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Spindrift 11N, Fiberglass question


BryanLee

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Hello, I just received the plans for a Spindrift 11N we will be building over the winter to use as a tender for our sailboat in the PNW for a while and hopefully to Mexico and beyond someday. The one we have now is a little small to carry me, my wife and two kids safely, at least if they grow anymore, which they seem to be reluctant to quit doing...

I have built a few small boats before, two CLC Kayaks and a couple small duck hunting layout boats from 1950s plans, all for other people. My first boat was for myself, but was built for less then $100 and was lots of fun but did not last very long.

Anyway, to the point, all 4 of the nicer boats I built where all made with Okoume plywood, with fiberglass covering the outside of the hull. I just assumed the Spindrift would be the same, but reading over the plans, I figured out the plans only call for glass tape on the seams, and epoxy coating only on the rest of the panels.

So my question is this... We tend to land the dingy on rock beaches with barnacles and such, and with the high tide ranges need to pull it up quite a ways before going for a hike or something. In short, I think we are fairly hard on the bottom of our dingy and I do not think it realistic to think we can be more careful all the time like we could be if we launched from a ramp for dingy races as such. How would just the plywood without glass hold up to the abrasion of rocky, barnacley beaches and kids rowing the dingy around and bumping into rocks and such?

Weight is also a concern, as we need to be able to haul this thing up on the bow of the boat without too much trouble. Yes we can do it one half at a time which will help, but I also do not want to add so much weight we can barely manage the loading / unloading the dingy in wind and waves and stay safe.

Has anybody looked at glassing the hull and may be using thinner plywood? Perhaps only thinner ply on the topsides, but not hte bottom panels? The glass and ply combined to give the same straight as thicker ply, but the glass to add abrasion resistance and thinner ply to lessen the increase in weight?

Or will the ply/epoxy without glass perform better then I fear and I should just stick to the plans?

Any advice or experience with these issues would be greatly appreciated.

Thanks!

Bryan

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Hi Bryan

In your situation I would glass the bottom for abrasion resistance.

Extra weight would approximately be- 5 sq metres by 330gsm (6oz) equals 1.6kg, plus same weight of resin is just over 3 kg (6.6lbs). If you could find marginally thinner ply, say 5mm instead of 1/4 inch (6.25mm) then that would probably work. I'd probably stick with 1/4.

Peter HK

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Thanks for the detail on the fiberglass weight, I had looked a little to see if I could find out just how much more that would add but had not found the numbers yet. 6 - 7 pounds sounds worth it for the extra protection, that is probably the route I will go.

Thanks!

Bryan

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Hey Bryan

It's even less than the 6 lbs.

I mistakenly used 330gsm which is actually 10 oz, so the weight is only 60% of my earlier estimate, ie 4lbs, if you use 6oz.

It's early in the morning here in Australia- must have been low caffiene levels :)

Peter HK

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If you could find marginally thinner ply, say 5mm instead of 1/4 inch (6.25mm) then that would probably work. I'd probably stick with 1/4.

Hmmm, I didn't know you could get 1/4" okoume or meranti.  There doesn't seem to be any quality marine ply made in the USA.  The suppliers I have checked only have 4mm or 6mm and of course thicker ones.  We keep a small supply of 6, 9, 12 and 18mm at work.  But we call it the nominal fractions of inches for our customers that don't use the metric system  ::)

Another option Bryan, would be to add some longitudinal sacrificial chafe strips to the hull.

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Hi Bryan,

I am building (when I get back to it) a Spindrift 10N on Vancouver Island and had some 5 mil okoume ply shipped from Noahs Boat Building.  The 5 mil is 6 lbs per sheet lighter than the 6 mil and is still five-ply.  Stitch and glue kayaks are often built with 4 mil ply but it is only 3 ply and I think would lack stiffness and strength.  I too intend on using fibreglas cloth (probably 6 oz) on the bottom and maybe the whole hull to increase toughness.    Graham has endorsed the thinner ply with the suggestion of maybe adding bottom stiffeners on the rear section of the boat if it is felt to be necessary.  My boat is currently wired together and collecting too much dust.  I am itching to get back to it soon.

