Building a Foam Core Powerboat

This site will report on the building of the 'Hawk41', a 41ft sea-going launch. It's specifications are: - Length: 12.50 m - Length waterline: 12.07 m - Beam: 3.27 m - Draft: 0.75 m - Displacement: 4.3 t - Engine Power: 184 kW.
The vessel will be constructed from a foam core sandwich using the 'controlled vacuum infusion' technique.

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Location: Utrecht, Netherlands

Friday, September 12, 2008

Reusing vacuumfilm: An improvement

I Improved my table.
Vacuumfilm as well as tackytape is expensive. To uncover the readymade parts I had to rip the film and the tacky gets lost. A lot of good material for the dustbin!
So I tried the following: I pasted on the rim of my table draught-list. I bought a yard of film that is used to make ponds. I did cut 4 strips of it, some 2 inches wide and sealed them together with an iron-heater so that the rectangle fits exactly to the rim of the table. On this rectangle I "tackied" the vacuumfilm.
Now I have a covering compound film that can be clamped to the table, on top of the draught-list using alumium strips and tableclothclamps.
A test showed that my pump switches on only 8 to 10 seconds every 40 minutes. Excellent for my purposes. Now I can take off the film by loosening the clamps and reuse it the next time. No extra tacky needed.
By the way: I finished in this way all interior parts of the frontside of the boat.
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Monday, June 16, 2008

Working at the table

After working with Adrie for some time, I learned a lesson: Infusion is not the way to go to make simple small parts. To infuse a panel of, say, 10 square ft, leaves you with a relative big quantity of resin in the overflow bucket. In such cases the method is not only cumbersome, but also expensive.
A better way is to make such panels on a 'vacuumtable', which is in effect little more than a table that has an airtight surface. The panels are made by hand lay-up on the table and immediately covered with a bleeder cloth and vacuumfilm that is glued to the edge of the table with 'tacky-tape' (butyltape). After that vacuum is applied to the whole package and the resin is allowed to cure before the pressure is released. The result is absolutely comparable in quality with that of the infusion method. As I do not have to handle or move the panels during this process, it is clean too. Of course I handle one side of the panels at a time. After curing they are turned over and the process starts again.
I constructed my table with two simple and cheap 'board doors', available at the DIY-shop for about € 24 each. I glued them together obtaining a surface of about 6.5 * 6.9 ft. Big enough to make almost all of my flat panels. I covered the table with one layer of 450 gr biaxial glass and epoxy resin, to make it airtight. I ran a test before actually using it, and it turned out to perfom amazingly well: It took three (3!) days to lose the vacuum after I had switched off the pump.
I expanded the construction by adding a 'rig' for a tent, covering it. As soon as I am ready with the hand-layup and the vacuum is applied, I set up the tent and blow in hot air. In this way the epoxy cures really well and fast.
To connect the vacuumpump to the table I use a suction cup from Festo. As it will not 'suck itself' tightly enough to the covering film alone, I found out that an old CD will do the trick: Punch a hole in the film, stick the disk on it with tacky and the cup will have all the grip it needs.
See you next time!

Tuesday, July 24, 2007

A whole new setup

I did mention that I am currently running an apprenticeship with Adrie Pijnen, shipwright. He is a frontrunner in the application of vacuum infusion, so there is a lot one can learn from him. He is also a nice man, happy to show what he has found out. He builds his own (but also many for others) vacuum installations.
I showed him my concoction. He laughed his head off. Such a little pump! A gastank! A vacuum advance unit for a pressureswitch!

I'll make you a tank, he proposed. Complete with all the connections to build a serious, however tiny, installation.
He welded a tank, 45*25*20 cm (17.7"*9.8"*7.8"). My little Robinair tightly fit on the top. Two valves, the pressure gauge, a connector for the pressure switch and one more connector in reserve. (Adrie, many thanks for this beautiful installation!)

He also gave me two ready to use pressureswitches. For him they were not applicable: Too little switching power, but more important, almost no hysteresis. The points at which the pump was switched on and off almost coincided. (In that case the pump switches on and off so rapidly that it will soon break.)
I took the two switches and put them together with a relay. The result looks funny, but in fact works very precise. The left switch controls the pressure at which the pump is turned off, the right indicates the point on which it is turned on again.

I am able to get the points as close as 0.04 bar together! (But also as far apart as I might wish)

I suppose I am ready now to experiment with my first injection.

Monday, July 23, 2007

A DIY pressureswitch

Ever heard of a "vacuum advance unit"? It's a small device used in car engines.
Has something to do with the ignition moment. It is a small "can", equipped with a membrane attached to a lever. It has a tubeconnector at the side opposed to the lever. See also the picture. It can be used to make a pressureswitch yourself. Here is what I did:
I connected the vacadvance to some copper piping built in a wooden box. The vacuum pulled by my pump is applied on the unit and therefore it retracts the lever. The lever in its turn operates a switch. (See the second picture) The whole contraption can be tuned by tightening a spring.
To get some feedback I mounted the pressuregauge on top of the box.

See the third picture for the end result. It works like a charm!.....

However.... The switch has a wide range of "hysteresis". In this case it means that the points at which the switch kicks in and out are a bit too far apart. On operation the pressureswitch switches the pump off at let us say -0.9bar. It switches on again at -0.7bar. Rather wide apart.

It will do for the time being, but when another solution comes by I will give it a serious consideration.

Sunday, July 22, 2007

A provisory vacuumtank

I arranged a tank. It's an old propane flask. The tank serves as a vacuum buffer. The next component is the vacuum switch. Tomorrow more about that.

Wednesday, July 18, 2007


I bought a pump. It's a Robinair 15151 (European 230V/50Hz version of the 15150). It can pull a deep vac that is quite sufficient for my app. I bought it over the internet at Fotronic. Only $ 133! (If I had bought the pump over here it would have cost me some € 700!!)
Next I need a vacuumtank and a pressure-switch. I'll come back on that soon.

Wednesday, February 28, 2007


Currently I am doing an apprenticeship with Adrie Pijnen.
I will come back on this soon.