Art,
Willy has 37 hp as rated by Mitsubishi. Vetus markets the same engine and claims 42hp. Westerbeke claims 44hp for the same engine. Take your pick.
But if you look at my Willard 30 and the Clipper I think you'll agree the clipper needs less power. Very pointy ends, less draft, less beam and far less weight. And Willy could do fine w 33hp. 30hp is plenty for the Clipper.
Heck, Eric.
We have 50 hp Johnson o/b on our 14'8" Crestliner tow-behind runabout. She gets 20/21 nmpg at 20/25 knot cruise. Light weight, fun, economical little devil... seats four comfortably with full windshield and bimini that shades all! Can reach 39+ nmpg in slack tide (per gps) with just me aboard.
Our 34' 20K to 21K gross lb Tolly has twin 255 hp i/b... running only one motor at slow cruise of 5.5 knots she gets 2.75 +/- nmpg. Running both engines while on plane at 16/17 knots = 1 +/- nmpg
How many nmpg does your Willy get at slow cruise? Must be darn good!
Although boat nmpg (over ground)
"mathematically" comes down to a juxtaposition of HP, speed traveled, total weight, length, beam, bottom design, type-of-engine/fuel used for propulsion, drive-line configuration, friction; i.e. sq. in. surface contact, bottom cleanliness, waves encountered, currents, wind direction/velocity, position of movable weights aboard... just to name a few of the interchangeable variables - lol
It's near impossible to accurately mathatmically calculate what a boat will average for nmpg. It seems that only carefully studied and performed tests under stringently controlled conditions can come close to accurate - for any boat.
Therefore, I ask:
So what if the Clipper in this thread has a bit more power than it mathematically seems is necessary?? In smallish engines (40 hp to 80 or 90 hp) (considering the compared engines' running efficiencies are the same) would it not be virtually the same nmpg at a same hp provided by a larger engine to travel through the water at same speed as an engine smaller in hp/size? And, would it not be good to have that extra power in larger engine available if needed for fighting rough seas as well as for towing something substantial... as may become required?
It appears you are a minimalist (to the fullest extent of that word) regarding engine size and hp available on "full displacement" boats. So as to barley let them reach cruise at recommended engine rpm, with WOT using every portion of the engine's available hp to at all attain the boat's designed top-hull-speed.
That said: I do mot consider myself a maximalist... however I do believe in having at least a few extra horses in reserve... for needs-be that can arise.
Happy H-Power Selection Daze! - Art