Semidisplacement trawler range and autofeathering props

[Smarten]

Hi,

I just bought a boat twenty years old powered by couple of DD J&T6V92TI 530 Hp. The boat and the engines need a major overhaul. The boat is a trawler 55 ft. LWL around 75.000 lbs with a semi displacement hard chine hull. The boat was reported to reach a speed of about 20 knots when new. That speed seems to me a waste of fuel and money so my target peak speed for this boat is today around 14-16 with a cruising speed that I would like to be manageable in between 8 to 12 knots according the range that I need (that's the problem) to be about 1800 mg. The fuel tanks are today 1000 gal. but increasable.

For economical reasons but also for the good fame of the engines I plan to derate the engine from TI to NA.There were 3 different version of 6V92 to choose among ranging 230-280 Hp.

To reach the range I would plan to have passages with only one engine running. To avoid drag I am thinking about auto feathering propeller coming from sail market. As you know some model would also offer the (interesting?)possibility to adjust manually (or auto adjust) the pitch for the need of the passage.

I would like to collect your opinions about the feasibility of my idea and probably alternative approaches.

Regards

[Portager]

I think you will find that the folding and self feathering propellers intended for sail boats will not be sized for or designed to withstand the power levels that your trawler would produce. At your power levels you would need to use controllable pitch propellers. The problem is that retrofitting controllable pitch propellers into an existing boat is very expensive. So expensive that you would need to circumnavigate the world several times to break even.

If your intent is to extend your range, then the simplest approach might be to remove one propeller. Once you reach your destination you could replace the prop and remove the other one and use the other engine for the return.

If your intent is to increase reliability and make the vessel track truer powered by a single engine, then you may want to consider coupling the shafts, either mechanically, hydraulically or electrically.

Regards;
Mike Schooley