Post by bluecrop on Dec 17, 2016 13:39:23 GMT -5
Frank,
What do you think of this?
I'm not sure how the various manufacturers come up with the ratings, but looking at your numbers, I wonder of the hp rating for the kingfisher is for two 250 hp, for a combined hp of 500? A good ballpark for sizing engines is take the gross weight of the hull, engine(s), fuel, crew, gear et al, and for a single engine, divide that by 25, for twins, divide that by 40. So lets say your gross weight is 6000#, for a single you'd want a 240 hp, bump it up to 250, and for twins, two 150's, though I might bump that up to 175 if I'd likely be carrying more weight. I can't see going to the expense of running twins if one of the engines isn't capable of getting the hull on plane.
Its stated on Kingfisher's website as a 250 MAX HP, the 2825 is rated for MAX 450 HP. The 28 footer weighs a tad over 5K, about 1100 pounds heavier than the 25 foot model. The formula you posted for sizing the motor is interesting, apperently it takes more power w/ twins? I dont dispute it, I just wonder why? Is it because smaller motors run smaller props, or something more complicated than that?
I have very little practical experience, but my inclination would be to power the boat w/ a single rather than a twin, until you reach a boat size that requires more power than can be obtained with one motor. At that point it seems to me a IB/OD starts making more sense.
As I stated before, this is my humble opinion at this time, trying to learn what I can before I make an expensive mistake.
No, it doesn't take more power with twins. You can run twins and just split the power of a single engine.
The problem with sizing the twins that way, is that should one engine fail, you have a very expensive kicker. I.e. that one engine won't get the hull on plane, but it'll suck a bunch of gas trying.
My point is, if you are going to set up a boat to run twins, you should size them so that one of them is big enough to get the hull on plane. The boat manufacturers have come up with the formula that the ideal hp is the gross weight divided by 25, the minimum hp is gross weight divided by 40. So when sizing for a single, divide by 25, when sizing for twins, divide the weight by 40 for one of the twins, that way you can get the hull in plane if you loose one engine.
Paul, Thanks, I get it now and that makes sense.
What do you think of this?
I'm not sure how the various manufacturers come up with the ratings, but looking at your numbers, I wonder of the hp rating for the kingfisher is for two 250 hp, for a combined hp of 500? A good ballpark for sizing engines is take the gross weight of the hull, engine(s), fuel, crew, gear et al, and for a single engine, divide that by 25, for twins, divide that by 40. So lets say your gross weight is 6000#, for a single you'd want a 240 hp, bump it up to 250, and for twins, two 150's, though I might bump that up to 175 if I'd likely be carrying more weight. I can't see going to the expense of running twins if one of the engines isn't capable of getting the hull on plane.
Its stated on Kingfisher's website as a 250 MAX HP, the 2825 is rated for MAX 450 HP. The 28 footer weighs a tad over 5K, about 1100 pounds heavier than the 25 foot model. The formula you posted for sizing the motor is interesting, apperently it takes more power w/ twins? I dont dispute it, I just wonder why? Is it because smaller motors run smaller props, or something more complicated than that?
I have very little practical experience, but my inclination would be to power the boat w/ a single rather than a twin, until you reach a boat size that requires more power than can be obtained with one motor. At that point it seems to me a IB/OD starts making more sense.
As I stated before, this is my humble opinion at this time, trying to learn what I can before I make an expensive mistake.
No, it doesn't take more power with twins. You can run twins and just split the power of a single engine.
The problem with sizing the twins that way, is that should one engine fail, you have a very expensive kicker. I.e. that one engine won't get the hull on plane, but it'll suck a bunch of gas trying.
My point is, if you are going to set up a boat to run twins, you should size them so that one of them is big enough to get the hull on plane. The boat manufacturers have come up with the formula that the ideal hp is the gross weight divided by 25, the minimum hp is gross weight divided by 40. So when sizing for a single, divide by 25, when sizing for twins, divide the weight by 40 for one of the twins, that way you can get the hull in plane if you loose one engine.
Paul, Thanks, I get it now and that makes sense.