" Hi Patrick,

This sounds like an interesting project. First let me start with your 2nd question regarding the modification of the boat from a gas engine to a diesel engine. Gas and diesel engines are fundamentally very different in design so to begin, it would be necessary to replace the gas engine with a properly sized diesel. From there on things would be reasonably straight forward. You would need to plum in a return fuel line back to the tanks as a diesel requires a feed and return whilst gas engines only require a feed. I would also recommend you flush the tanks to remove any trace of gas fumes before beginning any work on them, or before filling with diesel. I think changing from gas to diesel is an excellent idea, I am sure you are aware gas and its fumes are highly combustible. I would also recommend you consult an experienced diesel engineer concerning the specifications and the finer details of the project before you begin.

Your 1st question was regarding the possibility of placing a sail rig on the boat. From a positive perspective, indeed many trawling vessels traditionally carry small mizzen sails called Spankers, these were more to provide stability to the vessel in a rolling sea rather than to power the vessel. Linda Greenlaw, in her book about tall fishing tales describes working on a trawler for a guy who lost his engines, being too proud to ask for a tow, he managed to sail the vessel back to land under a jury rig he set up at sea. So, yes there is no reason you wouldn’t be able to rig a sail and gain something from sail power.

The big difference between a sail boat and power boat is lateral resistance, the ability of the boat to prevent from slipping sideways through the sea when the sails are rigged. For this reason sail boats have keels of some description. Designed for working offshore, your trawler will probably have a reasonable stability curve, but the lateral resistance will need to be addressed. There are many options to do this such as having a drop or swing keel which is retractable to enable you to still frequent shallow harbors, another idea would be to add a plate either side of the existing keel, so in effect you now have three keels, the benefit of this would be the ability to dry out on a beach to do bottom work.

My advice is to keep the rig short and your sailing expectations low, at best you are going to gain a little fuel economy and some slow sailing when the wind is aft of the beam, but it will give you the ability to make land if your engines fail. Again please consult an experienced naval architect before jumping in with both feet.

On the cost, this really depends on your specifications and the size of the vessel, how long is a piece of string.

Have fun with it and keep floating.

Ian Fagg
(Sailangle.com)
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