den 20 maj 2009, 1 kommentarer
Mail från Risto i Finland. Njorden börjar närma sig fullbordan - efter en och annan maildiskussion om grafit-epoxy...
Am about to launch the Njord with the graphite hull - have been calling it the "Njerd", since it won't have quite the max speed due to shorter length. ("Njörtti" in finnish). Hope you don't mind.
A few words about working with the graphite. It really does shorten the open time and will turn to jelly much sooner than clear epoxy. I think that the graphite powder insulates the inside of the batch and the heat quickens the reaction. This is doubly unfortunate as it takes time to mix the powder into a lumpless consistency.
One should thus mix not in a cup but a bowl, and use a flat metal tray, a large one. Had i figured this out earlier, some problems would have been avoided. Felt obliged to share these thoughts, given the many times i've asked this or that.
One thing i've come to miss in all the info about building kayaks: the fact that it is very difficult to find suitable spray decks for these narrower craft. Again, had i known of this problem ahead of time...
Maybe this could be added to the "choose kayak" pages?
The attached pictures hopefully show what happened to Njord's graceful deck, and why. I kind of lost it with those hatches...
Mitt mailsvar till Risto:
Nice - looking forward to pics and a review when you have launched the Njerd ;-)
As for mixing. When you mix epoxy and fillers of any kind the proper way to do it is to mix the epoxy base and filler carefully, and first then add the hardener. Then you have all the time you need with the critical filler mix.
A flat tray is good to stop accelerated heating/curing when mixing large batches (to increase the ratio of cooling surface/volume).
Spraydecks may be a problem, due to the small cockpit lenght (otherwise spraydecks for racing kayaks and multisport kayaks would fit. Buy from Reeds (chillcheater) in England - they are made to size - just submit the cockpit rim shape and size...
For a first try you can use just about any old spraydeck, with an extra elastic chord holding the fabric to the rim (I have on occasions used an old bicycle tire tube - mountain bikes sometimes have the right size wheels)
Where do you end up in weight, with all those hatches?