Re: ? on fuel effeciency
My Express 1870 MV jon hull weight is 550lbs., motor is 90HP Yamaha at 268lbs., so it's got plenty of power and speed...only thing is the relatively flat hull makes a lot of drag and boat will porpoise if trimmed up too much, so we cruise in the 25 to 30 MPH range. With your V hull, you can trim it up for reduced drag and more speed! The 10% is just a rule of thumb, varies with hull and 2 or 4 sroke motors, weight, prop, etc. Good Luck!
are you saying you'r 90HP has to much power for you'r boat?
60 knots is almost 70mph. Are you sure you want to go that fast in a 21' aluminum boat?
I'd be very surprised if 115hp would do it, but I've been wrong before. It takes a lot of power to push a boat that fast....any boat.
is it unsafe to go 60Knots in an aluimin? water conditions will be flat water for this every now and then speed, just to know I have the capability when I fell like surprising a real power boat.
My 16' Checkmate with a 115 Yamaha on it, trimmed up, would make 60MPH, but I doubt that 115 of yours is going to push that 21' aluminum boat much over 50MPH...just too much hull/drag in the water! You might do 60MPH with a 200HP on it.
maybe a fin on the motor will make it plane better and reduce drag I have one on my little 15' and it planes allmost instantly?
By
stevethebrain at 2011-10-07
This ain't rocket science. At WOT your 115 will burn roughly 11.5 gallons of fuel per hour. You have a 25 gallon fuel tank. 11.5 goes into 25 twice so if you ran wot for two hours you had better be within a 10 minutes or so of a marina or have extra fuel aboard. If your combination allowed the boat to reach 50 MPH you would have traveled 100 miles in those two hours. NOW can figure "miles per gallon. In case you are math challenged, that would be about 4 MPG. GPH is used as a fuel consumption measure by boaters because MPG is not known until the trip is over (gallons used vs miles traveled) unless you have a fuel flow meter and a GPS to determine distance traveled. A flow meter alone will tell you within 1/8 mile after you leave the dock what the flow rate (GPH). Based on the amount of fuel you have you know whether or not you can reach your destination (assuming you know how far it is to that destination). OK -- I've opened this can of worms.
I'm intending on a project boat that will require a repower so I'm basically researching HP, fuel, and speed before hand hopefully I can meet my expectations first time.
I did'nt know about fuel flow meters sound good. however I normalley go to the same destination in Destin, FL first trip will give me a good idea of the required amount of fuel.
?when carrying spare fuel tanks how is spare fuel filled into the main fuel tank w/ a funnel and just poured in? or can a bulb pump line be used?
a desired top speed of 60 knots? thats movin along quite well in a boat. speed costs money, and if yer worried about gph, and wanting to go that fast......you need a new hobby. jmo
not overly concerned w/ cost of speed just curious.
I have been boating in my small 15' since 1990 that's when I get a chance and have had lots of fun on the water. I'm finding out a 21' boat (basically a larger version of my 15' boat) is in a differnt league.
Thanks to all for explaining
