I still dont get it

[Gary]

Again i am lost with the lack of performance of my SAW boat. The boat was performing great. You can see in my videos {88 mph Miss attitude } that she stuck to the water perfect and would go 87-88 many times untill i ran out of batteries. Now i can not keep it on the water. Its hopping like crazy and blows over all to often. I changed nothing!!! I can tell you this.... the weather is at least 20 degrees hotter than my previous runs, if that matters. I dont know if the batteries are putting out more power sooner into the run and its accelerating harder than it can handle at lower speeds or what but it seems more violent and wants to lift very early in the run. It will blow over at 60 mph!!!! The only way to get a soso run is to verrrrry slowly get into the throttle and get up to speed. Anyone have these problems?

[Doby]

Must be temp related,,,,,you said it was 20 deg warmer....hot air rises....therefore more blowovers... Sorry, someone was going to say it eventually.

[domwilson]

Surface effects? http://orbitalvector.com/Aquatic/Sur...WATERCRAFT.htm

[nomedmon]

re: blow over

hey ill put my 2 cents in. Well I run my boats alot, that's a lot of putting in and taking out of the car plus tables benches that i set them down on; have moved my prop angle enough to make boat drive crazy. Just a few degrees made a big difference in how my favorite boat handled! I just took my boat out of winter storage, and re did the battery hold downs so that the batteries weren't sitting in the bottom of the V-hull, now it won't stay in the water. Just keeps trying to fly and/or spin out, but a lot of flying! I was hoping this would be my SAW boat, but now I just don't know. Last year, great at full speed; this year scared of it! Do what I do, check everything twice! LOL, I know you do too! Peace, have fun and hope that you figure it out!

[Gary]

Im starting to think mabe the hotter batteries are dumping so much power right away that the boat cant handle it when trying to get up to speed. Who knows.

[line6]

what are the temps when you put them in now. and what was it before. to me, mine seem to have more initial power if they are around 110 when i put them in. so if you have a 20 degree different in the lipos I would think they are putting out more power now. you might have to mess with the set up again.

[NitroVal]

I know the pro guys in on-road racing warm up their LiPos to get more amperage flow out of them. Warmer batteries= less resistance. Also the air is alot thinner when its hot, so you could potentially have less downforce from above, while the cooler air rising from the water may create a higher pressure under the hull..

[Gary]

Man ......this stuff is getting crazy now. All i wanted to do is go 90mph. Is that so much to ask from a toy boat? I dont think so.... LMAO !!!!!!! I guess i will have to factor this stuff in from now on. Tomorrow i will test again and try a few things and pay attention to temps and humidity. Good times.

[Ub Hauled]

Im starting to think mabe the hotter batteries are dumping so much power right away that the boat cant handle it when trying to get up to speed. Who knows.

Gary, hot air can lift airplanes, so a tiny boat (by comparison) is a certainty. You should probably place the CG a bit forward and/or change the angle on the strut a tiny bit (more negative). The fact that the cells have more punch IMO have nothing to do with it, 60mph is 60mph regardless of how fast you get there, if she was flipping over in the hole then that would be a different story... Aside of the the water temps, the hull is warmer and may be expanding to where it changes the angles a bit, but that a bit of a stretch.

[NitroVal]

The other thing I forgot about could be convection currents. Im not sure how low they actually go, but it is was paragliders use to increase alititude. Hot pockets of high pressure air.. To be hoesnt, at that speed, any little thing can happen. Its like trying to skate a piece of straw along the waterline... Im with the others, bring your CG forward a bit and see what happens

[Fluid]

If we assume that there were no changes to the setup - since you carefully recorded each setup change that should be easy to verify - then hot batteries are probably at least part of the problem. As stated the boat accelerates harder, upsetting the hull's attitude. I have to disagree that '60 mph is 60 mph '- harder acceleration can cause more transom squat and a higher AOA for the entire hull; it can also cause slight hopping that upsets the hull. A fast SAW boat is a careful balance of thrust, weight and drag, upset any one and it will become unsable. Did the rudder get bumped out of its original setting? Did you wax or oil the hull bottom?

Air density will have little to do with it, when running in ground effect any changes in lift and downforce will equal out (you are not flying at 1000 feet here, 'standard' aerodynamics don't apply.)

