Sharpie Schooner 42 with an outboard motor

Discussion in 'Boat Design' started by valery gaulin, Apr 6, 2018.

  1. gonzo
    Joined: Aug 2002
    Posts: 15,233
    Likes: 943, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    60 HP is grossly overpowered for that boar. The exhaust will be a problem and will probably kill everyone in the boat unless it it vented to the outside of the hull, which can't be done easily on an outboard (most of it comes out of the propeller). Also, hoping the cockpit bottom is high enough won't keep it from flooding; you need to design it properly. Finally, the center drain in the cockpit means that when you are heeling over it will have a foot of water or more on the leeward side. You can't drain it overboard either, since the outboard edge will be below the waterline
     
  2. M&M Ovenden
    Joined: Jan 2006
    Posts: 360
    Likes: 77, Points: 38, Legacy Rep: 527
    Location: Ottawa

    M&M Ovenden Senior Member

    Valery,
    We are probably about 1.5 hours from you. You should come by for a visit sometime to talk boat building. You might see something that gives you some ideas.
    Mark
     
  3. valery gaulin
    Joined: Jan 2017
    Posts: 177
    Likes: 4, Points: 18, Legacy Rep: 7
    Location: Montréal

    valery gaulin Senior Member

    @M&M Ovenden

    Yes this is an awsome opportunity. I will for sure accept this invitation! Did not realize did you are so close. I actually sail right now on Lac Des Deux Montangnes on my 1973 Grampian 26. You are just down the river!!! LOL

    I will try to contact you by email.

    Thank you for the offer.
     
  4. philSweet
    Joined: May 2008
    Posts: 2,429
    Likes: 250, Points: 83, Legacy Rep: 1082
    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    As Angelique pointed out in the Presto, a jackplate arrangement has a lot going for it. These are not trivial to build for a 9.9, let alone for a 60 with more extensive rigging. The high thrust OB makers would be well advised to offer a factory jacking option and publish rigging guidance and parts support for jackplate configurations allowing up to 30 inches of lift before having to disconnect stuff. It's not surprising it took the Presto folks a few tries to market one they are happy with. A factory exhaust bypass kit would be another nice-to-have.
     
    Angélique likes this.
  5. valery gaulin
    Joined: Jan 2017
    Posts: 177
    Likes: 4, Points: 18, Legacy Rep: 7
    Location: Montréal

    valery gaulin Senior Member

    @Angélique
    Why tilting outboard instead of vertical sliding bracket? My impression is that it will be a lot easier to install and use the power tilting option that come with the outboard. Just press a button and it is in the raise position, just press a button and it is in the down position. On my 1973 Grampian 26 it as a cut out at the transom for an outboard and this exactly what I have! It is a Suzuki 9.9hp with power tilt, electric start, fuel injected, 20 inch shaft. I love it so much!!! When alone, which is most of the time, just set your sail and press a button and the outboard is tilted up! When it is time to take the sail down, just press a button and it is tilted down, press another button and it start!!!

    Also the vertical sliding bracket would make the motor way too high in the cockpit, it will not look good! Also the center of mass of the outboard will raise by about 30-35 inch. With a 250lb outboard not sure it is the best!

    For the scarce aft buoyancy at the cockpit well that is something to think about!!! Let me get back to you on that one...
     
  6. chinaseapirate

    chinaseapirate Previous Member

    About how fast do you want to motor cruise at? The full 8 knots$$$$$$? 9 knots$$$$$$$$$$$$$? 7 knots$$$? or is plain old 5 knots$ good enough? I can't fill the number for $ but they are all represented of horsepower required. My guess is you are at 9 1/2 tons with 35 ft waterline and each $ = 2 1/2 ship horses...
     
  7. fredrosse
    Joined: Jan 2005
    Posts: 399
    Likes: 55, Points: 38, Legacy Rep: 56
    Location: Philadelphia PA

    fredrosse USACE Steam

    From Gonzo: "60 HP is grossly overpowered for that boar. "

    I second that statement, to reach displacement speeds about 1 - 1/2 horsepower per tonne of displacement is plenty. My 20 foot Sharpie hull 2300 pounds loaded displacement cannot use all the power from a 2-1/2 HP Suzuki.
     
  8. Angélique
    Joined: Feb 2009
    Posts: 3,003
    Likes: 330, Points: 83, Legacy Rep: 1632
    Location: Belgium ⇄ The Netherlands

    Angélique aka Angel (only by name)

    I like the 2½ hp Suzukis with no reverse gear. Instead they have 360° steering, so at 180° you'll reverse the boat. Do you have one of those Fred ?
     
    Last edited: Apr 8, 2018
  9. fredrosse
    Joined: Jan 2005
    Posts: 399
    Likes: 55, Points: 38, Legacy Rep: 56
    Location: Philadelphia PA

    fredrosse USACE Steam

    Yes, 2.5 HP ultra low emissions four stroke. Forward and neutral only, 360 degree for turning. Works very well, I wish it came with a lower gear ratio and bigger prop to push around my one ton steamer, but overall very satisfactory as an auxiliary/emergency power unit when I am on the big river.
     
  10. Angélique
    Joined: Feb 2009
    Posts: 3,003
    Likes: 330, Points: 83, Legacy Rep: 1632
    Location: Belgium ⇄ The Netherlands

    Angélique aka Angel (only by name)

    It's a bit of technical nitpicking Fred, so please don't mind me here, but High Gear Ratio means Low Gear, and Low Gear Ratio means High Gear, so what you need or want for your one ton steamer is a higher gear ratio and that would give you a lower gear. Then to mount the larger diameter prop you also need an enlarged prop mounting window on the leg.

