures and video in the comments below ⇓

Wavewalk 700 bow with DIY motor mount for an electric trolling motor and a cinder block  …
Old 15″ shaft Mercury outboard motor attached to W700 HD motor mount that’s mounted on upside-down

Read much more and see pictures and video in the comments below ⇓

More fishing adventures and outfitting tips with Capn’ Larry »

14 thoughts on “Short Shaft Outboard Thoughts”

  1. Thanks Larry,

    On this website, we tell people that we strongly recommend 20″ long shaft outboard motors and we do not recommend 15″ short shaft ones because some folks who have managed to outfit their Wavewalk with a short shaft motor (e.g. Rox, with a DIY mount and without a cinder block 🙂 …) enjoy driving it despite the fact that even when such setup is a full success, it’s still not a solution that’s as good as using a 20″ long shaft.
    Nothing beats perfection, in this case, but this is my opinion, and some people would say that using an old 15″ shaft outboard that they found in their backyard saved them a considerable amount of money that they would have had to spend on a 20″ motor.
    We could have said “Do not use a 15″ short shaft motor under any condition”, but saying so would have not reflected the possibility that someone may succeed in motorizing their Wavewalk with a 15″ shaft motor, and that such a sub-optimal solution would be good enough for them.

    Bottom line: Using a 15″ shaft motor means less safety, less convenience, less comfort, and more problems – even if you succeed.

    As for why we recommend the Tohatsu (and Mercury, which is the same), it’s mainly because it features a gear shift lever in the front, facing the driver, rather than on the side. This makes it easier for the driver to access it while they sit facing forward. Easy access the the motor and its controls is important.


  2. Yoav,

    I spent the morning modifying the transom bracket. Will post pics later. The boat runs so much better and the motor stays dry. If i jump in the W700 facing the short shaft motor to pull start, it only takes one 180 degree butt swivel to face forward to get underway. Still, find a small outboard with a 20″ shaft for optimum performance.

    Still looking…

    Larry J.

  3. Hi Larry,

    Learning curve…
    It’s doable, and it’s not that bad if you’re not into high speed and/or high performance motorizing.
    I agree with your decision to get a 20″ shaft motor, because you’d obviously want to have fun driving your W700.
    My gut feeling is that in your case 3.5 would be the minimum HP, and after some time you’d be looking to upgrade 😀


  4. Larry, if you want to play around and make that short shaft work for you, research some of the motorized archives for a transom mount that I build for mine. It rests on the back skirt of the 500 so no chance of water coming up, and brings the CG of boat farther forward so not as much squat in the transom on take off. I’m not sure if the 700 is deeper than the 500 so that could hider you if it is. The short shaft will not turn the boat as well as a long shaft though since prop wash hits the pontoons on sharper turns. Works for me though.

  5. Thanks Kevin,

    Great design indeed:

    DIY motor mount for Wavewalk 500 fishing kayak


    A similar concept should work even better with the W700 than it does with the W500 –
    As seen in the image below, you can insert a 6″ wide x 4.5″ high x 3/4″ thick board in the space that’s between the Saddle’s rear end and the rear wall of the cockpit, namely on top of the saddle bracket.
    Tip: Round the board’s corners before you start hammering it into place.

    The top part of this rectangular board is tucked under the gunwale, which adds support. Since the picture below doesn’t show this detail because of the wood’s light color, we added the red lines to help the reader visualize the location of that hidden part.
    Fixing this board in its place can be done by means of 2 or 4 horizontal bolts that would go through it and through the cockpit’s rear wall.
    Such stout vertical structure may serve either as a foundation for a mounting plate for an outboard gas motor, or as a mounting plate for an electric trolling motor.

    Support for W700 motor mount

    Inserting two vertical boards such as this and fixing them in place with bolts would create an even wider support for a mounting plate.

    My two cents, and just keep in mind that in any case, a 20″ shaft outboard works well, and a 15″ shaft cannot work as well.


