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What trailer/motor are you thinking of?  Will you buy new or secondhand, will you make trailer yourself?

Modern plans are done with CAD and the lofting is done on the PC to far more precision than required for this method. In my previous dinghy I had some gaps of over 10mm to fill with epoxy putty. No issues other than cost and weight. I am aiming to do a better job this time. 3mm (1/8th") is the precision of the plans. No more is needed. 

To draw a frame start be drawing the baseline and Centrelines on a sheet of ply. The centre line is the centre of the boat (vertical pencil line) the baseline is (in this case!) the top of the solem marked in red vivid. All measurements are taken from the CL and BL unless stated.  It is IMPERATIVE that these lines are perpendicular! I measured against the edge of the sheet multiple times over the line.

For tools I used a rafter set square, a fabric tape measure and a standard builders tape. The fabric tape measure is best for quick checks of distances along the sheet. One can use another sheet of ply as a straight edge and right angle if needed. The edges should be very close to square from the factory, but always check.

This frame is E (last frame in front of transom). It will form the motorwell bulkhead, reinforcing the transom and preventing swamping from waves over the stern. 

I measured left of the CL 822mm then directly down 70mm. Drew an X in pencil. Then up 641mm from BL and left 1015mm of CL. Repeat for the other side. Draw in the boundary in pencil then over in vivid so I can see it more easily when cutting. I found in my previous build that when holding something that will have your fingers off in a second you don't want to be losing the cutting line.

The top of the frame has a slight camber (curve) in it. This is a parabolic shape drawn by putting a batten through three points shown on the plans. The curve is for the side decks later. A batten is a really effective way to draw a nice fair curve. I'm using an Aluminium flat bar on edge from Mitre10, but anything that will bend with little effort in a fair way will work. Hold the batten down on three points and draw the line in pencil. The flat bar also makes a very useful and cheap straight edge. It will end up on the keel or rubrail later on. 

Easy as, just take your time and measure measure measure. 

I would like to get it in the water summer 2021, but that depends on being able to use all my holidays on her. I am a teacher so that helps.

It's a constant deadrise planing hull. 45 degrees at cutwater, but 10 degrees at the transom. Very very similar hull form to the Tolman skiff. Almost exactly the same deadrise chine width etc.

I know that several of these have been built and easily done 25+mph with a 50-60hp motor and several adults on board. Stepping up to 70hp is a fair bit more weight on the transom. 

Nice work. Did you build that? Do you still have it?

No I dont have it although it has recently been for sale (may still be), although she looks a bit rough around the edges now the hull is still as sound as the day she was built

Built a strongback to hold the jig.

Set up the tunnel house that will be the boats home until it is ready to go on the trailer. 

Cut out transom, clamping boards, all of the frames and stringers. 

First time I've screwed up a mix. I was using the dregs of the jug and the pumps weren't pulling. 

Next time I'll put it all in the same cup. Much easier. 

On Tuesday I screwed up the epoxy gluing the stringers. I took the day off on Wednesday to sit back and regroup. Got some other work done and asked a few questions on the Bateau forums about what to do. 

Bottom line: I can not trust the stringers, and the epoxy is cured very well in some places and others I could pick the epoxy off with my fingers. They will go to landfill. I will try to rescue the motorwell support braces at the back. 

So I ripped a board of 9mm (my last decent board) into strips roughly 125mm-130mm wide. I then tried to get my sad looking strips straight and parallel with a power planer and circular saw. No go. I did get within 3mm. 

This morning I went out and purchased a flush cut router bit. I used the straight edge of a sheet of 6mm ply to act as the jig and got it done. Amazing the difference the correct tool makes. 

Epoxy is on the way to CHCH, summer slow hardener, and I have bought a scale to do small batches accurately.

Next job is to cut out the hull panels, splice them together glue up the stringers again, laminate the transom and set up the jig.

Edit: just checked the data sheets. Slow has the advantage of slightly more elongation. But in most relevant properties they are the same. They can be used interchangably as well in any combination as long as they are the same ratio (5:1).  

Most important thing is to match temperature to hardener. I have used Fast in the summer before; but earlier in the day.

One oopsie on the cutting, circular saw grabbed and cut a little slash in the upper side panel. For now I've just patched the gap with epoxy, it will be covered up properly later. Didn't take a photo of that.

The best way to cut large panels that need to be symmetrical is to screw two sheets of plywood together and cut them at the same time. Otherwise little differences creep in. I then used a power planer to tidy up the places where I cut outside the lines, rebate a little bit where I'll splice the panels and drilled some stitching holes along the chines and keel. 

 

Have a bit more information here. 260kg is the calculated hull weight: Okoume plywood, epoxy, glass (calculated at 40% glass content) and some fairing putty only. 