Water properties will change with temperature and content. Different ponds can cause 2-5 mph or more speed differences, and a great setup on one pond can be terrible on another. With the 20 degree increase in air temperature your pond's water temp may have changed even more, and with a change in organic or mineral content this could be a contributor.

With more power from hot batteries you 'should' be able to go faster. You have several options - change the strut setting by lowering it and perhaps adding more down thrust; moving the CG forward; adding weight. The latter will probably be required anyway to maximize speed. As you increase lift (go faster) you need to offset that with weight, particularly with an air compression hull.

You may find an additional cause, but I believe that it is probably a combination of at least a couple of the above.




.

[Ub Hauled]

Well Jay,
I agree with you that if the hull attitude during acceleration has changed there will be consequences,
I figured by the way Gary described it, the hull was looking it's normal and that's where the "60 is 60" comment came from. I stand corrected on the lift comment, coming to think of it, there isn't enough altitude to generate that effect from the water to the hull's tunnel, sorry Gary.
At least the solutions that Jay came up with were the same as I had suggested, hehehehe.
Any reports on the run earlier today?

[Gary]

Well i should have said it seems like its "popping a wheely" when its trying to accelerate and at 55-60 it just starts lifting the nose and over it goes. But....anyhow......just came back from lake and learned a little more. I noticed that the boat will do some crazy things UNTILL its up on plane if i rush the run or use a short runway . This can be aliminated by very slowly getting into the throttle, being carefull to make sure its pointing straight, and moving at a good clip before i really get into it and can only be done with a lot of extra room aloted. For example: I can make the boat do a compelte 360 by just going full throttle at say 15 mph....Its funny as hell by the way......but this will never happen at full speed . If i get into it to early it hops uncontollably untill it crashes. But any how with a longer run , some added weight like you said FLUID and more patience on the run as far as distance and time goes and 15 degrees cooler air and batteries the boat ran a best of 89.5 mph and i was thrilled by that with a back up run 89.0 I guess i need to always remember that at these speeds i walk a fine line and any trip up and its disasterous to say the least. This saturday come hell or hi water this boat will see 90mph LOL But anyhow thanks to everyone for your input . I coudnt be running this fast with out your opinions. UB-HAULED , FLUID thanks again. By the way i only run 2- 11.1 batteries at 3400 mah each. Is there speed to gain by going to more MAH? I run these batteries because of there wieght and size. The next size is 4500 mah.what do you think guys?

[sailr]

Yes, you get more power when increasing the mAh. There is simply more capacity to PUSH the volts through. I can't explain it technically and argued about it a couple of years ago until it was proven to me. If you need to add weight to the boat to keep it on the water and you can do it with bigger capacity batteries rather than dead weight then that is a great advantage!

Well i should have said it seems like its "popping a wheely" when its trying to accelerate and at 55-60 it just starts lifting the nose and over it goes. But....anyhow......just came back from lake and learned a little more. I noticed that the boat will do some crazy things UNTILL its up on plane if i rush the run or use a short runway . This can be aliminated by very slowly getting into the throttle, being carefull to make sure its pointing straight, and moving at a good clip before i really get into it and can only be done with a lot of extra room aloted. For example: I can make the boat do a compelte 360 by just going full throttle at say 15 mph....Its funny as hell by the way......but this will never happen at full speed . If i get into it to early it hops uncontollably untill it crashes. But any how with a longer run , some added weight like you said FLUID and more patience on the run as far as distance and time goes and 15 degrees cooler air and batteries the boat ran a best of 89.5 mph and i was thrilled by that with a back up run 89.0 I guess i need to always remember that at these speeds i walk a fine line and any trip up and its disasterous to say the least. This saturday come hell or hi water this boat will see 90mph LOL But anyhow thanks to everyone for your input . I coudnt be running this fast with out your opinions. UB-HAULED , FLUID thanks again. By the way i only run 2- 11.1 batteries at 3400 mah each. Is there speed to gain by going to more MAH? I run these batteries because of there wieght and size. The next size is 4500 mah.what do you think guys?

[ED66677]

more capacity will simply make so that battery voltage stays higher under a given load (amp draw), less voltage drop, for example if you test and record (with any logger) the voltage of a 2000mAh 20C batt when the motor pulls 40A you see that it is slightly lower (few tenth of volt) than if you do the same with a 4000mAh 20C batt, so under load few tenth of volt represent few watt am I clear?