  6. Kevin and Yoav,

    I built an insert out of Azec plastic board and stainless torx head self tapping screws. I pre-drill the holes for accuracy and avoidance of splitting the material. Two 1/2 holes were drilled in the back of the transom to pull any water out that might collect.

    This keeps the short shaft motor down 5 inches from the long shaft transom position. The prop clears the hulls when turning. Water does not splash up onto the front cowling of the motor. Yes, you must be more agile to reach the extra distance aft.

    My concern is to find the best combination of weight vs. horsepower to attain about 10 knots cruising speed in the W700.

    I spent a lifetime hoisting heavy timbers into lumber packs during the day and toting huge bass amps and PA systems to gigs at night. My back has been there, done that.

    40 lbs. is my self imposed limitation on outboard motor weight because I remove and running rinse my small engines after every use.

    Presently looking for a low priced 38 lb. long shaft 2 cycle Tohatsu model with the neutral position. But, the short shaft Merc is not up for sale, yet.

    Take Yoav’s advice and avoid taking the longer course with the short shaft.

    My more than 2 cents worth for the day…

    Larry J.

    W700 HD transom motor mount modified for a 15

    W700 HD transom motor mount modified for a 15

  7. Hi Larry,

    Looks pretty good! 🙂
    The boat is a little stern-heavy for my liking, and although sitting with he left arm stretched behind your back is a common driving position in small boats and skiffs, it’s not exactly an ergonomic position, especially for long drives.
    A U-jointed (articulated) tiller extension can solve both these problems – The Ironwood Pacific company offers its Helmsmate U-jointed, adjustable-length tiller extension for $56 + S&H.
    Big bonus: Using this accessory doesn’t only make driving easier and more comfortable, namely from the middle of the boat and facing forward, it also enables driving standing, and that’s a blast, and I’d go as far as saying a must for a W700 owner 😀

    As much as driving with a U-jointed tiller extension improves things considerably, it is not as perfect as driving with a Joystick steering system, but the latter costs five times more…


  8. Yoav,

    The final incarnation of the W700 includes a 12 V. battery and my Minnkota Riptide 45 lb. thrust electric trolling motor in the bow. This balances out the rig and provides the main source of prowler power.

    The outboard motor is mostly a means to reach distant unyakked non-combustion zones were there is little fishing pressure. In a non-combustion zone, the I/C motor must be tilted up or a $500 fine may be imposed by the FWC. I know someone who got nailed for half a grand which is a miserable way to lose that kind of money. Electric motorized vessels are welcome to prowl those areas.

    Most of my standing will be behind the bow mounted Minnkota slowly searching the edge of channels. Any speed over a couple knots means that I set my butt down and keep my hand close to the throttle. Going fast, for me, is not about having fun but getting there before it is time to go home.

    I grew up with a 1965 Evinrude 5 hp Angler outboard that was purchased new. That simple little workhorse pushed a wide variety of vessels: a homemade pram, a wooden crab boat, a 17′ O’Day sailboat, a 12′ Sears skiff, and a 17′ Grumman canoe. She even brought a 25′ diesel powered KenCraft home twice from the Atlantic. The tiller in my left hand is as natural as shifting a three on the tree for country boys over 60.

    Bottom line is to find a long shaft outboard over 3 horsepower as Yoav has recommended.

    Larry J.

  9. Yoav,

    How many other kayaks or portable boats are capable of wallowing in a 3-4 foot sea and making it back to shore?

    The fact that you did not have to get rescued by the Coast Guard says that there must be saltwater in your veins despite your inland heritage.

    I probably won’t be dragging a timber hoist offshore or into the Everglades. If I catch a really big fish, my next door neighbor has a forklift.

    But, I might be wanting a bigger boat…

    Larry J.