Bruce

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Thanks for the input, I have seen Noah's Marine mentioned here, but had not looked into yet. Their prices are good enough compared to the local supply that shipping charges just might make it worth while, and they carry MAS epoxy which I have used before and really like but can not get local anymore that I am aware of. Hmmm... 5mm does sound like a possible way to go. (Wish you had yours done so I knew how it turned out  ;D ) 

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Don't use Dynel if you want to keep the weight down- it soaks up epoxy like a sponge- gets much heavier than glass would be. Much more abrasion resistant, but would cost more in weight in this case, then you would want to spend.

If it were my boat, I'd glass just the bottom with a 10 oz cloth, after taping of course. That would give you a nice balance between added weight and added abrasion resistance.

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Dave said

Hmmm, I didn't know you could get 1/4" okoume or meranti.  There doesn't seem to be any quality marine ply made in the USA

I was assuming you could still get 1/4 inch. Looks like the USA will be forced to adopt the metric system in the end ;)

Interestingly, I find 6mm ply from different suppliers varies quite a bit and seems to be getting thinner- the latest batch I had was 5.7 mm.

Peter HK

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lol- I think the US is ALREADY using the metric system. Regular US made, US dimensioned ply wood AIN'T what they call it. It's ALL undersized dimensionally. I suspect they build it to metric sizes and TELL us it's 1/4, 1/2 whatever. But if you cut a 3/4 dado for a 3/4 ply , it'll be too big. They even have started selling special router bits for the "new " plywood'

On top of that, the US made fir marine plywood I've seen in the last five years or so is pure junk. Last time I went to get some (100 mile round trip), to recut some frames for a Cross 34, I refused to buy the stuff and drove 130 miles one way the OTHER way from my house (AND into Houston) to get Hydrotec. Didn't need the Okume for that job- just good solid plywood. Wound up with some nice 9 MM ply.

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Yeah- I know that logically- but it sure SEEMS to oddly wind up close to metric.

And that's also a sign of the cheapening of US plywood. Thinner plys mean less wood used, which means more money per sheet. And believe me, they aren't using very big trees these days. Our place in east Texas is in the heart of the pine belt, with three mills close around- Champion Plywoods are the main source of jobs there. Another major is Temple-Eastex, now Temple Inland, owned by Time Magazine oddly enough..

It's really irritating, particularly to folks doing home repairs. I redid a kitchen once at our farm up in east Texas. Had one bad place on the plywood underlay. Had to sand down part of an oversized sheet so it would be the same as the old. Or relay the entire floor with new. Couldn't just buy a 1/2 inch (or whatever it was) that fit.

Structural timbers are the same thing. The house was built in 1956, using stock lumber yard 2 x 4 studding. You think they were anywhere close to 2 x 4s available today? Wrong!! Had to buy 2 x 6 and rip them to fit them into walls cause the "new" sizes were too small.

It just irritates the daylights out of me to have to do things like that.

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I believe american ply is still to english standard and then it is sanded down with a panel sander which makes it nominally thinner than spec.

I don't know the exact specs, but it seems to me that "1/2 inch" ply or OSB actually has a different fraction stamped on it. More like 15/32 or some such number. That could be due to sanding or because it's made that way. I know I glued up two layers of "3/4 inch" and with the glue line, it came out the same thickness as nominal 2x (1.5 inches). Seems to me that both were 1/32 or more under 3/4 inch. I have some 18 mm ply sold as 3/4 inch and it's nearly a full 1/16th under 3/4 inch.

On the bottom protection, I glassed the bottom on my Spindrift AND put a strip of Xynole on the V bottom forward of the keel.  Have had no problems, but I've not grounded either.

On your keel edge, instead of the metal strip, you might try Tom Lathrop's epoxy impregnated rope trick.

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