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Re: I'm a Boat Builder! G-L Ski Tow under construction!

Posted: Fri Jun 03, 2016 5:44 am
by Mark-NJ
I'm going to hold off on the drains for now. I can always add them later.

And I think I'm sticking with epoxy for adhering the sheets to the hull.

That said, I do have some questions about the attachment of the sheets:

First question: length of the screw.

- The side sheets are 1/4" thick.....I was thinking about using 3/4" screws, giving a good 1/2" bite into the sheers & chines.
- The bottom sheets are 3/8" thick....Here I was going to use 1" screws.

Do those lengths sound OK? I figure the glue joint is stronger than the wood itself, so it seems to me there's a little bit of "belt + suspenders" redundancy here to begin I can't see that much "hold" is needed.

Second question: bottom sheet attachment

The bottom sheets get screwed to the keel & chine. But do they also get screwed to the battens? If yes, are screws driven into all of the battens? Maybe just the center (of 3) battens? I've seen & read all variations.

Third questions: butt joints

- I'll need to butt join the sheets. On the sides, two layers of 1/4 is pretty thin. Using #6 x 1/2" seems almost pointless. Are screws even really necessary? I'll be epoxying the butt piece on the backside and encapsulating / glassing the exposed side. Seems to me the screws can only serve to weaken the plywood. Thoughts?

Last question: Filling the screwhead holes.

- The book says not to countersink the wood. So the screwheads....even if cinched down tightly...won't be "fillable" in the traditional sense. But it seems to me that the screws at the keel & chines will all be wetted / glassed over, then painted, since they'll be below the waterline. So my question: why fill at all? Won't the wetting & glassing fill them sufficiently?


Re: I'm a Boat Builder! G-L Ski Tow under construction!

Posted: Fri Jun 03, 2016 6:43 am
by DrBryanJ
In my malahini instructions it gives the size of screws that should be used and the spacing. I'm at work so I can't look it up right now. I did screw into the battens using the spacing provided in the instructions.
The malahini is one layer of 1/4 on sides. I screwed at the sheer and chine. At the butt joint, I backed it up with a second piece of 1/4 and screwed both pieces together as shown in "Building with Plywood"
The screws should be cinched down tight and filled. If you don't fill, the center of each screw will dimple in when wetting and glassing. I guess you can fill the dimples then, I just filled first.

Re: I'm a Boat Builder! G-L Ski Tow under construction!

Posted: Fri Jun 03, 2016 7:22 am
by hoodman
There should be a fastening schedule in the instructions. It has been helpful to me. I was able to clamp the butt blocks for the side planking on my build. If you look through my thread you'll see what I did a few pages back from where I am currently. My method for that doesn't work for the bottom butt blocks and I am using screws for those.

Re: I'm a Boat Builder! G-L Ski Tow under construction!

Posted: Sat Jun 04, 2016 6:17 am
by Mark-NJ
At first take, it may seem like I haven't read the instructions. That's not the case, I assure you.

Yes, there is a schedule in the plans. It was written long before modern epoxy existed, back when the glue needed the added help of screws.

With modern epoxy in use, where the joint will be much stronger than the actual wood, doesn't driving 1" screws every 3" into the chine seem a bit overkill? I was hoping that a more modern approach may have become commonplace, and I guess that's what I was asking about. Besides, perforating the ply to that extent can only serve to weaken the sheet, not to mention the strain of that much penetration into the chine & shear.

As for screws into the battens, the plans are silent to my 2nd question: do I screw the bottom sheet into every batten? Or maybe just the center batten?

Butt joint....the plans specifically calls for the use of 3/4" screws. A piece of 1/4" ply + a 1/4" backing block will leave an awful lot of screwpoint sticking out. Even if I use a 3/8" backer & a 5/8" screw, once the head cinches in deep enough to mud over it, there will be screwpoint sticking out. Moreover, the ply isn't 1/4" to begin's 6mm, so there's even less material thickness to work with.

I'm not trying to sound argumentative....really I'm not. And I'm very appreciative for the information that's being shared here. But these plans & the schedule were written a very long time ago. Before modern wood thickness, before modern epoxy, etc., etc., so I was wondering if there's an "acceptable, modern approach".

I want to build one boat once, and do it in such a way that I get good results.

Re: I'm a Boat Builder! G-L Ski Tow under construction!

