Hi TD
As you say the metal coil isn't exactly posh but it is effective, and you don't run your boat with the lid off do you?
I have boats with all three types of water cooling, and I prefer the silicone jacket by far, it is a little bulky, especially if space is a premium around the motor, but it is by far the most effective, but the most expensive.
The alloy machine jackets look good but in truth are large heatsinks with water cooling tubes at their periphery, this means that a lot of heat is retained in the jacket. But they do look nice.
The tried tested and extensively used cooling coil if fitted correctly using a heatsink compound between the motor and the coil is an excellent low cost option.
Ultimately the choice is yours, but "don't always judge a book by its cover!"
Hope this helps
Phil
