Thread: Nice rowboat, nothing fancy.

It's got nothing to do with Herreshoff's lines. It's entirely my own lines. I completely ingored Herreshoff's because, apart from being a fixed seat boat of reasonable performance, the Herreshoff boat lacked some characteristics I wanted and had some I didn't want.

However, it will still be a lovely looking boat. I made very sure of that when drawing the lines for it.

The Adirondack guideboats didn't have widely spaced frames. They were closely spaced, usually at around 6" centres. In terms of framing this one is, if anything, more influenced by the Norwegian faerings, with only three fairly hefty frames at 1 metre apart. The thwarts will be the Norwegian drop-in style too, tapered out towards the ends and notched around the frames.

Oh while we're on the subject of lines: the boat on the strongback is not actually the same as the lines plan shown in the OP.

What happened was that, as mentioned, I did change the Delftship model slightly to get a better looking stem profile, sheer and plank lines. This was a purely aesthetic change, but required redrafting all the patterns, which was a job I had put off until I got back into building in late September. So at the last minute, when it came to redrafting the patterns, I decided to take my last chance to change the whole boat.

It's still sort of the same boat though. What I did was lengthen it a foot, which is why the stem and transom are hanging over the ends of the strongback a bit. LOA is exactly 19 feet now (5.79 metres). I also pulled in the width of the bottom, first lap and sheer, and the second and third laps by slightly less. This gives the same wetted surface as the older version (or near enough to it), drops the upright metacentric height by about 50mm (making it the same as the Herreshoff boat) and gives a harder bilge above the waterline for secondary stability. Rowlock spread is down slightly to 1240mm but still adequate (and more than the Herreshoff boat anyway).

These changes give a predicted resistance 4% lower in the target speed range, with no change at low to moderate speeds, and while maintaining good carrying capacity and sufficient stability for mugs. It would be quite possible to go with a more radical midship section and save even more resistance, but in the interest of wider appeal I chose not to for this particular boat. It should still be pretty quick anyway.

So I was thinking about that trick of using a heavy plastic sheet over epoxy to bug-proof it and knock the lumps down. Having decided it is an effing good idea, the next thing was to figure out where to get suitable plastic sheet.

After checking around a bit, and drawing blanks in several places, I came up with what seems like a pretty good option: Bunnings plastic tablecloths. This stuff is available by the metre, in a variety of thicknesses from 0.1mm (4 mil for the Murricans) up to 1mm (40 mil). Surface quality is very good and the price isn't too bad. The price isn't too good either, but it should pay for itself in savings on epoxy, sandpaper and general stuffing around.

I went for the 0.5mm (20 mil) as a compromise between cost and weight. If I hadn't been concerned about blowing an extra $50 on a plastic tablecloth I would have gone for the 1mm, but I think the 0.5mm will do the job. The 0.3mm is getting a bit too thin, IMHO. This PVC sheeting isn't as stiff for its thickness as some other plastics, so the 0.5mm felt like a reasonable minimum for maintaining a degree of self-fairing. I figure I can always roller it out on both diagonals to help the fairing a bit.

Since the stuff is 1.37 metres wide (that's 4' 6" for Team America) I only needed 3 metres worth. The areas I want to use it for can come out of a half width, and I'll just butt join it for length (with tape on the join). This will allow me to cover both garboards and the bottom when glassing time comes around.

If you have any complex or compound curves, pre-fit your plastic and cut to size if necessary. If looking to just keep the finish clean and smooth, your plastic will work fine, but if looking to just prevent blush, you can run down to your other half's favorite fabric store and pick up some "rip stop" or other nylon or polyester fabric. It's cheap and works just like peel ply. Lastly, plastic sheeting often comes folded up, which sucks. Lay it out in your yard for a day, in the bright sunshine. Most of the fold will "fall out". If you pre-stretch the plastic, using a dowel at each end, tensioned between a couple of trees, this works better.

No compound curves on this bit. I'll just cut seperate panels for each garboard and the bottom panel. Obviously I wont be able to cover the actual chines themselves (they'll be slightly rounded over) but that's only a very small area and wont be difficult to sand.

What I'm aiming to do is get a good, clean flowcoat on the insides of the garboards before installation, then re-use the plastic to get a compact and clean glass layup on the outside of the garboards and bottom. Bote-Cote isn't supposed to blush anyway, but I'll probably wipe it down just to be sure.

I got the plastic straight off the roll, and put it straight onto a cardboard tube for transport, so there are no creases to worry about. We literally rolled it from the roll straight onto the cardboard tube, and I was lecturing them on getting it wrinkle-free. .

Just invented a nifty toy. It's probably not original, but I hadn't seen the idea before and figured it may be useful to somebody.

I was just doing the final fairing along the chine logs/bottom and was finding the severe twist in some sections was a bit of a nuisance when using a block plane. It didn't ride properly, and compensating by skewing it at a big angle to the direction of cut was rather awkward.

