SAWs boat Brakes?

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?

At the 2006 NAMBA SAWs at Legg Lake, Tim Higdon from Alaska had dual rudders on his rigger that splayed to slow down.

How about using what dragster cars use - a parachute ? Small and securely attached. Just thinkin' early without coffee yet :confused2:

Hi Paul,

Will there be a UK saw event this year?

My HPR 115 wen't 107mph (gps) on it's second outing on mid sized props,

my exocet is probably going to be built later in the year with speed goals of 120mph+

I know there was talk of a powerboat lake being used somewhere near Manchester? I don't think these boats would be very suited to the small SAW course we have :(

It will be a lot more momentum requiring slowing down....

Tony thanks very much for your input, do you know if it effected the boats attitude when he splayed them at all? or roughly what angle he splayed them to? When you say splay, I am guessing they went to the outside? and whether it was effective? Parachutes are not something I have considered, do drag boats use them too? I am worried that when it touches the water it would scoop itself down immediately and rip the transom off

vvviivvv, No not this year unfortunately all racing has been cancelled, hopefully next year though.

Only Mini class boats are suited to the lakes we have had for the last decade or so, and then it doesn't matter as they are not suited to our one day event format with no golden hours.
I have heard no talk, but it would be great to have a bigger lake. It will be a shame that a bunch of records hard fought for years will fall overnight to people playing a different game, but well worth it for a future of finally being comparable to the rest of the world and seeing how we actually are, probably still falling on our faces at first, but something to build on and showing a bright future ahead.

unfortunate about all racing cancelled.

records are there to be broken... I guess lots of the current records could be extended with a proper lake and the same boats that set them,


Going back to your original post, my day job is driving around a rather large boat.. our crash stop procedure if above 16kts is the 2 outer azipods rotated in to 30 degrees with 30 rpms and once below 16kts we rotate them the full whack and add more RPM.. below 10kts we used to use 'inboard 90' to slow down but bearings are very delicate and we tend not to do it anymore. They are tractor pods..
probably not much use for your application but the drag definitely helps, we can stop in just over a nautical mile from 24kts. - albeit with a lot of shaking and a high % chance of doing damage... like we discovered after sea trials.

Paul.
The Bluebird had a rod that was dropped on the transom as a brake after they added the more powerful jet, because they were running out of room on Coniston water.
Here's a video of a model of it.
https://www.youtube.com/watch?v=9tFoO_lW9uo

Back in the 80's full sized tunnels used a pair if air cylinders on the rear of the sponsons that had 1" stainless balls attached. Hit a button and they dropped and tripped and wet out the hull in a brake like action. They got outlawed as guys on the inside thought they could run hard in a turn and when air systems malfunctioned they ran over the outside boat. Not sure a drop down at high speeds wouldn't lift the transom and possibly stuff the bow.
Mic

Thanks for the info Paul, also, Bugger I thought I had invented that, but I must have just been dragging it out of some deep memory ,interesting to see that it is domed too, which ties in with Mic's info, thanks Mic. If I go down that route it will be domed and not chamfered as I had invisiged.

Hello Paul,

I guess stabilizer fin airbrakes will not be terribly effective given the length you need to slow down in.
Watch this video of a drag airboat. I believe they have some type of diverter elbow like a rooster shooter that slows them down. Forward to 7:40 mark.
https://youtu.be/dq0uj_kUEQI?t=460

St

I think twin rudders that open up in opposite directions will cause the tail to blow and stuff the nose.

-Tyler

I hope Chris Harris will not mind me sharing the pics of his S hydro. He had airbrakes above the rearward booms.
Attachment 169749

The only other idea I had was having a large secondary flap that was servo actuated and popped up near the center of lift to add a lot of downforce without effecting the fore/aft balance. Imagine having a second radio box lid that was hinged at the front and laid flat during a run, but popped up via a servo.

-Tyler

Use a car controller and apply the brakes. This worked great for SAW riggers in the 1990s prior to BL motor use and is not mechanical so if the ESC works - the brakes work. A big SAW prop has a lot of drag when stopped.


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Hi,
like Mic wrote , i remember the aicylinder breaks , i have seen mounted on Renato Molinaris tunnelhull. When he didnˋt slow down in front of a corner and all other fall back and then he hit the breaks and turns the boat to accelerat it direct . Very crazy . He had this cylinder direct behind the sponson . I think some rods at the strut or propshat wedge will do the job . Maybe build a mount tha can be angeled to find a pisition that will give sligtly downforce on the transom. We have tought about to make the rudder shaft longer and make it moveable to run it deeper after the straight , with a bigger dia ruddershaft it will break better.
And yes a stand still prop will break to but will lift the transom. A counter prop drive will have higher drag and can use a less drag ruder.
Maybe my diske ruder that has no drag .

Happy Amps Christian

Tony thanks very much for your input, do you know if it effected the boats attitude when he splayed them at all? or roughly what angle he splayed them to? When you say splay, I am guessing they went to the outside? and whether it was effective?


Paul, sorry for the late reply - I don't remember which way they splayed - that was my first big SAWs and I was so intimidated that I hid under the table most of the time.

Not sure where in the uk you’re based, but if it helps have you ever tried Nottingham’s regatta pond - Holme Pierrepoint, it’s a 2000meter pond only used for rowing events. It’s council owned last I knew, When I lived there, there were actual people based there at one end who ran and operated the pond, friendly folks.

