My first IOM build

At some point one need to take the jump and I did today with the help of a friend of mine.

I am a sailor and my strat experience is more gluing and fixing then building so any comments & advices welcome.

The boat:
We bought the mould of this IOM design from a friend of mine so I don’t have the plans but I do have all the measurements to install everything as part of the build.
The moulds being elsewhere for now but having hull and deck #1 with me for what was supposed to be boat #1 they came way too heavy at 586g for the hull and just over 300g for the deck - completely unusable for a competitive boat so I decided to use them as a male plug.

I got the idea and inspiration from reading posts from claudio and others

So my friends installed a wood structure to further strengthen the hull and deck and then gave it to me to sand down and get it ready. A bit of filler a bit of patience and a lot of elbow grease and the hull and deck are ready.

Next phase we sticked packing tape as used before by claudio ensuring overlap but not too much see photos.

next phase was the strat.

After much debate we decided to go for first hull with 2 layers of 135g (4oz) twill fibreglass cloth. I think 3 layers would have been better but agreed to go with 2 for see the weight and strengths.

I had pre-cut the layers of fibreglass and each weighed c60g (incl. excess cloth to hang the side) and mixed 50g of epoxy (west) + 10g of hardener + 3g of pigment
layed the 1 layer on the hull and started by the middle to the side on the whole length of the boat.

First issue is that it was easy to spread the mix initially but then it started to become tacky within 20mins or so (shed temp was 20C with 55% humidity).
Second issue we didn’t elevate the hull enough from the base and it was difficult to have the cloth sticking to the hull at the deck level.

Initially spreading the resine with a 2" brush, tapping the brush in parts to “force” the resine in the cloth and then a resine role (from west system) to have a more uniform volume of epoxy throughout the area, then a special lamination brush to remove any air bubbles. Looked good

then applied the second layer of fibre approx 20 mins after the first one and this time I used a little less hardener with the hope to get more working time. Same process as first layer - same frustration around the deck line due to the hull not being high enough, used 53g of mix this time

then applied the 95g peelply to cover the whole hull.

now I’m praying it will be ok :shake::shake::shake:

No idea the weight the hull will come out at, nor whether it will be stiff enough !

One question I have is - I don’t expect the hull to be perfectly smooth so what is your recommendation to have a really smooth finish with no pinholes ? this is to be a boat to race so surface is important as much as the weight. Was thinking if the hull is light enough to spread a final coat of epoxy thinned with acetone but don’t know by how much.

if the hull to usable but too flexible I am planning on addind another layer of 135g across the area where the finbox/mast will be.

Any recommendation, comments, advices welcome at this stage as we are still pretty novices

Sorry about the pictures - I saved them on my google drive but I can’t see them now - not the first files I can’t see… will post the pics as soon as i sort out this technical issue

My fried Gilbert in Greece we say that the start is 50% of the job.

So it is nice of you to start your project

Now about the epoxy…

First of all you CAN NOT ALTER ΤΗΕ resin – hardener ratio because
the chemical outcome will not be what you expect to be.

Second acetone and epoxy is not compatible and you can use it only for the cleaning of the tools.

Third… the only 2 ways to postpone the chemical reaction of epoxy are

  1. Play with the temperature of the mixture:
    If I want to have almost double the working time I am using 2 bowls with approximately 1 cm difference in size.
    I am putting water in the first one and then the second one (smaller) in side the first one (bigger) and then both of them in the freezer. When the water terns to ice, the bowl is ready for the job.

                 Do not use this trick if the humidity is higher than 60% because it is sweating also the inside of the bowl as the epoxy is heating.
  2. Play with the volume of the mixture:
    The more concentrated the mixture is the fastest it is going to set. So if you want to delay the set of it do not use a bowl, use a plate.


Every time wash the new object the next day with soap because the humidity produces amines.
Amines is a byproduct of epoxy that looks like soap on the surface of the new object.
This is the main reason that the sanding paper is going to be blocked very quickly and if you try to put another layer will never bond.

About the pinholes I discover that when you finish the layers that you are going to use you can apply one more with a 18gr/m2
witch you are going to wet by pressing it either with a dry brush or by a roller for the air bubbles.
This way you are adding less weight than an extra layer of plane epoxy and you end up with much better surface.

I know all of this ‘secrets’ about epoxy because of my profession.

Try them and you will see that they work.


thank you Kostas for these handy tips

I won’t change the ratio of the mix next time - it make sense that the mix started to set quickly we used small pots because I knew we were only going to use a small volume of mix but I guess it was sufficient to create that reaction for the mix to set ahead of it’s natural working time due to its mass. That is a good tip for next time.

