Fixing up old and antique plywood racing sailing dinghies – International Cadet, Sabre, Sharpie, Cherub, Heron, Snipe, Lightning, Windmill, Fireball, TS16

On the Oz Woodwork Forum one of the members picked up a rundown International Cadet to fix up for his son.

We looked here with the emphasis of whether the sail boat is a keeper as a racer or if it should just be ditched.

This would apply to many similar racing boats. Plywood boats fixed up well have been very competitive in many racing classes. Manly Juniors, Sabots, Windmills, Thistles, OptimistsGP14s, Hornets, Fireballs, Herons, Merlin Rockets, Mirrors,  and many more.

Also have a good look at my Boatbuilding and Repair FAQ if you are looking for actual methods.

General Epoxy Methods – saving time and materials

Originally Posted by meerkat
We’ve picked up a cadet Mk2 to fix up for our son to compete (and be competitive in) next season. The hull is in good nick but the deck needs replacing.

What is the best way to proceed ?

eg take the deck off as whole pieces to use as templates for the replacements etc. the foredeck is in 2 pieces should we do the same or make it one piece (if we can get a sheet big enough) etc.

I’ll be getting some piccies to show the progress shortly.

Howdy Andrew,

First thing is to have a look at the class rules to find out what you can get away with. Check your class website.

For the International Cadet

For a competitive boat you should use premium materials – gaboon plywood for the decks.

Any framing to be replaced should be Western Red cedar – or the cheaper and lighter Kirri/Paulownia.

Glue and sealing the panels before fitting to the boat – epoxy. With coating make sure it is rolled out thin so it doesn’t add too much weight – three thinly applied coats – but don’t thin the epoxy – see my FAQ.

Also see my boatbuilding FAQ for info on wet-on-wet epoxy coating to save some labour and use of cordless screwdrivers for holding everything together while the glue sets up.

Am in a rush now – but will put more info up later.

Plywood Deck Joins

lightweight simple plywood SUP - stand up Paddleboard -

oh, yes – deck sheets are best of one piece as far as possible – but can be scarfed or have butt blocks under (we had to repair a sheet on the Puddle Duck Racer thread – scarfs are 6 times ply thickness, butt straps are from the same ply as the deck and their width 20 times ply thickness.

Don’t make the mistake of joining the deck on top of an existing beam thinking it will be stronger that way. That is housebuilding and it is a weak method. Plywood joins should never have beams underneath the join unless the timber is very wide. 

The correct method is to do the join between the beams with a scarf or a butt strap

Choosing between scarfs and butt straps.

Scarfing ply and timber.

Refinishing. Often this is an early conversation. But there are more important things to consider below

Originally Posted by meerkat

hi Mik

I read through your FAQs (might I say quite interesting and well put together) and I have a few questions.

Rather than using 2 pt polyurethane you recommened using epoxy with a poly topping (1) is this right ? The coats of epoxy are as thin as you can get them.

So i’m thinking….
the deck has 2-3 coats of epoxy with a coat of poly

inside has the 2-3 coats of poly (unless the epoxy is good there too). The problem with the inside is that there is some drips of epoxy that has been left there from a previous attempt to repair the deck as well as some black lines going across the boat and up the sides(why I dont know). so I’m not sure how that will come out.

The hull will be painted.

Oh yeah, after removing the lid there are a lot of holes left by screws, copper nails and yes even steel nails that have rusted & expanded and left holes like what screws do !

Whats the best to fill these with and will that affect the nails going back in ?


Hi Andrew,

You probably don’t need to put any nails back in. See the FAQs I gave the links to previously about
Cordless drill and,
Eliminating fastenings.

As far as gluing you just need to hold things together while the epoxy sets up – no need for permanent nails or screws.

As far as drips etc on the inside remove them by sanding – random orbit sander is good here – about 100 grit paper  – Never use paper more coarse than 100 grit paper for timber if you want the glue or paint to stick properly – be VERY careful not to cut away at the plywood veneers!!!

Look at Class Rules to help you decide if the boat is a keeper or a short term proposition

Is the bargain boat worth restoring? Decision and direction.

Before committing yourself to lots of epoxy coating it may be worthwhile reading the rules about what is a and what isn’t counted in the hullweight and then weighing the boat in that condition.

