Building My First Dinghy

[Wilyum]

I'm attempting to build a small 8' Opti and was wondering how many layers of FG cloth to lay down, the plan so far is a 6" layer of 6oz cloth on all the seams, overlapping in the corners, then 2 layers of 6oz on the exterior and interior faces of the hull. I'm using regular plywood, not marine grade, due to availability where I am so the main priority is to encase and waterproof this wood. Would 2 layers accomplish this?

[Benz]

I'd go up to 10-oz, since it's easier to use: the 6-oz is difficult to work with, IMO.
Can't comment on schedule, since you didn't say what thickness of plywood.

[mikereed100]

On my dinghy I taped the seams and put a layer of 10oz (it could be 6oz, don't recall for sure) on the bottom to protect while dragging up beaches and rocks. 11 years on and going strong. No real need to glass the sides, just a coat or 2 of epoxy to seal the wood.

No need for marine grade ply, as long as you use a good exterior grade and seal it well.

[psk125]

Two layers of glass everywhere seems overly hefty. You're not building a tugboat. Optis are supposed to race, and heavy Optis are slow. You do not want your kid coming in last every time because his or hers is the heaviest boat. Optis get damaged mostly by having their corners run into things (Docks, other Optis...) so two layers on the outside corners (one of cloth, one of tape) might make some sense. Plywood, as a material, is pretty tough. As others suggest, 10oz should be sufficient.
We built a 'quick and dirty' rowboat out of standard ply and had issues with funky-looking bends because of internal voids in the ply. Beware of really cheap ply.

[carlosproa]

Since you are in Canada, maybe Noah’s have better plywood? Make it as light as possible, use peel ply, get the best and lightest plywood you can afford.

[MicHughV]

A long time ago, I built a wood dink from some sheets of 4x8 marine plywood.

I never used fiberglass, but did use WEST SYSTEM epoxy to coat both the inside and outside. Also used the epoxy, with some filler to do all the edges, etc.

After the epoxy, I sanded and painted it....lasted forever.

[Wilyum]

Originally Posted by MicHughV

A long time ago, I built a wood dink from some sheets of 4x8 marine plywood.

I never used fiberglass, but did use WEST SYSTEM epoxy to coat both the inside and outside. Also used the epoxy, with some filler to do all the edges, etc.

After the epoxy, I sanded and painted it....lasted forever.

Love it! Im using a similar style small strong back which incorporates the sides, so far turning out well.

[Wilyum]

Originally Posted by psk125

Two layers of glass everywhere seems overly hefty. You're not building a tugboat. Optis are supposed to race, and heavy Optis are slow. You do not want your kid coming in last every time because his or hers is the heaviest boat. Optis get damaged mostly by having their corners run into things (Docks, other Optis...) so two layers on the outside corners (one of cloth, one of tape) might make some sense. Plywood, as a material, is pretty tough. As others suggest, 10oz should be sufficient.
We built a 'quick and dirty' rowboat out of standard ply and had issues with funky-looking bends because of internal voids in the ply. Beware of really cheap ply.

good point definitely dont want it too heavy, maybe two layers of 6oz glass just on the bottom and one layer everywhere else, im curious what certified racing optis are made of, what thickness plywood and glass, I know they are pretty strict on specification/weight etc.

[Matt Johnson]

I'll echo everyone else's suggestions - Glass only on the seams. Fibreglass on the bottom more often than not traps moisture in the plywood and you'll rot it out faster when you get a knick.

Just coat all surfaces with a few coats of epoxy.

[MicHughV]

I used 1/4" marine plywood....but using the WEST SYSTEM epoxy, you could use regular plywood no problem.
I built a small rudder for it and a center board in the middle athwartships seat, a small mast was fitted thru' the front seat. I don't recall the sail area, but it was not big. Mast was maybe 8' tall.
For sailing, it was really a one person boat. Rowing the dink, with one person at the bow, and one on the stern, it was barely manageable, but worked.
It sailed quite well, actually, calm lake water off course.
The bottom of the hull was fitted with some glued on rub strakes...I think 4 of them, so when you beach the boat, the sand doesn't scratch the hull.

This was my first attempt to build a boat....first attempt to build anything...but it all came out well. I had it for a number of years, but finally outgrew it, and went on to build a 38' sailboat...it was a fun project though...

[SailingHarmonie]

Have you not done a google search of "building an optimist dinghy"?

There are SO many resources out there. No reason you have to make it up as you go and get it wrong.

[Wilyum]

Originally Posted by SailingHarmonie

Have you not done a google search of "building an optimist dinghy"?

There are SO many resources out there. No reason you have to make it up as you go and get it wrong.

yes but most of those plans use marine grade plywood, which is scarce up here and expensive to order, so my priority was to coat it in glass to keep the water out,

Originally Posted by Matt Johnson

I'll echo everyone else's suggestions - Glass only on the seams. Fibreglass on the bottom more often than not traps moisture in the plywood and you'll rot it out faster when you get a knick.

Just coat all surfaces with a few coats of epoxy.

i'm thinking since its going to be used by kids its going to get banged up pretty quick and I'm not sure if epoxy alone on the bottom would hold up to the abuse it will get and keep the water out?

[MicHughV]

The nice thing about epoxy is that you can mix it with some filler and smear it along the joints between the edges of plywood, etc.
This does two things...it seals the edges of the plywood from water penetration and also provides a watertight barrier to the plywood as a whole.
I used the WEST SYSTEM epoxy, but other brands will likely work just as well.
As mentioned before, I placed 4 rubbing strakes along the bottom....essential a 1" x 1/2" strip of wood, these were glued and screwed into place with the epoxy.
These will take the brunt of most beaching. Should there be any abuse along the bottom, this can be epoxied again. Fiberglass will also abrade, so I don't see much point in using it.

Marine plywood is much the same as regular plywood, except it has both sides without holes, voids, etc, but these are easily filled with epoxy.

I'm a big fan of the WEST SYSTEM epoxy. They have a lot of different additives, etc. You can google it for more info. Once hardened, it provides a very tough outer skin.

You can coat the dink with fiberglass if you want using either the WEST or regular fiberglass epoxy, either will work, but it will add weight.

I used only the WEST and never had any leaking problems anywhere. You can thicken it into a paste and fill gaps, etc. It is amazing stuff.

[psk125]

When I went to research building Optimists for my kids, I was told that the Class measurer would not issue a certificate for a wooden boat. It appears that the USODA has softened their stance since then; Appendix A allows for the use of plywood/epoxy construction: https://www.optiworld.org/uploaded_f...f_2893_en.pdf:
Pretty finicky on the measurements and equipment though.

[ggray]

There's the original Optimist as designed by Clark Mills to be home built of plywood (loose measurements).

Then there is the International Optimist, raced by kids for many years now, same boat but with much tightened specifications. Low level competition, I can't imagine anyone protesting as you will probably have a heavier boat.

Oh yes, then there is another version sold, at least a few years ago. It may have had a double bottom or some other additional flotation, but they weren't class legal.

As long as the boat is not left in the water, stored under cover, and dings repaired promptly, you could save the weight by skipping full 'glass coverage. Just seal well with epoxy. Weigh the boat first and see how close you are coming to minimum weight. For smoother edges along the taped joints, cut the selvage off the edges, if you have already bought tape, or cut the strips from cloth. Peel ply or packing tape on the cloth edges can save you some sanding.