Hull speeds

[domwilson]

I read alot of posts where people are saying that certain speeds cannot be obtained by certain hulls. I am curious as to the speed limits of various hulls. Not limited to the hull design like deep-v, hydro, cat, etc. But specifics as to manufacturer, type, size, model, etc.

[ozzie-crawl]

thats a good question,would be interesting to know as well when they say the hull wont reach that speed in what context they mean
as in are they saying it wont run in race water at that speed or it wouldnt reach that even in s.a.w trim

[domwilson]

Good points...

[kevinlew211]

there is no rules unless you go race, btw, i will pick a biggest hull my motor can handle, beside the sizes, weight is not less important.

[sailr]

Basically there is a limit after which the hull becomes airborne or otherwise uncontrollable. When you reach that point it becomes frustrating and no fun!

[domwilson]

Understood. But still, some say a hull won't go over a certain speed regardless of powerplant. For example, but this doesn't hold true, an SV27 can't go over 50 mph because the hull is not design for it. Trying to determine what others have found or what has been done as far as speed. Would like responses to include setup as well.

[Fluid]

All FE hulls require proper aerodymanics to run successfully. They generate more lift the faster they go. When they are designed, the maker has to compromise between lift and weight and speed. Drive a boat designed to weigh 5 pounds and 40 mph to 55 mph and it will likely become unstable.

Air compression hulls like hydros and cats are easy to understand - if they pack too much air and generate more lift than the weight of the hull - the hull flys off the water. That is the maximum speed for that hull in practical terms. Water conditions come into play, but since most of us don't have the luxury of running on glass smooth water very often, we have to set up our boats to stay on the water in our own water conditions. This is even more pronounced in oval racing.

The same holds true for monos. An example is my Tital 40. It was designed to race in the 40s with a 7.5 engine. When I installed a 4S setup and hit 50 mph the boat would not stay on the water reliably. To make it a reliable performer I had to add 1.5 pounds of lead, and now I can run the boat faster for longer. It is the most stable and reliable boat I race, and it wins much more often than it loses. If I wanted to go much faster I'd have to add even more lead, but then the mono would start to bog in the turns because it would be too far out of its design performance envelope.

The famous Dark Horse hydro was designed for speeds in the 40s and 50s, but I watched its designer run 80 mph with it. He added a lot of weight - 18 NiMH cells - and an air dam, and he moved the CG ahead of the sponsons. Yes, it ran 80+ mph but it was almost impossible to launch and it didn't turn well; it also didn't run well at under 40 mph. Even with all the modifications it still self-destructed in a high speed crash.

So when someone says that a certain hull can't go faster than xx mph, he really means that it is not a practical design for higher speeds. Modifications can add some additional speed, but eventually so much weight is added that the boat is no longer practical at lower speeds. Adding 6-8 ounces to the SV27 is one of the best mods you can make, but add 2 pounds and it will be little fun to run at anything but WOT. A successful R/C model is always a balance of speed, weight and lift.




.

[domwilson]

Thank you. That was well explained. The info. on your Titan is what I was looking for.
Even though the hull was designed to run in the 40's, you got it to go much faster. This was done, I presume, not by throwing bigger or more expensive motors in it, or more batteries, but by tweaking your setup.

C'mon guys, let's hear more.

[properchopper]

Jay, that was so well said that it should be reprinted and included in every piece of FE equipment , particularly the RTR's. Not to discourage setup experimentation but to avoid the perennial " Let's see how fast I can get this sucker to go : Zoom, SPLAT, row-row, Oh s*^@, more time & money, and repeat !" Having been there myself more times than I'd like to admit, I've since mellowed {some} and prefer run time & reliability over the one-time banzai run

[sailr]

Excellent explanation! I find it amusing that everyone wants to talk about how 'light' a boat is as though that means performance. I have found that weight (to a point) is your friend! It's OK, I just let the 'lightweights' believe it while I beat their butts.

All FE hulls require proper aerodymanics to run successfully. They generate more lift the faster they go. When they are designed, the maker has to compromise between lift and weight and speed. Drive a boat designed to weigh 5 pounds and 40 mph to 55 mph and it will likely become unstable.

Air compression hulls like hydros and cats are easy to understand - if they pack too much air and generate more lift than the weight of the hull - the hull flys off the water. That is the maximum speed for that hull in practical terms. Water conditions come into play, but since most of us don't have the luxury of running on glass smooth water very often, we have to set up our boats to stay on the water in our own water conditions. This is even more pronounced in oval racing.

The same holds true for monos. An example is my Tital 40. It was designed to race in the 40s with a 7.5 engine. When I installed a 4S setup and hit 50 mph the boat would not stay on the water reliably. To make it a reliable performer I had to add 1.5 pounds of lead, and now I can run the boat faster for longer. It is the most stable and reliable boat I race, and it wins much more often than it loses. If I wanted to go much faster I'd have to add even more lead, but then the mono would start to bog in the turns because it would be too far out of its design performance envelope.

The famous Dark Horse hydro was designed for speeds in the 40s and 50s, but I watched its designer run 80 mph with it. He added a lot of weight - 18 NiMH cells - and an air dam, and he moved the CG ahead of the sponsons. Yes, it ran 80+ mph but it was almost impossible to launch and it didn't turn well; it also didn't run well at under 40 mph. Even with all the modifications it still self-destructed in a high speed crash.

So when someone says that a certain hull can't go faster than xx mph, he really means that it is not a practical design for higher speeds. Modifications can add some additional speed, but eventually so much weight is added that the boat is no longer practical at lower speeds. Adding 6-8 ounces to the SV27 is one of the best mods you can make, but add 2 pounds and it will be little fun to run at anything but WOT. A successful R/C model is always a balance of speed, weight and lift.




.

[sailr]

Haha. I run into it all the time. Newbies who want to 'hop up' our stock boats which are already set up to run pretty close to their optimum. They usually spend a lot of extra money and end up going back. Go figure. I try to talk them out of it but of course the "newbie knows best" (sounds like a TV show). Go figure!

Jay, that was so well said that it should be reprinted and included in every piece of FE equipment , particularly the RTR's. Not to discourage setup experimentation but to avoid the perennial " Let's see how fast I can get this sucker to go : Zoom, SPLAT, row-row, Oh s*^@, more time & money, and repeat !" Having been there myself more times than I'd like to admit, I've since mellowed {some} and prefer run time & reliability over the one-time banzai run

[Flying Scotsman]

Jay, that was the best response I have ever read and as Tony, the guy who is still trying to figure out how to float his Harley. I also tried to run hulls, ESCs and motors beyond their limits and it was expensive and not productive. Now I putter arround with my boats and try not to burn up equipment.

Douggie

[FRED]

hull speeds

What Fluid and Sailr have typed has been going on since rc boat sites arrived in 1997 with RRH. Now its nice to help newbies but they seem to want exact info like given on a silver spoon instead of searching and learning by reading forums which in fACT has more info than any magazine out. This way newbies can ask a educaded question which leaves more time and space for others who may need help.*********** Now the other posting which brought out issues had to be said to clear the air and nothing is perfect but this site is to help others and doesn't need issues as the owner has enough to do in filling out orders of which he does in a prompt manner and i respect that with his honesty. Thankful we have him!

[Flying Scotsman]

Fred, and I am a newbie to most of the skills..always learning from my respected peers

Douggie

[domwilson]

Good responses here. I agree, newbies should read and learn as much as they can, and ask the educated questions they may have.

Keep those responses coming...