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.

My Photo
Location: Utrecht, Netherlands

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.