First boat. Glued Lapstrake method

Discussion in 'Boat Design' started by ggeorge, May 21, 2020.

  1. ggeorge
    Joined: Aug 2018
    Posts: 5
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    Location: Greece

    ggeorge Junior Member

    Hallo.

    Congratulations for the forum!

    I have been reading it the last days since I decided to construct a small boat. I have some small experience with woodcraft but this will be my first boat.

    I am thinking of making a boat with Glued Lapstrake method. I think that the Lapstrake method is the nicest method for traditional boats.

    I designed the boat of dimention 240x132cm as seen in the photos below.
    The boat will be used for fishing at sea at very short distances in Greece, at calm water

    I may add an outboard engine 2-3hp. I want the boat to be light and small but also to be able to accomodate me and one friend (70kgr each).

    I based the large beam on a boat I saw on line (240x236cm) which i find very attractive.

    Unfortunately i couldnt find the drawings to buy them.

    I would like to ask the below:

    1. I am thinking of using okoume plywood. Which is the minimum thickness i should use?

    2. I plan instead of using only resin to join the wood, to also add a layer of fiberglass with epoxy resin. What do you think? With the fiberglass which should be the plywood thickness. I am thinking of 6mm. I want to use the minimum thickness since i dont have steam generation equipment.

    3. I have designed the boat at bigger breadth for better stability. Most boats at this length are of 120cm breadth. Will it be ok the 132cm?

    4. How much should the inclination of the transom be? I have read it is usually 12-16 degrees.

    5. Do you see something in the drawings that you dont like?

    Thank you for your interest !!!! :)

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  2. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Welcome

    I can't comment on the hydro-analisis, nor on much structurally. However, I can say with all certainly that putting glass cloth on lapstrake is challenging. Fiberglass doesn't do corners well. You will lose the details of the lapstrake if you try to glass over it.

    Otherwise, it loses to be a lovely little pram.

    Good luck and have fun
     
  3. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Welcome to the Forum George.

    Re the dimensions of your boat - in imperial they are 7' 11" long and 4' 4" wide.
    Re building it with lapstrake plywood - in view of how the length is 7' 11" and you have a lot of curvature and width, you will not be able to use the 'standard' 8' long sheets of plywood - they will not be long enough for most of the strakes, apart from those near the keel.
    Can you buy longer sheets in Greece? If not, you will have to do either scarf joints or butt joints (with butt blocks on the inside) to make the strakes long enough.

    And I agree with Blue Knarr - don't even think about trying to apply fibreglass over your lapstrake hull.

    Re the boat that you saw on line which you liked, do you have a photo of it, or any link?

    Is it absolutely essential that the boat be very short and fat? I would be more inclined to make it a bit longer if possible, and maybe reduce the width a bit. If you can get plywood in 10' lengths (?) then you could design the length with this in mind?
    Or does it have to be 8' maximum in length, re transporting it (inside a van perhaps?)
     
  4. ggeorge
    Joined: Aug 2018
    Posts: 5
    Likes: 2, Points: 3
    Location: Greece

    ggeorge Junior Member

    Thank you for your responses!!!

    I hadn't really thought that fiberglass does not lay good on wood. I may carry out some tests to see how it looks.

    The boat i like is the below.
    It is made of fiberglass

    I copied its dimentions ( breadth and length) and at the rest i improvise. It differs on the shape from the amidship to the bow. Mine rises but the original one doesn't.

    In greece unfortunately i cannot find bigger piece of plywood (only 2500x1250mm, 8ft and 2 in x 4ft and 1 in).
    I haven't finished designing the boat and haven't made its projection to see the wood length. I planned to cut plywood diagonal even if it means i will waste it. I asked for marine plywood but i can only find simple okoume which is cheap around 30E a piece.

    I made it short so as not to make joints (but it seems it should have been shorter) whereas i made it wide for better stability and comfort for two persons onboard.
    Is it not absolutely essential that the boat be very fat but i thought i should try it

    The construction will be done at a slow pace at my summer house (1 month per year) because i dont have space on my main house. I just want to make it for fun because i already have another boat (purchased) and since i was a kid i wanted to make a boat on my own.
    Yesterday i bought cheap wood so as to construct a base so as not to have to lean.

