PDA

View Full Version : Neccessity of Fiberglassing...



SculptorSam
03-05-2002, 07:15 PM
Hi everyone. I just finished adding the 3" fiberglass tape to all the edges of my first boat
this afternoon, a 9.5' pram, when it got me to thinking. The plans are by John Gardner
and they call for the tape explicitly. However, I will be using this pretty little boat for fishing in
small, protected lakes here in MN and I wonder if I really need that level of reinforcement
on the edges. I will not be encountering any large waves, only the occassional boat wake
and will only launch it when I will actually be using it. Other than protection against soil and
rocks on the shore (which I can appreciate) is what I just did really neccessary. Thanks
for all the opinions.

Sam

JimD
03-05-2002, 10:18 PM
Hi ScuptorSam, to paraphrase a versatile old joke, fiberglassing is 'optional' the way lowering the wheels of an aircraft before landing is 'optional' - just my humble opinion. Of course there's countless great sea going woodenboats with no fiberglass anywhere, but when it comes to the little plywood boats a lot of us are making the fiberglass is a very good idea. On my favourite stitch and glue kayak the entire hull is glassed, the chines double taped, and the keel from stem to stern triple taped or more, I can't count the layers anymore because of the patching required from paddling/beaching/launching in 'protected' waters. For the strength and protection it offers its well worth the time and money to fiberglass.

nevrdun
03-05-2002, 11:05 PM
That must be the pram on page 32 of vol.#1. I built one some years ago and had the feeling that the goopoo and tape insured that moisture wouldn't get into end grain of the ply. As you plan to do, I store mine on shore turned over, where it still has to contend with rain, snow, and that damn piddling black Lab from the other cove. I'd do the goo.

PugetSound
03-05-2002, 11:49 PM
I'm not familiar with the design but basically I would say that it is a matter of how you made up the joint in question. If the panels are fastened together by other means then the glass tape isn't really necessary. At that point, the tape serves as a way to seal the joint against water intrusion (which is bad for the edges of the ply) but also serves as structural reinforcement. For a 'stitch-n-glue' type construction glass tape is, of course, vital.

In any case, you can pretty well count on having most of the knocks and dings occuring at or near the joints. Things just sort of work out that way. If you don't think you need the glass, then go ahead and finish the boat without it. You can always backfit the glass reinforcing later -although the job will be more difficult then.

Keep in mind that in the vast majority of structural failures, the point of failure is almost always at a point of discontinuity and that point usually involves a joint.

SculptorSam
03-06-2002, 12:03 AM
I was thinking it was in part to seal the endgrain of the plywood as well. The fiberglass really did set up rock hard, it is easy to see why it is desirable. The plywood panels are epoxied to a frame, no screws so far. It is hard to imagine the joint failing though. I understand that epoxy mixed and cured properly will yield a bond stronger than the material itself. At any rate, it is done and I will surely reap the rewards.

Sam

JimD
03-06-2002, 02:17 AM
Sam, if the boat has frames, its worth your while to sink a few screws. True, the epoxy is harder than the wood but the joints can still break, if the boat gets suitably stressed the epoxy will just rip off the top layer of plywood that its stuck to. Screwing will prevent that.

Jim

wolfietuk
03-06-2002, 05:50 AM
Sam,
From what I gather this is a little stitch and glue plywood boat. one big reason for glassing is matinance. While a beautiful lapstrake hull to me, is worth the extra matainence tokeep it beautiful and functional, a simple ply boat is just that, designed to be simple and low matainence. (that is why I am building one) Is there a big reason you do not want the glass?

Rick

SculptorSam
03-06-2002, 09:31 AM
Rick- Aside from the time and expense (for an already starving artist that unwisely has found another addiction) of the fiberglass, my reservations are mainly aesthetic. When the hull was planed and sanded down for final preperation, it looked rather nice. Then, after fiberglassing, all the lines were interupted/distorted. I understand it will take a bit of sanding and building up with more epoxy to sand the edges fair again but I also know that the planes of the boat wil never be completely straight, there will always be the slight flaring at the edges the thickness of the tape. This is the kind of minor distortion that keeps me up at night.

I do intend to add a few screws, thanks for the image of my plywood separating and ripping off of the frame. That would be hindered by the glass as well I guess.

Thanks,
Sam

JimD
03-06-2002, 02:56 PM
Hi again Sam, glad to hear I am not the only starving artist with a new (expensive) addiction.
As for the aesthetics of 'tape lines', with a bit of careful sanding the edges will not show nor will the added thickness leave anysort of visible bulge caused by the tape. So set plenty screws as flush as possible, dab a little thickend epoxy over the heads if necessary and sand flush after curing, fiberglass the whole shebang and sand carefully before painting, assuming you are painting. Your boat will be a floating sculpture, an image worth at least the proverbial thousand words.

wolfietuk
03-07-2002, 05:52 AM
Sam,
I understand where you are comming from, it takes a lot of sanding. But glassing, done properly, will not distort the lines of your boat. Before the epoxy is completely dry roll on another coat thickened with an additive to make sand easier. (I used the purple stuff from west). Then go over the whole thing with long boards. There are some fairing compounds for the bigger imperfections.

It is a lot of work, but you will make your boat last longer with less matainence. As I said before, make your next boat a lapstrake hull, or some other designed to be made without glass. Also the epoxy is probably showing up imperfections in the hull rather than making the hull imperfect. Make sure you are not too resin rich on the conrners where there are multiple layers.

Are you going to carve a figurhead for your boat?

Good luck
Rick

NormMessinger
03-07-2002, 09:37 AM
Well, okay, not knowing the design or even being sure I understand the question has never stopped me before, so.... If by "around the edges" you mean reinforcing joints, like where the side and bottom pieces meet or where two bottom pieces meet then, YES you should tape the seams. The glass is part of the structure. Glass is hell-fer-stought in tension but not in compression. Thus, one layer outside and two inside has been specified in plans I've studied.

You don't suppose Gardner was just making work or supporting the googue industry by calling for tape do you? One way to ease the transisition from the tape is to cut off the selvage and pull out a few strands long ways. That frays the edge which then lays flatter than does the selvage. Then preceed as others have suggested to fair the transition.

Build it as designed and you'll be happier next year.

Best wishes.

--Norm

SculptorSam
03-07-2002, 05:54 PM
I do assume that if the plans specify something then there is a reason for it. However, I also feel somewhat free to modify plans if I will not be using a design for its intended purpose. Maybe this is a character flaw of us artist types. I am further along with the edges now and they seem to be tapering out nicely. To show how convinced I am, I'm even thinking about glassing parts where the plans don't even call for it!!

I had thought about carving a figurehead for the front but felt it would not quite be appropriate for this design. However, that is on my mind for a future project. Any suggestions on a good type of wood to use?

Sam

JimD
03-07-2002, 11:00 PM
Sam, when you get done carving the figurehead, maybe you can fiberglass it! smile.gif