DRAGONFLY Trimarans User Forum

http://michel-christen.com/2T-H.pdf This compares two different failures, one bonded and the other not bonded. The top of page 6 briefly discusses the option to bond or not. Bonding doesn't matter if you switch to Marelon.

Most interesting to Dragonfly owners was the summary of the ISO 9033-1:1994 standard (the EU standard that a Dragonfly should have been built to) that says: "Through-hull fittings for water shall be corrosion resistant, defined as material used for a fitting which, within a service time of five years, does not display any defect that will impair tightness, strength or function."

Based on that alone, the thru-hull fittings in my boat have outlived the expected lifespan by a factor of 2, and are due for preventive maintenance replacement. Other Dragonfly owners should consider this if your boat is older than 5 years.

Follow up. I removed one fitting (the one that looked the worst) and found it was in excellent shape (11 years old). I had to cut it to remove it, so I could see the entire cross-section of the metal at the cut. There was no discoloration or indication of any corrosion or electrolysis, other than some green ambergris on the outside surface of the bronze.

Obviously no need to replace the others, as they're good for the foreseeable future.

I replaced the engine raw water intake several years ago because i found a crack in the threads.
It had been over tightened before I purchased the boat (a DF1000/1995).

Hi, I just read the web site on brass thru hulls that are often sold as bronze. What has been your experience with the dragonfly thruhulls ? I just read a survey with a scratch test being OK but the article and pictures show that that is not a reliable test. Should we change to Marelon ????

betsyderek wrote:Hi, I just read the web site on brass thru hulls that are often sold as bronze. What has been your experience with the dragonfly thru-hulls ? I just read a survey with a scratch test being OK but the article and pictures show that that is not a reliable test. Should we change to Marelon ????

The Dragonfly thru-hulls are bronze. If you replace with Marelon I do not recommend the Marelon mushroom fittings. When I replaced the fitting (as per my post above) I used Marelon and the mushroom head broke off with only moderate tightening. I ended up using a bronze mushroom head and Marelon valve (because I already had it). I will use all bronze from now on. Electrolysis has never been a problem on any of my DFs (I have owned 3 in the past 11 years.)