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    About high thrust outboards: - (Note it's about ‘‘thrust’’ as a propulsive force, and not ‘‘trust’’, although enough thrust gives peace of mind and trust.)

    The engine's crankshaft power output in Hp and torque and rpm stays the same regardless the gearing, a higher gear ratio gives a lower gearing and lower rpm at the prop shaft, the same horsepower at lower rpm means there's more torque at the prop shaft, which will put higher strains on the shafts and bevel gears down below.

    For this reason High Thrust outboards often have a leg of the next size up standard version, so they can house the bigger shafts and the stronger bevel gears that are needed to handle the higher torque, for the bevel gears enlarging the diameter brings down the force on the teeth.

    And the next size up leg, that often structural is needed when there aren't enough strength reserves, also comes with the larger prop mounting window, which is needed to house the larger diameter prop, which is required in order to convert the higher torque at a lower rpm, into a higher thrust at low boat speeds.

    And so this all makes a high thrust version of an outboard, of which the engine most often is still 100% the same with also the exact same settings, since high thrust outboard versions are all about the gearing in the leg and the used prop.

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    About the 2½ hp Suzuki, below some comparison, but as far as I know there are alas no high thrust versions available any near the 2½ hp range . . :(

    2-2.5 hp outboard comparison.jpg
     
    Last edited: Apr 9, 2018
  11. valery gaulin
    Joined: Jan 2017
    Posts: 177
    Likes: 4, Points: 18, Legacy Rep: 7
    Location: Montréal

    valery gaulin Senior Member

    @chinaseapirate

    You are right, my hull without the keel, the centerboard and the rudder displace around 19 000 lb.

    LWL: 37' 6"

    I think that if I can motor at around 6.5 knot it will make me happy. For this I think i would be OK with a 25HP high trust engine. For maximum hull speed it requires around 39 HP if i remember the calculations.

    There is no 40 HP high trust engine, then the next step up is a Yamaha 50hp. While at it the Yamaha T60 is exactly the same as the Yamaha T50 for about the same price!

    My thinking was that if I can fit in my design the biggest outboard, there should not be a problem room wise if I choose to go smaller.

    Probably if I would just get in and out of a marina the Yamaha 25HP high trust would be perfect!

    My plan is to travel with this sailboat and do quite a bit of motoring. I need to most fuel efficient to maintain around 6.5 knot cruising speed, the least noise as possible and available power when things get rough!
     
  12. Angélique
    Joined: Feb 2009
    Posts: 3,003
    Likes: 330, Points: 83, Legacy Rep: 1632
    Location: Belgium ⇄ The Netherlands

    Angélique aka Angel (only by name)

    Re post #25: - To illustrate the leg's size increase when converting an outboard to High Thrust I've grabbed a picture from a Suzuki brochure PDF

    The below 50 & 60 hp High Thrust outboards have the leg based on their standard 115 to 140 hp sisters (DF115A - DF140A).

    [​IMG]

    The thrust force increase for the High Thrust versions vs the Standard versions is far larger in reverse than forward because of the exhaust through the prop hub is for most Standard versions always at the backside of the prop hub.

    So in reverse the prop of a Standard outboard version is sucking up the exhaust gases, and as a consequence is ventilating in those gases, hence there's reduced thrust in reverse.

    In a lot of High Thrust outboard versions in reverse the direction of the exhaust gases in the prop hub is also reversed and leaves the prop hub at the leg side, hence in reverse on those High Thrust outboard versions the prop isn't spilling reverse thrust by ventilating exhaust gases.

    It's beyond me why not all Standard outboards versions also have this exhaust gas reverse system for more thrust in reverse.
     
    Last edited: Apr 8, 2018
  13. Angélique
    Joined: Feb 2009
    Posts: 3,003
    Likes: 330, Points: 83, Legacy Rep: 1632
    Location: Belgium ⇄ The Netherlands

    Angélique aka Angel (only by name)

    The 25 Hp high thrust Yamaha T25 is extreme heavy, to me it looks like the T25 has a leg that is based on the same leg as the T50/T60, which could come from a 100+ Hp standard version...

    2018 Yamaha High Thrust Outboards T60 T25 T9.9 comparison 1.jpg
    2018 Yamaha High Thrust Outboards T60 T25 T9.9 comparison 2.jpg
    5 × T60 - - (click the below images to enlarge, click again to shrink, each horizontal row is just one picture)
    [​IMG]

    5 × T25
    [​IMG]

    5 × T9.9
    [​IMG]
     
    Last edited: Apr 9, 2018
  14. M&M Ovenden
    Joined: Jan 2006
    Posts: 360
    Likes: 77, Points: 38, Legacy Rep: 527
    Location: Ottawa

    M&M Ovenden Senior Member

    Put in a little diesel. You should be able to find something for a good price if you aren't in a rush. The price difference between that and an outboard is nothing over the project cost, and performance will be substantially better.
    Cheers,
    Mark
     

  15. valery gaulin
    Joined: Jan 2017
    Posts: 177
    Likes: 4, Points: 18, Legacy Rep: 7
    Location: Montréal

    valery gaulin Senior Member

    Kubota 7kW Diesel Generator GL Series | GL7000 https://www.norwall.com/products/Kubota-Diesel-Generator-GL-Series-GL7000

    I took everybody comments and I am starting to look at the option of going With an electric pod and a small diesel generator.

    Would that generator above in the link is a good size and model to start with?

    I don't want a huge battery bank but enought battery to account for the time that i need the extra power for let say 10 minutes.

    I guess at 7kW i could probably power the electric pod directly and be able to get around 5-6 knot of cruising speed.

    Now any suggestion on a electric pod? I checked Torqueedo pod, any other?
     
    chinaseapirate likes this.
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.