I’m working on a small unmanned boat that has a length of 66 inches overall and a beam of 20 inches. It is a padded V hull with a small waterjet propulsion system in it that should be capable of speeds in the 25kts range. The hull is a 20 degree v and the pad is 4.25 inches wide and the weight is between 70 and 84 pounds depending on fuel load.
In recent testing the boat planes off nicely and zips along just fine up to about 18 mph. At that point it is riding pretty high on the pad. If we go to steer it at high speed just spins out. The boat does roll a very small amount, but it’s not a digging in and rolling up like a proper runabout should by any means. Since this is a waterjet there isn’t anything like an outboard fin in the water, nothing at all, and that’s obviously why it’s spinning out. The customer has some lower speed experience, but the plan is to go 25kts at which point this thing is going to barely touching the water based on what it’s doing now at 15 knots.
Obviously we need some sort of fin setup to keep this thing in line.
As we are getting to higher speeds the waterjet is also getting ventilated on small bumps, so I was thinking I’d configure a set of fins similar to my roll up “D” runabout (center fin a bit forward of the waterjet and a rear chine fin on each side in the back since I have to turn both ways). I was thinking that a fairly shallow fin (1" deep) and maybe 6" long forward of the waterjet but behind the CG location and a couple of 1" deep and maybe 4 inches long chine fins would do it.
Does anyone have any experience with fins on V or padded V hulls that can help steer (pun intended) me in the right direction? Remember there isn’t anyone on board, so you can’t “help” the boat take a set by shifting weight forward and to the inside of the turn, it’s just got to turn in and roll up by itself, which isn’t the way a classic roll up works.
I figure if anyone knows how to make a boat turn without spinning out it's the guys here, so let me know what you think.
In recent testing the boat planes off nicely and zips along just fine up to about 18 mph. At that point it is riding pretty high on the pad. If we go to steer it at high speed just spins out. The boat does roll a very small amount, but it’s not a digging in and rolling up like a proper runabout should by any means. Since this is a waterjet there isn’t anything like an outboard fin in the water, nothing at all, and that’s obviously why it’s spinning out. The customer has some lower speed experience, but the plan is to go 25kts at which point this thing is going to barely touching the water based on what it’s doing now at 15 knots.
Obviously we need some sort of fin setup to keep this thing in line.
As we are getting to higher speeds the waterjet is also getting ventilated on small bumps, so I was thinking I’d configure a set of fins similar to my roll up “D” runabout (center fin a bit forward of the waterjet and a rear chine fin on each side in the back since I have to turn both ways). I was thinking that a fairly shallow fin (1" deep) and maybe 6" long forward of the waterjet but behind the CG location and a couple of 1" deep and maybe 4 inches long chine fins would do it.
Does anyone have any experience with fins on V or padded V hulls that can help steer (pun intended) me in the right direction? Remember there isn’t anyone on board, so you can’t “help” the boat take a set by shifting weight forward and to the inside of the turn, it’s just got to turn in and roll up by itself, which isn’t the way a classic roll up works.
I figure if anyone knows how to make a boat turn without spinning out it's the guys here, so let me know what you think.
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