Posted: Sat Jun 04, 2016 9:50 am
by gdcarpenter
I may well be the odd man out here, but I used virtually no screws in my hull ply. In the few places that I couldn't somehow clamp the hull ply to the framing I used temporary screws that were removed after the epoxy set up.

Screws do have holding power because I am restoring a 15' 1957 Century 'Palomino' that has held together for over 50 years with screws, albeit in 7/16" mahogany and not 1/4" ply.

I epoxied my hull to all frame members, including battens. For what it's worth I have trailered my ZIP well over 6,000 miles, had her in the water for a month at a time, pounded her in some heavy waves, made a whole bunch of launches and retrievals, and she seems as tight and solid as the day she was launched.

With a residential carpentry background I have seen countless drywall screws 'move' after years of temperature cycling and wood movement and personally see screws more as a liability than an asset.

Not to mention having to 'fill in' all the (hopefully) recessed screw heads, a PITA in and of itself.

Re: I'm a Boat Builder! G-L Ski Tow under construction!

Posted: Sat Jun 04, 2016 10:32 am
by Mark-NJ
I've ready of your "no screws" in other post, too......and I may wind up being "the other odd man out" with you.

I may run a few screws in the "flat area", and I will certainly be screwing up forward...but I just can't see setting a screw "every 3 inches". And, in time, I think the chines & sheers will be stronger if they're not being strained every 3 inches.

Re: I'm a Boat Builder! G-L Ski Tow under construction!

Posted: Sun Jun 05, 2016 4:56 am
by jamundsen
My MonteCarlo has very few screws and I've managed to find them all when fairing and planing. I used Raptor staples for most of the laminations.
I didn't see much benefit in using screws in 4 mm ply.scrwes were used during framing. I found nails to be a total waste. For frame alignment drill holes for bolts prior to epoxy.

Re: I'm a Boat Builder! G-L Ski Tow under construction!

Posted: Mon Jun 13, 2016 1:09 pm
by Mark-NJ
Moving forward!

I woke up early yesterday and drove 2 hours to S. NJ to get Meranti Hydrotek plywood from a marina. Got it home & got to work!

I've been having nightmares about getting the skin on "just right", but it seems that taking my time to get the fairing right paid off & made the installation a breeze! Clamps & a few screws to let the epoxy harden, and the first piece is on! Now I REALLY feel like a boat builder!

I left the sheet a bit oversized and will trim it down tonight. I hope to get the other side on tomorrow.


Re: I'm a Boat Builder! G-L Ski Tow under construction!

Posted: Sat Jul 02, 2016 11:29 am
by Mark-NJ
Lots of progress being made! All side-skins are on, as are the aft bottom skins. Front hull skins are cut & fitted, but I'm out of epoxy, waiting for the UPS man to deliver more.

One thing that I've never been thrilled about is how little surface area exists on the stem for the hull to attach to. So I cut some "sisters", screwed them in place and continued the bevel, so the skin has more to land on.

I'll glue & encapsulate these when the epoxy arrives.


Re: I'm a Boat Builder! G-L Ski Tow under construction!

Posted: Tue Jul 19, 2016 7:04 pm
by Mark-NJ
Well, things are moving right along!

The front hull skins are on....getting 3/8 ply to bend in 2 planes is quite a process, but it's on. The starboard side was easier, because clamps had access. The port side was tougher, as you all know.


Lots of epoxy & screws....


The meeting joint where the 3/8" bottom sheet & 1/4" side sheet come together at the chine was a bit of a struggle, but I was able to fair then together and put a skim of thickened epoxy over the joint. After sanding, it's completely smooth....eyes closed, my hand cannot feel any transitions at all. Yes, it darkened the wood, but the hull will be painted, so it doesn't matter to me.


Now I'm reading up on the next step: fiberglassing. One thing that I'm learning is that the nice sharp edge at the chine & transom need to be rounded over, because the glass doesn't like a sharp edge.

So the question is: how "round"? Do I just break the edge a bit, or do I need to run a round-over bit down the edge?

Here's the sharp edge:


Lastly, I'm very happy with the straight, knife-edge symmetry of the bow where the sheets came together. That said, I'm thinking about installing a keel strip to run up the bow to add some protection from beaching, etc. Should I grind this nice pointy bow "flat" to make a surface to receive such a strip? Or should I fabricate a strip that has a "V" back that will mate up with the existing bow's edge?

Bad pic, but here's the bow right now. Hard to see, but it's a perfect knife edge...


