Whitelighter
Well-Known Member
Maybe it is my understanding, but an SD (Semi Displacement) hull will never fully plane, it will just constantly climb the hump. I dont argue that the Broom hulls arent very good, I just dont think they are a SD hull.
What is your fuel consumption?
- Thread starter kcrane
- Start date
whisper
Well-Known Member
Surely even large racing monohull yachts can and do regularly plane. Don't think you would describe them as having planing hulls though, would you?
I'm confused.
Don't Nelsons, Aquastars, Seawards all plane with big enough engines but they are all SD hull designs?
I'm confused.
Don't Nelsons, Aquastars, Seawards all plane with big enough engines but they are all SD hull designs?
D
Deleted User YDKXO
Guest
IMHO, it's too simplistic to say one hull is SD and the other planing. Fact is that any hull which can be made to go faster than it's displacement hull speed must be planing to a lesser or greater degree. Probably we should be calling SD hulls semi planing rather than semi displacement because IMHO, the only difference between a SD hull and a planing hull is that a planing hull is designed to lift higher out of the water and therefore plane more efficiently.
Definitely OceanFroggie's 38CL would be termed a SD or semi planing hull. It has a typical SD shape with a sharp V forward and fairly flat sections aft and a big keel as well. IMHO, if you stuck really big engines in such a hull, it would start to plane on the keel (as some older planing hull designs with keels did) so you could'nt call it a full planing hull
Definitely OceanFroggie's 38CL would be termed a SD or semi planing hull. It has a typical SD shape with a sharp V forward and fairly flat sections aft and a big keel as well. IMHO, if you stuck really big engines in such a hull, it would start to plane on the keel (as some older planing hull designs with keels did) so you could'nt call it a full planing hull
Whitelighter
Well-Known Member
OK, so its my understanding that is out. Fair enough. Thing is I have been on a few Nelsons etc that are described as SD and when you put on the power the nose rises on the hump, but never flattens out like it does in a planeing boat. So with its nose up, doing 16knts is this planing then? I thought you had to clear the hump and flatten out to be 'on the plane'?
D
Deleted User YDKXO
Guest
As I said, IMHO, any boat which exceeds it's theoretical maximum hull speed by a significant amount, by definition, has to be planing whether it's nose sticks up in the air or not. Actually this is not completely true as some lightweight very slim hull designs can exceed their hull speeds by a large amount but I don't think any typical monohull motor boat qualifies as one of these (maybe some power cats do though)
A Nelson 40 has, say, a waterline length of 35ft and would have a theoretical hull speed of 1.34 x sq rt 35 = 8 knots so, if it's doing 16knots, it's got to be planing IMHO.
A Nelson 40 has, say, a waterline length of 35ft and would have a theoretical hull speed of 1.34 x sq rt 35 = 8 knots so, if it's doing 16knots, it's got to be planing IMHO.