I will be running glass up the topsides (specs say only hull bottom) and will probably put another layer on the bottom. I'll also glass the sole with biaxial. I may or may not put a light glass (100 or 200g) on the cabin roof and other places. So add about 30kg there. 

I'm using Meranti for the hull panels and frames/transom. Add another 25kg or so. I'm planning to buy Okoume for the rest but may not. 

Add another 30kg-50kg for a couple of side benches(storage for tote tanks/ice box and leaning post for me. 

Add 50kg for rigging/steering/gauges/fishfinder/hatches/bunk cushions etc.

Add 50kg for anchor and batteries, 20kg each for up to two tote tanks (full.)

20kg ice, fishing gear, food and drink and other misc.

150kg for a BFT, 125kg for a Marlin , 400kg for a sword... or not.

110kg for a 60hp outboard,10kg for aux.

Subtract 10kg for not putting the rear lockers in, and if I manage a better than 40% glass content. Possibly subtract more as I plan to build the cabin from 6mm ply glassed with a light cloth rather than 10mm ply. 

85kg for me. 140kg approx for two/three others. (This could be more, but then it could be less.)

Add that all up: 845kg, call it 850kg. That will put the sole right at the waterline, unless I raise the sole. There is room to raise it 2.5cm or more. The PPI is 350pounds, 160kg per inch. Cockpit depth is at least 640mm plus any coaming.

Currently I don't really plan to raise the sole much if any. I will run elephant trunk scuppers out the rear, a bilge pump for leakage, and possibly side scuppers that will be plugged almost all the time. The side benches will be designed in a way that they act as temporary buoyancy chambers in the unlikely event of a swamping. 

I used scale for todays job: splicing panels. Had to chuck a batch when I needed to change epoxy bottles halfway through the pour, when I had the pump screwed in the new jug, I added the amount I thought it would be by memory, but didn't trust it. It cured in the pot ok.

Edit: My scale will auto off after a minute or so. Usually not an issue.

The designer assures me that:

Keep in mind that your boat would have much more load on the trailer than mine. 6m glass vs 5.3m wood epoxy composite. 

Cleaned up and ready for putty and glass. At least glass on the other side acts as a scrim for the putty, and I can fill it later. 

Surface area on a roller 7.5 square cm.  (rubber roller with the little flats.) 

That's about 5kg/cm2.

Multiplied by unknown factors for impact, and a safety factor of 5 (for long fatigue life.)

Anyway, I bit the bullet, decided that the stringers would need to be redone (again!) and scrapped the transom as well. Cost for two more sheets of 9mm marine ply =$200. I'm hoping to salvage some of the scrap for the cradle when I flip it or cleats or something so it's not a total loss.

This time I did what I should have done for the start. I used screws and plenty of them. Precoated both sides, spread the epoxy (thickened to at least mayo) and then used hand tightened screws in predrilled pilot holes. Worked a charm. 

Photos of new transom ready for last layer of 9mm ply.

On the brightside, I'm a lot better at ripping straight cuts with a circular saw. Used a sheet of ply as a guide, and done. Easy as. 

Clamping boards go right across, 4 layers of 9mm ply total. Will get glass both sides, one layer everywhere, plus overlaps and tape in stress areas and panel joins. 

I moved the rear scuppers. These will be just above the DWL over a sump for the bilge pump. Idea is that the pump deals with the normal stuff and the scuppers are emergency use only. They will get layflat hose or  or something similar. Still thinking that through.  

I predrilled and filled with epoxy plugs holes for the outboard. The plugs are 30mm diameter, vs the 12mm bolt size. Plenty of wiggle room. Also filled the holes that will drain the motorwell. They will also be redrilled at a smaller diameter into the epoxy: No possible path for water to get to the wood. 

There was an annoying 5mm inwards bend in the transom after the first lamination. After a bit of pondering I cut a couple of kerfs, filled with epoxy putty, and screwed the transom flat to the old transom. No more bend. Then the last layer of 9mm on the top with glass to follow. The epoxy filled kerf should be stronger than the wood, and it's in the neutral axis of a sandwich, no strength issues. 

This method does not require the accuracy of a traditional jig, which is just as well. CNC cutting would be the only option for me if that were the case. 

To complicate things the ground is not perfectly flat. I checked with a hose pushed into duty as a water level. One end of the jig is 100mm higher than the other. That's about 1.5 degrees off horizontal. 

The strongback is as level as I can get it on the ground like it is, and I will make first measurements off that, and then adjust the frames so they are lined up. Hoping for +-3mm everywhere if I can get it. 

Photo of the first attempt. I quickly decided that was too high and lowered the frames 20cm so I can reach the keel. Room to get around it will be tight. 

