Boat not stable with new motor at top speed
10-13-2003, 10:15 PM
#21
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I don't have a over powered boat by any means but I do find the when I run my Mirage plus for the better speed that she is what I call squirrely(not chine walking by any means) more so than when I run the bravo.No one has said anything about extending the drive down and if that could help boats that develop this kind of problem when we put the big power behind them and we get the hull so far out of the water that there is nothing left for the hull to do but act somewhat out of control.I don't think I would even consider the use of tabs to control this kind of problem as I usually only put them down when it is white capping.
Last edited by FloridianSon; 10-13-2003 at 10:21 PM.
10-13-2003, 10:50 PM
#22
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In lightweight hulls (18' outboards with 260's on them), they handle better and are more stable with LESS outdrive in the water. Less hobbyhorsing (slow oscillating porpoise), less chinewalking, better top speed.
It all gets weird and there is no single answer.
It all gets weird and there is no single answer.
10-15-2003, 11:00 AM
#23
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case in point on the drive depth... IN A QUICK nutshell
my 16 donzi classic would chinewalk terribly in bone stock condition at 55 mph with an alpha GEN II and vengence prop due to various reasons... prop, excessive bow lift, lack of inner strake length for balance, rounded keel, length vs width, etc... props helped alleviate this.. cleavers and small diameter stuff mostly...
enter the alpha SS, raising the propshaft 3 inches (C/L of propshaft is 5 inches below keel)... 76 mph now (yes more hp too) and essentially runs on rails with the quad IV... and I will be pushing the limits even further very shortly.
the deeper the drive the larger the moment imparted on the hull... remember mr newton and his 3 lovely laws... shorten the drive and you shorten the lever arm and moment. if the hull has issues with balance then a high drive can help it maintain it's narrow operating window for balance.
skeg area also helps with stability but there are tradeoffs in terms of drag. the added chord length of the CLE gearcase was also a help in terms of tracking and steering...
my prop rotation is right hand, therefore my hull falls to the left chine... the hook in the chine accentuates the chinewalk... you can feel it begin and you can drive out by applying a rythmic steering pressure opposite to the direction of fall in sequence with the tendancy to fall to the chine.. or drive in a large sweeping arc opposite of fall which maintains pressure on the hull to hold it flat.
my 16 donzi classic would chinewalk terribly in bone stock condition at 55 mph with an alpha GEN II and vengence prop due to various reasons... prop, excessive bow lift, lack of inner strake length for balance, rounded keel, length vs width, etc... props helped alleviate this.. cleavers and small diameter stuff mostly...
enter the alpha SS, raising the propshaft 3 inches (C/L of propshaft is 5 inches below keel)... 76 mph now (yes more hp too) and essentially runs on rails with the quad IV... and I will be pushing the limits even further very shortly.
the deeper the drive the larger the moment imparted on the hull... remember mr newton and his 3 lovely laws... shorten the drive and you shorten the lever arm and moment. if the hull has issues with balance then a high drive can help it maintain it's narrow operating window for balance.
skeg area also helps with stability but there are tradeoffs in terms of drag. the added chord length of the CLE gearcase was also a help in terms of tracking and steering...
my prop rotation is right hand, therefore my hull falls to the left chine... the hook in the chine accentuates the chinewalk... you can feel it begin and you can drive out by applying a rythmic steering pressure opposite to the direction of fall in sequence with the tendancy to fall to the chine.. or drive in a large sweeping arc opposite of fall which maintains pressure on the hull to hold it flat.
10-17-2003, 01:23 PM
#26
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The 280 is a stepped hull. Much different.
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