    I am thinking alternatively to make first a small construction stich and glue to learn how to work on epoxy resins. I mean something that will take 2-3days tops so as not to loose too much time from my main boat.

    Many thanks for your responses!!!!

    Dovetail Rowing Boat - For Small Lakes & Ponds | Heyland Marine https://heylandmarine.com/dovetail-rowing-boat/

    heyland-dovetail-rowing-boat12.jpg heyland-dovetail-rowing-boat19.jpg heyland-dovetail-rowing-boat16.jpg
     
  5. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Hi George,

    Your design is very similar to Iain Oughtred's Auklet - she is 7' 2" LOA.
    Oughtred Boats : plans kits building sailing rigging & lots of boat stuff : Iain Oughtred Designs http://straydogboatworks.com/oughtred/mainpages/dinghies.html

    Or this design from Nestaway -
    Nestaway 9ft Clinker Stem Nesting Dinghy - Nestaway Boats https://nestawayboats.com/shop/nestaway-9ft-clinker-stem-dinghy/

    Re starting off with a 'simple' stitch and glue design, there are some very neat little pram dinghies here - here are ssome typical examples -
    Catspaw / Two-Paw Plans https://bandbyachtdesigns.com/catsaw-two-paw/
     
  6. clmanges
    Joined: Jul 2008
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    Location: Ohio

    clmanges Senior Member

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  7. ggeorge
    Joined: Aug 2018
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    Location: Greece

    ggeorge Junior Member

    Thank you for the responses. I liked all boats you showed me.
    I will start with the easy construction. In parallel I will work on the design. Most propably though i will buy a ready design as you suggest.
     
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  8. Ilan Voyager
    Joined: May 2004
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    Location: Cancun Mexico

    Ilan Voyager Senior Member

    Lapstrake is not the easiest method for a beginner. The strips can be very S shaped at the bow thus challenging to draw like in classical wood. The further and sad problem with lapstrake plywood is that you get meters and meters of exposed end grain in the plywood strips sucking kilos of resin before being saturated by the epoxy. That means hours with a small brush adding resin until full saturation, and after hours of sanding the details while trying to not oversand the exposed corners...After a while it's not fun at all.
    I would love lapstrake while building in a beautiful fine grained wood that will be simply varnished or painted. Not the lightest, the cheapest or the easiest . It's classical or almost (high stretch structural polyurethane putty is a good helper for sealing the overlaps) boat building with copper rivets and tutti quanti. Very pretty, extremely high maintenance.
    As may others said it's impossible to glass correctly.
    For such small boats the pram style is not the prettiest but surely the easiest and the most effective method. It can be glassed thus withstanding lots of abuse.
    Besides the oars, make provision for a scull. Not the classical one which needs training and strong arms but the articulated style chinese one. You'll be surprised by the good performances and easiness of a that scullmatic.
    Scullmatix© https://www.duckworks.com/product-p/dw-sc.htm
     
    Last edited: May 23, 2020
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  9. ggeorge
    Joined: Aug 2018
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    Location: Greece

    ggeorge Junior Member

    Thank you for your response. I have already bought the plans of a pram boat 1.20m to learn.
    Irrespective of which method i choose
    I would like to know if with the lapstrake method i could use fiberglass/epoxy resin only on the bottom inside for strengthening and on the outside only epoxy resin.

    Do you think i could use 6mm plywood or thinner?

    At carvel method without nails the join of the wood is carried out with wire as the stick and glue method?I havent understood.

    Thanks
     
  10. clmanges
    Joined: Jul 2008
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    Location: Ohio

    clmanges Senior Member

    I wasn't impressed with the Scullmatix. Watching the first video, as soon as the guy got the boat turned toward the camera I began singing along, "Yaw, yaw, yaw your boat ..." I'll grant that it might have tracked better trimmed with some weight up front, but it fails on a number of counts. The blade shape is wrong, and the operator is going to get a really sore back. I think that if he lengthened the handle and stood further forward it would have worked better. Then he could lean side to side on the rope, as the Chinese do it.

    I think someone created a yuloh for a small boat, made so the operator sat down, and IIRC, it performed quite well.

    I thought his prototype in the second video, with the perpendicular handle, was better, but the most this thing has going for it is that it's cheap and uses existing oars.

