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Short Shaft or Long Shaft outboard for Y-Stern

Discussion in 'Open Forum' started by forestcomber, Nov 9, 2010.

  1. forestcomber

    forestcomber Curious about Wooden Canoes

    Hi all,

    For a 16-foot y-stern canoe would you use most often a short shaft 15" or long shaft 20" outboard motor.

    Anyone with experience with this ?

    Thank-you !
     
  2. Todd Bradshaw

    Todd Bradshaw Sailmaker

    I don't think I've ever seen a canoe in that size range that needed more than a short-shaft motor. You generally have a choice between 15" (short-shaft)and 20" (long shaft) from most of the manufacturers. This is partially because a whole bunch of the well known outboard companies buy the same Tohatsu motors for their small models and just change the color and stick their own label on them. Unless your canoe has a transom height well over 15", the short shaft is most likely the way to go.
     
  3. OP
    OP
    forestcomber

    forestcomber Curious about Wooden Canoes

    Thank-you for your reply. I was hoping that the short-shaft would work. I use a Honda 2hp short on my 16' symmetrical canoe. It is mounted on the side at gunwale level just behind the back seat. The setup makes things a little unstable and will roll the canoe (oops) if there is no weight in it. I love paddling but I'm also loving the motor. I'm sold on they y-stern design and I assume it will be much more stable than side mounting.

    In the photo at the link below a long-shaft is used but it is also a 20' canoe.

    http://www.islandfallscanoe.com/inventory-popup.asp?item=15463&pic=52489

    The attached image capture from the Honda 2hp manual says that the motor transom height on the short-shaft is 16.5" and the anti-ventilation plate should be between 0 and 2" below the bottom of the boat. Hmmm.. so this means that a y-stern canoe with a transom height of 15" should fit this motor, as you suggest ?

    Cool, I like it. I think I know what I am looking for now, thank-you !
     

    Attached Files:

  4. Jeffrey Ray

    Jeffrey Ray Curious about Wooden Canoes

    I use a short shaft Susuki 2.5 4 stoke on my 20 foot Y stern. With the canoe empty the prop is out of the water, but with someone in the canoe it is in the water plenty deep, but does not go below the keel. Works great in shallow water.
     
  5. Alm

    Alm Curious about Wooden Canoes

    ... And if Y-stern is 18"?

    Sorry for rekindling the old topic - canoe forums are scattered all around. I am pondering over new Algonquin Prospector Y-stern by Holy Cow, and as you can see, all their Y-sterns are 18".

    Look at the photos: in Goliath the "Y" consists of a deep "I" under the "V", which means that actual U- transom is about 13-15". But in Prospector the transom goes all the way to the bottom, minus 1" or so for the keel, so it has 17" transom.

    I tend to trust Todd's opinion (his knowledge of the subject is enormous), but 17" seems almost at the limit of 16.5" Honda or Suzuki (cavitation plate is 0.5" above the transom bottom, while it should be flush or 1.5" BELOW the transom bottom). And... with all my respect, Todd :) - not all 2hp motors are re-branded Tohatsu. 2.5 hp Suzuki is lighter than Tohatsu, less metal, and available ONLY with a short shaft - too bad, because it looks like a good motor.
     
  6. Todd Bradshaw

    Todd Bradshaw Sailmaker

    Uhh....I don't believe I ever said that all of the small motors are Tohatsus, just that a bunch of them are (Mercury, Mariner, Nissan and others have all at one time or another recently sold re-badged Tohatsus for their little ones). I guess it depends on your view of how many it takes to constitute a bunch. In any case, that 2.5 Suzuki looks like a nice little motor. We had a 4hp Suzuki on our Trimaran and it was quite dependable.

    As to the proper motor for that particular canoe, I think the first logical thing to do would be to contact the boatbuilder and since they have most likely tried the boat, I'd ask them what size and/or brand of motor they used and found to work well. It makes a lot more sense than trolling the internet getting opinions from strangers who have never been in or even seen one of those canoes (including me).

    Opinions seem to be all over the place with respect to the exact best location of the plate with respect to the bottom of the transom. A few I saw suggested slightly above the transom's bottom, most were about even with it and some were slightly below it. I suspect the more important question would be the plate's position with respect to the surface of the water, as it might make a bigger difference than the exact transom bottom level - especially on a canoe, where the rather small transom has far less drag and creates less disruption of the water than a typical, full-width powerboat transom. The plate's job is to prevent the prop from sucking air down from above the water's surface and ventillating the prop (causing it to lose power). That's why I think the relationship between the plate (and the prop below it) and the water's surface is probably more critical than it's relationship to the bottom of a small canoe transom.

    If our canoe has a 17" transom and draws 3"-4", which is typical for most canoes but depends on the load, then we would have 13"-14" of transom sticking above the water level at displacement speeds. A 15" shaft would put the plate 1"-2" below the surface, which most folks seem to think is about right.

    However, if your canoe gets up on a plane, the transom rides higher and the plate does as well. Some of the motorboat guys say that the plate should be at the surface when the boat is up on a plane, but I'm not much of a motorboater, so I don't know whether that's right or not. I've only truly planed reecreational-sized canoes with motors (oversized) a couple times and I found it to be rather scary and backed the motors down to a sort of semi-planing speed.

    Anyway, that's my take on the subject and I wouldn't really want to have to draw any conclusions from it at this point. If I was interested in the boat, I doubt there is a better source of information on what has been tried and works well than the builder.
     
  7. Dan Lindberg

    Dan Lindberg Ex Wood Hoarder

    Wow, 2 discussions about the same thing, at the same time, in 2 different places. :)

    If you are going to be planing your canoe/boat, you want the cavitation place just below the surface of the water (coming off the bottom of the boat).

    With this said, being that this is a canoe and you're looking at VERY small motors, I suspect it doesn't matter much where you place it, as long as the water pickup is still in the water. :)

    Dan
     
  8. Alm

    Alm Curious about Wooden Canoes

    Thanks!

    Todd - thanks a bunch ;) ... Didn't mean any offense, hopefully none was taken...

    Of course I've contacted the maker of that particular "cow", no response yet, it's a weekend. Numbers and ratios are better discussed "on the paper" or on the screen for that matter, rather than over the phone. Besides, it's not like I'm buying a boat now in January anyway..

    One thing that crossed my mind with that particular 18" Y-stern and 16.5" shaft is that stern is slanted (look at the photos of cherry-colored hulls in the link above). This places the propeller farther from the stern, and common sense tells me that this TAD loosens strict recommendations for location of the cavitation relatively to the stern bottom. The actual wooden plate for motor is plumb, which is good, but the boat transom is slanted.

    Plate depth under water is still important parameter - thanks for noting this. The boat will be loaded very lightly, and draft could be 2.0-2.5", but this is in the middle of the boat. Draft at the stern? Don't know. The boat builder might know. I can't see if this stern is upswept - and this affects how much of the transom will be out in the air. But then again with all the load (i.e. me and motor) concentrated at stern it will draw deeper at transom. Heck, nothing stops me from slicing an inch or two off the transom top (making a small U-cut in the transom) and lowering the motor deeper... They do this on some power boats...
     
    Last edited: Jan 22, 2011

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