Also read whether lead (metal) correction weights are allowable and checking whether there are any fitted – remove them before weighing.

The decision tree goes a little like this.

If the boat is much more than 5kg over – it is a short term boat – it will be pretty well impossible to get it down to the minimum. Clean it up just as much as you need to get it on the water. Your son will race it for a year or so and then will start to have enough experience to make a better boat go well. Don’t spend too much money on this type of boat.

If the boat is only a kilo or two over it is a good boat if it is ready to go in good sailing condition. Just patch up to keep going, you can’t afford to add much weight in epoxy (or anything else) so just two very thin coats. Bote Cote have a product called TPRDA that thins epoxy out without destroying its capacity to protect the timber – use it to the max allowed – roll the epoxy out well spread. Adding thinners to epoxy is not cool for boat use.

If the boat is under weight by a kilo or more – you’re in luck. Provided the hull is stiff and fair (the chines and panels have nice geometric shapes – nice even curves, no hollows and bumps) this is the sort of competitive boat that is worth fixing up and giving the full epoxy treatment to.

So weigh it and see what you’ve got.

The relationship between epoxy varnish and paint and where to do each

2 pot polyurethane is only really for finishing the decks off – it gives a very strong surface with a good appearance, you would need 3 coats minimum. As an alternative you can use a good spar varnish as an alternative or paint the decks with a marine enamel.

YOu wouldn’t use any of the above inside the bouyancy tanks as their purpose is to give a good appearance..

If the boat is two or more kilos overweight an alternative for inside is to use Varnish or Everdure/CPES – a couple of coats. I don’t like Everdure/CPES much at all as you are paying excessively for a mix that is mostly thinners and it is nowhere near as effective in keeping water out of the wood as using epoxy, but it doesn’t weigh as much.

Epoxy coating is good from a wood and weight preservation perspective, but it will add a couple of kilos to the hull weight – even if you are careful.

If the boat is going to end up being pretty competitive with that added weight (ie no more than a kilo over minimum) then epoxy is a worthwhile investment – depending on how much labour is involved. Or just add the epoxy as you do work on the boat.

Paint and Varnish

How much to spend, how much work to do on an older boat?

The most common pitfall is that someone in your position gets all excited about fixing the boat up. They lose track of the fact that the boat is probably pretty close to sailable now. I would suggest doing the minimum you can get away with until you find out how commited your son is.

Another thing is not to overcapitalise an old boat unless it can be competitive – ie close to minimum weight, fair and stiff. Don’t add new sails, new masts to an old clunker. Maybe pick up some second hand sails from some of hte top sailors in the class if the ones you have are shot. Replace other things as necessary. Then see how enthusiastic your son is after the first season.

A cheaper and a better way to get a fast boat is to buy a good second hand racing boat that is doing well in its fleet than to completely re-outfit an older boat with new sails, mast, rigging and fittings. The resale will be better.

So weigh the boat and inspect it so you know whether it is a goodie.

If it is a bit heavy or out of shape – just do the minimum to keep it going – after the season sell it for what your bought it for and get a current competitive boat.

Big performance jump without spending much money – foils

One labour intensive … maybe three or four days … but very effective way to lift performance is to make some highly accurate and smooth foils – rudder and centreboard. They can then be moved onto a new boat when the time comes.

Shape is important so you have to use templates – contact me on
if you are after templates and an instruction sheet. I can help with some boats depending on class rules and foil design and allowance.

More on weight targets and restoration methodology – how much epoxy coating?

Andrew’s hull ended up weighing around 7 lbs LESS than the class minimum.

You have done very well with selecting the hull! It sounds like a keeper!

Epoxy is the go if you have weight to spare or the final epoxied weight will only be a kilo or so over. It gives a good racing life without adding much weight over time.

Best Plywood choice for lightweight – Gaboon (okoume, gabon, occume)

The different names are the same timber. Fit Gaboon ply decks in the thinnest allowed by the rules.

The join in the decks (along the centreline) is in the right place for most economical ply and the foredeck mid stringer is wide enough in your International Cadet for both to land on.

Replacing fibreglass tape on chines

If you are removing the paint you’ll probably have to replace the glass tape on the chines too. See the method for coating the bottom and the glass tape whacked down at the same time.

