Deck Hatches and Tachometer

Wind looked high and unstable so we decided on a day's boat maintenance.

One of the problems we wanted to fix was something that had become apparent with the rain we had over the past couple of weeks, and that was that the deck hatches were leaking. Jacob and Marie, who clean King Malu, had mentioned that they thought the hatch above the saloon was leaking. This seemed very strange to us, since we had recently replaced the acrylic in the hatches and sealed it carefully with Sikaflex 291i. During the week, however, we noticed that the Sikaflex had not adhered to the acrylic and that when you pressed the acyclic you could see water between the window and the Sikaflex!

We talked to others about this problem and one person suggested that there is a known problem with Sikaflex and hot temperatures for making it fail to cure properly. Maybe this was the problem, though we only changed them recently and we didn't think the temperature was that high when we did it. Whatever the reason, the Sikaflex 291i hadn't adhered and Tim could push the windows out with his fingers!

We were recommended to try Hyperseak 50, so that's what Tim and Jacob spent their Saturday doing - removing the acrylic, re-masking it and then resealing the hatches. We'll know how effective it is when it next rains.

I (Richard) am working 3 day weeks till the end of the year and so decided to try and find a way of making some kind of tachometer for the Honda outboard, pending doing this for the new electric inboard, which should arrive soon. So I worked out the relevant NMEA sentence and tried sending that to the Raymarine C70 we have on board. I tried everything, but never responded at all. It appears that the C70 only responds to tacho sentences on the Seatalk line, and making a Seatalk interface was definitely not what I want to do right now, expecially as the language is not pure NMEA so would make it more difficult in the software too...

So I decided to try a different approach. The Honda 20HP tacho output gives pulses from a separate coil on the generator, which basically give an AC voltage between 6 and 100 volts depending on the RPM of the engine. So, I decided if I rectify that and smooth it with a 100uF capacitor and then voltage divide it down I should have a DC voltage between 0 and 5 volts that can be displayed on a LED bar graph. I used an LM 3914 IC to display this and 6 high brightness LEDs. Wasn't quite trivial to make it work, but it did work fine eventually (you need both a 12v and a 5v supply for the IC, so two regulators were needed).  So that was how I spent my Friday afternoon and Saturday.