I did some googling also...

we have plenty of suitable lakes for a good SAW event,

Peterborough and Nottingham look perfect if permission would be granted.. also rather central?

https://c8.alamy.com/comp/G3CAHX/aer...ham-G3CAHX.jpg

https://i.pinimg.com/736x/5c/54/dc/5...9b713da60e.jpg

Thanks Tyler, that airboat solution looks impressive but with the amount of water going up in the air it must be trying to stuff the tail pretty hard, not a problem when you have a flat bottom that wide, but if you just have a prop for support or a couple of skis at the most I can't imaging it not upsetting the boat.

Wow, Chris's boat looks awesome that really does give me some things to think about. I was thinking of the flaps hinged directly off the rear boom and being full width but maybe being smaller you can run them at a much higher AoA for the same downforce and get more airbraking effect, I may be able to do the same thing full width by running them at an angle of attack where they are stalled, but that would mean running them through a position where they are providing more downforce than I want as they move before they stall.

Looking at the front ride pads is interesting too, is that suspension, or just a screw ram to make the AoA easily adjustable? My dad thought about trying suspension like that on a race boat back in the 90s, but as far as I know he never took it off the drawing board.

I have considered a glider type spoiler on the tub, and discounted it as I didn't think it would add enough drag, but for some reason I had not considered a high aspect ratio jet type airbrake, that could work well.


Thanks Jay, I had thought of that, and it would be dead easy for me to implement as I use air ESCs that have a brake function that I can turn on, and I use wires so no worries about the flex unravelling. I have never tried it though for fear of it lifting the back and stuffing the boat though, if it doesn't have that effect, or the effect isn't too big I will try it out.


Christian, I have certainly never even thought of a disc rudder, that is well outside of the box, I guess you mean something like a pizza wheel on bearings with just the bottom in the water, it would spin with the water flow and effectively decrease the speed of the water flowing across it?


I have pondered the need for a water rudder at all. I will have at least 1 vertical stabiliser and putting a rudder on that/those would be fairly trivial. With contra-rotating twins I shouldn't have prop walk to deal with, so an air rudder may be enough to steer it down the course, not enough to get it turned round at the ends, but if I was to extend it down to strut height it would be out of the water when planing, and be in the water when at displacement speeds. Does anyone have any input on this idea?

No worries Tony, I would like more details but just knowing it has been done before is very helpful, do you recall if he took his boat back in a trash bag or if it went home in one piece?

Paul,

Again, I don't recall. He did have some issues but I don't remember what they were - it was 14 years ago. He's a forum member - try PM'ing him.

Here's an early attempt at dealing with the slowing down issue :

I've recently tested a new technique to stop; the Speed Pond Lateral Acceleration Terminator [ SPLAT ] and it works as described

http://www.youtube.com/watch?v=TzcSxfHyFfo

Hi Paul,
yes , your are a thinker , no need of tons of drawings and pics. Yes the pizzacuter is the way. I made small disce and looked for the same cornering force and messured the trust with an open flow water stream. The result is clear. If not only a bearing is mounted it can also be driven by a small motor so the ruder generate some trust.

Happy Amps Christian

Hi Paul,

The MGM and APD have synchronous rectification. They both have very elaborate brake functionality as a result .The 120 amp F3 controller might work for you if you want to try the inverters brake like Jay suggested.

Happy Harmonics
Hubert

Why can’t you program the controller to go into reverse . Not much is needed just so you have maybe 10% . Your not going to actually go in reverse but I think that Input will try to slow Down the motor that will slow the prop and break it.

Quote:

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Originally Posted by Bushmen77

Why can’t you program the controller to go into reverse . Not much is needed just so you have maybe 10% . Your not going to actually go in reverse but I think that Input will try to slow Down the motor that will slow the prop and break it.

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Not a good idea to spin a flex cable in the wrong direction

Food for thought.....

https://www.youtube.com/watch?v=DjALseBuBTY

Your not really spinning it backwards . You just using a little power to slow it down .
Example when we started to run electric slot cars . If you with wide open you were going too fast to corner. So my dad rigged up a battery on the controler . When the controler lever was at nutral it would apply a little power to go backwards. So I have to hold the lever part on to get the car to stay in one spot. When I raced I would come down the stright away wide open. The other guys tried to keep up. But just before I hit the turn I would release the lever and it would put the breaks on fast. It just slowed the car down. When we race the newer rc cars we can program it to break by doing the same thing to the motor. We use the motor to break. We have rc boats now that have revers built in doing the same thing. But I never went full throttle and hit reverse to try it. Maybe you have to adjust the amount of power in reverse till you get a controled slow done. I don’t see how it would not work once dialed in plus it’s just a radio setting . Get someone with a boat that has reverse and do a test and try it. I am will but can’t do it till summer. But the way it works your not spinning the shaft backwards just slowing it down faster.

Using the prop to brake or worse reverse results in a very bad condition where the tail lifts and nose stuffs. At high speeds this is catastrophic.
This happened to Joerg in Germany where he accidentally did not turn off reverse on his controller. He uses airbrakes which are enabled by reverse trigger input. There was delay in he reaction of the controller, but when it started reversing the prop the tail popped up and caused the boat to hop severely. I cannot recall if he stuffed, but reverse or braking was not a good idea.

Back when we used brushed motors and round cells, and FE SAW records were under 65 mph, Jim Auguston set many hydro records using an ESC with a brake. It worked for him when running on small lakes, but the high weight of riggers back then combined with the ?low? speeds apparently held the tail down. Chris Harris was the first I saw using air brakes on a rigger to be able to go 100+ on little Blue Lake in Valdosta and stop without hitting the bank. They were clamshell vanes on the sponson booms. Worked well too....



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