  10. The wind picked up on my way back (to the north), and at first I just let the waves deflect me from my course eastwards, towards the Cape Cod canal.
    The alternative to this course of (in)action would have been to go straight North (slightly Northwest, actually), and get hit by those waves on my broadside, and risking them going over the gunwale and getting some water to spill into the boat… Well, hmm…small detail I forgot to mention: I had not brought a real bilge pump on board on that trip! 😮 All I had with me was a tiny pump that would have not sufficed in such case.
    After some time, I got used to being tossed by the waves, and I also realized hat I was heading too far East, so I decided to correct my course and drive directly to Horseneck Beach, while reacting to each wave individually by leaning to the right (!) and making sure it would pass under me without breaking on top of me… That wasn’t easy at first, and I must confess that images of me drifting in the water and getting picked up somewhere near Cape Cod went through my mind… Such trick would have been impossible with another kayak, of course, due to balance issues. I think other small boats would have not offered me enough ‘grip’ and/or lateral stability to perform this maneuver over and over, and sooner or later I would have lost balance and fallen overboard.
    The joystick had become very helpful at this point, as it let me “become one” with the boat, and stay the course albeit the frequent changes in direction.
    After some time I got used to this weird and risky dance, and the wind dropped. The last part of the trip was fun, especially as I got close enough to shore and I was no longer afraid that I’d be lost at sea… – As my heartbeat went down and back to normal, I increased the motor’s RPM and started driving for fun, including standing up, as seen in the video.

    The sad part of this saga was that got sunburned big time, but that’s another story…

    If I ever write my memoirs, I’d call the book “The Diary of a Goof” 😀

  11. No need to “short shaft” yourself. There is nothing goofy about surviving at sea. Except for those sunburned knees.

    Wavewalk memories…

    Larry J.

  12. Here is something interesting that I just found on the Weather Channel:

    “Small Craft Advisory for Boston Harbor
    Issuing Office: Boston
    Source: National.Weather.Service
    1:02pm EST, Thu Nov 10

    I didn’t know such online SMALL CRAFT ADVISORIES existed, and in hindsight, maybe I should have looked for such info before going on that offshore trip.
    If 10 to 20 knots with gusts up to 30 knots are conditions deemed hazardous for small craft navigating Boston Harbor, a Wavewalk navigator has no business being in the open sea on such a day.

    Bottom line: Check for local SMALL CRAFT ADVISORY for your area before planning your trip in the salt, or the Great Lakes.


  13. A client sent us these pictures of a DIY setup for a short (15″) shaft outboard motor mount.
    This is a solution that presents another set of problems related to the fact that the propeller is prevented form rotating at the optimal depth recommended by outboard motor manufacturers as well as Wavewalk:

    Wavewalk 700 skiff outfitted with DIY motor mount for short shaft 3.5 HP outboard motor



    Again, let’s not forget that motorizing solutions for the W700 that are based on short-shaft outboard motors are sub optimal, namely that they deliver a level of performance that’s not on par to solutions based on a long (20″) propeller shaft.

    In the case of this DIY motor mount solution, the client added an inch to the height of the discontinued short-shaft Wavewalk motor mount, and this allows them to attach this short shaft motor closer to the cockpit, instead of several inches behind it, as you would have done otherwise.

    However, this solution makes the propeller draft an inch less, and consequently, the stream it generates is likely to hit the bottom of the hulls when its directed sideways, that is when you’re making a turn.
    That stream is powerful, especially at a high RPM, and the fact that its upper part hits the hulls instead of keeping going straight may make turning harder for you, and possibly even generate unwanted vibrations, as the hulls deflects some of the water back into the propeller stream, or to the propeller itself, depending on the angle of deflection.
    This may not be a major issue when you drive at a slow speed, but the faster you go, the more it’s likely to be felt.

    In this case, the numbers speak for themselves:
    The total height of the W700 from the bottom of its hulls to the top of the cockpit’s coaming is 17″.
    Outboard manufacturers recommend that the anti-ventilation plate on top of the propeller be immersed 1.5″ to 2″ below the lowest point in the hull. Since the motor is mounted away from the hulls’ rear tips, which is the boat’s lowest point, we can assume that a 2″ difference works better.
    This brings us to 19″ (17 + 2), which cannot be achieved with a short propeller shaft, even if it’s slightly longer than the 15″ stated by its manufacturer.


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