Well the stringers and transom are basically done, I am calling them done. Glassed over the transom top with two layers biaxial tape offset a little bit. Had to cut out a few voids in the first layer where it lifted. Filled with epoxy PB.  Second is curing now. 

The jig is nearly complete, Frames A-E all lined up as accurately as I can, with a lot of measuring of diagonals. The ground is on a slight slope, so I am squaring off the strongback then checking measurements and adjusting so the notches lie even with the stringer (useful straightedge). 

 I used the trick of drilling a 10mm hole in the frames at BL and CL and pushing a bike LED light into frame E. The light is visible through a hole clamped over the CL of frame A (Frame A doesn't go through the baseline.)

Coated the inside of the four hull panels with a very very thin coat of epoxy. The idea is to prevent moisture absorption when it rains. It may be a while before I get around to the flip and I dont' want too much swelling.

Fiddled around with the jig a bit, moved a frame left, then right, up then down. 

Then with help from my son we put the bottom panels on top of the jig. I checked the line up and then moved frame D up to meet the bottom panel. It is the hull panels that define the shape of the boat, not the jig. 

Finally I filled a few small holes in the transom, and put a generous fillet under the clamping board. I won't be able to see it once in the boat, so I want to be sure that there is no crack or gap for water to get in. It will also stop delamination and stress concentration at the edge. 

I'll get the side panels on today if I can and then stitch them. Transom will go last, supported on a couple of blocks.

Got the feeling that something is still missing though :)

You know I never actually checked the number of views until just now. I often post photos etc on my iPhone, which recently seems to be struggling with the post window, major slowdowns. 3000+ views! I was actually thinking that I was talking to myself half the time. It's good to know people are reading, so I put more effort into the posts. 

Anyway I didn't have time yesterday to do much. I had covered the boat with plastic as showers were forecast Saturday. A good thing too as Sunday morning I get up and found that I forgot to put the chickens away the night before. Big stinkalicious piles of poo on the hull and jig. 

 I also went around the boat checking the tack welds, and especially the sections where I taped the hull panels. Looking for voids and air bubbles partly and also trying to ensure a good secondary bond to the epoxy. 

I've been reading about adhesive bonding to cured epoxy especially. Technical information ahead.

A good adhesive bond requires that the adhesive wet out the surface to be adhered to. For epoxy to wood it soaks into the wood and bonds that way. If the epoxy is still a bit tacky then no surface preperation is required. As the epoxy reaches final cure chemical bonding becomes less achievable though some may still be there after a couple of days. 

The typical method for a DIY guy like me to energise the surface is sanding. (Other methods include media blasting, peel ply and plasma treatment.) Wet sand and wash first to remove containiments, then a good rough up with 80-120 grit sandpaper. Sanding into the glass itself is sometimes unavoidable but not recommended as it removes sizing (coating that allows wetout) from the exposed glass. The photos of the glass tape show the shiny areas where I will need to get in there with a small bit of sandpaper before I glass over. 

The bonding layer is only about 6 molecules thick. A fingerprint is about 1000 molecules thick and residue from a breath is about 50 molecules thick. Even well prepared surfaces lose surface energy after a few hours, let alone days. Containiments interfere with the attraction between the liquid adhesive and the surface. 

If you are wondering how well a surface is prepared a water droplet test is simple and reliable. If the water beads up on a surface bonding will be poor, but if it wets into and spreads out on the surface bonding will be good. Obviously wipe with a clean paper towel before coating with epoxy. 

In a Bowdidge boat all the interior frames are glued in while the boat is upside down, then filleted and glassed after flipping. This enables a direct bond of the frames to the hull but breaks up the continuity of the inside glass. In a Mertens design the interior structure is removed and the whole inside is glassed in one piece. Then the frames and stringers are glassed in with secondary bonds. I'm not sure which is faster or stronger, but I can tell you that both designers prefer their own way. 

helped a friend build a strip plank kaikatea hull,built over temporary frames,glassed outside first,turned hull over and fitted permanent bulkheads in before removing temporary frames,both inside and out glassed with tri axle cloth.

On the other hand, the natural inclination is to follow the plans, which call for glassing the bottom with frames and stringers out. Most of the boats are built that way, though I know at least one of the OB17s was built by an Aussie who did it the Bowdidge way.

 If I had a set of Bowdidge plans for a similar sized boat then I could see some of the finer details of the way he does it, or if his forum was open to all to see. If anyone has those details, now is a good time to share them. MarkE? Scampy?

I have some questions for you Mark:

There must have been some places where the hull panels (that define the shape of the boat) did not sit nicely against the frames. How did you deal with this? 

Any concerns with hardspots with frames pushing against unglassed wood? 

The more I think about it the more I realise that I should have considered this earlier. The stringers, especially do not have any preparation on them to take a good bond. I also have box tape in places between frames and hull as in the bateau method you do not want to glue them in at this stage. 

