Picture of Building a Rowing Shell
How to build a rowing shell using a hot-wire cutter and hand-layup fiberglass
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Step 1: Cut foam

Picture of Cut foam
Foam cutting is an easy way to get a smooth 3D shape. Pink housing insulation foam is also very cheap. If I remember correctly, it took about 10 sheets of 2inx2ftx8ft to build this boat. The process is simple. Cut jig pieces. I used 1/4 in luan plywood. I used a bandsaw for the rough cut, and a large hand sander to get the finish shape. If the shape is accurately drawn, this method can easily get shapes to under 1mm accuracy. The edges of the jigs have to be smooth, or the wire will catch. Make sure you mark the points around each template which you want to have line up when cutting

Building hot wire:

The wire will be best if you can find 1/32" stainless steel cable to cut with. In lew of this, bicycle shift cables are OK, but leave a pattern which needs to be sanded off. Stainless steel wire also works, but it's hard to get it strung on straight. The cable should be mounted to some frame which is very springy, as the cable lengthens a lot when it heats up. The springness lets you set the tension when the wire is cold, and have the same tension when it is hot.

Using hot wire:

Put a voltage over the hot wire cutter which makes it cut smoothly through the foam, leaving little foam fibers behind it. The wire should smoke just slightly once it's cut through the foam. Don't try to force it. It is cutting with heat, so pushing hard will make the wire bend and not speed up the cut. A bent wire means you get the wrong shape. Never hot wire a piece with one person. Get one person on each side of the wire. Mark points on the shape which you want to make sure line up. Number them, so both people are going the same direction around the part. Speed up or slow down to match the other person.

I use spray adhesive to stick the foam to the templates. The propellant in the spray dissolves the foam, so spray lightly from a long distance (1 ft?). Let the propellant evaporate, and then stick the template on.
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notanaj543 years ago
Hey ive been trying to find some decent cross sections to cut the foam with =, but as of yet have had no luck. do you know some place i can download them for free/ could you email me scans of the ones you used?


Did anyone ever share with you any sites with free rowing scull designs?

Thank you!

'fraid not.
dbuckley68 months ago
Fantastic job. So a few years in, how has the boat faired? I am very interested in building one following your instructions. 3 questions, 1-any idea of overall weight , 2 - any construction mods from long term use - 3 any idea where the pattern for the plywood jigs could be found?? Cant really do anything without pattern. Thanks
boblq1 year ago
LOL, this is my main problem. Right now I am trying to force myself to finish at least a half a dozen boats before starting another.


boblq boblq1 year ago
Examples of multiple projects needing to be finished
where did you get the pink insulation foam boards and carbon , fiberglass and did you a template and if yes were from ????
lminer21 year ago
How long are single scull shells normally. I'm talking about one someone would practice on.
hollywolf1 year ago
Where do I get the designs for the bulk heads, outriggers, etc?
Great project! Did you consider using the same process to make a pair of foam molds to lay the fiberglass INTO, instead of a core to lay the fiberglass on? Then you would end up with a lighter, hollow shell (though you would probably need another layer or two of fiberglass to make up for the loss of the foam structure). OR, another option to reduce the weight: the core sections could be hollowed with the hot wire, leaving a ~1" wall. Maybe it wouldn't make that much difference. How much does the finished boat weigh?
ssaleem32 years ago
did you leave the foam in the boat or did you take it out and if you did take it out how did you do the ribbing to maintain the strength of the hull
damonv (author)  ssaleem32 years ago
no ribs. The strength is carried by the skin, and the foam core keeps the skin from buckling.
Would adding some honeycombing or fiberglassing in a gunnel possibly help with stiffness? I have heard that if your shell isn't stiff, you can lose a bit of power during the stroke. I think I recall seeing carbon fiber honeycomb in Hudson shells (could be cost prohibitive though).
damonv (author)  showlov4anerd2 years ago
stiffening the top is good too. Honeycomb is more about limiting buckling or out-of-plane deflection than making the hull stiffer, so is not a big contributor to stiffness when the core is already a big block of foam. carbon at the corners of the deck in addition to on the bottom is probably the best EI increase. Making a hollow boat is probably the biggest weight savings.
notanaj542 years ago
Can you post scans of the crosssections?
so what you want to do is sand the extra coat of epoxy, and not the fiberglass?
Might that be autobody filler to bring up the low spots? Great ible, brings me back to my days on my college crew team.
la3l413 years ago
Looks great! How much does it weigh?
notanaj544 years ago
Do you know any sites where you can get the designs for free?
Do you by any chance know of a good set of plans?

