Hull glassing process clarification for a newbie

[TooManyHobbies]

Hello,

 

This is my first post on this forum so my apologies if these answers are easily found elsewhere. The instructions were a bit vague on this part so I wanted to consult a wider audience.

 

I'm working on a SD10N for my first boat and I'm loving the build so far. I've made what I think is decent weekend progress since July. Today I finished laying all the inside fiberglass at the seams and after a few more steps I'll be working on the outside of the hull.

 

As this is arguably what will make or break the boat I'm wanting to make I do it correctly.

 

1. If I plan to glass the outer hull do I still need to apply fillets and fiberglass tape to the outer seams then lay the sheet of glass on top of it afterwards or does glassing the entire bottom take care of the need for fiberglass tape on the seams?

 

2. Before applying the sheets of glass do I need to have a wet layer of epoxy present as a foundation?

 

Also here is the latest picture where the inner seams have been glassed. Not the cleanest job, but I'm proud of it for my first build. I'd love to here any constructive advice.

 

Thanks in advance!

[Paul356]

1.  I would still apply the fillets and tapes outside, then sand the tapes fair into the plywood.  That's my thought, others may differ.  But my thought is that there is o reason to skimp in strength and integrity at this point.

 

2.  Put the fiberglass cloth on bare wood, then unthickened epoxy on top and squegee or roll for a smoth attachment.  The cloth will turn clear as you adhere it to the wood, rather magically. 

If you put a layer of epoxy on the wood first, you run the risk of the cloth floating and not adhering to the wood.  Once the initial coat is on (top of) the cloth, you apply additional 1 or 2 or 3 filler coats on top, as needed,  to fill the weave and end up with a smooth surface on your cloth.  If you apply it hot (lower layer stiff but not fully cured), you can move pretty quickly.  If you are going to paint, you can add some thickner to the fill coats to help close the weave.  That's a trick I learned from Alan at B&B.  Thickened epoxy may interfere with the clearness if you plan to finish the bottom bright.   Main point, tho:  first layer of cloth goes on to bare wood, then coat and fill from the top.

 

 

[TooManyHobbies]

I appreciate the info Paul. That makes a lot of sense and also confirms my suspicion about using thickened epoxy as a top coat. As you suggested I'm planning to paint so that will work fine. 

 

Thanks again.

[Don Silsbe]

I will apologize in advance for adding confusion to your plan.

 

Why are you glassing the outside?  Three coats of epoxy and taped seams is all you need glassing just adds more weight.  It all depends on the service the boat will be subjected to.  If it is going to be dragged o to rocks a lot, then I’d go with Dynel, but that will really add weight.  Some coat the bottoms with epoxy thickened with graphite powder.  
 

 

[TooManyHobbies]

Honestly as I first time builder I was following suggestions in the designer recommended video. The instructions gave a decision of glass or just epoxy and tape, but glass seemed to be the more common path and what was shown in the video.

 

This boat will be used as a small sailboat for local lakes and not as a tender.

 

I don't plan to be leaving it in the water overnight, but I can imagine it will see it's fair share of scuffs and dings, so the extra protection of a layer of glass seemed appealing.

 

 

[Peter HK]

2 hours ago, Don Silsbe said:

glassing just adds more weight.

Not that much

Light cloth (6 oz/200gsm) for a spindrift would be about 3 sq m by 200gsm = 600gm. The resin weight is about the same for a hand layup so that adds up to 1.2kg (2.6 lbs). Proportionally less for lighter cloth.

I've glassed a few dinghies and it does make them more tolerant of abuse. Pros and cons I suppose.

Cheers

Peter HK

[Alan Stewart]

I'll throw in my 2 cents. If you're going to sheath the outside of a spindrift technically you should have at least 10 oz on the joints same weight as the tape so there is the same weight cloth on both sides. The minimum for 6mm ply for the joint to be as strong as the ply is 10oz. So if you use a lighter cloth like 6oz or even 4oz then you need to tape the joints too. 