So, I figured a modifed version of the dastardly torture board might come in handy. This little one is only about 200mm long by 50mm wide (8" x 2" in Texas) and is made from 3mm MDF with some cedar offcuts glued on for guide legs. All I had to do was hold one leg against the stringer, and the diagonally opposite corner of the board against the chine (which ones varied according to whether I was working forward or aft of midships). Since the stringers are rebated to hide the edge of the planking, and since the planking is also 3mm, riding the guide legs along the stringer automatically sands at the correct twisting bevel.


mini_board.jpg


I used the block plane to get pretty close (about half a millimetre off the line), then used the board. If there were any lumps when sighting along the line, I'd either give the a bit more of a sand or hit them with the block plane again, depending (the plane can give better control and quicker results sometimes). Anyway, it took very little effort and the chine bevel looks slick everywhere.

I also had to touch up the stringers about 1.3 metres from the stern, where they were slightly more twisted than they should have been. This seems to just be a result of how the wood tends to twist naturally, so I planed the inside of the rebate down slightly so the planking will sit well.*

It all looks fair, so that'll do. After lunch I'll start spiling garboards.


*ETA: By the way, the plane I used for that job was my old Stanley 90J. These don't seem to be available any more. If you ever see one, grab it. If anyone ever tries to take it from you, boil their gonads in oil. These little planes are worth their weight in gold. They look like a toy (the photo is about half life size) but once you have one you'll find all sorts of uses for it.

pl4166.l.jpg

Ended up doing a clean up before I started spiling. Things were getting a bit messy. Spiling is underway now. This is as far as I got before deciding it was time to make a pizza. Will do some more once pizza is devoured.

First section is fitted to the stringer and marked for the chine. Second is just a basic strip clamped in place at the moment. Just looking at what I've got so far, I'm pretty sure the plank development from Delftship isn't going to match the actual garboard pattern off the boat. I was thinking maybe they would be a bit different, and it'll be interesting to find out how much difference there is.

The cardboard box in the second pic is my infamous box of wedges. One can never have too many wedges.

I have a similar rig for making rolling bevels on lapstrake repairs, usually on site (fix or refit a plank on the boat). I have a power plane with adjustable legs much like above and it's used to rough in the bevel. The only caution is to control the weight of the plane so it doesn't cause the plank edge to deflect, but this is fairly easy once you get a feel for it. A very sharp chisel and hand plane often finish up the job. Sometimes, if the frames are widely spaced, like on old Chris Crafts, I place a backing block under the plank, clamped to the nearby frames, to support the "live" edge. If you want to be a boat builder, you have to be a clever, inventive cuss. Good job Sumbloak.

Yes I roughed mine out with a power plane too. Just freehanded it, but left a fair amount to the line. Power planes are a bit brutal on jobs like this.

I was thinking about how to rig up a hand plane for this. The problem is twist. Down aft the planking twists through about 70 degrees in 6 feet. That means even something fairly short like a block plane wants to ride on the diagonally opposite corners of its sole, with the result that the blade wont sit on the surface properly unless you use a stupidly large bite (which causes other problems). The obvious workaround is skewing the plane to the chine to shorten the effective sole length. That helps a bit, but is awkward to handle and difficult to sight accurately for bevel.

What's really needed is something that rides on only three reference points. The ideal bit of trickery would be something with negligible sole length, like a spokeshave. Get one of those, add a trailing, single point guide behind it to stabilise it longitudinally without trying to rock around on opposite corners, and have another guide out sideways to contact the stringer. It'd be a pretty weird and horrible thing to do to an innocent spokeshave, but it should work.

Got the garboard pattern sorted everywhere, and just out of interest I flopped it onto the floor and did some quick measuring to compare it with the predicted shape from Delftship.

As I suspected might be the case, there is some discrepancy between the pattern and the Delftship development. The general shape from Delftship is pretty much ok, but the pattern from the actual boat has about 25mm less curvature over its length. This isn't a bad thing, since it'll mean easier nesting and less waste, but might be a worry if anyone was thinking of trusting the Defltship prediction completely (like for doing stitch and tape panels).

To be fair to Delftship, it was coded for commercial steel vessels originally, and the amount of face stress in my garboard (around 8%) is well into the danger zone for steel plating. I think Delftship may do better with somewhat easier planks. I'm expecting the predicted development for the sheerstrake will be close to spot on.

Anyway, the pattern lays around the boat very nicely, even with only minimal clamping. It all just seems to sit as it should without any dramas, which is nice. Must have done something right.

Just in case anyone else is playing around with Delftship, here's some pix of the prediction for the for'd half of the unrolled garboard compared with the actual pattern for the same area taken from the boat.

The first pic is a perspective view of the relevant area, with Delftship's developability check switched on. As you can see from the red, the forefoot is not strictly developable. This is because I incorporated a curve in the lower stem just for looks, without bothering to do full developability along the panel (because doing that is a PITA, at least with the free version of Delftship). The lines are faired to control curves at the edges of the garboard, and another control curve along the centre of the garboard. The panel just takes the resulting shape, which is fair but has slight compound curvature in the forefoot.

This doesn't bother the plywood in practice, but I think it's what is largely responsible for throwing a spanner in the unrolled panel prediction. Just something to be aware of if using this or similar tools. For reference, according to Delftship the edge stress in this panel is 0, maximum face stress is 8.07%, and area difference is near enough to 0.

