Sanity check of 16 foot powered flat bottom skiff

Discussion in 'Boat Design' started by Turbopleb, Sep 18, 2019.

  1. Turbopleb
    Joined: Sep 2019
    Posts: 4
    Likes: 0, Points: 1
    Location: Sweden

    Turbopleb New Member

    Hello, this is the first time ever posting here, been looking around the forums a bit, at plans on various websites, and have found what I believe to be the most optimal boat considering ease of building, low speed performance, stability and clearance.

    The boat will be built using stitch and glue method, fiberglassed both inside and out. Bottom thickness will most likely be 12mm (15/32") while the sides will be 7mm (9/32") to keep weight down. Transom undecided, but I'll take more of a look to see what I need to handle around 40hp at best.

    The plywood sheets are 2,5m in length, and will get a scarf joint in the center of each part. Both the sides and the bottom will have the scarf in the same location as the boat is pretty much 4925mm out of 5000mm in the longest section. Bottom is 4405mm though so it's going to miss by about 500mm.

    I have decided to build a flat bottom skiff, powered with a outboard of about 30-40hp somewhere.
    It's planned to be used in big lakes and some rivers. Plan is to have availability to go all the way into rivers with trolling motor, but not have something too unstable to go out on the open waters.

    I am not very skilled at all with DelftShip, but I believe I've come up with a decent design. The boat must not exceed 5m (16'4) due to limitations of the plywood length.
    The transom angle is designed for 12 degrees, which is considered online to be the standard.
    The side angle is designed to be 11,7 approx. angle.

    I have since first version of the boat made the side angle more straight compared to before, and also made the bow more sharp angled, to better handle chop if weather decides so.

    The boat has a slight sweep to the front, meaning that the bow is both angled upwards in the bottom and the railing.

    The plan is to mostly fish in it in the rivers or the big lake.

    Is there anything I've missed that are glaringly obvious for the ones more experienced?
    I've attached various photos, and a link to the .fbm from DelftShip.

    bote.png
     

    Attached Files:

  2. Deering
    Joined: Feb 2005
    Posts: 477
    Likes: 22, Points: 18, Legacy Rep: 44
    Location: Juneau, Alaska

    Deering Senior Member

    I like the design. I’m interested in a similar dory design, a little bigger at 18’ with a BOA of about 5.5’. Most dory designs are significantly wider.

    40 hp strikes me as overkill for a light weight flat bottomed skiff.
     
  3. Turbopleb
    Joined: Sep 2019
    Posts: 4
    Likes: 0, Points: 1
    Location: Sweden

    Turbopleb New Member

    Absolutely. The plan is around 30hp but depending on how heavy it will end up with all the gear loaded, it might be needed. I need to read up on outboard efficiency with horsepower/throttle difference. Might be no difference to run a 40hp on half throttle compared to a 30hp on 3/4 throttle fuel wise. I just want to make the engine have the grunt if needed, but also decent fuel economy. The engine will only be used for initial transport to fishing locations, then trolling motor after that.
     
  4. Deering
    Joined: Feb 2005
    Posts: 477
    Likes: 22, Points: 18, Legacy Rep: 44
    Location: Juneau, Alaska

    Deering Senior Member

    Part of the issue is weight. Some 30 hp models share the same block as 25 hp (same weight) while 40’s and 50’s share blocks. For instance, the difference between a Honda 30 and 40 is 55 lbs, but no difference between the 40 and 50.

    My biggest concern with the 40 would be safety. Running empty with a flat bottom would make that a pretty squirrelly boat. Maybe OK for you, but if someone else was running it... Just something to think about. Maybe you could borrow an outboard for testing before making a final selection.

    If you’re going to troll with the main motor, then go smaller.
     
  5. Turbopleb
    Joined: Sep 2019
    Posts: 4
    Likes: 0, Points: 1
    Location: Sweden

    Turbopleb New Member

    Im having an electric trolling motor when I get to places. Plan is to have full power available if needed at all times. I'll take a look and see which engine blocks weigh a certain amount. Didnt think of that part.
    I never plan on going full throttle on a unloaded boat. Just want to have the option to open it up when needed. I'll be buying an used engine so pricing is not a whole lot different, so I can choose HP as I wish. But I'll definitely check out the weights of the engines.

    Plan is to fit a small console in the rear for steering/throttle for comfort and better steering, if possible with boat dimensions. We'll see, just need to get the hull looking good then I'll fit everything by eye after.
     
  6. Turbopleb
    Joined: Sep 2019
    Posts: 4
    Likes: 0, Points: 1
    Location: Sweden

    Turbopleb New Member

    Decided to add some deadrise in the end. Will do 7 degrees, need to adjust the sides to match the new angle. Doesn't add much more complexity and only takes one more cut. Will most likely add way more comfort in the end. Still keeping the overall design though.

    [​IMG]
     
  7. dlpanadero
    Joined: Mar 2016
    Posts: 25
    Likes: 1, Points: 3, Legacy Rep: 10
    Location: Tampa Bay FL

    dlpanadero Junior Member

    Turbopleb!? Your name has got me in 'stitches.' (I'll see myself out now...)
     

  8. fallguy
    Joined: Dec 2016
    Posts: 1,984
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    Location: usa

    fallguy Senior Member

    Jon boats are not suited for 'big' lakes.

    Most of the inland lake drownings over the last 100 years related to boats have been flat bottomed skiffs.

    I only have anecdotal evidence, so don't ask for citations.
     
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