So the epoxy won’t freeze then - and the cold helps keeping it from hardening.

didn’t get your point re washing - are you saying i should wash the hull with a soapy mix tomorrow ? are you using had soap or liquid soap like washing up liquid ?

gonna have to try the 18g/m2 trick on the next hull.

Gonna post pictures of the deck once I sort out the photo issue cos I’m scratching my head on how to strat light and strong in particular around the mast area where the aft deck goes up to meet with the raised foredeck…

Thanks Kostas

How long should I keep the rads in the shed to keep the temperature at 19C ?

The soapy wash down should be used if the first epoxy layer has completely set up. Amine blush is what it is called. Amines form on the surface of some epoxies when they cure, and it is a barrier for the next coat. It can be sanded off, or washed off with soapy water. Google it for more info.

But, you said your second coat was 20 min later, so the first was probably not set up yet. You should be good. The peel ply on the outside is a great way to NOT have to deal with amine blush, as it will give a great surface for another coat of epoxy, but if that was your final coat, it may add to the final finishing work.

I would suggest you do any finishing before you remove the laminate from your mold. Fill, sand and even prime and sand the hull before you remove from the mold.

I would add that extra glass layer in the finbox/mast/shroud area, maybe a couple of layers. But do it on the inside so you don’t change the shape of the hull. You WILL need to sand the epoxy on the inside before you add this, as it will be very shiny, from the packing tape. Any glueups inside the hull will be that way, knock the gloss off with sandpaper first.

finally google drive showing my pics …

Thank you hew565 for the clarification - I remove the peel ply few mins ago and the hull looks good and the finish is good too but not smooth as expected with the peel ply but it feels uniform which I guess is good. but now I need something light to have that really smooth finish - should I go with a final layer of west epoxy (not thinned with acetone then) ? after I give it a good wash with soapy water ?

here they come

What I did so I can upload photos in all the forums is that I Sighed on the IMAGESHCK.
After you upload a photo you go to your files and you pick the i (red circle) and you paste the blue title of the photo file .

Your job looks perfect my friend.
What is the weight of it?

To fill the texture left from the peel ply, I would mix something like West Systems Microlight Fairing Filler ( or similar, into your epoxy until it is thickened and will not sag. Then squeegee it onto the hull with something like a credit card. It will fill the low spots and weave of the glass/peel ply, and sands very nice. Then prime/paint.

Since you used peel ply, you really don’t need to wash the surface. Any amines came off when you pulled the peel ply.

Hi Kostas, I’ll check imageshack thanks - for the weight I don’t know cos I haven’t pulled the hull from the plug yet but absolutely dying to do so - I’m like a child with a present i can look at but can’t open … lol

Because it is done on a male plug I want to have the outside of the hull perfectly smooth before I lift it from the plug.

Thank hew565 I’ll do that today and will post more pics

UPDATE on the IOM built.

I followed your advice and added a layer of epoxy to remove the wave effect from the peelply and which I will now sand on wet to give it a perfect smooth finish - starting at 600 and up to 2500… this is next on the list

Strat the deck today with my friend and applied some of the learning from the hull strat + your advice
2 layers of 135g twill but because of the shape of the deck we did each layer in 2 pieces of f/g one for the aft deck incl. the vertical part of the front bulkhead and a bit of the top of the front bulkhead. Planned to have the overlap of the 2 layers in different places so to avoid too much of a built up of overlap.
then peelply. I did change the process from the hull in that after the first layer which was coloured in red pigment, the second coat is clear epoxy and I was a bit more generous and used 45g of epoxy to 35g of fibre to avoid adding an extra coat of clear epoxy like I did on the hull - don’t care as much re smooth finish on deck as on the hull. And didn’t use pigment on the second layer as I though the colour from the first coat should come through as I cloth get wet which worked out as planned.

I find the epoxy mixed with pigment harder to spread as it feels thicker which I suspect the pigment is adding to the viscosity of the mix.

At this stage I expect the hull to be at c250g and the deck <100g, c150g and if so that would be good - in fact would be happy with that

Again comments, critics all welcome as we are only beginning on our journey. Thx

next step is to sand the hull to smooth finish while the deck is curing at 18C in the shed for 2 days

What wood would you recommend to glue to the side of the hull to glue the deck on ? what was thinking 4x3mm balsa ?

Have fin, rudder and finbox ordered from Dave Creed.

Another little tid bit to keep in mind: Fiberglass cloth will “float” on top of epoxy. Meaning, do not add more epoxy than it takes to completely wet out the cloth. Any pools of epoxy that form, will not be on top of the glass, but the glass will float to the top of the puddle.

I use a “credit card” squeegee to go over the layup to pull any extra resin to the edge and off of the layup.