All happens in one process – wet on wet. Glass tape 50mm wide. Don’t round the chines too much – existing amount will be OK – but you want the last 3ft of the chines and transom corners dead sharp for clean water release – best to have a round there for the fibreglass tape to go on and then bog it out to a sharp edge with epoxy/filler powder mix.

Sounds like the hull is a good basis for improvements of sails and rig later on – but the first season with the existing ones.

Where to put the fittings on the boat.

There are probably some Cadet tuning guides usually available. Other types of common racing boats often have guides available. Most classes put them up on the net.

The Guide for your Class of boat may have things that you can do at this stage and also things like fittings placements on deck. You may need to work out where fittings will end up and glue the smallest possible pieces of 9mm ply (gaboon as well) under the decks to screw the fittings down to where you can’t use bolts (all bolts should be Nylock heads – it costs a bit more but adds hugely to the reliability of the boat.

Any screws or bolts should be dipped in epoxy to prevent water getting into the hull and it also increases the grip of the fastening manyfold (to remove an epoxied fastening you just heat it with a soldering iron for a couple of minutes).

How much epoxy (12 ft boat)

I would expect that you would use probably a little over 3 litres – so a 6 litre pack would make the most sense – or buy a 3 litre pack and be ready to buy a bit more as you need to.

You will need a kilo approximately of a powder modifier to add to the epoxy to thicken it into a gap filling glue. Only use the right high strength powder modifier. Fumed Silica or Wood Flour are the most common choices but epoxy manufacturers normally have a recommendation

Measure and mix the epoxy and hardener first before adding the powder/s!

I usually use mostly silica but add some wood flour to allow me to match the colour of the original timber. Silica is white … ugh … and pure wood flour is too dark. So I usually end up with about 20 percent wood flour in the silica. And it seems to make the silica mix into the epoxy better.

Also some TPRDA diluent for where you use the epoxy for coating the ply – it will help spread it out thinly. Don’t use the TPRDA in the epoxy where you are gluing or glassing. This is a diluent that doesn’t evaporate. It is not solvent. But it does weaken the epoxy bond. So never use for gluing or glassing which are structural processes.

I have also added a page to my site about what I did to get a geriatric Sabre in some sort of racing condition.
Getting an old Sabre Racing Dinghy into racing condition and how to stop racing nerves!

If the class rules give minimums and maximums sizes for different parts.

By the way – it might be worthwhile seeing if the class rules or class plans specify the minimum and maximum sizes of any of the solid timber parts. Use the minumum for everything except the width that the gunwales go out from the side of the boat.

Another place for large measurements if there is some weight to play with are stiffening stringers in the bottom of the boat. They are always just glued flat onto the bottom on one face only. Usually the width should be as narrow as the rules allow and the the height the maximum for stiffness. You can easily calculate the relative stiffnesses of different stringer configurations by multiplying the base by the height cubed.

The gunwale should be maximum to increase righting moment. In fact – it should be at the maximum from the shrouds to the back of the cockpit (where the crew will be – and minumum everywhere else to save weight.

Dealing with stained plywood

The Cadet had some stained timberwork – from water getting into the structure.  My mate Biting midge had a crack at a solution

Originally Posted by bitingmidge

Other than sanding, I’m a great fan of cabinet scrapers, which is a flash word for a bit of tin(steel really) which has been “sharpened”.

Hold with two hands and get all the stuff off in a pass or two.

If you need more info get back and I’ll try to find a few web references.



Ah midge – I disagree – this doesn’t happen often – so we can enjoy the novelty of it!!!

Plywood is made up of such thin veneers that the staining will go through the full thickness of the surface veneer. Scraping will make little or no difference. If it was a solid teak drawer fascia – I would be with Midge – but for ply – nah.

You can sometimes get a bit out with some oxalic acid solution. Don’t make it too strong and rinse the area well – but it won’t disappear. Oxalic is an acid so if you make it too strong it will weaken the wood fibres.

The only way to get it to disappear is to replace the panel 🙂

So Meerkat – have a bit of a play but you have to know in your water that it won’t disappear.

She is an old boat – and she will be a FAST old boat – but you can’t make her new again without replacing more of her.

