PK78--First time builder progress report and recommendations

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jacquesmm
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Post by jacquesmm »

Thank you for the post but I hope that it does not give a false impression. It is really not complicated at all to build a PK78.
Our basic stitch and glue tutorial shows the PK78:
http://bateau2.com/modules.php?name=Sec ... e&artid=20
and there is nothing more required than what we show.
For example, it is not necessary at all to use a jig to drill holes for stitches. I build 30+ S&G boats and never had any problems. Same for Devlin and all other builders.
A jig will not hurt however, feel free to work the way you prefer but I hope that those recommendations will not scare away potential builders.
A boat built with simple methods will be just as strong and seaworthy.

For the seattops, I agree that they rarely fit. Dimensions should be taken from the assembled hull because different builders and different plywoods will introduce some differences. We only supply the pattern because people ask for it but I consider it useless.
Sorry that you missed the width of the dagger board trunk, it is on drawing B131/5, bottom left.
We will soon post an new tutorial that shows how we put some temporary drywall screws through the edge of a 3/8 bulkhead. There is a trick . . .
Last edited by jacquesmm on Wed Nov 05, 2003 1:11 pm, edited 1 time in total.
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MNagy
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Post by MNagy »

I'm looking forward to that new tutorial. My problem right now is that I'm having a hard time visualizing how to do the stitching/filleting. I want to have the stitches out when I'm done, but I don't want to make things really hard on myself.

The only way I see right now is to make fillets inbetween the stitches, then remove the stitches and fill in the gaps between the fillets. I don't want to have to mess with trying to extract the stitching from an already finished fillet, be it with heat or any other method. Too much mess I think. Also, wouldn't it leave a hole through the plywood etc where there is no putty after the wire is extracted?

Making the stitches far enough away from the seam sounds good, but I can't see a way to get the putty under the wire when you're filleting, and I don't want to enclose the wire in the fillet.

Is this all much ado about nothing?

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Post by DaveProka »

MNagy,

Maybe it is much ado about nothing...it's just that designing is a science (mostly) and building is an art (mostly). If you expect a perfect construction method, you won't find it. Stainless seems to be looking for a perfect method of construction... ambitious, but an excellent idea from this reader's perspective. He's at least giving good feedback on different techniques that we commonly read about and rely on as amateurs.

I wouldn't worry about small stitch holes in any case. The greatest thing about this type of boat building, in my opinion, is that the materials are all forgiving. If you have a small hole left by a stitch, fill it with epoxy mixed with wood flour and it's sealed. If you have a big run in your fairing compound, spend three minutes with a sander and it's gone. Just about anything can be fixed.

BTW, I used the method that goes...stitch, weld with small fiberglass patches, duct tape behind seam, remove stitches, fill seam and stitch holes with epoxy/woodflour mix, tape seam, flip, remove duct tape and fillet/tape inside seams. It was the most annoying part of the whole construction.

-Dave
Modified GV13- Mad Russian

jacquesmm
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Post by jacquesmm »

MNagy wrote:The only way I see right now is to make fillets inbetween the stitches, then remove the stitches and fill in the gaps between the fillets.
Let's say that you use plastic ties as we specify, Build the inside fillet over the stitches, they will dissapear under the putty. Glass over etc.
Flip the boat, knock the corner down to 1/2" radius stitches included and tape over it. That's all.
Now, if you want to follow Devlin's advice instead of ours and use steel or copper wires it becomes complicated.
For larger boats on a jig we start outside with spot welds and remove the stitches.
I agree with you that it is a lot of worries about nothing or almost nothing. :) You'll see, it's easy.
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MNagy
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Post by MNagy »

So leaving the plastic ties in the fillet is not a problem? Devlin mentioned something about how metal ties expand and contract at different rates than the surrounding composite material, and if left in, they could cause damage over time. Why is this not an issue with plastic ties? Is it because thermodynamically plastic is closer to epoxy than metal is?

If plastic is okay to leave in, that would simplify things a lot.

Dave, were you using plastic or metal ties in the procedure you mentioned?

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Post by BillyV12 »

MNagy,

I built the V12 using the plastic ties. I did not use duct tape, because I could not get it to stick very well (dust or some other problem, good duct tape). Anyway, I did the inside fillets first, right over the zip ties. When I flipped the boat, I cut the ties flush, radiused the edged and when I filled in the remaining gaps, also filled in the little holes around the zip ties. They get glassed over anyway, so there is no way they can cause a problem.

This saved a lot of time of adding glass spot welds, partial filleting, removing the glass spot welds, finish filleting.......

Just the way so many other people did it, I figured it was okay, too.

See the pictures by clicking on the www. button below.

Hope this helps some.

Billy

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Post by jacquesmm »

MNagy wrote:So leaving the plastic ties in the fillet is not a problem? Devlin mentioned something about how metal ties expand and contract at different rates than the surrounding composite material, and if left in, they could cause damage over time. Why is this not an issue with plastic ties? Is it because thermodynamically plastic is closer to epoxy than metal is?
Exactly: you guessed it right. The calorific capacity of the metal influences the cure of the paint and "telegraph" it's shadow through the paint. Devlin is an artist when it comes to finish and he knows those things. However, with plastic, it's not a problem.
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Stainless
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Post by Stainless »

... It is really not complicated at all to build a PK78. ...
I don't mean to give the impression that it is a complicated boat to build. There just are lots of fiddly steps and I wrote them all down (as I warned everyone, I can be fastidious and particular :wink:).
... it is not necessary at all to use a jig to drill holes for stitches...
I agree the jig is not necessary, but it makes it idiot proof. I gave that job over to my 11 year old son and he did it just fine.

