I used a 2" hole saw made for cutting cement. Hole saw fits on
same arbor as a wood hole saw. They're a little more expensive, but
cut a good hole (with the resulting core intact). The one I found
was at an Ace Hardware store, with a more expensive version at BOW. (A cement hole saw has a carbide edge that is abrasive instead of the "teeth" of a wood hole saw). I used a regular drill (around 600 RPM). I'm sure that a hammer-drill would increase the cutting efficiency significantly, but with a little patience (muscle limited in my case) a regular drill did the job just fine. Don't use a hammer drill with a hole saw. It will destroy the abrasive edge.Go as slow as is feasible and using plenty of water as a lubricant/coolant will also help BUT BEWARE of mixing water with electricity. Make sure you have earth leakage protection on the circuit you plug your drill into. Also be aware that running a variable speed hand power drill on it's slowest speed means the cooling fan in the drill is not blowing as much air as it needs to keep the armature cool, especially when making the drill work hard, as it would in this case. Every now and then lift the drill and run it flat out with no load to help cool the armature.Another hole cutting option may be a local business who specialise in cutting or boring into concrete. They use diamond tipped hole saws and generally do an excellent job on concrete.Anyone had experience with diamond tpped core drills on a ferro cement boat? Colin perhaps?

Regards, Norbert norbertg@iprimus.com.au

 How did you cut through the steel armature with the hole saw?

Hal Johnson. haljohnson@angelfire.com

 Hole saws are expensive to hire and difficult to use, and as Hal suggests there can be problems when striking the stringers of the armature. The method described in my book using a small masonry bit and hammer drill run at it's high safe cooling speed is the easiest and cheapest method.

regards Colin Brookes colin@hartley-boats.com