Re: I'm a Boat Builder! G-L Ski Tow under construction!

Posted: Tue Jul 19, 2016 7:27 pm
by mrintense
Nice work Mark, congrats on getting this far. It is a challenge to get those skins down isn't it?

I went through the fiberglassing stage a bit under a year ago and here are my observations for what it's worth. The round over is necessary because the fiberglass cloth won't take corners well (if at all). Most of my corners were rounded as if hit with a 1/4" round over bit on a router. This includes the transom trailing edge.

The glass laid over these curve just fine. After I finished glass the hull, I used thickened epoxy to build up a sharp edge on the transom. It seems tough enough as long as you don't hit it with something like a hammer. When I say sharp edge, that is relative. Too sharp and it will chip off, so a very small amount of smoothing (1/32") should be fine.

As for the bow, I too really liked the sharp leading edge, but knew that the first blow to this would break it. Furthermore, you need to wrap the fiberglass around the bow leading edge anyway, so it will need some sort of rounding. I ended up flattening the leading edge to a point approximately 1/2" wide, then bonded two 1/8" strips of oak which were subsequently rounded to probably 3/16" This was then glassed over. After paint it looks just fine. If you decide to later add a cutwater, then perhaps you could dispense with the oak. But I think the exposed plywood edge would be risky.

One thing I would highly recommend is the use of thin foam rollers when you start glassing. They are a wonder and aid immensely in keeping the amount of epoxy on each layer at a minimum. Glen L's book on Fiberglassing is also very good information and it's reasonably priced.

Good luck with the next phase.

Re: I'm a Boat Builder! G-L Ski Tow under construction!

Posted: Tue Jul 19, 2016 8:17 pm
by Mark-NJ
Thanks for the info! Greatly appreciated.

The idea of flattening my "perfect bow" seems a shame, but I suppose it needs to be done.....and I like your idea of setting an oak strip(s) on it. That was what I was thinking. And it needs to be rounded for the glass anyway, I guess.

To be clear, you set the strips...then glassed over them while glassing the hull, right? I was torn between that, or glassing first, then setting strips. Will the glass lay OK over a keelstrip like that?

I have the Glen-L fiberglassing book & video, too......both have been helpful.

I suppose I'll hit the sharp edges with a sander and try to create about a 1/4" roundover....

Re: I'm a Boat Builder! G-L Ski Tow under construction!

Posted: Wed Jul 20, 2016 2:19 am
by mrintense
Yes, laminate the strips first, then rounding, and then glass over them. As long as the radius of the round over is sufficient, the fiberglass will lay over the leading edge with no problems. You can pull it taught as you wet it the first time. Experiment on a piece of rounded over lumber and you get the feel for it very quickly.

As for the other edges, please feel free to get other opinions on this. I was less concerned about round over on the sides because I added spray rails full length. The spray rails were added AFTER fiberglassing and themselves DO NOT have fiberglass over them, only epoxy and paint. I am not sure if this is the best decision but I wanted to maintain relatively sharp corners on these to keep the spray deflected downward and the consensus seemed to be that these are considered somewhat sacrificial (although I will only repair them, not replace them if ever needed)

Re: I'm a Boat Builder! G-L Ski Tow under construction!

Posted: Wed Jul 20, 2016 3:41 am
by Mark-NJ
I've been debating spray rails as well....and I'm thinking the best way is to add them after fiberglassing, and only epoxy & paint them. From what I read, they're fairly essential to a "dry ride". If it matters, this boat will see only occasional use on a calm lake in Maine.

I guess the next order of business is to get working on the keel strip. I have some long strips of white oak, so that's good...

Re: I'm a Boat Builder! G-L Ski Tow under construction!

Posted: Wed Jul 20, 2016 8:41 am
by rbrandenstein
Another option on the stem is to add hollow back stainless steel rub rail.
I call it my poor man's cutwater.
Since the stem was rounded to take the fiberglass cloth, the hollow back SS rail fit perfectly and was pretty easy to form and attach.
I think I also rounded the edges with a 1/4" router before glassing.

Finally, if the lake is calm, you probably don't need spray rails, but if your lake is pretty busy with wakes and chop, you might appreciate the spray rail to keep you dryer. I added rails after the first summer. It would be a lot easier to add now rather than later. And, I would do what you suggest: glass the hull, then form, encapsulate, and attach the rails with caulk, not epoxy. (You probably should steam and bend them to shape first. )