    All that aside, this is a rowboat. Oars work fine, as long as you don't mind looking backwards, which is why I got rid of the rowboat I used to have.
     
  11. NoEyeDeer
    Joined: Jun 2010
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    Location: Australia

    NoEyeDeer Senior Member

    As some others have pointed out, unless you have a particular reason for restricting length to 2.4 metres it may make sense to give the boat a bit more length.

    1/ 6 mm. Although you can get away with 4 mm as long as you don't plan on abusing the boat. If you have sandy beaches and your friend is not going to jump up and down inside the boat, 4mm would be fine. If you have stony beaches and rambunctious friends, 6 mm would be better.

    2/ Glassing the whole boat shouldn't be necessary, and will add weight. If you are going to glass the outside, you can use thinner ply. 3mm ply with one layer of 200 gsm glass outside is surprisingly tough. 4mm would be plenty. But, as others have said, glassing the outside of a lapstrake boat is not easy or fun. It's possible, but you have to fillet the laps, and it works best with only a few wide planks, and with boats that have an easy shape.

    Alternatively, you can glass individual planks before fitting them to the boat. This may be worth considering if you want to make the bottom planks more resistant to stony beaches.

    Regarding steam generation equipment: it's easy to make your own if you need to. I generally wouldn't be steaming plywood in a steam box though. You can do other tricks with plywood, like applying rags soaked in boiling water to difficult areas, or even using a portable steam cleaner on some sections. You can even douse it with alcohol and light it with a match. Seriously, this used to be the preferred method for getting a sharp twist in the garboard of some racing dinghies. The alcohol burns at a low enough temperature to soften the wood without charring it, as long as you don't leave it on fire for too long. :)

    3/ Define "OK". It will be more stable, and carry more weight, but it will be harder to push through the water and harder to plank.

    4/ Doesn't matter. It's only for looks. Choose what looks best, but on such a short boat you don't want to waste any waterline length.

    Ok. Do not cut the plywood diagonally. Use scarf joints to make longer planks. These are not hard to make, although you may want to try a few short practice pieces. The main things to watch are:
    a/ Make sure they are cut cleanly, so the visible edge inside the boat won't look ragged.
    b/ Make sure you have your gluing and clamping worked out well in advance.

    You need to get good even pressure across the joint, and you need to make sure that the top piece of ply doesn't sit too high because of glue trapped in the joint. You should also use some masking tape just outside the joint on what will be the inside of the boat, and clean up any excess epoxy while it is still liquid. If you get it right, which is not that hard, the resulting joint will look fine even with a clear finish. :)

    If your okoume is not called "marine ply" then check to make sure it has a waterproof glue. Also check to make sure it doesn't have significant voids in the inner layers (look carefully along the edges).
     
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  12. ggeorge
    Joined: Aug 2018
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    Location: Greece

    ggeorge Junior Member

    Thank you very much for the so analytical response!!! You helped a lot for many issues, dilemmas i had.

    As you all suggested i will slightly increase the boats length to propably 2.60-2.70m (or buy ready plans). The beaches dont have sand but very small pebbles but i will be very carefull.

    I am thinking of following a mid solution of what you suggest, 4mm plywood and glass. I found plywood of 3100mm length in Greece but they sell it at large qtys, 200 pieces. I think i will manage to find it where it is sold at small qtys and therefore i will avoid the scarf joints.

    The plywood glue is waterproof

    Temporarily i will start the stitch and glue boat to work on epoxy and glass.

    Thank you again very much!!!
     
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  13. Ilan Voyager
    Joined: May 2004
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    Location: Cancun Mexico

    Ilan Voyager Senior Member

    You're right for the scull, and some have problems for rowing not facing the direction. By experience I can say that a well made "scullmatic" works pretty well but a true chinese articulated scull with the small rope works even better, and it's ridiculously easy to use. For rowing if you are able to work and weld metal you have pretty good designs (but a bit complicated to make it properly as there are mechanical links) with which you are rowing facing the "good direction".
     
  14. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    If you are going to laminate the hull for strength on one side only, it is always done on the outside. Lapstrake is a really bad choice of construction method for a hull that will be fiberglassed over.
     

  15. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    One of the best boatbuilders I ever knew said that there are few things harder to build than a short dinghy with a stem.It gets a bit more difficult if you have plank lands on clear view.
     
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