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Hi all, I am one of a small group of SAWs racers in England, we have a bit of a problem with lakes here, with the rise of environmentalism, conservation and the ever increasing popularity of worm drowning, there are not many lakes here that allow fast boats, and not everyone is willing to travel to the other end of the country so we need a central location which limits our lakes further, for the last few years we have been running on a lake with approximately 190m (207yd) of usable space.
Our course is 100m (109yd) long, so if we start 10m from the bank or reed bed (which looks rather close at a distance from our un-elevated driving position) that leaves us only 35m (38yd) for acceleration before the course and a 45m (49yd) area in which to stop and get turned around.
I have the highest speed record at 84mph, with my L6 rigger, a stretched, forward motor JAE.21 which I know is a hell of a lot slower than most other places in the world, but given the limitations I think is pretty good for a modded retired race boat, and I'm proud of it.
Typical SAWs high pitch props don't work for us, I see higher speeds on the GPS, above 1.4, but to avoid prop walking I have to feet the power in slower so low speed acceleration suffers and the trap speeds go down. I hit a stick and wrecked my boat, but I was increasing rudder size by steps to reduce prop walk and get the power on earlier, on my final runs I was at least at full throttle on the start line (though still accelerating). I think if I had continued going in that direction I may have been able to get 90, but 100 is well out of reach for a boat that isn't specially designed for it.
As well as acceleration being a problem, braking is too, I was off the throttle before the end of the course and still I got stuck in the reeds twice. Hanging it non a big turn fin and not slowing down gives unreliable runs as it often takes a while for our system to reset for the next run, so you can get a slightly higher speed one way then the way back doesn't count my I found it best to have a small fin to get it turned at the other end in displacement mode as tight as possible, allowing the lift off to be as late as possible.
The wreck is reparable, but that boat has reached the end of its road and to do significantly better requires a different approach so now is the time for a new boat.
It will have twin motors so prop walk shouldn't be a problem, I hope to be at full speed before the start line, and I should be able to reduce the rudder size considerably giving me less drag.
That leaves me the problem of getting stopped from an even higher speed (hopefully over 100) in only 35m, so I can get turned around in 45m (49yd).
My first solution is to put the rear boom on the CoG, then I can have a movable fairing on that boom that will reduce the drag at high speed and can go tail up when off the throttle to give downforce applied evenly to the boat. That seems pretty safe but maybe not a strong enough effect alone.
I have also considered twin rudders and a mix to make them oppose each other when off the throttle, which would be a massive effect, but that amount of force could do unpredictable things, maybe nose the boat down and make it submarine at high speed which would be disastrous, and it would also increase the rudder drag.
Another thing I have considered is having a bellcrank push a vertical rod down through the bottom of the skis, but to avoid it becoming a planing surface the bottom of it would have to be angled opposite to the bottom of the ski, so it couldn't be flush and would effectively leave a gaping hole in the bottom of the ski, I would have to mount it well forward of the transom to avoid it being a source of drag, which means it would be unsupported for a fair distance and I worry about getting enough strength.
Have any of you seen any of these braking methods use, and can they give me any information about their effectiveness and/or side effects?
Can anyone suggest any improvements to those braking ideas, either to increase there effectiveness or to reduce their side effects/ downsides?
Has anyone seen any other braking methods used.
Does anyone have any other ideas for braking methods?
Our course is 100m (109yd) long, so if we start 10m from the bank or reed bed (which looks rather close at a distance from our un-elevated driving position) that leaves us only 35m (38yd) for acceleration before the course and a 45m (49yd) area in which to stop and get turned around.
I have the highest speed record at 84mph, with my L6 rigger, a stretched, forward motor JAE.21 which I know is a hell of a lot slower than most other places in the world, but given the limitations I think is pretty good for a modded retired race boat, and I'm proud of it.
Typical SAWs high pitch props don't work for us, I see higher speeds on the GPS, above 1.4, but to avoid prop walking I have to feet the power in slower so low speed acceleration suffers and the trap speeds go down. I hit a stick and wrecked my boat, but I was increasing rudder size by steps to reduce prop walk and get the power on earlier, on my final runs I was at least at full throttle on the start line (though still accelerating). I think if I had continued going in that direction I may have been able to get 90, but 100 is well out of reach for a boat that isn't specially designed for it.
As well as acceleration being a problem, braking is too, I was off the throttle before the end of the course and still I got stuck in the reeds twice. Hanging it non a big turn fin and not slowing down gives unreliable runs as it often takes a while for our system to reset for the next run, so you can get a slightly higher speed one way then the way back doesn't count my I found it best to have a small fin to get it turned at the other end in displacement mode as tight as possible, allowing the lift off to be as late as possible.
The wreck is reparable, but that boat has reached the end of its road and to do significantly better requires a different approach so now is the time for a new boat.
It will have twin motors so prop walk shouldn't be a problem, I hope to be at full speed before the start line, and I should be able to reduce the rudder size considerably giving me less drag.
That leaves me the problem of getting stopped from an even higher speed (hopefully over 100) in only 35m, so I can get turned around in 45m (49yd).
My first solution is to put the rear boom on the CoG, then I can have a movable fairing on that boom that will reduce the drag at high speed and can go tail up when off the throttle to give downforce applied evenly to the boat. That seems pretty safe but maybe not a strong enough effect alone.
I have also considered twin rudders and a mix to make them oppose each other when off the throttle, which would be a massive effect, but that amount of force could do unpredictable things, maybe nose the boat down and make it submarine at high speed which would be disastrous, and it would also increase the rudder drag.
Another thing I have considered is having a bellcrank push a vertical rod down through the bottom of the skis, but to avoid it becoming a planing surface the bottom of it would have to be angled opposite to the bottom of the ski, so it couldn't be flush and would effectively leave a gaping hole in the bottom of the ski, I would have to mount it well forward of the transom to avoid it being a source of drag, which means it would be unsupported for a fair distance and I worry about getting enough strength.
Have any of you seen any of these braking methods use, and can they give me any information about their effectiveness and/or side effects?
Can anyone suggest any improvements to those braking ideas, either to increase there effectiveness or to reduce their side effects/ downsides?
Has anyone seen any other braking methods used.
Does anyone have any other ideas for braking methods?
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