Most of the 53s came with 8V71 Detroit Diesel engines. The suffix letter N is for Naturals while TI is for Turbo-intercooler engines. The standard HP for 8V71TIs is 435 HP, which is what it takes to plane the boat and cruise on plane. The planing speed will be from 14 to 18 knots, depending on a lot of factors such as weight, prop size/pitch, hull cleanliness, wave conditions, etc. Weight is affected a lot by fuel and water in the tanks, dinghy and davits, furniture and gear on board, etc. A 53MY with 435 HP that has 1/4 fuel, 1/4 water, no dinghy, no gear and no waves may max at 18.5 knots and cruise nicely at 16.5 knots. The same boat with full fuel, full water, a big dinghy, lots of gear and 2 ft. chop might not even get up on plane.
A 53MY with 8V71Ns will not plane and are therefore really a 9 to 10 knot displacement hull boat. The hull is made to plane, but it can't. The benefit is substantially longer engine life between overhauls and engine cooling can easily keep up with the heat produced, so fewer overheats. Plus, since you have to go slow, much better fuel economy.
8V71TIs that have more HP than 435 will get on plane easier and go faster but have substantially less engine life between overhauls. The problam is that as you approach closer to a 1:1 ratio of HP to cu. in. displacement, the engine life decreases quickly. Engine life also depends even more on how they are maintained and how they are run. Poor maintenance and running them hot can reduce engine life to very short intervals.
See previous thresds here about 53MY fuel use in gal per NM.
See previous thread ini frequently asked service questions about 53MY sea trial and inspection things to look for.
Doug Shuman