It may be that with real marine (boatbuilder grade) plywood you don't use all of the holes, but the fir "marine" plywood I brought home is stiff. I maybe could have skipped some ties in the middle of the large seams. Everywhere else, I was glad I had them at 4", and at the corners I actually had to go to 2" and less to pull things together nicely.
... For the seattops, I agree that they rarely fit. Dimensions should be taken from the assembled hull...
I would love to hear how others go about fitting seat tops. What are the steps? I still have to cut out the bow seat. I have some ideas, but no experience. Perhaps we should start a different thread on this topic (easier for others to find)?

On a related topic, I'm wondering about grain direction on the seats. In order to fit the wood I had, I set grain in the athwartships direction, but thinking about the stresses and supports makes me wonder if it should be fore and aft instead.
Sorry that you missed the width of the dagger board trunk, it is on drawing B131/5, bottom left.
I take full responsibility for missing the exterior trunk dimension. I just wasn't thinking when I did the first cuts on the mid bulkhead. I was fixated the interior dimension being 1" and managed to forget that it was made of 3/8" plywood. I didn't think hard enough about the lines on the bulkhead plan at the time... :oops:

I'm still thiinking about how to center the trunk straightly when installilng it though. For this little boat, being off a little bit won't matter, but a bigger, more performance oriented boat wiill require more care. What are the chances of showing where the cuts will be on the plan for the bottom panels? (Can you intersect the rectangular volume through the curved panels and then flatten the panels to show where the cut out needs to be?)
We will soon post an new tutorial that shows how we put some temporary drywall screws through the edge of a 3/8 bulkhead. There is a trick . . .
I'll be interested to see how you used drywall screws on the edge of a piece of plywood without screwing it up (so to speak :wink: ). drilling a few holes and running wire through them and cinching it up was easy and worked well.

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Post by st »

I would love to hear how others go about fitting seat tops. What are the steps? I still have to cut out the bow seat. I have some ideas, but no experience. Perhaps we should start a different thread on this topic (easier for others to find)?
I read a post where Evan suggested using cardboard and a hot melt glue gun to make a template for the seat. Thats what I did and mine came out almost perfect - I say almost; the template was perfect, my cutting was not. I made templates for every seat I have. Too easy.

Scott

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Post by Stainless »

I am by no means an expert, but my experience is still pretty fresh in my memory. As always, your mileage will probably vary. Here are my two cents on the stitches/ties discussion:
The only way I see right now is to make fillets inbetween the stitches, then remove the stitches and fill in the gaps between the fillets. I don't want to have to mess with trying to extract the stitching from an already finished fillet, be it with heat or any other method. Too much mess I think. Also, wouldn't it leave a hole through the plywood etc where there is no putty after the wire is extracted?
It wasn't a problem for me. I think that once you get into it, you'll see that it's not a problem. I'll try to explain in more detail what I did and what happened.

After pulling all of the seams up fairly tight, we taped exterior of the joint with masking tape. I used 1.5" 3M blue tape. Making sure that you get a decent seal around the wires can be a little fiddly, but I had my 14 year old boy helping me and it went pretty fast. What worked best for us was to rip the tape in ~4" lengths and work it in between each "stitch".

Then we flipped the boat back over--made sure it was not twisted/warped by the flipping--and painted epoxy where the fillet was due to go. I didn't epoxy before bending. I like the idea of the epoxy helping to hold the shape rather than being stressed with the panel (probably delusional). I let this cure until it wasn't at all tacky.

Then I mixed up some epoxy putty, put it in a bag, cut the corner and squoze out a 3/8" bead down the seam. I smoothed the seam with my smaller fillet shaper (but a tongue depresser would do just fine). I just worked "around" the wires. When I came to a wire, I made sure there was putty under it, maybe scraped excess off of it, and started shaping again on the other side of it. I did all of the hull seams and bulkheads.

The key here is to make sure that you have everything at a pretty low profile. It's all going to get buried in the big fillet anyway. Just make sure that you don't leave anything around that will mess up the large fillet. One key consideration is to not leave a mess on the sides. The sides is where the shaper will run, and if it's rough, it will cause waves/roughness on the large fillet.

I let the fillets cure about 18hrs and then removed the masking tape and pulled the wires out of all of the stitches but the ones at the corners. As you might have noticed in my other postings, I'm dealing with some pretty stiff plywood and I was nervous about the corners.

About two days later, considering the epoxy to be fully cured, I pulled the wires from the corners. No problems.

To pull the wires I cut them on the interior and pulled from the exterior. I had the boat up on sawhorses for this whole filleting process (I'm about 6"6" and I hate working on stuff on the ground). This made the exterior seams very accessible. To pull from the exterior I used nail puller pliers (for lack of a better name). For stubborn wires I put a piece of 1/4" plywood between the pullers and the hull to avoid marking the hull. All of the wires came out without any problem. I didn't have to heat them or do anything special.

I then put down the large final fillet--the 1" radius fillet. This was so much bigger than the first fillet that there just wasn't any problem. It went over the little fillet smoothly, and it was wide enough to fill almost all the wire holes as it went. Where it wasn't, I had putty and a spreader in my hand at the time, so I just filled them then. No problem.

For what it's worth, I think that zip ties probably work great with less stiff plywood. You don't have the removal step. You only have to build one fillet. I would caution however to drill the holes close to the seam in this case. You don't want the ties to interfere with shaping of the fillet--you want them well buried in the putty. It was my original intention to use zip ties but they ones I had weren't strong enough for the plywood I ended up with. Maybe next time.

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