I just bought the book Rowable Classics thru amazon. It strictly refers to wooden shells

At the back of the book there are plans with cross sections of a nice shell with similar lines to this boat.

you could probably enlarge them on a copier and come pretty close to this boat.
schkip19734 years ago
this is an AWESOME!! 'ible.. any chance you can tell me where to get the pink foam in Australia? Or what other brand names / chemical name it might be marketed under? I have checked at Clark Rubber with no success. Thankyou
The foam is extruded polystyrene foam insulation.

In general building suppliers are a good source if not DIY shops

BUT Be aware this foam melts when polystyrene resin is applied. You must use epoxy resins to avoid this.
Possibly you might be able to protect the foam surface by painting or coating with paper and PVA but experimentation needed.

randomray4 years ago
Wow , very nice job . I don't even want to build a shell and I learned a lot , thanks so much . A heads up , fiber glassing is not real expensive and not that hard to do compared to building wooden boats . Make sure you wear hand protection and face masks or you will regret it the rest of your life . Wear the right stuff and it's not a problem .
Were can one purchase the foam blocks you guys used for the boat. Thanks And thanks so much for posting this!
It's housing insulation found in Home Depot and Lowes and most other lumber/home centers in the States . It comes 2" thicknesses , 2ft x 4ft ? , Owens Corning .Probably other brands in other countries and areas .
This is great for a first instructable!
Im really interested in building a shell for offseason long was your boat, and about how much did it cost you to make, also what were the other dimensions, thanks
ethanbradek4 years ago
I'm interested in this project, I just have a few questions. How much did the over-all build cost? Also, Is it built without a keel? That's one of the parts that I was curious about when considering building my own shell. Thanks and great job!
uphrsn5 years ago
I am very new using this web site so maybe I am in the wrong location for this request. I have a couple of questions for the builder of this rowing shell and I would be much appriciated if they could be answered.
  1. After the foam is sanded did the fiberglass resin go directly on to of the foam? My experiance is that resin will disolve the foam similar to the spray on glue aresol.
  2. How did you decide on the plywood temptate dimensions and were they 24 inches apart? Also were they left attached to the foam pieces and glasses over?

I don't think epoxy melts that Dow pink foam stuff.  Perhaps you are thinking of Polyester resin? 
Jobar0074 years ago
The only problem that I can see with this is using the pink foam. It will delaminate if it is impacted. The fiberglass will pull from the foam and create and air pocket that will fill with water. You could instead go with boat building foam instead to avoid that.
moneymaker5 years ago
What's an estimate for the cost of this project?
 Have you considered a set of real sculling oars? You'd get away with smaller oarlocks.  Boat looks unsinkable thanks to the foam remaining inside the hull.  good for offshore sculling.  Good project.
hinkle_adam5 years ago
This is a great process. Where did you get the pattern for your jig pieces? I can't find anything like it on the internet and I want my boat to cut the water properly.
Hardcore. Take that Vespoli and your $8000 fussy shells! What city is that?
dwc2305 years ago
I love this plan. It is so interesting, and I learned a lot from reading through it. I want to build a boat too, partcularly, a skull. I don't know anything about so many things, like the hot wire for cutting (shaving) the styrofoam. I guess I'll have to do some research. Thanks!
Hoaxinmi5 years ago
Holy Cow. I cant believe you did this. Nice Work!
I was the random visitor on Sunday Sailing a few weeks ago when you brought out the rowing shell. That's the first time I've attempted to use one and although I was always on the edge of tipping over and going for a cold swim in the SF bay, it was great fun! Next time I need to put the wetsuit on before boarding the rowing shell so I won't be as worried about capsizing. Thanks for letting me use it and giving me vital tips like "never let go of the handles".
shooby6 years ago
Looks good. Where's the first photo taken?
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