Regarding JC's $18 (CDN; =$17.11 USD) per hour cost, that's great, but relatively meaningless unless we know what your cost-per-gallon is. If it's $10 a gallon, you're doing great. If it's $1.50, notso- hotso. What's your gallon-per-hour consumption?
To Russell: Hull speed on a 46 waterline length would be 9 knots (the formula is square root of waterline length x 1.34). If you're cruising at 10 knots, you're not planing, but you're pushing past hull sped and just digging a huge hole - the most inefficient speed. Either slow down a knot or so, or shove it up enough to get on plane. Those 671 turbos have a very, very narrow efficient running speed - about 200-300 rpm below wide-open-throttle (WOT). Run them slow, and at slightly-above-hull-speed, and you'll suck fuel like a wino with a quart bottle of Thunderbird. Plus, slow running is hell on two-stroke Detroit Diesels. They were designed to run at high RPMs. If you don't have fuel-flow meters, install them and experiment with them. Your interest isn't gallons- per-hour, it's miles-per-gallon. While you'll get the best MPG by cruising at hull speed or a smidge below, those engines won't like it and you'll pay for it in increased maintenance. What you're looking for with those engines is best MPG when you're on-plane. If you only ever want to cruise at hull speed, ditch those Detroits and repower with small (probably no more than 200 hp) four-stroke Diesels. Check with a marine power expert; you may not even need 400 hp to move at slightly under hull speed. As an example, consider the 42 Grand Banks. According to the McKnew- Parker Powerboat Guide (2008 ed.), standard twin 210-hp Cats cruise at 10 knots; twin 375-hp Cats cruise at 14-15 knots. So 330 extra hp on a full-displacement hull buys you 4 to 5 knots. Not very efficient. The difference is, your hull is a planing hull, which the GB is not. So running your 46 (which is the old Pacemaker 46 hull) at the most efficient planing speed with your 410-hp Detroits gives you a cruise around 16-17 knots (again according to the McK-P guide). One possibility would be to repower with four-stroke Diesels of approximately 400 hp each (your Detroits should be rated at 410 hp). Four-stroke Diesels will tolerate slow running better than two- strokes. That would give you the choice of a slow cruise (about 8.5 knots), but still have the reserve to run for shelter at a high planing speed if the weather gets nasty. Again, however, even four-stroke Diesels don't really like being underloaded; but they're somewhat better in that regard than two- strokes. Your best bet is to consult with a marine repower expert rather than listen to my half-baked rants. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "UnifliteWorld" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/unifliteworld?hl=en -~----------~----~----~----~------~----~------~--~---