 

Personally I think the biggest advantage of glassing the outside is to eliminate the fairing in of all the tape seams on the outside which significantly reduces sanding for a smooth exterior. Though how much less sanding i supposed depends on how good a job you do. It could easily make the job harder than just fairing in the tape if you do a messy job. But If you have to use tape too then that benefit is a bit negated and I'd just use the tape. So it's really 10oz cloth or 10oz tape. If your argument is you want extra "abrasion resistance" on the bottom (which glass doesn't really provide much of) then you could just put the 10oz cloth on the bottom panel and overlap the chines 1 1/2" as the tape would and leave the sides bare. Then you just need to add a piece of tape up the stem and on the transom edges. That would be a lighter choice but still with tape seams that need fairing in on the topsides. 

 

A better method for adding abbrasion resistance is to add rub strips out by the chine (pic below). Graham mentioned recently he prefers these. Bronze works for them and you can drill and tap holes and screw pieces on from the inside of the hull sealed with butyl rubber caulk so they can be removed for refinishing. Or glue a strip of wood to the outside and cap it with a piece of metal or uhmw with fasteners isolated to that outer piece of wood. But for a sailing dinghy that won't be pulled up on a beach all the time i probably wouldn't bother. 

 

When glass sheathing 10oz I usually just wet it through the glass over bare ply as Paul said but the sides especially on larger boats are harder because the surface is vertical. In that case rolling epoxy into the wood first helps speed up the wet out process a lot. If you do wet the ply first do it with a roller for an even coat before rolling the glass back out so theres no chance of puddles under the glass. It does speed up the wetting out process which can help a lot if you're glassing in colder temps like below room temp. Higher than room temp i'd just pour it on the cloth over bare ply. 

 

We like to spread a microspheres and epoxy mixture over the glass a few hours after wetting it out once it gets tacky so fill the weave in one step. This mix is lighter than straight epoxy and sands a little easier. importantly, we don't use cabosil for this as that would be very hard to sand. 

 

 

[Don Silsbe]

The trimaran I just built (for someone else) called for 4 oz taped seams with a sheath of 4 oz over that.  The thin fabric “tape” required little or no sanding of the edges.  I cut the “tape” from a bolt of glass cloth.

 

Instead of microspheres, I use West 410 filler mixed 2:1, epoxy:filler by volume.  This is applied with a 3/8” shaggy nap roller.  I learned this from an OffCenter Harbor video by Russell Brown.  This is now my go-to method.  Here’s how it looks on my masthead float.

And here’s a link to the video.  I don’t bother with the foam roller.

https://www.offcenterharbor.com/videos/mastering-epoxy-russell-brown-part-8-fill-coating/

[Don Silsbe]

@Peter HK— The real weight addition with a glass sheath is that the thickness of the glass cloth requires more epoxy to fill it up. It is the weight of the additional epoxy that adds weight, not the glass itself.  With Dynel it is worse.  In addition to the epoxy filling the gaps in the weave, the fibers actually absorb the goo.  It sucks up a lot of epoxy, but it makes for a bulletproof skin.

 

@TooManyHobbies—My Two Paw 8 has taped seams and three coats of epoxy inside and out.  She’s 5 years old, and doing fine.  In the second photo, I’m adding a rub strip of ash.  This came unglued after one season.  Since then, I’ve replaced it with an epoxy-soaked piece of nylon webbing.  I included it here so you could see how the bottom is holding up without a sheathed bottom.

 

To me, the most important thing you can do for durability is use a two-part polyurethane paint, inside and out.  The cost of it is staggering, but it wears like iron.  I used to get a lot of paint scuffing from nesting, when I first painted Two Bits with Britesides.  This doesn’t happen, now that I switched to two-part poly.

 

And don’t apologize for asking questions.  Yeah, your question might have been asked a few years ago, but good luck finding it!  Besides, we love giving free advice.  Just remember that the advice we give is worth every penny you paid for it.

[TooManyHobbies]

Thanks guys, you've all given me a lot to think about and a few more options to consider. 

 

Thanks for the pro advice.

[Don Silsbe]

“Pro advice”— HAH!  The problem with asking for advice here is that you get too many answers.  (Probably a good thing.) Now, you have to sift through the mire and decide for yourself.  It’s all good.