Right, forget bloody PVC tablecloths. Useless as tits on a bull. What a waste of time, money and resin. I'll still have to scrape and sand the panels anyway.

First problem is that, in actual practice when using Bote-Cote resin, PVC has zero self-fairing ability. It might have some if you went for the 1mm thickness, but even then I wouldn't bet on it being great.

Second problem is that to get this to work, I think you'd have to make sure there were no air bubbles under the plastic as you rolled it out. In other words, it's not going to be a one person job. More like three people at a guess: two to slowly roll the plastic out and one rollering like crazy to get the air out as it goes. Trying to get air out after it is trapped is a recipe for disaster.

Third problem: the ply and the surface are going to have to be dead flat and perfectly aligned if you are doing more than one plank (or section of a plank) at a time. If anything lifts at all anywhere, you have trouble.

End result is that the roll of PVC, with half my resin stuck to it, is currently roughly bundled up and thrown under the strongback. I'll sort it out when it stops being sticky.

The pieces of garboard are currently sitting around with about half as much resin on them as they should have had, and will need finishing by scraper and sandpaper in the morning.

Conclusion: if you want to try this trick use very heavy plastic (far heavier than you think you will need) and practice on a very small area only, and get the air out as the plastic goes down, and use the hardest roller you can find. Otherwise, you'll be wasting your time.

PS: And is he going to try peel ply when he glasses the outside of the bottom and garboards? Stay tuned for more exciting adventures.

I'm just taking a brief coffee break from scraping down the pieces of garboard, and have had some thoughts (as you do).

First thought is about this plastic-on-top idea. To get it to work you really need either a glass layup that will hold a certain thickness regardless of pressure, or you need plastic that is effectively thick enough to act as thin planking (otherwise it wont self fair). Plastic that thick is not cheap, and in a boat like this the materials bill is quite low. If it worked perfectly it might be worth it, but I suspect it would only start to pay for itself if it could be re-used for several boats.

Also, I think a thin resin is far more likely to be successful than a thick one, just because you'd then have some hope of getting bubbles out from under the plastic. Bote-Cote actually has a thixotropic addiitive to improve coating on sloping/vertical surfaces, so is probably one of the worst resins to try this with.

If anyone else wants to try this I would suggest using a test patch of around 300x300 (a foot square). This will be wide enough to give you dramas getting bubbles out (good for the experience) and cheap enough to throw away. See how much work it takes to get it really perfect, because if it aint there's not much point doing this. That means totally fair surface from any angle. Then figure out how you're going to get an equally good result for the whole boat (or whatever you'll be using it on). See if that feels like it will be practical before the resin starts gelling.

One thing I can tell you: those articles that blithely say "just lay plastic on top and drag a roller cover across it" are not telling you the whole story. You have been warned.

Then there's surface keying. Having a plate glass finish on your pox is all very well, but you'll be coating your pox with something else on top, which means you'll have to scuff up that plate glass finish anyway. At this stage you might be wondering what the point is.

Anyway, I do have a very solid and very expensive drop sheet now, so I suppose it's not all bad.


Second thought is what alterrnatives are there, apart from just rolling the stuff on and sanding most of it off to get rid of the lumpy bits? Peel ply is one possibility, but that again relies on having a glass layup underneath to hold a certain thickness. Without that, the peel ply will simply be rolled down until it's in contact with the timber surface, meaning your film thickness is SFA. However, peel ply would keep bugs out of your pox (yay!) and should give a good surface for subsequent coatings or gluing without needing delumping (also yay!).

So, the second thought is that for pre-coating panels on lightweight boats like this, the best way to do it is probably to use a very light cloth or surfacing tissue with peel ply on top. That would give film thickness plus a good surface (assuming it doesn't go to hell in a handbasket). Having a thin glass layup makes a certain amount of structural sense too, since lightweight planking like this will be 3 ply with the face grain running along the panel. Adding some glass, even if not much, will add substantially to athwartships panel strength (3 ply is rather weak in this respect). The finished weight shouldn't be much more than just resin alone, and would in any case allow external glassing to be reduced while maintaining impact strength.

Worth considering, IMO.


Having gotten all that out of the way, here's a pic of a quickly scraped surface compared to one straight from the roller. Scraping is a lot nicer work than sanding. What I do is scrape the main surface without worrying about ends or edges. The reason is that it will need some (not much) finish sanding anyway to give a better key, and a sander tends to naturally take more off the panel edges. So it all works out if I just scrape to near the edge.

Right, so, after having had a chat at the bloke at Boatcraft Pacific, I have gone and bought myself some peel ply. I've also bought some slow hardener, so I might have a chance of getting the peel ply on before the reactor has a meltdown.

I may yet regret this, but peel ply is supposed to be good stuff when it works. I'm not quite at glassing stage yet, so I have a few days to ponder the all-important question. Namely: How many ways can this f**k up? If I spend a few days thinking about this question, I should be able to head most of the gremlins off at the pass. That's the theory, anyway.

We shall see.