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Thread: Hudson Bay transom heights and compatible outboard shaft lengths?

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    Member BluNosDav's Avatar
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    Question Hudson Bay transom heights and compatible outboard shaft lengths?

    Scott (Abitibi&Co) Hudson Bay canoes appear to come with two different transom heights. Some HB transoms run flat / straight across from corner-to-corner, while others have a pronounced step-down of a few inches. The web-site lists the HB's "stern height" as 22.5", but, doesn't mention what the actual transom height(s) is (are)?

    Most outboard motor shaft lengths are listed as: Short = 15" / Long = 20" / XL = 25".
    Which length outboards would be appropriate for HB's with flat VS step-down transoms?

    Thanx, Dave.
    "Luckily, enforcement reads these forums, and likely will peruse this one...Especially after a link of it is forwarded to them....." - AlaskaHippie.

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    Dave I ran a Short Shaft Yamaha 8 HP & a 20 HP Tohatsu on my Scott HB I used to own. But dont know what it measured for height, thought it had a little drop from the splash well height.

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    Dave,
    Good question!

    I have the HB with high transom and had a previous one with low transom.
    I'm running a 20" shaft motor on the high transom and it works well.....but....

    For years I ran a 19' Grumman with 15" shaft on a transom that I raised 4" as on a jacklift and it worked well without cavitation.

    I'm guessing that the stern design of the HB will allow use of a short shaft motor of moderate power on a high transom boat but I haven't proven that yet. I recently got a nice 8HP short shaft motor from KK and intend to try it on my high transom HB this summer.....

    The raising of the motor 5" prevents a lot of prop strikes.

    Sorry i don't have a definitive answer at this time but my buddy has an old low transom with a jacklift and I'll look at it to see how high the motor sits when lift is down.

    Outboards >20hp are not as common in new models.

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    HB transom.jpgHB transom2.jpg

    Here are views of my HB transom with the winter cover peeled back.
    The lift at its lowest setting would be similar to a transom without the indent, which is three inches deep. The top of the lift as it sits here is 19 inches above the bottom of the boat not including the center keel, which is an inch deep.
    I run the HB exclusively with this lift as is or two or three inches higher depending on the water conditions I expect to see using either a 9.8 Tohatsu or 20 Honda both SS, but the bigger motor has a bit longer lower unit. It works very well raised like this probably because of the shape of the transom.
    RandyS

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    Thanks Randy!

    Your experience goes a long way in my theory that we can run our SS motors on high transoms.

    I left an incomplete sentence above.......Short Shaft motors above 20hp are not as common as they once were on showroom floors.

  6. #6

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    HB canoes with there wine stem transom, bow is slightly trimmed up which makes motor run deeper. When I ran Verns 8 hp Yamaha with a lift I could
    run motor raised more without cavitation. Semi displacement hull always had a lot of stern water. Loved the HB stern for following seas.

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    If this weather keeps up, we can be on the lakes early this year.

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    Some owners / operators report a lot of splashing when running a Hudson Bay at speed.
    Is this a serious problem or just a nuisance?

    Scott (Abitibi&Co) recommends a 20hp outboard for the Hudson Bay.
    What speed is possible with a 20hp motor?

    Would a 25hp motor be too powerful?
    "Luckily, enforcement reads these forums, and likely will peruse this one...Especially after a link of it is forwarded to them....." - AlaskaHippie.

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    In the old Scott HB thread I started several years ago posted speeds with a 20 HP in a HB around 17 mph as I recall.

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    17mph would be about top speed with a very light load.

    Spray rails knock down that high speed wet ride.

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    I agree that spray rails are effective and needed.
    You will not be disappointed with the speed from a 20 even with a load, though I have not measured it. In deep, calm water.
    RandyS

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    Would a short-shaft 25hp push a lightly loaded HB faster?
    Or propel a heavily loaded HB to the same speed?
    Or are there other limitations that come into play above 17mph?
    "Luckily, enforcement reads these forums, and likely will peruse this one...Especially after a link of it is forwarded to them....." - AlaskaHippie.

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    BND

    The weight of the 25HP may be a consideration.

    To over-power a semi-displacement hull can be counterproductive. If power and speed becomes excessive, the canoe will be a planing hull and it's not designed for that.......when planing, the canoe can be squirrely.

    For top fuel efficiency when loaded, I watch for excessive bow wake as an indication of too much power.

    17mph is quite fast in a canoe and I don't suggest it for most. The object of a canoe type hull is power efficiency whether it be human powered or fuel powered.

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    Thanx Vern!

    All of my canoes have been human-powered, so far, even a square-stern 17' Old Town Sport in which I used oars instead of paddles. I've also owned & operated multiple power-boats, and researched quite a bit about various hull shapes: full-displacement, semi-displacement, planing, catamarans, etc. Which makes me very curious about how canoes behave under power. I've always thought of canoes (like sailboats) as displacement hulls. But, after reading about many freighter canoes being propelled to speeds in the high-teens (mph/kts), I realize that they can't be strictly full-displacement. You refer to the HB as semi-displacement. But, the "hull-speed" of a 21' boat is: 4.58kts or 5.27mph, and at 17 mph, your HB was moving at 3.23 times it's hull-speed, which already puts it into the realm of a "planing" watercraft. Yet, there is some gray area between each class of vessel, so, the technical definitions must give way to the practical applications.

    So, if your lightly loaded HB ran at 17mph with a 20hp motor. What would you estimate the same canoe could run when loaded to the maximum factory rated load? Would it be just a little less (15mph?) because the HB hull is so efficient? Or significantly less (9mph?) because the hull would be so much deeper in the water? And while a bigger motor (25hp) could definitely push a lightly loaded canoe into squirrely territory, maybe it might also be able to move the heavily-loaded canoe just a little bit faster (12mph?) without making an excessive bow wave?

    Interesting stuff . . . . Thanx to everyone who has replied to my question!

    P.S. - the new Yamaha EFI outboards share the same power-heads between the 25hp & 20hp models, so, they weigh the same: 126 pounds.
    "Luckily, enforcement reads these forums, and likely will peruse this one...Especially after a link of it is forwarded to them....." - AlaskaHippie.

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    BND,

    Some of my remarks are experience and some are pure speculation from previous experience with smaller canoes.

    A fully loaded [2000 lbs] HB I'd guess to move at your estimate of 9mph or so with a 20hp. I doubt if I'll ever get my HB
    loaded to that capacity. For fuel efficiency, I'd guess we have to back off the throttle quite a lot. With an 800 pound load,
    I run my 20HP at about 3500-4000 rpm for 10mph but I haven't calculated fuel burn.

    I look at canoe hulls as semi-displacement when moderately loaded and a displacement hull when heavily loaded.......no science behind it....
    just my thoughts.

    Back in my early days, I had extensive experience with 15-17' canoes and 3.5 HP motors. We moved some tremendous loads sometimes with two canoe lashed together as a catamaran. But our rivers weren't nearly as fast as these Alaska Rivers.

    I recently found a very old 35MM slide from my early days that illustrates this very well. I haven't kept up with pic posting lately.....maybe KK can post it for me.

    That's good to hear on the new Yamahas. Now if someone would come out with twin cylinder 2hp-5hp outboards.

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    Curious what the best/most versatile transom height would be: get the lower transom and add a spacer oif needed, or get the high and just run long shafts
    Fighting gravity is never cheap.

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