I need to tell you about boatbuilder’s eye too. We all get used to eyeballing our projects from a distance of 6 inches. We know every nook and cranny, every mistake and defect. BUT NO ONE ELSE WILL EVER SEE THEM. They will be so impressed at the end result that they will never look over the whole surface from 6 inches away. You have to do a few projects before you realise just how oversensitive we all get to each one.

Let’s just say she has a lovely patina for an old boat.

Getting the timber bits to look neat and fair – gunwales

There was discussion about whether a plane, a router, powerplane of belt sander would be best.

Midge pointed out that he’d seen me use a belt sander for a similar job.

WELL, I was going to say …

The plane is the best choice for removing bumps in gunwales and other bits of trim.

I was only using the belt sander because I have a pretty good feel for the use of it – I can keep it pretty flat or even follow a bevel. And also the PDRs that Midge was watching me work on are boats to not be too precious about.

Still like ’em to look luvverly – but there is no timber trim to get on dead flat after the cleaning up with no changes in the glue joint width through crappy handling of the belt sander (which I CAN do on the right day as well!).

For goodness sake Midge – I’m not some sort of hand tool expert! 🙂

My method is do a bit, stop and review – one thing I have learned over the years is when to stop!!!! Perhaps that is the difference between the amateur and the professional.

I tend to use the biggest fastest most monster tool available, but stop to change to slower, more accurate tools at (usually) the right time.

The router would be a slightly risky choice if there are any subtle changes in bevel or irregularities in the deck or glue drips down the face of the timber the ply is being finished flush to. With the Cadet the angle will vary the whole length a little bit.

But then I’m not a hand tool expert!!!!

By the way spend a bit of time getting the edges of the boat fair – get your eyes low and look along each of the edges you have created. If you see any bumps in the curve set a handplane to cut very fine and hassle the bit away – sight frequently.

Keep an eye on the minimums and maximum sizes allowed by the class rules.

Rigging and fittings

This is where a lot of cost can hide. One of the reasons for choosing a competitive boat.

In general, there are two mindsets about how to set up boats. Adjustable everything or focus on essentials.

Given that you are looking at this page, you probably don’t really know which way you want to go.

I would very strongly advise avoiding the first mindset as you will spend far too much on your old boat and you will never get it back. Just focus on essentials.

It is very important to get mast rake right. Too far forward or too far back and it will be slow. So look for tuning guides for your class of boat.

Tuning guides often talk about maximum adjustablity. If you are a whiz already then you can make your own decisions. But if beginning you have to decide where to spend your focus. Compulsive fiddling with multiple adjustments will kill your speed.

These are the important controls.

  • Vang. Needs to be  easily reachable and powerful. Check class rules to see if maximum power is limited. Kid’s boats 6:1. Adult boats 8 to 12 to 1.
  • Cunningham/downhaul for luff tension. Adjustable mainsail, but just tie off the jib to average conditions on each raceday.
  • Outhaul. Critical on single sail boats. But I still leave the adjustment on the boom to prevent over fiddling. Simplest system is the Laser one.
  • Mast ram/lowers/chocks. On some boats these are used to control lower mast bend. Just set to averages and focus on sailing. If too much power in the lulls then let the mast go forward until you have the right power in the lulls.
  • Traveller. Once popular has largely been superseded
  • Jib sheet angle. This must be 10 degrees for boats that are quick and around 12 degrees for boats that slow easily in waves. No need for adjustment, but needs to be right. Cats a bit narrower.

Everyone will want to talk you into ball bearing blocks. Not necessary if the boat is temporary. Use thin Spectra lines through standard size blocks.

In general keep rope sizes to the smaller end of suggested sizes. There is a lot of reduced friction in smaller lines. Plain bearing blocks with properly sized lines will have far less friction than ball bearing  blocks with improperly sized line.

It will be too hard on my hands!

GET GLOVES. Or just sail a lot!

Cleats for sheets are OK for Jib; cam type quick release.

Only amateurs use cleats for mainsheets unless there is an effective traveller system on the boat which can be played. Cleated mainsheets lead to capsizes and general slowness in straight lines and corners; chuck the mainsheet cleats overboard.

Cleats for control lines should be the metal clam cleats. Like CL211 mk2. Below without the black thing.

They accept lines of 4mm diameter or less. Plastic clam cleats are useless as they wear out very quickly. The metal ones will last a very long time and are inexpensive. Relatively.

(bottom of his woodwork class at high school)

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