A quick review of the specified method with photos of a C17 built ten years ago.

Hull panels left in with temporary glue spots for the flip on to a cradle to support the hull. Cradle is prebuilt on the upside down hull to fit it exactly. 

Then the interior is removed and the inside glassed in one strong continuous lamination. 

Then the structure is put back in. Stringers first, then frames.

It answers a lot of your questions - re taping, frames in out on flipping etc etc
 

IMO - if the hull is well glassed (outside) and caution is used to turn the boat then there shouldnt be an issue.

Benefit is that you can then glass / tape the seams in full lengths

I've been wrestling with some changes in the panel shapes recently. Humidity changes swelling the wood, causing some uneveness.  The inside has a very thin coat to prevent this, but the outside is still bare. I'm hoping that I can coat it tonight, then glass tomorrow while the epoxy is still green. 

1. That I'd do the best job that I was capable of considering my experience at the time. 

2. That I'd post the bad and the good online, so I could get reliable advice. Brag posts are for my Facebook page. 

So I had a bit of a setback during the hull glass layup. I've layed up glass before, but never so much. 

Anyway day dawned fine and hot so I got into it. I had decided to glass one side of the boat at a time with secondary bonding along the keel. 

One layer 400g along the bottom running down the hull side. Glass isn't required all the way down the side. A second layer on top. Wet on Wet 

So I started. Cut out the first layer of glass, and got it wet out in about 3 hours. It got hot, probably about 35 degrees C pushing 40 in that tunnel house. Even with WEST Slow  I had to hurry at times. 

That layer actually wet out ok. There were a few air bubbles here and there, but nothing to cry about. 

After finishing at about 2pm I  was buggered. So I went inside and took a break. I was beginning to feel the heat, which may explain why I left my bubble buster roller outside rather than in the container of acetone. 

Anyway time for the second layer. The first layer was barely tacky by then and I was beginning to worry about getting wet on green without sanding.  

So after considering whether I should just stop at one layer for the day, I started being in "get 'er done" mode.  Mistake. 

The problems started almost immediately. I managed to get the glass spread out fairly smooth with a bit of wrestling. But as soon as I started wetting out, bubbles! A lot of them, mostly small buried under the glass.  I tried pushing them out with a lot of force from the squeegee, but I really needed that roller!

So anyway 7pm done, quick shower and off to a restaurant for tea. This morning I  drilled out all of the bigger bubbles, injected epoxy in those that I could, filled the weave with epoxy thickened to ketchup consistency and put a first light coat of fairing on the sides.  

But the more I look at the remaining bubbles the more it bothers me. I think that they aren't a structural issue, due to the first layer of cloth laying down well. I am worried about water getting in. 

I know now how to prevent most of this happening again: Fill the weave between layers, and apply in the pm when it's cooling down. But I have a bit of pondering to do. 

Photos to follow. 

Being my own QA, I am currently thinking that I will reject that job and introduce the layup to my Saw-max diamond blade. Then a belt sander, much bigger radius on the corner and retape with some generous overlaps.

Lesson learned. One of the kids in my class asked me why I didn't stop. I told him that I was hot and tired and made some poor decisions. AKA I was stupid. 

Brief update. Tried the grinder and a heavy sanding disc. I did not like it at all. The amount of dust kicked up was phenomanal. So switched tactics and bought a power planer from the Toolshed with Tungsten Carbide blades. This was a lot better. Pictured is my planer with my dust collection. The vacuum hooks into the top of the cyclone on the bucket  and sucks the dust through the side. 99% of the dust can't follow the air and gets left in the bucket. 

I'm taking it down to wood along most of the chine and keel, and removed about 95% of the bubbles on the rest. I'll touch it up over the next couple of days aiming to get all the rest of it and then move to taping the seams. 

This probably wouldn't have happened if I had had a workshop to build in, or one of those shelter logic carports. What I get for being cheap but what's done is done. 

I'm a bit concerned about glassing over it. The surface is not as fair as it once was, so there's bit of sanding and filling before I can glass again.

EDIT: If it went perfectly the first time I think it would be less satisfying when it was all said and done. I've had a few projects before (none as big as this) that have required significant re-work, and while its frustrating at the time, I think it adds to the end result in a strange way.

as long as youre consistently at it, youll have it done before you realise.

i like to remember - 'never go to sea in a boat that was launched on time or on budget'

The main thing is that the glass goes down tight and strong and the planing surface is flat and smooth. There are a few places where not much glass was taken off, and others where I'm down into the first or even second ply of the core, so they will need smoothing. I spent over an hour today on the RO sander, and am happy with about 99% of the bottom. I'm sure I've missed a few bubbles, but not many and nothing bigger than 1mm.