IOM wood build planking

Can anyone please advise the best size of planking to cut for a wooden IOM such as Nimbus, Noux etc. is 3mm deep x 10 mm width a good starting place. Also can I please advice on SP v west epoxy for coating in glass matt the hull. Is there a weight in grams which is favoured. I live. In Costa Rica and want to generate some interest in IOM, so I figure to do this I will need to have two boats to begin, so people can try and maybe I will get a small fleet in a couple of years. Any responses gratefully received.

A great reference for building in wood is the US1M building guide. Download from.

I build a balsa stripper to make my planks. I used 1/8th inch balsa and cut strips 3/8 in wide.

I would recommend building a hull and then put on a layer of glass (4 oz cloth would be fine). Sand that smooth and then use it as a male mold and pull off glass copies. I use the packing tape method as the parting agent.

For the hulls, I would lay on two layers of 4 oz and an outer layer of a light cloth like 1 oz. Once off the mold, add another layer of 4 oz around the areas of the shrouds and fin box, and up front, under the jib rack position for extra strength.

For the deck, only one layer of 4 oz and one of the 1 oz should be enough.

I use Resin Research Project 21 resin #2000. I prefer it to West as it mixes 2:1 which I find to be much easier to be accurate. Plus it is cheaper and excellent quality.


Thank you John for replying. I will see if resin research project 21 is available in San Jose. There be some beautiful local woods I could use to plank and hopefully turn out a nice boat. I a thinking of a Noux or vektor. If you have any thoughts on designs please let me know.

Another resin I am really happy with, easy to work with, odorless and safe to use indoors.

EpoxAmite® 100 Laminating Epoxy

I use the 102 med. hardner

There’s some good technical how-to’s at the site …

Welcome to the board…
I have been building IOMs for the past 30 years and Have sen alot come and go… you dont have to make it compliacted… the first thing you need is the right tool. you need a balsa stripper… you can buy one or make one… they are easy. also you well need to find balsa in either 48 inch length ( nothing added to them) or 36 inch . in which case you will need to add a section. This is not hard to do… all you need is wax paper and CA with some 220 grit sand paper… cut the section you need to add to the 36 inch. glue the section to the 36 inch and them sand the glue joint… the sand dust will fill the crack and basicly make a stronger joint… Now when it comes to planking. alternate the glue joint. once at the bow and then at the stern…

epoxy resin is great stuff but it is expensive… I use poly resin and not of my boats have failed… you need to find out what works best for you… what works for me… might not work right for you… keep an eye on this forum. come the fall… there is something coming that might help you…

something very nice :

with this technique with balsa stripping - it can be also first layer with balsa and second with veneer wood

or red cedar strip planking as :

the all covered with 2 layers of 50g/m² of glass fiber outside and 1 layer inside


i am interested in your view re epoxy as it is expensive and it seems impossible to buy in Costa Rica, but there is polyester resin, so i will go with this ’ two applications with a light glass fibre cloth, and keep an eye on the digital scales. if anyone has a web site, photos or anything visual on a home made balsa stripper i would be grateful. should i bevel each plank as i work up towards the keel line. the natural curvature of the hull means i should slightly “angle” each new plank aso it butts neatly against the last. should i do this or leave it to a good sand and coating later in the build. Thanks to all who replied

Hi Stevo.
The link I gave you for ResinResearch includes the price of shipping in the list price (may be slightly higher to you).

If you want to use polyester, it should work fine - we used to use it in the 1970’s before we had access to epoxy. It smells a lot worse while curing. When you talk of two applications, put on the two layers of cloth in one layup. As Polyester cures, it creates an outer layer of wax which must be sanded off before a next coat.

I made my own stripper (Cannot get a photo as it is out on loan). I used two pieces of ply about 12 inches long - one for the base and the other as the backboard fence. Then I made a block the desired width of the planks as a spacer attached to the backboard and attached a craft blade to the spacer, point down into the base. To use it, just push the balsa sheet forward against the fence and into the blade. Let the back board project down from the flat to be able to hold on a vice.

There are two planking techniques - one involves tapering each plank at both ends - so the total number of planks exists at all point on the hull. - Take the max girth and divide by plank width - total number of planks. Then take the girth at the bow and divide by the number of planks, that gives width of plank at bow - repeat for stern. Then make a sanding jig and clamp the planks and sand off the excess at bow and stern. This is only worth doing if you want the planks to show on the finished product.

The easy way is to start planking from the centre line outward and from the gunnel inward. Undercut each plank to get a tight fit (just a light sanding works with balsa). As the gap closes taper the end of the plank to fit. Work evenly up both sides to cancel any stresses. The is much easier and faster, and is fine if you will paint the hull. I use cedar planks for the centre planks (keelson) and gunnel planks for additional strength.

Build the boat a little over length so you can trim to 1M after the bow bumper is installed and the hull is finished.

These are pictures of my Frank Russell EMO planked and then used as a male mold to pull off a glass hull.


nice job on the planking John…
Stevo… remember If this is your first boat . expect mistakes… I am not trying to say it will not work. but IF the planks are not 100% butt ended, it is ok. YOU can use filler to fill the gaps in the planks. I use dry wall compound. easy to sand and easy to apply. I have been building for a very long time and i still cant plank perfect. I am still using filler…But all my boats work, I use the cheap stuff and it works. the only time I have ever used the “good” stuff was for my marbleheads… my IOMs are just as good using the poly.
What john said was spot on. plank from the top down and the deck up and you will meet in the middle…the one thing you MAY want to do. ( alot of poeple dont do this, I do) glue a peice of Black fishing line to the bow and glue it to all the center point on the bulkheads… this will give you a centerline when you plank… it comes in handy when you cut the fine box and the rudder hole…

Thanks to John and Cougar. i will proceed and let you know of progress. i have to find some wood here, some ply for bulkheads and a flat building board. i have ordered plans and am going to make two at once, as i know the planking is slow going, so i can switch boats at night. also IF i have a disaster i will learn but still have a boat to rig. hopefully i will have two good boats at the end. i want to finish in wood as they look superb and will attract interest at the local lakes, which is the idea. MYC San Jose is the end game. wish me luck and THANKS for your time gentlemen.