If you use peelply, it should keep the cloth under the resin layer.

yep not my best idea but I didn’t use all the epoxy I mixed as intended but the peelply did absorb the excess quickly which indicated to me that I did use too much and whilst my idea was to save more weight by avoiding to put an extra coat of epoxy.

Today I removed the peelply and the surface is not as pretty as expected and I’ll have to put that extra coat of epoxy to get a good finish. So yep you are right and I learned this the hard way but one live and learn and this is important. As the next strat I’ll do will be better I 'll have made the mistake on this one.

what wood and size of the baguette I will have to glue to the hull at deck level to glue the deck on should I use ?

Hi Celtic Spirit,
Hew comments have merit, but you need to be really careful of not sanding through the glass when using filler. I’ve built numerous IOM hulls using packaging tape as a release. The one problem you will have is leaving small ridges on the tape overlaps. I’ve found that at the peel ply stage try using automotive lacquer primer brushed on thickly will work perfectly well. Dont worry about runs just get plenty on. Then use a guide coat, any cheap aerosol can will do so you are able to see brush marks and low spots. Wet sand using a block. If you sand down to the tape lap marks be careful not to sand through the high spots. The primer is softer and lighter than micro balloons so its easier to control the sanding through problems.

As I said earlier Hew’s method is perfectly okay as long as you are confident you have plenty of thickness to work with. But remember thick layup means weight.


Any polyuethane paint will stick to this primer.

I know and my aim is to have a hull + deck after strat and sanding before starting the assembly of the boat itself at 400g.

Hoping to sand the extra coat of epoxy I laid on the hull to get a near perfect finish - expect to remove c 8-10g through the sanding but really not sure how realistic that is.

All in all a really good experience for boat #2 once this one is finished.

thank you all for your contribution - they all helps and are appreciated :slight_smile:

After sanding from 240 down to 2500 a a coat of rubbing compound to get a really good finish I took the hull off the plug and I had to weight it and was surprised to see 182g - wow that is light - though I think this enables me to add a coat of f/g across the hull where the finbox/mast will be and also a small square where the rudder is gonna be. then I need to glue the strip of wood on the deck line to glue the deck on. all this will add weight.

Couple of things, the colour is not as deep as we though - we did put more pigments in the mix for the deck - and the hull is a bit pale after the sanding but nothing a good polish should fix - however we pay the price of not having the plug high enough of the table as the excess cloth was touching the table and created wrinkles, which during the sanding were bursted and so to fix that I will have to use to some of the excess cloth cut bigger than the wholes and apply them on the inside of the hull to fill and seal the whole while providing a good waterproof patch.

Update on the build -

the deck was too soft so we decided to add another layer of 135g of f/g just on the foredeck to see the difference and it did made the foredeck that much stiffer but I’m not gonna add that extra layer on the aft section as i find it stiff enough for the effort it will get. I took it out of the plug without too much trouble and it left the plug nice and ready to mould another deck if needed.

On the hull I added a piece of f/g 135g epoxied to the inside of the hull where the finbox is gonna be to strengthen this critical area. Thinking of adding 3cm band of f/g half way between the finbox and the bow, another one where the main post will be epoxied to the hull and a 3rd one where the rudder shaft will be to further strenghten the hull with minimal weight - comments if you think that will do it ?

All in all the overall weight of the hull (cut to approx 3mm of deck line) with an extra layer of 135g of f/g where the finbox will be + the deck (also roughly cut to 3/4 mm of the proper deck line) = 380g

I think it is pretty good so far though through this I am not going to build another hull with only 2 layers again - light yes but too soft.

any views, comments ?

pics to follow did get time to take them yet

Today I was sanding the deck to remove as much as the overlay of the f/g - the 3rd layer of f/g really made the fore deck much stiffer - I managed to sand the excess resine and some of the overlay without too much trouble but used 3 sheets of 120grid - was dry sanding and the paper was clogging up with the resine relatively quickly. But the aft deck remained somehow almost sticky ?

would that be the result of badly mixing the epoxy before laying it on, or temperatures too low ?

I have also epoxied a band of f/g on the aft of the hull to reinforce it there and a smaller band half way between the the bow and the middle reinforcing band at about midship. again to reinforce the hull.

Good morning Gilbert,
It has been long since I replied because of my loaded program but I see a lot of progress.
Way to go my friend.
About the sticky deck try to wash it good with soap (dish soap is ok)
and then try to put it in a worm place for 12 hours.
Try not to be too hot because it might deform.

It has been 11 days so it shouldn’t be sticky even if there was a problem with mixing.
I suspect that the problem is the portion of catalyst.
Any way sand as much of the epoxy excess and then try a thin layer in both sides.
If you still have problem maybe you have to consider of a new deck.